A long, long time ago (I know, because I found my posts during construction) I built a pair of the 31 inch Jx92s transmission line speakers. I didn't have any measuring equipment.
They never excited me. No bass.
Fast forward nearly 20 years. Measurement is easier, and so are my finances. I just bought the Dayton Audio DATS v3, and measured the impedance of the speakers (free air).
Hello! Fs is almost twice what it's supposed to be? (95 Hz instead of 50 Hz). Pull out the second speaker... same thing. Other parameters are nowhere close to spec.
OK... I have a pair of Tang Band W3-881s hanging around. Listed Fs of about 100 Hz... and that's what I measure.
Other parameters are at least close to spec.
So - what have I got going here? Is my measurement technique off? (Yes, I calibrated the DATS.) Did I get a bad couple of Jordans? Any help would be appreciated.
Mike aka Cheesehead
They never excited me. No bass.
Fast forward nearly 20 years. Measurement is easier, and so are my finances. I just bought the Dayton Audio DATS v3, and measured the impedance of the speakers (free air).
Hello! Fs is almost twice what it's supposed to be? (95 Hz instead of 50 Hz). Pull out the second speaker... same thing. Other parameters are nowhere close to spec.
OK... I have a pair of Tang Band W3-881s hanging around. Listed Fs of about 100 Hz... and that's what I measure.
Other parameters are at least close to spec.
So - what have I got going here? Is my measurement technique off? (Yes, I calibrated the DATS.) Did I get a bad couple of Jordans? Any help would be appreciated.
Mike aka Cheesehead
Hmm, all I really know is that way back when Jim Griffin did his little two way it's JX92S measured within spec and performed quite admirably down through the mid-bass, ditto some others lower tuned MLTLs done locally (metro Atlanta), but that said, I guess time and/or excessively starched spiders could double Fs.
Yeah, since your TB measurements jive and knowing how stiff, to locked solid, ancient Altec, JBL can be and a Jensen LS 15 I just checked is, just about got to be the drivers and if this stiff when new, then good luck getting the starch out of them at this late date without cracking them.
Then again, I wonder how much small baking/broiling oven heat they can withstand (he asks rhetorically). Planning a vacation in the lower half of the Southern 48 or have any friends/relatives you can send them to sunshine bake/grill?
Then again, I wonder how much small baking/broiling oven heat they can withstand (he asks rhetorically). Planning a vacation in the lower half of the Southern 48 or have any friends/relatives you can send them to sunshine bake/grill?
In the last year or two when I listened to my near-new-in-box JX92S naked and in a makeshift TL, the bass was VERY extended. Just as ten years ago I didn't like the 2-4khz dip (see published FR), there even with the G2Si ribbon. Suggest EQ up 2-6k to boost dynamics a bit. I might give it another try by tweaking the XO to that effect.
My ~15 year old pair appear to be from the EAD production run and still measure close to spec on most parameters. A pair of original rubber surround NHT woofers conversely display the same behaviour as your Jordans. The suspensions may have hardened,
@wchang, both my Jordans have very low distortion until about 2-3 kHz, followed by a significant region of elevated 3rd order. The rising response in that region doesn't help. They measure beautifully crossed over to a tweeter below 2 kHz but I didn't find the textbook uber-wide dispersion realistic. Trying them full range again but response tailoring is mandatory.
@wchang, both my Jordans have very low distortion until about 2-3 kHz, followed by a significant region of elevated 3rd order. The rising response in that region doesn't help. They measure beautifully crossed over to a tweeter below 2 kHz but I didn't find the textbook uber-wide dispersion realistic. Trying them full range again but response tailoring is mandatory.
Since you say both Jordan's are quite close, & you say they 'never had bass' I suspect something is awry somewhere in their suspensions. Your piston diameter rating is too high: 4.5in = 11.43cm or 102.6cm^2 when JX92S has a rated Sd, as I recall, of about 78.5cm^2, which may not be helping some of your measures, especially of Vas etc. but that's probably incidental here.
Fs, Q will typically come out higher & Vas lower in DATS than in some other systems; it measures on a very low voltage, & T/S parameters generally vary significantly with voltage drive. Still, those are sufficiently far out that I doubt it's the hardware You can push DATS to its maximum possible drive level by opening the oscilloscope mode & setting Z sweep amplitude to its highest 11.4dBu value, then re-testing. That may help a bit. But my money is on the drivers being out from the off. You sometimes get a rogue pair unfortunately.
Fs, Q will typically come out higher & Vas lower in DATS than in some other systems; it measures on a very low voltage, & T/S parameters generally vary significantly with voltage drive. Still, those are sufficiently far out that I doubt it's the hardware You can push DATS to its maximum possible drive level by opening the oscilloscope mode & setting Z sweep amplitude to its highest 11.4dBu value, then re-testing. That may help a bit. But my money is on the drivers being out from the off. You sometimes get a rogue pair unfortunately.
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Good point. I was playing around with the value to try to see if Vas was anywhere close, using the listed Mmd. But yeah, that's incidental, it only changes the value of Vas.
I'm driving them hard right now with the REW sub calibration. I drove them for a couple of hours last night, and the Fs dropped almost 20 Hz.
That can help -just go careful putting them to high excursions on a constant basis. The Jordans are many things, but a subwoofer isn't one of them -like MA drivers, that cone is microns thick & it's possible to warp it on repeat extreme loads. Unlikely, but worth keeping an eye on.
It’s nearly impossible to screw up impedance sweep, so your driver are not up to spec. Too low drive level might result in too high Fs, but the variation almost never exceeds 20-25%.
I would give the spiders and surrounds a vigorous massage, then leave for a few hours driven to near Xmax by infrasound. This method improves the consistency and lowers Fs somewhat, but would not help if your drivers were assembled with spiders two steps too stiff, unfortunately.
I would give the spiders and surrounds a vigorous massage, then leave for a few hours driven to near Xmax by infrasound. This method improves the consistency and lowers Fs somewhat, but would not help if your drivers were assembled with spiders two steps too stiff, unfortunately.
I'd be very wary about trying that with Jordan units -not hammering them to Xmax for hours with an infrasonic signal anyway. It can work for some drivers (woofers, some fairly robust midbass & the like), but that's as good a way of warping the cone of a JX92S as any I can think of.
Are there other options? So far I've dropped Fs from 95 to 64 Hz by running with a 30 Hz signal for about 6 hours, running them just short of Xmax.
Hobbiest T/S measures vrs factory kit vrs factory (not a JX92) of the same driver. 20% variation in Fs so 25% is belivable.
Note that there will be “weather” differences in the measures.
rdf’s comments could explain why JX92 drives me nuts.
dave
Thanks to everyone. After 6 hours of pounding with 30 Hz they're not getting better any more. Fs is 65 Hz instead of 95; still not 45, but better. Putting it into the enclosure & doing a frequency sweep gives a reasonable response curve after equalization.
Time to do the same to the second one and put them both back in their enclosures.
(Picture - overlaid, 6 hrs of 30 Hz close to Xmax vs no treatment.)
Time to do the same to the second one and put them both back in their enclosures.
(Picture - overlaid, 6 hrs of 30 Hz close to Xmax vs no treatment.)