artto..a room question if you will

[steve]

I have read a lot of posts in the archives, and of course your room is something else to behold! You obviously are very knowledgable about room acoustics, so i'd like to ask you this..I have KHorns, and have always noticed a lack of bass in my dedicated music room..the ceiling is sloped, from 79" on one side to 112" on the other side..that's measuring on the long wall..and the long wall measurement is 251", and the depth is 171"..the Khorns are in 1/2 false corners (back wall real, side walls false corners due heat register etc). Anyway, I have tried amps that are 100-200W SS to SET 300B amps, and of course the higher power amps produce "more" bass (although I prefer tubes) but there's still no comparison to the bass I have heard from these speakers in my previous living room. As a matter of fact, I can walk around the music room and feel a "suck out" of bass in certain areas, especially on the left side in front of that speaker..this is where the ceiling is at the highest. So, is it the room?? Can I do anything to improve it without going broke? Or would i be better off with, say RF-7s, where the placement is more flexible? Room treatments aren't out of the question, to a certain degree, but I'd rather spend the money on speakers that will work in this room, than the treatments..if this makes sense. Any expertise on your part is greatly appreciated. I've read, and read many posts and links here, and I guess I don't quite get the 1-1.26-1.59 ratios.

On a final note, although the room I have is ground level, (not sunken) I have to come down three stairs from a landing (outside a closed door) due to the the attachment of the house..at the top stair, when I am leaving the room, the bass is ENORMOUS! So is everything trapped in the high end of the room??

Thanx again for any recommendations!

Regards,

Steve

[DrWho]

ok, purchasing different speakers because of your room is a backwards approach...speaker position just shifts which frequencies are getting cancelled out and where those cancellations occur (sometimes you get lucky and can minimize problems at the listening position).

The simplest way to go about fixing your situation would be to walk around the room and note locations where there is a lot of bass...and then put a bass trap in that location. What you're essentially doing is absorbing the build up of the bass that is reflecting back to the listening positioning (which is out of phase with the direct sound....resulting in cancellation).

The lenrd bass traps from auralex would be a good way to go....though I've read recently about an online only dealer (via ebay) that sells the exact same stuff for cheaper. I can't remember off the top of my head the name of the company.

Spending money on treating the acoustics of your room will have way more of an impact on the sound than differences between amplifier topologies (which is seems you've been trying everything). And with a little creativity it doesn't have to look like crap either.

[steve]

thanx Dr. Who..I've thought about that, and seeing how it's my dedicated stereo room, the WAF doesn't apply here, as she says it's all mine. What was wondering is, how many (and what size) panels should i start with?? I notice most of the bass up in the high ceiling corner on the left..it's an enormous amount compared to the rest of the room..so i guess I could start there. However what scares me away is I see room "kits" going for thousands of dollars..I don't mind spending some hard earned dollars, but not to the point of spending what I have in equipment. Another thing, is that I'm happy with the treble, so i don't need absorption there. So if I need bass traps alone, do I fill up the entire ceiling to wall area where I'm having trouble, of just part of it? Sorry to sound so ignorant.

Regards,

Steve

[formica]

Ideally, I think you should measure your room's response so that you know exactly what is going on. Even a simple software and the RatShack SPL can get give you a better idea of bass response problems.

You are already on the right track, as your accumulation will definitely be in the corners so that is the best place to start.

Since your main concern is bass, you can look into getting simply the bass traps of your choice. There is Auralex that DrWho mentioned www.auralex.com with the LENRD Bass Traps model... but there is also www.RealTraps.com and the www.foambymail.com who seems to be cheaper through eBay.

Notice they are Wedge shaped and are designed to be installed in the room corners (Wall-Wall, Wall-Ceiling, and even Wall-Floor)? This is due to the fact that bass will peak in the corners in most rectangular rooms... and the triangular shape allows for a thicker unit. The thicker the acoustical treatment (of the same material), the better it's low frequency performance will be. This applies to the three dimensions, including the length of the unit. That is why stacking multiple traps will improve it's low frequency performance.

Treble is most affected by it's first reflection spots which fortunately won't coincide (rarely do, actually) with the proposed bass treatments in the corners. So you can bass trap to your hearts delight. The catch is most treatments are quite poor at very low frequencies... so you may not be able to smooth it all out with just bass trapping.

That was one of the reasons I mentioned measuring the room response, to see where the worst modes were.
Later...
Rob

[artto]

Sorry about not getting to this sooner. For the most part Ive been absent on the Forum in recent months, simply busy with other stuff.

<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

First lets start with the Khorns. In order to get the best out a Khorn you must remember that it was designed, very specifically, to be used in a corner, a trihedral corner. This creates a situation where the speaker is in what is known as one-eighth space (translation: the speaker performs with efficiency in the lower frequencies as if it were actually 8x larger than what it actually is).

Now for the false corner part. When the speaker is in the corner, a full sized, true room corner in an enclosed space, there is more low frequency acoustical reinforcement from the room than say, if the speaker were in the same room with false corners away from the walls. So unless the false corners are very large, and the room also rather large, there will always be a loss of low end from the Khorn with false corners. Being able to move the Khorn around or reposition it with the use of false corners is not an advantage to improve imaging or interaction with room modes as some people have mistakenly proposed. It simply shifts the audible modal interactions to different locations, the standing waves and resulting cancellations are still there, their relative locations in the room, relative to the listening position have changed.

In reality, any room which has any of its dimensions less than several times the wavelength of the lowest frequency to be (re)produced will have modal influences. The reality of this is that in almost all domestic environments, what you are really hearing is the influence of the room, on your recordings, on your electronics and most certainly on the speakers. You are, literally, listening to the room. You probably recall hearing many times about how good speakers should just disappear. IMO, not only should the speakers disappear, the room should disappear too.

So to answer your question about spending money on room treatments verses speakers that have more flexibility, I have to say that IMHO, ANY speaker, its associated equipment, and recordings will benefit from acoustical improvements. There is no substitute (at least not yet). No need to go broke doing acoustical improvements. My room is rather large and I spent probably around $1000 to $1500 on acoustical specialty products from Auralex and Sonex, maybe another $500 to $1000 on things like Celotex rigid insulation board and Masonite panels. No other single or combination of components can produce the same or better resulting improvement in sound reproduction at any price. So one must ask whats expensive? If your speakers cost thousands of dollars, and the rest of your components cost thousands, and the room they are in cost thousands moreseems like a small price to pay for a major improvement that is not achievable by any other means.

The room ratios are only for simple rooms with parallel surfaces. Once curved or angled wall surfaces are introduced the calculation of room mode (resonances) becomes much more complex. They are referred to as modes because there is more than one resonance caused by the room dimensions. There is a fundamental resonance for each of the axial dimensions, as well as related tangential and oblique modes, fundamental room resonance, etc. Each of these can and will influence the other, often compounding the effects of their resonances, which are called modes. Most people tend to think of room sound reflections much the same way they think of rays. But were really talking about waves and wave interaction which can be both constructive (increases amplitude) and destructive (cancellation).

http://id.mind.net/~zona/mstm/physics/waves/standingWaves/standingWaves.html

http://id.mind.net/~zona/mstm/physics/waves/interference/constructiveInterference/InterferenceExplanation2.html

http://id.mind.net/~zona/mstm/physics/waves/interference/destructiveInterference/InterferenceExplanation3.html

The bass typically piles up at room boundaries, especially at room boundary intersections such as corners, so the enormous bass you are hearing at that particular location is where there is a standing wave problem. This is precisely where you should install bass trapping. What is happening is that the standing wave situation at that location is causing the opposite effect, or cancellation of low frequencies, in other areas of the room.

[steve]

thanx artto..I should have checked the architectural category before posting another question in another category..

would you suggest bass traps (in the trouble area) in the wall/wall corners, or wall/ceiling?? Or both? And should i do something in all corners just to be safe? I read that you can't really have too much bass trapping on auralex.com.

Thanx again for answering my post.

regards,

Steve

[artto]

I guess my first question, where is the stairs/landing located?

<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

You see, what is happening is that if the bass sounds enormous in the area of the room where the stairs are located, there is where a standing wave problem at that location. It is where one (or more) of the room modes coincide with certain frequencies (which frequencies, we dont care at the moment) are produced by the speaker(s). The result is a peak in response as the waves build up with coinciding sound waves produced by both the speaker, and recurring reflections. But as these same sounds are reflected back into the room, back towards the speaker, when they reach the speaker (or other parts of the room), they are out of phase (out of time) with the same frequency the speaker is producing (dont forget, that at 20Hz this happens 20 times per second, at 100Hz it happens 100 times per second, etc). So in your case, at the speaker, where the high ceiling is, certain low frequencies are getting substantially cancelled (just the opposite of what happening in the other location).

My best advice is to start with something like a box of Auralex LENRD bass traps. Put them in the area where you hear the most bass, and take a listen, all around the room. Then move them to the rear vertical corners and do the same.

In my room I have a 6 stack of Auralex MegaLENRD in one rear corner and one LENRD/MegaLENRD on an open riser support in the other rear corner. Theres about 16 of LENRD across the back wall/ceiling intersection which was installed first. When I added the MegaLENRD in the corners, what was interesting is that the orientation of the modes seemed to rotate about 45 degrees making the loudest bass more towards the middle of the back and side walls instead of in the corners. So you may experience some rotation of where the perceived wave build up/cancellations occur depending on where/how you place the bass traps. And remember, we are dealing with this in three dimensions! You can hear the interaction of room modes produce different results as you move in the Z axis (up and down), as well as horizontally. You can hear this effect very easily with sine waves, especially at higher frequencies.

IMO, Khorns sound better with a reflective surfaces around them, so personally I wouldnt recommend putting bass traps like LENRDs near them. However, Klipsch has one MegaLENRD on top of each Khorn in one of their demo rooms and it sounds fine. But their room is not acoustically treated to the Nth degree as mine is. Also consider that the large curved Masonite panels provide some degree of bass trapping and ability to break up standing waves. This works fine above or nearby the Khorns because the surface is still reflective for middle/treble frequencies while providing superior diffusion so the room doesnt become too dead from too many absorptive surfaces.

[steve]

the stairs are on the left side of the room..note the extra corner due to the stairs, otherwise the room would be a true rectangle. The right side (lower ceiling, not shown) doesn't have the "extra" corner.

All the bass is trapped up there by the top of the stairs. I"m going to order a box of 8 LERDT bass traps Monday..was thinking about stacking 2 in both upper corners (that would put one set above the shown speaker..not a good idea?) and the other 4 spaced where the ceiling and wall meet on the high side.

Would this be a good place to start?

Thanx,

Steve

[DrWho]

Would this be a good place to start?

Sure, just try not to do any permanent installation until you are satisfied with the results.

[artto]

Try starting with this. You nay need tp go to with MegaLENRD in the vertical corner. You can start with the regular LENRD and use them elsewhere if you decide you need the Mega.

You can attach the traps to the wall with 2" long steel "T" pins available at fabric stores & office supply. It will leave a very tiny hole and do minimal wall damage if you decide to move them around.

[steve]

thanx Artto

I'll order 8 regular traps tomorrow, and see how they do. The worst part will be the shipping costs I'm sure! Thanx for the tip on attaching them temporarily..will post my results when I'm done.

Appeciate all tips and info.

Regards,

Steve