Passive crossover for subs

Hi all

I have two active 15” tannoy subs. One of the sub amps is now dead.

My plan is to use the two subs as passive boxes and drive them with a spare Bryston 3b I have in my studio.

Can someone advise me how I can build a couple passive crossovers for them? I’d like the cutoff to be around 80hz with perhaps a 12db/octave slope.

Is this viable using inductors and capacitors? Any issues with quality?

TIA
 
Because of the large values required, film capacitors and air cored inductors would be very large and expensive.

You would probably be restricted practically and financially to the use of NP electrolytic capacitors and ferrite cored inductors.
 
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diyAudio Moderator
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I have used speaker level (passive) crossovers many times at sub frequencies. It is a means to an end and it can give satisfactory results. Your concern about component quality, whatever that means, seems out of step with the more important properties of where to cross, the slope, the speaker configuration and room positioning.

In some instances an inductor core may be rendered ineffective by using it at sufficiently high levels, and if you discover a problem you can rectify it. Also, inductors don't get hot except via their parasitic resistance when used at high levels so feel/smell them early in the process to see they're handling the way you're using them.
 
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Go price out the cost of a 3rd order passive filters for this because 2nd order won't be enough and even a 3rd order is marginal IMO... there will still be audible mids getting through, and then look at what buying a used analog active crossover would be. Ebay has units like the DBX 223, Rane AC22 and soe others for about $100, these have 4th order LR filters and some also have summing options.
 
music soothes the savage beast
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I would just add this on bryston input and be done.
 

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Hi all

I have two active 15” tannoy subs. One of the sub amps is now dead.

My plan is to use the two subs as passive boxes and drive them with a spare Bryston 3b I have in my studio.

Can someone advise me how I can build a couple passive crossovers for them? I’d like the cutoff to be around 80hz with perhaps a 12db/octave slope.

Is this viable using inductors and capacitors? Any issues with quality?

TIA

Yes, a passive low-pass filter is easy enough to make. I've never believed phase shift matters much outside of a spreadsheet or a laboratory. The other option (dependent on the TANNOY amp specs) is to connect the cabinets in parallel - active monitor style. Simply create a Speakon output working amp, and am input of the dead one. This of course, assumes the drivers are 8 ohms and the plate amp is capable of 4 ohms.
 
I have two active 15” tannoy subs. One of the sub amps is now dead.

My plan is to use the two subs as passive boxes and drive them with a spare Bryston 3b I have in my studio.
If going the air-cored inductor route, then they will likely have a quite high DC resistance. This will result in a lot of power being dissipated in the coils. A 2nd-order filter might be somewhat lacking in steepness if the original subwoofer amplifier used 4th-order low-pass filters. A 4th-order passive low-pass filter would need very large component values, which means the inductors will be quite costly.

Under these circumstances, maybe a replacement subwoofer plate amplifier is a viable and more cost-effective approach?