Curious, can a whole wall be an energy absorber (for bass control) or will that kill the overall sound?

I think I  stumbled across a version of this approach purely by accident.

 

My listening room is essentially a tin shed in the backyard and the walls and roof, which are insulated and lined with gyprock, are innately quite flexible.  Moreover, the space is reasonably large.  This means that bass control is much easier than might otherwise be the case.  We have no close neighbours so the walls reacting to the bass and radiating it out isn't an issue.

 

But this aspect of  my ongoing pursuit of SQ is definitely a case of good luck rather than good management! 🙂 

 

 

 

Edited August 27, 2025Aug 27 by Tony M

Thanks for the reply Tone but you didn’t answer the question. Do you have a wall that is one big insulated wall? And if so, does the wall absorb most of the bass energy? 
 

No, I don't have a single wall treated to absorb bass energy.

 

The whole structure of my room tends to be somewhat more permeable to bass energy than more proper (solid) construction and this seems to help with bass management. Hence I called it "a version of that approach"

 

You asked about a wall being an energy absorber and I thought an alternative idea of walls being energy transmitters was worth a mention - maybe out of theoretical interest rather than practicality.  It seems to work in my case, but I'm not really sure to what extent as it's not feasible to try alternatives. 

 

My response is  tangential to your original question rather than a specific reply, but it seemed relevant to the concept of walls reducing reflected bass back into the room.

In a normal listening room, it is impossible to apply too much bass absorption.  However, it is possible to apply too much absorption to mids and highs. 

Cheers Tone.

I’m considering converting my garage into a music room, and I need to keep the noise in.

I can build a room in a room but internally the biggest I can get it is only about 70 cubic metres which means I have a lot of bass energy to deal with (2x powerful subs). I have the means to make the front and back walls deep absorbing walls if that will work but what I’m worried about is will the huge absorption walls kill the mids and highs and make the overall sound crap? 

10 minutes ago, acg said:

In a normal listening room, it is impossible to apply too much bass absorption.  However, it is possible to apply too much absorption to mids and highs. 

This is the answer I was after, so essentially too much energy absorption will kill the sound. 
I thought that might be the case, cheers

Too much absorption in the wrong frequency areas will kill the sound, but you can certainly absorb only bass frequencies using something like VPR's.  Absorbing all the sound behind you is a good idea but a huge fibre trap on the front wall would have to be skinned with something that reflects back the mids and highs...easy to do...bass goes straight through and is more or less absorbed but other frequencies are reflected back into the room.

1 hour ago, acg said:

Too much absorption in the wrong frequency areas will kill the sound, but you can certainly absorb only bass frequencies using something like VPR's.  Absorbing all the sound behind you is a good idea but a huge fibre trap on the front wall would have to be skinned with something that reflects back the mids and highs...easy to do...bass goes straight through and is more or less absorbed but other frequencies are reflected back into the room.

Ok now this sounds interesting, is there a particular product you would recommend to use as a ‘skin’? 

4 hours ago, Toeknee said:

I can build a room in a room but internally the biggest I can get it is only about 70 cubic metres which means I have a lot of bass energy to deal with (2x powerful subs).

 

I'm questioning your statement that 2x powerful subs ==> a lot of bass energy.

 

I have 2x 15" sealed subs in my 52 cu m room - each has an 800w amp.  So I would call that reasonably "powerful "!  Yet I don't 'suffer from excess bass energy ' - my overall FR (assisted by DSP) is the classic gentle slope downwards, towards the higher frequencies.

 

Given you're in Northcote ... by all means come over for a listen.

 

Edited August 27, 2025Aug 27 by andyr

32 minutes ago, andyr said:

I have 2x 15" sealed subs in my 52 cu m room - each has an 800w amp

 

Yeah, there is no such thing as too much surface area for bass transducers.   I have 4 x 18", 6 x 15", 16 x 10" in my room to handle everything below 100hz.  Almost zero excursion at whatever spl you want, and flat to 10Hz without dsp.  Drums feel like drums.

 

 

3 hours ago, Toeknee said:

Ok now this sounds interesting, is there a particular product you would recommend to use as a ‘skin’? 

 

No particular product that I am thinking of, but would probably require some trial and error (and research) to get right. 

 

My room is smaller than yours,  is soundproofed to the rest of the house but has windows to the exterior.   I built VPR's to control the crazy bass behaviour in a soundproofed room and they worked brilliantly.  I skinned them with some wood panel/ polyester panels that soak up maybe one or two kilohertz and higher to solve the specific problems of those VPR's.   Different bass traps would probably be skinned differently. 

VPRs?🤷‍♂️

9 hours ago, andyr said:

 

I'm questioning your statement that 2x powerful subs ==> a lot of bass energy.

 

I have 2x 15" sealed subs in my 52 cu m room - each has an 800w amp.  So I would call that reasonably "powerful "!  Yet I don't 'suffer from excess bass energy ' - my overall FR (assisted by DSP) is the classic gentle slope downwards, towards the higher frequencies.

 

Given you're in Northcote ... by all means come over for a listen.

 

Hey Andy, my current room is huge because it opens out to the kitchen, dinning area etc but it has little in the way of arresting low frequencies.

At normal listening volumes the room is great but it turns to crap as the volume dial goes up. I haven’t recalibrated the subs since I last moved them (costs me $200 every time!)
My subs are Perlisten D12S (1500w each).

The new room (if I build it) will be 74sq/m3 (golden ratio) so it will need a lot of bass absorption or it’s a disaster. Fortunately I can go nuts with absorption either end so thats why I asked the question. Is it possible to absorb that much energy???
I’d be very happy come over for a listen, PM me. 
Tony 

8 hours ago, acg said:

VPR?

 

A bit more info in this thread.  There are other threads about here and elsewhere with a bit of info about VPR's. 

 

I made my own panels.   They are enormously effective, quite thin at 120mm or so and their bandwidth can be tuned according to their size and materials used.  Am happy to share my recipe and how I used them but you still need a lot of them because you are working with bass wavelengths which are huge...I covered the front wall and side walls and even some on the shitty sounding cathedral ceiling above the listening position.   I can measure good effect even at 20hz, great effect at 30hz and all done by 600hz.  Gotta skin them as the metal panel sounds rubbish otherwise. 

 

2 hours ago, Toeknee said:

The new room (if I build it) will be 74sq/m3 (golden ratio) so it will need a lot of bass absorption or it’s a disaster. Fortunately I can go nuts with absorption either end so thats why I asked the question. Is it possible to absorb that much energy???

 

There's the 'LEDE' concept - 'live' one end and 'dead' the other.

 

From previous experience, I would suggest having diffusion behind the spkrs - and absorption at the other end.

 

2 hours ago, Toeknee said:

I’d be very happy come over for a listen, PM me. 

 

Will do.

 

12 hours ago, acg said:

 

Yeah, there is no such thing as too much surface area for bass transducers.   I have 4 x 18", 6 x 15", 16 x 10" in my room to handle everything below 100hz.  Almost zero excursion at whatever spl you want, and flat to 10Hz without dsp.  Drums feel like drums.

 

 

WOW!  Sensational!  👍  Yes, I can imagine you can't see much excursion, with all that cone area.

 

On 27/08/2025 at 3:58 PM, Toeknee said:

I’m considering converting my garage into a music room, and I need to keep the noise in.

Conflating achieving "great in room sound" with "sound proofing/sound isolation" is a big mistake - they are separate goals, and can work against each other.

 

Achieving both great "in room sound" and great "sound proofing/isolation" is possible - but expensive.

 

On 27/08/2025 at 3:49 PM, acg said:

In a normal listening room, it is impossible to apply too much bass absorption.  However, it is possible to apply too much absorption to mids and highs. 

I totally agree with this.

 

Coming back to your original question

On 27/08/2025 at 9:53 AM, Toeknee said:

Curious, can a whole wall be an energy absorber (for bass control) or will that kill the overall sound?

The simple answer is yes - a whole wall could be setup to absorb bass, and not kill the overall sound...ie not absorb too much top end.

 

The challenges start when you want to achieve both great "in room" bass control at the same time as great isolation/sound proofing.

 

Standard light weight room construction using Gyprock on studs is pretty good at letting all the low bass leak out, unless you have brick behind it (eg brick veneer construction). The Gyprock is sufficiently compliant to operate as a membrane trap to absorb bass also...with fluffy insulation in the walls behind the Gyprock, even with brick veneer outer walls you'll have some bass absorption from the room walls operating as a membrane bass trap.

 

@Toeknee - if you're wanting to achieve sound isolation, you need to read all the great information here:

  https://www.soundproofingcompany.com/soundproofing-101

None of the approaches absorb top end - only improve sound isolation and "in room" bass absorption.

 

Greenglue and multiple layers of Gyprock is expensive, but I'm not aware of effective alternatives.

 

Back to a whole wall operating as an energy absorber - don't ignore the ceiling.

 

An SNA member, who doesn't post anymore - @svenr, used flooring vinyl as a "limp mass membrane" on the ceiling of a room - converting the entire ceiling of the room into a massive bass trap, without absorbing any top end.

 

Cheers,

Mike

On 28/08/2025 at 6:45 AM, andyr said:

From previous experience, I would suggest having diffusion behind the spkrs - and absorption at the other end.

 

IME, the opposite is the way to go. 

 

The wall behind the listener is often the most problematic, as it reflects sound directly back toward the listening position. To address this, it's important to use diffusion on this wall to scatter the reflections and reduce comb filtering and echo. Tuned QRD panels are pretty much the king for this treatment. 

 

The wall behind the speakers should be treated with high-frequency absorption, such as a thick felt curtain or acoustic panels covering at east 80% of the entire wall to reduce early reflections, slap echo, and improve imaging.

 

@Toeknee it is common practice to create fully absorbing walls or roof spaces. Best option is a limp mass absorber system with the membrane facing the room. Needs fabric face covering, and is expensive to build. 

I've built many control rooms in such small footprint. The best option for absorption control is VPRs below 1.0m elevation, and broadrange absorber panels above and on the ceiling. Wall construction for noise insulation dual staggered stud walls, each with 19mm MDF plus 10mm gyprock, complete rockwool filling. Greenglue is a waste of money - their own measurement data shows only about 2dB difference in transmission loss in such heavy wall constructions. The challenge for noise insulation lies in doors, windows and your ventilation system. Keeping dust and moisture out of the rooms also turns out to be a challenge in Australia.

 

There is no harm in excessive absorption in small listening rooms. What is important is the balance across the spectrum.

You can check out these rooms for proof of concept:

https://www.bigtreestudios.com.au/about

https://deadonsound.com.au/studio/

3 hours ago, svenr said:

Best option is a limp mass absorber system with the membrane facing the room. Needs fabric face covering, and is expensive to build. 

Agree completely, limp mass membranes work very well "whole or most of the side and rear walls", with experience in 2 separate rooms. 12.5m2 across 3 walls in one listening area. A complete wall in the rear of another room, with 1m to 1.5m tapered gap to the cement wall behind, the area behind was completely filled with XDR acrylic sound absorber, this fake wall, was no more than a normal pine frame with the limp mass membrane suspended behind the pine frame, a layer of restrained XDR bats then a fabric layer facing into the room. 

The photo depicts 2 of the wall mounted limp membranes, on the RHS of the system in front there is another on the LHS of the system 1.3m x 3m, wall mounted as well. Note, fabric overlay, framed in 200mm/19mm painted pine board. There is an inner frame which was bugle screwed into the wall structure, which the membrane frame was suspended and actually then sealed for air chamber to the wall. 

Needless to say both stereo systems/room interaction changed profoundly to the ear, to measurements below 150Hz if not for the simple large scale of the treatments. All DIY, self learned, measured and documented in a thread I did a few years ago.

@acg mentions that you cannot have too much bass treatment in a room and agree, I also agree with "more is better" above depiction 4 x 21" drivers as pairs in 650 liter enclosures with band pass of 20 to 250Hz, drums sound like drums, bass sounds like bass, rocket take off, sounds like a rocket take off  ! 🙂 No substitute for size, none,,,,,

On 19/10/2025 at 1:23 PM, playdough said:

No substitute for size, none,,,,,

the motoring analogy...there's no substitute for cubes, and if in doubt, bore it out 👍

 

I'm thinking Hoffman's Iron Rule applies to bass trapping the same as it does for sub design.

Hoffman's Iron Rule for sub design says you can only have 2 out of 3:

1. low bass extension
2. efficiency
3. small box

Pick your chosen 2 and compromise on the 3rd.

 

I think bass traps are the same.

 

Mike