Expert advice needed for Dahlquist DQ-12 quasi-dipole woofer retrofit

[jdb]

I have a pair of Dahlquist DQ-12s that have blown woofers. The foam surrounds are cracked and rotten and one of the spiders is torn. I know that Regnar can rebuild the woofers, but I am not sure if I want to go that route. I have found very little information on these speakers. Here is what I do know:

The tweeters and mids are Vifas.
The woofer is a Gefco built 4 ohm (I believe) similar to the ones used in Advents.
The woofer sits in a sealed 0.64 cubic foot enclosure.
The crossovers are at 400 Hz and 3500 Hz.
Bandwidth is stated as being 38-22,000 Hz with a +/-2.5 dB from 52-20,000 Hz.

I guess the first thing to do is find out if it really is a 4 ohm driver. Will a multimeter across the woofer terminals tell me this even if the speaker is blown? I am looking at three possible replacements right now:
1. SD215-88 Looks good in the 52-400 Hz range that I am interested in, with the enclosure I have.
2. RS225-4 Doesn't look as good to me, however, like the original driver it is a "woofer." Any other opinions?
3. Vifa PL22WR09-04 Looks like the closest to the original. 12th item down in first chart . Exact same box size with fairly close f3 point. Also made by Vifa like the tweets and mids. Much more expensive.

Now the DQ line of Dahlquists (especially the DQ-10 and DQ-20) are praised by many for their imaging. Conseus is that a major part of this is because of the complex "time-delay-corrected" crossover design. I really don't know enough to re-engineer this crossover for a different woofer. If I just dropped in one of the above woofers would it sound like crap? If the speakers are going to sound really bad there is no sense in using the more expensive Vifa drivers.

This might be a stupid question, would there be any upside or downside to using the "subwoofer" (SD215-88 ) versus the "woofer" (RS225-4)? The 52-400HZ operating range is pretty narrow and the "subwoofer" looks like it could handle it. Sorry if this post is a little overwhelming. Any help would be appreciated. I am open to other suggestions as well.

Jeremiah

[ThomasW]

Have the stock woofers rebuilt unless you are willing to go to the time, trouble, and expensive of having new crossovers designed and built.

[jdb]

Thanks for the reponse Thomas, that was what I was afraid of.

Jeremiah

[JoshK]

Have Bill @ millersound rebuild them for you. He is very reasonable and quite good.

[jdb]

Thanks JoshK!!! I called Bill - very knowledgable, friendly guy. He has great prices and a quick turnaround. I will be shipping the drivers today. I appreciate the responses. Have a good weekend.

Jeremiah

[jdb]

FWIW, Bill (Millersound) used to be the factory service center for Dahlquist. :T

Jeremiah

[thruston]

Dq 12 Woffers and tweeters

I have a pair of Dahlquist DQ-12s that have blown woofers. The foam surrounds are cracked and rotten and one of the spiders is torn. I know that Regnar can rebuild the woofers, but I am not sure if I want to go that route. I have found very little information on these speakers. Here is what I do know:

The tweeters and mids are Vifas.
The woofer is a Gefco built 4 ohm (I believe) similar to the ones used in Advents.
The woofer sits in a sealed 0.64 cubic foot enclosure.
The crossovers are at 400 Hz and 3500 Hz.
Bandwidth is stated as being 38-22,000 Hz with a +/-2.5 dB from 52-20,000 Hz.

I guess the first thing to do is find out if it really is a 4 ohm driver. Will a multimeter across the woofer terminals tell me this even if the speaker is blown? I am looking at three possible replacements right now:
1. SD215-88 Looks good in the 52-400 Hz range that I am interested in, with the enclosure I have.
2. RS225-4 Doesn't look as good to me, however, like the original driver it is a "woofer." Any other opinions?
3. Vifa PL22WR09-04 Looks like the closest to the original. 12th item down in first chart . Exact same box size with fairly close f3 point. Also made by Vifa like the tweets and mids. Much more expensive.

Now the DQ line of Dahlquists (especially the DQ-10 and DQ-20) are praised by many for their imaging. Conseus is that a major part of this is because of the complex "time-delay-corrected" crossover design. I really don't know enough to re-engineer this crossover for a different woofer. If I just dropped in one of the above woofers would it sound like crap? If the speakers are going to sound really bad there is no sense in using the more expensive Vifa drivers.

This might be a stupid question, would there be any upside or downside to using the "subwoofer" (SD215-88 ) versus the "woofer" (RS225-4)? The 52-400HZ operating range is pretty narrow and the "subwoofer" looks like it could handle it. Sorry if this post is a little overwhelming. Any help would be appreciated. I am open to other suggestions as well.

Jeremiah

I found a vendor on Ebay that replaced the surronds on my DQ12's for $60 a set. Look up Geoaliwil on Ebay. He did a very good job. I ordered new tweeters from Madisound for $22 each. The orginal tweeters are no longer made, but the replacement for them is Vifa D27TG6-05. I haven't installed these yet, but will let you know how they work out.

Jim

[---k---]

Google???
I sometimes laugh at people responding to almost 3 year old posts.

[m.oreilly]

Google???
I sometimes laugh at people responding to almost 3 year old posts.

well, google brought me here , thank goodness, as i now have known sources, tried and true, for driver issues that may arise with my newly acquired dq-12s

[wkhanna]

Then you most likely also found this

Those were the first 'high-end' speakers I heard forty years ago.

I have heard refurbished ones since & they still sound lovely.

For any work you may not wish to tackle yourself, I highly recommend Vintage HiFi of Pgh

Tom and Anders are quite familiar with the Dahlquists & have done expert work for me & many of close friends on our prized components while freely offering expert advice if you should have any questions.

[m.oreilly]

yes bill, that first link was like finding land after being set adrift, but after seeing those prices...

[m.oreilly]

after finding one original woofer cone had separated from it's spider, i ordered two of the scanspeak 22W/4534G00 4ohm ($79 each). i may never mess with having the originals redone because of the price point of the scanspeak drivers...

[wkhanna]

If the Thiele Small parameters of the replacement driver are significantly different than the OEM driver, they may result in less than acceptable performance.
The OEM xo's were not designed to work with the parameters of the new drivers if they are not the same.
Do you have them installed?
How do the speakers sound?
If the OEM drivers have always been defective since you have had the speakers, you will not have a 'benchmark' for how they should sound.

Did you ever try to contact Tom?
I know he has a couple sets of Dahlquists' at the shop.
He may have some exact drivers laying around.
Otherwise, he may be able to repair your old OEM units.

[m.oreilly]

the scanspeak kick ass! what an upgrade! i would be worried more about subbing mid and tweeter re the final outcome. i did some software models with the scanspeak driver, and it fit the profile for the dahlquist enclosures , although a bit more damping may be in order. the scanspeak are just awesome in these boxes atm (hiphop, elecronica, acoustic jazz, dubstep...). if at some point in time i want to abandon the xo's, i'll tri-amp them. that was kinda my intention originally, as a tube amp is powering them atm, bi-wired, backed by two pro amp powered subs that now may be out of the picture, thanks to the scanspeaks.