I've wanted to play around with metal-coned drivers for years, and thanks to this forum I've finally got my hands on a pair. Mine are the H1252-08, which is the 8" midbass.
I like the idea of rigid metal cones as they're acting as a piston throughout their range. The by-product of that behaviour is that, when they hit the bell-mode resonances in the kHz range, it looks like a mountain range, with the peaks 10dB higher than the nominal range.
These 8" drivers are probably intended for use in a conventional 3-way system with a 4" mid and a 1" dome. Indeed, that would probably be a nice speaker. However, I like to make life difficult for myself, so I'm going to eek out everything these 8" drivers can do, and have them running up to about 1kHz.
I happen to have a set of drivers that look suspiciously similar to B&C DE250s, on 18Sound XT120 horns. I suspect they're just re-labelled, but there is the possibility that they have some tweaks. Geddes runs his DE250s down below 1kHz, so I'm confident I can get them integrated with the 8" cone.
So, I came up with a 22L (internal) sealed box that roughly conforms to the Golden Ratio. No particular reason for choosing that. It'll probably spread standing waves out a bit, but I just wanted to set the cabinet dimensions so I could get on with the woodwork.
Installed the drivers, and took some graphs. These are in-room, mic at about 1m on axis with the woofer, cabinet back to the wall. Nothing calibrated, but the mic is flat. Should be pretty obvious which curve is which. The HF section will be fairly easy to work with - just needs a shallow notch in there to get the 3.2kHz peak down to flat.
The full-range response is just something I threw together in DSP so I could listen while I assembled the second speaker - 1kHz low- and high-pass, plus an EQ filter to drop that 3.2kHz peak.
I need a simple easy-to-use HiFi system, so these will have a passive crossover. Stay tuned.
Chris
I like the idea of rigid metal cones as they're acting as a piston throughout their range. The by-product of that behaviour is that, when they hit the bell-mode resonances in the kHz range, it looks like a mountain range, with the peaks 10dB higher than the nominal range.
These 8" drivers are probably intended for use in a conventional 3-way system with a 4" mid and a 1" dome. Indeed, that would probably be a nice speaker. However, I like to make life difficult for myself, so I'm going to eek out everything these 8" drivers can do, and have them running up to about 1kHz.
I happen to have a set of drivers that look suspiciously similar to B&C DE250s, on 18Sound XT120 horns. I suspect they're just re-labelled, but there is the possibility that they have some tweaks. Geddes runs his DE250s down below 1kHz, so I'm confident I can get them integrated with the 8" cone.
So, I came up with a 22L (internal) sealed box that roughly conforms to the Golden Ratio. No particular reason for choosing that. It'll probably spread standing waves out a bit, but I just wanted to set the cabinet dimensions so I could get on with the woodwork.
Installed the drivers, and took some graphs. These are in-room, mic at about 1m on axis with the woofer, cabinet back to the wall. Nothing calibrated, but the mic is flat. Should be pretty obvious which curve is which. The HF section will be fairly easy to work with - just needs a shallow notch in there to get the 3.2kHz peak down to flat.
The full-range response is just something I threw together in DSP so I could listen while I assembled the second speaker - 1kHz low- and high-pass, plus an EQ filter to drop that 3.2kHz peak.
I need a simple easy-to-use HiFi system, so these will have a passive crossover. Stay tuned.
Chris
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It looks like the smoothing applied to the graph smooths the cone resonances. You could try to use less or no smoothing when setting the DSP notches.
The only DSP notch was on the HF driver, to smooth the 3-4kHz range.
The crossover filters I'm using are Powersoft's "FIR" slope, which I set for 1kHz. It's 24dB down at 1.4kHz, so I think that's enough attenuation for the woofer's peaks.
When it comes to the crossover, I'll be trying a "bottomless" notch filter across the driver, effectively shorting it out at 4.5kHz. That'll put a little more stress on the low-pass inductor, which I'll size accordingly.
I now have them up and running in stereo, and am quite impressed. Unfortunately, the amplifier I'm using (a T604) won't be used in the final HiFi system, as it's needed for PA duties. So, I must make a passive crossover.
Chris
I used an L22 in a two way a few years ago. Quite an exciting and dynamic sound. Needed to x/o at 1.5kHz though.
I also found it necessary to use two notches. From memory 0.2mH/4.7mfd and 0.1mH/3.3mfd.
I also found it necessary to use two notches. From memory 0.2mH/4.7mfd and 0.1mH/3.3mfd.
I've used the bigger L26 which had a 4KHz breakup. A series notch was enough plus resistor on the capacitor leg of the 2nd order circuit to shape the response.
My target XO was 220Hz - way lower than yours (was used in a 3 way design).
I'm not sure how high you could get away with it. I found the L15 breakup was audible at 2.7KHz (primary node 8.1KHz) and ended up settling on 2.3KHz for the L15 to tweeter (as it just sounded better than the tweeter playing lower - especially louder).
I'd recommend you use Room EQ Wizard and do various HD measurements at various power levels to see if you are attenuating the prominent 3rd order peak enough which will occur ~ 1.3KHz. That would be my upper limit to crossing over.
The above lends itself to a waveguide loaded tweeter if you want a 2 way.
My target XO was 220Hz - way lower than yours (was used in a 3 way design).
I'm not sure how high you could get away with it. I found the L15 breakup was audible at 2.7KHz (primary node 8.1KHz) and ended up settling on 2.3KHz for the L15 to tweeter (as it just sounded better than the tweeter playing lower - especially louder).
I'd recommend you use Room EQ Wizard and do various HD measurements at various power levels to see if you are attenuating the prominent 3rd order peak enough which will occur ~ 1.3KHz. That would be my upper limit to crossing over.
The above lends itself to a waveguide loaded tweeter if you want a 2 way.
Yeah the 4.5kHz breakup needs a 4th order @ 1300Hz or lower so with the DE250 you'll be fine. The breakup of the 4.5kHz creates a peak in the 3rd order hamornic distortion of a similar magnitude to the amplitude peak in the frequency response.
So a 1.5kHz HD3 peak with a potential rise of 18dB. Your xover being 24dB down at 1.4kHz should be perfect. With that low xover you've basically handled all the issues metal cones have.
So a 1.5kHz HD3 peak with a potential rise of 18dB. Your xover being 24dB down at 1.4kHz should be perfect. With that low xover you've basically handled all the issues metal cones have.
Looks like I need to try some high-level sweeps. At the levels I tested at (comfortable in my living room), the distortion profile appears to be flat, but also very close to the noise floor.
The steep crossover was afforded by DSP, but I'll need to do something with a passive crossover for the final product - the T604 is for PA duties, and I don't want it in the home HiFi for the upheaval that would be caused every time I was putting on an event.
The passive crossover I've designed in XSim looks promising - the notch and lowpass filter put the 4.5kHz peak >50dB down, which should be ample damping. The lowpass is also around 20dB down at 1.4kHz, which isn't far off what's achievable with DSP.
So far, there are fourteen crossover components.
I need to re-do the measurements, though, as the phase curves are all over the place, making it difficult to tell when the crossover has actually integrated the drivers.
Chris
I`ve resumed a 3-way using exactly the same woofer. Can post my measurements, if interested (planned for next weekend). Pretty good woofer in my opinion, up to 350hz distortion was lower than the slightly smaller Revelator (18cm one). I massively disliked the surround layout - they have a printed Seas logo on it and it is not on the same spot neither centered to a screw hole - looks like a defect on a pretty stunning finish now...
Just a quick note to say the crossover parts are on their way. It's quite a complex one, with 15 components:
LF: 3rd order lowpass, Zobel, "bottomless" notch at 4.5kHz
HF: 3rd order highpass, notch at 3.5kHz, L-pad
Everything has its place, though - I wouldn't call any part of the crossover superfluous.
Impedance minimum is 6.5ohm, with quite a lot of the range being over 10ohm. Should be a nice easy load.
Chris
LF: 3rd order lowpass, Zobel, "bottomless" notch at 4.5kHz
HF: 3rd order highpass, notch at 3.5kHz, L-pad
Everything has its place, though - I wouldn't call any part of the crossover superfluous.
Impedance minimum is 6.5ohm, with quite a lot of the range being over 10ohm. Should be a nice easy load.
Chris
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