The Thiel 3.5 EQ works from 70 Hz down. The last I heard Thiel had some left at a cost of $600. IMHO, it's silly to have the 3.5's and not use the EQ. It even has different settings for 40 Hz and 20 Hz to adjust for smaller rooms.
The complaint that the reviewers had about the 3.5s was that the equalizer compromised the sound overall by robbing the speaker of naturalness in the mid and upper frequencies; they felt the speaker deserved a better equalizer. There were a number of companies, including JPS, that modified the equalizer to make it more transparent and more up to the level of the speaker otherwise. I used the equalizer with my CS3 and heard it in and out of the 3.5 at my dealer. Given that I like deep bass and listen to a lot of music with it, I was willing to accept the tradeoff, and I really didn't feel that the equalizer did as much harm as the reviewers might have led you to believe. I also felt that the equalizer made the speaker slightly more spacious sounding, even in the upper frequencies (perhaps that was upper frequency "hash" that the reviewers didn't like?).
The units are no longer available from Thiel. They will refurbish any units though. They have good deals on discontinued CS6 and replacement drivers for many units.My suggestion is to leave the speaker alone and get a mid priced shb and cross the sub at 60-80 hz
JPS made the Golden Flutes which was an upgraded replacement equalizer for the 3.5. These were a significant upgrade to the Thiel unit. They do occasionally come up on the used market. The theory is that as the bass naturally roles off at the lower frequencies, the equalizer boost the same frequencies in order to keep the response flat. Go to the Merlin website and read about the benefit of the Merlin BAM and you will get an idea of what to expect.
I still own a pair and use them in my home theatre as the front channels. I agree with Vernneal's suggestion to just supplement the low end with a sub. The midrange unit on the 3.5 goes quite low, and with it's first order crossover point, it can receive excessive bass especially with the eq in the circuit and set to 20hz. I blew a midrange unit years ago when the eq was in the circuit. Theil replaced the unit at no cost (thank you Theil). Since then, I use them without the eq and have not had a problem since. FYI, I also feel that the eq effects the sound in the mid/highs imparting a slight transistory flavor to the sound.
Thanks for the advice and insights. I enjoy the sound of the speakers as is, but I'm curious to hear the differences with the EQ. A friend who is letting me demo these speakers has one in storage that will be accessible in the Spring.
The midrange units on the 3.5's are paper, while they have a pretty large magnet, and are otherwise well built they do have a tendency to need rebuilding from time to time. Thiel is very good about this. Even if one wanted to use a a sub-woofer I'd recommend using the EQ and using the 40 Hz setting. If your not going to use the EQ, you might as well go with a smaller, cheaper Thiel that will actually go lower than a non-EQ'd 3.5. The EQ does put demands on the amplifier though. I think most of the objections to the EQ are based upon some sort of purist's prejudice. Of course one alternative is to put the EQ in a pre-amps tape loop and depending to the music, one could switch it and out. The only real down side, is an extra set of cables and having the signal passing through the pre-amps circuitry one more time. Once in a while you can find a used 3.5 EQ on e-bay, a much less expensive and less complicated alternative than adding a sub-woofer. The 3.5's EQ's stereo bass will be much better than a cheap sub-woofers.
Like Unsound said, be careful with midranges. I owned a pair of 3.5s and probably went through 4 midranges. The problem is that they use a first order crossover, that while yielding excellent phase linearity, burdens the midrange with having to deal with significant mid/upper bass energy due to the shallow slopes. Thiel was extremely helpful with providing replacement units, even after the speaker was out of warranty.
Keep in mind that the same cross-over philoshpy hasn't seemed to burden Thiel's other lines of speakers the same way. My 3.5's have only had their midrange drivers rebuilt once and they're over twenty years old. This was just a few years ago, Thiel did it gratis despite being well out of their ten year warranty. Kudos, Thiel!
I'm not sure if any of the drivers have been replaced, but it's good to know that Thiel stands behind the speakers so well. I will try the EQ this Spring and I like the option of putting the EQ in the tape loop. Thanks Unsound.
Using the Thiels without the EQ is like buying a Maserati simply to drive to and from the supermarket - you may enjoy the ride but you'll be missing out on what the overall intent was in designing it. I am currently "driving" my 3.5's with a Macintosh Mc275 tube amp which, for some people, may appear to be too little power for what are legendarily "power hungry" speakers. I listened with and without the EQ in line and I can testify that the EQ is necessary. It could be my ears alone which detected better imaging with the EQ in, but that's my story and I'm sticking to it. I love these speakers.
Another deliriously happy 3.5 owner here. I’m also a huge advocate of the equalizer. Interestingly, I used to own KEF Reference 107/2’s and pretty much hated what the KUBE equalizer did to them, essentially sitting on the sound terribly. The 107/2’s, not in the same class as the 3.5s in my view, sounded far better sans KUBE. It’s quite the reverse with the 3.5s.
The Thiel equalizer doesn’t interfere with the sonic character of the 3.5s and merely allows them to accurately plunge the Stygian depths, but only when recordings dip to 20HZ territory. The 107/2s sounded very colored in the low end, to these ears at least.
I don't believe Thiel still sells them but they can be repaired
You can always get something like DiracLive or miniDSP and configure your own. If they can be bi-amped, you can relegate the EQ to the bass amp.
^CS 3's had two pairs of binding posts on each cabinet, the 3.5's only one pair.
Check out my posts in the last few pages of the Thiel Owners thread. Others have also weighed in on the equalizer on that thread.