Musical accuracy in subwoofers

I'm hoping some members who are more musically & technically knowledgeable can answer my questions about subs. While sub shopping, web research and sales people make referrence to subs with accurate timbre. The Linn & REL lines were reported to be more accurate than Sunfires in this respect. After playing my sub at a 45-48 hz. crossover without the main speakers, listening leaves me wondering how timbre ( at this low a crossover point) can be an attribute of a sub when most aspects of timbre are a product of higher frequencies. It seems that pitch accuracy, lack of bloat & "overhang," freedom from cabinet resonance, and the ability to tune crossover, volume, & phase accurately are paramount. But timbre?
Higher frequencies you may think are unaffected by a subwoofer, because they have no bass. Actually every note comprises a fundamental frequency and harmonics which comprises a much wider frequency spectrum than the fundamental note being played. This is why a high note played on a piano sounds different from the exact same high note played on a violin, which sound different from the same note on a flute, clarinet, oboe, and so on. The hardest thing for a full range speaker to reproduce accurately is the lower frequency bandwith.

Ever notice how a large open building like a cathedral or concert hall has a sound? You can sense you are in a large building. They have a certain ambience. A good musical sub will fill in the lower frequency spectrum of the instruments playing, as well as the room ambience you can feel, as well as hear. High notes become clearer when the whole sound is reproduced to the fullest.

Sugarbrie is right. To test for timbre I suggest the following:

Set your crossover point on the sub to its lowest possible setting, preferably to 30hz. Play a disc containing a lot of bass information at your normal listening level with the rest of your equipment switched off, so that you are solely listening to your sub. The sub, which allows you best to distinguish between a base guitar, a double base, the lowest notes of a concert grand and the low pedals of an organ has the best timbre. Cheers,
Right on Detlof! I was focused on the high notes because of Photon's question. The improvement in the low notes is also worth a listen. On some orchestra recordings I have; what was originally just the strings playing very low, became the Cellos and String Basses playing a very low cord with the sub added. I could hear the separate instruments better with the bottom filled in. If the cord changed slightly, for example the Bass Strings changing slightly from a E natural to an E flat against the cellos, it was much easier to hear clearly with the sub than without it.
Excellent question. It's probably that the timbre issue is the result of semantic confusion. Pitch accuracy coupled with low overhang should result in accurate timbre.
I don't know what "timbre" in a sub is; its just alot of fluffy adjectives the audio world has because the world of mathematics is beyond these forums, its not practical that's for sure. A loudspeaker driver just moves in-and-out to a series of electrical impulses and any non-linearity in that movement is called distortion. The sunfire has quite a bit more than alot of high-end subwoofers, 10% pushing its max. However since its small, it can use the corner of the room as a "horn" and operate more in the 3% range. Its an innovative sub, but giving no consideration to its design, strictly its performance; its just an average high-end sub; i.e. its not that accurate. Not to discredit you question, but I wouldn't worry about the issue of "timbre." You'll know a better sub from another when you here two. Timbre isn't an "attribute of a sub" to sort of use your wording, or any loudspeaker for that matter. All speakers do is reproduce the signal they get. My wording may not be the best. Put maybe another way, What kind of timbre would you want in a sub? None, you'd just want it to reproduce the signal its given. Technically, a phrase like musical accuracy (which I have caught myself typing in other parts of this and having to omit it, so I am guilty too) is redundant- accuracy is musicality so there's no reason to make distinctions in accuracy. Maybe it helped???
Thanks all for your responses. As suggested, I tried disconnecting the mains & listened to the reproduction of various instruments. There are very clear differences between a closely miked electric fender bass, an acoustic bass, & tympani strokes. But so many of the clues we depend on for an instruments unique aural signature are well above the subs range. My initial posts reference to timbre was instigated by quotes from others who said this or that sub is more accurate at reproducing a given instruments timbre. I agree with Ezmeralda11, I don't want any inherent timbre in a speaker. Will.
The distortion figures in a sub effect the timbre of the reproduction more than is often realized due to the Fletcher Munson loudness curves. For a simplfied example: a 30 Hz pure sine wave with 10% second harmonic distortion played at around 70 db SPL (think the fundamental from a double bass or contrabasson) will also produce an additional tone at 60 Hz at about 10 db down. However, at that frequency due to the Fletcher Munson effect, the harmonic will be percieved as equally loud as the fundamental which will seriously distort timbral perception. While the effect flattens out at louder volumes even 3% harmonic distortion can shift the perceived timbres of of lower bass instruments (assuming of course that the room distortions don't swamp the lower bass response).
Its the timbre of the instrument being reproduced, I referred to, not the timbre a subwoofer might have. If the sub has timbre, a sound of its own, it distorts and you will never get the timbre of the instrument reproduced right. You have to have a lot of intimate experience with live music to test subs this way, i.e. to see if it reproduces the timbre of differet instruments properly. If you don't have this experience, Esmeralda is right, stick to maths. By the way, its necessarz to develop a language to describe musical experience. No maths will tell you, how a rig will sound.
I've only been to about 1000 professional live classical performances and counting. Aside from degrees in physics and EE so I know some math, I also completed a major in musicology and played french horn in a student orchestra. I have also have measured a fair amount of live and reproduced music. I stand by my example, 3%-10% harmonic distortion will significantly shift the reproduction of timbre in the lower bass octaves.
Nobody said it didn't.
while low-frequency extension is obviously important, i agree that thd is a critical spec for subwoofers. perhaps that's why the vmps subs, when used w/a quality outboard electronic x-over, are such over-achievers at their price-point. vmps' published distortion specs are, if not the lowest in the industry, right up there w/whoever is. most subwoofer mfr's don't even publish their distortion specs.

doug s.

10% distortion from a sub playing at a sound pressure level of only 70db is ridiculously high, assuming the sub is engineered for 30hz performance (alot aren't sadly enough, then again they aren't true subs), which shouldn't be a problem for the $1k+ subs like REL, Velodyne, VMPS, etc. Now then again, maybe I don't know, I haven't seen all their specs. But, I can only see those type of massive acoustic anomalies plsl mentions kicking in at somewhere towards the subs maximum output, not normal listening. This is all assuming we are talking "real" subwoofers since Photon mentions REL, Linn, and sunfire, along with others in the price range like the Velodyne's (which claim very low distortion values) not the $449 msrp Jamo's.
fyi, vmps' most expensive sub, w/options, lists for <$800, which includes shipping - not an insignificant amount, considering it weighs ~140 lbs & is *big*. dealers *will* discount, as well. specs for this sub are 17hz-250hz, w/0.5%thd at 92db/1w/1m; 2.5%thd @ >115db. at this price, ewe can get two, a good outboard x-over (i like marchand), & a quality used amp (or two), & it will still cost less than *one* quality powered sub like a velodyne hgs18 ($3k), or a rel stentor ($4k). w/two subs, soundstage is improved, room integration is easier, and, for given spl's, thd is even less.

ymmv... doug s.

ps - no, i *don't* work for vmps - yust a satisfied customer! ;~)