Bass Trap and general room treatment advice please

[KlausR.]

Regarding the 0.4 seconds reverb time. You are writing things that either seem to confirm the 0.4 seconds claim, things that contradict it or things that have nothing or little to do with it. And beware, I am talking about smaller listening rooms. Not rehearsal nor mixing rooms.
If you think a 1 second reverb time is no problem, then good for you but to others I would say, would you prefer to listen to music in a living room or in a bath room?

Since the number of reflections per second in a room decreases with room size reverberation time automatically increases. A mere figure which is not related to room size is hence of little value anyway. 2 seconds in the concert hall is just fine, in your living room it is a disaster. In Weisser’s experiment there were two rooms of similar reverb time but very different size

1. 85 cbm, 1 s
2. 186 cbm, 1.05 s

Room 1 got much more positive rating than room 2.

The three rooms that got positive rating were
a) 186 cbm, 0.56 s
b) 97 cbm, 0.72 s
c) 85 cbm, 1 s


The remaining 4 rooms with lower rating were
d) 82 cbm, 0.25 s
e) 105 cbm, 0.39 s
f) 186 cbm, 1.05 s
g) 27 cbm, 1.65s

This time two rooms of similar size (c and d) but different reverb times got different ratings.

When I said the reverb time in the bass is always going to be double or triple the rest of the spectrum, I did not mean this was not desirable. Quite on the contrary, it is desirable and normal. But not 9 seconds!

As I said, with 9 seconds, what was measured was not true reverb time, but more likely modal decay time, quite another beast in the herd.

It puzzles me what Charles Lindbergh’s arrival in NY has to do with psychoacoustics…

What was investigated were masking effects of noise generated by the crowds.

PS: I will look up on the studies that put 0.4 seconds forward as a kind of norm. I do not have that information at hand now.

Any study w.r.t reverb time is welcome, thanks.

Klaus

 

[Dennis Foley]

Hi,

I am building a new home cinema/critical listening room. The dimensions are 5.2m wide by 5.6m long by 3m high. The walls are 100year old 10"+ solid rock/lime mortar mix, so pretty solid. The floor is concrete with a small amount of insulation underneath. The ceiling will be 3/4" ply.

The plan is to line the walls with paper backed rockwool panels with the soft side facing the room at the front sides and rear and with the paperside facing towards the room at the rear side walls and on the bass traps...

For the bass traps, I plan on making wood frames for two foot square traps on the side and rear ceiling corners and all vertical corners. Rather than use cut up panels stacked on top of each other, my builder has suggested lining the frames with geotextile membrane and filling the resulting bags with blown-in fibreglass fibres from the loft space.

This sounds a good solution to me, and because the fibre is blown in, the light fluffyness of the fibres is maximised and, from what I have read, light and fluffy beats firmer rockwool or fiberglass wool panels when the bass traps are quite substantial.

The ceiling, between the basstraps will be treated with 3" acoustic wedge panels. When I am happy with the sound of the room, everything will be covered in fabric to make it all look smart.

I would welcome any comments on my plan, before I set-to

Many thanks,

Steve

Steve,

Do not get caught up in the myth that a limp mass material such as building insulation will absorb enough energy to attenuate 30 - 100 Hz. You need to choose a technology that can attenuate energy at those frequencies since based upon your room dimensions, you will be faced with large peaks at those frequencies. Stay away from treating the corners when looking for low-frequency management. Axial modes are produced by two parallel wall surfaces not two corners. You must treat the complete wall surface.

 

[kach22i]

Steve,

Do not get caught up in the myth that a limp mass material such as building insulation will absorb enough energy to attenuate 30 - 100 Hz. You need to choose a technology that can attenuate energy at those frequencies since based upon your room dimensions, you will be faced with large peaks at those frequencies. Stay away from treating the corners when looking for low-frequency management. Axial modes are produced by two parallel wall surfaces not two corners. You must treat the complete wall surface.

The real Dennis Foley?

I've been posting links of yours recently.

Welcome to the forum.

EDIT:

I am interpreting this correctly, you do not promote corner traps such as (link), and favor an whole wall/ceiling air space dampening system on resilient strips or viscoelastic material?

None of the normal building construction methods seem to be overly effective at low energy absorption, meaning the lines below are not flat, all fail at absorbing bass.

https://www.acousticsciences.com/products/wall-damp/technical

Why don't the corner traps below work?

https://www.soundoctor.com/projects/project_1139.htm

I've read about your Acoustic Fields diaphragmatic absorber.

VIDEO
https://www.acousticfields.com/how-to-build-a-bass-trap/

 

[Ron Resnick]

Welcome to WBF, Dennis!