There is something that everyone but me has missed and I  did go into it.

 

For treating sub audible frequencies in a timber dwelling, the solution has to stiffen the structure of the dwelling.

 

Has little to do with the membrane, or does it ?

1 hour ago, almikel said:

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

Is it wrong to ask for more information to back any claim someone has made ?

 

Is this not part of the forum policy ?

 

I like  @davewantsmoore 's input also but even if someone is very knowledgeable and every one else seems to agree, good on them. 

 

This thread is more about facts found via actual findings, Maths, Links work of others, within the topic of the thread.

 

It's ok to discuss these things, but it's not ok to ignore the Author of any thread if they require moore that just educated guessing.

 

That is the conjecture

 

Sorry but for this thread to progress, technically some evidence of claim is to be put forward and that evidence discussed.

 

If you cannot do that, well there is a thousand million other threads to post on.

 

This project and it's Engineering has been mulled over for years, I'm here for facts NOT conjecture, otherwise I won't post on it and go else where, with my Study of ULF Membrane Trap Technology.

 

Is this a real Engineering /Trade task,,,,,,,,,,? You bet it is.

Are there 3rd parties interested in this actual Technology, yea, heck yea.

 

So please excuse me if I ask for more information It's the way I get work done.

 

 

 

5 minutes ago, playdough said:

Is it wrong to ask for more information to back any claim someone has made ?

Of course not.

I don't think he was saying that either.

I think he was just saying that it's unlikely that what I was saying was "an opinion or conclusion formed on the basis of incomplete information".

 

5 minutes ago, playdough said:

Is this not part of the forum policy ?

Since when have we really cared about this? 😉

 

5 minutes ago, playdough said:

require moore

I see what you did there... ❤️

 

5 minutes ago, playdough said:

that just educated guessing

I can assure you I'm not guessing.

 

There are few link to "maths or papers" for anything that I've said... because nothing I said, is anything more than the very basics.   I could link you to the maths of a "mass on a spring", and show how that is tuned to a certain frequency (which is exactly what your trap is) ... but that wouldn't help you, I suspect.

 

Like a real life mass on a spring.   Your real life trap performs a little different to the simple calc, cos the real spring is hard to model.

 

5 minutes ago, playdough said:

So please excuse me if I ask for more information It's the way I get work done.

Out of the dot points I posted in the long post a few post up.

 

Can you be specific about which one you want more info on?.... (ie. which one(s) are you not certain to agree with?)   They are very uncontroversial statements, but.... I'll help where I can.

15 hours ago, davewantsmoore said:

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

 

They actually have to be really deep, and really heavy by what this Mathematical standard model, this model has no surface area or volumetric area of enclosure.

 

I get the fact you can make 10 smaller deeper enclosures that are tuned to a frequency, limited by depth  , but

if the same MLV material that went into the 10 deep boxes went on the face of a single  shallow box have a higher calculated frequency, the same, or lower to the  10 smaller deep boxes ?. 

This is not computable with the above calculator or any simulator, which is a bugger.

I wish it was, does anyone know of a sim that can do this ? Surface area ? 

 

EDIT, maybe chatGBT or some AI can solve it. Siri cannot, tried

 

 

Edited August 19, 20232 yr by playdough

Meanwhile the 3D Printer jobs are getting chunkier, the smaller ones nearly done (4 off)  so decided to do 4 moore 

New one with lower Hz target and larger higher elements. 120mm highest element. 205 x 205mm, 56 hours to do one.  Will take nearly 2 weeks to make 4 of the chunky ones.

 

Mainly doing these for eye candy as they really are a nice print to look at, stack, move about 🙂 

https://danylastchild07.files.wordpress.com/2016/05/trevor_j-_cox_acoustic_absorbers_and_diffusers.pdf

Hope everyone had a nice weekend

While a 54 hour 3D QRD print is going on,,,,, 

Doing some more testing hunting down the last of the bass reverberation problems, with my old Audio control third octave RTA, tone gen, via REW

 

Behind the speakers in particular seems to be the source of the problem,

 also the only surface in the lounge that hasn't had any real work done on it, so seems reasonable.

So, cracking on with it, measure about this one will be around 2m long, 1.1m x 0.2m, under a long window that is in the top half of the wall. Not quite as big as the last pair. 

Harder to isolate wall flexing as it's mostly been fixed. Vast difference to no trapping at all.

Should be a good thing under the long window. Whole wall will be a sort of bass trap, will have over whole front wall of the house 7m, a double slider door, 2 windows (double glazed) and the MLV Trap.

 

Have to move the whole stereo system again, not fun 🫣 

 

Think I may have found some better 18" LF drivers, to go in sealed boxes, which I don't have so will need to model and build them, that will be a big job, there are 4 of those, should be enough LF SPL and most likely smoother ULF  response than the ported enclosures wo the phase inversion at port/cone transition. Heavy things, close to 20Kg each.

 

 

 

Edited August 21, 20232 yr by playdough

A fun track I use at times when I'm getting physically  sick of the tone gen, anyone hear the lowest frequency ? It becomes more apparent as the trapping goes in

 

 

Edited August 21, 20232 yr by playdough

On 19/08/2023 at 7:55 AM, DVDHack said:

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

No, they are generally not here. They do like the music and over time developed their own play lists, which are quite ok.

I use ear muffs although at the frequencies I'm dealing with, they do not do a lot. It's about getting it (testing) done relatively quickly. It's hard on me and my  dear old weatherboard.

I think it's ok for them to learn new long and technical words and a little about acoustic environment and speaker response as well as operations, I won't be on this Earth forever (getting older) so someone has to take it on, or it get's broken up and sold. Would prefer some of the gear accumulated over the years is kept and loved.

I'm always keen to teach what I know to anyone, including the our young. Music is in our hearts over, precedence to what the TV is showing.

 

Playdough.

 

@DVDHack

There is also a hard limit of 25w applied, per cab.

To go to 250w, that would be just silly. 1mm excursion from the quartet of LF drivers is well enough.

 

Out in the wild, there is a pair of Bridged EV P3000's to run them 20mm peak to peak.

They are a rather special thing to me to hear (very personally) outside, from 100m away,. They go downnnnn.

Edited August 21, 20232 yr by playdough

On 19/08/2023 at 6:36 PM, playdough said:

For treating sub audible frequencies in a timber dwelling, the solution has to stiffen the structure of the dwelling.

 

Has little to do with the membrane, or does it ?

Expanding on this and the whole process, while waiting for a QRD 3D Print to finish, no one about to feed or look after today.

 

An evolving conclusion developing, of the whole process, to an Audiophile who knows what to listen for and hates reverb/combing (if this sounds like you read on) purely and simply put  reverberation adds nothing to the fundamental reproduction other than harmonic distortion, like it or not.

 

Starting with high frequencies, it's fairly obvious the bare minimal Acoustic treatment is required is to effectively  deverberate a simple clap test and only at the listening positions. If you catch someone doing a single clap test in your listening zone, it's because there might be something  unappealing sonically, and fundamentally  going on, acoustically, as they may be used to something else that is fundamentally far and away better.

 

Gold plated stereo equipment or not. OCD tidy or a mess, makes no difference.

If you get a ping a ringing or any other audible harmonic  anomaly, seated at sweet spot within the listening sound stage immediately after a clap, it absolutely requires mitigation as a priority, to do nothing will do no justice to the remainder of the HiFi system as a whole sum of individual quality components, normally cobbled together over a couple of dozen years at a fair average cost.

 

All with a single clap to the trained ear. Is this you ?

 

In some cases, the room subject to the clap test will perform surprisingly well, on with the show. They are normally completely furnished, wall cabinets, book shelves with books, chairs, tables and fully wall to wall carpeted as well as being half full of equipment. Some are tidy, some are not (don't let your eyes deceive or OCD take over) , both audition the  same. 

Cannot cheat a clap test, as simplistic as it is.

 

For a medium sized open plan modern square set hard floor room, furnished with the bare minimum OCD af, 2.4m ceiling, minimal treatment mitigating the clap  will be an absolute necessary. Necessary even if the room looks really good, like wow.

 

Not that hard to achieve and can enhance not only the listeners sonic perspective, but also if cleverly done can enhance the look of an ultra modern room scape.

 

40mm thick DIY covered frames with a heavy (quality) core of stable acrylic insulation bat or chopped layered wool blanket, will do the job at first reflection points only. 1m2 for start at each point. I don't advocate the use of glass fibre inside in any case, just a bad practice as the core  will leak glass fibre through the cover of the panel over time, yikes.

 

An online calculation will state that the 40mm of a porous core, with 10mm of sag from the cieling will treat at an absorption  co efficient 0.8  from   2000Hz and up the frequency scale,

 

Looking closer at the calculator graph, will not be as effective at lower frequencies, but will still have some effect all the way down to 500Hz, and still have a co efficient of 0.4 (or half as effective). There it is large as life and  rather encouraging. 

The thicker 80mm core obviously has more effect, however 40mm is seen by myself (through trial and error) as a good compromise, keeping the sonic quality of the area, lively, not "deadened", but survives the clap test.

 

Acoustic treatments for Under 500Hz 

 

Why would someone actually go to this extreme ? Depends on how the Audiophile likes his bass served up, in a nutshell.

 

It is quite rare to find an adequately treated listening zone, for low bass and you literally have to DIY it yourself or Employ a Pro., once it's done, you will have trained those ears and grey matter to listen out for it.

 

If the speaker system in place had a narrow band of operation say -3dB at 42Hz, the following testing may not be possible and for that matter acoustic treatment for very low frequency bass may not be necessary, practical or otherwise. If this is you click away now 🙂

 

The necessity of this my modern open living room/kitchen project came about only because the HiFi speaker in place can and does operate efficiently with no boost or cut EQ to 35 Hz and much lower with small amounts of EQ, these frequencies, typically get right into physicality of  structural members of the average dwelling,  wall and ceiling lengths/height , and whole wall surface areas.

We all know the symptoms, bloated bad sounding Bass, shaking walls evident at very low SPL

 

Fighting the symptoms of low frequency reverb and how to overcome them.

 

A hands on approach feeling your way across the walls, with a tone generator at line level and RTA method, not very conventional, probably not anything new, and most likely very old school.

 

Observed, by a humans hands, eyes, ears and calibrated test mic.

 

The low frequency sound waves just pass straight into, out of and resonate the structural elements, the RTA mic when placed near one of these shaking resonant structural members and covering drywall, the magnitude of the SPL increases, at symptomatic frequencies, typically lower than 40 Hz.

 

Really quite typical with a pine or light metal studded/nogged, Gyprock new dwelling, old hardwood studs and double plaster green glued are not exempt either, in fact they make the situation worse by leaking less SPL, more like a solid block wall.

Solid walled brick dwellings, with brick internal walls are quite different and another story for later. Interested to tell that story if anyone is interested.

 

The structure and it's inner plaster drywall cladding actually acts as a sympathetic passive transducer and is easily recognisable. Does nothing for bass clarity, in fact it can be quite a nuisance. PITA 🙂 windows, doors, plaster against studs, the list is long, but fixable.

 

The MLV sealed, enclosed and damped and used across the whole wall in this application has been deployed, but using  a different approach (not normal like me) , to the actual symptoms seen, felt, measured. rather than calculated.

 

The membrane trap calculator is a useful tool as a guide, however it does not account for the symptoms of flexing walls at very low frequencies at low SPL.

 

To be continued next post, nose bag time. Enjoy a quick snap shot reveal of this modern brand new lounge, pictures tell stories.

THe system is to be moved  today from back wall work, over the week, and fit the giant double blind that arrived finally. The upholstery material can come down, although it's a great emergency block out curtain.

 

Playdough. 

 

 

And a quick snap of the finished QRD's, 5Kg of filament and will obviously keep the printer rolling along.. My faithful companion 9years young, the micro dog, yes it's a real dog, tall in attitude, short on actual courage 🙂

1 hour ago, playdough said:

In some cases, the room subject to the clap test will perform surprisingly well, on with the show. They are normally completely furnished, wall cabinets, book shelves with books, chairs, tables and fully wall to wall carpeted as well as being half full of equipment.

 

Cannot cheat a clap test, as simplistic as it is.

 

👍

 

I think most people know what you're talking about, because most people (are familiar with, and) hate these sorts of rooms (ones which have the bad clap) .... for audio, or even just reading a book in silence.

 

 

1 hour ago, playdough said:

10mm of sag

Not important

 

 

 

Ah, reading in silence, one of life's little pleasures.

So the last membrane trap went together, this one is the longest built at 2.4 x 1.1, (black panel with the dog in frame). 

Features  MLV  either side of the damping  timber frame 75mm apart. In the 75mm between the MLV membrane (sealed section)

3 x 20mm sheet poly bat went in. Stapled restrained, There is also a sheet of Poly on the face into the room, same as the others and the rear membrane has the same stapled restrained Poly sheeting. 4 more layers will go onto the wall frame.

 

Have the hardware for the outer case 190mm DAR pine, and wall frame, so will go up over the weekend. 

There is 5.5m2 of MLV sitting there, with a 12.5m of Poly 20mm sheet 🙂 getting heavy. 

Sort of thing I'll sit a sub next to 🙂

 

3D QRD Printing is going along ok. Just have to feed it PLA filament. Learning a few tricks along the way like keep the heat (75 degrees or more) into the bed for the first half of the print, try keep the plastic job on the heatbed at above 55, as long as you can, to about 35mm Z axis. from there it's fairly structurally sound. Always cure in the freezer.

Prints that run overnight (3 nights and days) and the room temp drops to 15 degrees, there can be corners lift on the print job, which is not ideal. Always glue the bed on the corners, if you forget, the corners lift about 4 hours in 🫣

 

Put my eyes on a pair of Duntech Crown Princess today. Looks like they are mine. They need a driver repaired and probably a little restoration work. Bit of a Legend Speaker, in my Town someone knew someone and I was mentioned, history, Looks like they can be set up in front of the JBL's, enough room.

 

Back on Membrane Bass Deverberation 

The new trap with the double membrane was to stick to the core principals of adding limp swinging pendulum mass  structurally to the wall. 

The super large heavy limp membrane trap have an tendency to operate when the walls resonate, frequencies below 50 Hz to 0Hz and work with a wide Q factor.

 

In this case 2 x 15Kg limp membranes sealed together by a chamber. (75mm), which is sealed against the wall  (115mm) 190mm total projection finished case.

 

The membranes in parallel, well, I just thought it might work better cancelling each other out and be of a different tune up to the other 2 already working.

 

No air gap in this last trap all Polymax, deliberately constrained and stapled so as the limp membranes can swing free. At these frequencies air gap does nothing, it's al about controlled damped deverb. 

 

Just listening to the single speaker radio ATM, which is clean and clear, big difference acoustically in this area has the last couple of weeks. 

The area is as inviting as the Cinema, with the smaller sounds system playing adds.

 

Job nearly over and and with a couple of measurements.

 

Playdough's pre production showcase lounge.

 

 

 

 

 

 

 

 

Edited August 25, 20232 yr by playdough

In the last couple of days of work on the project  to completion and looking forward to setting up some sort of stereo again,

Materials used

 

1. Upholstery materials  17meters at 1350wide
2. Polymax 20mm x 1200 sheeting,  52Lm
3. Macrocarpa pine 75 x 50mm. 15 LM Rough sawn air dry, fairly heavy things.
4. Pine DAR 40 x 20mm , 60Lm
5. Pine MGP10 Studs, 90 x 45mm , 35Lm
6. Pine DAR 190 x 20mm, 20Lm
7. Pine MGP10 75 x 40, 10Lm
8. 100mm phillips  screws, 20
9. 45mm phillips screws, 300
10. 75mm phillips screws 
11. PVA Glue
12. 2000  x 11mm staples
13. 30 x 85mm gal Bugle Screws
14. Sealing tape, 60m
15. 1 woollen carpet remnant, sewn edge with underlay, 4 x 5m
16. Some Polyurethane sealant. 
17. 10lm MLV,  full 70Kg roll

Labour 4 weeks full time 1 person to design and install, has been fun but has been testing at times, mainly the actual passable integration with the space. The actual designs for the Bass Trapping as these cannot be modelled and not a lot more than intuition (fairly good educated guess) as to how they really work,  a gut feeling and most importantly experience from another lounge that received this sort of love and attention to detail.

Modern colours to suit, best of all none of the room additions have encroached into the space x more than 190mm

All are surface treatments, nothing is glued to plaster only screws and easily removable ready to re paint  in a day.

Would not like to think how much something like this would cost, completed walk in finished to the 9's., $22K+ at a guess

 

QRD Printing so far has yielded 6 x 180 x 190mm cells of varying frequency targets. 4Kg of filament used so far.

 

I no longer sit in a sea of insulation medium or pieces of things propped against the walls, which was to b fair not a good look and doesn't actually work, not healthy, with the stuff blowing about inside.

None of the treatments sit on the floor so maintenance of the area, with nothing other than a couple of compact recliners and a coffee table. 

 

Leaves the floor and skirt lines completely free to vac, sweep and mop. It's the best case scenario.  

 

Back to work. 

Enjoy the day and hava good week end.

 

Playdough.

 

 

 

 

 

Edited August 26, 20232 yr by playdough

There is a cunning plan a foot to hang a group of QRD's at a first reflection point, problem is there is a great big window, these will hang in front of window furnishings, from the top arc by thin wire braid, and fixed  at the bottom arc. Blind will work ok and the QRD's are not a terrible thing to look at, to me anyway. Window reflection SOLVED.

Time to shatter the Saturday morning silence and run in  some 85mm bugle screws. Last bass trap install today all the elements are made and ready.

Whilst fanging down a pie and chips, progress.

 

Thought I'd show the seal crushing ceremony.

To get the outer case seal to crush and actually seal, a little helper by the way of a primitive jacking method.

Place the piece of rusty angle iron, pre drilled with a few holes, on the case, leaving 10mm to the frame (jacking distance)

Screw it onto the outer case with some short screws, they hold fine.

Place a screw through a hole in the angle iron and pull it up to the iron, from there a few pulls of a fairly large rattle gun, brrrt the screw and literally pull the frame into the wall.

I set it up every corner and centres of the top/bottom of the outer case.

 

Pulls a 9mm seal down to 2mm. Sometimes there is a little wall/case run out, mark and plane a bit, when within 5mm, it's ok, the seal and jacking does the rest.

 

Core assembly next, chop up yet another roll of Polymax, better get cracking a Mate is coming around to help lift the 45Kg bass trap in an hour.

 

 

 

Work finished, now to tune in a soundstage.

Not much to do now other than replicate the first Test. Same mic position, same EQ. Before and after comparison.

Beyond that another power amp is sitting here 25w x 2 to go 6 channel. The 25 x 4 will be relegated to just operating the 4 x 21's channel per driver.

 

On 19/08/2023 at 6:36 PM, playdough said:

There is something that everyone but me has missed and I  did go into it.

 

For treating sub audible frequencies in a timber dwelling, the solution has to stiffen the structure of the dwelling.

 

Has little to do with the membrane, or does it ?

In my experience, lightly constructed rooms have fewer low bass issues than rigidly constructed rooms, as the lightly constructed room (eg timber weatherboard/stud/insulation/Gyprock) absorbs some bass lets a lot through (annoying other house occupants and neighbours), whereas the more rigid room (eg concrete filled besser block) reflects it back into the room where it bounces around taking ages to decay. 

 

For a lightly constructed room with Gyprock as the inner skin - the Gyprock does act as a membrane trap, and absorbs energy through flexing a bit, and lets most of the low bass right through.

 

Where light construction falls down is when isolation (sound proofing) is also a goal - reducing the level of sound passing through the walls.

This is where specialist products such as Greenglue is used between multiple layers of Gyprock, and isolating vibrations from studs using whisper clips etc.

 

Rattles are a totally different issue - very evil and hard to track down and remedy 😞

 

Mike

 

23 minutes ago, almikel said:

In my experience, lightly constructed rooms have fewer low bass issues than rigidly constructed rooms, as the lightly constructed room

I'm not sure how you'd conclude that.  I think each construction has its own issues but light weight construction would have issues of multiple resonance frequencies depending on the bracing.  Where bass is absorbed by the walls it's likely to be a quite uneven absorption and unless it happens to coincide with a room mode you're just seeing dips in addition to modal peaks and troughs.  Solid walls at least reflect just about everything audible equally.  In my experience it's unevenness that's hard to treat more than a long Rt60.

6 hours ago, playdough said:

Not much to do now other than replicate the first Test. Same mic position, same EQ. Before and after comparison.

Try to show "same frequency response" .... so if we create a chart that flicks back and forth between them, we don't see the (initial) frequency response change, only the "time decay" change.

 

27 minutes ago, almikel said:

the Gyprock does act as a membrane trap, and absorbs energy through flexing a bit

With the plasterboard fixed to ~450mm studs, and the flexibility of plasterboard ....  then it isn't the plaster which flexes at very low frequency, its the entire wall.    Hard to say for sure if this is an acceptable thing.

On 20/08/2023 at 12:46 AM, playdough said:

 

They actually have to be really deep, and really heavy by what this Mathematical standard model, this model has no surface area or volumetric area of enclosure.

 

I get the fact you can make 10 smaller deeper enclosures that are tuned to a frequency, limited by depth  , but

if the same MLV material that went into the 10 deep boxes went on the face of a single  shallow box have a higher calculated frequency, the same, or lower to the  10 smaller deep boxes ?. 

This is not computable with the above calculator or any simulator, which is a bugger.

I wish it was, does anyone know of a sim that can do this ? Surface area ? 

 

EDIT, maybe chatGBT or some AI can solve it. Siri cannot, tried

 

 

I think there's a fundamental assumption in the formula based on some model...clearly the limp mass is working against a volume of air...the depth parameter is based on this model...as I said above there's less science available for limp mass traps than say QRD diffusers or plain absorption.

The only commercial use of limp mass I'm aware of is the Primacoustic Maxtrap - and they don't even seal theirs! so who knows what science/maths they use?

 

I'm sure you could swap depth with volume somehow...I'll leave that to people smarter than me to determine.

 

I think MLV traps are a great concept - a regular poster here on SNA who I haven't seen in ages ( @svenr ) used flooring vinyl deployed on the ceiling for an inexpensive large MLV bass trap targeting lower frequencies.

 

One thing that will never change - traps for low frequencies need to be large, whether area or depth

 

mike

 

 

 

 

Edited August 27, 20232 yr by almikel
clarification

On 25/08/2023 at 9:00 AM, playdough said:

There is a cunning plan a foot to hang a group of QRD's at a first reflection point, problem is there is a great big window, these will hang in front of window furnishings, from the top arc by thin wire braid, and fixed  at the bottom arc. Blind will work ok and the QRD's are not a terrible thing to look at, to me anyway. Window reflection SOLVED.

don't forget windows make great bass traps...but the QRDs will let the bass through anyway...

Do you need QRDs at 1st reflection points?

I thought Duntech's had a good "off-axis" response?

 

The Toole/Olive perspective is not to damp/alter 1st lateral sidewall reflections so long as your speakers have a smooth "off-axis" response, such that the 1st lateral reflection has the same spectral content/frequency response as the direct sound....

....If placing treatment at 1st lateral reflection points, QRDs are likely better than absorption...but you'll still change the spectral content/frequency response of the 1st reflections.

 

If your speaker response varies a lot between "on axis" and "off-axis", then treatment at 1st lateral reflection points can't hurt, and may improve the "in room" sound.

 

Mike