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Old 13th October 2011, 01:16 AM   #1
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Default Reinforce woofer cone and lower fs

I would like to buy a large MCM woofer but most of them have high fs. How can I reinforce the cone while lowering fs?
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Old 13th October 2011, 12:30 PM   #2
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you could use 2 inch strips of fiberglass and use the epoxie resin and then put it on the back of the cone in a radial pattern, just make sure you weigh all the materials first. also take into account the epoxie resin will lighten after drying.
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Old 13th October 2011, 12:32 PM   #3
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Thanks for your help.
Ted
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Old 13th October 2011, 01:52 PM   #4
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i used carbon fiber treads,and plain wood glue.this was for a repair of a 18" beyma woofer.
still works after 15 jrs.
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Old 14th October 2011, 07:46 AM   #5
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Default Be prepared to ship them back...

Don't buy MCM unless you can measure the drivers TSP's. I've tested a few of the MCM drivers including the 18" with the stamped basket and with the exception of the 55-2421 8" the published specs are total fabricatons. The 55-2421 was very close though.
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Old 14th October 2011, 07:55 AM   #6
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Quote:
Originally Posted by NEO Dan View Post
Don't buy MCM unless you can measure the drivers TSP's. I've tested a few of the MCM drivers including the 18" with the stamped basket and with the exception of the 55-2421 8" the published specs are total fabricatons. The 55-2421 was very close though.
You could well have just been measuring the T/S parameters on a different part of the curve and the 55-2421 has a more horizontal set of curves.

When i want to stiffen cone & add mass to lower Fs (and efficiency) i use multiple coats of mod-podge, front & back.

dave
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Old 14th October 2011, 08:23 AM   #7
NEO Dan is offline NEO Dan  United States
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You could well have just been measuring the T/S parameters on a different part of the curve and the 55-2421 has a more horizontal set of curves.

When i want to stiffen cone & add mass to lower Fs (and efficiency) i use multiple coats of mod-podge, front & back.

dave
While operator error is possible, 0 degrees phase is what it is... I'm not doing it manually.
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Old 15th October 2011, 07:52 AM   #8
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While operator error is possible
am not suggestting operator error. What you said assumes that T/S parameters are scalars. They are not. They are curves. It is possible to make 2 equally valid sets of measurements from different points on the curve and get 2 quite different sets of numbers.

That your numbers are different than MCM's does not automatically invalidate them.

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Old 16th October 2011, 11:28 AM   #9
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Well I'm not sure how many different methods there are to correctly measure but I do think that the equipment/software I use very precisely finds the point of 0 degrees phase at FS and then the points of maximum inductive and capacitive phase on either side. Then a second test may be performed with an added mass or a sealed test box to measure the shift in FS. VAS/compliance is then calculated based on the change in FS. I'm not so sure you can measure something else and get valid consistent TS results.

The problem with the MCM drivers was the motor force was very weak. The 18" driver had a Qts ~.7. Not something a different test method will ameliorate methinks.
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Old 16th October 2011, 03:13 PM   #10
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Quote:
Originally Posted by NEO Dan View Post
Well I'm not sure how many different methods there are to correctly measure but I do think that the equipment/software I use very precisely finds the point of 0 degrees phase at FS and then the points of maximum inductive and capacitive phase on either side. Then a second test may be performed with an added mass or a sealed test box to measure the shift in FS. VAS/compliance is then calculated based on the change in FS. I'm not so sure you can measure something else and get valid consistent TS results.

The problem with the MCM drivers was the motor force was very weak. The 18" driver had a Qts ~.7. Not something a different test method will ameliorate methinks.
I'm gonna have to chime in and second Dan here. While I have has some luck with MCM drivers in the past, and they are certainly not the only ones publishing "optimistic" specs, the last set of drivers I bought from MCM were nowhere close to advertised specs. If I recall, Qes was 1 full unit higher than specified, 1.3 instead of 0.3. The drivers were also extremely light weight - suggesting that there was not nearly enough steel and ferrite in the frame and motor.

Fortunately, they have a great return policy.
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