DCM Time Window

[aslan7]

Does anyone here have any opinion on the DCM Time Window vintage speakers? I was in a hi-fi store and heard them playing quite by accident and was amazed at the sound. I had gone to hear some restored Ohms and the DCMs killed them, especially for orchestral music. These were just the original 1 model and some prefer the 1a ones. I don’t have particularly sophisticated taste in speakers and am extremely pleased with my Larsen 6.2s which have come under criticism here. The DCMs would be for my second system. I was thinking about Revels but the significant other would blow a gasket at the expense. As luck would have it a totally restored pair of the DCM 1a model is available ten miles away.

 

[mhardy6647]

Excellent loudspeakers of their time -- the original timewindow was one of numerous early forays into working with a room (rather than against it) to provide "spacious" sound. Not the pinpoint accuracy that became fashionable in later decades, but a bit less diffuse than Prof. Bose's approach (e.g.).
The earliest timewindows used very good but inexpensive Philips drivers to very good effect (actually, I am not sure of the provenance of the woofers, but the tweeters are Philips polycarbonate domes). The enclosure, you probably know, is made of cardboard (Sonotube) and MDF, rendered in the form of two differenly tuned (as I understand it) transmission lines.

The original timewindows were also quite easy to drive even with a low powered, high output impedance amplifier.
The 1A is fine, too.

I have a very ugly pair that I acquired very inexpensively. I really should restore them cosmetically someday.
From my perspective, they're tonally excellent.


Don't be dismayed by the bordello red carpeting! That had been removed from the 'bonus room' of our old house in MA. I put the biggest chunk in the (unfinished) basement, which is where the photo was taken.

PS There's apparently no truth to the story that the Ann Arbor, MI based DCM took its name from its hometown: Drug Capital of the Midwest.

PPS If you like the timewindows you'll probably love Roy Allison's Allison One and Allison Two. They tend to be a bit pricey nowadays, though.

 

[aslan7]

Thanks very much for the info. I am tempted.

 

[sam_adams]

There were various iterations of the TW-1 that used different drivers in them. The ones pictured in @mhardy6647's TW-1s are the Heppner 4846-SD. The tweeters are the Philips AD0162-T8. Earlier TW-1s used a Philips hexagonal-framed woofer and different Philips tweeters.

As far as the 'transmission line' design, these are basically a bass reflex design with very short port tubes. The port tubes are just 2" diameter PVC pipe about 7.25" long. The enclosure volume is around 1.75 cu ft with a port tune of around 35 Hz.

The enclosure is tightly filled with polyfill to control the resonance of the sonotube and the reflections from the port tubes and bottom of the enclosure. The bottom half of the cabinet is stuffed with a higher density polyfill than the upper half and it's in there so tight that little—if any—sound comes out of the ports at all.

Example response of the Heppner woofer:

Nearfield response of ports with no fill in the cabinet:

The schematic below is for the TW-1 XO (from units with serial numbers of about 23xxx):

These are hard to service because the drivers are glued and screwed in place. The sealant around the woofers and tweeters is some butyl rubber substance that is very tough to remove. The 'wood' part of the cabinet, the dihedral front panels, is 1970's style MDF. It's more like chipboard than anything else and it is very porous and breaks apart very easily. Removing the drivers if the XO or drivers need service will damage the material.

You can see in the pictured speaker above on the left of the top cap that the 'wood' is splitting. It's not really wood but some sort of very thick fiberboard with a woodgrain appearance to it. It's doweled and glued to the top of the enclosure and there is no way to get it off without destroying it. The only way to gain entrance to the inside to service the XO is to take out the woofers. Later versions used a threaded steel rod that ran from the bottom plate to the top with a nut on the bottom so that the top plate could be removed to access the XO. Those versions had real Oak for both the bottom and top plates.

Overall, from a subjective point of view, these are very nice speakers. They have a large and enveloping sound field to them and are not bright or fatiguing. Since they only have two 6.5 inch woofers they are a bit light on the low end. When combined with the very rare Time Bass dual eight inch woofer bass modules, they have good low end extension that really rounds out their presentation.

 

[restorer-john]

I've owned Timewindow 1 and 1as.

The early 1s used Philips woofers and dome tweeters and the 1as used a later Philips bass driver and Vifa D19 tweeters. The old TW1 woofers have rubber surrounds which go hard. I have a basket full of TW1 woofers from stripped speakers. The spider and suspension collapse also. The later 1a woofers last longer for sure. You can always tell original drivers from the orange chalk marks DCM used to match the drivers. Peer through the 1a grille with a torch and you will see.

As discussed above, they are not hybrid transmission line, they are simply a dual ported (short ports at 90 degrees) in a large volume cabinet.

They are made of cardboard (cement forms cut to make the rear) and chipboard, with the 1as held top to bottom with a long threaded rod into a captive nut on the top panel. The 1as used solid oak top and bottom panels whereas the 1s had veneered/painted fibreboard.

They can sound absolutely amazing, but you will need to spend a lot of time positioning them and they simply don't work in some rooms at all. If you want pinpoint imaging, forget the TWs, they are all about a diffuse sound. An out of box experience if you know what I mean.

 

[TimF]

I had a pair of them. It was hard to get good and stable stereo imaging out of them. Also, now a days there are many, many speakers that provide better tonal accuracy. You can do better.

 

[dlaloum]

I had a friend that owned them in the early 80's - sounded great as I recall - probably not ideal for a critical listening system nowadays - but ideal for a shared family environment.... (if you have the right room, to leverage the reflected sound..)

 

[phoenixdogfan]

I heard them over 40 years ago when I took a friend shopping for speakers. I took my LS 3/5a's along with us, because we were both familiar with their sound (which we really liked). It was a place in Cincinati called, I think, Audio Lab, and they had an a/b comparator. The sales staff were gracious enough to hook up my LS 3/5a's and we compared them. They sounded more dynamic and open with deeper bass, but not as focused on imaging, and missing the magical LS 3/5a vocals. I thought they were very good, and so did Mike. He bought the pair, and AFIK still has them.

Obviously, they can be surpassed by many of today's offerings. But if your Goodwill has a pair, and you don't have much to spend by all means go for it.

 

[DavidMcRoy]

I love the excellent posts about this classic! Thanks for filling in some history for me.

I was very much in love with DCM Time Windows in their heyday and I still am. I recently bought a pair of restored original ones (from prior to the Time Window 1A) to add to my collection of vintage gear that I enjoy pulling out to listen to. They’re very entertaining in 2-channel stereo mode if you can place them optimally and aim them as recommended by DCM. They also make a very good side surround speaker, but I prefer traditional cardioid polar response for the front channels in a surround system.

There were a number of versions, the first simply called DCM Time Window or Time Window (Improved), like mine. Mine reportedly had a pair of Philips upper 6.5-inch midrange drivers, (since replaced by who-knows-what during restoration) with a pair of Philips tweeters mounted beneath them, and a crossover network that delays the tweeters‘ signals to time-align them with the woofers.

The Time Window 1A steps up to Vifa tweeters, I believe, a worthwhile design improvement in my opinion. (The superb DCM CX-17, 27 and 31 have an excellent Vifa or Visaton tweeter, both modified for DCM with ferrofluid cooling. I own some CX-17s with Visaton tweeters and I love them.) Coaxial mounting in most of the CX-Series improved imaging and the Vifa and Visaton tweeters are cleaner and flatter than the Philips was. A modified transmission line bass loading cabinet was a common feature to all, at least through the CX-Series, that I’m aware of.

The Time Window 3 got significantly bigger. There was also a Time Window version designed for use with a dedicated DCM Soundstage Center dialog speaker and finally a grandly executed Time Window after that, the name of which escapes me.

None of the earliest Time Windows like mine were the last word in neutrality, having a distinct lower midrange emphasis. The later versions were better and the CX-Series of time-aligned conventional box speakers better still.

I welcome any corrections to my recollections about the history of the line, the mists of time being what they are.

 

[DavidMcRoy]

Is this the tweeter time delay circuit?

 

[restorer-john]

The 1a's tweeters certainly were not coaxially mounted. The Vifa D19 sits below the woofers of course and there are half felt 'covers' over the woofers attached (stapled) to the baffles and under the knitted sock. I have a schematic of the 1a and some caps, along with a letter and brochure from DCM (Mitek) when I obtained a few drivers many years back.

 

[mhardy6647]

The coaxial reference was, I am pretty sure, to the (much) later "CX" DCMs. Those were interesting loudspeakers. Very banal looking boxes. I think they were "sleepers" when on the market as DCM had be more or less forgotten as a serious loudspeaker company. I've heard nothing but good things about them, though.

Great to see so much info on timewindows here in this thread. They were not uncommon --but still slightly obscure loudspeakers! I'd forgotten the Philips woofers (I have seen them in some timewindows) and, obviously, I drank the internet Kool-aid about the alignment, so the clarifications were most welcome. I still think the design of the enclosure was innovative in the unironic sense of the word (since innovative has become a term used by any entity which actually wants to be anything but innovative ).
The timewindows were in production for a long time (special order, I think, towards the end). The TW3 was a pretty... complicated design. I've never encountered a pair in the field.

Since no-one's mentioned the DCM Timeframes, I will. There, I just did! There were several models, and they're well liked in many circles. I don't have much experience with them, though.

 

[aslan7]

Thanks very much for all this wonderful, detailed information. Tomorrow I am going to listen again to the 1 model and after that the 1a. I am leaning towards the latter because the pair has been restored and was of course improved. Years ago I had line transmission speakers in the form of Bud Fried”s IMF Studio IIIa speakers and liked the sound. I liked everything Fried made being from Philadelphia where he was highly regarded. The lack of pinpoint imaging doesn’t bother me because I enjoy rich, suffused sound like sitting somewhere before an orchestra. But I do listen to chamber music, especially trios, where the imaging is a plus. Again, thanks very much and I’ll report back on the 1a situation because I must ascertain how they were restored and what exactly was done.

 

[DavidMcRoy]

The 1a's tweeters certainly were not coaxially mounted. The Vifa D19 sits below the woofers of course and there are half felt 'covers' over the woofers attached (stapled) to the baffles and under the knitted sock. I have a schematic of the 1a and some caps, along with a letter and brochure from DCM (Mitek) when I obtained a few drivers many years back.

Thanks for the correction. I edited my post to omit that reference.

 

[restorer-john]

I've often toyed with the idea of a Timewindow 'tribute' as a DIY project.

There's plenty of forms (cardboard/fibre/even poly pipes that could be used and apart from the bevelled angles of the two front baffles needing to be right, the project would be inexpensive and fun. There's literally a ton of 6.5" mid bass drivers we could use and dome tweeters galore. Tuning the cabinet to the woofer is simply adjusting the port lengths and it doesn't even need to look all that pretty (cabinet work) because the entire speaker is covered in a knitted 'sock'. The top and bottom panels could be whatever timber people want as they are really end caps, not functional to the cabinet.

You could run the drivers straight to the terminals (all 4 of them) and then do the whole thing in DSP or get a crossover guru to design a passive network. There would be a lot of opportunity to 'steer' images if you did all 4 drivers per speaker in DSP.

 

[mhardy6647]

^^^ do it, do it, do it!

The tall, narrow form factor of the timewindow is quite modern, too, isn't it?

 

[restorer-john]

^^^ do it, do it, do it!

The tall, narrow form factor of the timewindow is quite modern, too, isn't it?

Yes, I agree. What would be modern, would be some of that light bleached ash style timber end caps and that white/grey/cream woven fabric like Ikea use on everything. Like this:

 

[sam_adams]

The DCM speakers of this vintage—20th century—that used a coaxial driver arrangement were the following:

Half Time
Time Frame TF275
Time Frame TF400
Time Frame TF600

The TF600 had tweeters on the angled rear panels, also.

The link below shows some guy butchering an original pair of TW-1s with the Philips woofer, AD 7066/W8 and Philips tweeter, AD 0163 T8. This is one of the earliest models stuffed with fiberglass—not polyfill—note how much is in there. Note the XO and the type of coils used. Note the different arrangement of the port tubes, also.

https://forum.polkaudio.com/discussion/181707/dcm-time-window-overhaul

@DavidMcRoy, here's some SPICE plots of the electrical response of the XO into a simple resistive load (close enough for understanding how it works):

Green plots are woofer (frequency response and group delay), blue are tweeter, and red are combined response (Zoomed in, the frequency plots are solid lines and the GD plots are tiny dots.):

Full plot (click to embiggen):


Zoom in (click to embiggen):


The filter for the the tweeter is actually an Elliptic or Cauer high pass filter and if we zoom into the plot around the XO frequency—about 2.5 KHz—we can see the difference in the delay between the woofer, the tweeter, and the result on the combined response.

 

[restorer-john]

The link below shows some guy butchering an original pair of TW-1s with the Philips woofer, AD 7066/W8 and Philips tweeter, AD 0163 T8.

Actually the TW1 also used (in the later round woofer) version, the Philips AD 0140 T8. You can tell those as DCM stuck a rubber 'foot' in the centre of the acoustic lens on the tweeter so it sat flush under the fabric and didn't vibrate.

Here's a pair:

Here's an internet pic of a partially chopped up TW 1:

Here's another internet pic. Notice the red chalk marks and the little rubber bump-on/foot they stuck in the centre of each tweeter lens. Also notice, this is supposedly a TW1, but the ports are now one above the other and close to the centre. The woofers are like the TW1a, but the tweeter is still a Philips. My TW1as used the Vifa D19 which they clearly pushed into service very early in the 1as run.

 

[solderdude]

These need to be shipped to Danny.
A redesigned X.O., wiring and tube connectors will lift performance to unseen heights.