What I learned:
1. If you have a good box, you can retrofit good drivers into it.
2. An 8" woofer really fills out the bottom end and lower mids better than many smaller woofers.
3. A flat MLS does not necessarily sound good.
4. Work to use lower order xo if you can. It will give a smoother transition.
Project 4 just did not work out and I had these nice tower boxes. I think the two key shortcomings of the original project were the poor MCM woofers and trying to get too much base from a 6.5" woofer. Lesson learned.
I found a pair of unmarked Peerless 8" woofers on ebay and won them for a great price. They turned out to be of fairly high quality with a nice motor. My T/S testing which is still not very accurate said they would work in the tower boxes sealed. So I was taking a chance on this one. I used the Jasper jig to cut a plug and filled in the old woofer holes, then recut holes for the Peerless woofers. This brought the woofer right up to the tweeters, a lucky cut. The woofer also went right to the edge of the cabinet. I like the look.
OK, my baby girl got an update on her system. :) The Vifa's are now in son's room.
These are the comments from
DIY 2002 in
Extremely smooth and listenable
Very natural sounding
Nice bass performance
A little soft in the treble department
Relaxed Effortless vocals
Demonstrates the merits of an 8" midbass
Right from the start everything made sense. After working with the MCM woofers my confidence was not very high. The Peerless acted like it was supposed to and modeling with LspCAD worked. The Peerless tweeter also continued to work well and getting a flat MLS was not that hard. The only down side was I was using steep XO to try to get to 1800Hz. The tweeter is a good tweeter but really did not want to cross that low. So now we have . . . The tale of the flat MLS:
The first xo on this unit was a 4th order on the tweeter with a third on the woofer. I also had a bypass resistor on the main woofer coil. This produced a very steep acoustic order and everything looked good.
Most of the smaller waves on this MLS are most likely room reflections. The drop after 10K is my mic. But generally a pretty flat MLS. Looks like 1/6 smoothing.
In listening tests there was a slight ring in the tweeter just above the XO. It was not that noticeable but it really bothered me. I also found I could hear the transition from woofer to tweeter. This was surprising since the MLS was so flat. There was also a nasty drop in impedance to about 3 Ohms right around the XO.
Pulling the XO and starting over, I found the woofer really did not need third order and the tweeter did well with third order. I got rid of the bypass resistor on the woofer. Baffle step did was not a problem on this speaker, perhaps due to the 8" or the narrow baffle. So I let go, became one with universe, used The Force, and let the flat MLS slide a little.
Again, I know most of it is room reflections. There is a real small hump at 1000Hz that I decided not to fix because I think it made the woofer sound a little less 8ish. The impedance looked a lot better too. This xo is not as flat but really sounds a lot better. I know my MLS system does not read the upper treble well. In listening tests I found the tweeter a little high. So I brought it down a little. Looks like 1/24 smoothing.
This sounds the best to me. After all this fooling around with measurements, I know the drop after 10k is my mic, the little dip at 450 is room. I had Dennis measure this with his system and he got a lot flatter line. I don't understand why my wife just does not think a testing chamber is a priority.
There is a distinct upper range and the small hump at 1000HZ that (in my
mind) keeps the 8" from sounding 8"ish. In AB tests with my MB-1,
this 8" driver really fills out the under 500Hz section. I like this one
so much I have another ebay 8" Peerless on the way. This time a Peerless
XLS. I will keep you posted. I also found that the existing port worked well. I
did all the tuning with the port stuffed. I found I could tune the speaker
pretty well by stuffing the port different amounts. At a recent VA event, the
consensus was to stuff the port, but if you like a little more bass, you can
run with an open port.
Copyright Peter Jay Smith 2005 Return to helarc.com