Adjusting Room sound using material damping methods (not DSP)

[A.S.]

I repeat the sole point I see relevant to this -

• the only sound we want at our ear drum is the direct sound
• we do not want any 'second hand' reflected sound from any part of the room at our ears
• we are spraying the whole room with sound from the speakers when our ears represent the tiniest portion of the room's volume and area
• that sound will touch every surface point in the room - it cannot pick and chose
• by implication, since none of the surfaces are 100% absorbent, sound will be reflected off the various surfaces and will go rattling around the room until they are fully absorbed
• headphone listening where there is no room and hence no reflections is likely to give a pressure wave at the ear drum which is more faithful to whatever is on the recording than speakers in an untreated room, but it is a different and private listening experience compared to loudspeakers

As I said earlier ...

So, your two ears represent only 0.00031% of the total surface area which means that 99.99969% of the sound energy sprayed into your listening room by the two speakers is not only wasted energy but degrades from your listening experience as it becomes tainted with the room's sonic characteristics. That's why attending to the room's characteristics and damping is the most important upgrade you can make.

I was just considering the pressure at any one point on the surface as the leading edge of the initial wave front touches any point on the surface of the room relative to useful wave that arrived directly from the speaker to our ear.

The point remains that we are exploding a tremendous about of sound energy into the 3D volume of the room (i.e. we're pumping a lot of power into the room) just so that a tiny pressure "beam" of sound passes directly from the speaker(s) to impinge upon our ear drum and make its way to the brain = a hugely wasteful and inefficient process when all we want is that initial sound "beam". Sadly we can't have the wanted "beam" without pumping the room with sound, none of which is useful to our ears.

[BAS-H]

OK. I agree with all of the above.

May I add some of my observations and suggest some facts? They may well be wrong so please feel free to moderate.

Many rooms have an undesirable bloom in frequency response in some ranges. I suggest this is due to pressure waves bouncing off a surface and arriving at the ear in addition to the direct wave from the speaker.

OK. Off what surface is the the wave bouncing? Let's assume we have a rogue bass bloom. We know that moving the speakers back towards the front wall makes it worse. We could summize that the main bounce surface is the front wall. What can be done about it?

We know we can't absorb waves of that frequency; there is too little room for the thickness of material that would be required. Can we then place an angled surface behind the speaker so waves bounce off more than one surface, losing energy each time, before reaching the ear? Has anyone tried this?

Ben

[STHLS5]

I repeat the sole point I see relevant to this - the only sound we want at our ear drum is the direct sound[*]we do not want any 'second hand' reflected sound from any part of the room at our ears..

Alan, I follow you so far, but as I was discussing with my friends about the role of reflected sound I thought I should bring your attention to your generalization, that " we do not want any 'second hand' reflected sound..". The said statement cannot be correct since you have previously mentioned that some reverberation may be good. That was my purpose of the earlier post to put a certain value to the reflected sound.

I know for certain that you are not suggesting that the best listening experience is a room devoid of any reflection, i.e. the anechoic chamber. Perhaps, I am thinking ahead....

Please delete this message if you feel I have deviated from your topic.

ST

[A.S.]

I know for certain that you are not suggesting that the best listening experience is a room devoid of any reflection, i.e. the anechoic chamber. Perhaps, I am thinking ahead....

Well, let's break down this statement.

First, I don't necessarily believe that you have correctly interpreted what I've said. That's not a problem; I could have said it. But I honestly don't believe that it stands up as a philosophy.

If we agree that the room (inevitably) is being blasted with a tremendous sonic energy of which only a tiny proportion is direct to our ears - the useful part - it surely follows that only that portion - the direct sound - is, within the limitations of achievable high fidelity, what was laid down on the recording. You'll recall that at the very beginning of this thread I said that what we hear at home in our listening room (a box) was replayed by speakers (also boxes) of a recording made in a studio or hall (another big box) possibly of stringed instruments (also boxes) .... hence home hifi is the sound of a box, in a box in via a box in a box. Inevitably, each step along the reproduction chain collects the characters of the preceding box and adds to it the character of the current box. Does that sound like a really sensible idea and a substitute for 'being there' at the hall? Perhaps not. It certainly doesn't to me, unless a serious effort is made to minimise the acoustic contribution of the room/speaker boxes.

You mentioned the sound of the anechoic chamber as a possible extreme solution to listening to speakers - that is, you put the speakers in a completely dead room and avoid any 'room sound'. You've heard for yourself what recording in an anechoic chamber sounds like and the dry acoustic is totally unnatural. But that is definitely not to say that the reproduction of live music, recorded under normal (non-anechoic) conditions would necessarily sound wrong or unnatural if the room sound was completely removed from our listening-at-home experience. If we are honest we'd have to admit that whatever bloom or hardness or echo or whatever our room added to our listening experience is no more welcome than some quirk of the speakers. The addition of the 'room sound', the acoustic character of the room (which I'll assume to be mainly additive) simply cannot be considered to take us a step closer in fidelity to what the microphones picked-up. I'm sure we agree on that. But what the room can do, in the correct and small proportions under optimum conditions, is to synthesise (another word for fake) an acoustic which by happy coincidence under optimum conditions to our ear adds a certain amount of echo (etc. etc.) which fools our ear into thinking that we, the home listener, is in a bigger and more glorious acoustic space than we are actually in.

But as I stress, that's under optimum conditions, and those conditions absolutely mandate that there are no strong twangs of the sort I've demonstrated on the sound clips, otherwise the illusion of being in a big smooth, characterless space not only breaks down but it reverses. And by reverses I mean that if the room has a dominant sound it is an absolute give-away that we cannot be in a large space. We might well be listening inside a tin can or cupboard.

So perhaps your comment could be turned around to ask something like 'Recognising that the room sound is not part of the composition, not part of the recording, not intended by the producer or artists and varies dramatically from room to room, is there anything we can do to minimise the room's contribution? And is there a degree of deadness in the domestic room sound beyond which fidelity could actually be impaired?' That's surely the real question isn't it?

[BAS-H]

I've changed my mind. I think Alan's right. Music recorded in a good hall, reproduced in an anechoic room appears to be the best logical solution.

...is there anything we can do to minimise the room's contribution?

Other than filling it with soft, decorative stuff (don't ask your partner to clean it—DIY) and placing the speakers and listening position away from walls and the floor, perhaps not. Also, if there is a basement or room under the listening room floor, by decoupling the speaker stands from it using suitable spike boots?

[A.S.]

I've changed my mind. I think Alan's right. Music recorded in a good hall, reproduced in an anechoic room appears to be the best logical solution.
...

After a couple more demonstration clips (I don't have time today ... we're off to the Snow White, the pantomime!) I'll make them.

Yes there really are some thing we can do to the room, but we don't want to over-do the damping. So we have to have a strategy for damping. Incidentally, we are so conditioned to listening to speaker in rooms that we are not conscious of the room's contribution, even if it is quite bad. But play the recording over, say STAX headphones (I have a treasured pair of Pros) and you have really hear how much the room masks of the small details in the music. I'm not sure if STAX are still in business. (I think the boss of STAX Corp. was Hayashi san.; I met him some years ago and was impressed with his technology)

[STHLS5]

..

So perhaps your comment could be turned around to ask something like 'Recognising that the room sound is not part of the composition, not part of the recording, not intended by the producer or artists and varies dramatically from room to room, is there anything we can do to minimise the room's contribution? And is there a degree of deadness in the domestic room sound beyond which fidelity could actually be impaired?' That's surely the real question isn't it?

Yes and you have answered it in the preceding paragraphs of the same post.

..Yes there really are some thing we can do to the room, but we don't want to over-do the damping. So we have to have a strategy for damping.

OK, now we agree that the room shouldn't be over damped. At one point of a time, I was thinking since recording already captured the venues reverberations shouldn't the most accurate recording playback be in anechoic like room but then I was wrong and able to demonstrate that even though recordings sounded detailed and analytical but they lack the soul or bite or liveliness, etc., etc..

That begs another question why it doesn't sound right? IMHO, we are used to hear sound with reverberation. But when we capture a live recording sound with reverberation, can we say that reverberation is the same reverberation that we hear when we are at the live event?

To simplify, let's take a SINGLE speaker playing a recorded sound with reverberation in an anechoic chamber. The reverberation we hear originates from the speaker. In real life, the reverberation originates from all around us not from a single source like a speaker. I believe that make a very big difference to our musical enjoyment.

ST

p.s. A Very Happy 2011 to all. I indulged myself with a IPAD and a modest donation to Wikipedia. How about you guys?

{Moderator's comment: yes Harbeth UK also made a contribution to Wikipedia recently as we often quote from it.}

[A.S.]

.... The reverberation we hear originates from the speaker. In real life, the reverberation originates from all around us not from a single source like a speaker. I believe that make a very big difference to our musical enjoyment...

Yes, maybe we "expect" reverberation and maybe if the recording was made in a dry, reflection-free studio (many are) a little reverb added in the ordinary domestic listening room could, as you suggest. spice-up the recording. And if the recording has more 'acoustic' because it was recorded in a hall rather than a studio, a little more ambience from the home listing room may not draw attention to itself.

But we must be absolutely clear about this: if we are using the sonic signature of our own listening rooms to add-in something to our listening pleasure, it is a psychoacoustic trick, the extra wow factor is definitely not a characteristic of the recording and it will vary from room to room even though it may be an experience we like.

My concern has been from the outset - and I hoped that I'd demonstrated this is the early, carefully selected demonstration clips and my words - that the issue is not a smooth, characterless reverberation that dies away evenly (all the best halls have just that acoustic) but when due to an unfortunate combination of surface absorption, room dimensions and speaker placement an acoustic 'twang' lays across everything replayed in the room.

Believe me, when I contribute and go to the trouble of selecting, preparing and uploading clips or text I have a very definite game-plan, and from the outset my focus has been killing the twang, not killing the liveness of the home listening room, which I agree, would not necessarily be beneficial. But like it or not, the room is adding (usually adding, not subtracting) something to the recording which is definitely, 100% not there on the recording. Good headphones reveal just how much the room adds. Sometimes in the middle or upper frequencies, the room 'works' to our benefit, but not if there is a twang. And in the bass frequencies, I'd say that the room never works sympathetically with us - it always degrades the sound.

If you want to hear what is really on the recording buy a pair of really good headphones.

[honmanm]

In the context of domestic listening, what it's all about is enjoying music rather than appreciating recording techniques. If the listening environment were completely dead it would be very clear that one is listening to a recording... with all the sound appearing to originate within the arc between the speakers. This is a completely unsubstantiated guess - but the guess is that the reverberations of the listening space assist in the illusion that it has been "grafted onto" the recording venue... as long as they are small compared to the reverberation in the recording.

[STHLS5]

I am with you that room should be damped as much as possible. All I am saying that most listeners may find the new experience to be radically different. Noticeably, a toned down highs.

[I used a decent AKG and Sony headphones to replicate the same sound during the room treatment process. But then there's something called cross feed in headphones......]

ST

[P.C.]

Quote from#99 [Alan said]
'Recognising that the room sound is not part of the composition, not part of the recording, not intended by the producer or artists and varies dramatically from room to room, is there anything we can do to minimise the room's contribution? And is there a degree of deadness in the domestic room sound beyond which fidelity could actually be impaired?' That's surely the real question isn't it?

As I'm unable to use any room treatments. I've just recently tried positioning my M30s in the middle of my room. The theory is explained here:
http://www.immediasound.com/Speaker%20set-up%202009.pdf
What I'm hearing so far has been very positive.

[BAS-H]

Has this thread stopped developing? It's a pity - I was following it with great interest and was looking forward to it coming to a conclusion. Thanks to Alan and contributors we now have a good grasp of what room sonics are and how they are generated.

{Moderator's comment: no Alan has not been able to take the remaining pictures *in daylight* and will try to do so in next day.}

[A.S.]

Earlier in this thread we showed that the amount of energy that the speakers pump into the room is very largely wasted. Only a small fraction of it reaches our ears directly; the remainder splashes about the room long after the note has ceased. None of that reflected energy as we ultimately hear it is present on the recording, and how much or how little it colors the overall sound depends entirely upon the rooms dimensions and specifically, how absorptive the rooms various surfaces are.

Fortunately, humans can tolerate a substantial amount of 'room roar'. The point I made earlier is that it's not the general reverberation or 'liveness' of the room that is the issue - it may even enhance fidelity by creating a fake ambience through making the domestic listening room sound more cavernous - it's the twang or slap-echo when a sound wave is trapped between opposing surfaces and bounces back and forth. Since (acoustic) music doesn't have that sort of natural effect it is fatiguing because it's overlaid onto every note and phrase - and must be a man made phenomena in the reproduction chain.

We've also noted that to make any really worthwhile reduction in echoes or twangs we need to introduce absorbing material that has a reasonably large surface area, since there is no acoustic black hole that can be purchases to sit quietly in a corner soaking up unwanted reflections. And finally, we must be sensitive to 'her indoors' who obviously will not tolerate a wholesale redesign or redecoration of the entire listening room. So we need a cheap, portable solution that we can bring out from the cupboard before our listening session and pack it away afterwards. And that's what I'm going to show you. Construction time is about 5 minutes per absorber. Two absorbers would allow you to tame the side-wall reflections; four, the side wall and floor or behind the speakers.

Material and tools needed:

1. Rockwool in hard pre-shaped batts NOT fibreglass. Sold in packs of 4 or 6 here. Don't cut the pack open until you are ready to complete the task. No need to cut - we'll use the full piece.
2. Spray carpet glue - good quality, heavy duty. DO NOT SPRAY ONTO YOUR CARPET!
3. Big scissors
4. Thin woven material. Mine from a garden centre used to suppress weeds. Bought off the roll, 2m wide. Buy more than you need.

Follow the instruction in the picture. Be as neat as possible. The kitchen floor is an idea work surface in case you overspray glue - very easy to do! Good luck!

P.S. I cannot control the order that the pictures appear in, but the construction sequence is numbered.

>

[honmanm]

Thanks very much! And tomorrow we'll be driving past Wickes who seem to have a suitable product. [Correction: that is a soft batt, this one is probably what Alan meant.] For once it helps to be living in a cold part of the world...

I think the film (or something similar) can be had in various colours but haven't found a source in the UK (in Brazil it's called TNT, which translates to something like non-woven fabric. There you can get it from stationery and craft shops). If one wanted a really classy cover it'd probably be possible to order some Maggie "socks" from the Magneplanar speaker people. There are going to be some "looks" anyway when Maggie-sized objects are reintroduced into our living room!

[A.S.]

...we'll be driving past Wickes who seem to have a suitable product!

Please do check that it is Rockwool not fibreglass. Functionally they will give the same results but there are significant health/handling issues with fibreglass which do not seem, apparently, to be so with Rockwool. If you are going to use fibreglass it's really important to use gloves and a face mark when handling it and to be absolutely sure that you cover the entire absorber surface front and back to catch any fibres which are an irritant to the skin and lungs. Personally, I wouldn't use fibreglass for those reasons: acoustically it's fine.

I'm not an expert, but I don't believe that Rockwool has these issues.

[BAS-H]

Superb! Many thanks for the effort in demonstrating this cheap, practical solution. In my case, there's an unavoidable snag... the point of reflection off one of the sides is right in front of the fire!

I wonder if the panels would be suitable for suspending off the ceiling using a few straps and hooks? Would they be rigid enough to 'hold their own', as it were?

[A.S.]

I wonder if the panels would be suitable for suspending off the ceiling using a few straps and hooks? Would they be rigid enough to 'hold their own', as it were?

Well, they are rigid enough to be free standing so I should think that they definitely could be suspended. Again, the garden centre sells coils of 2mm wire which I'm sure would be strong enough to support a hanging panel. But the Rockwool will de-laminate when handled a lot, the edges will become soft and lose their crisp 90 degree cut.

[honmanm]

Please do check that it is Rockwool not fibreglass. Functionally they will give the same results but there are significant health/handling issues with fibreglass which do not seem, apparently, to be so with Rockwool.

I had a look at the Wickes products today... the packaging gives no indication of whether the contents are rockwool or fibreglass, but the texture is the same as rockwool products and for what it's worth the products come up when searching for "rockwool" on the Wickes site (purely circumstantial evidence). What is more convincing is that the safety information is the same as the branded Rockwool products.

The product I originally linked to linked to above is a soft batt... the hard batt that you recommend is here. Wickes also sell a black weed control fabric (no I don't work for them...) that is the same stuff as the Brazilian "TNT" - which BTW you can buy at a pound shop as a DIY "drop sheet" 1.5m x 1.5m, in white.

This investigation was done in the company of my dearly beloved, who displayed the expected levels of shock & awe when shown the batts. After a bit of thought she said: "maybe we should think about some ethnic wall hangings..."

(which is rather like the way we ended up with P3ESRs after trying out Quad ESL63s in our living room).

[A.S.]

The product I originally linked to linked to above is a soft batt... the hard batt that you recommend is here.

Ok maybe that is Rockwool. Certainly Rockwool batts are much more dense than the rather fluffy pink or yellow fibreglass. I think you'd be able to tell by weight - the Rockwool is more dense and hence, a batt is really rather heavy. A pack needs some effort to haul around.

Rockwool seems to always be a drab greeny/brown colour - maybe you could ask if they'd puncture the bag and let you see inside? Rockwool is a trade mark, possibly patented, and I don't think there are any clones; fibreglass is of course just a generic name.

Yes, I can well imagine the shock and awe! I think you'll be happier with a light, white covering; that black weed control material covering the DIY absorbers will make the listening room much darker, which is why I didn't select it myself.

[T.W.]

I recently moved from a house built in 1970 to our new (very old) one dating rom 1790. The 1970s house was built with bricks and beton. The 1790s one is a timber framed house with clay walls and wooden floors. Our new listening room is under a pitched roof. The walls are out of wood with isolation behind.

In the 1970s house I always had many room problems with too heavy bass. I wasn't able to fix these problems with simple damping alone. Panels don't help in case of heavy bass problems. (Already discussed in other threads). I used electronics (Lyngdorf Room Perfect) to get rid of the bass problems. But I always wanted to have a better sound without using any electronics just by mechanical damping.... The electronics do a good job, but they always also change the characheristics of the speaker. It always sounds a bit to "clean" and lifeless for me.

The new room is excellent. When I first turned everything on, it knocked me off. The bass is just dry and deep without any drone. The stereo image is perfect. Initially I thought that I reverted the phase of one speaker and double checked this many times ... The old 1790s house seems to "eat" all unwanted bass. The antiparallel walls help to avoid standing waves. The side walls are far away so that there is no trouble with first reflections. The big sofa and the pillows do the rest. The Room Perfect module is disabled now...

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