[Housteau]

I have the chance here to do an interesting experiment.  Currently my dedicated listening room has no low frequency issues.  It measures flat to pink noise within 2.5 - 3dB.  That is due to room construction, present treatments and some manual DSP.  I have nothing against DSP correction, but feel it should be the last resort and not the first to turn to in fixing a room, assuming that there are other possible options.  Not everyone has other options.

The best wall for bass in a room is no wall at all.  What if you could make one wall, say the one behind your listening position transparent to low bass, yet reflective and diffusive to the higher frequencies?  The rear wall in my room is shared by a single car garage.  It is faced with sheetrock on the listening room side only and I believe has helped in taming the low frequency modes up to around 40 Hz.  It would take little to no effort to replace that sheetrock, in part or completely with thinner plywood to allow higher bass frequencies to pass through and be controlled.  I would like a turnover frequency, the one where the wall becomes more reflective, to ideally be around 150Hz.  I am currently using some DSP in the 50, 60 and 90Hz areas.

The questions then become:  Should I first cut large windows into the wall as a test and then second what thickness of plywood would work?  The plywood would be backed by 4 inches of rockwool insulation.  In effect I would be creating a very large and tuned velocity bass trap placed in an ideal location to catch 1/4 bass wavelengths.  It all seems logical and easy enough to do.  I was thinking that 1/8 inch plywood might be a good place to start and it would be easy enough to double up to 1/4 inch if that was better.  Has anyone put together a chart showing how different wall materials react to low frequencies? 

I was wondering if anyone else had tried a similar experiment?  The end goal for me would be the reduction of needed DSP.



   

[WGH]

Interesting idea, there may be some answers in the 46 articles written by A/V Room Services
https://avroomservice.com/articles/

It’s All In The Acoustic Details
Part III: Bass Resonance



You wouldn't want to accidentally make a drum.

A/V Room Services does consulting, modeling sound quality, construction methods, and voicing which includes testing of: speech intelligibility, reverberation times, low frequency articulation, noise floor, system frequency response, plot of room reflections, laser alignment of speakers, subwoofer x-over & level calibration, equalization correction, rattle & buzz check, surround sound calibration, image, soundstage, etc.
https://avroomservice.com/

These are the same guys in the Stereophile article that use an abandoned nuclear facility for their acoustic measurements.



NWAA Labs: Measurement Beyond The Atomic Level
https://www.stereophile.com/content/nwaa-labs-measurement-beyond-atomic-level

You need a big space to measure the effects of reverberation times of a room with and without absorption.
"At very low frequencies," Ron interjected. "NWAA Labs can measure accurately down to 25Hz because it resides in a floating room inside a floating room, separated from the outside world by roughly 25' of concrete. The room's background noise at 1000Hz is an astounding –43dB!"

[Housteau]

A lot of good information there.

[JLM]

If it ain't broke don't fix it.  Seems like you're inventing an itch to scratch.  The hobbyist in you is showing through.  Seems like your room is near perfect.

I have a (practical) well sized/shaped/insulated/dedicated listening room too.  Have added 10 absorption panels, 3 tall bookcases that act as "casual" diffusers, and 3 subwoofers.  Also tried a couple of DSP room correction products (agree with Earl Gedde that they should only be used as icing on the cake).  Overall none of the panels, diffusers, subs, or DSP do much in the nice room.  BTW my room independently ended up being very similar to Earl's. 

[richidoo]

I use a thin folding wall and thin door to partition between noisy kitchen/dining area and my listening area, mostly to knock down midrange echo in the listening area, which it does well. Bass goes through of course.

Like you I have minimal bass problems due to the flimsy modern building code. The house doesn't fall down, catch on fire, it keeps out moisture and it holds in heat, that's all the code requires, nothing about sound. The walls are typical 1/2" wall board, 2x4" frame, insulation, 3/4" OSB, tyvek and vinyl siding. Bass goes right through. Floors and ceiling are 12" engineered wood I beam joists with 16 foot span which pass LF easily.

If you only have single layer of wallboard between living space and garage I don't think that have to make the sheetrock thinner. All the bass below 100Hz is already passing though easily. Insulation in that wall will help acoustically if there isn't any. Code has special requirements for walls between garage and living space, for fire and fumes you might want to check out.

In the past I have experimented with this concept of no hard bass reflective surfaces to see how bass improves. I made small pseudo anechoic chambers like igloo of FG panels. The bass and everything else was crystal clear, so it was a success. The detail is extreme even with the midfi components I was using at the time. I could hear every detail and flaw, audiophile's dream/nightmare. It required equipment I couldn't afford at the time, but I do hope to investigate the bass permeable wall concept again. This time with less jitter, and standing headroom and ventilation

[Big Red Machine]

https://www.acousticfields.com/how-to-build-a-diaphragmatic-absorber/#:~:text=A%20diaphragmatic%20absorber%20is%20a%20sealed%20box%20that,in%20speed%20and%20then%20enters%20the%20cabinet%20inside.

[Housteau]

If it ain't broke don't fix it.  Seems like you're inventing an itch to scratch.  The hobbyist in you is showing through.  Seems like your room is near perfect.

All true enough.  It is basically a thought experiment that is semi-easy enough to test out.

[Housteau]

If you only have single layer of wallboard between living space and garage I don't think that have to make the sheetrock thinner. All the bass below 100Hz is already passing though easily. Insulation in that wall will help acoustically if there isn't any. Code has special requirements for walls between garage and living space, for fire and fumes you might want to check out.

Interesting.  I could test to see exactly what is passing through my existing construction by measuring frequencies in that other room on the other side of that wall.  I had not thought of doing that.

[Housteau]

https://www.acousticfields.com/how-to-build-a-diaphragmatic-absorber/#:~:text=A%20diaphragmatic%20absorber%20is%20a%20sealed%20box%20that,in%20speed%20and%20then%20enters%20the%20cabinet%20inside.

Yes.  I am familiar with Acoustic Fields and their diaphramatic absorbers.  They are designed to capture bass trapped within a closed space.  My thoughts were to open that space to allow the bass to leave on its own.

[Housteau]

If you only have single layer of wallboard between living space and garage I don't think that have to make the sheetrock thinner. All the bass below 100Hz is already passing though easily. Insulation in that wall will help acoustically if there isn't any.

I had been busy lately, especially through Halloween. I spent 4 days visiting friends in downtown Houston and attending parties.  It was quite a wild ride.

Anyway, I did some tone testing and sure enough the turnover frequency at which my back wall starts to become more reflective is right around 100Hz.  So, I guess a contributing reason to why my room is already pretty good below 100Hz is indeed due to the construction.  I have no idea how much of that energy, if any is returning back into my room.  I could easily construct large (4' x 8') portable absorptive panels that could be placed in that garage spaced away from the wall to attempt more 1/4 wavelength capture.

If I changed the material in my back wall appropriately it looks like I could get it to work above that 100Hz hinge point where it is right now.  That zone between 100 - 200Hz could always use a bit of smoothing.

[Housteau]

Speaking of Halloween in Houston.  The party started at 3mA Audio and then moved on to some of the best restaurants and clubs.  A big thumbs up to Johnney and all those at 3mA.