A customer of mine just informed me that he has an old set of 3-way hi-fi speakers that he wants refurbished, and these things also have a compression mid horn and tweeter so I may be seeing some of the same issues you are currently dealing with.
Actually the specs are the same. If they did copy the driver itself, they copied the spec sheet as well.
https://avgearshop.com/selenium-d25...YFja_2Qw-OqRCKTkGsjoRiJR978XosVRLH2bVy7qgCL-n
I chose to XO mine at about 800 for power handling purposes.
Just a quick remark: it's a 2nd order high pass. So reversed polarity probably makes sense.
The only other inexpensive 1" compression drivers I know of that play low are the Dayton D1075T, D40T & D100T. They have 70V transformers attached that can be bypassed/removed. Note the 1075 is 16ohms when this is done, not sure about the 40/100
@noggers - It is so noted; thank you.
BTW I did hear back from PRV Audio suggesting that I tighten the cover screws on the buzzing driver. As an engineer it seems to me that if the driver is that sensitive to alignment of the two halves of the enclosure, they needed to have used cap screws that could be used with a torque wrench and some Loctite to keep the screws from backing out. Furthermore - again, if it's that sensitive - then there's going to be a certain off-center load placed on the interface between the two halves when the driver is going to be held up by the horn, which I assume it would be in almost all applications.
BTW I did hear back from PRV Audio suggesting that I tighten the cover screws on the buzzing driver. As an engineer it seems to me that if the driver is that sensitive to alignment of the two halves of the enclosure, they needed to have used cap screws that could be used with a torque wrench and some Loctite to keep the screws from backing out. Furthermore - again, if it's that sensitive - then there's going to be a certain off-center load placed on the interface between the two halves when the driver is going to be held up by the horn, which I assume it would be in almost all applications.
UPDATE: I went at the distorting PRV Audio driver with a Phillips-head screwdriver and was able to reduce the distortion but couldn't eliminate it. I set up a mic feeding into REW's RTA so I could see added harmonics instead of just relying on my ears. The other driver doesn't have any problems. Thankfully, having ordered them from Amazon, setting up a return is very straightforward so I've done that and will try my luck with a replacement. BTW while I was all set up with the mic and REW I tried the same test with the two Timpano drivers. They don't have the harmonic-adding distortion with sinewaves but they still sound markedly different with white noise, as do the PRV Audio. Among the "biggies" like Eminence, JBL, Altec, etc. would units of the same model sound pretty much the same from unit to unit? I'm dismayed that there's so much variability in the PRV Audio and Timpano units; I wouldn't think it would even be possible.
There seems to be an 'age old' problem with cheaper drivers having different sound / tone + output efficiency.
I recall this going right back to the Radio Shack / Tandy days.
Back in about 1980 I bought at high discount, six 3.5" X 10" metal horns from Tandy. Last year, when I dug them out to finally use two,
I found that I had two decently matched units out of six > that's very poor quality control 😕
I recall this going right back to the Radio Shack / Tandy days.
Back in about 1980 I bought at high discount, six 3.5" X 10" metal horns from Tandy. Last year, when I dug them out to finally use two,
I found that I had two decently matched units out of six > that's very poor quality control 😕
I was able to easily return and replace the PRV Audio compression driver but to my horror, Amazon sent this rather heavy and dense device in one of those thinly-bubblewrapped bags and so when I cut it open, I found that the driver had spilled out of its cardboard box and the bipolar electrolytic cap they supply with it had been smashed so I assumed the worst, but it passed the kazoo test and sounded pretty close to the driver I'd kept, so I'm going to roll with it!
So I moved on to the phase test - the point of which is to help establish how forward/back the 15"x5" midrange horns should be positioned atop the cabinets. So with one horn set on the floor a few feet from one of the cabs aimed straight up with a microphone hovering over it right at the horn mouth, I put another mic on a stand in front of the cab with the mic positioned in front of the bottom 12" even with the rim of the speaker. I ran both mics into an audio interface and sent the output to my oscilloscope. 500Hz is the crossover point between the 12"s and the horns, so that's the frequency of sinewave I fed them with. With the scope set to XY mode, it's easy to see the phase relationship:
It turned out that pulling the mic in front of the bottom 12" two and a half inches was enough to make the Lissajous trace become a diagonal line, which means that the horn mouth should be six and a half inches back from the front of the cab. I could do this, but I don't think it's a good idea to have the horn opening be that far back without also raising it up a few inches so that a reflection off the top front of the cab doesn't figure in.
So I moved on to the phase test - the point of which is to help establish how forward/back the 15"x5" midrange horns should be positioned atop the cabinets. So with one horn set on the floor a few feet from one of the cabs aimed straight up with a microphone hovering over it right at the horn mouth, I put another mic on a stand in front of the cab with the mic positioned in front of the bottom 12" even with the rim of the speaker. I ran both mics into an audio interface and sent the output to my oscilloscope. 500Hz is the crossover point between the 12"s and the horns, so that's the frequency of sinewave I fed them with. With the scope set to XY mode, it's easy to see the phase relationship:
It turned out that pulling the mic in front of the bottom 12" two and a half inches was enough to make the Lissajous trace become a diagonal line, which means that the horn mouth should be six and a half inches back from the front of the cab. I could do this, but I don't think it's a good idea to have the horn opening be that far back without also raising it up a few inches so that a reflection off the top front of the cab doesn't figure in.
Hello again -
I redid the phase measurement because I realized that there was a proximity effect associated with putting a microphone in front of the two vertically-stacked 12" speakers. I was doing this with a sinewave set to 500Hz which is the crossover point between the 12"s and the 5"x15" horn. I started out with a microphone 12" in front of the mouth of the horn while it was connected to the mid output of the crossover and set up in another room. The wavelength of 500Hz is almost exactly 27" so instead of accepting the closest in-phase location of the microphone, I moved it back from that location another 27" and made a fine adjustment, and then repeated that process another 27" away. So the actual in-phase point - or rather where it would have been without the proximity effect - was 2-1/2" forward of the front of the cabinet. This means that the front of the horn, in order to be presenting signals in phase with the 12"s in the crossover transition range, ought to be set back 9-1/2" from the front of the cabinet. This means that the horns are going to have to be raised up somewhat lest there be a bounce off the top of the cab. It's making me wonder if I need a larger (perhaps sectional?) horn, but I'm going to just carry on with the 5"x15"s for the time being.
I redid the phase measurement because I realized that there was a proximity effect associated with putting a microphone in front of the two vertically-stacked 12" speakers. I was doing this with a sinewave set to 500Hz which is the crossover point between the 12"s and the 5"x15" horn. I started out with a microphone 12" in front of the mouth of the horn while it was connected to the mid output of the crossover and set up in another room. The wavelength of 500Hz is almost exactly 27" so instead of accepting the closest in-phase location of the microphone, I moved it back from that location another 27" and made a fine adjustment, and then repeated that process another 27" away. So the actual in-phase point - or rather where it would have been without the proximity effect - was 2-1/2" forward of the front of the cabinet. This means that the front of the horn, in order to be presenting signals in phase with the 12"s in the crossover transition range, ought to be set back 9-1/2" from the front of the cabinet. This means that the horns are going to have to be raised up somewhat lest there be a bounce off the top of the cab. It's making me wonder if I need a larger (perhaps sectional?) horn, but I'm going to just carry on with the 5"x15"s for the time being.