DIY Crossover/Filter: Power Handling - diyAudio
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Old 19th October 2012, 09:29 PM   #1
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Default DIY Crossover/Filter: Power Handling

Hey everyone,

Been creeping the forums for years, asked a few questions a while ago, but now I'm actively building and playing around with stuff.

I've searched around as much as possible, but I'm still confused about crossover power handling.

I've been working on 2 bass cabs for a friend, a 1x15 and a 4x8. On the 4x8 I'd like to add in a high pass filter set around 500hz, and the required numbers were easily figured out using a few calculators I've found.

I'm still stumped at the power handling of crossovers. I understand that for the capacitors it's based off the voltage, and with the coils it's the wire, but how do you reach high power handling?

The 250v caps, which are the highest voltage caps I've found (and I think exist?) can handle 500w. Then depending on the coils, it's anywhere from 180w to 600w. Is the power handling additive? As in if I used a 250v cap and a 180w coil, I'd have around 680w of power handling for the crossover? How does it work?

My dilemma is that the four 8's can take 600w RMS in total. Granted they aren't going to be pushed by that much power, but I wanted to be safe and also understand this for future high power builds.
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Old 19th October 2012, 11:01 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

For a live rig its highly unlikely a 1x15 and 4x8 will work best with a 500Hz x/o.
Raw parallel will usually work a lot better. A capacitor for the 4x8 might work.

rgds, sreten.

Owner of the old school 1x15 + 4x10 bass set up.
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Old 20th October 2012, 03:38 AM   #3
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Is there a reason why that would be? My reasoning was so that the 15 will just have to focus on the lower frequencies, and the 8's can handle the mids/some low mids and there wouldn't be a chance for over-excursion of the 8's. Is that correct?
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Old 20th October 2012, 04:04 AM   #4
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Quote:
Originally Posted by RattusNorvegicus View Post

250v caps, which are the highest voltage caps I've found (and I think exist?)
Fast Capacitors 630v-1500v PPE, PPM & PESG Polypropylene

dave
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Old 20th October 2012, 11:09 AM   #5
AndrewT is offline AndrewT  Scotland
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I would choose speaker capacitor voltage ratings (just like the Zobel caps across the output of power amplifiers) at twice the maximum output voltage of the power amplifier.

500W into 4r0 is equivalent to 63Vpk.
Double that would be 126V as the minimum rating according to my method.
250V would be 4times your maximum voltage. That seems excessive.

If I had PA speaker experience I might be tempted to try 100V capacitors, but I don't have that experience to inform that decision.
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Old 20th October 2012, 12:30 PM   #6
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by RattusNorvegicus View Post
Is there a reason why that would be? My reasoning was so that the 15 will just have to focus on the lower frequencies, and the 8's can handle the mids/some low mids and there wouldn't be a chance for over-excursion of the 8's. Is that correct?

Hi,

If the amplifier can handle both cabinets together over the range they
both work together output will increase by up to 6dB over one cabinet.

As a bass player I'd like the option of just using the 1x15 on its own
and adding the 4x8 when needed for more midrange punch and top end.

Depending on the drivers and cabinet designs and the amplifiers power,
the 4x8 may not run out of steam in the bass before the 1x15 does,
noting the 1x15 will be reproducing much more of the low bass.

This happens with well matched cabinets, no x/o are needed at all.

A bass "Bright Box", say a 2x10 for a 1x15, has restricted bass
but decent power handling. At lower levels with some bass boost
it can be used on its own. With the 1x15 it goes at lot louder due
to less overall bass boost in the signal being applied to the cabinet.

rgds, sreten.
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Old 20th October 2012, 06:18 PM   #7
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Quote:
Originally Posted by AndrewT View Post
250V would be 4times your maximum voltage. That seems excessive.
Sometimes that is the lowest voltage you can get (ie Solen FastCaps)

dave
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Old 22nd October 2012, 03:58 AM   #8
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Thanks for the input everyone, just found out that the amp has a crossover so I'm going to leave the cabs without filters. Thanks sreten. It's only putting out 200w rms per channel supposedly, so I doubt that's going to cause any problems.

@planet10 thanks so much for that link, I'm guessing those high voltage caps can handle a lot more power. So helpful that it's a Canadian link too, really, thanks a lot.

For future reference though, I know I was talking about filters but how would an actual 2 or 3-way crossover's power handling be calculated?
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Old 22nd October 2012, 09:30 AM   #9
AndrewT is offline AndrewT  Scotland
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A crossover is made up from filters.
In it's simplest 2way form, the crossover is a single pole high pass filter plus a single pole low pass filter.
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