DIY - Room Acoustics..

[prateekatasniya]

How can 2 inch gap be a substitute for thickness?.. = 12inches seems a tall claim.. Probably 8 (or) 9 inch inch at best..

Am trying to interpret the absorption co-efficient from the table that was shared earlier..

From the the above table, as the thickness increases for the same density, absorption at low freq (below 250) seems higher..

On wall for same density (48 Kg/m3) - 3 inch panel has 0.53 for 125 Hz and 1.19 for 250Hz, but at 6 inches it is 1.19 for 125Hz and 1.21 for 250Hz..

If a 6inch panel can absorb more lows, then why use airgap for 3 (or) 4 inch panel?.. Drawing inferences from the table, an 8 inch panel on wall with same density would absorb even more lows, negating the airgap required..



Hmm.. I think it would be impractical to have it 16 inches away from wall..

Just for calculation & reasoning :

2 inch panel onwall (48kg/m3)+ 16 inch airgap makes 0.40 at 125Hz.. But, 3 inch thickness onwall of (48kg/m3) does 0.53 at 125Hz.. I think you would save 15inch of space..

The 6 inch panel data looks promising..

 

[sound_cycle]

The 6 inch panel data looks promising..

how can you absorb more sound than you put in - for it to work at 119% efficiency, will it work that way in real life ? (ans in the Ethan Weiner linkie i posted above)

ciao
gr

 

[sound_cycle]

Which of the above is good (or) if you have any other options.. Please let me know..

Broad band absorption is best at the corners. You would probably meet your mode busting goal with chunky traps floor to ceiling. (I am planning to do this if the wife lets me.) Why is the best ? See any discussion on pressure vs velocity based treatment or the dispersion of bass - roughly your room is a battery for sound energy with the bass collecting in the corners. Why did I not do this for one I was playing across the room, I was using drc for attenuation and absorption for a reflection free zone.

How much should you have. Remember I was telling you the noses of the mountains in your waterfall should be even ? The BBC had a rule of thumb :
No third octave decay time should differ from it's neighbours by more than 10% over a spectrum of probably 100-4K.

Ciao
gr

 

[elangoas]

The 6 inch panel data looks promising..

The earlier ones shared was for fiberglass.. Rockwool seems to have slightly better absoprtion than fiberglass..

Here is absoprtion co-efficient of rockwool density, from this page - https://badracket.com/acoustics/

Looks like 4 inch panels of lower density offers more absorption..

I think you should build simple corner bass traps.. More corners you treat better the sound will get.. tried and tested method..

From the Ethan winer article shared by @sound_cycle earlier, some critical points..

Generally speaking, most rooms need as many bass traps as you can fit and afford. Although it is definitely possible to make a room too dead at midrange and high frequencies, you probably cannot have too much low frequency absorption. The effectiveness of bass traps is directly related to how much of the room's total surface area you treat, which includes the walls, floor, and ceiling. That is, covering thirty percent of the surface with bass traps reduces low frequency reflections far more than covering only five percent.

At the minimum I recommend placing bass traps in all of the corners. For even better results, put additional traps on the walls and optionally on the ceiling.

Note that two adjacent two-inch panels absorb the same as one piece four inches thick, so you can double them up if needed.

Besides the corners where two walls meet as in Figure 3a, it is equally effective to place fiberglass in the corners at the top of a wall where it joins the ceiling.

how can you absorb more sound than you put in - for it to work at 119% efficiency, will it work that way in real life ? (ans in the Ethan Weiner linkie i posted above)

Didn't get this.. You mean it wouldn't be 119% efficiency, but lesser?..

 

[elangoas]

Broad band absorption is best at the corners.

Ok.. You mean the entire height of side walls where it meets front walls right?..

You would probably meet your mode busting goal with chunky traps floor to ceiling. (I am planning to do this if the wife lets me.) Why is the best ? See any discussion on pressure vs velocity based treatment or the dispersion of bass - roughly your room is a battery for sound energy with the bass collecting in the corners.

Ok.. Great..

How much should you have. Remember I was telling you the noses of the mountains in your waterfall should be even ? The BBC had a rule of thumb :
No third octave decay time should differ from it's neighbours by more than 10% over a spectrum of probably 100-4K.

Hmm.. Seems a tall ask for my room.. Will see how much the decay time reduces after absorption in the room..

 

[sud98]

Ok.. You mean the entire height of side walls where it meets front walls right?..



Ok.. Great..



Hmm.. Seems a tall ask for my room.. Will see how much the decay time reduces after absorption in the room..

Elango,

The Rockwoool sheets are available at Auralexchange at 4500 for 9 sheets of 1m*0.6m. Also, in the NRC table you shared, they are slightly different products. Whats available in India is SafenSound which has fairly good absorption.

Can one build a triangular wooden frame and have all three sides with these boards and have an air gap in between? Will that be an effective design?

So effectively you have 4" from every side and the air gap in between.

 

[elangoas]

Elango,

The Rockwoool sheets are available at Auralexchange at 4500 for 9 sheets of 1m*0.6m. Also, in the NRC table you shared, they are slightly different products. Whats available in India is SafenSound which has fairly good absorption.

Ok.. I think the one aval on aural exchange is safensound (roxul) and the link which i shared on rockwool India seem to be different..

Can one build a triangular wooden frame and have all three sides with these boards and have an air gap in between? Will that be an effective design? So effectively you have 4" from every side and the air gap in between.

Should work.. But, if you are building a trap, you can get loose wool with lower density (if aval) and stuff it nicely and space it in your room with airgap .. Planning to have them in front corners of the room?..

Not considering wall mounting them as it is with a frame?..

If you want Rockwool India contact for Bangalore, i can check with the supplier for a contact and update you..

 

[blackscorpio]

 

[elangoas]

Got to know from a chennai FM abt local aval of Felt fabric - http://www.madrasfelt.com/

Here is a link on density of the product - http://www.madrasfelt.com/product/hard-felt-sheets/ However, there is no acoustic properties of the material aval (specific to absorption rate of freq and NRC).. Yet to check on the pricing,,

Could this material be considered as an alternative to rockwool / fibre glass?..

 

[tapmal5]

View attachment 30266View attachment 30267
Subwoofer placeed on the tile.
This corner of the room had EXTREME boominess . So high that sitting 5 minutes on that side table while playing a bass heavy track would cause headache.
Total floor is raised by 4 inches using wood. Then carpet on it.

what type of carpet are you using, interested in that. Pricing info?

 

[prateekatasniya]

what type of carpet are you using, interested in that. Pricing info?

Its pretty thick..
Got it for 230rs/sqft.

Maintaining carpets is a pain..
Better to treat ceiling IMO.

 

[elangoas]

Planning to do false ceiling for my living room of 14 ft (W) x 11ft (L) x 9.7 ft (H), with plywood (Carpenter to visit and yet to provide estimate)..

The present room height is 9.7 ft, plan to drop it by 12 ~ 15 inches from ceiling.. 12 ~ 15 inches will become the depth of the false ceiling..

Below is what i thought of..

Note : As of now, i have only a pair of height speaker.. Have made provision to add an another pair of height speakers in the room..

My listening position is below top rear speakers in the room..

I have partitioned the ceiling space as A,B,C... A + B + C = 14 ft (W) x 11ft (L)..

Option 1 : Do a plywood ceiling for entire room, looks aesthetic and all height speakers & subwoofers with seperate enclosure neatly snugged into it..

Option 2 : Do the plywood ceiling to only a portion of it (B), ans use the portion of A and C (with wood structure & fine stainless steel mesh) to hold some rockwool panels inside it..

Portion A and C, would be roughly 11ft (L) x 2.5ft (W)ft x 12 ~ 15 inches deep.. ( I thought of using this space to hold the rockwool panels stacked one above the other.. The benefit which am assuming i would get is, 8ft x 2.5ft panels, 12 ~ 15 inch thickness.. More surface area of rockwool exposed to the room for absorption..

Am also guessing that height room mode might shift in frequency due to the dropped ceiling..

Would such an arrangement work? (or) would it absorb too much?..

 

[sound_cycle]

Planning to do false ceiling for my living room of 14 ft (W) x 11ft (L) x 9.7 ft (H),
Would such an arrangement work? (or) would it absorb too much?..

If the aim is to attack room modes, this should do, but is it overkill ? Or unecessary expensive ?? I am not sure if I can answer no.

I had got a preliminary estimate for false ceiling at my place. My problem is my neighbors wear concrete slippers and play basketball in them, with gas cylinders. The carpenter wala drop wire from the ceiling and make pretty plaster pattern thing (acoustically useful ????) would not do, I was looking for an aluminium frame on which to place my rockwool batts. Wife would not agree, was too expensive.

I found it cheaper to get Dirac to kill my room modes. It does exactly as much as I want, is easily reversible etc.

Ciao
GR

 

[elangoas]

If the aim is to attack room modes, this should do, but is it overkill ? Or unecessary expensive ?? I am not sure if I can answer no.

Ok.. Thx.. I will see how much of this is feasible once the carpenter drops in..

I had got a preliminary estimate for false ceiling at my place. My problem is my neighbors wear concrete slippers and play basketball in them, with gas cylinders. The carpenter wala drop wire from the ceiling and make pretty plaster pattern thing (acoustically useful ????) would not do, I was looking for an aluminium frame on which to place my rockwool batts. Wife would not agree, was too expensive.

Ohh.. Sad.. Hope you planned for a portion of ceiling..

I found it cheaper to get Dirac to kill my room modes. It does exactly as much as I want, is easily reversible etc.

Have the Audyssey XT32 here with mobile app.. Yet to check the customisation it offers..

I hope you had some panels on ceiling too.. So in that regard, am guessing having absorption on ceiling in my case should fairly help in that aspect..

Here is visual pic of room modes from net..

A weird thought- Am visualizing this from ceiling, thinking what if i could make more partitions in the ceiling and absorp where the pressure is more.. (Exclude the cost factor for now).. Weighing if the option would be more effective in absorption..

 

[prateekatasniya]

I think you have increased to budget.. Is it so?

 

[elangoas]

I think you have increased to budget.. Is it so?

I can stretch the budget to 30 ~ 35K for treatment..

 

[prateekatasniya]

https://homeacoustics.org

https://questai.com

I seriously feel that you should take professional help.

Questai is owned by the founder of homeacoustic.org
He charges 150usd an hour for consultation.
Otherwise his package for consultation starts from 500usd.
Have a look at it.
Register on the website as a pro and you will get access to their first level class notes.
I have gone through it and found it really informative and easy to understand.

 

[elangoas]

I seriously feel that you should take professional help.

Thx for the suggestion..But nope, don't want to spend on a consultant.. I have the microphone, and can learn around REW with help from members and articles.. i don't mind taking multiple measurements if it is wrong..

He charges 150usd an hour for consultation.

If someone would charge me Rs 2,000 INR for a visit, am fine.. Doesn't feel right to spend US $150 in India for consultation, while i can buy half of the panels for my room for the same money..

Otherwise his package for consultation starts from 500usd.

Thanks again.. But nope.. I would like to do it myself with some understanding, trial & error method..

 

[prateekatasniya]

Thx for the suggestion..But nope, don't want to spend on a consultant.. I have the microphone, and can learn around REW with help from members and articles.. i don't mind taking multiple measurements if it is wrong..



If someone would charge me Rs 2,000 INR for a visit, am fine.. Doesn't feel right to spend US $150 in India for consultation, while i can buy half of the panels for my room for the same money..



Thanks again.. But nope.. I would like to do it myself with some understanding, trial & error method..

Okay... Then just go through the home acoustic website.. register as pro and go through that PDF file. Will be of very helpful.

 

[elangoas]

Came across one more post in AVS forum, where the member has done 4 inch broadband absorption on ceiling - https://www.avsforum.com/forum/19-d...ic-home-cinema-construction.html#post29626506