Options for high-pass to monitors?

[Rbrockman]

I'm looking for some practical advice on what equipment some of you are using to high-pass between monitors and bass-bins/subs when not using a receiver in a 2-channel audio only environment.

My current setup is as follows:
Duet --> DAC --> Amp --> Monitors

I'd like something able to pass 50-80hz and up at 12db/oct

For passive devices, I've found:

http://www.audioc.com/accessories1/misc/balhp.htm

(anyone DIY something like this?)

Active devices include:

http://www.hsuresearch.com/products/high-pass-filter.html

http://www.behringer.com/CX2310/index.cfm?lang=ENG

I suppose the active cross-over would allow for adjustablility and tweaking, but is this at the expense of fidelity? I'd really rather not go thru another A/D conversion.

Since this is a DIY forum, any DIY efforts would be interesting.

Your thoughts appreciated

[Kal Rubinson]

1. Take a look at the Marchand offerings which you can built or adapt. No need for an A/D conversion.

2. Build a simple passive HP filter, before or after the amp.

3. Build a simple active HP filter for before the amp.

I am assuming your subs are self-powered but it would help if you told us more.

Kal

[Rbrockman]

Thanks Kal, I'll check out the Marchand offerings.

Yes, bass-bins/subs will be self-powered with their own crossover network.

I'm primarily interested in preserving as much quality as possible in the signal being sent to the amps driving the monitors.

Let's say that I want to place a HPF in between the DAC and AMP. What are some of the tradeoff's between passive and active filters?

I'm assuming that passive would preserve a purer signal with some insertion loss, but the active would allow for adjustment?

[Kal Rubinson]

Thanks Kal, I'll check out the Marchand offerings.

Yes, bass-bins/subs will be self-powered with their own crossover network.

I'm primarily interested in preserving as much quality as possible in the signal being sent to the amps driving the monitors.

Let's say that I want to place a HPF in between the DAC and AMP. What are some of the tradeoff's between passive and active filters?

I'm assuming that passive would preserve a purer signal with some insertion loss, but the active would allow for adjustment?

There are, undoubtedly, websites that cover these things but I can only recommend two books:
Colloms' High Performance Loudspeakers
Dickason's Loudspeaker Cookbook

Kal

[BobEllis]

Thanks Kal, I'll check out the Marchand offerings.

Yes, bass-bins/subs will be self-powered with their own crossover network.

I'm primarily interested in preserving as much quality as possible in the signal being sent to the amps driving the monitors.

Let's say that I want to place a HPF in between the DAC and AMP. What are some of the tradeoff's between passive and active filters?

I'm assuming that passive would preserve a purer signal with some insertion loss, but the active would allow for adjustment?

Passive crossovers have a couple of disadvantages:

1. limited to first order unless you are willing to live with

2. Insertion loss. If you implement passive higher order filters you'll lose large portion of your signal. Unless your amps have high gain, you may not be able to drive them properly.

3. You'll also have a lower signal to noise ratio, since the signal has been attenuated and you've added resistor noise.

4. They are also a bit more difficult to calculate than active since each succeeding stage presents a different load to the filter affecting its response. You also need to include the input impedance of your amps when calculating filter values.

IMHO, active is the way to go since most current mid/bass/mid drivers really need at least second order electrical filters to control cone breakup and limit low end excursion. I and others have made active crossovers on perfboard, not as easy as using a PCB, but doable with care and patience.

AFAIK, the Marchand units use a state variable topology that create high and low outputs from a single filter. Many are happy with the sound, others are dissatisfied and prefer the sound of Sallen-Key topologies. I haven't heard a Marchand.

The disadvantage of state variable in my book is that it does not give you the flexibility to have different cutoff frequencies, slopes, corner shapes or spread frequencies that allow for phase compensation and EQ without a separate stage. Straight textbook symmetric filters are fine if your drivers are reasonable flat for an octave or so beyond the crossover frequency, so you might not need the flexibility.

A good reference for active filter design is http://www.linkwitzlab.com/filters.htm

Construction hints - make a good power supply (my discrete regs were a big step up from 7815 regulators), decouple the opamps well with good qualtiy 100 nf caps, use decent opamps. The OPA2134 is a nice sounding amp. There are others that are favored by audiophiles, but if they're good enough Linkwitz, they're good enough for me and they do sound better than the NE5532 without costing an arm and a leg.

[alias2]

You can reduce the amplifiers input capacitor to form a filter.
You can also built a 2nd order highpass using the amplifier as a big op-amp.

For the 1st possibility you can also drive an inverse 1st order filter from
the amplifier output into the subwoofers inputs, then use sub as normal.