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[Chris Grimshaw]

Another thing to check - are the "bad" HF drivers the same rated impedance as the good?


The curves look a little bit like you might have 8ohm diaphragms where the crossover is expecting 16ohm.

Hopefully it'll say on the back of the compression driver. If not, disconnect the driver and use a multi-meter to check the resistance.

Chris

[Tim Padrick]

There were a bunch of Yorkville U15 in which a crossover choke's lead would break near the solder connection and cause a big response change.  Stress these leads while listening or measuring the continuity of the chokes.

[John Schalk]

Another thing to check - are the "bad" HF drivers the same rated impedance as the good?


The curves look a little bit like you might have 8ohm diaphragms where the crossover is expecting 16ohm.

Hopefully it'll say on the back of the compression driver. If not, disconnect the driver and use a multi-meter to check the resistance.

Chris

For a next step, we plan to pull the drivers off of the good horn and a bad horn and see if we can spot any differences visually.  Testing the resistance of each one is a good idea.  I had not thought to do that test.

[Tim McCulloch]

For a next step, we plan to pull the drivers off of the good horn and a bad horn and see if we can spot any differences visually.  Testing the resistance of each one is a good idea.  I had not thought to do that test.

DC resistance is typically about 70-75% of rated impedance.  A nominal 8 ohm coil should measure around 6 ohms.  The DC resistance may be on the drive or loudspeaker spec sheet.

[Jim McKeveny]

Recently my cousin acquired three used EAW JFX 290i speakers.  They compliment his existing inventory of four JFX 260i speakers.  One of them supposedly had a blown "tweeter" but I fixed it by moving the cross-over switch to the passive position.  No charge for that repair

This week I had some time to play so I setup my Smaart rig in the parking lot at the shop and hauled all 7 JFX speakers outside to capture some baseline transfer functions.  Things were going fine with the existing 60 degree speakers, but when I got to the new 90 degree boxes I found a couple of anomalies.  Two of the speakers, Garth & Kid Rock, have pretty big dips centered around 3 kHz (first screen shot).  At first I thought that maybe it was a polarity issue with their horns, but that was not the case.  Trisha (red trace) is the good speaker.  She matches the responses of the four JFX 260i speakers pretty closely.  All of this testing was done with the cross-over switches in the Passive position and no additional DSP was used.

Today, I went back to the shop and measured the three 290i speakers again, but this time I put them in Active mode.  I used a preset that I had created for a 260z so, while it's probably not quite correct, it is close enough to let me look at how they respond with the internal cross-over bypassed.  I tried a number of things, but the one that I feel is most revealing is a comparison of the three speaker's Hi outputs.  Trisha is in red again.

My question for this tribe is; what is the most likely cause for the high frequency response differences in Garth & Kid Rock?  I opened up Kid Rock and his horn driver is definitely an EAW part (p/n 0011626)  It also has DN14/3002-8 on the back of the driver.  My guess is that they have non-OEM replacement diaphragms in them.  Is that it, or could there some problem in their passive cross-overs?

I have a similar issue with one of the Meyer UPA1 (passive) speakers at a club where I work so I'm interested to hear what the experts here think could be the cause of the variation in these transfer functions.

Contact corrosion, non-OEM diaphragm or incorrect impedance diaphragm, leaky caps, devalued resistors, blocked throat,....

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