Ghetto subs

manu et deo

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I'm trying to run some ten inch subs on the b speaker input but I'm sure I need a filter to cut off the highs. Any advice? Thanks in advance.
 
a choke (inductor) in series with the signal being applied can be used as a "low pass" filter to feed the "subwoofers". You need to know the (nominal) impedance of your woofer(s).
This is a first order crossover topology (6 dB per octave rolloff).

calc_cr_06db.gif


(the "bottom" figure above shows what you'd want to do for your "subwoofers".)

Here's a calculator -- you'll have to enter impedance values for the 'high pass' (which you don't need) and the 'low pass' legs to use it.
http://www.apicsllc.com/apics/Misc/filter2.html

This calculator will also 'do' a second order crossover (12 dB per octave), or even higher order, if you prefer. I'd suggest at least starting with a first order topology, though, as it's simplest :)

PS "Air core" inductors are generally preferable to the "iron" (or ferrite) core inductors, if size and cost aren't major factors.
 
Thanks for replying. They are Dayton sda270a-88 in 2ft3. Amp either b side of. Kenwood m2a or Fisher ca276 or crown whatever I have laying around:)
 
If you have a parts bin laying around with some fairly large inductors there would be a cheaper way as posted by mhardy. Trouble is if you have to buy L1 it's going to be rather large.
 
I once ordered "passive subwoofer" crossovers from Parts Express for a similar project, many years ago. It actually worked great, BUT you need a way to balance the high output vs. the low output....you'll probably need a lot more power going to the "subwoofer" than to the main speakers. Just using the "B" speaker outputs on an amplifier, it will be a little harder to do this.
 
Manu, if you have extra power amps lying around, why not make a simple line level crossover (R/C network) and go bi-amp?
 
It's not necessary to buy an electronic crossover in order to have a true bi-amp system. You can make simple high-pass and low-pass filters that connect between your preamp and multiple power amps. There are online calculators intended for speaker crossover design that easily scale up to line impedance level, or you can work from filter cookbooks or published sources such as THIS.
 
I just ordered a Rolls SX45 crossover for system, but I'm concerned it may not be up to the quality standards of the rest of my equipment.

Building my own is an intriguing idea, but I doubt if I have the ability to do it. I can solder PC boards no problem, but can't design circuits.

I'll start here: https://en.wikipedia.org/wiki/RC_circuit

It's not necessary to buy an electronic crossover in order to have a true bi-amp system. You can make simple high-pass and low-pass filters that connect between your preamp and multiple power amps. There are online calculators intended for speaker crossover design that easily scale up to line impedance level, or you can work from filter cookbooks or published sources such as THIS.

You're saying I can step up the impedance of a passive crossover, and use it at line level. Line level crossover networks are active, not passive.

I would need to boost the gain, right ?

What's the easy impedance conversion from speaker level to line level ?
 
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Line level crossovers can be active or passive, but active crossovers offer more flexibility. Additional gain is unnecessary as long as the power amps have adequate sensitivity. When using an online calculator for passive networks, just enter the amp's input impedance instead of driver impedance. Alternatively, you could load the crossover network with an arbitrarily low resistance, to swamp out amplifier input Z variations. You can make high-order passive line level crossovers with inductors, but inductance values can get awkward and termination loading can become problematic. Here's another article that might be helpful.
 
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