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In Reply to: Let's get back to basics: What test signal are you measuring and where is the meter placed for the measurements? posted by Richard BassNut Greene on November 16, 2004 at 10:57:34:
The room is new to a quality system. It is the dreaded great room with a fireplace under a mild peak cathedral ceiling approx dims 18 by 20 with the TV in the corner/speakers on each side. Two open ended hallways out the back. It also has a stone fireplace on one side and a patio door on the other side(covered with fabric vertical blinds). With the speakers pulled out 10" in front of the TV, surprisingly it doesn't sound bad except for way too much mid-bass. The bass starts nulling around 60 and down, but thats livable. Imaging and soundstage could be better, but with my layout, I can live with that also if I can clean up the bass. I only used 1/3 octave warble tones. I have since obtained several other test CD's, but have realized as you inferred, the proof is in the listening. And it needs help. I have moved speakers, seats and TV all over the place and while every change makes a difference, none is very significant. I had ASC do a thorough design analysis and tried all kinds of absorption in the corner behind the TV to simulate the 11 traps they recommended. I also built a false wall in the corner to simulate the effect of drywalling the corner. Contrary to what most acoustics folks thought, the corner boost effect is not as big a problem as the modes out in the room itself. I am getting some boost from the artificial corner behind the speakers where the TV comes against the wall, but putting absorption in that area kills the air dead and only helps 1-2 db. Traps out in the room would probably help a lot, but I just can't work them in, or helmholtz devices either. Spent the last year talking with folks at CEDIA and experimenting, and while it pains me greatly, I'm convinced a pure signal path is not in the cards for me, so it comes down to finding the best equip available for a reasonable price. FYI, I was planning on spending up to 12k or so on the preamp/processor/EQ. Hope this helps. Thanks.
I've been studying and measuring the effect of home listening rooms on bass since about 1980.
My best advice is not to spend a lot of money on audio equipment for a room that does not sound good.
You can quickly check a room by sitting where you expect to sit while listening to the stereo while a male friend, preferably with a deep voice, sits where you expect to place a speaker (also at the other speaker position if the room is not symmetrical) and just talks to you. Or even better if he can sing. Female voices can miss exciting wome frequency response problems in the 100-200Hz. octave.
If you can't identify speaker and listener positions where his voice sounds natural, you probably have serious room acoustics problems that can be confirmed with measurements or just listening.
The worst room I have even been in was a listening room at Sound City in Denville New Jersey that was roughly 20' by 20' by 20' = a cubical echo chamber that was the Joseph Audio speakers room ! What a disaster -- I'll be back there Thanksgiving week to see if they changed the room -- the rest of the listening rooms are decent.
The good news is about 10% of rooms are really good and won't benefit audibly from parametric EQ ... while about 10% of rooms are really bad ... and sound best with small "no-bass speakers" ... or a room full of bass traps (interior volume of tubular bass traps equal to at least 2 to 3% of the internal volume of the room !) That's a lot of bass traps and the one room I've been in with so many bass traps was too dry for my two-channel tastes (I like a more lively than average room) but trhe roughly 16-bass-trap-filled-room was good for movies which often seem too bright to my ears.
The bad news is your room description suggests a lot of potential problems from the dimensions (near-square) to open hallways on the back wall. However I will not suggest suicide ... yet.
"The room is new to a quality system. It is the dreaded great room with a fireplace under a mild peak cathedral ceiling approx dims 18 by 20 with the TV in the corner/speakers on each side.
First of all walls with large openings (over 1/3 the area of the wall) can be invisible to bass -- a more distant wall on the other side of the opening(s) can set up a standing wave rather than the listening room's walls. That's hard to analyze without observing the room in person.
Open hallways especially in the rear of the room can set up their own resonances sort of like Helmholtz resonators -- bass can reflect back and reach your ears in-phase or out-of-phase with the bass still coming from your speakers. Perhaps in phase reflections in your case.
Your 20 ft dimension can set up a 565/20 x2 = 57Hz, second order axial standing wave with peaks near each wall and in the middle of the room while nulls are at 1/4 and 3/4 of the way between the walls.
Your 18 ft. dimension can set up a 565/18 x2 = 63Hz. second order
axial standing wave with peaks near each wall and in the middle of the room while nulls are at 1/4 and 3/4 of the way between the walls.
You didn't specify your ceiling height. I have a cathedral ceiling 8' high on the left side and 12 ft. high on the right side of my listening room. That slanted ceiling sets up a strong 57Hz. standing wave between the cement floor and the ceiling as would happen with a roughly 10ft tall flat ceiling. If your ceiling height was similar to mine (12 ft at the peak) you'd have the following:
(1) A 57Hz. standing wave between the walls 20 feet apart
(2) A 63Hz. standing wave between the walls 18 feet apart
(3) A 57Hz. standing wave between the floor and ceiling (I'm just wild guessing on your ceiling height from your vague description of a "mild peak cathedral ceiling")
These peaks would be loudest if you sat in the middle of the room where there are nulls for several first order nulls. Sitting in the middle of your room will have loud 55-60Hz. bass and weak bass one octave lower. I think your room resembles that remark.
It would be best to place your speakers at or near 1/4 of the way into the room and your ears at or near 3/4 of the way into the room -- both at second-order axial room mode nulls.
It would be best to place your speakers at or near 1/4 and 3/4 of the way between the side walls -- both at second-order axial room modes nulls.
The null for the floor to ceiling standing wave is halfway between the floor and ceiling. That's a problem unless you sit on a high chair. Well sit on a high chair then and at least try it.
I designed a vertical tube subwoofer that places my upfiring sub driver in the null of my floor to ceiling standing wave but only a BassNut would do that.
Two open ended hallways out the back.
Not good -- can you cover with anything temporarily to experiment?
It also has a stone fireplace on one side
Not good -- I cover my side wall fireplace with four 2" thick
24" by 24" Sonex panels -- prevents a mid-range echo from inside the fireplace that disturbs the soundstage. No measurable effect on bass.
And a patio door on the other side(covered with fabric vertical blinds).
Not good. I have three 6' by 3' windows in my left wall.
Fabric covered blinds are good if closed but I suppose you want to look out too? I removed my vertical blinds for a better view and simply keep my speakers more than 5' away from the bare windows and toed in (I listen near-field from 6' from speaker = less effect from the room -- the back "wall" is 100% windows from the floor up to 12 feet tall but is over 12' from my ears)
" I only used 1/3 octave warble tones. I have since obtained several other test CD's, but have realized as you inferred, the proof is in the listening. And it needs help."
REALLY bad news:
If the bass is that bad with warble tones that smooth the frequency response, then it is much worse with steady state sine waves (technical term is "oye vey")
I go to Mountain Lakes NJ every Thanskgiving and by the day after I'm bored and visit Sound City for lack of anything else to do.
What Joseph speakers do you recommend for use as stand-mounted satellite speakers played at a modest average SPL in the 75-80dB
. range ... to replace my EPOS ES 11 satellite speakers used with a
70 Hz. 24dB/octave Marchand XM9 active crossover).
About five years ago I tried but just could not listen to music in that Sound City room.
So I tried other speakers in other rooms.
I asked to listen to the new version of Paradigm 100's which I noticed after about five seconds were hooked up out of phase!
I know I should have asked to hear the Joseph speakers in another room but was so frustrated by that time I had to lecture the employees to put good speakers like the Joseph's in their best room and use the cubical room as a storage room ... then I was out of there.
We have great dealers in Chicagoland, and in New York City-
email me for the info.
for your application the RM7si Signature Mk2 or RM22si signature Mk2 would work well.
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.
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
Original Poster wrote:
"a bass suckout from around 125hz-400hz or so"
"This has to do with what is called "floor bounce"
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.
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
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".
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 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.
My room seem to suffer from nulls rather than peaks.
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).
"I am unable to eliminate a bass suckout from around 125hz-400hz or so. Looking around the room,"
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.
Thanks for the detailed response Richard. I am in the engineering field and do know that analysis does not always pan out. The corner arrangement and the very complicated shape of the walls/ceiling that I did not totally explain reak havok with calculations. I do know a good room from a bad one though. Aside from the bass peaks, voices sound good, I hear no brightness, the bass in not boomy, just amplified. I think the room is saveable. From my cursory knowledge, the room sounds like a good candidate for EQ, no? My thinking is a high quality decent Q multiple notch filter unit would get me pretty close. No? But it of course needs to be transparent, is that possible? And perhaps I could get lucky with the tact and improve some higher freq anomolies?? I do understand the problems/limitations of EQ'g. I already spent the big bucks before I knew the room was an issue. My problem is the dearth of test reports/first hand knowledge of the current EQ products, even though "room correction" is a hot HT topic lately. I'm looking for those who may have first hand experience with the tact/parc/meridian who can tell me how they really perform. Thanks again.
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