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Old 16th October 2011, 08:10 PM   #11
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I used to impregnate paper cones with Polyurethane glue, just paint the whole cone liberally with the glue so it can soak in, when it hardens it will foam a bit, but the results were a more controlled bass
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Old 17th October 2011, 08:48 PM   #12
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Dan,

You aren't getting the point. I am saying you cannot dismiss the factory numbers because they are different than yours.

I doubt there is anything wrong with your measures You are thou just measuring a single point on the T/S curves. Measure elsewhere and the numbers will be different. 2 ways that you can shift where you measure on the curves is change the voltage drive or the weather.

As an example, here are the results of 2 measures on the same driver (+ factory for ref).

Click the image to open in full size.

Mine, which is likely using similar kit to yours, and one done with 1 of the 2 pieces of kit the factories use. Both measures are valid (and the factory also shown, when you consider that a batch of drivers within a case can be quite large. The fostex -- which are pretty tight parameter wize -- can easily vary +/- 15%, i'd be surprised if the MCM drivers didn't have a greater variation.
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Old 18th October 2011, 12:27 AM   #13
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You are missing a couple numbers there:
SD = 62.534
Cms = 1782.56 um/N
Bl = 4.097

The MCM drivers parameters are orders of magnitude different than the driver you are using as an example. I'd venture to guess that 20 seconds of heavy breathing near that driver of yours would cause a significant shift in parameters. Not so with the MCM, it just sucks...

I measure drivers just out of the box, after a short pre conditioning, again after it's run in for several hours, and yet again after it returns to room temp. That driver was so far off that I didn't save any data, otherwise I'd have already posted it with an explanation of what specifically was the source of the deviation.
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Last edited by NEO Dan; 18th October 2011 at 12:30 AM.
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Old 18th October 2011, 12:44 AM   #14
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Looking back at the design the driver in question is the 55-2954.
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Old 20th October 2011, 12:11 AM   #15
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Quote:
Originally Posted by NEO Dan View Post
...The MCM drivers parameters are orders of magnitude different than the driver you are using as an example...I measure drivers just out of the box, after a short pre conditioning, again after it's run in for several hours, and yet again after it returns to room temp. That driver was so far off that I didn't save any data, otherwise I'd have already posted it with an explanation of what specifically was the source of the deviation.
What he was trying to say by "curves" is that Thiele-Small parameters change with the drive level, the test signal (sine vs. MLS etc), and so on. The exact same setup will deliver different numbers on different days. A different setup could yield noticeably different numbers, for Q in particular. Both could be "right" and they will both be "wrong" in the sense that you cannot represent a driver too precisely with one set of these numbers. It's kinda like Heisenberg!

Now, things shouldn't be off by an order of magnitude, which I doubt you meant literally. Resonance and mass and compliance I'd still expect within 10% on different setups with small signals. Q can vary more since it's calculated from that-one setup might give you 0.4 and another 0.5. Unfortunately this makes huge differences in non-sealed box calculations.
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Old 20th October 2011, 03:18 AM   #16
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Default MCM

Dan, what was the fs of the 55-2954 for use as a sub-woofer?

I tried using Titebond to seal and hold some 5.5" drivers in an array. It seemed to work pretty well if the hole was routed accurately but I did not use this much because the comb filtering was too bad. I learned a lot about arrays. My present design uses a horn tweeter crossed low with the midbass time aligned and focused.
Thanks for all that have contributed.
Ted
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Old 20th October 2011, 04:01 AM   #17
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Quote:
Originally Posted by head_unit View Post
I'd still expect within 10% on different setups with small signals.
I regularily see larger deviations across batches of drivers from the same case on the same day measured at the same time.

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Old 20th October 2011, 05:33 AM   #18
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Quote:
Originally Posted by ted4412wilt View Post
Dan, what was the fs of the 55-2954 for use as a sub-woofer?
Hi Ted,
I'm sorry but I really don't remember. I was testing several different drivers and I just don't recall. All I really remember was being nothing in that batch was a keeper. IIRC there were quality issues with that one too, due to a lack of adhesive at the back of the cone surround joint, so it started making clicking noises under light to moderate excursion.
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Last edited by NEO Dan; 20th October 2011 at 05:36 AM.
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