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Topic: Acoustic treatment (Read 17961 times) previous topic - next topic
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Acoustic treatment

To the acoustic experts :

Is there any benefit in placing acoustic treatment behind speakers? I have two broadband panels placed behind my main speakers because it was recommended by GIK acoustics

My room is fairly small and my speakers are positioned quite close to the wall. Now they never explained the merits behind it so I just assumed it would be beneficial.

I also have panels on the rear wall. I get why treatment should be used on the walls floor and ceiling to treat reflections, but why behind the main speakers?

Has anyone here put acoustic treatment behind their speakers and did it improve anything?

Acoustic treatment

Reply #1 –
Quote from: Rich B on
To the acoustic experts :

Is there any benefit in placing acoustic treatment behind speakers? I have two broadband panels placed behind my main speakers because it was recommended by GIK acoustics

My room is fairly small and my speakers are positioned quite close to the wall. Now they never explained the merits behind it so I just assumed it would be beneficial.

I also have panels on the rear wall. I get why treatment should be used on the walls floor and ceiling to treat reflections, but why behind the main speakers?

Has anyone here put acoustic treatment behind their speakers and did it improve anything?


Just an educated guess. If the speakers have ports on the back, there is low frequency sound coming out. When close to the wall it will directly bounce back at the listener, but at certain frequencies they can cancel or amplify the sound coming directly at you. That can give a boomy sound and not a neutral sound. When absorbing those you can bring that effect back a little. Another way is to put plugs into the ports. Many speakers support that (my B&W DM603s3's and 602s3's do).

It can also be more convenient for your neighbours when they are attached to your house.

Acoustic treatment

Reply #2 –
Quote from: Fairy on
Quote from: Rich B on
To the acoustic experts :

Is there any benefit in placing acoustic treatment behind speakers? I have two broadband panels placed behind my main speakers because it was recommended by GIK acoustics

My room is fairly small and my speakers are positioned quite close to the wall. Now they never explained the merits behind it so I just assumed it would be beneficial.

I also have panels on the rear wall. I get why treatment should be used on the walls floor and ceiling to treat reflections, but why behind the main speakers?

Has anyone here put acoustic treatment behind their speakers and did it improve anything?


Just an educated guess. If the speakers have ports on the back, there is low frequency sound coming out. When close to the wall it will directly bounce back at the listener, but at certain frequencies they can cancel or amplify the sound coming directly at you. That can give a boomy sound and not a neutral sound. When absorbing those you can bring that effect back a little. Another way is to put plugs into the ports. Many speakers support that (my B&W DM603s3's and 602s3's do).

It can also be more convenient for your neighbours when they are attached to your house.


Speakers are front ported.

If I look in acoustic forums I see many people who place acoustic treatment not directly behind the speaker but to the outside of the speaker on the front wall.

I have never tested to see what difference the panels have made on the front wall, but I assumed it would make positive impact. Problem is I can't take the panels down, it's a mission for me.

I just need to know if absorption behind the speakers (whether rear or front ported) is a good practice and if there are any potential benefits to doing so.

Acoustic treatment

Reply #3 –
Quote from: Rich B on
Quote from: Fairy on
Quote from: Rich B on
To the acoustic experts :

Is there any benefit in placing acoustic treatment behind speakers? I have two broadband panels placed behind my main speakers because it was recommended by GIK acoustics

My room is fairly small and my speakers are positioned quite close to the wall. Now they never explained the merits behind it so I just assumed it would be beneficial.

I also have panels on the rear wall. I get why treatment should be used on the walls floor and ceiling to treat reflections, but why behind the main speakers?

Has anyone here put acoustic treatment behind their speakers and did it improve anything?


Just an educated guess. If the speakers have ports on the back, there is low frequency sound coming out. When close to the wall it will directly bounce back at the listener, but at certain frequencies they can cancel or amplify the sound coming directly at you. That can give a boomy sound and not a neutral sound. When absorbing those you can bring that effect back a little. Another way is to put plugs into the ports. Many speakers support that (my B&W DM603s3's and 602s3's do).

It can also be more convenient for your neighbours when they are attached to your house.


Speakers are front ported.

If I look in acoustic forums I see many people who place acoustic treatment not directly behind the speaker but to the outside of the speaker on the front wall.

I have never tested to see what difference the panels have made on the front wall, but I assumed it would make positive impact. Problem is I can't take the panels down, it's a mission for me.

I just need to know if absorption behind the speakers (whether rear or front ported) is a good practice and if there are any potential benefits to doing so.

Even front-ported speakers can be a bit bassy (in my experience) when their backs are too close to the wall. Hopefully, someone else on here can explain the reason.

As ideal speaker placement does not always chime with domestic acceptability, especially in small rooms, some absorption could be a help in that situation. A lot of the commercially-sold room treatment panels, however also look a bit ugly/odd.

Acoustic treatment

Reply #4 –
Like so :



This is not my system, just an example but my system is similar in that my panels are positioned behind the speakers but on the outside of the speaker.

I have treatment on the rear wall (4 panels behind the couch area) and two panels on the ceiling. Unfortunately, like I said, I couldn't test each subsequent change, so what I experience is just the overall effect and I must say, I think the sound quality in the room sounds very good to me.

Still, I don't know if what I'm doing is a good thing, a bad thing, or a stupid thing. Or if its even needed at all.

Acoustic treatment

Reply #5 –
Quote from: Rich B on
To the acoustic experts :

Is there any benefit in placing acoustic treatment behind speakers? I have two broadband panels placed behind my main speakers because it was recommended by GIK acoustics


Depends on the rest of the room and the speakers.

Quote
My room is fairly small and my speakers are positioned quite close to the wall. Now they never explained the merits behind it so I just assumed it would be beneficial.


Most listening rooms are too reverberant without treatments unless they have a lot of the right kinds of furniture, unusual shapes, or many large openings to the rest of the house.

Quote
I also have panels on the rear wall. I get why treatment should be used on the walls floor and ceiling to treat reflections, but why behind the main speakers?


Sound ends up bouncing off the front wall if for no reason that it may first bounce off the rest of the room.

Quote
Has anyone here put acoustic treatment behind their speakers and did it improve anything?


Yes.

Take it down and see if you like the sound better without it!

Acoustic treatment

Reply #6 –
Quote from: Rich B on
To the acoustic experts

I'm not an acoustic expert, but I play one on TV.

Quote from: Rich B on
Is there any benefit in placing acoustic treatment behind speakers?

Easier to see them that way, during sighted listening.

Quote from: Rich B on
This is not my system

Yes, that begs the question why someone with many (system specific) questions doesn't post pics of their own system.

Quote from: Rich B on
Still, I don't know if what I'm doing is a good thing, a bad thing, or a stupid thing.

It's a your thing, as in your (sound) preference, the only one that matters.

cheers,

AJ
Loudspeaker manufacturer

Acoustic treatment

Reply #7 –
There's not much advantage to be had putting treatment behind your monitors, unless it's to deal with a room mode or to improve the overall SBIR.  If your speakers are rear-ported, you need bass treatment (the usual rockwool probably won't do much) because you really want LF absorption to mitigate the unavoidable nodes from bass freqs reflecting back.

http://www.gikacoustics.com/speaker-bounda...-response-sbir/
https://www.gearslutz.com/board/studio-buil...-diffusion.html
http://realtraps.com/art_front-wall.htm
http://www.soundonsound.com/sos/dec07/articles/acoustics.htm

Worth a watch: https://www.youtube.com/watch?v=B9u7k2V4YPw -- the mirror trick is a great one, I've used it. Also, the clap test around various parts of the room can identify weird spots. (get someone to sit at the mix position and move round the room)

Early reflections are your nemesis, you need to side wall and ceiling treat to eliminate those.
Don't forget International Talk Like A Pirate Day! September the 19th!

Acoustic treatment

Reply #8 –
Although I fully endorse the concept of room treatments, there's also a ton of snake oil out there. I recently saw a pair of these in my local audio salon and initially thought they might be some sort of artsy monitor stand, but after asking a salesperson I almost burst out laughing at his reply. They are said to be endorsed by Steve Hoffman:


They are called Hallographs made by Shakti innovations. $999/pair

Acoustic treatment

Reply #11 –
Quote from: ErnestS on
Quote from: christopher on
If your speakers are rear-ported, you need bass treatment

I don't think it matters where the port is located regarding bass treatment.


It can matter, but it doesn't have to.

All rooms aren't the same.

All speakers with rear ports aren't the same.

All speaker placements within a given room aren't the same.

The sound coming out of the port of most ported speakers is concentrated at low frequencies.  But what are low frequencies? For a very small speaker they might be concentrated  below 150 Hz. For a large floor stander, they might be concentrated at 50 Hz or below.  Those are huge differences.  Concentration of energy below 150 Hz can range from warmth to boomy. Concentration of energy below 50 Hz can be firm bass or thuddy. It all depends where in the room the speaker is, and what the room is like.

Low frequencies are very non-directional.  That means that where the come from can easily be of lesser importance.

I love it when people try to make up very narrow hard-and-fast rules for room acoustics. "All generalities are false (including this one!)".


The rule about room acoustics that is always right and matters is that if it sounds good, then it is what it is. If it sounds bad, then it is probably fixable with some combination of speaker choice, speaker placement, acoustic treatment(s), and equalization.

Acoustic treatment

Reply #12 –
Thin panels stuck to the wall will have practically no effect on low frequencies. Regular speakers usually do not radiate significant amounts of mid/high-content to the rear.
Assuming you have such speakers, the panels do not seem to target sound directly emitted by the speakers. Maybe there are still significant amounts of reflected sound in the room, despite of the existing treatment?

Other options (in no specific order):
- Your speakers do emit mid/high-frequencies to the rear (e.g. strong cabinet vibration, wind-noise from the port)
- General room acoustic weirdness
- You have bought something you do not need

Acoustic treatment

Reply #13 –
Quote from: Gecko on
Thin panels stuck to the wall will have practically no effect on low frequencies. Regular speakers usually do not radiate significant amounts of mid/high-content to the rear.
Assuming you have such speakers, the panels do not seem to target sound directly emitted by the speakers. Maybe there are still significant amounts of reflected sound in the room, despite of the existing treatment?

Other options (in no specific order):
- Your speakers do emit mid/high-frequencies to the rear (e.g. strong cabinet vibration, wind-noise from the port)
- General room acoustic weirdness
- You have bought something you do not need

When you say "regular speakers", maybe you should describe what you mean by that, to make your advice more generally useful.

Acoustic treatment

Reply #14 –
Quote from: Gecko on
Thin panels stuck to the wall will have practically no effect on low frequencies.


Totally agreed.  Even 6" thick panels have pretty limited effects in the bottom most 2 octaves, unless their area is very large.

Quote
Regular speakers usually do not radiate significant amounts of mid/high-content to the rear.


IOW speakers that lack bipolar or omni directional design features that actually work.

Quote
Assuming you have such speakers, the panels do not seem to target sound directly emitted by the speakers. Maybe there are still significant amounts of reflected sound in the room, despite of the existing treatment?


...such as the usual longitudinal mode of most rectangular rooms.

Quote
Other options (in no specific order):
- Your speakers do emit mid/high-frequencies to the rear (e.g. strong cabinet vibration, wind-noise from the port)
- General room acoustic weirdness
- You have bought something you do not need


Or something that could work if scaled up significantly.

Or, something that does work though its effects at higher frequencies changing the percpetion of lower frequenies. For example dealing with mid bass resonances can allow true bass to be heard more accurately.

Acoustic treatment

Reply #15 –
Quote from: christopher on
Early reflections are your nemesis, you need to side wall and ceiling treat to eliminate those.


Except when they aren't.  Much depends on the off-axis performance of your loudspeakers.  And personal preference, of course. 

Floyd Toole has written a thing or two about this.  His book contains a good summary. 


Acoustic treatment

Reply #16 –
Quote from: JabbaThePrawn on
- Your speakers do emit mid/high-frequencies to the rear (e.g. strong cabinet vibration, wind-noise from the port)


No well designed speaker has  incidental audible emissions of these  kinds.

Cabinet vibrations are IME way over-hyped.  I've seen so many construction articles about reinforcing speaker cabinets that I  know from direct experience already have coffin-like rigidity. I suspect it is the cabinet maker's equivalent of crossover capacitor upgrades.

Port chuffing is a design flaw, pure and simple.

Acoustic treatment

Reply #17 –
In my (limited) experience most speakers will start to show some wind-noise when driven hard. Maybe Rich is of the purist kind who doesn't believe in subwoofers but wants the whole cinematic experience through his regular speakers. But it doesn't appear as though he is willing to share any details so it's all just speculation anyway.

Acoustic treatment

Reply #18 –
Quote from: Gecko on
In my (limited) experience most speakers will start to show some wind-noise when driven hard.


Driven hard, or overdriven?

Most speakers can be made to sound bad by overdriving them. I say most because a number of modern active speaker systems turn back the gain when the user attempts to overdrive them.

Quote
Maybe Rich is of the purist kind who doesn't believe in subwoofers but wants the whole cinematic experience through his regular speakers. But it doesn't appear as though he is willing to share any details so it's all just speculation anyway.


I seem to recall that he has $5K power amps and $500 subs.  I've got nothing against spending money where it can produce truly awesome results, but those numbers have things reversed.

Acoustic treatment

Reply #19 –
Quote from: Gecko on
In my (limited) experience most speakers will start to show some wind-noise when driven hard. Maybe Rich is of the purist kind who doesn't believe in subwoofers but wants the whole cinematic experience through his regular speakers. But it doesn't appear as though he is willing to share any details so it's all just speculation anyway.



Hmm, don't actual theaters use...subwoofers? 

Acoustic treatment

Reply #20 –
Quote from: krabapple on
Quote from: Gecko on
In my (limited) experience most speakers will start to show some wind-noise when driven hard. Maybe Rich is of the purist kind who doesn't believe in subwoofers but wants the whole cinematic experience through his regular speakers. But it doesn't appear as though he is willing to share any details so it's all just speculation anyway.



Hmm, don't actual theaters use...subwoofers? 


Of course.

Most commercial theaters are umm, engineered as opposed to being assembled from whatever is cheapest or most expensive or hippest.  They are often professionally operated, as opposed to being cranked up.

Case in point - I recently saw some complaints about the SQ during a viewing of the movie Interstellar in a well-known allegedly high end venue. 

I recently viewed it in the IMAX theater at The Henry Ford Museum here in Detroit (Link to my local IMAX venue) and it sounded wonderful.  Not exactly a widely renowned venue.

The difference could have easily been a 3-6 dB difference in playback level, the better sounding of which simply avoided grosser amplifier clipping.

There are two very reliable ways to avoid port chuffing. One is to simply turn the SPL down, and the other is to carefully high pass filter the signal to the speakers.

Acoustic treatment

Reply #21 –
Quote from: Gecko on
In my (limited) experience most speakers will start to show some wind-noise when driven hard. Maybe Rich is of the purist kind who doesn't believe in subwoofers but wants the whole cinematic experience through his regular speakers. But it doesn't appear as though he is willing to share any details so it's all just speculation anyway.


Sorry, I've been very busy lately.

Here is a pic of my living room, with panels installed :




My panels behind the speakers are the GIK 244 panels : 4" thick with 2" air-gap built in to the panel, and the larger Monster traps in the rear and ceiling are 6" thick, with 2" air-gap.

I've since lowered the front panels, as advised by Bryan over at GIK. I don't know, I think I can hear a difference, but I would have to measure to confirm.

I'm getting my Umik hopefully next week so I can do some measurements. Not sure what else I can do to my room to improve things further, besides treating the ceiling/wall corners, but then my room will look like a studio, which I'm trying to avoid.

Acoustic treatment

Reply #22 –
Quote from: Rich B on
Quote from: Gecko on
In my (limited) experience most speakers will start to show some wind-noise when driven hard. Maybe Rich is of the purist kind who doesn't believe in subwoofers but wants the whole cinematic experience through his regular speakers. But it doesn't appear as though he is willing to share any details so it's all just speculation anyway.


Sorry, I've been very busy lately.

Here is a pic of my living room, with panels installed :






Umm Rich, are your arms long enough to touch your speakers while seated in your preferred listening location? ;-)

The above looks to me like it is way into near field monitoring, and not really a typical listening room.

Its probably some distance into headphone listening as opposed to what music sounds like in a good performance venue.

As far as the pictured bass absorption panels  go, standard calculations show that a 6" thick absorber including a 2" air space starts loosing efficiency as an absorber at about 200 Hz, and by 50 Hz its absorbency has dropped by about 80%.  I don't call that much of a bass absorber, but maybe that is just me!  This can be somewhat overcome by covering the whole wall, floor to ceiling and adjoining wall to adjoining wall.

The absorbency of the heavy curtains is even more disappointing.

Porous Absorber XLS-based Model

Acoustic treatment

Reply #23 –
Quote
Umm Rich, are your arms long enough to touch your speakers while seated in your preferred listening location? ;-)


I'm sitting 2.3 meters back, so I guess my arms don't stretch out that far.

Quote
The above looks to me like it is way into near field monitoring, and not really a typical listening room.


Uh, well I'm in a apartment and the space and dimensions is typical for an apartment. Not sure what you mean by 'typical listening room'.

Is 2.3 meters back really considered near-field?

Quote
Its probably some distance into headphone listening as opposed to what music sounds like in a good performance venue.


Headphone listening? What on earth are you even talking about?

Quote
As far as the pictured bass absorption panels go, standard calculations show that a 6" thick absorber including a 2" air space starts loosing efficiency as an absorber at about 200 Hz, and by 50 Hz its absorbency has dropped by about 80%. I don't call that much of a bass absorber, but maybe that is just me!


I never said they were bass traps. They are broad band absorbers, and that's about as thick a panel as I can possibly manage that would work below 100 Hz. Is there any constructive criticism you can offer, or are you just trying to rip me a new one?

Quote
This can be somewhat overcome by covering the whole wall, floor to ceiling and adjoining wall to adjoining wall.


In case you hadn't noticed, I don't have much more space I can allocate for more trapping. I clearly can't cover the whole wall floor to ceiling in my space which would no doubt deaden the space further, which I don't want.

Quote
The absorbency of the heavy curtains is even more disappointing.


What's disappointing, exactly? How do you know what the absorbency is? You seem to be doing a lot of criticising here, which is probably what I should have expected.
 

Acoustic treatment

Reply #24 –
The center speaker looks too big for the room to me. You might find the rear speakers at the side of you work better too, they should really be lower according to what Dolby/DTS recommend but whatever works for you.

Arnold, it's a fairly typical size for flats/apartments in the UK, but it's even closer than I had my setup in a flat