A passive low pass filter with only 2 series coils can be at most 4th order, so are you saying the driver has a nice neat 4th order roll off of it's own with no serious breakup through it's roll off region ?
When I looked earlier it looked like 20dB on the coral and 60dB on the Fostex, maybe a image downsize artifact or the like, when I zoom in (now) they look fine.
I retract my complaint!
Bear ,
You are right and I was mistaken. The woofer network looks like an electric 4th order filter with a Zobel. The only extra component is a C parallel to the second coil in the filter. Relatively simple stuff therefore. Nice thing is that the first coil can be used to compensate the baffle step. What is even nicer is that the notch not only creates a very steep slope be can, when properly tuned, be used as suck-out for Alu or Kevlar/glassfibre coned drivers.
Regards,
Eelco
You are right and I was mistaken. The woofer network looks like an electric 4th order filter with a Zobel. The only extra component is a C parallel to the second coil in the filter. Relatively simple stuff therefore. Nice thing is that the first coil can be used to compensate the baffle step. What is even nicer is that the notch not only creates a very steep slope be can, when properly tuned, be used as suck-out for Alu or Kevlar/glassfibre coned drivers.
Regards,
Eelco
The Modafferi Infinite Slope, and the Joseph Audio speakers that are descended from the Infinite Slopes, claimed a 100dB/octave filter slope, and they certainly didn't have sixteenth-order filters in them... Carefully combining a 3rd or 4th order filter with an LCR notch along with the driver's acoustic rolloff can yield a very steep crossover.
One would imagine that Modafferi did the necessary engineering and measurement...
I apologize to the thread starter for the diversion, but we will return to normal programming after this brief interruption.
The Beyond the Ariel project continues. The Azurahorn AH425 has turned out very well, and delivers very flat response with the Altec/GPA 288 and the Radian 745P 1.4" (large-format) compression drivers.
I am collaborating with a colleague in Texas on a complementary bass unit. We're taking a dual-track approach. The first approach is a hybrid front-horn with a vented box - Bjorn Kolbrek is doing the simulations on this one. The second approach, which will be suitable for smaller rooms, is a dual 15" woofer using Altec/GPA 416-16's (or similar, like the AE TD15M's) in resistive-vented cabinets.
If we can't get satisfactory performance from the more complex hybrid front-horn, the simpler resistive-vented box with dual 15" drivers should be a reasonable fallback - it will also be smaller and more suitable for smaller rooms. Planet10 has given me good suggestions for the starting point for the resistive-vented enclosures for the Altec/GPA 416's.
The AH425, as used with the Altec/GPA 288, Radian 745P, or the Yamaha 6688 (as used by Martin Seddon of Azurahorn), does not need equalization. Constant directivity was never a goal, but constant power loading on the diaphragm was - and the real system follows Bjorn's BEM simulations very closely. The polar pattern is free of sharp edges or fingering patterns, and mimics a direct-radiator in terms of a smooth and gentle off-axis falloff. Diffraction appears to be low, based on the frequency response, impulse response, and freedom from sharp cutoffs in the polar pattern. (Diffraction typically causes in ripples in all three domains.)
A 2nd, 3rd, or 4th-order (electrical) crossover anywhere from 630 to 800 Hz is suitable, since the system response is ripple-free right down to the 425 Hz horn cutoff. The 2.88" aluminum diaphragm has the first breakup around 10 kHz, as expected, but continues out to 15 kHz. The differences between the 288 and the Radian come down to the different suspension of the diaphragm and the different phase plugs. The AH425 has become part of Bjorn's and Martin's personal systems, with BK using his vintage Altec 288C's, and Martin his Yamaha 6688's (measurements are shown on the Azurahorn website).
I'm moving on the bass system and then overall system integration. The original goals of very flat first-arrival response, low diffraction, high efficiency, and generous dynamic headroom remain, along with a passive crossover that is not too complex. My original idea of a dipole has faded in response to the requirements for heavy equalization, which is not too attractive with passive crossovers, and active EQ asks for too much from direct-heated-triode amplifiers, where 20 watts is a monster amplifier.
Returning back to the thread, I have mixed feelings about elliptical filters in the crossover. You can aim for adequate phase-tracking (between drivers) close to the crossover frequency, but it seems it would be lost as the tweeter drops like a stone below the crossover. Of course, if phase tracking is lost when one driver is already 20 dB down, it probably doesn't matter much, since the driver is already so low in level compared to the other one - in subjective terms, it would be nearly silent.
And elliptic filters might have real value on horn systems, where the cutoff is so sharp, and you absolutely want to keep unwanted energy out of the diaphragm when the horn is fully unloaded. In my new system, the diaphragm is a theater-sized large-format driver, but in a small-format horn, an elliptic filter might really be of benefit.
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Bear,
Why are CE's not simple, and why should they be a mess? Simply plug starting component values for a chosen electric filter topology in LsP/SE and start optimizing. The Optimizer functions on the software will do the job a 30 seconds or so. The beauty of these steeper slopes is dat lobing is substantailly better than with lower order, including acoustic LR4, filters. There is nothing revolutionary about this, it has been done and it works fine.
High order/steep slope filters were something that gave True Audiophiles (Whoever that may be) the shivers in the past.
We see now that steeper filter slopes are becoming more widely accepted because of the greater accessabilty of affordable digital filter equipment such the Behringer, MiniDSP, Universal Equalizer, Thuneaus's stuff etc. Especially if the phase response of the system is also equalized then, you can literally have the best of both worlds.
Eelco
Why are CE's not simple, and why should they be a mess? Simply plug starting component values for a chosen electric filter topology in LsP/SE and start optimizing. The Optimizer functions on the software will do the job a 30 seconds or so. The beauty of these steeper slopes is dat lobing is substantailly better than with lower order, including acoustic LR4, filters. There is nothing revolutionary about this, it has been done and it works fine.
High order/steep slope filters were something that gave True Audiophiles (Whoever that may be) the shivers in the past.
We see now that steeper filter slopes are becoming more widely accepted because of the greater accessabilty of affordable digital filter equipment such the Behringer, MiniDSP, Universal Equalizer, Thuneaus's stuff etc. Especially if the phase response of the system is also equalized then, you can literally have the best of both worlds.
Eelco
If you'll forgive a newbie question, here it is:
Can we assume that impedance correction is a given? For both tweeters and midrange?
I'm (constantly) working on a 3-way with the XT25 and Peerless 850488. Drivers shown here:
Peerless HDS 134 +
With dual Vifa M22 woofers.
This thread is beyond illuminating re impedance peaks. Lynn's comments regarding simple versus complex material is a mind changer. Thanks.
Can we assume that impedance correction is a given? For both tweeters and midrange?
I'm (constantly) working on a 3-way with the XT25 and Peerless 850488. Drivers shown here:
Peerless HDS 134 +
With dual Vifa M22 woofers.
This thread is beyond illuminating re impedance peaks. Lynn's comments regarding simple versus complex material is a mind changer. Thanks.
Boden, I've worked with them... it's not that difficult if ur careful. But the planned response (simulated) and the actual response are two different animals. The specific and highly tweaked values in the xover change the response curve's before rolloff peaking and the depth of the initial dropoff, as well as the ultimate attenuation... then you start to look at the phase shift graph and notice that there are some things there that you may want to pay attention to as well, that are also part of the previous balancing act... this is before you look at the real world impedance looking into this circuit, and the fact that the actual driver is a reactance, not the nice easy resistance or even fancy speaker simulator that may have been used in the simulation...
So, it's really no more of an issue than actually getting any xover optimized in reality, just that the balancing act seems to be a bit more "high strung" than on things like a 4th order LR or any Butterworth.
That's just been my experience with it so far, you might knock it out in a jiffy.
_-_-bear
So, it's really no more of an issue than actually getting any xover optimized in reality, just that the balancing act seems to be a bit more "high strung" than on things like a 4th order LR or any Butterworth.
That's just been my experience with it so far, you might knock it out in a jiffy.
_-_-bear
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