Equalization isn't always the answer

[mustang guy]

I have been reading a technical document which has given me a bit of a revelation. There are those who insist on equalizing to correct issues of lacking bass, or too much mid frequency, etc., for room correction. When the adjustment requires large corrections, this is why it fails:

Dips are caused by acoustical cancellations

• The problem is

very

position sensitive – it will be

different at different positions in the room. In fact

that leads us to the solution: move the speaker, the

listener, or both. A few inches may be sufficient.

• Trying to fill the dip is foolish! A 10 dB boost

uses 10x more power! A 20 dB boost uses 100x

more power! You have just added a 10 or 20 dB

resonance that will be clearly audible at most

locations other than the one at issue.

The Science of Audio

- a series of lectures by Floyd E. Toole, Ph.D. Vice President Acoustical Engineering

Harman International Industries, Inc.

8500 Balboa Boulevard, Northridge, CA 91329

The reason for the above is too complicated to explain here, as it talked about this on the 29th page of the document. If you would like to read this document yourself to find out the mechanics of the above, go here. It's a worthwhile read.

[tube fanatic]

If the rolloff in bass is due to the characteristics of the speaker (say it's down 4 or 5 db at 40 Hz) you can compensate somewhat, if using a tube amp with voltage feedback, by using a frequency selective fb network which decreases the fb a bit as the frequency goes lower. This creates the perception of a relative boost without necessitating increased power. The few db of decreased fb at the bass frequencies, although increasing the distortion a little, doesn't seem to cause any audible problems. It's a neat way to "cheat" and get the desired result.

[Quiet_Hollow]

Neither is the "volume" knob in most cases. []

[tube fanatic]

Neither is the "volume" knob in most cases.

Right on! In our zeal we often ignore the simplest approach!!!

[derrickdj1]

Is there any role for a parametric EQ in the HT beside for the sub?

[pzannucci]

Is there any role for a parametric EQ in the HT beside for the sub?

nm.... that that is what Audyssey is... for trying to correct rooms, Audyssey has made a ton of money for a problem that may be considered uncorrectable.

[WMcD]

The Toole papers are terrific.

Reading closely, he seems to be saying that room resonances are different than reflections from modes. Resonances can be lowered with equalization.

The dips arise when a mode causes two signals (signal A and signal to arrive at the same location, one (A) being 180 degrees out of phase from the other ( which is reference 0 degrees. You get a very deep dip which is narrow.

Both signals originate from the speaker. You can try to eliminate the dip by increasing power to the speaker in that narrow freq range. But what you're doing is to increase both A (180 degree) and B. Therefore the dip is still there. A "node".

Moving the speaker changes the phase relation if not the intensity. The dip might move to another location in the room. But a dip at another freq might move into that original location. So Toole presents the complicated process needed to even out things.

One suggestion is to add a second subwoofer. He starts with putting the two subs in the front corner. Seems just like PWK's corner placement. Toole says this might be good only for the front row of seats.

Best,

WMcD

[Quiet_Hollow]

The reader can also completely miss the forest for the trees when cherry-picking his technical papers, which by nature in writing don't encompass the entire engineering process.

There's no one parameter to get overly fussy about, but that was / is his job.

[derrickdj1]

Seeing the forrest is using multiple subwoofers for best bass performance if I am getting the article. Plus or minus the addition of room Tx's and judicious use of a parametric EQ.

[garyrc]

Is there any role for a parametric EQ in the HT beside for the sub?

nm.... that that is what Audyssey is... for trying to correct rooms, Audyssey has made a ton of money for a problem that may be considered uncorrectable.

But in their ads Audyssey keeps saying that their EQ is not parametric, and that parametric EQ won't do as good a job (in fact I think they point out that parametric EQ often "fails."). I don't know what the reality is, but they claim that differences between their approach and parametric EQ include 1) Theirs addresses the time domain as well, & 2) Audyssey applies correction at hundreds of points. All of those points of correction are disabled if the user then applies something like Base Copy (not Bass Copy) in order to move the virtual sliders to tweak the EQ to that user's preference. Even some dealers don't seem to know that. Audyssey says that if you move the sliders you end up with an unknown EQ, and they point out that there are very few virtual sliders on typical AVR or Preamps, whereas running Audyssey will give you those hundreds of points. Audyssey claims they are set up for "reference, not preference" and to personalize the EQ to your preference or the needs of some program material you would have to use the AVR or Pre-amp's rotary tone controls -- if they will work after using Audyssey (some will, some won't) -- or use their pro system. I haven't decided yet whether Audyssey is good or bad for my application.

[ClaudeJ1]

I like what Audyssey does for my speakers and room. It's the ultimate global feedback system built in to mid range receivers. Since I only use milliwatts to listen in 5.1 or 2.1 from my receiver source selector, power is not an issue, but signal compensation is.

The key for me, has been to limit the mike placments to strictly around my head in the sweet spot, resulting in amazing sound correction. I won't listen without Audyssey on.

[pzannucci]

Garyrc,

Based on their technical docs, the current multieq setup is an inverse of the original signal to level out the sound. There appears to also be time domain work being done. If you think of it logically, to modify in the time domain you change all the phase characterisics which is in stereo what gives you imaging. Also doing both time domain and eq for various locations has to modify the output sound though maybe they have found a point at which it does not get perceived.

SRS Labs used to change the phase characteristics but then you only have one location where those changes work 100%

[mustang guy]

I have been reading a technical document which has given me a bit of a revelation. There are those who insist on equalizing to correct issues of lacking bass, or too much mid frequency, etc., for room correction. When the adjustment requires large corrections, this is why it fails:

Dips are caused by acoustical cancellations

• The problem is

very

position sensitive – it will be

different at different positions in the room. In fact

that leads us to the solution: move the speaker, the

listener, or both. A few inches may be sufficient.

• Trying to fill the dip is foolish! A 10 dB boost

uses 10x more power! A 20 dB boost uses 100x

more power! You have just added a 10 or 20 dB

resonance that will be clearly audible at most

locations other than the one at issue.

The Science of Audio

- a series of lectures by Floyd E. Toole, Ph.D. Vice President Acoustical Engineering

Harman International Industries, Inc.

8500 Balboa Boulevard, Northridge, CA 91329

The reason for the above is too complicated to explain here, as it talked about this on the 29th page of the document. If you would like to read this document yourself to find out the mechanics of the above, go here. It's a worthwhile read.

I wasn't cherry picking the document. When I got to that point in the article, it was something that really stood out for me.

What the article tells me is that speaker choice, speaker placement, accurate measurements (1/10th octave or better) throughout the room, room construction, seating position, and acoustical treatment should be the first steps. Once that is done, bring in Audyssey, or whatever if you still feel it isn't good enough.

Throwing Audyssey and bass management at a room that hasn't been worked out is like waxing a car before you wash it.

[pzannucci]

I like what Audyssey does for my speakers and room. It's the ultimate global feedback system built in to mid range receivers. Since I only use milliwatts to listen in 5.1 or 2.1 from my receiver source selector, power is not an issue, but signal compensation is.

The key for me, has been to limit the mike placments to strictly around my head in the sweet spot, resulting in amazing sound correction. I won't listen without Audyssey on.

I think you just pointed out what I was stating in the previous response, the bigger the sweetspot and mike placement, it makes sense that the larger the effect on the sound very possibly in a bad way.

[mustang guy]

I like what Audyssey does for my speakers and room. It's the ultimate global feedback system built in to mid range receivers. Since I only use milliwatts to listen in 5.1 or 2.1 from my receiver source selector, power is not an issue, but signal compensation is. The key for me, has been to limit the mike placments to strictly around my head in the sweet spot, resulting in amazing sound correction. I won't listen without Audyssey on.

I think you just pointed out what I was stating in the previous response, the bigger the sweetspot and mike placement, it makes sense that the larger the effect on the sound very possibly in a bad way.

I agree completely! I like my LaScalas because they reproduce sound very accurately. The last thing I want is for Audyssey to muck with that so I can have a bigger sweet spot. I would much rather get the room acoustics right! If I wanted to hear poorly reproduced sound, I would have a Bose system.

[sunnysal]

A good rule to live by is that when trying to tailor room response cutting band by band EQ is preferable to boosting EQ, it has less risk and generally causes less damage. regards, tony

[Quiet_Hollow]

I wasn't cherry picking the document.

I wasn't implying you were. My apologies if it came across that way.

The info you highlighted in your first post is an excellent tip. [8-|] I just think it's a shame that Toole had to bury it in there.[|-)]

My response was a blurb to highlight a common pitfall associated with technical articles.

[artto]

I have been reading a technical document which has given me a bit of a revelation. There are those who insist on equalizing to correct issues of lacking bass, or too much mid frequency, etc., for room correction. When the adjustment requires large corrections, this is why it fails:

Dips are caused by acoustical cancellations

• The problem is

very

position sensitive – it will be

different at different positions in the room. In fact

that leads us to the solution: move the speaker, the

listener, or both. A few inches may be sufficient.

• Trying to fill the dip is foolish! A 10 dB boost

uses 10x more power! A 20 dB boost uses 100x

more power! You have just added a 10 or 20 dB

resonance that will be clearly audible at most

locations other than the one at issue.

The Science of Audio

- a series of lectures by Floyd E. Toole, Ph.D. Vice President Acoustical Engineering

Harman International Industries, Inc.

8500 Balboa Boulevard, Northridge, CA 91329

The reason for the above is too complicated to explain here, as it talked about this on the 29th page of the document. If you would like to read this document yourself to find out the mechanics of the above, go here. It's a worthwhile read.

I wasn't cherry picking the document. When I got to that point in the article, it was something that really stood out for me.

What the article tells me is that speaker choice, speaker placement, accurate measurements (1/10th octave or better) throughout the room, room construction, seating position, and acoustical treatment should be the first steps. Once that is done, bring in Audyssey, or whatever if you still feel it isn't good enough.

Throwing Audyssey and bass management at a room that hasn't been worked out is like waxing a car before you wash it.

EXACTLY

Now see what I started! 2002 on this Forum, and all the way back to 1984 in the Stereo Review article. []

Of course I didn't really "start it". But as far as "audiophiles" go it's nice to see this finally coming along.

Like Alan Parsons said, "audiophiles spend way too much on equipment and don't pay enough attention to the room" (or something close to that)

[djk]

Equalizers can fix minimum-phase amplitude-response problems in loudspeakers (frequency response).

The cannot fix time-domain problems (room-modes).

While your meter may say that you fixed it (at one position), it will not sound right.

[ClaudeJ1]

I think you just pointed out what I was stating in the previous response, the bigger the sweetspot and mike placement, it makes sense that the larger the effect on the sound very possibly in a bad way.

Exactly. This has been borne out by others who have tried Audyssey according to the generic directions in their poorly written receiver manuals. Worse yet, some of them have tried to EQ by ear using the manual settings, which kills all time domain adjustments that are part of the "chip Voodo math" that Audyssey provides so well. Without exception, once they all narrowed their mike sampling for a single listener location (one cubic foot), the sound got really tight at the sweet spot, which, is mostly how we all listen anyhow. Where really fancy room design comes in, is where we want to have 6-12 seats in a custom build home theater, where most of the $$, time, and effort should be spent on the room anyhow.