View Full Version : Bass Question
Ok...I am seeking any experience with bass from 43XX cabs. I have a room that is 12' 3 across and 27' long. There is a jog in the room at about 16 feet which cuts off about 3 feet of the width of the back wall. I have experimented with my listening position from anywhere from 12' to 15' feet from speakers. My speakers have been moved around too...and I have found the best spot so far is about 7'8" apart. I have noticed that I have nodes of lower bass, but the upper bass frequencies are not detectable at all?? Any ideas on how to solve this issue?
Here is a drawing of the room...the brick mantle is treated with a dampening material. Speakers are sitting on top of granitel slabs..3 inches thick. I know the room is a stereo nightmare, but its all I got for now and any help is appreciated.http://members.shaw.ca/mbeka/room.bmp
So I've made a discovery or two in the last week or so. First off my speakers were too far apart. I moved them closer together (approx. 6.5 feet center to center) and the soundstage improved dramatically. Rather than everything appearing to funnel down from the center the instruments have taken their places as did the vocalists. Now I also moved them back to 12" from the back wall...(two inches from where they originally sat) and the bass has improved too. Now I'm still experiencing cancellation of a bass frequency or two, but not as noticeable as before. Also moved the listening position in about 11.5 from front of speakers (for a decent image). Any last ideas?
07-03-2003, 02:03 PM
Hi -- have you ever tried placing the cabs across the corner ? This was very effective for me as it got the speakers out into the room and gave me a much smoother response. It also allows for a much deeper soundstage. I have my S3100's about 10 ' apart.
I have tried them in the corner, but the soundstage was muddled and their is too much separation. As I moved the speakers towards one another, the soundstage improved. I have them approx. 9 feet from outside of cab to outside, and listening position at 12 feet away.
07-03-2003, 03:38 PM
I would like to suggest a solution but I am not sure there is one. If you have cancellation problems, they may be the notorious floor reflection that have the an effect in the 100-200Hz band. Look for some information relating to Roy Allison (the “Allison Effect”) who, as a designer, worked to negate this problem in many of his designs. Because it involves a reflection/cancellation, one obvious solution is to move the speakers close to the side walls to shorten reflection. The curse here, of course, is that this works against the imaging and localization qualities we seek by placing the speaker’s mid and high range frequencies out and away from reflecting surfaces. If placed very close to the side walls, sometimes turning the boxes so that the axis of the drivers is somewhere out in front of you (in other words way toed-in) can tune out some of the problem reflections in the upper bands. Still, it may not provide a natural soundstage.
Bernard, I think, is referencing a corner reflection technique similar to what Paul Klipsch preached for corner placement of his horns. This would require that conventional boxes are situated so that the axis of the drivers aim 45 degrees out of the corners. This may indeed reduce the reflective effects in the upper bass, but may produce unwanted effects in the mid bass. Also, you still risk reflective problems in the upper frequencies. If your systems use horns, that may not be as much of a problem due to the controlled dispersion of horn drivers.
Its a b**** trying to get those last little grains out of the picture, no doubt about it.
07-03-2003, 10:10 PM
It sounds like you either just got these or are running them in a new room for the first time. No bass at all?... Have you checked your phasing (for the pair; and each driver in cab)? We may have no magic bullet solutions because each room and system combination is different. Things to try and what to listen for are what we can offer if you do not have access to sophisticated equipment such as a RealTime Analyzer (RTA). A pro audio shop will rent you a mic & RTA by the day for not too much denaro. Burst test computer sig analysis is needed to collect reflection pattern data. Even then you need to know what to look out for.
It helps me to think as if you are inside a speaker cabinet. The same rules of design apply as far as AVOIDING-- parallel walls without one being absorbtive, geometry ratios which naturally resonate, and unbraced panels which buzz.
I frequently see 2D top view plans for a room and seldom see elevation side views supplied. Even if the ceiling is low and flat (not ideal), the vertical placement of speakers can have as much effect as the horizontal position and orientation. The type of flooring has a major effect on bass resonant response. Raising the speakers and the type of mounting (flat base, rubber iso feet, spikes, stand construction, etc.) has much influence in the upper bass down to the mid bass spectrum. Damping isolation has more effect the lower the speaker's bass response goes (we want to move sound through the air, not the floor).
A carpeted surface is generally preferable to wood flooring. Ground floor is generally preferable to upper floors due to there being less of a flexible span to vibrate at bass frequencies and undertones. The general idea is to avoid floor resonance reinforcement near the speaker's natural boomy points and find a floor/room resonance favorable to the room's inherent acoustic nature.
Placement of absorbtive and reflective furmishings in depth and height is a final room tuning measure (often functional and decorative considerations overrule, here). There are acoustic tuning materials that are available to tune out corner resonance/reflection patterns, main/rear wall reflection damping, side wall boundary layer effects, protrusions (like you have) and openings.
A good site with specific acoustic room tuning advice is http://www.tnt-audio.com/clinica/tweaking_e.html. Start with the "WASP" article for alternatives to initial setups. Then I could not find the reference or article to the room tuning products when I just looked, but believe it is in there somewhere. And as long as you are moving speakers around like a husband in a new house to find that right spot for the couch, this may help http://www.tnt-audio.com/accessories/glisdome_e.html.
Their other articles are helpful-- especially the speaker tuning section. Few people realize crossover capacitors age over time. This is especially important when dealing with vintage speakers as much as this forum's members do. The other speaker tweaks in this article are about improving electronic construction and mechanical enhancements for clarity or specific tonal changes desired.
An automatic digital room solution, sure to spark audiophile controversy, is http://www.tnt-audio.com/ampli/sigtech.html. Some of the site's authors have apparent axes to grind, but who doesn't? WTTW; they may engage in lengthy debates when challenged. They are pleasant and not industry-biased folks.
There are software programs available for room acoustic modeling out there. I know Bose used to have a free or low cost program for recreational usage, though I have not tried it. I heard it was mostly useful for dispersion and reverberation modeling so it would tend to make the Bose merry-go-round design look attractive on screen. There are much more sophisticated modeling programs geared toward pro audio at much higher prices. A cool web page of software optimized for array driver placement is http://www.meyersound.com/support/papers/mapp_prediction/index.htm. Perhaps other forum members can recommend something more appropriate for you-- as in between a toy and Madison Square Gardens modeling software that is effective for certain parameters.
BTW, hanging speakers a little down and out from a 4:12 (120 degrees, combined) gabled ceiling/wall top plate produces exceptional projection and stereo field patterns. The drywall over stick framing bandshell effect from my former house ceiling was better than any floor or wall positions. Not for the mechanically-challenged or decorator-sensitive, though. Make sure you use sizeable eye screws screwed into the ceiling joists or rafters and engineer grippage for side slippage. My red nylon (rated 600 lb. each) suspenders did hold them up through a 7.1 earthquake like nothing happened!
Thanks for the info guys. I have found a decent placement for low bass thats for sure. I am experiencing some midbass cancellation, but not as much as before. I suppose I had them placed to close to the outside walls. The soundstage was an appearance of the same instrument on both channels not blending into one. Now the image is centered and the instruments mixed to one channel stand out!! I have built some DIY panels for the brick mantel and back walls for reflections, and am going to look into my ceiling for treatment too. I may jump into a decent eq to clean up the cancelled out frequencies, but its improved X 10. The speakers are approx. 7 feet center to center of drivers. I mounted them on granite slabs (3 inches thick, three feet by three feet), yes its overkill , but works well. The bass is not a single boomy note but smoother and more transparent on the lower notes. I'm borrowing a test cd from a friend and will run it to determine the frequencies that are cancelled and then will either eq, or attempt more treatment.
I will post my findings at a later date as my wife and I are going to the hospital tomorrow to give birth to our first child.:eek: :D Again thanks for the info..
07-04-2003, 12:10 AM
I think your wife may be wanting your full attention for a while.
I have the benefit of running my sweep generator through the ranges to detect resonant & antiresonant points-- as opposed to the fancy analyzers more suitable for roughing in a concert EQ (w/o dealing with reflections and cancellations). A good test CD will provide a swept signal or enough tones to do much the same. Just don't run the tones too loud-- especially on the low end. Continuous tones are tough on speakers.
Best wishes with the young one and good luck.
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