Electronic Crossovers Unleashed

Dynamic Range

(Read my Electronic Crossover Primer first if you are unfamilier with electronic crossovers.)

2010-01-19. I wrote these pages more than 10 years ago, using the best information that was available to me at the time. I recently discovered one page that is much more authorative than mine. See Siegfried Linkwitz's (of Linkwitz-Riley fame) site. In particular, see his page on active filters. Spend some time on the rest of his site, especially on the pages linked from the "Concepts" section. If you want to really do it right, follow his advice.

Now that you have that CD player with all those wide digital dynamics, wouldn't it be nice to actually hear some of those dynamics? Conventional speakers that are usually used for home stereo use have a sensitivity rating hovering around 90 db. (Probably worse.) Audax's professional series PR170X0 6 1/2" midrange driver is interesting, because it has a sensitivity of 101 db! That's with no steenkin' horn, just mounted in a baffle. You would probably have to use 4 or 8 conventional "hi-fi" drivers, driven with several thousand watts of power to equal the output. And the PR170X0 is a high fidelity device. It goes from 500 to 7,000 Hz. You can get it from Madisound or Zalytron. (About $100 each.)

I'm less impressed with Audax's companion PR120I1 horn tweeter for home use, because the dispersion is too narrow. And it's a horn. But the combination makes a killer PA top end with only one tiny steenkin' horn at 7k rather than the usual large steenkin' horns that PA speakers usually use that cover the critical midrange that the PR170X0 covers hornlessly. (Professional (i.e., PA) high effiency, high power woofers are less attractive for home use, because they have a tendency to either not have sufficient low frequency extension (80 Hz), or to want a 10-20 cubic foot box. HOWEVER, you could use one of the 80 Hz woofers (say, from the Audax pro line) in conjunction with the PR170X0 to get 100 db sensitivity from 100 Hz up in reasonable (less than 3 cubic feet) sized boxes. And then get creative in subwoofers, say by building several 10 cubic foot boxes in your basement, vented into your listening room.... Well, why not?)

If you are interested in upgrading your system to have a wide dynamic range, then a reasonable starting point, if you already have a typical collection of medium power receivers and commercial speakers, is to get a pair of PR170X0s and a $250 electronic crossover (see below). Mount the PR170X0s in some small box with some acoustic stuffing. (Parts Express has suitable boxes for $16 ea. Get a $10 bag of Acoustic Stuff (acoustic stuffing) while you're at it.) Power down! Connect your CD player directly to the electronic crossover. Set the x-over to 500 and 3-5,000 Hz. Connect your receiver/amps to the outputs of the x-ver, with the low going to whatever of your existing speakers has the best bass, the PR170X0s to the mid, and the highs to some small speakers that have half decent tweeters. Power up the x-over first, then everything else. Turn the master volume on the x-over to a low setting. Turn the low amp down. Play a CD. Adjust the balance of the high and mid. Then turn up the lows to taste. When you get the outputs balanced, you can then turn up the main volume. Note that while you shouldn't set the low crossover point much below 500 Hz, you can twiddle the high (3-5,000 Hz) point, UNLESS you are using a bare tweeter instead of a finished speaker that already has a crossover, and, hence, won't be damaged by low frequencies.

After a bit more tweaking you should have a system with much greater dynamic range than you (probably) ever heard in a living room. The midrange (coming from the PR170X0) should be very lifelike. The rest.... Well, you are now in a real good position to upgrade the rest WITH NO PASSIVE CROSSOVERS. (You might want to do a little bit of research on driver protection before you connect a bare tweeter directly to the output of an amp. I use amplifiers that mute the output for a few seconds after power on.)

What? You say that your wife is making comments about all that junk piled up with a million wires? Note that that inexpensive pro sound x-over that you just bought is rack mountable. If you are a woodworker, check one of those pro sound catalogs until you find rack rails. (About $40) Also note that pro sound amps are rack mount. (Watch out for loud cooling fans, though.) You are a woodworker.... If you are not a woodworker note that you can also buy various kinds of rack style consoles for several hundred dollars, or so.

What? You aren't impressed with plugging your CD player directly into the electronic crossover and having to adjust the left and right master volume controls spearately? Well, if you are lucky, one of your receivers will have separate preamp out/power amp in jacks. Look on the back for any jacks with a u-shaped metal strap connecting them. If you do, good. Power down, double check the label on the back panel, and remove the strap. Connect the jacks labeled Preamp Out to the input of the x-over. Connect the output from the x-over that used to go to a regular input on the receiver to the (recently unstrapped) Power Amp In jack. Finally connect your CD player to a normal input jack. All set. Now the controls on this receiver will control everything (volume, tone, input switching) like you want it to.

Not so lucky? The next cheapest solution is to mount a volume control in a box and make a "passive preamp." Radio Shack makes a audio selector box that costs about $15. You want one of these, a 100k dual gang volume control ($3) and a knob. If you already know what to do from here, do so. Otherwise, you might want to ask a technical friend. Hint: it involves a drill, an Exacto knife, wire, and a soldering iron. (You won't blow anything up no matter how you put it together. The worst that could happen is that it wouldn't work.)

The next solution is to go to a reasonably high-end stereo store (not Radio Shack!) and buy a preamp. You probably won't be amused when you find out that just buying the front one third of a receiver (the volume control and selector switch) will probably cost about $300-600 (or more if you go to an audio salon instead of a plain old stereo store). Ask the friendly stereo store salesperson (or audio salon personal consultant) why this is so. Right after you ask to see his selection of 3-way electronic crossovers. Or a receiver with pre-out/power-amp-in jacks.

Note that my discussion has been assuming that you are using a regular old two channel stereo system. If your system is a home theatre surround sound system, I'm referring to what are now known as the front channels. And you probably do need a separate preamp, probably something like the Carver CT-26v A/V Preamp/Tuner that has all the Dolby Pro Logic stuff and preamp outs. $599 from Crutchfield. You also might find one (or two) of their 5 channel power amps handy.

Power up, power down. One other tricky thing is having to turn the x-over on before the power amps (and off last), in order to avoid speaker damaging THUMPS. Crutchfield offers the Panamax Max 100 Plus AC line conditioner that has sequential start-up/shut-down. $279. Sigh. Well, if this was easy, then everybody would be doing it. (If you decide to buy new power amps, get ones that have the speaker outputs disconected during power on--power-on mute.)

One of the Raven high efficiency ribbon tweeters might be a good tweeter for the PR170X0 for home use, if you want to use a passive crossover (I use electronic) but expensive at $200-$400 each. Available from Zalytron, MCM Electronics, and Speaker City U.S.A. They have a waterfall plot that is to die for!

Otherwise, choose a good, reasonably high power handling dome tweeter. Because most dome tweeters designed for home stereo use are about 8-10 db less efficient than the PR170X0, you pretty much have to electronically cross it over. Still, having such a tweeter driven directly, rather then getting the left-overs that are dribbled out by a passive crossover is much more satisfactory. Cymbals don't wimp out on the loud parts anymore!

One further advantage of the path that I am trying to lead you is a tendency to to keep each driver in a separate enclosure. This helps prevent unwanted enclosure resonances from interfering with other drivers. Also, you have a "mix-and-match" system that you can upgrade in piecemeal fashion. Also, if for any reason you have second thoughts about a completly electronically crossed over system, it is real simple to substitute a pre-built commercial speaker in for the high-frequency parts and use the low frequency driver as a subwoofer.

You might want to delve a little bit further into learning more about speaker design. The main thing to remember with this approach is that the roll off from an electronic crossover is symmetrical and you should look for drivers that are reasonably flat in their pass band, because you can't easily correct driver response abnormalities using an inexpensive electronic crossover. Try to choose drivers that are flat beyond the region that you will be crossing them over. The Madisound catalog contains frequency response graphs for all the drivers that they sell.

Thus far, I have not really mentioned setting levels. Even though you can probably do it by ear, I really recommend a good speaker testing system. I use the Liberty Instruments Audio Suite.

For an example of a commercial, very highly regarded (but expensive, alas) system using the PR170X0 and an electronic crossover, see the Waveform Mach 17. ( Closeup view.) See Stereophile, June 1997, and The Audio Critic, Issue 24. (Hint: take a good close look at the Vifa D27TF-35-06 tweeter ($25 ea.).)

Note that the Waveform company is now out of business and the Mach 17 is no longer availabile. But it was a very highly regarded speaker system.

1999-10-17 Note. Apparently the Audax PR170X0 has been discontinued. Waveform is now using a different, but similar, Audax midrange driver.

2010-01-19 Note. Waveform is no longet in business. But equivilent components are still available. See the 2010-01-19 note on for more. I guess I need to update this every decade, or so.

Wayne Larmon can be reached at wlarmon@nycap.rr.com

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