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Re: "Fast TL's"

Sorry for the book.

“While ALL vented systems will show dual resonances and impedance peaks, TL's ( if properly designed ) do this the least. Their frequency response is typically very linear in the bass region with little to no noticeable "humps" in the lower regions. This results in both tighter bass and a more consistent load for the amp.”

TL’s are resonant systems. They are not necessarily more linear than any other system, and they certainly cannot be more linear than a low Q sealed system unless the line is so stuffed that it becomes purely aperiodic, and this will likely eliminate any “TL” sound the designer was after in the first place. Some TL’s may offer an easier load for the amp, but this generally is a side benefit. The linearity of a bass system is not necessarily contingent on how easy a load it is for the amp. Many TL’s have quite lumpy output from their terminuses (or must I use the Latin plural?), due to standing wave problems in the line, and like vented systems radiate most of their acoustic power from the terminus at the resonant point. So I’m not sure how this translates to “tighter bass.” I haven’t heard the gamut of TL offerings, but the “trademark” sound seems to be that they just sound highly damped. This can be achieved with any type of bass system, vented, sealed or otherwise.

I’ve seen/heard a TL system where if you removed the stuffing (most of it was towards the terminus), the woofer would go into large over excursions. This is the same thing that happens when you build a very large vented system, such as a 6 cubic foot box for a 5.25” woofer, then take a 4” tube, install it into the box and tune it to some really low point, say 30 Hz, and then play music with deep bass on it. The woofer goes all over the place. But then stuff the vent. The over excursions will stop and the system will play surprisingly deep, “quick” bass (if the vent was not overstuffed, otherwise the bass will be very modest – just what you’d expect from a tiny woofer in an infinite baffle enclosure). Do an impedance measurement. If you didn’t overstuff the vent, you will see two rounded impedance peaks, just like a TL.

“What you are describing is essentially a large "vario-vent" design. While it does offer similar electrical measurements and characteristics of a TL, the sound of the system "in-room" is measurably different.”

No… if the system has two impedance peaks, it is not aperiodic, which a variovent system is. The sound can be markedly different between a TL and my big, damped vented example because the terminus of the TL may be physically quite a ways away from the woofer with some of the bigger TL’s, which changes the power response in the room. The sound is not different because of some special TL property.

“While the systems' Q is quite important and will tell quite a bit about what you should expect from the sound, I have to agree with Clayton on this. A sealed box with a very low Q ( 0.5 ) typically sounds very "dry" whereas one with a reasonable Q ( 0.7 ) will tend to sound very full without the nasty ringing of a higher Q design.”

This is due to the lean magnitude response that is attendant with .5 Qtc systems, not because of the Q itself. If the system is shelved so that you have flat, extended deep bass, then there is no longer this subjectively “dry” sound. But it boils down to subjectivity at this point. Some people prefer “warmth” (high Q) and some prefer “speed” (low Q). My delineation of the term “fast” was to associate it with “damped,” since “fast” is a misnomer.

“We are dealing with two different things here under one subject. YES, speed does matter a great deal when mating dynamic woofers with planar's or E-stat's. If the woofers don't respond fast enough with the proper damping, they will always sound slightly bloated ( compared to the razor sharp & fast mid / treble ) and slightly behind the pace of the rest of the music. This tends to give a very disjointed sound and can really slaughter the performance of an otherwise excellent system.”

No, speed is completely irrelevant when mating woofers with planars or electrostats. Again, woofers already respond redundantly fast enough. If they didn’t there wouldn’t be any bass at all (just subsonic garbage). Speed is velocity… if you increase it with an oscillating diaphragm, the frequency increases. Speed has nothing to do with this subjectively “fast” sounding dynamic woofer bass that is sought after here. That is entirely due to Q (and perhaps power response and the RT60 in the bass range in room). ALL woofers respond fast enough because they can produce bass in the first place. Acceleration capabilities (directly related to BL product) dictate efficiency and max SPL capability. The higher the acceleration, the higher the SPL. But that instantaneous V at the 180 and 360 degree point (where the sine wave crosses “zero”) of a diaphragm’s oscillation does not change. If it is increased, then the frequency is increased. This is why there is no such thing as a “fast” woofer. Small woofers move no faster than big woofers at bass frequencies. And Q describes the bass system’s intrinsic damping capabilities.

Finally, I’d like to comment on your reference to “razor sharp & fast mid /treble” which I assume you attribute to electrostats. Electrostats certainly have a unique sound, but it is not because they are “fast.” They are not faster in the midrange or treble than any other speaker on the planet that can reproduce midrange and treble frequencies. Again, if they were, they’d just be shifting their output to higher frequency bands. They have certain full range attributes with unique diaphragm motivation, and a detailed look into such behavior will likely explain why they sound the way they do. For one thing, the diaphragm of electrostats tends to “shimmer” in a fantastically random way… their transmission line modes (in the diaphragm itself) seem to greatly dominate any piston behavior. And the force that motivates the diaphragm is very weak, much more so than the force that motivates a typical tweeter or midrange. Despite the fact that over a given area the diaphragm has extremely low mass, the typical electrostat is astonishingly inefficient. If you built an electrostat with a diaphragm the size of a 5.25” midrange and applied the same electrostatic force to it that it would have had in the full size version, you will discover that it is staggeringly inefficient compared to a typical electromagnetic 5.25” driver. So, despite having a super low mass diaphragm, the “push” from the electrostatic force is extremely weak (this means the acceleration of the diaphragm is modest, especially when compared to dynamic drivers).

The behavior of electrostats is extremely complex and hard to analyze, but they certainly aren’t “fast.” “Conventional” drive units accelerate faster. That’s why they are so much more efficient.

Regards,

Biggleswurth.



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