Adjusting Room sound using material damping methods (not DSP)

[NikPer]

From personal experience id agree most with the latest post, since i've found that aligning the speaker with the listener is far more important than lining it up to the walls. Also one must not assume (as its my case) that walls are perfectly 90 degrees to eachother, floors and ceilings are perfectly horizontal etc..

[A.S.]

This thread concerns techniques that have been used to treat the listening room. Much research was undertaken by the BBC who had a thorough grasp of the technical requirements of well balanced studio and monitoring environments as long ago as 1930. These solutions involve new-build considering the room acoustics right from the first architectural drawings and to damping (lagging) existing rooms.

[A.S.]

The document covering the 1932 construction ..... (to follow)

[Superman]

Hi! Good Day!

I recently purchased a Harbeth HL-P3 ES2 (still in transit from overseas)...I am currently using a Conrad Johnson Evolution 200wpc Power Amp (w/ 4 x 5751 inout tubes), Counterpoint SA-1000 Tube Pre-Amp and a pair of floorstanders...I've been to a friend's store and the P3s are giving me sleepless nights after I've heard them...So I've taken a bite at the bullet and purchased a pair (in Eucalyptus Real Wood Veneer)...My room size is approximately 11feet x 15feet...I have been used to the "low-end" that my floorstanders deliver...With this room size, would you think (given the proper placement and toe-in), the P3s will give me sufficient bass particularly for fast music like rock, acid jazz??

Thanks! :D

[joel]

An effective, flexible and cheap (assuming you already have the raw materials) solution to bass issues in room is a strategically placed bookshelf or two (or three or four). Books and speakers

The bookshelf in the picture has also helped deal with some grievous corner loading issues.
Books have also allowed me to fine adjust damping and resonance control. It's very cheap and easy to do.

The Yamaha speakers are excellent (3-ways approx same size as M40s), but I'm looking forward to the M40.1in Japan (finally)!

[jaybar]

Hi Alan and Others:

Alan, when you design Harbeths, are you assuming that a listener will be seater at least a specific distance from the speakers? I am seated about 5.5 feet from the speakers measured from my ear to the woofer. Alan, in another post, you referred to Harbeths as having a Low Q, relaxed sound. Well, at that listening distance, My Monitor 30's are anything but relaxed. The sound is definitely high intensity, particularly when I listen with them pointed at me.. They are slightly more than 50" from the wall behind them.

Because of my room's concrete construction, it really holds onto bass, which is why I place the speakers so far out into the room. Also, the wall behind the speakers has a large expanse of glass window and positioning the speakers well out into the room, helps with that. I also have heavy drapes and quarter-round bass traps in the front corners. Listening off-axis does reduce the level of intensity and yields a more relaxed sound at a slight loss in detail and less pin-point imaging..

I am wondering if I am violating any design principles with respect to how close I can sit to the speakers? Can good results be achieved with really nearfield listening and if so, does one have to make any accommodations for listening very hearfield?

Thanks,

Jay

[A.S.]

Um. You have a very difficult acoustic environment - concrete walls (+ floor/ceiling) is really the worst possible situation for listening to hi-fi. What you are experiencing is a sound at your listening position which is dominated by the room's surface reflections.

To visualise what is going on inside your room, its easier to imagine waves in water than sound waves in air. Don't try this at home! - but this may help. Imagine your listening room is completely sealed and water tight. Fill it with water right up to the ceiling and wearing your diving gear (with oxygen bottle) get into the room with a heavy cricket ball. The ball will represent sound waves as they radiate from the speakers. Stand where the speakers would be and throw the ball towards your listening seat. Observe ....

1. As the ball travels towards your listening seat it leaves in a wake its path ...
2 ... this wake will radiate as an expanding cone behind the ball in along the height and width directions i.e in 3D ...
2. ... the wake spreads out behind the moving ball until it touches nearby surfaces ....
3. ... by the time the ball passes your seat the wake has widened out so much that it has reached the floor and probably nearest side wall, and shortly thereafter the wake will touch the ceiling ...
4. ... the ball continues past your seat until it hits a surface behind your seat, probably the rear wall ....
5. ... according to the angle the ball hits that surface it reflects at the same angle off the surface (as all tennis players know) ...
6. ... and probably arrives at the opposite side wall, and according to the incident angle it hits the side wall it bounces off ..... until it runs out of energy seconds later ...
7. ... meanwhile, the wake the itself also bounces off surfaces according to the incident angle ....
8. and within a few seconds the entire room has been transformed from tranquil, still water to a thrashing mass of ripples as every molecule of water (air) in the whole room space has been energised and is in motion.

- and that's just with the first pulse of sound, the first note, from one speaker! Imaging the seething confusion of ripples when two speakers are playing a distance apart! It is a miracle that the human brain can tease out of this sonic mess anything that resembles natural sound. Even the most complex computer would have the greatest difficulty doing that.

So, what can you do to help improve the situation? The simplest way is to sit closer to the speakers so that what you hear is more of the direct sound from them, and less reflected sound from surfaces. Second, you can make the surfaces more absorptive, especially those surfaces near to the speakers - floor, side wall and behind the speakers so that those early reflections (from surfaces near the speaker) are robbed of some energy, so that there is less they can reflect and pass on. Those really are the only options available.

Incidentally - if you don't fancy flooding your room (and who would!) you can achieve a somewhat similar effect next time you are in the dentist's waiting room. Wait until you are the last one in the room, put your hand into the tropical fish tank and furiously agitate the water; watch how the ripples fill the tank. (Caution: think of the fish; think how you can explain the wet arm to the dentist as you lie dripping in his clean chair).

Does this help?

[jaybar]

Alan

Thanks so much.

You have only scratched the surface of how bad the room is. The walls are concrete and cinder-block with a skim coat of plaster. The floor and ceiling are 18" of concrete. It is L shaped with no true rear wall (opens into an entrance foyer) and it is only 12 feet wide. I have rugs and drapes and a bookcase on the left wall near the speakers and LP's on that same left wall.

Questions:

1) Is there a minimum distance regarding how close one can sit to the speakers?
2) In this type of room nightmare, should the speakers be fireing at you (on axis) and pointing at you or your ears?

Thanks,

Jay

[A.S.]

I feared that might be the way your room was constructed. To answer ...

1). No minimum. You can 'wear' your Harbeth speakers like headphones. One of the remarkable properties of a Harbeth is that even very close, they sound sweet. Try that with other speakers and they harden-up as you get closer to them.

2). I truly can't answer that. Listening off axis (i.e. speakers are parallel with the walls and you sit at the apex of a triangle) will slightly reduce the energy at the bottom of the tweeter band a little. This may reduce harness - conversely, it may spray more energy into the room, and onto those side walls in that irritating frequency band. See how difficult it is to give advise? I'd strongly recommend some sort of drapes over the side walls, and then play around with to-in.

[jaybar]

Thanks Alan

Drapes along the side walls. That would start WW IIII. I have bookcases and 2000 LP's along the left wall, so that should help a bit. The pleated drapes on the wall behind the speakers, which has widows the width of the room and half-way up the wall, really cut down the energy.

I am usually reluctant to draw the drapes, since we are blessed with a NYC skyline view that is spectacular, but I may have to resort to that for serious listening. I have oriental rugs on the shorter right wall that opens into the "L" and in the adjacent open dining area..

There is only so much that I can do and maintain domestic harmony.

Thanks so much.

Jay

[A.S.]

Yes, I fully understand. It's all about absorbing energy.

A trick that can show you where best to place the wall absorbers ... seated in your listening hot spot in a darkened room ask an assistant to hold a mirror on the side wall somewhere between your seat and the speakers. Shine a torch at the mirror and according to the angle-of-incident theory (just like snooker or squash) where the light beam hits the mirror it will reflect off at the same angle. Adjust the position of the mirror forwards/backwards until the light beam strikes the speaker. That is the shortest path that the reflected sound wave can travel from the speaker to the side wall to your ear. Put most of your wall absorber at that place and you'll achieve maximum absorption for minimum surface area of treatment.

As for the LPs - their jackets are hard and will reflect but the small air gap between them will help absorb. So, they'll help absorb but in a frequency selective way. And of course, because only one side wall is treated, it will skew the stereo image a little (but humans are good at mentally correcting for that).

Books, especially with the spines inwards (difficult to know what they are then!) are better, but with the spines outwards, much more reflective. Heavy curtains or drapes - spaced away from the wall - are best of all. If they are on tracks then they can be slid into the listening position or put back in the corners for normal domestic life.

[A.S.]

Here is a video showing how the treatment of the walls and other simple sound deadening solutions improved the environment in a nursing home. Of particular interest is the treatment of the walls with what looks like BASF's Basotect melamine fireproof panels. I used these in our listening room and they are an excellent sonic solution. The material comprises of millions of microscopic 'pores' and dust settles in these pores and cannot be completely removed not even by vacuum. Note that the ones they are handling in the video seem to be covered in a (washable?) cloth. Basotect can be cut/shaped to any size.

[redryder]

Hi Alan,

I would appreciate some advice on setting up my new P3-ES2s in a small room. Room size and possible layouts are shown in the diagram below. I've bought the speakers but haven't set them up yet.



My original intent was to go with option 2, but the Harbeth dealer I bought from said that this option would lead to sound bouncing off between walls B and C, negatively affecting the quality of music. The other alternative would be option 1, where there is more room to move the couch further or closer to the speakers. My concern there is that the right speaker is too close to wall B, although I don't know what impact that would have on the sound. There are curtains along wall A, and bookshelves along Wall C. Unfortunately I can't test both configurations as that would necessitate a lot of furniture movement, and the wife wouldn't like that.

Any opinions would be much appreciated, thanks!

[A.S.]

That's an excellent drawing which makes is so much easier for us to understand your set-up. I encourage others to make a similar drawing when they enquire about room layouts - even a scan of a hand drawing really helps us to give best advice.

OK. I see your problem. In the real-world, neither Option 1 nor Option 2 are ideal. I also fully appreciate the domestic practicalities of dragging the furniture around in your room to experiment with the sound, and how that would irritate a wife. It certainly would irritate mine. Frankly, I think that you have to put domestic bliss before the last degrees of sonic perfection. You also have to consider the visual symmetry of the room; even if one Option gives a better sound than the other if it makes the room look visually unbalanced or markedly asymmetric it will disturb your listening pleasure because you just won't feel comfortable sitting in there. Agree?

So - judging from your drawings, I suggest that you're really obliged to go with Option 2 regardless of whether or not Option 1 sounds better (or not) because Option 2 looks neater and more visually appealing. The question is - how will it sound? I note that you say you have bookshelves along wall C and curtains along wall A. Both are definitely worthwhile, although the books would soak up even more if the spines are against the wall - but totally impractical as you wouldn't be able to read their titles!*

You don't say how far you can bring the P3s into the room from wall B, but judging from the fact that the wall A is 2.8m then I suppose that the maximum distance from the wall can't be more than about 0.5m. It may even sound better with the speakers closer to the wall - it's one of those things that you'll have to experiment with yourself; at least moving a pair of P3s around is a much easier prospect than moving the furnishings.

* Books, especially when the open pages face the sound source (the speakers), really do soak up sound. Have you walked in a wheat, rice, maize (corn) or similar tall grain field just before harvest time and shouted at the top of your voice? It's like being in an anechoic chamber - the grain ears and stems are exceptionally good at trapping sound. One of the best ways to reduce road traffic noise is to put a cereal crop field between housing and the road; the attenuation of sound by the field is almost total - until harvest day!

[redryder]

That's an excellent drawing which makes is so much easier for us to understand your set-up. I encourage others to make a similar drawing when they enquire about room layouts - even a scan of a hand drawing really helps us to give best advice.

Thanks for the quick reply Alan!

Its sad that neither option is ideal but that's real life. I could move the speakers to a much larger living room, but then I won't have the freedom to listen to what I want, anytime I want. Cest La Vie!

[A.S.]

Yes, I think that it is absolutely vital that we remember (as I do at the design stage) that we're making real value speakers used by real people in real rooms, not by a few rich folks under absolutely perfect conditions.

I attach a picture of me during a listening session during the development of the C7ES3 as I make adjustments to the crossover. As you can see, the development room was literally a small unused bedroom at home and the speakers are in a very non-ideal situation close to the wall and near to the door.

My strongly held opinion is this: if I can design Harbeth speakers sound good in such an imperfect environment they will sound fabulous given a little more air in a bigger, better room. We design for the least fortunate listener, listening in the smallest, hardest acoustic environment to be 100% sure that everyone can enjoy the Harbeth sound in their own home.

[Forberg]

I plan to upgrade my system with new speakers, possibly M40.1s. I feel, though, that the present acoustics of my listening room will not do credit to these speakers, so I will try to make some improvements. The easy bit will be to use absorbers to kill off the first reflections. To clean up the bass, I could need bass traps, but hesitate to litter the corners of my room with such bulky items.
I have, however, an interesting option (at least so I think). I could actually make holes in the sidewalls in my front corners, holes that open up to attics running alongside the room. These attics have a triangular shape 1,5 times 1,5 metres and some 15 metres long. They are heavily damped on one surface with 200 mm Rock Wool (roof thermal insulation). The holes in the walls could be quite large, 1 times 1 metre, or larger. The idea behind this is, of course, to allow the high pressures caused by standing waves to dissipate into the attics. Since ALL standing waves in a room have pressure maximas in the corners, I imagine that this just might be a very efficient bass trap arrangement. The holes would be covered with fabric.

Unfortunately I am not an acoustic engineer, so I would be very happy if somebody out there has experimented with similar arrangements and would be willing to share his/her experiences. Good ideas are also extremely welcome. Tips on literature that could be useful are also very welcome of course.

Thanks
Forberg

[Forberg]

I plan to upgrade my system with new speakers, possibly M40.1s. I feel, though, that the present acoustics of my listening room will not do credit to these speakers, so I will try to make some improvements. The easy bit will be to use absorbers to kill off the first reflections. To clean up the bass, I could need bass traps, but hesitate to litter the corners of my room with such bulky items.
I have, however, an interesting option (at least so I think). I could actually make holes in the sidewalls in my front corners, holes that open up to attics running alongside the room. These attics have a triangular shape 1,5 times 1,5 metres and some 15 metres long. They are heavily damped on one surface with 200 mm Rock Wool (roof thermal insulation). The holes in the walls could be quite large, 1 times 1 metre, or larger. The idea behind this is, of course, to allow the high pressures caused by standing waves to dissipate into the attics. Since ALL standing waves in a room have pressure maximas in the corners, I imagine that this just might be a very efficient bass trap arrangement. The holes would be covered with fabric.

Unfortunately I am not an acoustic engineer, so I would be very happy if somebody out there has experimented with similar arrangements and would be willing to share his/her experiences. Good ideas are also extremely welcome. Tips on literature that could be useful are also very welcome of course.

Thanks
Forberg

[Ferdinand777]

Hello,

ASC bass traps will work but they are quite pricey esp when you factor in freight cost from Oregon to Sweden. Also, the more traps, the better. I use a total of 14 in my listening room with the SHL5s.
I use bass traps for many years and they do wonders.
However since you are in Sweden, i suggest you look at the Lyngdorf room correction from Denmark. These are very very effective & I also use them.
Good luck.

Ferdinand

[Forberg]

Hello Ferdinand,

You use 14 ASCs pluss a Lyngdorf?! I am sure all that stuff works, but I really hesitate to go down that road.
I think I?ll test the idea of using my attics a while longer, but thank you for your comment.

regards
Forberg