Upgrade The Dahlquist DQ-10 Midbass

With vintage speakers you can face driver failure at any time, either induced by loud playing or just age.
For instance, in the case of the Dahlquist DQ-10 just about every owner has replaced the foam woofer
surround or had the woofers rebuilt. I’ve replaced the surrounds, but they otherwise sounded fine. To me,
the midrange/mid-woofer and the mid-dome are the heart of the system. But, I felt after extensive listening
that the midrange/mid-woofer could be improved upon. As you probably know there is a site who does
“factory authorized”, so-to-speak, modifications and replacements, and a competitor who offers lower
cost replacements based on their own evaluation, and more power to them. Being a hobbyist I of course
had to do my own sleuthing. Even though I simply inherited the speakers, there was a limit to what I was
willing to spend and I expected real value considering the state of driver manufacture. Now some of you
may be asking yourselves "Why do I need a midbass when the crossover is as high as 400hz, isn't this the
midrange?". The highest concentration of energy for a symphony orchestra is the octave 250 - 500hz, so to
smooth the transition to the midrange it's useful to have a driver that can take the handoff from the woofer.
Remember that the first octave of 400hz is 800hz and even with the crossover slope, significant energy will
still be transmitted, hence the importance too of the impedance compensation. I ran the numbers on the
midrange with the Woofer Tester to get some idea of what I’d need to do. The midranges that I looked
into with similar specs were hardly an improvement, so I decided to just get a good performer and integrate
it the best I could. I chose the Dayton RS125S-8 5” aluminum midwoofer with solid phase plug and
rubber surround. It has good comments, is very reasonable and is definitely current technology. I installed
them right out of the box to see where I was at. Immediately I noticed that the rising output was intruding into
the mid-dome’s response. I ran a simulation with X-over Pro by Harris Technologies and added impedance
compensation, and there was an immediate improvement. Because the cone breakup for this driver is so far
out of its operating range in the Dahlquists, I didn’t do anything further in that regard. Again more listening,
and the output seemed to need padding, so I added a 1.5 ohm resistor. More listening, and they seemed a
little forward with the original felt damping, so I removed it altogether. The new drivers have enough oomph
with totally open backs, and integrate fine with the other drivers. That seems to have done the trick. The
midbass response blends very nicely and certainly, at least to my ears, doesn’t overwhelm at all. I auditioned
lots of percussion, string orchestra, viola da gamba, piano and jazz bass, and concluded that this was definitely a
success. The electronics of the Ozric Tentacles was startling. Voice, too, has been preserved. I would have to
say that the clarity of this driver, in contrast to the softer sound of the original, may take some getting used to;
but I think that it’s more in keeping with the electrostatic qualities of the mid-dome. Now that I’ve opened
Pandora’s Box, I’m wondering what those marvelous Vifa P13WH-00 5-1/4 inch mineral-treated polys would
sound like. Yikes. I realize that some have replaced the whole mid-tweeter range with just two ribbons, but to
me they’re no longer the original five driver marvel anymore. Might as well just do a new DIY project. Let me
know if you take the plunge by going to the Contact Best Speaker Parts page. If this site meets your needs
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