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Mr_Gadget

Foam panels on back wall

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Hi guys, would something like these work well for a back wall behind listening position installed in one of these Ikea Kallax shelving units?

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Probably slightly better than having none.

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If they fit the openings then it's a cheap and easy solution, but not necessarily a good one, for two reasons. First, foam panels around that thickness only work for part of the midrange. They can make a room sound dead by reducing treble reflections without addressing the midrange well. Second, you may not always want to add significant absorption to the rear wall.

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14 hours ago, Paul Spencer said:

If they fit the openings then it's a cheap and easy solution, but not necessarily a good one, for two reasons. First, foam panels around that thickness only work for part of the midrange. They can make a room sound dead by reducing treble reflections without addressing the midrange well. Second, you may not always want to add significant absorption to the rear wall.

I thought due to the shape of the foam panels that they would act to disperse the sound?

 

Am I right in that sound should be dispersed on the rear wall and absorbed at the first side reflection points and front wall?

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Guest Hensa
51 minutes ago, Mr_Gadget said:

Am I right in that sound should be dispersed on the rear wall and absorbed at the first side reflection points and front wall?

 

I don't understand why this would be the case. Surely the rear wall also has first reflection points so why do they need to be treated any differently to side and front wall reflection points? I would have thought that whether one uses dispersion or absorption at various points in a room would depend on the 'liveness' or 'deadness' of the room as well as any other unique room characteristics that affect the sound. I'd also assume that all of this would need to be determined through acoustic measurement of the room.

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2 hours ago, Mr_Gadget said:

I thought due to the shape of the foam panels that they would act to disperse the sound?

 

Am I right in that sound should be dispersed on the rear wall and absorbed at the first side reflection points and front wall?

 

Creating a profile does two things. First, it reduces the effective thickness, which reduces absorption in the midrange. Second, this only works on the sound which is not first absorbed. So you get a reduction in absorption at the low end mixed with a very slight scattering at higher frequencies. But mostly, the profiles just make them look the part.

 

If you can effectively use diffusion on the rear wall (ie it's not too close) then I'd suggest it's often a good idea. In practice there are many factors not known here which lead to the best way to treat a particular room.

 

The front wall reflection has a strong relationship with the depth of the sound stage and the speakers chosen and their placement. There are many diverse approaches that may or may not work here for different systems.

 

The side walls often get a lot of attention but it's not always the best solution to absorb the side wall first reflection points. In a studio this is much easier to answer. I've had clients who felt that treating side wall reflection points made a big difference. I've had others who preferred the sound without.

 

1 hour ago, Hensa said:

 

Surely the rear wall also has first reflection points so why do they need to be treated any differently to side and front wall reflection points? I would have thought that whether one uses dispersion or absorption at various points in a room would depend on the 'liveness' or 'deadness' of the room as well as any other unique room characteristics that affect the sound. I'd also assume that all of this would need to be determined through acoustic measurement of the room.

 

With monopoles, the front wall has reduced treble and it contributes most notably to sound stage depth, which is also influenced by speaker placement. Generally more treble energy is radiated to side walls and the impact of treatment here is actually different. Side wall reflections contribute more to perceived spaciousness.

Measurements are part of the process of working out what works best for a room but if we use a car analogy they are more like the speedo and less like a GPS.

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No wonder people give up on this, I feel like I need a degree in acoustical engineering (is there such a degree?).  How would the average Joe measure a room and do it properly? Is it still not worth it to just add a few absorption panels around the room in the typical positions?

 

My room is far from being a dedicated music/theatre room with a corner window in the front left corner and door openings on both sides (one in front of me on the right wall  and another behind me on the left wall and floor boards! (but I have nice thick rug between me and the speakers now).

 

I guess I'm just trying to reduce the echo (using the very technical clap test) as a first step.

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Guest rogerthat

Just get some cut 1500mm x 600mm Polymax panels and play around with them. I have 21 of them in my office. 

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The boys above kinda made it seem too difficult but at the end of the day you just need to remember theses:

 

  • Use proper acoustic absorption material such as fibreglass, wool, polyester etc.
  • If in doubt, stick with either Polymax XHD or Acoustisorb 2 or 3.
  • Place them behind the speakers, behind the listening seat and the ceiling if possible.
  • Use some thick carpet on the floor.

Sidewalls. Some argue you don't need to treat them. You can still give it a go by using the mirror method.

 

The clap method is rather inadequate I think. You're listening to your speakers not your clapping.

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On 6/28/2017 at 11:12 AM, Paul Spencer said:

 

The side walls often get a lot of attention but it's not always the best solution to absorb the side wall first reflection points. In a studio this is much easier to answer. I've had clients who felt that treating side wall reflection points made a big difference. I've had others who preferred the sound without.

 

I can attest to this. I've tried multiple arrangements treating first reflection points and in the end... I didn't like it. I actually prefer it without any treatment in these spots (for these speakers in this room).
As you said, it takes away the spaciousness of the room. 
Second reflection points I'm still testing out. Though the room is quite balanced as it is with only ceiling treatment. 

Edited by Dylan86.exe

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On 9/26/2017 at 3:30 PM, Mr_Gadget said:

Shooting from the hip here, I feel this panel will work considerably better than the foam panels you mentioned earlier.  

It's still not the best panel available since when you look at this panel's acoustic spec, it does very little below 350Hz.   Some other types may do better than this one below 300Hz, so it really depends on what frequencies actually cause you problems (and hence Hensa's suggestion of finding out via some measurements).

Edited by marten

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On 6/28/2017 at 11:12 AM, Paul Spencer said:

With monopoles, the front wall has reduced treble and it contributes most notably to sound stage depth, which is also influenced by speaker placement.

Good info in your post, Paul; if I may just unpack this quote to get a better grip:

You seem to be saying the front wall gets hit by less treble energy than side walls.  Check, all good.

 

But you also say the front wall reflections contribute notably to sound stage depth.  Two questions on this:

 

1) Given that reduced treble energy gets to the front wall, is it nonetheless the reflection of that same treble (not LF) that contributes to soundstage depth?

 

2) To counter the front wall SBIR effect, we could place absorption on the front wall.  But now we don't want to dampen the treble - so does that mean our front wall panels should ideally absorb LF and reflect HF?

 

 

 

 

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Bass traps in corners and diffusers on the front wall. 

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On 6/28/2017 at 11:12 AM, Paul Spencer said:

 

Creating a profile does two things. First, it reduces the effective thickness, which reduces absorption in the midrange. Second, this only works on the sound which is not first absorbed. So you get a reduction in absorption at the low end mixed with a very slight scattering at higher frequencies. But mostly, the profiles just make them look the part.

 

possibly a jaundiced view, but IMHO the profile does a 3rd thing....it allows the manufacturer to create more panels with less material...

 

On 6/28/2017 at 8:45 AM, Mr_Gadget said:

I thought due to the shape of the foam panels that they would act to disperse the sound?

 

I think you meant "diffuse" the sound - and no, the shape of the panel won't effectively do that.

On 9/26/2017 at 3:30 PM, Mr_Gadget said:

I haven't tried them, but they appear similar to polyester batts, and will work in a similar fashion, so with appropriate sizing they will do the same job as poly (or fiberglass) batts.

 

On 6/29/2017 at 9:13 AM, Mr_Gadget said:

I guess I'm just trying to reduce the echo (using the very technical clap test) as a first step.

Slap echo, as demonstrated by the clap test, is not too hard to control with soft furnishings/curtains/rugs etc, but is not usually the place I start if treating a room.

Treating for slap echo can certainly assist in making a room better for speech intelligibility if you have a room full of people with many conversations going on at once (eg dinner parties etc) - I wish more restaurants would look at this aspect with the trend in many hard surfaces.

 

Where I start with treating a room for audio is in the bass region - get that under control first, and likely you no longer have slap echo to deal with.

On 6/29/2017 at 9:13 AM, Mr_Gadget said:

No wonder people give up on this, I feel like I need a degree in acoustical engineering (is there such a degree?).  How would the average Joe measure a room and do it properly? Is it still not worth it to just add a few absorption panels around the room in the typical positions?

 

IMHO, room treatment is the cheapest most effective "bang for buck" upgrade to room sound possible.

Awesome stereo + bad room = ordinary sound

Reasonable stereo + good room = awesome sound

 

Given you're in Melbourne you could engage the services of someone like @Paul Spencer to measure your room and suggest appropriate treatment - this would be a much more targeted approach than "just add a few absorption panels around the room in the typical positions".

 

I have no commercial connection to Paul, but have great respect for his products and services.

 

On 6/29/2017 at 9:13 AM, Mr_Gadget said:

 Is it still not worth it to just add a few absorption panels around the room in the typical positions?

This can work - but much harder in a shared space compared to a dedicated room - you will not likely get approval from other decision makers in the household...

...my starting point would be 600mm wide x 200mm deep floor to ceiling Polymax XHD straddling corners - this would make a significant change to bass management in your room - but good luck getting it approved - plus it wouldn't necessarily be needed.

 

Interesting anecdote - when we moved into our current house (7 years ago), the stereo was setup in the lounge room, which is a cube - and the sound was woeful.

I started making suggestions on applying treatment to the lounge room - the boss said no way, and take the stereo to the spare room/store room downstairs and treat as much as required.

Well that was 7 years ago, and my downstairs dedicated room sounds damn fine (but ugly), and the boss can't understand how people listen to stereos in untreated rooms.

 

If your goal is to significantly improve the sound in a shared room with minimal treatment, I would suggest some money spent upfront on getting a professional to measure and recommend treatment would be very well spent.

 

I'll say it again - IMO appropriate room treatment is the best "bang for buck" stereo upgrade you'll ever make - but it's much harder in shared spaces.

 

cheers

Mike

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On 9/27/2017 at 10:25 PM, marten said:

1) Given that reduced treble energy gets to the front wall, is it nonetheless the reflection of that same treble (not LF) that contributes to soundstage depth?

Hi Marten,

"Soundstage depth" is in the recording, and the room can at best "not hurt" this, or worst destroy it - with everything in between.

 

With monopoles, even when heavily toed in, no treble hits the front walls from a "1st reflection" perspective.

Horns even more so.

 

I think Paul is saying that treble reflections off the front wall don't affect soundstage, because there are none (not first reflections anyway - and secondary reflections won't "help" soundstage).

 

On 9/27/2017 at 10:25 PM, marten said:

2) To counter the front wall SBIR effect, we could place absorption on the front wall.  But now we don't want to dampen the treble - so does that mean our front wall panels should ideally absorb LF and reflect HF?

I agree we may wish to maintain treble energy in the room, so the room doesn't get too dead, but reflecting the HF from the front wall will not help soundstage...as @frankn says above, better to apply diffusion on the front wall.

 

SBIR from the front wall is definitely something that should be considered, but primarily for mid and bass frequencies

 

Room "spaciousness" is a different thing altogether, and a little contentious...

Toole recommends no sidewall absorption, so that sidewall reflections maintain their spectral content (ie the reflections don't have some frequencies absorbed more than others).

Geddes recommends a lively room (minimal absorption) with controlled directivity speakers (eg Geddes' Summa).

 

This is all a bit "off topic" for this thread, and likely adding to @Mr_Gadget 's view that an Acoustical Engineering degree is required to get good sound in a room (it's not).

@marten feel free to start another thread to discuss further.

 

cheers

Mike

 

 

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Thanks Mike for the good detail in your post.

 

I'll let the topic rest until a future point when I get my measuring act together a bit better.  For now, my own take-away for monopole speakers and the front wall:
1) Diffusion is probably preferred.   
2) Only if front-wall SBIR causes dips then ameliorate via speaker positioning or LF-specific absorption.

 

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Well I've bought a few absorption panels, will experiment with placement in a couple of weeks when they are delivered. 

 

I don't think I'll have the issue of a dead room with corner window and 2 room openings (no doors).

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3 hours ago, Mr_Gadget said:

Well I've bought a few absorption panels, will experiment with placement in a couple of weeks when they are delivered. 

 

I don't think I'll have the issue of a dead room with corner window and 2 room openings (no doors).

what did you purchase?

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Installed the panels today. See bottom of my post in the link below for photos.

 

 

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Hi Mr G,

I would expect that slap echo performance has improved markedly, same for voice intelligibility when the room is full of people?

 

cheers

Mike

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1 hour ago, blakey72 said:

Would this stuff from Selby work or is it a ripoff?

https://www.selby.com.au/system-tweaks/sound-panels.html

they don't publish any acoustic specs, so a bit hard to tell.

 

It also depends on what you're trying to achieve - for absorption to be effective to trap "bass", they need to be large and deep.

Just looking at the "extra large bass traps" ARTBASS2 - assuming the 295 (w) and 295 (d) are the right angled sides, a quick calc gives 417 mm front face and a depth in the middle of 208mm.

That's not really big enough for much performance below 300Hz or so, but stacking them floor to ceiling in multiple corners would certainly help a lot.

 

If you don't need it to look good, a few bags of ordinary fluffy batts like this would work as well if not better than the Selby bass trap:

https://buybuildingsupplies.com.au/r25-greenstuf-ceiling-batts-1160x580mm-batt-pack-p-26758.html

 

leave them in the bags for structure/self supportiveness, and cover in fabric for looks.

2 stacked (1 on top of the other) in each vertical room corner (need something to stop it falling over) would clean up the 150Hz-500Hz range quite well.

 

The Selby bass traps look good though.

 

Mike

 

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