Stupid speaker test question...please help a n00b

THD below 50hz at highish SPL (90 db +/anechoic or quasi anechoic) is off the charts for most speakers. Per Sarcher's post, this test is sometimes run by HT websites, especially for subwoofer testing. Subwoofers are purpose designed for clean response in this range and most of them still suck.

No one wants to see that # for a typical full range speaker.

Marty

I'm not so sure about squarewave testing being meaningful. It will reward first order (analog) x-over designs, but the audible benefits are debateable. I won't take sides in that debate, but Siegfried Linkwitz has written extensively on the subject, and he comes down squarely (pardon the pun) on the side of higher order designs that won't fare as well on squarewave tests.

Linkwitz certainly qualifies as an authority, since the Linkwitz-Riley crossover solution (even order only for "true" L-R, odd order "quasi" L-R is possible for 3rd order and above) is pretty widely considered a classic bit of design theory. Obviously, there are great designers (Dunleavy, Vandersteen, et al) out there using first order crossovers so.....

While L-R is NOT universally accepted as an optimal solution, Linkwitz's analysis does cast some doubt on the real world benefits of goood performance on a squarewave test.

Marty

PS For those pointing out that THD tests, etc. are of limited utility in judging a speaker's performance, I'd say that this is one more example where test results for speakers may raise more questions than they answer.

Johnnyb53 wrote:

Basically, if you create a loudspeaker to measure well in an anechoic chamber (the only way you can accurately evaluate its output), it will sound unnatural in a number of ways when placed in a room.

I might have said "different" rather than "unnatural" to describe the in-room performance, but his point should be taken. An anechoic chamber is (for measurement purposes) infinitely large - with no contributions to the measured performance from reflected sounds. To achieve this in your listening room (for instance, to eliminate quarter wave reflections), the speakers would need to be +/- 5 meters from the nearest wall (including the floor, to be a purist). I thinks Johnny's generalization is pretty safe: few rooms will allow such speaker positioning.

Marty

PS The contribution of reflected energy is usually VERY audible. Audyssey is - broadly speaking - a system that attempts to adjust your system's in-room response to something more akin to anechoic response. A simple "before" and "after" test with Audyssey will quickly demonstrate just how far from "anechoic-ish" response you will get in your listening room.

PPS I'm pretty confident that anechoic testing arose to "level the playing field" for comparing speaker test results. Unfortunately, the level field is IMHO also the wrong field. If you want to determine which is the better of two football teams, by all means schedule a head to head game. Just don't play it on a basketball court.

Marty

Where should they play, in a water polo pool?

I'm tempted to say that that would be roughly as useful as an anechoic chamber, but that would be a (slight) overstatement.

I never said that I had a better place to measure than an anechoic chamber (other than the "right", but impractical answer: In your own listening room), I just said that an anechoic chamber is a poor environment for simulating real world performance (per Johnnyb53). If you want to make the case that any baseline is better than no baseline, I won't argue, but....

Hopefully, my point was understood: Anechoic measurements may be the most logical way to measure a speaker, but IME, they're not very useful for predicting in-room performance. By the way, "not very useful" isn't the same as "useless". Above 250hz or so, smooth anechoic FR usually translates to smooth in-room response in that region. Below 150hz, IME, anechoic response is pretty much useless. Again, IME, for predicting critically important (to me) octave to octave balance, anechoic FR only weeds out the really bad desgns.

This thread has morphed into the question of which measurements might be useful in evaluating speakers - and my conclusion is that, generally, anechoic FR is of sharply limited utility.

Marty

Unsound,

While I completely agree with your observation re: vast majority of music lies >150hz, the octave to octave balance of a speaker is priority one for me. If the 3 octaves (or so) below 150hz aren't well balanced with the remainder of the speaker's bandwidth above, I won't be able to live with that speaker. To me, this concern is far greater than midband accuracy, imaging, dynamics, etc.

Anechoic response is often used to demonstrate how well balanced a speaker is from bottom to top. IME, once you get that speaker into a listening room, the story is wildly different.

Marty

PS I now use Audyssey on my 2.2 channel main system for this reason. It eliminates the guesswork.

I agree with a lot of your observations here. However, (whether true or "quasi" - and, as you note, it's often hard to say how the numbers came to be) the anechoic data that I've seen published for speakers has not been very useful for my main FR concern - determining that a speaker has an acceptable octave to octave balance in my room.

The published data has had little (if any) correlation to what I hear (and measure, for that matter) in my own listening room. Obviously, I can't speak to your experience applying this data. If you find it useful in "apples to apples" comparisons, that's great. I just can't say that it's been useful FOR ME in that regard.

Marty

I know that some independent testers (HTShack.com) use a parking lot for anechoic style testing. The Canadian Nat'l Lab has a large chamber that some Canadian manufacturers use and Stereophile uses a "quasi-anechoic" measurement technique that I've never seen thoroughly explained. Either way, the FR numbers that result from any of these tests never particularly reflect what I get in my own room.

Marty