My acoustically treated Home Theatre (updated)

[sarumbear]

Most recent update is here.

I have been posting about benefits of acoustic treatment of a room, especially in larger rooms. I believe that if done right it is a better, and if you have basic carpentry skills, a much cheaper option then using multiple subwoofer setups. I have the degree to do it right and thankfully the means to hire a carpenter. Here on I will present you my Home Theatre (HT) system where I applied my knowledge (and money!). As you may guess from the layout the room it is not visually a purpose built HT. it is our main living place that combines, sitting & dining rooms and the kitchen! It is light and bright as it use an HDR TV.

Acoustics​

Other than the specifically designed shape and layout of the room I only use five Helmholtz resonators to tame the major room modes (standing waves). Three are in the ceiling and two are on the ends of the false wall where the TV, and in-wall LCR and main subwoofers located. The resonators are inside the false ceiling. They are made of 5m long 25cm diameter plastic water pipes. Ends are blocked and there are variable area opening on one end to tune the resonator. Each one cancels one room mode. The remaining two are at the sides of the false wall and use the otherwise unused volume.

The first image is the room response to pink noise measured at three sitting location separated by colour. Measuring locations are shown on the room layout image that follows as 1-3. Individual position FRs are also provided. Chart resolutions are 1/6 octave.

No EQ is used.

Note: I could have adjusted the resonators so that they don’t over-compensate in the 30-60Hz octave but it required a change to the front resonators in the false wall, which was already build twice! However, as the dip is within 3dB I decided Trinnov to supply a small lift.

Layout​

​

Speakers​

LCR: 3x KEF Ci5160REF-TH as Left, Centre & Right speakers, in-wall
SB: 2x JBL Synthesis SSW-3 as main subwoofers, in-wall
SS & SR: 4x JBL CBT70J-1 as side & rear surrounds, on custom stands
SP: 2x KEF Ci200RS-THX as spatial speakers on the ceiling
LFE: JBL Synthesis SSW-2 as unmanaged LFE channel
Not shown: 2x KEF Ci200RS-THX as height speakers above the L&R flush to the ceiling, in-wall

Equipment​

Apple TV
Sky Q
Fire TV
Trinnov Altitude 16
JBL Synthesis 2x SDA-4600 & 1x SDA 8300

Connection diagram​

Please feel free to ask questions or let me hear your comments. However, due to personal reasons I am not willing to post photographs.

 

[Zaireeka]

Your room response is beautiful, I'm sure it also sounds quite well

Do you have at least photos of the said resonators?
Also how does one calculate their length and opening dimension to target a given frequency?

 

[sarumbear]

Your room response is beautiful, I'm sure it also sounds quite well

Do you have at least photos of the said resonators?
Also how does one calculate their length and opening dimension to target a given frequency?

Thank you. Here is a calculator that you can use. Make sure plan for a variable opening so that you can fine-tune the build.

Helmholtz Resonator Calculator

Find the resonant frequency of an acoustic cavity with out Helmholtz resonator calculator!

www.omnicalculator.com

 

[abdo123]

Other than the specifically designed shape and layout of the room

Thank you for sharing!

Would love if you could elaborate further on this.

 

[sarumbear]

Thank you for sharing!

Would love if you could elaborate further on this.

The right hand wall (top in the image) is made of large, ceiling to floor sliding doors, which are angled to reduce slap echoes. There’s also a lightweight curtain that drops down from the ceiling, which covers the entire width of the window (the dotted line). It is used when serious film watching is done. It helps to reduce RT60 further and gives privacy & light reduction.

The rear wall has two large dressers that act like diffusers and reduces reflections.

 

[DVDdoug]

Looks good!!! But where's the "before" graph?

I believe that if done right it is a better

Yes, I'd consider that an axiom. That's assuming your speakers are adequate. If you have crappy speakers that's the place to start. Ideally, EQ (if any) would be the "last thing". But since EQ is free (or essentially free) it's often the 1st thing or the only thing.

and if you have basic carpentry skills, a much cheaper option then using multiple subwoofer setups.

In most cases it's usually cheaper to add a subwoofer or two than remodeling or effective (usually extensive) acoustic treatment. ...And, more subwoofers "never hurt".

 

[sarumbear]

Looks good!!! But where's the "before" graph?

There isn’t. The room was built from ground up, acoustical treatment was part of the architectural design.

In most cases it's usually cheaper to add a subwoofer or two than remodeling or effective (usually extensive) acoustic treatment. ...And, more subwoofers "never hurt".

What multiple subwoofers can’t do is to reduce decay times of room modes. You can reduce the accumulated amplitude but in the time domain you will most likely still have the long tails.

 

[-Matt-]

I'm very interested in the specifics of the Helmholtz resonators (were these DIY)?

I've been reading up on these a bit and am coming to the conclusion that attenuating specific room modes would probably be more beneficial than adding more subs (more bass energy), only to then eq lots of it away.

 

[sarumbear]

I'm very interested in the specifics of the Helmholtz resonators (were these DIY)?

They were designed by me and hired workmen built to that design, supervised by me. They were not shop bought.

What specifics you want to know further than what I already said on this thread?

I've been reading up on these a bit and am coming to the conclusion that attenuating specific room modes would probably be more beneficial than adding more subs (more bass energy), only to then eq lots of it away.

That’s what my education thought me that to be the case. When I finally had the chance I applied that knowledge to my own room.

 

[-Matt-]

I only have screenshots from the Audyssey app to hand but...

I think the blue arrowed peaks near 30Hz and 60Hz are probably room modes. There is generally enough bass already, and 15dB of attenuation is a lot to ask from the eq. If I add more subs (already have 2) I think it is just going to further reinforce those room modes.

I think the dip in the red arrowed region is due to SBIR (behind the speakers) and LBIR (behind the listener) which happen to be similar distances. This I likely can improve a bit with broadband absorption.

 

[sarumbear]

I only have screenshots from the Audyssey app to hand but...
View attachment 221319

I think the blue arrowed peaks near 30Hz and 60Hz are probably room modes. There is generally enough bass already, and 15dB of attenuation is a lot to ask from the eq. If I add more subs (already have 2) I think it is just going to further reinforce those room modes.

I think the dip in the red arrowed region is due to SBIR (behind the speakers) and LBIR (behind the listener) which happen to be similar distances. This I likely can improve a bit with broadband absorption.

Is that equalised or not equalised response? Have you tried measuring at different locations?

 

[-Matt-]

Is that equalised or not equalised response? Have you tried measuring at different locations?

That is without eq.

The Audyssey app asks you to take measurements at 8 different positions. I guess this is probably an average of all 8 but can't be certain what their proprietary code chooses to display.

 

[abdo123]

I only have screenshots from the Audyssey app to hand but...
View attachment 221319

I think the blue arrowed peaks near 30Hz and 60Hz are probably room modes. There is generally enough bass already, and 15dB of attenuation is a lot to ask from the eq. If I add more subs (already have 2) I think it is just going to further reinforce those room modes.

I think the dip in the red arrowed region is due to SBIR (behind the speakers) and LBIR (behind the listener) which happen to be similar distances. This I likely can improve a bit with broadband absorption.

your response is very very typical of an untreated small room. low bass boost, upper bass null and midrange boost. There is no magic formula to fix this without some sort of work.

Low bass should be the least of your issues since it can be solved with EQ.

 

[sarumbear]

That is without eq.

The Audyssey app asks you to take measurements at 8 different positions. I guess this is probably an average of all 8 but can't be certain what their proprietary code chooses to display.

I suggest in investing a microphone and use the free software REW. Averaging will hide the room modes.

 

[sarumbear]

Low bass should be the least of your issues since it can be solved with EQ.

The problem with EQ is it will reduce bass for all positions. What if that boost is only at specific locations only (which room modes likely will be)?

 

[Zaireeka]

For the record, here is a super interesting research paper on Helmholtz Resonators I found elsewhere on ASR...

https://arc.be.uw.edu/wp-content/uploads/sites/12/2020/08/Vidhya_Rajendran_ARC_report_NBBJ_updated.pdf

 

[-Matt-]

I do have a UMIK 1 and have done REW measurements. (And mindsp 2x4hd).

The peaks at 30Hz and 60Hz appear consistently across all of my speakers and those frequencies correspond closely to predicted room modes given my room dimensions.

I was thinking that knocking down those peaks would help to smooth the <100hz bass.

I'm currently researching and planning what room treatments to make. (Always having to consider that this is our main living room and not a dedicated theatre).

 

[sarumbear]

For the record, here is a super interesting research paper on Helmholtz Resonators I found elsewhere on ASR...

https://arc.be.uw.edu/wp-content/uploads/sites/12/2020/08/Vidhya_Rajendran_ARC_report_NBBJ_updated.pdf

Excellent paper. Concentrated on the speech range but it explains everything you need to know about acoustics of resonators eloquently.

 

[sarumbear]

I do have a UMIK 1 and have done REW measurements. (And mindsp 2x4hd).

The peaks at 30Hz and 60Hz appear consistently across all of my speakers and those frequencies correspond closely to predicted room modes given my room dimensions.

I was thinking that knocking down those peaks would help to smooth the <100hz bass.

I'm currently researching and planning what room treatments to make. (Always having to consider that this is our main living room and not a dedicated theatre).

Then two resonators tuned to those frequencies is a good start.

 

[abdo123]

The problem with EQ is it will reduce bass for all positions. What if that boost is only at specific locations only (which room modes likely will be)?

It’s better than no fixing at all.