Hi.
Let assume I'm pretty cheap and bought some compression-drivers with zero data-sheet. Yes, that's a gamble, but they were very cheap. I've tested one with a 24db HP @2200Hz and it sound OK for a party-speaker. 1,5" diaphragm, and magnet around Ø100mm. Appears pretty solid.
So now, I'm considering a new design where I would want to cross lower. Maybe around 1300-1500Hz. How would you determine the lowest cross-over for a unknown compression-driver?
Based on resonance-freq, distortion chart (at high power?), others?
Design-goal: one comp-driver in a Mrh-80 horn from Monacor (115mm deep), paired with 2*6.5" midbass with a sens. of 91dB. Electronic cross-over and power for midbass around 300W peak.
Kind regards TroelsM
Let assume I'm pretty cheap and bought some compression-drivers with zero data-sheet. Yes, that's a gamble, but they were very cheap. I've tested one with a 24db HP @2200Hz and it sound OK for a party-speaker. 1,5" diaphragm, and magnet around Ø100mm. Appears pretty solid.
So now, I'm considering a new design where I would want to cross lower. Maybe around 1300-1500Hz. How would you determine the lowest cross-over for a unknown compression-driver?
Based on resonance-freq, distortion chart (at high power?), others?
Design-goal: one comp-driver in a Mrh-80 horn from Monacor (115mm deep), paired with 2*6.5" midbass with a sens. of 91dB. Electronic cross-over and power for midbass around 300W peak.
Kind regards TroelsM
Successively higher amplitude sweeps attached to the horn monitoring harmonic distortion. Usually you see a sudden increase below a certain frequency*. Check out this M200 datatsheet:
https://www.communitypro.com/sites/default/files/M200.PDF
In the harmonic distortion 10% power graph you can see a rapid rise below of the minimum crossover frequency of 400Hz. One thing to be careful of though is that REW lowest excitation frequency is 1/2 the minimum frequency selected in the sweep so you may want to use a sine tone and use the FFT to check distortion if you are honing in on the limits of the driver. You may find if the driver is cheap that 2.2kHz is already too low due to a metal surround.
*A mic capable of very high SPL helps a lot with this as you can just put it in the mouth of the horn.
https://www.communitypro.com/sites/default/files/M200.PDF
In the harmonic distortion 10% power graph you can see a rapid rise below of the minimum crossover frequency of 400Hz. One thing to be careful of though is that REW lowest excitation frequency is 1/2 the minimum frequency selected in the sweep so you may want to use a sine tone and use the FFT to check distortion if you are honing in on the limits of the driver. You may find if the driver is cheap that 2.2kHz is already too low due to a metal surround.
*A mic capable of very high SPL helps a lot with this as you can just put it in the mouth of the horn.
Hi.
Thank you for the input.
I suspect that the Arta/steps could be used to make this test.
Are you saying that all compression-drivers with an metal-surround have limited X-max and thus must be crossed over relatively high?
Kind regards TroelsM
Thank you for the input.
I suspect that the Arta/steps could be used to make this test.
Are you saying that all compression-drivers with an metal-surround have limited X-max and thus must be crossed over relatively high?
Kind regards TroelsM
Both the horn and your woofers are around 6.5" wide so the 2200Hz is propably better crossover point (directivities match). Have fun!🙂
Two considerations when running a compression driver lower than the manufacturer might've intended:
- The Xmax of the driver itself
- The loading that the horn provides at the bottom of the passband
Obviously, higher Xmax means more output towards the bottom of the passband. There are mechanical limits in compression drivers: one is the linearity of the suspension and motor, and the other is a hard limit - distance to the phase plug. My 18Sound ND1460s have hammered the phase plugs before now (turns out the rep demonstrating some new amps hadn't programmed them correctly), and you definitely notice that one.
A horn with good directivity control at the bottom of the passband means you get more on-axis SPL for a given amount of diaphragm displacement. ie, the same amount of energy is being focused on a smaller area, so it's louder.
Generally speaking, compression drivers are intended to be paired with 10-15" drivers and driven to PA levels.
Now, your 2x 6" drivers might not get to PA levels, but at the same time, they might. I have some super-compact PA speakers here which use an 18Sound 6ND430 per side, and while you have to drop some power in there, they do perform very well. If you're using midbass drivers of a similar calibre, I'd keep the crossover towards 2kHz.
Chris
- The Xmax of the driver itself
- The loading that the horn provides at the bottom of the passband
Obviously, higher Xmax means more output towards the bottom of the passband. There are mechanical limits in compression drivers: one is the linearity of the suspension and motor, and the other is a hard limit - distance to the phase plug. My 18Sound ND1460s have hammered the phase plugs before now (turns out the rep demonstrating some new amps hadn't programmed them correctly), and you definitely notice that one.
A horn with good directivity control at the bottom of the passband means you get more on-axis SPL for a given amount of diaphragm displacement. ie, the same amount of energy is being focused on a smaller area, so it's louder.
Generally speaking, compression drivers are intended to be paired with 10-15" drivers and driven to PA levels.
Now, your 2x 6" drivers might not get to PA levels, but at the same time, they might. I have some super-compact PA speakers here which use an 18Sound 6ND430 per side, and while you have to drop some power in there, they do perform very well. If you're using midbass drivers of a similar calibre, I'd keep the crossover towards 2kHz.
Chris
Hi Chris.
Thank you for the insight. I've followed your diy-endeavors in the PA-world.
The 6" were a used-sale from a guy changing drivers in his line-array ( me being cheap again..) So we are close to "professional-level", but these will be active speakers and thus amp-power is known and controlled with a 2-stage limiter ( peak and RMS).
I don´t think its realistic that I'l ever get above 300W power total for the 6" midbasses. My plan is to drive the CD with an LM3886 so power is limited.
I'm only considering lowerings the cross-over because I want to test a configuration where the 6" are partly covered by the horn and the resulting cavity will limit HF-response from the 6".
Kind regards TroelsM
Thank you for the insight. I've followed your diy-endeavors in the PA-world.
The 6" were a used-sale from a guy changing drivers in his line-array ( me being cheap again..) So we are close to "professional-level", but these will be active speakers and thus amp-power is known and controlled with a 2-stage limiter ( peak and RMS).
I don´t think its realistic that I'l ever get above 300W power total for the 6" midbasses. My plan is to drive the CD with an LM3886 so power is limited.
I'm only considering lowerings the cross-over because I want to test a configuration where the 6" are partly covered by the horn and the resulting cavity will limit HF-response from the 6".
Kind regards TroelsM
