SEAS Thor Speaker / NCMS Rhythm 9500 Unlimited

I've read about these new speakers from SEAS designed by Dr.Joseph D'Appolito and have quite an interest in them. The most recent issue of Audio Express talks about them at length and they look to be a really nice design for those of us who like a well built transmission line speaker. If you haven't seen them yet got to and go to "kits" and they're at the bottom.

My question is,"Has anyone heard these speakers or tried to build them yet?" I'm curious for some input if you have heard them. I don't like the fact that Madisound has opted to delete the base plinth that was part of the original design so I will most likely have to build the cabinets myself. The article has a mini review but I'm looking for more reactions to these speakers.

The other kit that I've been looking at is the North Creek Music Systems / Rhythm 9500 Unlimited. Again, if you have not seen it check out,
Costwise the NCMS Rhythm 9500 Unlimited is qiute a bit more expensive but comes from some great sound guru's. Any thoughts on these would be appreciated.

This speaker sounds nearly identical to the living voice avatar. Same configuration, same design concept. These are wonderful sounding, tonally accurate and well controlled. Responds very well to tubes. I have the avatar obx which is the same cabinet but with crossover components located in seperate boxes. Check it out at
Bryhifi your on the right track with the kits as well as the SEAS as choice..there are designers on the MAD web that can help you in finding a speaker built to your driver picks..thats the route i'm going SEAS W22 + SEAS W12CY + PHILIPS RT8P..good luck
Just put together a NCMS Rhythm Signature. I had Lee Taylor make the cabinets and xo boxes. Already these speakers best my Vandersteen's- better imaging, more efficient, bass extension. Although they certainly need some time to break in, my initial experience has been really positive. I will have more comments as they break in.

Good luck on your search.

Thanks guys, I'm still not sure which one I'm going to go with yet. I really don't want to give up bass extension at all if possible. Some have commented that the Thor will not extend down to much below 40hz where as the NCMS Ryhthm does at least get down to 30hz with more output. I don't need them to play loud but rather full balanced at low volumes for nocturnal listening if you know what I mean. I've got 2 pairs of quality speakers that can more than handle the mid to live levels of acoustic music but seem to collapse at very low levels. These effects happen in either system and either room of mine.

The system that I use late nights is in a 19'x16'x8' living room at the other end of the house as to not keep my wife awake. My dedicated room is directly under the master bedroom and is too large(28x16x10) for low level listening. The night system consists of BAT VK-3i & VK-200, Proceed PDT-mkIII, Krell Studio dac.

If there is another kit or homebrew that you think would work better in this room and system please feel free to say so.

**Karl, which Vandy's do you have?

I had the Vandy 2ci's for the last 7 years. I loved them. The VK200 should handle dynamics well even at low volumes with the NCMS. I drive the Rhythm sig's with a VK500. Have fun.

Bryhifi i just read a thread on madisound about the Thors..they say its a disappearing speaker sound..and has great bass and beautiful mids..i have the Seas W22 woofers are they are of superior craftmanship. I would say this is possibly the "best" speaker going.
After stumbling across a magazine written by Joe, in a bookstore far from home this weekend, I can honestly say I am disappointed in the Thor.

Please understand my perspective, a person who learned a heck of a lot about speaker design by Joe D'Appolito via Kimon Bellas. I had always held the utmost appreciation for his talent, creativity, and experience.

However, I feel that we as speaker enthusiasts are no longer living in the world we used to. By that I mean, late 1980's - mid 1990's. Many of us have rediscovered what used to reign supreme. Tubes, low power, more simple, more truthful, more natural sound.

During this metamorphosis, speakers have needed to evolve as well. The speakers of 15 years were much more difficult to drive. Built to take the idea of the speaker designer as far as he could go. Most of these designs were a supremely punishing load for an amplifier, they required massive amounts of current. As audiophiles have turned their focus back to tubes, speaker loads have become more benign. Speakers have changed.

Joe D'Appolito's thoughts have changed some also. The Thor is a transmission line.

However, in reading the article I was most curious to see what his crossover design would be. The feeling as if I was looking at something written in 1992 came over me. Lots of capacitors, lots of coils. This speaker presents a lot of components between the drivers and amplifier. It takes current to knock down those obstacles.

Joe, please do not take this the wrong way. But, please give a more simple crossover a try.
Trelja Thanks for this very perceptive comment. You are correct. The MTM Thor design does in fact take a nice size ss amp. Very load demanding. And in my opinion a good tube amp delivers more musicality than a good ss amp. The Thor has dual W17's, and these 7 inch woofers only down to like 40 hz. But your amp needs to push 4 woofers!! I think a single W22 will produce a nice solid 30hz and will be tube friendly. I'm not looking for alot of sound, superior sound is what i'm after. The Seas line of Excel woofers just got better! They are releasing their new W26 Excel!! She's georgeous! 20hz!!! - 1000K hz. Those of you who are about to buy a sub (REL's), you may want to hold off to consider the W26. Seas > Excel > new
Tweekerman, thanks for the kind words. I agree with you very much. Especially, that a good tube amp offers more musicality than a good solid state amp.

My own tube amp drives Seas P21 Excel mids with no problems. In addition, it also drives a pair of subwoofers with Peerless 10" woofers. No sweat at all, it will play at quite high volumes. Down to 22 Hz. The secret is the simple crossover, which I described in my last post. The only thing standing between my amp and drivers is a coil and a cap. A good simple, first order parallel network. Sure, it isn't glamorous, and "techies" may complain about this or that, but it just plain sounds good.
Trelja, It just so happens that Linkwitz picks the Peerless XLS 12 as his best pick for sub. That big curl surround looks superior design. Which tweeter are you using? Linkwitz says the active xover gives your amp a big boost. My 40 watt tube is the entry level and offers plenty of power. If i want more power i can get the next level up. What's your thoughts?
What i'm trying to say is like you , i believe "less is best" in xovers. So active seems to me to disrupt the clean fq's of your tube amp? Yes you get a louder sound, but active to me implies that your placing the tube amp further from the speakers...??
Tweekerman, my tweeters are a very common model from Vifa. I feel it is probably the best bargain in tweeters, very underrated and underappreciated. At just $25, it takes one to spend $100 to best it. However, I really should have upgraded it to the ScanSpeak Revelator, which is a direct replacement(in my speakers), long ago.

As, I am putting together a second system right now, and that system already sounds terrific, the tweeter upgrade is on the back burner.

I feel the Revelator offers improved smoothness and refinement, in comparison to the Vifa. I also have another pair of speakers with a Hiquphon tweeter. That is a really terrific driver, offering every last bit of detail, with no harshness or brightness. My kind of tweeter. I have read the pair goes for $275, but I have never priced them, so I am unsure if that is correct. Whatever the cost, it certainly deserves to be more well known than it is.

By the way, I am so enamored with the Vifa tweeter, I bought another pair(not so wise, should have just used the ones I have when I upgrade) for my next speaker building project. Just a little two way monitor. Will feature 1" thick solid maple outer walls, possibly with a layer of viscoelastic inside of that, and finally a layer of 3/4" MDF. This one will use a series crossover. But, it will be simple nonetheless. The other driver is a 6 1/2" mid - woofer, also from Vifa. If I need more bass later, I can assemble a pair of subwoofers, which can also serve as stands if I want. The subs would use the same 8" wide maple, with the drivers on the sides. Probably go with Peerless or Vifa 10" woofers. Sometimes, I kind of like having subs in the corners(not always the "approved" means, but I don't care), and monitors out in the room.

I don't have any experience with active crossovers, but have always kind of wondered...

In my opinion, less is definitely more. I am a big proponent of a first order network, be it parallel or series in configuration. Series crossovers offer something special in the way of cohesiveness in the sound. I also like running mids flat out, without any crossover components in their circuit at all. Now, one can't get any "less" than that. Only the tweeter really needs anything, a cap, just to keep it from getting fried.
Yes i've heard very good about the Hiquphon's. Dave Ellis uses them in his kit Ellis 1801's with a Seas W17. Another experienced builder says the OW1's are his best pick. This Danish DIYer has a Skaaning + ATC + Scan-Speak, very nice speaker! the Hiq's are like $160/pr, they have 2 models OW1 OW2. Some folks like the Scan-Speak's others the Seas tweets. Why do you use budget speakers? But i have to say the Peerless 10 and 12 sub's is the best bang. Very nice looking units. Some folks dissagree that you cannot tell what it sounds like from the looks. Tell us if i'm right on about your Peerless 10's. But i'm going with no sub. I'm satisified with the 30 hz's of the W22. But i've got plans for the new W26's that will go to 20 hz! And the good thing about the Seas is their clean upper bass. This Danish guy says the Seas will do at least 90% of the Skaanings at way less than half the price! I need to order that intro book on xover networks.
If you are still debating between the two, here are my thoughts.
I have built both - the NCMS system based on scan-speak drivers a few years ago, and the Seas based Thor last year.
The Rhythm is a well behaved system. Good bass extension, lots of mid-bass, strong detail.
The Thor system is more open/ airy / more detailed with less bass extension, but more "accurate" bass (quicker transients comes to mind) in my opinion.
I believe the reasons for this difference stems from two basic differences between the two systems. First, The Thor is a TL, and the Rhythm is a vented design. The vented design type has more overshoot, and less control of the driver around the resonance frequency. The TL behaves like a closed box around resonance, with better cone control (more damped behavior). Second, the midbass drivers themselves exhibit different behavior. See Siegfried Linkwitz's website ( for his testing and analysis of the underlying driver's stored energy characteristics.
The tweeters used are both excellent. I continue to use both in my "personal" designs.
For the record, both are excellent kits. Both are (IMO) likely the best examples of the use of the drivers in question. I have kept the Thors, and disassembled the Rhythms - I am going to build a Transmission line for them and see how they compare to the Thors one-on-one.
Any questions... please ask. Any different opinions... please comment.
Keith Van Vleck
Keith , Very nice post! Is it true the Thor MTM is best with ss amp? What db changes take place in the 2 W17's? Alot less sensitivity correct? Thus ss amps can supply bigger ohm load?
Just returned from Jamaica then Hilton Head,,,,,3 weeks without access to the net!

I still have not made up my mind yet on which one, but the itch is getting intense! I've got to do something soon!!!!

Trelja, I think we need to get in touch again. As always your points carry much validity and your interest in speakers sparks my old time passion for them. If you remember, we live rather close to each other. (Discussed Community Audio) Your preference for Vifa is a solid one. I used them to a great degree back in the late 80's to early 90's for custom built jobs and they always won the price/performance contest.

Keith, thanks for the direct comparison between the 2 kits! That is exactly the kind of thing I was looking for. Question??? Since you built your Thors last year which cabinet plan did you end up using? There was discussion of the original plans at SEAS website being preliminary blue prints and ended up not being what J.D. finished with.

Tweekerman, Thank you for all your input on this topic too. I love your enthusiasm for the hobby! Keep me posted if you hear anything else at M.A.D. please. I've got a ton of catching up to do after being away for 3 weeks and know I will miss something.

Best Regards,
The big thing going on at Madisound for me at least is the 3 threads on midranges. Seems the Zellaton by Goerlich, Germany is voted "best" by one Greve, a DIYer who says he's got ATC's , Seas, Accuton's and a bunch other midranges on his work table. But seems to be a problem for me, the Zell's are 4 ohms, i've got a 8 ohm kit going. There's always a catch. The Eton's got big votes as well. But their sensitivity is low, like 85db. So i don't think that'll work with my Seas + Ribbon. BTW Seas has a new W26 beauty out in June. I'm trying to see if a 2 way may work, with a ribbon that goes to 1K hz and the W26 goes upto 1Khz. Will this be doable? Or give me your pick with this driver in a 2 or 3 way.
Bryhifi, your last post jogged my memory. It's good to hear from you!

From what I remember, you lived in the Collegeville area? If so, we are about 15 - 20 minutes away from each other. I live between Conshocken and Manyunk, in Whitemarsh Township.

Are you going to the NYC Stereophile HiFi Show? If not, maybe we can get in touch via a different means.