Hope you all don't mind me posting frequently about speakers I'm building!
Some of you may remember the ones I've mentioned on here before that are something of a Monitor 10 copy. I've worked on them, got frustrated and put them away, pulled them out and worked some more, etc., for a while now. Now I think I've finally come up with something that I'm going to keep.
A little background, since I don't feel like looking up the old thread to link to it: I built this pair of cabinets probably 10-15 years ago. They initially housed Radio Shack drivers, an 8" ported two-way setup that sounded, .. eh.. I USED to think it sounded O.K. The cabinets were not bad for being put together by a guy with practically no tools and precious little skill. I even veneered them in cherry and they looked pretty good.
Fast-forward to about a year ago. Now pretty heavy into DIY speaker-building and armed with some measuring tools and crossover design software, I decided to take another crack at them: See if I could make them into something I might use somewhere besides the garage.
I've never owned Polk Monitor 10's and I've only listened to them a couple of times in the past. It's not a speaker that I really have much of an opinion on, one way or the other. I do know that it was a very sucessful speaker from a sales point-of-view and probably did much to put Polk "on the map". Most folks who know a little about speaker design will tell you that it's not a good design. I think even some of the Polk-folk have said as much. The side-by-side horizontal arrangement of the midwoofers produces an undesirable radiation pattern that tends to cause lobing along the horizontal plane, and it mucks up the imaging because the sound from one of those drivers reaches your ears before the sound from the other one. Time alignment type thing. I knew this before I started these, so why did I do it? Well, several reasons. Probably some of the same reasons Polk did it: I had a wide-baffle cabinet to work with, a lot of smaller diameter midbass drivers which really needed to be used in pairs, and I thought it looked cool. I looked at it as an experiment really, since I was breaking several rules. At the least I figured I would end up with something better than what I had before I started.
Since it was an experiment, I took it a little further: These woofers modeled pretty well with a port, but I've done lots of ports. Russ sent a couple of 10" passive radiators home with me after TX PFII, and, again they looked cool on the front baffle. The lack of specs proved to be a challenge. So did the little Audax neodymium tweeter. The woofers needed to be rolled-off about an octave below where the tweeter really should be crossed.
I put them together and posted some pictures and most everyone agreed that they looked cool. Sound-wise though, I was about ready to write them off, stick 'em back in the garage, etc.. I posted a couple of weeks ago inquiring about the crossover in the Polk Monitor 10, wondering if they did anything "different" to deal with the horizontal array, but it doesn't appear that they did. My woofers are in series (another one of those things that some say not to do), so you can't do something to one without doing it to both.
A few days ago, I set them up again and took a fresh set of FR measurements, paying close attention to what was happening off-axis. Before, I had been modeling my crossover on the on-axis response and trying to get the off-axis acceptable. This time, I worked on the 30 degree response and let the on-axis take a back seat. Scrapped the entire crossover that I had been working on, and started again. What I found was interesting: Most of the bad things that the woofers were doing (FR wise) on-axis, went away naturally just a touch off-axis. By 60 degrees they were getting ugly again, but I think in normal listening you're going to be somewhere around 30 degrees off-axis from each speaker, if they're not toed-in. Anyway, it allowed me to design a much simpler crossover that sounds, to my ears, pretty decent. They're still not terrific imaging speakers, but they're not bad. Not the last word in bass either (F3 models to be about 53Hz and they work best right up against a wall) but what's there is tight and controlled. I can listen to these. I'm actually quite pleased with their sound! Wish some of you could hear them so you could give me your opinions!
Here's a not-so-great picture.
Thanks for reading this and sorry for the length!