Acoustic Panels and Bass Trapping a new lounge

[DVDHack]

When you're done you'll be able to rent it out as a band practice room.

[playdough]

 

She took my good speakers in the divorce, 

Sorry we we are stuck with these for testing

 

There is a room suck out room  anomaly in the graph and some minor things in the FR we should just smile and watch on, it;s part of the graph and getting better

I'll run  a book shelf later for a "sanitized looking graph", wo the 21"s, won't look cool however, sanatised.

 

@almikel had mentioned some things in a previous post and I would like everyone to discuss that, not my rig FR

This is more of a try hard DIY Test the wears on the walls, anti speaker thread, not transducer accuracy test.

 

 

 

Edited August 18, 2023 by playdough
spelling

[playdough]

58 minutes ago, DVDHack said:

band practice room

It's turning out to be a nice area to listen to things that make noise. 

I seem to have fixed the 

 

Room flexing, bloat reverb, room pumping at very low, insanely low Fz, without interfering with the lively HF, this large space seems to have. Everyone has heard this trait, mostly.

 

This only seems to happen in effect locally at the listening position where the traps are deployed

 

Edited August 18, 2023 by playdough

[davewantsmoore]

1 hour ago, playdough said:

We could use a book shelf speaker which would probably give you what you want Dave, a sanitised FR that drops off the scale at 30Hz or we could use the rig in place which is a bit lumpy, but quite obviously useful outputting from at 10Hz and beyond

You have misunderstood what I said, or why I said it.

[davewantsmoore]

2 hours ago, playdough said:

We could use a book shelf speaker which would probably give you what you want Dave, a sanitised FR that drops....

No, I'm just trying to help you analyse the room response properly Glenn.  

 

It too late now, unless you are going to take the traps down....  but you can still use the "before" data, if you show the spectrogram(s) normalised.

[davewantsmoore]

1 hour ago, DVDHack said:

I've had speakers that only sound good when they're loud, as an example.  

Typically a frequency response problem, related to Fletcher Munson.

 

1 hour ago, DVDHack said:

I have a mate who optimised his room

The key is fixing acoustic issues at any (relevant) SPL.

Setting a "target curve" can be done later, independantly.... but their target will depend on overall SPL (see above)

 

1 hour ago, DVDHack said:

The second room sounds better now and I've only done a few things.

Rooms and speakers are hard, because most of the acoustic issues you have (major SBIR, early reflections, spare room modes at LF) cannot be solved with typical "account treatment" that doesn't also over damp the room..... but it's hard to generalise.

 

Using acoustic sources to solve these issues is another angle of attack, and something that's been around for a long long time, but fallen out of favour in the past 30 years ..... "flanking woofers" ... even 3-channel (stereo+centre) ... and more recently things like Dirac Live ART.    My gravitation towards dipole speaker, and many subwoofers, is somewhat because of this issue (SBIR, LF modes, direct to reflected sound ratio, etc.)

1 hour ago, playdough said:

A very loud test.

Yes, I would test at your loudest SPL that you will have in real content.   ~105dB seems right.

 

1 hour ago, playdough said:

room flex

Yeah, you don't want that  

[playdough]

3 minutes ago, davewantsmoore said:

 have misunderstood what I said, or why I said it.

It's ok Dave, Im trying to. 

We have different work methodology  processes to end at the same goal.  Will get to that one day after I've smacked down the reverb at 30 and fixed the suckout at 50Hz.

 

I think I have worked out areal  mathematical calculation tool  to actually model, from outcomes of the work done already done here to build a trap, 200mm deep to target a narrow band at 30Hz as a wall surface treatment.(pink unic horn myth ATM)  my thinking is it may fix the 50Hz issue.

I'm kind of keeping that quiet for now, I'll put it up later when I know it works for sure. 

 

Future Work

I'll make the 3rd trap, for the rear wall, it will be "longer" as that forms part of the Maths Equations im into Narrow Band, high sensitivity anti 30Hz reverb tool with narrow Q 

 

Sound ok ?

 

[DVDHack]

5 minutes ago, davewantsmoore said:

Using acoustic sources to solve these issues is another angle of attack, and something that's been around for a long long time, but fallen out of favour in the past 30 years ..... "flanking woofers" ...

I've concluded that's why I don't have low frequency issues in my secondary room, the room is 12.8m x 6.5m x 3.1m so it doesn't have as many issues as a smaller room any way but I have the subs (2 x PerListen d15s) located either side of me, just worked out to be a good spot, I also have them pulled out from the wall a bit.  I still run the JBLs full bandwidth with a crossover roll off at 15Hz, the subs cut out at 50Hz if I recall correctly..  

[davewantsmoore]

1 minute ago, DVDHack said:

I've concluded that's why I don't have low frequency issues in my secondary room, the room is 12.8m x 6.5m x 3.1m so it doesn't have as many issues as a smaller room any way but I have the subs (2 x PerListen d15s) located either side of me, just worked out to be a good spot, I also have them pulled out from the wall a bit.  I still run the JBLs full bandwidth with a crossover roll off at 15Hz, the subs cut out at 50Hz if I recall correctly..  

I was more thinking in terms of the strong SBIR you get > 100Hz for "flanking woofers" .... so you may find benefit to running your subwoofers up a lot higher.

 

... but yes, more LF sources (if they are in very different places) usually helps a lot.

 

 

 

[playdough]

https://www.webconversiononline.com/wave-length-calculator.aspx?frequency=30&scale=hz&medium=air

 

The 30Hz wavelength in air is close to 11.88m, the trap will fairly well be a half that wavelength,, maybe a quarter.

Note, must check I have 5 m continuous MLV. The width of the trap  may well be a quarter wavelength or even an 8th

200mm depth as a socially acceptable amount of room space taken, by the hardware.

This is a simplistic view and "throwing it out there" forall to see. as there are a few other factors that are unknown, like ductility of the MLV, the air volume enclosed and many other variables.

 

[DVDHack]

12 minutes ago, davewantsmoore said:

I was more thinking in terms of the strong SBIR you get > 100Hz for "flanking woofers" .... so you may find benefit to running your subwoofers up a lot higher.

 

... but yes, more LF sources (if they are in very different places) usually helps a lot.

 

 

 

Im still finalising the treatment in that room, I've got it all sitting in the positions but need to tidy up and mount it or create stands for corners.  When it's done I'll have a play with the cut off frequency but before I do that I need to optimise the speaker positions and do a time alignment of the subs.  It's a new room setup, sold the old speakers out of that room.

[davewantsmoore]

24 minutes ago, playdough said:

The 30Hz wavelength in air is close to 11.88m, the trap will fairly well be a half that wavelength,, maybe a quarter.

Note, must check I have 5 m continuous MLV. The width of the trap  may well be a quarter wavelength or even an 8th

There is no need to make the dimensions (area) of the trap any size vs the wavelength.   ie. the trap will work for 30Hz whether it is 30cm x 30cm, or 5m x 5m.... the only difference is the amount of effect, but this is related to the size of the room (ie. the % of the room covered in trap), not the wavelength of sound.

 

24 minutes ago, playdough said:

200mm depth as a socially acceptable amount of room space taken

[playdough]

8 minutes ago, davewantsmoore said:

dimensions (area) of the trap any size vs the wavelength.   ie. the trap will work for 30Hz whether it is 30cm x 30cm, or 5m x 5m

I dunno about that Dave and it's exactly my mission to categorically, mathematically dispel that exact "normalised" theory I keep hearing about.

I may be completely barking up the wrong tree and that's ok, it's on me with the hardware. We hav an opportunity to really see what if anything goes, in the real, in a problematic odd shaped living area 2.4m high, smack in the middle of the lives of those here who to be fair are egging me on right now, They, non Audiophiles are loving what's been done to the place visually and acoustically.. After the plaster episode, things were strained for a bit. 

[playdough]

5 minutes ago, playdough said:

30Hz whether it is 30cm x 30cm, or 5m x 5m

Show mw the maths/model/ca/sim whatever, you came up with to make such a broad statement 

This is meant to be fun, let's all grin about this. 

[DVDHack]

The trap will only absorb the pressure that hits it.  These are pressure traps so they will absorb energy by the membrane converting the sound (air) pressure to mechanical energy on the membrane and some in the absorption to heat.  If the traps don't have enough surface area only a small portion will be converted.   I still think the best way to build these is the either, know what you're doing, which I don't, or adding more treatment until it meets the threshold I'm looking for.  That's why I use 600 x 1200 modules.

 

Thats my understanding 

Edited August 18, 2023 by DVDHack

[davewantsmoore]

23 minutes ago, playdough said:

I dunno about that Dave

The area of the trap vs wavelength of what it absorbs is irrelevant.

The area of the trap does relate to the efficiency.   ie. a small one will have low "efficiency".

 

Think about a woofer.   It is small, but it can make 30Hz.... it just has "low efficiency".

 

You can use a woofer in reverse, as an "active absorber" of sound ... or as a microphone (by recording the voltage generated when the sound moves the woofer) .... and you can see that a small area "membrane" does work on low frequencies.

 

23 minutes ago, playdough said:

exact "normalised" theory I keep hearing about.

What do you mean by "normalised" ?

 

23 minutes ago, playdough said:

I may be completely barking up the wrong tree and that's ok, it's on me with the hardware. We hav an opportunity to really see what if anything goes, in the real

The thing you build may have an effect ... but whether it does or not has nothing to do with the area vs wavelength (aside from how that related to efficiency).

 

23 minutes ago, playdough said:

loving what's been done to the place visually and acoustically.. After the plaster episode, things were strained for a bit. 

 

 

20 minutes ago, playdough said:

Show mw the maths/model/ca/sim whatever, you came up with to make such a broad statement 

 

If you look at the maths (beyond the simple calculator) for the radiation of sound.... you'll see there is nowhere that puts any sort of limitation on a tiny trap being able to absorb a large wavelength.   It simply doesn't work that way....   a membrane the size of 50c, tuned correctly, can absorb 20Hz (or whatever) .... with the obvious, limited efficiency relative to the area the sound was radiating in.   eg.  in a room a 50c sized trap is useless.     If the space the sound was radiating into was only the size of a tennis ball, then a 50c sized "trap" might do a very good job.

 

To get a bit more "practical" ... you can understand this is true, if you look at the design of active absorbers.    Like a subwoofer, but it doesn't radiate sound, it absorbs it.   The membrane moves and absorbs the pressure.   These work, even with membranes the size of a typical subwoofer.     On the flip side, a subwoofer is above to wiggle a (small) membrane, and generate low frequencies (it's all, to some degree, the same thing).

 

17 minutes ago, DVDHack said:

The trap will only absorb the pressure that hits it.

Yes

 

17 minutes ago, DVDHack said:

I still think the best way to build these is the either, know what you're doing

Simplistic calculators do an ok job at getting a ballpark.

 

The tricky part is, when you pick your real world materials, knowing the real mechanical properties of them (absorption, stiffness/compliance, etc.) to be able to put those values into a calculator.   They're difficult to measure... and so if you calculate a trap that will work over 30 to 50Hz, it is easy to get one which works over a different range.    It best to build things and measure their result, and then build another (different) one if needed, ie prototype.... rather than doe some sort of perfect simulation.

[DVDHack]

16 minutes ago, davewantsmoore said:

The tricky part is, when you pick your real world materials, knowing the real mechanical properties of them (absorption, stiffness/compliance, etc.) to be able to put those values into a calculator.   They're difficult to measure... and so if you calculate a trap that will work over 30 to 50Hz, it is easy to get one which works over a different range.    It best to build things and measure their result, and then build another (different) one if needed, ie prototype.... rather than doe some sort of perfect simulation.

I've done some calcs and looked at the profiles calculated on the acoustic calculator sites.  What I will do when I've finished current projects is to build some modules at 3 different depths.  I'll divide a 1200x600 module into 3 pockets of 400x600mm with slightly different depths by changing the position of the back panel.  With insulation to increase the Q I should be able to get a better broad spectrum affect targeted around my main room modes that manifest in the corners I can position treatment.  I know some modes are down the middle of the room but I can't treat those.

[davewantsmoore]

8 minutes ago, DVDHack said:

build some modules at 3 different depths

The properties / tuning / compliance of the membrane is the tricky bit.   Absorbers, not so much.

 

You can build very shallow traps that work at low frequencies, just that they work over a limited Hz range, and are highly tuned.

 

Very smart people these days are building much more complex "traps" which works over a wide frequency range that are quite shallow, using "segments" that couple together in ways where the result is much more than the sum of the individual parts.   Some manufacturers even using this sort of thing inside speaker enclosures.

[playdough]

9 hours ago, davewantsmoore said:

You can build very shallow traps that work at low frequencies, just that they work over a limited Hz range, and are highly tuned.

 

 

Dave, you really need to start backing your facts with some actual 

 

Link to a website

Show me the maths

Show me anything that you have made.

 

I have gone over everything you have posted and it's not leading to anything  only your conjecture.

 

 

 

[playdough]

The work went well and thought I could share a few thoughts

 

Summary from the last 3 weeks

 

Every thing has been hand made fairly well from scratch, Bunnings and Spotlight

Specialist materials, the 20mm sheet Polymax, I've had for a while, waiting for a job like this. The MLV was a grant, from someone who has a very keen interest in this my project and it's now realised outcomes, including the 3D Printable QRD

 

Completed so far.

 

5 x 40mm thick panel traps targeting first reflections and the dead centre of the ceiling, 

That calculated to work 2000Hz and up, theoretically but combined with a carpet, performed better than expected. 

It would probably do for most, that and wall diffusors at first reflection

 

Symptoms that hardware solved mainly stereo image firmed up and became far more detailed and notably less fatiguing (even the kids said it was easier to listen to), more relaxing and inviting. Obviously the stereo was far more interlegible, engaging and simply transformed, from when it was in an empty room.

 

The notable acoustic attributes of the room these initial treatments did not solve was in essence the combing or summation effect over short distance from the listening position, driven mainly from the bare walls. Low med and medium frequency's in particular . Moving across the couch showed this. Walking about the room, and the Test mic also showed this.

The stereo image was Ok, but still could have had more engagement and definition. Shrouded and veiled in reverb from the walls. Ok but not great.

 

Printing a nice set of QRD Taps, number 4 on the printer now.

 

Manufactured and installed the 2 wall traps

 

What the wall traps solved was frequency combing completely gone, night and day difference evident on install immediately when they slipped into the tight recess

 

This was surprising as only a 20mm layer of Polymax was facing the room, under the membrane although the Membrane had a soft 6mm HD closed cell foam coat, also facing into the room, combined only 26mm, which is calculated at 4000Hz and up, minimum HF Treatment

 

Seemed to do a lot more though which after taking it all in for a day, yea, combing was really gone, complete area character change for the better . 

 

It only got better, the actual bass trap it's self is genius TBH, instantly ridding the timber built room of bloated bass, room pumping, wall flexing and door rattle, relaxed the massive bass summation off and on boundaries, particularly well in the corner the 2 membranes are closed to. 

 

To hear the bass without those artefacts' well, monumental success, not less.

 

I'm no engineer so please forgive me if the graphs I try to show do not read  well. Illl possibly get better if I'm shown rather than bagged.

 

What I've seen in the graphs of the effect of the traps was improvement across 15 to 140Hz  broad band high sensitivity, with 200mm of surface panel depth.  With added benefit of eliminating combing across the whole listening area of 4 seats.

Fact

You don't know how bad the combing is until you actually treat the walls.

They have made a corner boundary a good place to listen to the stereo (which is weird) has to be experienced first hand it's too good

 

I was told what I have done is not possible on MANY OCCASIONS 

 

Told time after time ad nauseum, Mate look a the calcs, can't be done,

 

Be prepared, I'll drop a link to this my own personal build thread if I see it done again as it's BS.

 

Substantial soundproofing and carefully built Low profile wall treatment via custom MLV for sub and audible low Bass frequency (15 to  140Hz trapping is very achievable in a light timber floored and clad dwelling.

 

The most personally satisfying thing the job has brought isn't what you may think

 

The area is the heart and soul of the dwelling (kitchen lounge)  I have managed to Integrate my Audiophile hobby, 21's , treatments, everything very successfully, to the rapturous applause of the others that inhabit it. 3m from the sink, 5 from the fridge.

 

Did I mention the fact that although this area is open plan, when you step onto the carpet out of the kitchen, you change acoustic zones.

 

Everyone here actually loves this feature, because they had not experienced it before in other peoples homes

 

There are no negatives to well thought out acoustic treatments, they are part of the tool kit for an Audiophile.

Keep it simple, treat the first reflection points, first, build from there.

 

There should be encouragement, not words like, be very careful and you will soak up the HF, it's mainly BS too. Or my fav,,,,,,,,,,,my room sounds great with out treatments, only furniture. I'll Kill the sound, loose details, the waffle on utter  BS, 

 

Not finished, have to tap down the 30 and fix the 50Hz. A bigger than "normal MLV Trap  will do that and that one will be tuneable probably in a few ways.

 

Next week, I've got kids home, I love them more than the stereo

 

 

 

 

 

 

 

 

 

 

 

[DVDHack]

7 hours ago, playdough said:

even the kids said it was easier to listen to

Well now it makes sense that you did the testing at up to 105dB, you have kids listening....

 

7 hours ago, playdough said:

when you step onto the carpet out of the kitchen, you change acoustic zones.

That's basically the same scenario as my secondary room.  I have the listening area at the opposite end to the kitchen.  The kitchen is effectively the rear wall and if you're like me and struggle to put things away in the kitchen and accumulate junk there, it makes a great diffuser.  Unfortunately I can't treat the first reflection point easily because that's where the window wall intrudes and an armchair sits in the opposite side.

 

Im glad it's worked out to your satisfaction.  .  

[davewantsmoore]

10 hours ago, playdough said:

only your conjecture

Sorry, I figured you would accept the claim that a LF acoustic device could be relatively shallow, but this would naturally play into the Hz range it was tuned over.... as this is just the basic principles of how such a device works.

You can see this even in the basic calculators, eg. on acousticmodelling.com

 

[davewantsmoore]

To go a little deeper.

 

It's the "compliance" of the membrane which dictates what frequencies it moves (more efficiently) at.

The simple calculators use quite a simple model to calculate that (mass and air volume), so it doesn't necessarily represent what you'll get (but it's reasonably close, like a lot closer than +/- 1 octave)

You can build a trap with a small area that absorbs LF .... but it needs to have the same compliance of the membrane, as the larger trap (to work in the same frequency range) ... so this might mean using a different material, or a different air, or whatever (to get a tiny trap which works at 30Hz, for example)....  the area doesn't have any relationship to the wavelength of sound it will work in...... BUT, if you use the same depth, and same membrane, making it bigger will make it work at a lower frequency, and make it work more (because more area in relation to the room).... but it's nothing to do specifically with size of trap vs wavelength of sound like you were saying earlier.

 

You can see this in the simple maths.    More complex math is very problematic, because it comes down to how you calculate the compliance (how complex you get).    It's honestly not even worth looking at - for a simple device you should just build prototypes based on the simple models, and measure their results.

 

More "modern" acoustic devices (ones you will read papers on if you google it) are very complicated as they used multiple elements coupled together try to get the acoustic effect happening with a much smaller device than would otherwise work (but they only work on a very very narrow bandwidth .... like how a moving membrane trap works over a narrower range than a porus absorber.... just 100x more tuned again).

[almikel]

18 hours ago, playdough said:

Dave, you really need to start backing your facts with some actual 

 

Link to a website

Show me the maths

Show me anything that you have made.

 

I have gone over everything you have posted and it's not leading to anything  only your conjecture.

Hi Glen,

 

...just saying...I've learnt more from @davewantsmoore than any other source along my audio journey.

Dave's posts are never conjecture, rather quality input based on good science.

 

cheers,

Mike

[davewantsmoore]

1 hour ago, almikel said:

Dave's posts are never conjecture

<shrug> To be fair.  I didn't say "why", aside from "'cos I said so".  Glen doesn't need to accept anything I say without anything else to go on.

 

I was making assumptions, that certain things are accepted fact (which let's be clear, they are plain as day) .... but asking for "more" is always understandable.... and I may have been misinterpreted as pointing to faults in things which I am not ... and some of the things that I am trying to point out might have been missed or misunderstood as a consequence.    Let me be clear, this is all I've been trying to say (I'm not trying to thow shade on anything much --- 'cept the charts don't let me see the result clearly/at all) :

 

 

• To compare "decay" (type) charts ... it is essential to correct the frequency responses so they are the same.
  • You can do this by using a "normalisation" on the data
  • You can do this by actually correcting the SPL to some common response before you take your measurement(s) (but this won't always be practical if there are big dips/cancellations - but you can do your best)
  • This isn't about "using DSP to do the job of what acoustic treatment could/should" ... it's just about how to analyse the acoustic treatment performance.

• Acoustic devices don't need to have an area which matches (or is a fraction of) the wavelength of interest

• Acoustic absorbers do (usually) need to have a depth which matches the wavelengths of interest

• Acoustic devices can be built which are much much shallower (less deep) than the wavelength of interest ... but they work over a narrow(er) frequency bandwdith.  That is what Glen is making here.

• "Modern" acoustic devices (especially in the last 10-15 years) have become very very advanced building tuned devices which are impossibly thin (not deep) for the low frequencies they work to.   By coupling multiple acoustic impedances together to formed a very "tuned system".

 

• It's hard to predict the frequency range over which a trap like this will work, when you are using material that have unknown/unmeasured properties (eg. the mechanical compliance/resistance, etc.) .....  and rather than using "complex maths", even experts don't bother, and just build prototypes based on fairly simple approximations, and keep building / measuring / building / measuring, until they get what they want.  The "simple calculators" do give quite a good approximation ... but not enough to rely solely on.   What you build won't be drastically different from what they say - but it will be different.

 

I'm sure the traps works good, and that the house mates are happy now the nightmare is over and the tunes sound better.

It would be good to see the charts presented in a way where the performance achieved is clear --- 'cos it is probably better than good, I just can't tell.

 

 

I've not build a lot of tuned sound absorbers, and no really really low frequency ones.   Quite a few (pours) absorbers, some big ones.    But I've followed quite a few detailed builds, read lots of papers, and talks on things like how to measure them, etc.

 

I think the two biggest things to keep in mind is that

• The materials are complex... which is why Glen shouldn't bother with the math (you'll need a degree in mechanical engineering and complex software just to get started).   Just build things based on simple physics and then see what they do, is the way to go (which is basically what he's doing right now, so :thumbup:)
• Measuring the devices is complex (or at least I mean, the results are complex).   When they don't appear to work as expected in the "real world" (in your living room), this is because it is very difficult to measure them in such a complex environment (reflections, resonances, modes, etc. etc.) ... measuring them in the free field or in a much larger, bare room, would give clearer results.... that isn't to say you have to measurement them like that .... just that weird results in the living room, can often be explained by "in the living room", not "I broke the laws of physics".

Edited August 19, 2023 by davewantsmoore