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In Reply to: So how do you feel about H*E*A*D*P*H*O*N*E*S ? (but seriously here's my armchair analysis) posted by Richard BassNut Greene on November 16, 2004 at 15:23:21:
You mention that you have a fireplace on a side wall. I have a similar setup. How does something like a fireplace effect bass. My room seem to suffer from nulls rather than peaks. I've got to rolls of fiberglass and bales of cellulose fiber in the two front corners, and while that did help a bit, I am unable to eliminate a bass suckout from around 125hz-400hz or so. Looking around the room, I began to wonder if the fireplace might not be part of the problem. Any suggestions. I tried shoving the bales of cellulose insulation into the opening, but that didn't really make any difference.Thanks,
Follow Ups:
This has to do with what is called "floor bounce" and has to do with the placement of the drivers on the speakers baffle and their height above the floor and / or distance from the sidewalls. It is a VERY common problem that most manufacturers completely overlook. Then again, most speaker manufacturers lack a thorough grasp of acoustics and / or don't count on a consumer being able to verify whether or not said speakers will perform as claimed in their actual listening room.The reflections from the driver off of the floor and / or sidewalss at those frequencies end up cancelling out the primary signals, leaving you with a big dip in that region. How severe and wide the dip will have to do with the design of the speaker and how you have it configured in the room. One can manipulate this by playing with speaker placement, height of the speaker above the floor, the use of a "baffle beard" ( an extension of the baffle towards the floor on a stand mounted monitor ), etc... You can make the baffle extension as pretty or ugly as you want, depending on your woodworking skills and availability of matching materials. Sean
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Original Poster wrote:
"a bass suckout from around 125hz-400hz or so"
Your response:
"This has to do with what is called "floor bounce"
My correction:
Floor bounce would cause a 1/4 wavelength cancellation at a narrow band of frequencies in the 125-400Hz. range, however it would not cause weak bass from 125Hz. all the way to 400Hz., which is what I believe the original poster wrote and something I said was very unusual.It's also unusual for audiophiles to complain about a floor bounce cancellation because we live with this effect throughout our lives in every room where there is live or reproduced sound.
RG: Floor bounce would cause a 1/4 wavelength cancellation at a narrow band of frequencies in the 125-400Hz. range, however it would not cause weak bass from 125Hz. all the way to 400Hz., which is what I believe the original poster wrote and something I said was very unusual.Sean: There was no mention of the speakers used, nor could i find a system listed in AA's inmate system listing. The use of multiple woofers or mid-woofers at staggered heights can provide the aforementioned problem. On top of that, it is not uncommon for the dip to spread almost one octave in bandwidth with a single woofer / mid-woofer, let alone multiple woofers / mid-woofers. While multiple woofers / mid-woofers mounted at various heights would tend to fill in the depression somewhat and lessen the severity of the dip, it is still quite possible to have a depression of very measurable amount over a wide frequency range. A dip of 6 - 10 dB's in the warmth region is not that uncommon with a single woofer / mid-woofer.
RG: It's also unusual for audiophiles to complain about a floor bounce cancellation because we live with this effect throughout our lives in every room where there is live or reproduced sound.
Sean: While the effect of this is quite audible, most people don't know what they are listening to or for. As i've mentioned many times before, hearing and listening are different things.
As far as this taking place in every room, this is true. The difference is that radiation patterns differ quite drastically when comparing acoustic instruments to amplified reproduction through "coffin" type speakers.
On top of that, it is quite possible that this person and others may have taken measurements on their system and found the hole that was mentioned. Once one is aware of the problem, takes steps to correct it and hears the difference that it makes, the lack of output in that region becomes even more noticeable when one encounters it. This is kind of like looking for the picture hidden within the picture. Once you find the hidden item, it is hard to look at anything else. Such is the case with specific problem regions when working with the speaker / room interphase.
For further information directly dealing with the room / speaker interphase, i would suggest studying the information that Acoustic Research published in 1978. As far as i know, this is the most advanced and thorough research available on the subject. Stereophile made note of this a few months back. We can thank such folks as Edgar Villchur, Henry Kloss, Roy Allison, etc.. for providing us with this info as it was accumulated over a period of appr 20 years. Sean
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While floor bounce and other 1/4 wavelength cancellations are usually deep, they are usually narrow too.Other than that generalization, we really don't know enough about the speakers / stands / room / how measurements were made / to do any meaningfull "armchair analyses".
However we could argue with each other to entertain ourselves !
You mention that you have a fireplace on a side wall. I have a similar setup. How does something like a fireplace effect bass.
RG:
My fireplace is on the right side wall and had no measureable effect on bass vs. being covered with plywood.There was a small echo that affected the midrange and interfered with the soundstage so I use Sonex to cover the opening while listening to music and the problem disappears.
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My room seem to suffer from nulls rather than peaks.
RG
Under 80 Hz. standing wave bass peaks are the most common complaint, but every standing wave has both peaks and nulls.Parametric EQ can address the peaks at one listening position and that often benefits nearby seats too.
The nulls are best addressed by moving your ears, assuming you have the flexibility to move your ears a few feet in any directions, you can almost always avoid the deepest portion of standing wave nulls (can be -15dB to -30dB) which are physically narrow.
But even after finding the best seating location, you will almost always hear at least one null under 80Hz., and often two nulls, but hopefully no worse than -6dB .
For subwoofer bass frequencies -6dB is subjectively "half as loud", so even -6dB is a significant null ---(for midrange frequencies -10dB is subjectively "half as loud", as many audiophiles already know).
The best subwoofer/listener location I have found in my own room has a null at 58Hz. about -4 to -6dB deep. It took me since 1987 and hundreds of measurements, to find those optimum positions.
Above 80Hz. the most common complaint are nulls caused by 1/4 wavelength cancellations (aka comb filter cancellations).
These are best addressed with bass traps as EQ has no effect on nulls.
Without bass traps you can move the speakers nd your ears but all that does is change the frequencies of the cancellations.
However it's a good idea to place speakers so they are not the same distances (or multiples) from more than one room surface.
A worst case might be a woofer 3 feet off the floor, 3 feet from the side wall and 3 feet from the back wall (measured around the front baffle) and the two speakers 6 feet apart.
Those dimensions would cause stacked 1/4 wavelength cancellations (multiple cancellations at the same frequency that are additive).
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"I am unable to eliminate a bass suckout from around 125hz-400hz or so. Looking around the room,"
RG:
I stop using the term bass at about 150Hz. -- you seem to have lower mid-range problems.However I've never measured, or even heard of, weak output that covered such a broad range of frequencies (almost two octaves) in that range.
Is that what you hear, or just what you measure?
Do the speakers measure properly from one foot away?
"Is that what you hear, or just what you measure?"That is what I measuire
"Do the speakers measure properly from one foot away?"
Yes they do, +/- 2db with the RS meter about a foot out from the center of the two speakers.
-Tony
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