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Old 8th July 2010, 07:15 AM   #21
Legis is online now Legis  Finland
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I though you had measured some BMS's driver and talked with experience? So what are you basing your opinion on exactly?
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Old 8th July 2010, 11:32 AM   #22
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Spider of 18" Mael and 18N860:

Ps. I'll try to do some THD measurements at different SPLs once I get the SPL meter I ordered (digital Radioshack, not used for actual measurements).
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Last edited by Legis; 8th July 2010 at 11:35 AM.
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Old 8th July 2010, 04:00 PM   #23
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Actually looking at the BMS graphs it appears that the THD is approaching 15% in some spots with the 2nd hm distortion being around -17db in a few spots. As Calvin noted this sort of thing has to be taken with a grain of salt because a 32hz tuned BR is going to limit the amount of excursion used. Also since there is only one drive level presented the rate of THD increase can't be determined. 3rd it's a manufacturer supplied graph. I'd suspect that BMS used a drive level and enclosure tuning combo that performs well for their driver.

Just because a driver can be driven to a certain excursion level with a relatively minor amount of noise does not mean that it is linear although it is a good quality to have. The suspension could be tightening up and the motor losing large amounts of force by that point. This causes the output to not scale accurately with input power (compression). There is also an undertermined amount of distortion being produced. We'd need to see power compression tests and BL, KMS curves to determine things.

I happen to think that the BMS 18N860 is probably a very good driver btw. Anybody know what the xmech is rated as?

SDX15's
Illka did test these in his last round and they did ok, but with higher distortion levels than expected. Even so the THD stays below 12% down to 30hz even at a very high drive level that would correspond to about 18mm 1 way excursion. Distortion skyrockets below 25hz even at the lowest drive levels regardless of the excursion used indicating that this is not simply due to the increased excursion demands. I happen to own a pair of SDX 15's and they seem to perform consistent with Illka's tests. IMHO the useable xmax is closer to 18-20mm than 30mm. They will go past 20mm but with increasingly distorted output. They are other than that a decent driver, but far from my favorite. Illka had noted that the Klippel test of the ones he tested had an "interesting" BL curve. A far cry from 70% strength at 30mm. Did he actually post that data somewhere Legis? It appears that is what you referenced in one of your posts? BL curve at 70% at 12.84mm?!

Either way I would not look at that as a judgment against XBL^2, just that like any other tech it can be implemented badly and having that licensed for use in a product is by no means a guarantee of performance or quality. I've heard the Mal-x ver 1 and it's little brother the Shiva X also ver 1 and they were quite good even when driven fairly hard, but without serious testing like Illka's or klippel, who knows what the real performance is.
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Old 9th July 2010, 05:57 AM   #24
Calvin is offline Calvin  Germany
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Hi,

instead of the -at that time unobtainable- 18N860 I got a sample of the 18N850, which is lying around after evaluation and guess why its just lyin around ....
I regard the 850 as a quite good driver, but it didnīt fulfill the demands of a true longthrow subwoofer driver. Besides I dislike to get 3 different sets of parameters for the same driver from a manufacturer. None of the parameter sets actually fitted my own meassurements, with the own measurements resulting in TSPs which certainly disregarded the driver as subwoofer.

Since its bigger brother the 860īs shares the same parts or parts of similar dimensions, the behaviour will be similar. Increasing the length of the voicecoil doesnīt make a good driver into a good longthrow-driver.
It needs special magnetic circuit designs (XBL et al) and/or special voicecoil designs (split coil, nonlinear wound coils) and special large diameter spider designs (too, often double or even triple spiders) and special surround designs. Apart from demodulation rings in the magnetic circuit the BMS features no other real specialty.

jauu
Calvin
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Old 9th July 2010, 07:24 AM   #25
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Been away for a few days and I started to write this before...

Quote:
Originally Posted by Inductor View Post
One, the first, is calculated (from a pseudo Xlim or Xmax.limit of movement).
In the case of Exodus drivers it is done on a Dumax or Klippel tester where the Bl is plotted against the excursion both in and out. I have seen the curves posted but can't seem to find them ATM. When I do, I'll link.

Below is one I have stored for an B&C 8NDL51. I forget where I got it so no attribution.

A single measured THD figure doesn't tell you much - I'd rather see the shape of the transfer function or the sprectra from a number of tests at different levels.

There never has been a definition of how to measure and specify Xmax in the same way as small signal T/S are defined. Manufacturers use what they want to make products look better.
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Old 10th July 2010, 03:25 PM   #26
Legis is online now Legis  Finland
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Quote:
Originally Posted by Josh Ricci View Post
Anybody know what the xmech is rated as?

SDX15's
Illka had noted that the Klippel test of the ones he tested had an "interesting" BL curve. A far cry from 70% strength at 30mm. Did he actually post that data somewhere Legis? It appears that is what you referenced in one of your posts? BL curve at 70% at 12.84mm?!
BMS stated that the spider hits the top plate at the point in which the voice coil is 5mm away from the bottom plate, and thus protects the voice coil from destruction. The xmech is according to my simple excursion tests maybe +/- 30mm or little more.

Ilkka posted the data regarding the SDX15 on finnish forum DVDplaza (the reference I used), Zipman = Ilkka. I don't know how much the BL is down at 12,84mm, maybe 30% if that value is often used.
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Old 10th July 2010, 03:50 PM   #27
Legis is online now Legis  Finland
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Quote:
Originally Posted by Calvin View Post
Hi,

instead of the -at that time unobtainable- 18N860 I got a sample of the 18N850, which is lying around after evaluation and guess why its just lyin around ....
I regard the 850 as a quite good driver, but it didnīt fulfill the demands of a true longthrow subwoofer driver. Besides I dislike to get 3 different sets of parameters for the same driver from a manufacturer. None of the parameter sets actually fitted my own meassurements, with the own measurements resulting in TSPs which certainly disregarded the driver as subwoofer.

Since its bigger brother the 860īs shares the same parts or parts of similar dimensions, the behaviour will be similar. Increasing the length of the voicecoil doesnīt make a good driver into a good longthrow-driver.
It needs special magnetic circuit designs (XBL et al) and/or special voicecoil designs (split coil, nonlinear wound coils) and special large diameter spider designs (too, often double or even triple spiders) and special surround designs. Apart from demodulation rings in the magnetic circuit the BMS features no other real specialty.

jauu
Calvin

Do you have any actual data to show?
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