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Author Topic: LR-4 crossover still allows lows in tweeter. Cap on negative output of tweeter?  (Read 11107 times)

Jeff Schoonover1

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PS - Jeff, sorry for the off-topic post.
No worries!  I like the stained cabinets.  Sets you apart, and touch-up is simple.
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Jeff Schoonover1

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I've been operating with the underlying uncertainty that if the FRD file doesn't have the 7kHz spike, then it may be based on measurements that are not valid.
If that is the case, then any design work done on the basis of that file may also not be valid.
David -
Now I know where I'm miscommunicating to you guys. Apologies for not being clear myself. 
Okay, so we know that when the drivers are measured alone, with no processing, etc. we get the response (and the .FRD files) I linked to in post 75. - i.e. no 7K spike.
We know a 7K spike is introduced when my passive X-over is placed in the series.  This is what we're troubleshooting.
 
BUT - and here's what I'm getting at.  When we switch from my PASSIVE crossover in the box, to the ACTIVE one in my amp (same cable, same amp, box, connectors, drivers) we get the SAME 7K spike.  IOW, why is that spike still there with a supposedly optimal active, digital crossover?
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David Morison

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David -
Now I know where I'm miscommunicating to you guys. Apologies for not being clear myself. 
Okay, so we know that when the drivers are measured alone, with no processing, etc. we get the response (and the .FRD files) I linked to in post 75. - i.e. no 7K spike.
We know a 7K spike is introduced when my passive X-over is placed in the series.  This is what we're troubleshooting.
 
BUT - and here's what I'm getting at.  When we switch from my PASSIVE crossover in the box, to the ACTIVE one in my amp (same cable, same amp, box, connectors, drivers) we get the SAME 7K spike.  IOW, why is that spike still there with a supposedly optimal active, digital crossover?

Well, the answer is whatever was different about the measurement run that generated the spike-less data.
It might not be obvious, but there must have been something else different.
When you got the flatter measurements, was the switch perhaps out of circuit, but in circuit for every other measurement?
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Chris Hindle

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BUT - and here's what I'm getting at.  When we switch from my PASSIVE crossover in the box, to the ACTIVE one in my amp (same cable, same amp, box, connectors, drivers) we get the SAME 7K spike.  IOW, why is that spike still there with a supposedly optimal active, digital crossover?

The passive X-over is COMPLETELY disconnected from ALL the drivers, right?
Chris.
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Ya, Whatever. Just throw a '57 on it, and get off my stage.

Jeff Schoonover1

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The passive X-over is COMPLETELY disconnected from ALL the drivers, right?
During "active" mode (the amp's crossover is being used with both channels) The negative of the woofer remains connected to the negative of the passive x-over. But there is nothing in series on that pathway, from the woofer to the negative terminal on that channel. The high side is switched to its own channel and not connected to the passive crossover at all.
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Jeff Schoonover1

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Well, the answer is whatever was different about the measurement run that generated the spike-less data.
It might not be obvious, but there must have been something else different.
It 'could' be possible that I didn't defeat the EQ when running the full-range tests, but I really doubt it. Plus, I would have had to do that twice. Still, 'doubt' and 'sure' are two different things.  I'll check when I can.
When you got the flatter measurements, was the switch perhaps out of the circuit, but in circuit for every other measurement?
When I inadvertently leave it on, depending on which output jack its connected to on the amp, it either crosses over the lows only side from the active or already crossed over mid/high and sounds... very. very. bad. LOL. It's very obvious and I wouldn't have missed it.
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Jeff Schoonover1

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Well, the answer is whatever was different about the measurement run that generated the spike-less data.
I feel dumb, LOL  I didn't take the EQ out for the run in post 75.  The driver with no EQ applied attached to the horn in the box has the 2-3K slump, and the 7K spike.  I have a strong feeling it's because of the small, non-optimal horn.  Unless I want to make a much larger box to accommodate a better horn, I'm stuck with what I have.  Practicality overrules box size because I don't want to have a much bigger box to haul around for a bass rig.

So, when the active OR the passive X-over is run, without EQ, they both display very similar curves.  A slight improvement might be had to bring the passive response closer to the active response with a re-make of the passive x-over.
But since both crossovers are pretty similar already, the bigger issues - the 7K spike and 2-3K slump - aren't going to be improved with a crossover redesign nearly as much as with the right horn.  Barring that, EQ applied yields greater results.
One thing is for sure, I'm learning a lot from you guys, which is always cool!
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Jeff Schoonover1

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So I was looking at phase shift.  There was quite a bit at the x-over frequency.  I hard-wired the CD out of polarity, which got rid of the phase shift at the x-over frequency.  As a bonus, much of the 2-3K slump was gone.  Now I just had the 7K spike to deal with.  I was able to apply 2 fewer bands of EQ to flatten things than before.  Now I'm only using two bands of EQ, and getting pretty close.
I played around with the X-Over sim quite a bit today.  To really set things right would require a start from scratch.  Resistors aren't practical, because I was seeing as much as 60 watts dissipation necessary to do some of the repairs we talked about.
The 2-3K slump and 7K spike is from the horn I'm using, I'm pretty sure.  To *really* do it right means a new box with a more well-suited horn and a crossover re-make.  A project for another time perhaps, but for a bass rig, it will do for now.  No one listens to the bass player anyway ;)
I sure appreciate everyone's help and suggestions.
« Last Edit: April 08, 2018, 03:54:15 pm by Jeff Schoonover1 »
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