Live Sound & Production

[richsmith79]

I had a pa sub that quit working last night.  I took it apart today and direct wired the speaker and it works.  I believe it to be the internal crossover.  Here is my question.  Can I direct wire the sub to the input jacks and bypass the crossover or do I need to replace it?  Will it still perform the way it did before?

[abzurd]

I'm guessing the "crossover" is just a choke coil. If you're using an external crossover then it's perfectly fine, and perhaps even preferable, to remove it. If you're not then it's not a good idea as you'll be sending full frequency audio through the sub, which isn't a great idea.

[RoadRanger]

I've burned out a few of them freakin' coils in subs  - they've always gone on me when running WAY below the driver's rating  - I've never smoked a sub driver .

[Shaster]

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richsmith79 wrote:

I had a pa sub that quit working last night.  I took it apart today and direct wired the speaker and it works.  I believe it to be the internal crossover.  Here is my question.  Can I direct wire the sub to the input jacks and bypass the crossover or do I need to replace it?  Will it still perform the way it did before?

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As abzurd has stated if you're using an external crossover that's just fine.  If you're not using an external crossover the sub will not perform as it did before.  It will perform somewhat like a driver receiving the full range,  but in a sub box. You don't want that.  All kinds of sounds that should mainly be going to your top boxes will be present in the sub - if you don't have an external crossover. 

In fact even with an external crossover the sub probably won't perform exactly as it did before - but that could be a good thing.

[agedhorse]

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richsmith79 wrote:

I had a pa sub that quit working last night.  I took it apart today and direct wired the speaker and it works.  I believe it to be the internal crossover.  Here is my question.  Can I direct wire the sub to the input jacks and bypass the crossover or do I need to replace it?  Will it still perform the way it did before?

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Have you tested the driver or is this just a guess?

First, verify that you have correctly identified the problem.

[tlbonehead]

if you aren't using the internal crossover it is much preferred that you bypass it anyway.

[Mutha Goose]

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RoadRanger wrote:

I've burned out a few of them freakin' coils in subs  - they've always gone on me when running WAY below the driver's rating  - I've never smoked a sub driver .

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On what? I've never seen a choke wired with small enough wire to fuse before a voicecoil.

[richsmith79]

I found a wire from the coil that came off the board.  I was able to sauder it back on and it works.  It turns out it was a design flaw.  The had the coil held to the board by zip ties that failed causing the coil to separate from the board.  I put new zip ties on it and put some extra electrical tape on it.  Thank you all for you're input!! One last question.  I have never ran an external crossover.  The guys in my band have talked about getting one with a sub output.  Does it help bring out the low end better or am I wasting my money. 

[RoadRanger]

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Mutha Goose wrote:

On what? I've never seen a choke wired with small enough wire to fuse before a voicecoil.

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Actually those were all Madison's with 500w drivers, and about half of them cracked the PCB rather than cooked the coil (at least the first time they died ). Come to think of it I've not cooked the coils in any of the Peavey subs I've used (PV118, PRSub). The PRSub's that I own have had coil-ectomies and speakons added.

[agedhorse]

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Mutha Goose wrote:

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RoadRanger wrote:

I've burned out a few of them freakin' coils in subs  - they've always gone on me when running WAY below the driver's rating  - I've never smoked a sub driver .

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On what? I've never seen a choke wired with small enough wire to fuse before a voicecoil.

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Nor have I, except on really poorly designed products... but that wasn'tthe fault of the wire.

[agedhorse]

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richsmith79 wrote:

I found a wire from the coil that came off the board.  I was able to sauder it back on and it works.  It turns out it was a design flaw.  The had the coil held to the board by zip ties that failed causing the coil to separate from the board.  I put new zip ties on it and put some extra electrical tape on it.  Thank you all for you're input!! One last question.  I have never ran an external crossover.  The guys in my band have talked about getting one with a sub output.  Does it help bring out the low end better or am I wasting my money. 

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Good.

What speaker was it? Sounds like some manufacturer took the poorly designed way out...

[Mutha Goose]

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richsmith79 wrote:

I found a wire from the coil that came off the board.  I was able to sauder it back on and it works.  It turns out it was a design flaw.  The had the coil held to the board by zip ties that failed causing the coil to separate from the board.  I put new zip ties on it and put some extra electrical tape on it.  Thank you all for you're input!! One last question.  I have never ran an external crossover.  The guys in my band have talked about getting one with a sub output.  Does it help bring out the low end better or am I wasting my money. 

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Good to hear. Sounds like the old SR47XXs maybe?... but then again, I've seen this on quite a few older passive cabs....

While you're at it, touch up any solder joint that looks even remotely suspect, and re-secure any other large parts. It would also be a good idea to go through your other speaker's crossover while you at it.

A decent crossover could be a very good investment if set up correctly.

[abzurd]

Yes a crossover would be a good investment. It's a better way to keep the highs out of the subs, but frankly more important, IMO, but overlooked or misunderstood, is that it will keep the lows out of the tops. This will allow the woofer in your tops to focus on the mid bass frequencies instead of flapping wildly back and forth with every beat of the kick. The result is a cleaner sound with more vocal intelligibility. Also gone are the side effects associated with putting the same frequencies through 2 different speakers.

[nchangin]

I would bet a dollar he has pv 118's (briefly skimmed this) that had the Xover go bad and I know they have the coils ziptied to board.

[Pro Sound Guy]

The series coil is an inductor.  A series coil can be put in place for those not interested in using

an active crossover for the sub bandwidth.  Typically these inductors should be removed if you

are running active.   Also, the series inductor causes a 90 degree phase shift and this is something that

is also eliminated when bypassing the inductor.   Also, there is some insertion loss with any passive

xover.   

The only component I would have any type of inductor or capacitor on in an active system is a DC blocking

capacitor on the compression driver.   If I xover a compression driver @800hz I then put a series cap that

will block from 400hz and up.  Keep in mind that even with a series cap you have a 90 degree phase shift.

[RoadRanger]

^ 

[agedhorse]

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Pro Sound Guy wrote:

The series coil is an inductor.  A series coil can be put in place for those not interested in using

an active crossover for the sub bandwidth.  Typically these inductors should be removed if you

are running active.   Also, the series inductor causes a 90 degree phase shift and this is something that

is also eliminated when bypassing the inductor.   Also, there is some insertion loss with any passive

xover.   

The only component I would have any type of inductor or capacitor on in an active system is a DC blocking

capacitor on the compression driver.   If I xover a compression driver @800hz I then put a series cap that

will block from 400hz and up.  Keep in mind that even with a series cap you have a 90 degree phase shift.

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You are forgetting that an active crossover causes exactly the same phase shift.

Using a blocking cap at HF one octave below the active crossover frequency means that any additional phase shift would occur when the signal is 24dB + 6dB (slope plus corner offset for an LR filter) down from flat.

[guitarman3001]

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nchangin wrote:

I would bet a dollar he has pv 118's (briefly skimmed this) that had the Xover go bad and I know they have the coils ziptied to board.

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Yep, those PV118s are notorious for that.  My band has one and that internal x-over has blown a couple of times.  We sent it back for repair and within minutes of getting it back it blew again.  I ended up running a speaker wire directly to the speaker and bypassing the x-over.  Those things are terrible.  I will never buy another Peavey sub if I can help it. 

[Pro Sound Guy]

OH YEA...

For some reason I was thinking there was no phase shift /active.

However, insertion loss is kind of a biggie isnt it? 3db?

Explain corner offset? 

Are you saying using a Linkwitz Riley at 24db slope?

Just curious what you mean

[agedhorse]

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Pro Sound Guy wrote:

OH YEA...

For some reason I was thinking there was no phase shift /active.

However, insertion loss is kind of a biggie isnt it? 3db?

Explain corner offset? 

Are you saying using a Linkwitz Riley at 24db slope?

Just curious what you mean

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On a good passive crossover, the insertion loss can easily be as low as 1/2 dB (in the bandpass of course) with the proper components

Corner offset is -3dB for most filter alignments, but a LR filter alignment is by definition a -6dB corner offset because it's a constant power summing function and the -6dB term is required due to the squared factor in the power equation.