New tweeter from fostex

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New fostex tweeter

Gimmick? Or the real deal? Knowing fostex, I'm thinking there's something to this.... the Le looks nice and low, Fs is reasonably low, there's something to be said for oversized magnets, and poly/resin chassis are usually pretty good when done right.

But more than the unusual magnet structure and dome material and chassis/waveguide (yeah yeah, shallow I know), the UDR surround is interesting here. A tweeter would seem to be the ideal place for such a deal.

Sort of a 'what's your take'/FYI thread I suppose. Maybe we can con(vince) John Krutke into aquiring a couple samples for testing, mmmm?
 
Hmmm....

No obvious resonant peaks in the >15kHz range. :yes:

The huge magnet and high sensitivity combination doesn't make sense to me. :no:

With DC electric motors, if you increase the magnet strength the torque increases but RPM decreases. Likewise, a large magnet on a speaker implies a low Qes together with low sensitivity. 90dB/W isn't that low, which could be explained by the low inductance, but then the question is: why bother having a low inductance anyway?
 
CeramicMan said:
Hmmm....

No obvious resonant peaks in the >15kHz range. :yes:

The huge magnet and high sensitivity combination doesn't make sense to me. :no:

With DC electric motors, if you increase the magnet strength the torque increases but RPM decreases. Likewise, a large magnet on a speaker implies a low Qes together with low sensitivity. 90dB/W isn't that low, which could be explained by the low inductance, but then the question is: why bother having a low inductance anyway?

I'm not really following you- you're saying a bigger magnet means weaker? That's not my understanding, can you elaborate? Note that low sensitivity speakers have magnet sizes ranging all over the place, but high sens usually are pretty big....
 
badman said:


you're saying a bigger magnet means weaker?

It's do with motor theory (most of which I've forgotten :D ). Basically a strong magnet x small gap height x large Le, produces a relatively high torque (low Qes), but low RPM (SPL) due to the efficient build-up of back-EMF which opposites the applied force.

It also explains why ribbon tweeters tend to have very high sensitivity despite (or rather because of) the magnet gap height being very large.

Edit:

For example, try comparing Visaton's AL130 M and AL 130 bass mid.

The only difference is that the bass midrange has a longer voice coil, which gives it a lower Qes (and Qts) and lower sensitivity.
 
CeramicMan said:

Edit:

For example, try comparing Visaton's AL130 M and AL 130 bass mid.

The only difference is that the bass midrange has a longer voice coil, which gives it a lower Qes (and Qts) and lower sensitivity.

Hi,

Those two are not directly comparable.
The lower Qts is due to the lower Fs.

Generally if you make the coil longer Qts
increases, sensitivity drops, and vice versa.

:)/sreten.
 
sreten said:


Hi,

Those two are not directly comparable.
The lower Qts is due to the lower Fs.

The theoretical Fs is only a function of the mechanical damping, mass, and suspension stiffness. But yes you're right - the 'm' speaker also appears to have a tighter spider, giving it a Vas of 9L instead of 13L, which, along with the lighter mass (because of the shorter voice coil) would explain the difference in Fs.

Generally if you make the coil longer Qts
increases, sensitivity drops, and vice versa.

:)/sreten.

I think you'll find that as damping (1/Q) approaches infinity, sensitivity will approach zero.
 
when a loudspeaker is designed to have high acoustic source impedance, it behaves as a constant velocity source. most of the loudspeakers which are radiating into free space have high source impedance types(not headphones). High impedance loudspeakers have high mechanical impedance diaphragms (high mass MMD, high stiffness (high CMD) and high damping RMD) and are backloaded by high acoustic impedances (RAB).

By adjusting the electrical motor parameters (increasing the force
factor Bl and decreasing voice coil impedance) can increase the sensitivity of the loudspeaker

regards
renjish
 
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