Legis,
I used to use a Burr Brown OPA512 power op amp to drive servo voice coils in transconductance mode. I can't see why this can't be used for HiFi audio - it has 20 kHz power bandwidth and accepts supply voltages up to +/- 50 volts and can deliver 15 amps. They are not too expensive ($144 ea) considering what they can do.
http://www.ti.com/lit/ds/symlink/opa512.pdf
I used to use a Burr Brown OPA512 power op amp to drive servo voice coils in transconductance mode. I can't see why this can't be used for HiFi audio - it has 20 kHz power bandwidth and accepts supply voltages up to +/- 50 volts and can deliver 15 amps. They are not too expensive ($144 ea) considering what they can do.
http://www.ti.com/lit/ds/symlink/opa512.pdf
for my use and in small cabinets, more magnet sounds more dynamic than 12LTA - Eminence has made many good custom cast frame coaxial with and without horn - but they cost more than `12LTA and a helper tweeter
here's an 80oz slug Eminence coax with ASD1001S borrowed from my Silver Iris - its pretty much the same sensitivity as 12LTA but better jump factor and more subjective control. (some of course depends on the xover and compression driver)
here's an 80oz slug Eminence coax with ASD1001S borrowed from my Silver Iris - its pretty much the same sensitivity as 12LTA but better jump factor and more subjective control. (some of course depends on the xover and compression driver)
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Is the conclusion that current drive is good for this driver only applicable to the open baffle scenario, or is it more general?
More general, not just OB. Some drivers benefit less than LTA12, some will benefit more. I haven't been using regular voltage drive for middle or high frequency drivers since I tried the current drive for the first time.
By the way, by adding the shorting ring to the motor of LTA12, it's impedance drops at HF, and thus the driver receives more current drive at HF. This also means that the hf response won't rise as much as it does now, when current driven. It all depends how constant impedance can be realized with the shorting ring. Silver plated copper shorting ring might be the best alternative if one could manufacture one.
By the way, by adding the shorting ring to the motor of LTA12, it's impedance drops at HF, and thus the driver receives more current drive at HF. This also means that the hf response won't rise as much as it does now, when current driven. It all depends how constant impedance can be realized with the shorting ring. Silver plated copper shorting ring might be the best alternative if one could manufacture one.
its 50 pieces minimum for Eminence to build a new custom driver. I'm not sure if they have in-house shorting rings for such as project (?) - a note to Tony Lucas might get the answer. I would want a stronger motor to reduce cabinet size and gain some dynamics - if that can be balanced.
The world's most trusted brands have Eminence inside | Eminence Speaker
The world's most trusted brands have Eminence inside | Eminence Speaker
The volume knobs worked OK:
Today I made longer aluminum plugs (found 50mm aluminum rod from a shop nearby):
The fitting of 50mm aluminum rod is perfect after slight sanding. I made M8 threads to the plug's back, easy to put in place with a bolt through the motor's venting hole.
The bigger plugs reduced inductance slightly more, according to my inductance meter from approx. 0,8mH to ~0,74mH. The motor has massive cooling capacity because of the ~470 gram aluminum plug attached to the pole piece. The front response is marginally better with the bigger plugs. I think this is the phase plug of my choice. They also look damn nice, simple and beautiful!
I have also damped the edges of the whizzer cone with Truoil and grounded the basket (to the minus-terminal). The aluminum plug and the back plate/pole piece are ungrounded at present, but I might ground them also.
An externally hosted image should be here but it was not working when we last tested it.
Today I made longer aluminum plugs (found 50mm aluminum rod from a shop nearby):
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
The fitting of 50mm aluminum rod is perfect after slight sanding. I made M8 threads to the plug's back, easy to put in place with a bolt through the motor's venting hole.
The bigger plugs reduced inductance slightly more, according to my inductance meter from approx. 0,8mH to ~0,74mH. The motor has massive cooling capacity because of the ~470 gram aluminum plug attached to the pole piece. The front response is marginally better with the bigger plugs. I think this is the phase plug of my choice. They also look damn nice, simple and beautiful!
I have also damped the edges of the whizzer cone with Truoil and grounded the basket (to the minus-terminal). The aluminum plug and the back plate/pole piece are ungrounded at present, but I might ground them also.
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Now listening with "tuning socks" what I think sippy also meant a while ago. They are made out of ~1,5mm thick felt.
An externally hosted image should be here but it was not working when we last tested it.
And yet another sock!🙄
Freq responses (80cm from the driver, current driven!) from top to bottom a) without sock b) with the black felt sock and c) white furry sock.
An externally hosted image should be here but it was not working when we last tested it.
Freq responses (80cm from the driver, current driven!) from top to bottom a) without sock b) with the black felt sock and c) white furry sock.
An externally hosted image should be here but it was not working when we last tested it.
I have found that sealing the back vent of the magnet, or the exit at the front, makes the ~2,5kHz resonance worse no matter what. Even if the motor's hole is plugged with a foam ball, the 2,5khz resonance always gets worse. All phase plugs do the same (even a foam plug). I also tried a "foam circle" with a hole in the middle, in phase plug's place and it did the same thing, but to lesser extent.
With nothing in holes the response is easier to the ears.
It seems that it's related to blockage of the openings but I don't fully understand the mechanics. Is a transmission line resonance cancelling partly a cone resonance or something...? Or is it air compression related, ie. the resonance gets worse because the air flow pathways are blocked. Anybody know if the spider of the 12LTA is "vented" (low flow resistance through the spider)?
With nothing in holes the response is easier to the ears.
It seems that it's related to blockage of the openings but I don't fully understand the mechanics. Is a transmission line resonance cancelling partly a cone resonance or something...? Or is it air compression related, ie. the resonance gets worse because the air flow pathways are blocked. Anybody know if the spider of the 12LTA is "vented" (low flow resistance through the spider)?
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put wool/stuffing behind the whizzer cone and in the pole vent, that helps with certain ugly responses.
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I like the looks of the volume knob plug and your graph. Regarding "True-Oil" - is that the gun-stock finish? - how should it be applied to paper whizzers? - can it be used to good effect on a speaker cone?
here's a graph I took some years ago of Eminence's first model B102 vs 12LTA with both outside in the EV Aristocrat - there was no false corner to properly set system tuning. I may get one of those Edcor transformers to get a taste of current drive with open baffle.
here's a graph I took some years ago of Eminence's first model B102 vs 12LTA with both outside in the EV Aristocrat - there was no false corner to properly set system tuning. I may get one of those Edcor transformers to get a taste of current drive with open baffle.
An externally hosted image should be here but it was not working when we last tested it.
Yep, that's the stuff. I have applied it only to the edge of the whizzer in 12LTA but I have douped some other paper cones fully with Truoil before. It's quite balanced (rigidity/damping), goes IN the cone, and is more natural sounding than for example pva to my liking. It goes so well into the cone that one must use a sealer after couple of layers (if small added mass is a goal) and then make the top layer that gives the glossy look.
thanks - what sealers would be appropriate to halt too much truoil from soaking the cone? (I wonder if Bastanis uses similar-?)
Many water based glues do the job. I use Tesa glue (non-pva) diluted with water, it dries to a very thin transparent layer.
Tried stuffing the back of the whizzer with 4-5 grams of regular polyester wool. Current driven, no phasing plugs.
Also acts as a mechanical/acoustical low pass filter. Will try with 10 grams and put the stuff so that it reduces diffraction at the edge of the whizzer. Might also color the wool black, looks nicer.
I really would like to find a way to tame the 2,5kHz resonance, to my ears it's the most objectionable and pretty much forbids using any kind of phase plugs (or anything that block the air vent through the motor) with metal music at this state of the burn-in process.
An externally hosted image should be here but it was not working when we last tested it.
Also acts as a mechanical/acoustical low pass filter. Will try with 10 grams and put the stuff so that it reduces diffraction at the edge of the whizzer. Might also color the wool black, looks nicer.
I really would like to find a way to tame the 2,5kHz resonance, to my ears it's the most objectionable and pretty much forbids using any kind of phase plugs (or anything that block the air vent through the motor) with metal music at this state of the burn-in process.
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Have you tried a longer sock on the phase plug to damp any eigenmodes between itself and any others across the driver?
GM
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