T-S parameters for Fostex FF225K

[bzdang]

Measured with CLIO, driver has been broken in. Note BL is included, which is not in Fostex's published specs.

[Lionel]

Thank you for sharing.
I am very interested in this driver.
I must say that I don't really know why because it is not really popular...
What about the sound ?
Why have you done this measurement ?
Have you a project with this driver ?

Lionel

[GM]

Thanks for sharing, though I've never seen any compression driver with such a low Qes/Qts, much less a point source driver, not to mention such a high 1k/Le, Vas, Sd for an 8" FR driver, so I have to question these specs.

GM

[bzdang]

GM
Sorry, I hadn't actually looked at the values, just posted it in a spare moment, I will ask the fellow to remeasure on Monday (along with my peerless woofer!)

Lionel
I have used the FF225K in the rcafan horn (see audioasylum) but that cabinet is too large for my wife to accept. This driver is more polite than the sigma and whizzer-cone units that I've tried, so I want to see what it can do in an MLTL cabinet.
Dave

[bzdang]

UPDATE

Remeasured.

[Lionel]

I am still interested (yes I am) but what does it means ?

[GM]

This driver is more polite than the sigma and whizzer-cone units that I've tried, so I want to see what it can do in an MLTL cabinet.

Depends on how low you want Fb to be or how small it needs to be for SAF or how much SPL you are willing to trade for LF extension. For example, adding 6 ohms series R allows a T/S max flat Vb = Vas/Fb = Fs, but linear power handling rapidly disappears above a fraction of a watt, and of course some BSC will be needed if well away from the back wall:

(all dims inside)

L = 35.15"
CSA = 120.612"^2 - suggest 14" x 8.625"
Driver down 14.55"
vent = 2" dia x 0.75" near/at the bottom
damp to suit

So what are your performance goals?

FWIW, these specs are still way off from the published specs, and while this isn't uncommon, they are usually off such that they still calc ~ the same cab specs, but these don't:

Published = 4.41L/90.9Hz Fb
measured = 9.17L/71.1Hz Fb!!

Also, I found that I had to lower Sd to 221cm^2 to get the measured BL/Cms/Mms to get 'in the ballpark' of the calc'd ones.

GM

[Sandy H.]

GM,

I don't know anything about this driver or the measurements taken, but have recently purchased SE and am reading up on measuring. Could you post some conjecture as to what would cause the measurement errors you are seeing. Sometimes it is hard for a newbie to understand why something is wrong and a better understanding of where the parameters are coming from and what would cause errors will lead to a better result.

Thanks for any insite you can provide.

Sandy.

[bzdang]

I would like to have a single-driver system in my livingroom, and since I have access to borrow one of these drivers for testing purposes, I decided to do some tapered-TL and ML-TL simjkulations and build a test box. The problem was that there was no BL in the published specs and guessing created large variation in the mjk simulation depending on the BL value chosen. Hence the attempts to get it measured.

Performance goals include

- box size that is movable by one person (the backloaded horn was too large/heavy)

-very modest spl capability

-adequate bass, which is why I'm looking at the 8" and not smaller

-minimal listening fatigue

-electrical simplicity


Yes Sd should have been 221cm^2 if the published 'equivalent diaphram radius' of 84mm was used.

I have thoroughly broken in this driver. Are the differences in T-S consistent with having some miles on the driver?

I will try to get the fellow who measured it to explain why there are differences from published specs.

[Nelson Pass]

Originally posted by bzdang
UPDATE Remeasured.

Assuming that was the fundamental resonance, it's interesting
because mine came out in the middle at 50 Hz.

Also, it's worth noting that the response is about 15 dB down
at 15 KHz on this driver. You're going to want a tweeter above
10 KHz.