sealed vs vented subwoofers

Shadorne - my bad! You are absolutely right; sealed boxes have LESS group delay than vented boxes. I was thinking that, but carelessly typed the exact opposite.

That first sentence should read:

"A sealed box will have less group delay than a vented box..."

My compliments on your restraint in not calling me the idiot I certainly appeared to be.

Duke

I got around to looking on the HT Shack site. I had somehow supposed this to be connected to Radio Shack. I find that it is run by Home Theater Mag. , to which I subscribe but seldom read. I had always thought it axiomatic that the requirements for home theater bass were different from, and less stringent than , music reproduction. Sub reviews by mags like Hi Fi News and Hi Fi Plus state this explicitly. I will be glad to provide citations. I was surprised to see subs apparently being tested in the middle of a parking lot. At first I thought they might be preparing an article on Hi Fi for the Homeless but then surmised that they were doing free air testing of the woofers. This mirrors the testing procedures of 30 years ago when anechoic chambers were used to test speakers. I have not seen this done in years as it became apparent that to take a speaker out of a room was to take away most of the value of the measurement. Since the REL are explicitly designed to be placed close to a wall I cannot see what their performance in a boundary less environment can tell us. The room is the most important component in any system, removing a speaker from a room does not provide an equal playing field; it will favor those designed to be placed well out into a room. In a good test of a component the measurement is done AFTER the listening test in order to explain what the panel has heard. As often as not the measurements contradict what the panel has determined, i.e., the product with the least distortion or greatest frequency range is seldom the best. This does not mean some mystic power is at work but that we have NEVER succeeded in constructing a set of rules which will tell us what makes a component sound good. Stan Curtis, who has spent a lifetime designing amps, is currently writing a series of articles about his career ,describing much of it a process of forgetting theory and trusting experience. For example, that point to point wiring is better than circuit boards and that higher quality parts make a sonic difference even when the measurement of their performance is the same. Peter Walker often remarked that he could design an amp that would look good on every measurement but which would render familiar tunes unrecognizable. 40 years ago I had memorized the Stereo Review and High Fidelity performance graphs of about every amp on the market [not hard in those days]. It was a total waste of time. A friend recently chided me for not paying enough attention to the theory behind a product we both use and like. I told him I didn't care if it worked by channeling Angels from heaven if it sounded good. The only way to determine if you will like the sound of a component is either to listen to it in your own home [by far the best] or read a test by a person or group whose ears you trust of the item in question actually in use in a home environment. NO measurement or design principal has ever been shown to give a close correlation with sound quality.

NO measurement or design principal has ever been
shown to give a close correlation with sound quality.

I agree in the sense that no single measurement does - it is usually a
combination of measurements and design principals that correlate to sound
quality. Often there is more than one way to skin a cat.

BTW - The student who ran these subwoofer tests in a parking lot has been
hired by Genelec - to
work in their R&D department. He will have access to anechoic chambers
now. I suspect the parking lot is just a way to get raw baseline comparable
measurements under controlled conditions - for sure these need to be
interpreted carefully. As Duke points out - a roll off is probably more
desirable than a flat response to 20 Hz - due to the in room wall boundary
boost effect.

Genelec is not well known to audio consumers but they have a strong
following in the music recording business.

Stanwal, I almost agree with your statement about the failure of measurements to correlate with subjective preference. I think it's fair to say that the audio industry has been measuring distortions that are easy to measure instead of measuring distortions that correlate well with human hearing. However, there has been progress made in this area recently which you are probably unaware of.

If you have access to the Audio Engineering Society's library, you might want to take a look at "Auditory Perception of Nonlinear Distortion - Theory" and "Auditory Perception of Nonlinear Distortion", both by Earl Geddes and Lydia Lee. Therein you will find described a rather complex metric that correlates well with subjective perception. The industry has largely ignored it, aside from this article from Audio Express magazine:

http://www.gedlee.com/downloads/THD_.pdf

See also this letter in response to the article:

http://www.gedlee.com/downloads/Comments%20on%20howard.pdf

Duke

Duke,

Thanks for the link - interesting reading. In simple terms, GedLee is saying
that higher order harmonic distortion is much worse than low order
distortion. This means 2nd order is better than 3rd order ...etc. etc. This jives
with everything we know - Class A amps sound better at low volumes - IMD
distortion is the worst - and that the "masking" effect means that
we may not hear nearby frequencies to a fundamental as easily as we might
hear a 9th harmonic (BAD).

This matches what Ralph has said so many times on these forums...high order
odd harmonics are bad - even in relatively much smaller amounts. To take
your example above, 30% second order harmonic distortion (barely or not
quite audible) may be akin or equivalent to 0.3% distortion in the 9th
harmonic. In that sense, an amplifier with THD of 1% all in the 9th harmonic
would likely sound much worse than an amplifier with 10% THD but all in the
2nd harmonic.

One could jump on this and say that all measurements are meaningless,
however, one must reflect that if an amplifier has a measured THD at full
power of less than 0.004% (vanishingly small) then it will likely sound good
anyway - irrespective of a GedLee higher weighting to the higher order
harmonic distortion (as, be it low order or higher order, the distortion is
simply very small).

Perhaps the problem (what listeners observe) begins when you hook up an
amplifier to a complex load and make the poor amp send bucketloads of
current to drive the woofer and then mere milli-amps to drive the delicate
little tweeter. When the rubber hits the road (in the real world and not a lab
test) the amp find itself being asked to perform two rather diametrically
opposing tasks: extreme butterfly wings delicacy and elephant brute force. A
case where IMD distortion seems inherently likely - so why does the industry
stick so vehemently to this design approach? And why is GedLee largely
ignored in manufacturer spec sheets?