Active crossovers

Active crossovers are a tricky topic, imho.

I'd recommend using an active xover for subwoofers and a passive xover for the rest in general.The advantage here is that you can use a clean, high power amp for the sub bass and select an amp that is optimal for the main speakers (as compared to driving everything from one amp)

It is very easy to muck up some very high quality sound with a not so wonderful HP filter made from not so wonderful opamps and caps (not to mention the power supply).

On the other hand it is possible to implement surprisingly clean and good xovers with both tube and solid state parts. Regardless, it is a good practice to compare the speaker in question with and without an active xover in line.

Much depends upon you, your ears, and your system as to wheather or not an electronic xover will be an improvement or a deficit. Which means there is NO single answer.

In general, the commercial "pro sound" products do not have truly audiophile "sonic signatures" so I would be cautious about them in general.

The advantage of an electronic xover for a DIYer is certainly one of flexibility and ease of adjustment, so it has merit on that point. On the other hand you do need an extra amp or so to use it, so perhaps the money is better spent in other directions?

Ymmv with electronic crossovers in general.

_-_-bear

Matching two amps is trivial.

There is no matching to be done, other than level setting. Just about every electronic crossover has level adjustments for every band.

Regardless of the "gain" of an amp, when you increase the input by 3dB, the output goes up 3dB. So, all you have to do is to put a level into amp 2 that when compared at the speaker output using pink noise gives the *same* level on your SPL meter as does amp 1. Of course, your ear will be the final arbiter of the precisely perfect relative levels.

If your electronic xover does not have level controls, and your amp does not either, you can either build a fixed pad into a small box - after measuring the dB difference with no pad. Or you can buy an after market in-line adjustable attenuator box to put in line with the amp that is "too loud" to reduce its level. Alternately, you can drill some holes into your amp and put a small rotary switch with MF resistors and make your own attenuator built in,or just put a decent pot there... I do that all the time on Phase Linear 400s that are used as subwoofer amps from time to time (on the front panel of the PL400, to match the PL700).

All done.

_-_-bear

Let's be clear, these are LEVEL controls, NOT "gain" controls!!

We call them "gain" but 99% of the time they set the output level of a fixed gain circuit. To change the gain of a typical solid state circuit you need to change the feedback resistor. Few circuits (for good reasons) actually permit you to adjust the gain of a stage directly.

It is standard practice to build in "excess gain" so that you can set a level control midway - in fact the volume control only LOWERs the level down from maximum.

On power amps 99.9% of all level controls are right at the input of the amp, before any active circuitry. Again they only serve to lower the input level to the front end.

There are some exceptions, like the Crown Macro Techs which if I recall actually has a neat circuit that adjusts gain, not level, in order to *set the level* then sent on to the fixed gain remainder of the amp...

Again "gain" is not an accurate description of this control, although we all tend to use the term!

_-_-bear