Advice on acoustic treatments for my unusual home theatre room

[Bartonfields]

Hi Guys, I’m looking for some advice regarding Acoustic Treatments for my rather unusually shaped Listening/Cinema Room. I am hoping some of you can point me in the right direction as I am new to all this.

As you'll see from the attached plan and photos I am running ESL9s for Main L & R, an Electromotion ESL C for Centre and Electromotion ESL for Surrounds. My rear L&R are Dali Zensor 2s and my front and back height speakers are Dali Alteco.

The room has some really awkward spaces left and right behind the front speakers, where I’m sure sound is getting bounced around and causing all sorts of issues. The front wall is a mix of exposed wooden roof trusses in-filled with plasterboard (Drywall) over Brick. The Large Archway is solid brick with plasterboard directly attached, as are the lower walls around the rest of the room. The angled ceiling/roof is all plasterboard over insulation and a tiled roof. The floor is carpeted throughout over an old solid semi-concreted floor.

The back wall directly behind the listening position is dominated by a big ugly brick chimney breast and even with my limited knowledge I realise that I will need some decent absorption panels there.

I’m thinking I will need something behind my main L&R ESL surrounds too, perhaps a freestanding panel that provides both absorption and diffusion and a bass trap in the nearby corner?

I have found that 2 Channel listening is surprisingly good with excellent dynamics and a great sound stage, I can easily pick out individual instruments/vocals and overall there is lots of detail and good separation.

However with multichannel it’s just not quite the same and it’s difficult to describe what is ‘lacking’. Don’t get me wrong it’s still sounds pretty good, but I know it can sound even better and I’m sure that the room acoustics are a big factor in all this. Apologies for my lack of technical vocabulary, but if I were to try and explain it I’d say that the front sound stage can seem a little “flat” as though everything is coming from the centre channel when I know it isn’t and my levels are all good. Surround effects, in terms of object based positioning, and movement around the room are reasonably good, but are less defined up front. I know there is a big compromise at the rear with speaker placement which is far from ideal, but I have to work with what I have.

I've opted for one of the best Audiophile AT screens available and I don't believe that is necessarily the cause of the problems. Screen Excellence say that their Enlightor Neo is “The most advanced AT Projection surface available” with “negligible acoustic insertion loss of <1.0db”. Could this still be a contributing factor?

I do need to fine tune my room calibration and I am using Room Perfect on a Lyngdorf Processor for Multichannel sound, but as you know there can be issues calibrating a room with Electrostatics, so I'm thinking I need to get the room's acoustics sorted/improved before going any further with the calibration.

Having read some posts here, the general consensus seems to point towards diffusion on the front wall behind the speakers, particularly when they are more than 3-4ft away, but am I correct in thinking I need some absorption there as well with those awkward spaces?

I have spoken with GIK Acoustics here in the UK and one of their suggestions is to use several of their "Sound Blocks" on the front wall. If you google this product they provide both Absorption and Diffusion and are designed for “High-end audio rooms and home theatres”. They have also suggested full spectrum “Monster Bass Trap” absorption panels on the back wall chimney breast, freestanding “Alpha” panels behind L&R Surrounds and “Soffit Bass Traps” in all corners. I did explain I was using Electrostatics and they say they have taken this into account when suggesting suitable products.

Sorry for the long post, but wanted to give you as much info as possible and would really appreciate any advice or suggestions on how best to treat my room and improve the acoustics without spending a fortune.

 

[JonFo]

Thanks for the details and especially the plan; that really helps.

You are correct; the space around the mains definitely needs some acoustic treatments.

I'll chime in with details in the morning (I'm on EST in the USA) once I've ruminated on it and had a cup of coffee or two.

 

[Brad225]

My initial thought was whether you have compared the mains where they currently are or forward enough to clear the brick wall on each side. I would think where they are would be detrimental to the sound but, only you can know for sure.

 

[JonFo]

The room has some really awkward spaces left and right behind the front speakers, where I’m sure sound is getting bounced around and causing all sorts of issues.

Yes, that is the primary challenge with this room and layout. So the goal should be to minimize the amount of energy being sent into that area.
First, let's address the dipole ESL panels energy, for accurate surround sound reproduction, and because of what's going on room-wise, you will want to absorb (100% absorption) heavily the rear wave of the ESL, so 4" thick pure absorbers on the wall directly behind them, offset by 3" from the wall to increase the effectiveness in the 250Hz+ range.

To mitigate likely bass resonances caused by that large cavity, I'd first do a 20 - 200Hz sweep with REW to identify those resonances in that area by placing the mic behind the center speaker.
Also, take a reading at the MLP, as there might not be a big deal, and ARC on the MLs can compensate.

My guess is that some bass absorbers at the left and right ends of the nook would be helpful.

I’m thinking I will need something behind my main L&R ESL surrounds too, perhaps a freestanding panel that provides both absorption and diffusion and a bass trap in the nearby corner?

Absolutely, as right now, the localization of the surround field is marred by all the reflections from the rear wave bouncing off that wall behind them. Using an abfusor might work, but I'd start with a pure absorber, as your speakers are directly to your side.

I use an abfusor behind my rears, but then they are behind the MLP, and the added 'spread' from the diffusion helps put some energy onto the side walls. In your setup, absorption is probably best.

As for GIK's recommendations, I'll disagree with some for the reasons listed above.
However, their Sound Block product can be ordered as a full absorber, so covering the front wall in that nook would work, or at a minimum, two columns (three high) of blocks behind the L / R ESLs.
Given that you have a nook, and not a fully open room, you do NOT want any reflections bouncing around in there, so nix the pretty patterned solid facings, only cloth and absorption.

They have also suggested full spectrum “Monster Bass Trap” absorption panels on the back wall chimney breast,

That I'd totally agree with.

 

[JonFo]

freestanding “Alpha” panels behind L&R Surrounds

Hum, again, a big NO from me on that, as we are trying to manage the sound field and the added rear energy both add comb-filtering to what comes out the front of the panel, and the specular diffused out-of-phase sound bouncing off the rear and front (the walls next to the opening to the nook) destroys localization in surround / immersive material.

So I'd recommend a 244 panel with their stand option, placed about 2' behind the speaker. Double-check with them that the 244 does NOT have any limp-mass elements in it, as those are reflective in the high frequencies.

Quick general comment on over-dampening, as their materials on the Alpha go on about that. When looking at acoustics for ESL vs dynamic speakers, there are a bunch of factors, such as dipole vs. monopole and placement in the room. Still, one that gets rarely mentioned (or considered) is radiating surface areas.
A typical dynamic speaker has a tweeter with at most a square inch of radiating area, then a midrange with a few more square inches, but an ESL panel speaker has square feet worth, or 405 square inches in the case of your ESL9. But that is just the front of the panel, an ESL is a dipole, so you also radiate to the rear with another 405 square inches of area. So this speaker has 810 square inches, or 5.6 square feet of radiating surfaces. It's going to take some serious dampening to quell that.

I know; my entire rig has 68 square feet of radiating surface area (counting woofers and subs, not just panels).

 

[JonFo]

I've opted for one of the best Audiophile AT screens available and I don't believe that is necessarily the cause of the problems. Screen Excellence say that their Enlightor Neo is “The most advanced AT Projection surface available” with “negligible acoustic insertion loss of <1.0db”. Could this still be a contributing factor?

Your screen is fine, it's not impacting the sound much at all. A slight loss of dB in the HF is easily compensated for by the room corrector.

I do need to fine tune my room calibration and I am using Room Perfect on a Lyngdorf Processor for Multichannel sound, but as you know there can be issues calibrating a room with Electrostatics, so I'm thinking I need to get the room's acoustics sorted/improved before going any further with the calibration.

Yep, get the room acoustics tuned up and then run the calibration.

Tip: run it multiple times, it takes practice to get a good measurement run, see my other tips on DRC here: Room correction setup guide for ML’s

 

[Bartonfields]

Wow, thanks @JonFo, some really great advice there, you’ve left me with plenty to think about and I really appreciate you taking the time to go in to so much detail about what I need and why.

Could I ask, how crucial is getting some readings with REW. I only ask because I’ve never used it before but I guess I can invest in a suitable mic and download the software? Would the results have any bearing on your suggestions for the nook areas?

GIK suggested 3-4 of their Sound blocks mounted directly on the wall between the trusses, and I too had thought the free standing option might be better, 2 columns 3 high. But I had wondered if their freestanding 244 Bass Traps might be a suitable (more cost effective) alternative? A total of 4 of those (1200x600mm), 2 each side behind the speakers would only cost me about £500 with stands, where as 12 sound blocks come in at £1600 !! What do you think?

 

[Bartonfields]

My initial thought was whether you have compared the mains where they currently are or forward enough to clear the brick wall on each side. I would think where they are would be detrimental to the sound but, only you can know for sure.

Thanks. I don't think there are any reflection issues from the brick wall on each side, particularly as the speakers are toed-in, but I can try pulling them forward a little to see what effect that has. The screen drops down in front of the speakers, so I can only move them forward by 10-12", otherwise they'd be almost touching the rear of the screen.

 

[Heyfey]

Thanks. I don't think there are any reflection issues from the brick wall on each side, particularly as the speakers are toed-in, but I can try pulling them forward a little to see what effect that has. The screen drops down in front of the speakers, so I can only move them forward by 10-12", otherwise they'd be almost touching the rear of the screen.

I suggest pulling the LCR speakers out a bit beyond where the screen drops and give it a listen. If there's significant improvement, then consider constructing a support for the screen to accommodate where it now would have to drop from. I know, easy for me to say, but it sure doesn't seem like you've taken any shortcuts on this.

 

[Bartonfields]

So I'd recommend a 244 panel with their stand option, placed about 2' behind the speaker. Double-check with them that the 244 does NOT have any limp-mass elements in it, as those are reflective in the high frequencies.

just had a reply from GIK regarding this and they say “the 244 can go on stands and has no limp mass elements in the full range version. Only if you add a range limiter.”

 

[Brandon Hartwick]

Could I ask, how crucial is getting some readings with REW. I only ask because I’ve never used it before but I guess I can invest in a suitable mic and download the software? Would the results have any bearing on your suggestions for the nook areas?

If you're going to spend all that money on store bought acoustic treatments it would be silly not to spend $150 or so on USB mic.

If you don't need the fancy wood faces on your acoustic panels they're stupid easy to DIY.

 

[ttocs]

Could I ask, how crucial is getting some readings with REW.

It is highly recommended in order to actually have an idea of how treatments can affect response.

Would the results have any bearing on your suggestions for the nook areas?

I think it would. You'd then be able to use some of the various tools in REW that can show things like Decay in addition to peaks/nulls. Some things don't change as much as you'd think they would.

 

[Bartonfields]

Thanks for the advice, I’ve been speaking to an audio engineer acquaintance of mine, and he’s put me in touch with a room acoustics expert who is going to come and survey the room for me. I have zero experience of REW and for not much more money I thought it would be worth getting someone in. He’s going to provide a full report and advice on acoustic treatments. I’m going to send him a link to this thread too so they can look at JonFo’s advice. He’s also offered to calibrate my speakers post installation. I’ll update again soon.