Looking for input: Crossover /w adjustable A/B components

[technodanvan]

I'm looking for some input on an idea that I wanted to bounce off the smart guys here.

Whenever I read some of the ideas and opinions behind choices in crossover components and heck, even whole speaker and amplifier differences I'm exposed to descriptions that have no definition in my head. Things like "switching to NPE's will suck the life out of the speaker" or "XXX capacitor provides more air and definition than YYY capacitor". Things like this. Some people have drawn pretty distinct lines and will only go one way or the other. Some may debate whether such difference or audible at all, or whether they may be related to variations in crossover components values more than the type of cap, resistor, etc. I have always had some opinions but they have only been based on other people's experiences - I'd like to experiment a bit to hear what I hear and come to my own conclusions.

To that end I'll be putting together a set of Tony Gee's "Black Box" speaker in the next year or two. I'm still accumulating the parts slowly as I'm really in no hurry. Links to the design (and some related commentary) can be found here, here, and here. I'm sure plenty of people will mention that I could do this experiment with a much cheaper design or at least one with a more conventional crossover. I'm really not interested in this input - the choice has been made and the speakers will be constructed (more or less) as-is.

I intend to build both crossovers in a single separate box for a couple reasons, the primary one being I doubt my capability to make them nearly as compact as Tony managed to do it. It also opens up the ability to have those options I'd like to try out.

Depending on the amount of room I have available I probably can't cram all the options I want in there. Yes, I'd like these to be easily adjustable in the future to remind myself what said differences can make. As simple as it would be to use a breadboard or something I'd like it to be permanent if possible.

Some of my goals at the moment:

1. Can I hear a difference between NPE and non-NPE caps?

2. Can I hear a difference between an NPE cap and an NPE cap with a decent bypass cap on it? Does it matter the quality of the bypass cap?

3. Can I hear a difference between other caps of varying qualities? (i.e. Jantzen Z vs. Dayton Poly?)

4. In the design Tony mentions a certain resistor can be changed to different values for a more forward midrange. I'd like to put all of his available options in there to try them out and hear what I hear.

5. I'm open to other suggestions as well.

So, on to the questions.

First problem is I'll either need to construct my own cables or have three pairs of interconnects going to each speaker from the crossover box. I'd rather make my own cable using Speakon connectors. Question: Will I have an issue running all three pairs of cables running together like that at a length of ~8 feet? Are there potential problems using a Speakon connector?

Next, I'll be constructing the crossovers either in a custom made A/V-sized box OR (and the more likely option) I'll just buy a nice empty amplifier chassis from the diyaudio store (or similar). Differences in components will be selectable by either toggle switch or knob on the front panel. I assume that simply by using switches and whatnot that I'll introduce at least some (hopefully) minor effect in the audio path. Is this something that could ruin the whole project? Are there "better" switches that I could invest in to avoid potential issues?

Other questions:
Will switching individual components, while under power, be an issue for the health of individual drivers, crossover parts, or the amplifier?

Will having an A/B switch (i.e: set the left speaker to "ideal" crossover components and the right to other settings and switch between them, while having the option to run both) cause amplifier issues?

I should note I don't have an amp I was intending to use for this. If that makes a difference please feel free to mention it.

I think this covers most of my initial questions. Like I said it's going to be a while, but I'm looking for any input and/or ideas. I'm sure some of you guys have done something similar (if not less permanent) in the past.

[BOBinGA]

Hi Danny,
In my last project, I built a switchable crossover with both 2pi and 4 pi versions that I could flip a switch and change. I did that under power more times than I can count without any problems with either amp or speaker crossover parts. Also as part of my development efforts I also used an external switch box that used a mechanical rotary switch to change the output of my amp between two separate speaker pairs. Again, no problems.

I don't think you will have any problems with your plans as long as you use a solid state amp. Solid state amps have no problems with open circuits. It short circuits that they don't like. Any switch will have a split seconds between switch positions where it is open momentarily and solid state amps should not have any problems with this. However, tube amp are the opposite. They must have a load at all times and do not like open circuits. So use a transistor amp and you should be fine.

-Bob

[technodanvan]

Thanks for the input Bob, I'll definitely be using a solid state amp. Glad to know I should be okay to switch between components during operation.

Any input on the switches themselves lending a 'voice' that could negatively effect the experiment?

[BOBinGA]

I can't say if the switch would have a "voice". but I doubt it. You are just switching wire to wire. In my case, I was switching between entirely different speakers that had their own differences that were easy to hear and I doubt the switch had anything to do with the differences. As long as your wire runs to each speaker are similar length and are reasonably short (under 20 ft or so) and at least 16 gauge, you shouldn't hear a difference caused by the switch itself.
-Bob

[technodanvan]

Thanks again for the input Bob, it makes me sleep better at night knowing I at least have a shot at making this work.

[Bill Schneider]

First problem is I'll either need to construct my own cables or have three pairs of interconnects going to each speaker from the crossover box. I'd rather make my own cable using Speakon connectors. Question: Will I have an issue running all three pairs of cables running together like that at a length of ~8 feet? Are there potential problems using a Speakon connector?

With a short run of 8', you might not have any crosstalk problem with your cables, especially if they are separate. If separate, I wouldn't worry. However if you use a 6 or 8 conductor cable, you might get some crosstalk with longer runs. I used PE's 8c speaker wire with active crossovers for my LX521s, terminated with Speakons.

A member of the Orion/Pluto did some crosstalk measurements as a result of Linkwitz' caveat to be careful about the conductor pair choices. The wire he (Drew) used was either an older version of the PE wire or Belden wire, and had different color codings for the conductors. I put his results into a spreadsheet and correlated the best pairs to the PE wire that I used...

[technodanvan]

Thanks Bill, I didn't expect graphics!

I'll probably wind them all together, though I suppose I could do it with four wires instead of six. We'll see. Thanks again!

[Bill Schneider]

Thanks Bill, I didn't expect graphics!

I already had the graphic on the web, so adding a link was easy. Your plan sounds fine.

My memory is getting so bad that if I don't put construction notes and diagrams on the web, I forget how I did things. I suspect that my last audio project, spanning three lengthy web pages of notes, is a reflection of how bad I'm getting. 8O

[BOBinGA]

Danny,
Here is the switch box I built many years ago while I worked in an audio store. We wanted a way to play the same speakers and same source while switching between power amps to see if we could hear the difference between amps. It actually turned out to be quite adaptable for many purposes. It's basically a two position 24 pole switch.

Here is the working end. You attach a low level input LR pair and it is switched between the two output pairs near the rear of the box. I have it set up at the moment backwards to switch two different computers to use the same amp attached to the front pair near the switch.


Here is the speaker switch end. Again, One input pair and two output pairs. I am not using this section at the moment.


Here are the guts of the switch. Don't ask me to diagram it. But it uses a two position rotary switch that I think cost about $25 in 1975, so its probably $100 now if you can find one.


Finally, here is the little AXXESS car audio load balancer from PE that I use when I switch between power amps running different speakers to get the volume of both speakers nearly the same.


-Bob

[technodanvan]

Any idea where decent quality rotary switches can be purchased? I'm thinking up to 4 position, if possible.

[BOBinGA]

Allied looks like they have a good selection:

http://www.alliedelec.com/sensors-switches-relays/switches/

Maybe something like this:

http://www.alliedelec.com/search/productdetail.aspx?SKU=70152226

It looks like you would want a non-shorting type. 1 amp @ 100v should be enough unless you are planning full power testing.

Try Mouser, Newark and digikey too.

-Bob