Using transformers or autotransformers to match sensitivity does work better with compression drivers then a resistor due to the peaky impedance of compression drivers. I use autoformers myself for years.
On last thing on the modification of the bms drivers, give them hell, and with hell I mean hell at the paeks they where designed for, earbleading spl levels you will never ever reach in your home environment unless you want to become deaf within 5 minutes. I let mine work very hard on pink noise in a deadened "burn in box" for a couple of days. The drivers got really hot but after this little power excercise they smooth out a lot. works with other drivers as well.
On last thing on the modification of the bms drivers, give them hell, and with hell I mean hell at the paeks they where designed for, earbleading spl levels you will never ever reach in your home environment unless you want to become deaf within 5 minutes. I let mine work very hard on pink noise in a deadened "burn in box" for a couple of days. The drivers got really hot but after this little power excercise they smooth out a lot. works with other drivers as well.
Hello guys,
DIY newbie here, I have some questions regarding the xo here. Help is much appreciated.
I have recently bought the Beyma CP380M to be used with the DDS ENG 1-90Pro waveguide, specs are here
http://profesional.beyma.com/ENGLISH/pdf/descarga.php?pdf=CP380M.pdf
I have also bought the Beyma 10MW/Nd
http://profesional.beyma.com/ENGLISH/pdf/descarga.php?pdf=10MWNd.pdf
I am intending to build a 2-way with the xo of ~1.6kHz 3rd order.
This is for home usage, I guess i would not need SPLs of higher than 110dB for peaks. In fact 90% of the time when i am sane, the peaks probably would be staying below 100dB.
I am using a tube amplifier, thus sharp impedance curves are not well tolerated I guess.
--------------------------------------------
For the CP380M,
At the xover region of 1.6k and above, there is a sharp rising impedance peak of 13ohms @ 2kHz.
My understanding is that we can tame this impedance peak for high freqs with a zobel network. To calculate this, we need the Re and Le, the specs do tell the Re of 4.7ohms (my meter says 5.1 ohms).
Question : How do i measure the Le? With a LCR meter? The specs do not provide Le.
----------------------------------------------------
For the 10MW/Nd, there is a slow rising impedance curve, I guess I'd build a zobel for this, the Re and Le for this is given as 5.5ohms and 1.7mH. I calculated the R needed to be 6.88 ohms and C needed to be 35uF. Is this correct?
The huge impedance peak of 170 ohms at about 47Hz, how do i correct this also?
As I am still learning slowly, any comments/help rendered is much appreciated. Thanks a lot!
DIY newbie here, I have some questions regarding the xo here. Help is much appreciated.
I have recently bought the Beyma CP380M to be used with the DDS ENG 1-90Pro waveguide, specs are here
http://profesional.beyma.com/ENGLISH/pdf/descarga.php?pdf=CP380M.pdf
I have also bought the Beyma 10MW/Nd
http://profesional.beyma.com/ENGLISH/pdf/descarga.php?pdf=10MWNd.pdf
I am intending to build a 2-way with the xo of ~1.6kHz 3rd order.
This is for home usage, I guess i would not need SPLs of higher than 110dB for peaks. In fact 90% of the time when i am sane, the peaks probably would be staying below 100dB.
I am using a tube amplifier, thus sharp impedance curves are not well tolerated I guess.
--------------------------------------------
For the CP380M,
At the xover region of 1.6k and above, there is a sharp rising impedance peak of 13ohms @ 2kHz.
My understanding is that we can tame this impedance peak for high freqs with a zobel network. To calculate this, we need the Re and Le, the specs do tell the Re of 4.7ohms (my meter says 5.1 ohms).
Question : How do i measure the Le? With a LCR meter? The specs do not provide Le.
----------------------------------------------------
For the 10MW/Nd, there is a slow rising impedance curve, I guess I'd build a zobel for this, the Re and Le for this is given as 5.5ohms and 1.7mH. I calculated the R needed to be 6.88 ohms and C needed to be 35uF. Is this correct?
The huge impedance peak of 170 ohms at about 47Hz, how do i correct this also?
As I am still learning slowly, any comments/help rendered is much appreciated. Thanks a lot!
You can tame the rise in impedance with a zobel network.
Once you do that, fix the impedance peak at FS.
Once you've done these two steps, you can start making a proper filter.
You won't be able to make it perfect - do your best with the fewest components possible. The more components you use, the complexity of the circuit will grow accordingly.
Whatever you do, don't bother to do this with trial and error. You ABSOLUTELY must use a computer program. The impedance of a compression driver is far too complex. In addition, don't rely on the manufacturers data. You must measure the impedance yourself ON THE WAVEGUIDE.
Personally I measure the impedance with the Parts Express Woofer Tester II, then I model it in Speaker Workshop.
I found that it saved a lot of time to use a published crossover; for instance I used the Unity crossover which you can download here.
Once you do that, fix the impedance peak at FS.
Once you've done these two steps, you can start making a proper filter.
You won't be able to make it perfect - do your best with the fewest components possible. The more components you use, the complexity of the circuit will grow accordingly.
Whatever you do, don't bother to do this with trial and error. You ABSOLUTELY must use a computer program. The impedance of a compression driver is far too complex. In addition, don't rely on the manufacturers data. You must measure the impedance yourself ON THE WAVEGUIDE.
Personally I measure the impedance with the Parts Express Woofer Tester II, then I model it in Speaker Workshop.
I found that it saved a lot of time to use a published crossover; for instance I used the Unity crossover which you can download here.
Well, I bought the CP380M just based on the recommendations from posters here and AA.
The CP385/Nd is good and probably similar to the CP380M, but approx 30% more expensive. I am not sure if the neodymium magnet in the 385 gives you a "better" sound than the 380. (only in audiophile speak, of course).
The CP385/Nd is good and probably similar to the CP380M, but approx 30% more expensive. I am not sure if the neodymium magnet in the 385 gives you a "better" sound than the 380. (only in audiophile speak, of course).
augerpro said:
augerpro said:
I've used Selenium, B&C, BMS, Radian and JBL. Here are my opinions, FWIW:
B&C: Great value for the money, great quality control. One of my favs.
BMS: IMHO their neo compression drivers are almost unbeatable. I think this is why JBL rebrands BMS drivers. Amazing sound and value.
Radian: After hearing all the positive feedback on Radian, I bought a pair. They don't measure the same. Is this a quality control problem? I don't know, because I bought mine used. But I never bought another pair, and stick to B&C and BMS now.
JBL: Hideously overpriced. If you don't mind buying used, you can get amazing deals on Ebay. I have a set of Alnico JBL compression drivers which are to die for. I had to replace the diaphragms with Radian, but now they work great (and they match!)
I've had similar experiences. After looking over measurements available online, taking a pile of measurements myself, using a bunch of them, and talking with people I trust, I'd have to say the three units that seem to be the only reasonable choices are:
BMS 4540ND
B&C DE250
Beyma CP380M
What I'd really like to see is these three compared in a comprehensive test. Put them all on a 15" oblate spheroidal waveguide and measure the raw voltage transfer function. Then EQ them as they would be in a system and take distortion and power compression measurements at 80, 85, 90, 95, 100, 105, 110, 115, and 120 dB (1m). That would show IMO what are the two things to be taken out of measurements: (1) if there are any linear problems that can't be corrected and (2) when distortion and compression become nonnegligible. Somewhat incomplete information is already available on the first item, but nothing is available on the second. Anyways, this is getting somewhat side-tracked, so I'll stop.
BMS 4540ND
B&C DE250
Beyma CP380M
What I'd really like to see is these three compared in a comprehensive test. Put them all on a 15" oblate spheroidal waveguide and measure the raw voltage transfer function. Then EQ them as they would be in a system and take distortion and power compression measurements at 80, 85, 90, 95, 100, 105, 110, 115, and 120 dB (1m). That would show IMO what are the two things to be taken out of measurements: (1) if there are any linear problems that can't be corrected and (2) when distortion and compression become nonnegligible. Somewhat incomplete information is already available on the first item, but nothing is available on the second. Anyways, this is getting somewhat side-tracked, so I'll stop.
I can confirm the above. Mine go straight up to 17 or 18 kHz or so, on a PH230 horn (which is in fact a very broad diffusion horn and thus theoretically less supportive of UHF). Also subjectively, the CP385ND holds the comparison - UHF-wise - with a Beyma CP21 slot tweeter etc.
I have early FR curves of the CP385 published on separate datasheet by Beyma when this driver was just launched; the curves were measured on 3 different horns and two of these show no real drop. I think this website shows these early measures: http://lautsprechershop.de/pdf/beyma/beyma_cp385nd.pdf
Chris.
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