New tweeter from fostex

[badman]

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?

[Willitwork]

My router threatens to quit if I even think of using that tweeter.

[Salas]

Must be tested soon indeed. Any idea of its price?

[badman]

Madisound Catalog Page

Catalog page from madisound. $263 ain't exactly cheap, but it does look like a hell of a tweeter- all that copper pays off in the astonishingly low Le-- the impedance only rises from 8 to 12 ohms at 100kHz (!)

[Timn8ter]

Originally posted by Willitwork
My router threatens to quit if I even think of using that tweeter.

That faceplate is intended to be surface-mounted, similar to the FT207D.
Pretty exclusive company in that price range; Scan-Speak 2904, Seas Crescendo, Accuton C25......

[Tenson]

Most interesting is the quoted Xover of 1.5KHz with a second order filter - that is pretty damn low for a super-tweeter!

I don't think you can really tell a lot about it until you see real measurements though, as the PDF doesn't say a lot. Disto and CSD will tell the tale.

[CeramicMan]

Hmmm....

No obvious resonant peaks in the >15kHz range.

The huge magnet and high sensitivity combination doesn't make sense to me.

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?

[badman]

Originally posted by CeramicMan
Hmmm....

No obvious resonant peaks in the >15kHz range.

The huge magnet and high sensitivity combination doesn't make sense to me.

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....

[CeramicMan]

Originally posted by badman


you're saying a bigger magnet means weaker?

It's do with motor theory (most of which I've forgotten ). 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.

[sreten]

Originally posted by CeramicMan

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.