If your computer fan spins at 2000rpm it will show up as a finger at 33Hz (2000/60). 

 

I have made all these mistakes! Spent way too much time staring at my measurements in utter confusion. I wondered why I managed to fix a peak at 33Hz but the waterfall still showed no decay. Eventually I worked it all out. Computer fan. 

10 hours ago, playdough said:

Informative reading, thanks  to the OP.. Good job.

Photo is of a lounge with 4 x 21" bass system, after bass trapping installation.

 

 Fundamental is still a little wonky, however sounds "high and tight" with no real noticeable pumping or colouration at the listening possi.

Nice picture! Very impressive and smooth, appreciate for critical listening and quite comfortable for symphonic music too.

6 hours ago, basscleaner said:

Nice picture! Very impressive and smooth, appreciate for critical listening and quite comfortable for symphonic music too.

Hi Andrey

Thanks and  yes music of all types actually, there is a lot of content in the lowest octaves unlocked for listening pleasure, although it's compromise is the physical size and weight. The system does a great reproduction of grand classical, like the Star Wars theme and others.

Was a big job to DIY.

20 hours ago, playdough said:

Informative reading, thanks  to the OP.. Good job.

Photo is of a lounge with 4 x 21" bass system, after bass trapping installation.

 

 Fundamental is still a little wonky, however sounds "high and tight" with no real noticeable pumping or colouration at the listening possi.

Hmmm, fairly flattened bass. I find (with my hardware and room) that will sound good for very well recorded audiophile stuff or electronic music. But for modern Pop, Rock, Metal and even most Classical my target curve is starting to tilt up at about 160Hz and by 20Hz it is 7dB up. For movies I have a target curve that is about 3dB up at 20Hz which includes the LFE channel. Using Dirac Live I can switch between 8 differnet profiles. I also use LOUDNESS correction that changes with volume setting, so effectively dyanamic EQ for the bass frequencies. I suggest you experiment with a sloping up target curve. Perhaps start with 3dB up at 20Hz and then 6dB up.

4 hours ago, Satanica said:

that will sound good for very well recorded audiophile stuff or electronic music.

G'day Paul

You guessed my favourite music !, well not so much a guess, sounds to me like you know your stuff and your gear.

Yes I do run a few profiles (miniDSP Flex8/DAC) and do enjoy some metal and pop, more pop than metal but mostly grand orchestra and  other tracks that some HiFi Systems have trouble with normally.

 

Tilting up 3 or more dB down from 160Hz can (the other profiles) take away from  reproduction of some music.

It necessitates a brick wall HP filter at 20Hz as sub frequencies do present as quite a lot louder (clean and loud), you start to pick up foot falls and other attributes in the sub region, can make me feel queasy and upset the tummy at slightly higher than normal volume levels (I've had other folks feel a sense of dread or uneasiness, that and take away from (dominate) the information rich frequency range above omni directionality.  

Otherwise yes can and do fiddle with the PEQ and time delays manually. Haven't come into the world of auto EQ, Dirac or any other such electro wizardry at this point being from the school of old, predominately a listener of music rather than continual fiddler/Engineer, with the fundamental. Only times I do play with those functions is if something changes within the listening area, as it is built and re calibration of the response is required. Calibration is done in REW/Umik1  and with an Audio Control SA 5030/calibrated mic.  Rough but accurate. Horns have their own challenges as they can be shouty or have other slightly undesirable issues, hence a few dips in the HF, to mitigate these issues.

All fun.

https://www.youtube.com/watch?v=egdwy_Z4k1E&list=PLL6SQlmAb064kkU26uqGNv7sjnCpt1wU7&index=25

 

 

 

Edited November 22, 20241 yr by playdough

18 hours ago, Keith_W said:

If your computer fan spins at 2000rpm it will show up as a finger at 33Hz (2000/60). 

Yep, "constant magnitude anomaly" is probably better term to use than "the/a finger" 🙂 

The lounge is close to a busy road and there is a chipper mill running on the adjacent hill, 24/7, that as well as being a couple of blocks from the CBD, appears as rumble at <50Hz.

Soundproofing is great but, in a timber suspended home/floor, proofing below 50Hz is nigh on impossible as is treating for reverb/decay below 50Hz. Below 15Hz the building is in all practicality transparent (bonus), these frequencies just rock on through and are a given with any measurements here.

The bush block hut setting is more isolated and will give much better noise floor clarity, no fridge or PC fans either.

It's a bugger with super sensitive microphones, noise floor in a DIY ad hoc testing arrangement, new users of REW take note 🙂.

Bush blocks have their own challenges. I was surprised how loud the crickets were the last time I stayed in one. I was convinced the little bastards were in the house. 

10 minutes ago, Keith_W said:

I was convinced the little bastards were in the house

True, however there is a solution, free range chickens,,,,,,I was amazed they strip the place of almost every insect, except the bees and ants. 5 chickens on 5 acres. I feed them but free range them as well, they are well destructive things (turn over everything) on insects and vegie patches crickets are a favourite. Can't mulch anything outside the tube house vegie patch, chickens get into it.

On 14/11/2024 at 7:17 AM, Keith_W said:

Since there have been more threads asking about room treatment, I thought it would help if I wrote a short article to explain. 

 

PART 1: THE SCIENCE OF REFLECTIONS

 

First, a quick primer on how we hear. When we place speakers in a room and sit down to listen to music, we hear the direct sound of the loudspeakers and reflections from the room. The nature of these reflections is very important, but also very controversial. In general, there are people who believe that "the soundstage is in the recording". These types of people will want more absorption, and use controlled directivity monopoles. This approach creates a "they are here" kind of sound. There are also people who believe that "the room creates the soundstage". These people will want less absorption, more diffusion, use dipoles or omnis to create even more reflections, and this results in a "you are there" sound - in other words, the room creates the ambience. 

 

There is FAR from universal agreement about which approach is "better". All I can say is that either approach, when taken to extremes, is bad. If you put an omni in a small, reflective room, it will be bad. If you put a narrow radiating speaker into a psedo-anechoic chamber, it will be bad. The key is to understand where the middle ground is. I firmly believe that personal taste plays a big part in this. 

 

These are the important aspects of reflections: how early, how loud, from where, and how long.

 

How Early, and How Loud? 

Reflections that arrive within less than 20ms of the direct sound are within the Haas fusion zone and are perceived as part of the direct sound. If it is more than -15dB in relation to the direct sound, it has the effect of smearing the sound, reducing clarity. If it is between 20ms to 150ms (depending on frequency), it is perceived as ambience and spaciousness. If it is > 150ms, it is perceived as a separate event - an echo. 

 

"How early" can be estimated by measuring the distance between the loudspeaker and the first reflection points (don't forget the ceiling and floor in addition to the side walls and rear walls!) and calculating it using the speed of sound. The formula is t = d/c * 1000  where t is time in milliseconds, d is distance in meters, and c is speed of sound (343m/s). For example, a 5m distance will create a reflection that is 14.5ms delayed with respect to the direct sound. As a rule of thumb, every 1m adds 3ms of delay. 

 

 

It is far better to measure the timing of reflections. The relevant measurement is the energy-time curve. The image above shows how to read the ETC. We can see that in my room, the main reflection (1) that arrives in the first 20ms is more than -15dB attenuated with respect to the direct sound, which has been normalised to 0dB. The second reflection is -25dB to the direct sound. 

 

From Where? 

Note that the ETC does not tell you "from where". Psychoacoustic research into the perceptual effects of the direction of reflections is surprisingly lacking. It is generally agreed that reflections that arrive from the side, if within reasonable limits, are beneficial (Toole and Olive 1997). Reflections that arrive from the front, and especially from the rear, are deleterious because they correlate with the direct sound (Imamura 2013) although this was a small study and no other studies corroborate it. Reflections from below are required because if they are absent, it will sound unnatural. 

 

Research into diffusion is somewhat lacking. A number of studies now suggest that diffusers create "mini reflections" and the sum of these "mini reflections" is perceptually the same as a single large reflection, suggesting that diffusers are a waste of time. Again, few studies, not much evidence. 

 

How Long? 

The last aspect of reflections to be discussed is "how long" - also known as reverberation or ringing. What is reverberation? All wavelengths form room modes and standing waves. Short wavelengths form thousands of room modes which are so close together that they overlap and form a reverberant field. As wavelengths get longer, the room modes start to separate out and they become more apparent, so they no longer form reverberant fields. You may get a reverberant bass field in a basketball stadium or concert hall, but certainly not in a typical domestic listening room. We need to bear this in mind when we look at the relevant measurement, which is the RT60, T30, or T20. 

 

The RT60 stands for "time for a reverberant field to decay by 60dB". This has little relevance in our application because (1) the noise floor is typically about 40dB, meaning you have to measure at ear splitting levels to obtain a 60dB decay, and (2) reverberant fields do not form at long wavelengths as already discussed. Fortunately, sound decay is linear. So we measure the T20 (time for sound to decay by 20dB) or T30 (decay time of 30dB) and extrapolate it to 60dB by simple multiplication. The T20 or T30 given by your software program can be used interchangeably with the RT60. Note that the reverberation requirement is ignored so the T20/T30 needs to be interpreted with caution! A single spike in the T20/T30 at low frequencies IS PROBABLY A ROOM MODE and may not actually be prolonged decay time! 

 

 

RT60's have a target. The target depends on room volume and application. Here you can see Acourate's RT60 display which shows the upper and lower RT60 tolerance for room volume and different standards. 

 

In general, the RT60 target should be 250ms - 500ms depending on taste. A lower RT60 creates a more "dead" sounding room, and there is evidence that it paradoxically reduces clarity if it is too low. Symptoms include having to turn the volume so high to obtain clarity that you have to shout at someone else to be heard. A higher RT60 creates a more "lively" sounding room, but there is a high risk that if the speaker does not have controlled directivity, spectral distortion will result. This can cause speakers to sound too bright or too thick depending on where the spectral distortion occurs. When done right, music can be heard clearly at low volumes and you will still be able to hear normal speech without having to raise your voice. 

 

TAKE-AWAYS

Thus the research suggests that the goals should be: 

 

- reflections within 20ms of the direct sound need to be -15dB or more to avoid smearing the sound, 

- reflections arriving between 20-150ms are beneficial if you want to create a "you are there" experience. 

- late arriving reflections are bad. Fortunately our listening rooms are too small to create loud late reflections. 

- rear reflections are especially bad. 

- both over-treating a room and under-treating a room are bad. There is an optimum in between. 

 

Thus concludes Part 1 of this exploration. 

In general it's very useful presentation. However it is not free from need for some clarification.

1.      Quote: Reflections that arrive from the front, and especially from the rear, are deleterious…

Comment: Reflections from front wall are not always deleterious, it depends on stereo base and may add to signal-to-noise ratio and timbre positive value.

2.      Quote: A lower RT60 creates a more "dead" sounding room, and there is evidence that it paradoxically reduces clarity if it is too low. Symptoms include having to turn the volume so high to obtain clarity that you have to shout at someone else to be heard.

Comment: There is nothing to be surprised. Because when you are into “echoless chamber” our brain immediately begins to reduce our noise level sensibility to avoid hearing damage. You may sense it like “Wool in the ears” effect. Hence, we need to up loudness to be heard.

3.      Quote: reflections within 20ms of the direct sound need to be -15dB or more to avoid smearing the sound.

Comment: It’s not always right. Because this depends on the aim you follow to during listening. Some of the reflections (bad reflections) need to be deleted, some (good ones) not. There is well-known "plates method" to discover this separation.

4.      Quote: Reflections from below are required because if they are absent, it will sound unnatural.

Comment: What is the difference between “below” and others? Does it mean, that there is the acoustical difference in values between reflecting surfaces?

5.      Quote: rear reflections are especially bad.

Comment: that’s right. Especially when you listen concert records. If your rear wall is rigid, you will lose hall sense, music becomes flat.

 

On 22/11/2024 at 6:22 PM, basscleaner said:

A lower RT60 creates a more "dead" sounding room, and there is evidence that it paradoxically reduces clarity if it is too low. Symptoms include having to turn the volume so high to obtain clarity that you have to shout at someone else to be heard.

Hi , yes may as well pick it apart 🙂 expand on it.

 

From a little "hands on building and evaluating" I don't completely agree with this statement and to add to your comment above for this.

 

Noise cancelling headphones can be an example, personally seem to operate the headphones at a much lower volume level as the noise floor is  much, much quieter,,,,

With a HiFi and treated lounge,, to treat the area to the point of a "dead" sounding environment, in all practicality is actually not that easy to achieve. There has to be a serious amount of acoustic treating hardware installation performed on every surface.

 

I may suggest that overtreatment with inappropriate amounts of the wrong type of frequency co efficient (particularly high frequencies) might  be more common.

Normally a correctly treated room will actually much improve "human voice intelligibility" to a high degree with a content rich, highly detailed non reverbative  treated zone.   Music can be played at lower levels for highly defined centre image from the stereo soundstage , speech within the zone is more intelligible. Lower noise floor, less reverberation. Quote

A lower RT60 creates a more "dead" sounding room, and there is evidence that it paradoxically reduces clarity

Unquote

I would like to see the literature, link, whatever suggesting this rather misleading statement.

 

In all practicality  the opposite in application is evidence actually, frankly and is the reason Professionals treat acoustically,

An Engineered solution, within the treated  zone will provide a more comfortable and understandable in general audibly and for any reproduction/performance will  less "coloured by reflections" , this includes and is not limited to, reproduction, live music and speech.

 

The overly "dead" sounding treated zone is most likely a poorly Engineered mistake/erroneous, rather than overtreatment

@Keith_W Interested to hear what you have to say about this.

Matt

 

Edited November 23, 20241 yr by playdough

On 14/11/2024 at 7:17 AM, Keith_W said:

PART 2: DIFFUSERS 

In my opinion, diffusers are a waste of time for most rooms. This is for the following reasons: 

 

1. Toole says that the perceptual effect of a series of mini-reflections from a diffuser is the same as a large reflection, 

2. Diffusers need to be very deep if long wavelengths are to be effectively diffused, and 

3. Most normal room furnishings (shelves, furniture, curtains or blinds, general life clutter, etc) already provide effective diffusion at higher frequencies. 

 

The exception is an utterly bare bones room that nobody wants to live in. 

 

Diffusers need to be prohibitively large if they are to work at low frequencies. The depth needs to be 1/8 of the wavelength. A 100Hz frequency has a wavelength of 3.43m, meaning that the diffuser needs to be 43cm deep. This means most commercially available diffusers are ugly room decoration only, or a flex to other audiophiles. Shallow diffusers are products that you do not need, especially if you have shelves or storage along the walls. If you really need to have one, the best type to use is a Quadratic Residue Diffuser (QRD). You can use QRDude to help design your diffuser. 

 

 

PART 3: ABSORBERS 

There are two types of absorbers: pressure absorbers, and velocity absorbers. 

 

3.1. Pressure Absorbers

First, pressure absorbers. There are two types - membrane absorbers, and Helmholtz resonators. Both types of absorbers are more effective for low frequencies, have a narrow band, and need to be tuned to target the frequency in question. They both need to be placed where the pressure of sound is maximum to for maximum effectiveness - preferably the corners of the room, or if not, the walls. Dry walls and glass windows are effectively untuned membrane absorbers, so most listening rooms already have a degree of bass absorption, though it is narrow band and can't be tuned. 

 

Pressure absorbers can target bass ringing, but can not phase or timing issues between subwoofers and mains. The biggest problem is how difficult they are to tune. Membrane absorbers are tuned by changing the tension of the membrane and the absorbent material behind the membrane, and by deploying more absorbers. Helmholtz resonators are tuned by changing the surface area of the inlet, the length of the throat, and the volume of the enclosure. There are some variable Helmholtz absorbers on the market, but you need a lot of them. 

 

For this reason, DSP is the superior tool for tackling low frequency bass problems. DSP ticks all the boxes - finer control of amplitude, able to correct phase issues, and it can even tackle ringing. Dirac ART and Trinnov Waveforming are multi-subwoofer schemes that cancel ringing, but there are DIY options such as a DBA, and to a lesser extent, a VBA. 

3.2. Velocity Absorbers 

These work by increasing resistance to air particle movement and converting sound to heat through friction. The most common type is acoustic foam. Unlike pressure absorbers, velocity absorbers are broadband and absorb a wide range of frequencies. They are also more suitable for tackling high frequency anomalies and almost useless for low frequencies unless one is willing to put up with excessive room intrusion. The important variables are: 

 

- thickness of the absorber: the thicker it is, the longer the wavelength that can be absorbed. As a rule of thumb, the absorber needs to be 1/8 the wavelength of the lowest frequency. Its effectiveness drops below that. 

- density of the material: the more dense the material, the more absorption will occur, but up to a limit. If the density becomes too high, it will reflect sound. Denser material is better at absorbing low frequencies. 

- shape of the material. Some acoustic foam has ridges to increase its effective thickness and direct sound to be absorbed. 

- surface area. The more % of a room's surface area that is covered, the more absorption will be provided. 

- spacing. If the foam is spaced from the wall, it lowers the effective frequency. But this is not the same as "free thickness" because it is not accompanied by more density since we now have air occupying the gap. 

 

The absorption spectrum is specified by the NRC or Noise Reduction Coefficient or Absorption Coefficient. An NRC of 1 indicates 100% absorption (an acoustic black hole), and NRC of 0 is 100% reflection. IDEALLY, companies that are serious will publish the NRC at various frequencies, like this: 

 

 

Sadly, most acoustic foam companies gamble on the ignorance of consumers and publish inadequate data with the assumption that consumers do not know what to look for, or how to interpret the data if it was presented. At most, some will say something like "NRC 1.0 (200Hz)". 

 

Even if the NRC is published, bear in mind that measurement of the NRC is challenging and prone to errors. The standard required is ASTM C423, and requires a special reverberation chamber, humidity and temperature control, control of background noise, proper mounting of the panel to a fixture, specific microphone positioning, and proper test tones. If the chamber does not form a reverberant field at some frequencies, it might make the product look as if it performs better than it actually does (for obvious reasons, companies do not mind this). This is why you might see an NRC of greater than 1, where absorption exceeds 100%. Most average sellers of acoustic foam products do not have access to an ASTM C423 compliant test chamber. 

 

Some room furnishings, e.g. carpet, cushions, curtains, and tapestries will absorb sound. These are usually thin and low density, meaning that they only affect shorter wavelengths and do not provide much attenuation. This is a good thing, because gentle attenuation is usually enough. 

 

The effect of foam absorbers is profound especially if you have a lot of them. As you can see from the curve above, absorption across the audible spectrum is not uniform. These things have a real potential to colour your sound, selectively absorbing some frequencies more, and others less. What is worse, nearly all of them leave bass frequencies alone and only attenuate higher frequencies resulting in a lifeless top end and boomy bass when deployed carelessly. 

 

Because foam absorbers have so much potential to change the sound and the multiple pitfalls, selection and placement needs to be done carefully and with acoustic measurements to avoid spectral distortion. If you think you can buy a random well reviewed brand name absorber and tune it by ear, you are wrong! At the very least, you need a microphone and you need to know how to interpret acoustic measurements. 

 

Fortunately, most rooms reach the ideal RT60 target (albeit, the higher side of the target) with normal room furnishings alone so acoustic treatment is not needed for most people. 

 

At this point, many people on SNA will recommend a professional to measure and install acoustic products. This has its own pitfalls. They usually have a direct financial interest in selling you acoustic products, and they are usually overzealous. I have been to listening rooms that have been "professionally treated" but are actually overtreated, unpleasant spaces to be in. They take a room that measures and sounds OK and turn it into an overtreated space with spectral distortion. Some of them know that DSP is a better tool for low frequencies, yet they don't recommend DSP. Probably because they don't understand it and because there is irrational resistance from some consumers. And for the consumers who want to use DSP, it is so difficult that it turns many people off. 

 

My recommendation is to be an enlightened consumer. The best thing to do is to obtain a microphone and take your own measurements. Visit other hobbyists and do acoustic measurements of their rooms so that you know your preference. "RT60 = 500ms" sounds abstract because you don't know what it sounds like. If you engage a professional, ask them what their target RT60 is going to be, and what their recommendation is to tackle bass problems because these are especially challenging. 

 

Disclosure: I do not sell acoustic services, nor am I involved in any way in this industry. 

My remarks to the very good presentation, to my opinion - the best among many similar.

Part 2

I absolutely agree with Keith. A lot of diffuser constructions (with rare and very expensive exception) begin to work above 500 Hz.

Part 3

1.      Quote: First, pressure absorbers. There are two types - membrane absorbers, and Helmholtz resonators.

Comment: there is one more. Tube resonator, which absorbs LF energy by wall vibrations. The tuning of such a absorber is possible by use of lids opening at the ends of tube.

2.      Quote: spacing. If the foam is spaced from the wall, it lowers the effective frequency. But this is not the same as "free thickness" because it is not accompanied by more density since we now have air occupying the gap.

Comment: let us compare two absorber positions. First: all the ceiling is covered by absorber panels. Second: these panels suspended vertically. Question: is there any difference in absorption and where? Answer: yes. Second position will provide better absorption for high frequencies and worse for mid range. Conclusion: the placement method affects on the absorption.

On 14/11/2024 at 7:17 AM, Keith_W said:

PART 4: PUTTING IT ALL TOGETHER 

 

I have made this point several times in the past: your room is divided into different zones based on room volume and reverberation time T20/T30/RT60. 

 

 

The Schroder Frequency defines these zones. It can be calculated with this formula: 

 

 

Below the Schroder Frequency (Fs), wavelengths are too long to form reverberant fields and form room modes instead. The important thing to realise is that as long as the speaker produces bass, it is the room that dictates the frequency response. 

 

As wavelengths become shorter, the behaviour of sound transitions from waves to rays. This is the transition zone, between Fs and 4Fs. Above 4Fs, sound behaves as rays - the diffuse field. In this zone, it is the speaker that dictates the frequency response. 

 

The other relevant zone is the pressure zone, which where a half wavelength is longer than the longest dimension of the room. Modes can not be formed, so the room is pressured instead. This is usually pretty low - for example, a 30Hz sound has a half wavelength of 5.7m. This is not to be confused with the pressure zone adjacent to walls - where reflections (which are in phase with the incident wave) cause an SPL build-up of up to +6dB which extends to 1/4 wavelength from the wall. This is why pressure absorbers work best when placed against walls. But anyway, I digress. 

 

What is relevant is that > 4Fs and <Fs should be thought of and managed differently, since the physics of sound is different. Everything is affected - from how we take and interpret measurements, to our strategies to deal with problems. 

 

Below Schroder Frequency - the Modal Zone

There are broadly two ways we can tackle peaks and dips that are found in every room - room treatment and DSP. Neither option is particularly easy.

 

There are some people (notably Ethan Winer) who advocate for a room treatment only approach. As we have seen, pressure absorbers need to be specifically tuned to tackle problem frequencies and this is not easy. How do you know how much tension to apply to a membrane absorber? The performance of Helmholtz resonators can be predicted with a Helmholtz Resonator Calculator but note that the amount of attenuation can not be predicted since it is room dependent. Velocity absorbers need to be unbelievably thick, and even then the attenuation is not even. Accurate bass control will never be the outcome of this approach. 

 

By far the best outcome will be achieved with DSP and multiple subwoofers. This really ticks all the boxes - it is not as physically intrusive as room treatment, it is far more predictable, and it can be tuned to way below audible limits. There are many different schemes and strategies for multiple subwoofer deployment, even some that do not use DSP like Earl Geddes multi-subwoofer method. The disadvantages are obvious: cost of multiple subwoofers, having to reconfigure your system for DSP, added complexity, and the learning curve. 

 

Above the Schroder Frequency 

The first step to listen. If you like what you hear, then chances are it's probably OK. Toole made the point that we become acclimatised to our listening rooms. Over time, repeated listening makes this our preference. I like the sound of my listening room - to me it sounds spacious, tonally correct, and clear. 

 

Do not forget that everything you put in your listening room is also "room treatment". I made the point earlier that the RT60 target can be achieved with normal room furnishing, albeit at the higher end of the target. 

 

If, after all this, you still have a problem, then the solution of choice is room treatment and not DSP.

 

This is because DSP can not deal with short wavelength reflections. The only reason DSP is suitable for long wavelengths is because microphones measure only one point in space. A long wavelength means that that particular measurement is likely correct over a larger area (like how much your head moves when you are listening). I typically correct for an area of 50cm to give leeway for some head movement during listening. The typical head is about 15-18cm wide, so I account for 3 head widths of movement. A long wavelength is many times the dimension of my head - a 20Hz wave is 17m long. On the other hand, a 20kHz wavelength is 17mm. This means that DSP would be correcting for a single extremely specific point in space. It does not represent reality! 

 

DSP can be used for speaker correction. For upper frequency room correction, DSP should be applied very broadly. And note that all that it does is change the tone - it does not change where the reflections come from, or how long they ring. Neither can DSP lower the noise floor of the room. 

 

Room treatment can only attenuate reflections, it can not change the delay. The delay is set by the distance the reflections have to travel - it is a function of room size and choice of speaker placement, toe in/out, and speaker type (monopole vs. dipoles or omnis). The advantage is that it can selectively attenuate the reflections from some directions and leave others alone. 

 

So where should we place room treatment? We need to find out where the problem is coming from. It is best to follow these steps: 

 

1. Take a measurement of L and R speakers individually and look at the energy time curve. 

2. Look for peaks arriving within the first 20ms which are more than -15dB to the direct sound. 

3. Note the timing of the peak and calculate the distance from the delay. Let's say the delay is 9ms, this corresponds to a distance of about 3m. This means the reflection travelled 3m longer than the direct sound. 

4. Get out a tape measure. Measure the distance between listening position and speakers. Then measure the distance between the listening position and all the first reflection points including the ceiling and double it. That will be your culprit. 

 

 

My remarks to this part 4.

1.      Quote: Below the Schroder Frequency (Fs), wavelengths are too long to form reverberant fields and form room modes instead.

Comment: Schroeder Frequency formalism contains some deceit. A reverberation in LF range is strongly changes with points of measurement and hence can’t be the base of analysis. Moreover, interference value can compete with modal ones in FR in some cases.

2.      Quote: There are broadly two ways we can tackle peaks and dips that are found in every room - room treatment and DSP.

Comment: speaking about a room treatment, it never occurred to anyone, that any room in rigid boundaries is a simple resonator and if try to change the room dimensions by a little bit, then one may to get LF room response better, than initial? Look, among all possible Room sizes there are definitely the best ones. You may ask, how? In most cases bigger – no. But to make them less, for instance, by soundproofing layers, - why not?

3.      Quote: Take a measurement of L and R speakers individually and look at the energy time curve.

Comment: one more important thing – test of phase shifting between L and R speakers. There is no secret, that some of speaker producers don’t pay attention at this fact. There are many causes, why by producing, this effect arises. For this test you need to place two microphones – every unit at equal small distance to power point of every speaker and to compare results. You have to get the same FR or to turn for this aim your sound control device.

On 22/11/2024 at 6:56 PM, playdough said:

Hi , yes may as well pick it apart 🙂 expand on it.

 

Discussion on reflections is always a can of worms because the experts do not agree. If they don't agree, we have little chance as hobbyists. I think I made that clear in my discussion. 

 

 

On 22/11/2024 at 6:56 PM, playdough said:

Noise cancelling headphones can be an example, personally seem to operate the headphones at a much lower volume level as the noise floor is  much, much quieter,,,,

 

Headphones are not speakers. There is ample evidence that many audible thresholds for headphones do not apply to speakers because the listening room muddies things up considerably - so any research done on headphones should be interpreted with caution when it comes to speakers.

 

Regardless, I take your point that a lower noise floor is beneficial. However, we have already seen that the typical noise floor in rooms has a rising bass response because rooms act as low pass filters. Typical absorbent room treatment would distort that even further. 

IMO a room's noise floor is a function of the construction of your room. I live in a glorified tent and I suffer from a heck of a lot of sound intrusion. Some of it can be mitigated by properly sealing the room and plugging all the air gaps, but the real solution would be to do something about those walls. I am not talking about putting treatment on top of it, I mean filling the gap between the brick veneer and drywall with acoustic insulation, or knocking down the whole house and building a new one out of solid brick. I understand you work in construction, you should know a lot more about this than me. 

 

On 22/11/2024 at 6:56 PM, playdough said:

Quote

A lower RT60 creates a more "dead" sounding room, and there is evidence that it paradoxically reduces clarity

Unquote

I would like to see the literature, link, whatever suggesting this rather misleading statement.

 

Imamura and colleagues, 2013: link, quoted in Toole's book Ch. 7. I have the AES paper somewhere in my collection (I think!) but I can't find it. 

 

Thanks for the reply, well received , Keith 

16 hours ago, Keith_W said:

Discussion on reflections is always a can of worms because the experts do not agree. If they don't agree, we have little chance as hobbyists. I think I made that clear in my discussion. 

Yep, agree. It shouldn't be though. It's as though personal opinion is winning over correctly applied science.

 

20 hours ago, Keith_W said:

Headphones are not speakers. There is ample evidence that many audible thresholds for headphones do not apply to speakers because the listening room muddies things up considerably

Well, ok, again without the any published (freely available) literature,,,headphones can be considered listening without the room involved, or the actual reference to the fundamental.

Personally a believer that any reverbrent ambience or effect in any given media is to be portrayed by the speakers/headphones rather than superimposed over by room reverberation.

I've never known of a music or media producer to actually rely on a specific influence of any given listening zone, this simply doesn't exist, although I hear of it. I've asked a couple of Producers, to have the question met with quite a lot of scepticism, actually.

(You don't want to know what they say, it's not nice toward some segments of the Audio Industry)

 

20 hours ago, Keith_W said:

we have already seen that the typical noise floor in rooms has a rising bass response because rooms act as low pass filters. Typical absorbent room treatment would distort that even further.

Not really, erroneous poorly identified problems with reverberant frequency magnitudes, as stated are measured and identified.

 

Typically, a prescription of treatment is determined, before hardware is installed, within the listening zone not the other way around.   

 

20 hours ago, Keith_W said:

but the real solution would be to do something about those walls. I am not talking about putting treatment on top of it, I mean filling the gap between the brick veneer and drywall with acoustic insulation

Sound proofing for mitigation of intrusion of noise floor,  is actually a very sharp double edged sword. 

Sound proofing via means of double brick, will not be advantageous within the listening zone. actually in real life.

Soundproofing and acoustic treatment is/are two entirely different disciplines and should always be treated as such. Using an example may well be an easier more understandable way of explaining this.

Example.

A brick room was identified as a great place to set up a HiFi system as it relatively sound proof. 

The room was tested and identified as grossly reverberant, through the bass frequencies.

Higher frequencies were deemed to be reasonable and fall within the definition of being ok through mid range and higher frequencies, due to the fact book shelving was installed and possessions placed   for the full length and height of the left and right walls and a thick natural fibre carpet with underlay placed on three quarters of the tiled floor. A high ceiling was identified as not being an issue either.

Front wall was windowed so was identified as a leak for the lower frequencies and an actual bonus, with regard to the acoustics within the room

Prescription for treatment was the installation of a timber frame at a measured and calculated distance from the rear wall (listening end of room). this area behind the new timber frame was filled with a known high performance sound absorbent and the wall clad with a limp mass loaded membrane and formed a large bass trap, full width and height.

Room re measured, with obvious outcomes.

 

In conclusion, I'll reiterate again sound proofing through construction methods, is not acoustic zone treatment.

 

21 hours ago, Keith_W said:

Imamura and colleagues, 2013: link, quoted in Toole's book Ch. 7. I have the AES paper somewhere in my collection (I think!) but I can't find it. 

Pity this information is firewalled behind Membership and cost. 

In accordance with the statement, that any room having hard rigid boundaries, is the resonant chamber for LF range, I disagree with: "Soundproofing and acoustic treatment is/are two entirely different disciplines and should always be treated as such." Allow me to say, that is not quite so, significantly, is quite not. The basement of  Theory of Acoustical Room Dimension tells, that there is connection between ARD, minimum FR distortion and power point positions of LF speaker system (and point of listening too), because they form boundary conditions for wave equation and determine its solution. That's why, to my opinion, correctly selected room dimensions for the LF source(s) model define the relationship between soundproofing and treatment for a room. 

 

 

2 hours ago, basscleaner said:

The basement of  Theory of Acoustical Room Dimension

Interested, yes indeed there  would be a room of ideal area dimensions that will/can if constructed from scratch, the majority of us (hobbyists) do not have luxury of being able to construct the "perfect dimensional area" 

Please do tell, link or literature, thanks. information required for this.

 

 

Might I suggest that the task at hand is one of finding a good balance, or a synergy of elements that act well together in relation to the needs of the Operator.

Some of these elements are fixed (such as room dimensions), cannot be changed, due to whatever constraint and either a compromise is made or solution sort/calculated and built to make the best of a given situational constraint.

 

2 hours ago, basscleaner said:

Theory of Acoustical Room Dimension tells, that there is connection between ARD, minimum FR distortion and power point positions of LF speaker system (and point of listening too), because they form boundary conditions for wave equation and determine its solution.

There are a number of well documented "sub frequency speaker"  position theories, as well as stereo speaker, listening position guides.

Google is a friend here.

 

2 hours ago, basscleaner said:

That's why, to my opinion, correctly selected room dimensions for the LF source(s) model define the relationship between soundproofing and treatment for a room. 

To be fair this isn't a logical statement. Yes I get it, in relation to room dimensions and speaker placement in relation to the listening possi.

 

Otherwise there is no real relation between soundproofing or acoustic treatment.

One could suggest in some situations, the acoustic treatment is by its very  nature a sound proofing aid, but it's rare. 

 

A good real life example is

Example

A lightly constructed weatherboard/timber type construction will have excellent bass reverberation characteristics however it will pose little to no sound proofing imposed on the bass and the neighbours might not be happy about that.

One could suggest that no bass reverberation treatment is required and  in all practicality, integrated in the construction method, although a compromise in practice.

 

Soundproofing has a direct relation to room construction whether it be a large tent or pre formed cast slabs of concrete.

 

Acoustic treatment has a direct relation to the reverberation characteristics of every individual  given construction.

 

Sound proofing is measured outside the listening area, as a function of performance and  characteristics of what frequency co efficient the proofing (actual construction method) has. Or in layman's terms, at what frequency's and how many dB is attenuated, how the area leaks sound.

 

Acoustic treatment is  measured within the acoustic zone, as a function of mitigating undesirable, excess reverberation, with a calculated engineered mitigation strategy, within the zone.

🙂

 

 

While we are at it I have a question about a comment made, earlier

On 22/11/2024 at 8:04 PM, basscleaner said:

Comment: one more important thing – test of phase shifting between L and R speakers. There is no secret, that some of speaker producers don’t pay attention at this fact. There are many causes, why by producing, this effect arises. For this test you need to place two microphones – every unit at equal small distance to power point of every speaker and to compare results. You have to get the same FR or to turn for this aim your sound control device.

Are you suggesting a pair of stereo loudspeakers will have differing performance (phase shift) between the speakers ? 🙂 At manufacture ?

 

Or are you saying that calibration of each speaker should be performed, in relation to a speaker/room calibration

Sorry having trouble following the theory presented,  testing method, the speaker malfunctions or corrections required and what Manufacturers of the speakers could do better.

 

We have to remember correct room placement of speakers would likely mitigate this problem as  stated.

 

Cheers

playdough

 

 

Edited November 25, 20241 yr by playdough

Let me first introduce you with some base statements of ARD theory. The investigation, concerning a search for the acoustical room dimensions, has a rich history. Many of researchers spent much time for it. Discussions were held on the search of "gold proportions", " absolute best dimensions" and so on, but without great success. Well-known acousticians R.Bolt, T.Cox and others made a significant contribution in this problem. However with the advent of high-quality EQ the problem has lost its urgency, but was never resolved. The question of what should considered as set of acoustic dimensions, also remains unclear. Researchers opinion were divided by two parts. The first of them calls Acoustical Room Dimensions any set of them, where you get good behavior of FR at listening point. This means, how it's easy to see, that ARD for them not exists at all. The second part suggests, that the acoustical room dimensions are those of them, where good behavior of FR for LF is observed in the maximum number of listening points for system "Source(s) - Listener" under certain boundary conditions. These conditions determined by power point(s) of source(s), limited wall (ceiling) thickness, which defines room volume reducing, distortion limiting level, possible stereo (or any) base and Listener positions (system's triangle for stereo), shape and, of course, dimensions set. Besides, there is a question of absorption and furniture influence, but I leave it out for now. The proponents of the first part have developed the approach  with the help of Trinnov technology (www.trinnov.com), where they use many LF sources to achieve "good FR" in LF range for many listening points. For investigations for second part FEM (final elements method) was used, where the search was carried out for such a room dimension. The results of calculations for some rooms of shoebox shapes led to the following conclusions: 1. ARD exists as a relative concept, connected with the initial room dimensions. An other words, for any initial room dimensions there is the best with accordance of real conditions. 2. Of particular interest is the worst room dimensions. If you have them as initial, it means, that your speaker system is in irreconcilable conflict with your room. 3. Real choice of your room dimensions when projecting is always the compromise decision, depending from some restrictions, caused by ergonomics, design at cetera. But such an analysis allow to do conscious choice and increases the probability of successful installation.

I suspect, that this is new for you and invite you to discuss, if it seems to you interesting. Some years ago I discussed this with Trevor Cox, but after there were only two articles in Russian scientific journals and did not receive completion.

Sorry, that I can't answer other questions for now. But promise to answer closest time tomorrow. Thanks a lot for it!

@basscleaner

Gday.

Thinking over any relationship between Acoustic treatment and Sound Proofing and  after actually doing a little work in those disciplines is.

 

The more soundproof a  room or building  construction is, the worse its acoustic performance will be. 🙂 

The double edged sword.

 

Try imagine the acoustic performances between a solid brick room and a large tent of the same dimension.

 

playdough

Well @basscleaner lives in Moscow. Most buildings there would be solidly constructed to keep the winter out. I have been to Moscow, it's the coldest place I have ever visited. It somehow felt even colder than the ski fields in Japan and Canada. It's not like he lives in the awful glorified tents that we live in. Can you imagine someone constructing a Queenslander in Moscow? 

 

Anyway, you make a valid point about construction and acoustics. Most of the homes we live in are brick veneer + drywall. Exception is WA (mostly double brick) and Queensland (mostly light construction). A home like a Queenslander is like living in a box surrounded by membrane absorbers on all sides. It would leak bass like hell, annoy your neighbours, and let environmental sounds in whilst doing a poor job of thermal insulation and an excellent job at ventilation. But it would have fewer bass problems. A WA double brick home would have hardly any bass absorption, so it would be an acoustic nightmare. But also less sound intrusion and sound leakage. 

19 hours ago, playdough said:

 

 

Interested, yes indeed there  would be a room of ideal area dimensions that will/can if constructed from scratch, the majority of us (hobbyists) do not have luxury of being able to construct the "perfect dimensional area" 

Please do tell, link or literature, thanks. information required for this.

 

 

Might I suggest that the task at hand is one of finding a good balance, or a synergy of elements that act well together in relation to the needs of the Operator.

Some of these elements are fixed (such as room dimensions), cannot be changed, due to whatever constraint and either a compromise is made or solution sort/calculated and built to make the best of a given situational constraint.

 

There are a number of well documented "sub frequency speaker"  position theories, as well as stereo speaker, listening position guides.

Google is a friend here.

 

To be fair this isn't a logical statement. Yes I get it, in relation to room dimensions and speaker placement in relation to the listening possi.

 

Otherwise there is no real relation between soundproofing or acoustic treatment.

One could suggest in some situations, the acoustic treatment is by its very  nature a sound proofing aid, but it's rare. 

 

A good real life example is

Example

A lightly constructed weatherboard/timber type construction will have excellent bass reverberation characteristics however it will pose little to no sound proofing imposed on the bass and the neighbours might not be happy about that.

One could suggest that no bass reverberation treatment is required and  in all practicality, integrated in the construction method, although a compromise in practice.

 

Soundproofing has a direct relation to room construction whether it be a large tent or pre formed cast slabs of concrete.

 

Acoustic treatment has a direct relation to the reverberation characteristics of every individual  given construction.

 

Sound proofing is measured outside the listening area, as a function of performance and  characteristics of what frequency co efficient the proofing (actual construction method) has. Or in layman's terms, at what frequency's and how many dB is attenuated, how the area leaks sound.

 

Acoustic treatment is  measured within the acoustic zone, as a function of mitigating undesirable, excess reverberation, with a calculated engineered mitigation strategy, within the zone.

🙂

 

 

While we are at it I have a question about a comment made, earlier

Are you suggesting a pair of stereo loudspeakers will have differing performance (phase shift) between the speakers ? 🙂 At manufacture ?

 

Or are you saying that calibration of each speaker should be performed, in relation to a speaker/room calibration

Sorry having trouble following the theory presented,  testing method, the speaker malfunctions or corrections required and what Manufacturers of the speakers could do better.

 

We have to remember correct room placement of speakers would likely mitigate this problem as  stated.

 

Cheers

playdough

 

 

Quote: There are a number of well documented "sub frequency speaker"  position theories, as well as stereo speaker, listening position guides.

Re: The only "valued" parameter for LF source for wave equation solving is the coordinates set for his power point. This is approximation, of course, because any LF source really is a flat surface. This will demand in signification in future.

Quote: A lightly constructed weatherboard/timber type construction will have excellent bass reverberation characteristics however it will pose little to no sound proofing imposed on the bass and the neighbours might not be happy about that.

Re: For bass recording the best "room" is absolutely empty space. But we are talking about a room acoustics influence, don't you? Because we want to listen, moreover, individually "timbred" sound. Lightweight cladding on heavy walls, as Keith said right, plays the role of bass filtering device. If you don't have masonry wall, then, you are right, it will be headache for your neighbors. And the difficulty is to achieve smoothness, maintaining the linearity of the personal trend (it can have different slopes). Repeat, that we are talking about LF range, because it is the basement for further well-known treatment.

Real connection between sounproofing and treatment is only for LF range. Because namely the room fences form basement for LF behavior inside.

Quote: Are you suggesting a pair of stereo loudspeakers will have differing performance (phase shift) between the speakers ?  At manufacture ?

Re: I can't say for sure, that this only happens with speakers. You have a deal with all way for sound track, including all parts. But to my practice, believe me, it's a common story. It's very good, if manufacturers requires to do calibrating procedures and we do it by applied microphone for every speaker. But it doesn't mean, that both speakers work without mutual phase shifting.

6 hours ago, Keith_W said:

Well @basscleaner lives in Moscow. Most buildings there would be solidly constructed to keep the winter out. I have been to Moscow, it's the coldest place I have ever visited. It somehow felt even colder than the ski fields in Japan and Canada. It's not like he lives in the awful glorified tents that we live in. Can you imagine someone constructing a Queenslander in Moscow? 

 

Anyway, you make a valid point about construction and acoustics. Most of the homes we live in are brick veneer + drywall. Exception is WA (mostly double brick) and Queensland (mostly light construction). A home like a Queenslander is like living in a box surrounded by membrane absorbers on all sides. It would leak bass like hell, annoy your neighbours, and let environmental sounds in whilst doing a poor job of thermal insulation and an excellent job at ventilation. But it would have fewer bass problems. A WA double brick home would have hardly any bass absorption, so it would be an acoustic nightmare. But also less sound intrusion and sound leakage. 

Quote: 

The more soundproof a  room or building  construction is, the worse its acoustic performance will be.  

The double edged sword.

Re: That's not quite true. It depends on, repeat, the goal you try to achieve. Any treatment is the compromise solution. Do you want to have maximum pleasure from music listening or to have significant estimation from recording quality? These are two poles of room responce and real result is between them.

11 hours ago, Keith_W said:

Exception is WA (mostly double brick)

Is this a good thing as I live in WA and my room is double brick 😊

14 hours ago, basscleaner said:

Re: That's not quite true.

In an engineered actual  reality "real life off paper or outside imagination" , there are grounds to well support the statement. Please provide an example/lnk/document or more of your experience to support your suggestions.

 

14 hours ago, basscleaner said:

Any treatment is the compromise solution.

Any treatment, well designed and installed is an improvement. 

 

14 hours ago, basscleaner said:

Do you want to have maximum pleasure from music listening or to have significant estimation from recording quality?

Please expand on this as it is an "anti statement" it it's own right.

 

well designed and installed acoustic treatments improve listening pleasure, no ?

 

Cheers

playdough

 

P.S. answering questions improves everyone's understanding of the Topic, that and direction for improvement.

14 hours ago, Sean Perth said:

Is this a good thing as I live in WA and my room is double brick 😊

 

As the other posts have indicated, it's a double edged sword. Solid construction in a house like yours is better for sound insulation - less sound comes in, less goes out. Provided you have also paid attention to sealing all your air gaps (windows, doors, ventilation holes, etc). But it also provides less bass absorption since drywall is a membrane absorber so you would have a heck of a lot of bass ringing. One reason why high end HT builds have a "box in a box" design (i.e. a room built into a room) is to provide more isolation. But you pay the price of more room intrusion and high construction cost. IMO this kind of design also creates a windowless "dungeon" feel that I am not a fan of. But we are not here to talk about aesthetics, we are here to talk about sound