Adjusting Room sound using material damping methods (not DSP)

[Chayro]

The listener often arrives with a somewhat numb ear that is not ready to pick out the details a good reproduction can offer (I sympathize and need to warm up my ear to someone else’s system to). Do you have any technique for sensitizing your listener’s ears (short of tying them into a chair for a long period of time)?
Thanks in advance.

I am a great believer in starting a listening session at a level that seems too soft at the time. I agree that our ears are numbed from the constant noise and when we listen to soft music, the ears seem to "open up", almost like your eyes dialate when going into a room with soft light. After a tune or two, I will nudge the volume up just a bit and the music sounds full and vibrant, but still at a lower volume than most people would have started at.

I think that too many people think that the ear-damaging level they listen to music on their Ipod with is what a home audio system is supposed to do.

[A.S.]

Whilst searching on Wikipedia, I found this. Scroll down to the section marked as above ..... simple, effective and accurate. No tools required!

http://en.wikibooks.org/wiki/Acousti...pots_In_a_Room

[airdavid]

very useful, thank you Adam !

regards,
David

[vaughn3d]

Here is a math question for you. If I want to toe in my new C7s, say 10 degrees, is there an equation I can use to measure the two back corners of the speaker from the wall to know the angle that I have? There must be, I just don't know what it is.

[A.S.]

Here is a quick calculator for you. Please double check my result!

All you need to do is decide upon distance d1 from the rear wall to the speakers nearest back corner (in mm, cms or inches) and the toe-in angle which in this worked example is 10 degrees.

Then, using a pocket calculator find Sine 10 = and that number you fit into a equation as you do the distance d1. The number that falls out of the calculation (d2) you add to distance d1 and that tells you how far away from the rear wall the furthest back corner of the speaker is.

Hope that helps.

[vaughn3d]

Thank Alan, that is perfect. Now I get to count down the days until my Skylan Stands arrive...until then I'll stare at the C7s sitting patiently in the corner of my room.

[Don Leman]

Taking advantage of Google's spreadsheet tool I have made the following from Alan's post. I am not aware of how to protect the cells containing the formula so make sure to only change the cells that are blue in colour.

NOTE: Unless I discover a way around it, I now realize I need to give individual access to the spreadsheet for you to be able to edit. Please send me an email at westcoastaudio@shaw.ca and I will be glad to do this and send you the link. As an alternative if you have excel I could email you the spreadsheet.

If you have any questions please contact me

Don

[A.S.]

Don: that's a really great idea, but when I try and run it it is locked for viewing only. If you supply me (privately) with the XLS file, I'll see if we can make it available directly to our Users and without file locking.

PLEASE NOTE: this is not resolved yet to allow users to enter data into the spreadsheet.

[T.W.]

My living / listening room is about 6.8 x 4.2 x 2.5 m. This gives me some quite
heavy room resonances. With my old HL5LE this wasn't a big problem. But with
my M40's, which have much deeper bass, it's a serious problem in the moment.

A tool calculated resonances at 25, 50, 76, 101,... Hz. I verfied the ones at about 75 and 50 with a test CD. At 75Hz you have the fear that the walls come down :-)

Moving the speakers helps a bit, but not enough.

I read a lot of acustic foam in the corners and helmholtz resonator that seem to be quite easy to build. There are also some companies around selling special wall panels and other stuff.

Damping the room with big boxes of mineral wool would probably help, but this is not an option. I also haven't yet tried to put socks into the vents. I may try this.

I'm looking for another and hopefully nice looking solution.
Does anyone have an idea or any experience in this area?

Thanks,
Thomas

[A.S.]

I think you are not going to be able to put enough thickness of sound absorber on the walls to make a real difference, so a better strategy is to reduce the amount of bass from the speakers. Suggestion: remove the grilles of both speakers and stuff the ports with foam or even (clean!) pairs of socks.

The attached picture shows how poor general-type absorbers are at soaking up low frequencies.

[T.W.]

Thanks Alan,

That's exactly what I assumed. Next I will try some socks. I hope that I can find clean ones. Does it matter if they have holes? :-)

Have you ever tried these bass traps? Here is a link to a company that seems to be quite professional in studio technology. (Sorry it's in German)
http://www.mbakustik.de/main.php?tar...onanz_absorber

With some nice painting the may even look quite good.

[T.W.]

I stuffed all the vents with damping material. They still have some output, but much less than before. That really helped! But this also removed some of deep bass I love. Unfortunately, we can't have everything ...

I have to experiment a bit more. Maybe it's a good idea to fill just one vent or not to fill the vents completely.

My understanding is that damping just changes the Q-factor of the bass reflex tuning and not the characteristic frequency. Is that true?

[A.S.]

... we can't have everything ... my understanding is that damping just changes the Q-factor of the bass reflex tuning and not the characteristic frequency. Is that true?

Not quite so simple I'm afraid! According to my empirical observations the Q will fall (i.e. the LF system output will broaden over a wider range of frequencies) and so will the level at very low frequencies. Also, I note that the centre frequency of the Q will shift (upwards I recall) by a few Hz.

It's difficult/impossible to beat the physics here of deep bass in small, untreated domestic rooms. Those bass traps look very interesting indeed.

[Ned Mast]

In my room - not too different in size from yours - I found getting my M40s away from the walls helped. Also, getting them on high enough stands - at least 23". But ultimately I also added equalization to get a really flat frequency response.
A simple analog equalizer helped, but the digital pre-amp/room correction unit I have now is more refined and effective.

[T.W.]

Yes an equalizer / dsp is propably a good idea. But for now I don't want to have another part in the chain where I can play with...

For me room acoustics is an interesting theme. I never really cared about it. But the more I read or "google" about it, the more interesting it becomes.

I may ask a professional to analyze my room and to give some advice what to do. It seams to be affordable.

When I have moved forward I will post my results here.

Thanks,
TW

[Chayro]

Because of my room, the most I can mangage is approximately an 8' equilateral triangle between my head and the speakers. One thing I love about Harbeths is that, due to their monitor heritage, they work very well in the nearfield.

I couldn't care less about what "order" crossover is in a speaker, but I have heard that you need to sit further away from speakers with first order crossovers to make them sound coherent. Is that true, and why is it so? Is 8' going to work or is something more necessary.

The reason i'm asking is because I'm going to audition the M30s, which my dealer believes is extraordinary. However, he is also a Sonus Faber dealer and he thought I might like to listen to the Cremona Auditor, roughly in the same price range. I know these speakers have a 1st order x-over and I thougt i'd ask.

I'm heavily biased towards the M30s, although I'm willing to listen. Thanks for you help.

[A.S.]

... I couldn't care less about what "order" crossover is in a speaker, but I have heard that you need to sit further away from speakers with first order crossovers to make them sound coherent...

I don't know much about 'first order filters' used in some other speaker crossover networks but I think what you are referring to is the overlap of energy where the drive units are simultaneously reproducing sounds around the crossover frequency. Not ideal.

What is a 'first order filter' - or indeed a 'third order filter'? It's simply a way of describing how steeply the sound is handed over from one drive unit to another through across the audio spectrum, how the designer makes a cross-over between the top end of the woofer and the bottom end of the tweeter.

If the crossing over is very gradual covering a very wide frequency range as it would be with a 'first order filter' which is a very simple network with as few as two components (!) this seems to be asking for trouble. At worst, it means that the tweeter is forced to pass not only high frequencies, for which it is optimised, but some mid frequencies which leak trough to it because of the simplicity of the network. It also means that at the very top end of the woofer/midrange driver (where the response is no longer perfectly smooth because if it was you wouldn't need a tweeter!) it will be attempting to reproduce high frequencies which have leaked through to it via the simple crossover network.

The solution is of course to use more components - hence a higher 'filter order' (third order being a higher order than first order) where each drive unit is fed sound appropriate to its optimum capabilities. When you listen to hi-fi speakers you can quite often hear tweeters 'barking' and that is a sure sign that they are being operated uncomfortably low and are under mechanical stress. You can also hear a loss of purity - a sort of mush - because bass/mid drivers are far to heavy to trace the lower high frequencies properly and is fighting the tweeter's contribution.

As I understand it, with a first order filter you need to be some distance away so that in the crossover region the sound waves from the two drivers can somehow merge according to the position of your head vertically and/or you can find a point vertically where you can hear more tweet and less mid.

This sort of issue is the result of the designer taking a strong line on a particular aspect of the design - as we all do in our own ways. If the designer strongly believes that fewer components in the crossover must sound better then he is trapped by his low-order filters with all their (insurmountable) issues. If he takes the line (as I do) that every real-world drive unit has its optimum working range then he'll go for whatever complexity is necessary to get the best from them.

Hope that helps.

[Chayro]

Alan - thank you for your detailed reply, but as it turned out, it wasn't a problem. As my dealer explained, the listener should not worry about what's in the box, just what sounds better. Sensible advice, I think. In any case, after the audition, I'm sitting in front of my computer listening to my new Monitor 30's. Well done Alan.

[al2002]

Yes an equalizer / dsp is propably a good idea. But for now I don't want to have another part in the chain where I can play with...

TW

Here are some ideas for the bass:

http://www.sennheiser.com/klein-hummel/globals.nsf/resources/tmt2002.PDF/$File/tmt2002.PDF

http://www.avsforum.com/avs-vb/printthread.php?t=837744

I trust Frau T. W. will not object......

[ronaldg]

This isn't an exactly an answer but I thought it might be of interest. This is my toe-in adjustment technique.

Gather up a piece of string or fishing line that will reach from the back of the listener’s chair to at least the rear of your loudspeaker. Now insure that the listener’s chair is centered and equidistant to the loudspeakers. Anchor one end of the string to the center of the back of the chair at ear height with strong tape, tied to a weight, or attached to a safety pin. Holding the other end of the string bring it to the inside front corner of one of the speaker cabinets. Mark that point on the string with a permanent marker. Now adjust the toe-in so the outside front corner is that same distance and recheck both corners. Okay, do the other speaker using that same mark for the inside and outside corners. When all corners are the same distance from the anchor point the speaker cabinets will be equidistant to the listener and tangent to an arc with the center point (focus) approximately at the listener’s ears.

Ron