Should I use my KEF T27 SP1032?

[Tucker_515]

I bought a bunch of speakers from a guy, and among them were these super heavy, but not super large speakers he threw in because he didn't know what they were, and believed they were homemade. They are two ways, with one 8 inch mid/woofer and a tweeter. I pulled the woofer, it is a KEF SP1014, and the tweeter is a KEF T27 SP1032. The crossover setup is very large, and the back of the speaker has a dial that controls tweeter volume, and a three way switch that I believe allows a change in the crossover frequency. They sound great and the boxes are the maze type which is why they are so heavy. I did some checking and found that the T27s are valuable and easy to blow out according to someone on a website. I am debating whether or not I should remove the T27s and put in a different tweeter because I feel like they are being wasted on me as I doubt I could tell the difference between a high end tweeter and a lesser one. My plan is to use these speakers as my centers in my 7.1 setup with my Yamaha DSP-A1 reciever. My mains are Bic Venturi Formula Sixes, my rears are Optimus 25s, and an M and K V125 Subwoofer. Sorry for the long post, I am very new to speakers and stuff.

 

[macgolf]

I understand coming across more expensive equipment that I'm accustomed to having, but still enjoy using that equipment.

Welcome to AK and pics would help us identify your speakers.

 

[swechsler]

I wonder if this was a KEFKIT. Back in the day, KEF sold a lot of kits with the drivers, crossovers and front baffle, and the purchaser was expected to build the rest of the system. Here's one example.

 

[Wildcat]

I wonder if this was a KEFKIT.

KEF also used to sell the bare drivers--Madisound used to carry them back in the 80s.

They sound great and the boxes are the maze type which is why they are so heavy.

It might be a "transmission line" type of cabinet.

 

[infullview]

Welcome to AK @Tucker_515. Sounds like you have a very eclectic collection of speakers for your surround system.

 

[Tucker_515]

Welcome to AK and pics would help us identify your speakers.

I asked for the thread to be moved, thank you! In the meantime, here are some pictures. I don't have a tape measure on me, but the rough dimensions are (in inches) 40 tall, 10 wide and 10 deep. And it weighs roughly 55 lbs. Wildcat, I drew on one picture with what I think is the internal baffle design. Also, swechsler, it could be a kit, although the crossover looks very homemade, I don't know if the kit would've come with a premade crossover or just come with the components.

 

[Tucker_515]

Welcome to AK @Tucker_515. Sounds like you have a very eclectic collection of speakers for your surround system.

Something like that! Yesterday I picked up a set of Realistic 40-1299A crossovers for 10 bucks and installed them in the 25s, and they now sound great for what they are because before they only had caps for the mid and tweeter, the big woofer was full range making it very muddy and weak. I also have a set of Optimus 40s that have new Dayton DC200-8 mid/woofers coming for them. My current centers are JBL 62ts which are very clear for voices because of the titanium tweeters. I pretty much buy what I can for cheap and hook them up and see if I like the sound!

 

[Wildcat]

Wildcat, I drew on one picture with what I think is the internal baffle design.

That does appear to be like a transmission line, although it seems a bit short for that. If I'm not mistaken (and getting a little technical here), transmission lines have often been sized to a one-quarter wavelength of the resonance frequency of the woofer. And the transmission line narrows as it reaches its exit on the cabinet.

Also, swechsler, it could be a kit, although the crossover looks very homemade, I don't know if the kit would've come with a premade crossover or just come with the components.

Most likely it's made from components and not a kit. There is a very active community building their own speakers. Sites like Parts Express and Madisound offer parts to build your own speakers, and I know Parts Express even has a forum dedicated to speaker building, and I believe the DIY Audio forum does as well.

 

[Tucker_515]

That does appear to be like a transmission line, although it seems a bit short for that. If I'm not mistaken (and getting a little technical here), transmission lines have often been sized to a one-quarter wavelength of the resonance frequency of the woofer. And the transmission line narrows as it reaches its exit on the cabinet.

I love technical as long as I understand it! So the resonant frequency of the woofer (KEF B200) is 25 Hz. That makes the wavelength 45 feet, and a quarter of that is 11.25 feet, so unless there is way more to the baffling than I think, its not tuned to that frequency. Could it have been tuned higher for some reason?

Also, another question. Both drivers are 8 ohms, does that make the speaker 4 ohms because if you hook the two up in parallel you get 4 ohms, or am I overthinking it and it's an 8 ohm speaker? I haven't checked them with a multimeter yet, but it's on the docket.

 

[swechsler]

Most likely it's made from components and not a kit.

Agreed. I can't imagine any manufacturer stapling down splices like that (although I suppose it's not unheard of; some production crossovers look pretty amateurish).

 

[Wildcat]

Could it have been tuned higher for some reason?

It's also possible that it is not a transmission line design, even though it somewhat resembles it. I'm going from memory on this also, as I haven't read about designs like these in a couple of decades! However, this might be worth a read if you're curious:

http://www.mh-audio.nl/Calculators/TML.html

The only manufacturer of transmission line speakers I can remember is British manufacturer IMF. TL systems in general had larger cabinets due to the length needed for the 1/4 wavelength.

Both drivers are 8 ohms, does that make the speaker 4 ohms because if you hook the two up in parallel you get 4 ohms, or am I overthinking it and it's an 8 ohm speaker?

With the crossover, it still works out to be an 8-ohm speaker. Any system I own with nominal 8-ohm drivers ends up being around 8 ohms nominal. (But like any speaker, impedance varies with frequency. For your purposes, though, you "technically" should have an 8-ohm system here.)

Agreed. I can't imagine any manufacturer stapling down splices like that (although I suppose it's not unheard of; some production crossovers look pretty amateurish).

Ouch! I didn't notice that at first. Yes, definitely not the work of anyone outside an amateur (or a white-van speaker manufacturer ).

 

[Tucker_515]

Yep, the amateur wiring shockingly failed where the lugs are attached. Neither of them work, I bought some new ones that I'm going to cut in. Other than that, as sketchy as it looks, the connections are all soldered, even the stapled ones.

 

[crdm6]

I think the crossover is a home made version of a KEF 104ab or Calinda crossover. Most likely the 104ab version because of the switch which looks from the picture to be selecting taps on the woofer inductor assembly. They added an L-Pad and the fuses to protect the T-27. Probably.

The B200 SP1014 has been used in transmission line arrangements where it's relatively high Qts didn't matter as much.

Like most old KEF drivers they sound quite good for the age of their design but they had very low upper power limits.
Made for tiny English living rooms with mostly classical music.

 

[SaSi]

These are certainly DIY enclosures and crossover. Certainly have nothing to do with the Reference 104, as that utilized a B200 SP1039 and also a passive radiatior.
The "labyrinth" is not a transmission line. More like a way to make a very large and longer port for the enclosure. But the cross section is so large, the length becomes inadequate.
You can enter he TS parameters for the SP1014 and the port dimensions and length into Winisd or other simulation s/w to get an idea of the expected response. Without having done that, I would guess they will perform slightly better if you close the mouth of the port. The box will then be more or less sealed and a bit on the large side for the B200, giving a low Q alignment that will give well controlled and smooth rolloff bass.
I would not be scared to use the T27. They are "legendary" and were good in their time but many complained about their resonance and sqwaky response. I personally like them. Bear in mind that the original designer of the T27 has re-engineered them and Falcon Acoustics are running small production runs of brand new versions that are equivalent with the original ones for about $150 each.
It would be worth to trace the crossover and provide a schematic to see and let you know if it's OK for these drivers or not. Of the top of my head, the T27 needs to be crossed at about 3kHz (it has a 1kHz resonance) best with a 18dB/octave crossover. From the picture it doesn't look like you have a 3rd order crossover.

 

[crdm6]

"Certainly have nothing to do with the Reference 104, as that utilized a B200 SP1039 and also a passive radiatior."

Not exactly true. All the B200s have a similar upper end response. The "big magnet/voice coil" versions DID require a much different box but a home constructor with a B200 and a T27 could do a lot worse than copy the crossover from a 104ab. Actually tracing out the crossover would be interesting. Just eye-balling the photo, it does look like a 104ab.

The crossover for the Calindas, which I happen to own, is almost exactly the same as the 104ab. Actually lots of KEFs use that "Acoustic Butterworth" type tweeter crossover. KEF published a paper about it. All the speakers that have some type of B200 have different bass crossovers obviously but that has little to do with the cabinet type. The B200 family was used in a mind boggling number of speakers not all of which were made by KEF. At the time it was probably the best 8" driver which could be purchased outside of a complete speaker. The Spendor 8" was great but they only came in BC1s.

If Falcon starts making them again I will be sorely tempted even though they will be stupid expensive. There is a rumor they will.

 

[Tucker_515]

Thanks for the responses, just last night I installed new wire lugs and listened to them for a while. They have a very smooth and deep bass even at low volume. But like crdm6 said, they do not take a lot of power. The tweeters are, for a lack of a better term, screechy or hissy when there is a shhhh sound. I will draw up a schematic of the crossover if anyone is interested. One thing, the inductors are not labeled and one of them has 3 wires coming off of it. I'm not sure how to represent that in the schematic.

Also, I have the L pad turned down a bit, and the fuse is a 1/2 amp, will this keep the T27s safe? Granted I will not be blasting them, they are going in my bedroom which is roughly 10x12 with 12 foot ceilings.

 

[crdm6]

If I'm correct that the crossover is a copy of the 104aB, there might be a problem with the L Pad. One of the aB network goals was to compensate for the voice coil inductance. If an L Pad was added between the T27 and the network that might mess that up. KEF always directly connected the tweeter to the crossover. Of course the values the maker used might be wrong too.

It would be great if you could draw up a schematic. I am assuming you can't take it apart to actually measure the coils but if you could get any capacitor values that would be good.

Here's the 104aB schematic. Note squiggly line labeled 2.0/2.7/3.5mH. That's a coil with taps. Signal goes in on the left and comes out the right OR from one of the two lines in the center. Not shown is a jumper to select one of the three.

 

[Tucker_515]

Here is a crude schematic I whipped up. It does look similar to the 104aB, but the 3 way switch is very odd. It seems that in both the up and down positions, all 3 terminals are connected, and in the middle position just the top two terminals are connected. When I use the switch, the top and bottom sound the same, and when put in the middle, it shuts off the mid woofer. Also, two of the legs off of the large inductor are together on one of the switch terminals. Also, the two large dark cylinders in the bottom picture, by the large inductor and switch, have no markings, I assume they are resistors and I measured each to be 3 ohms with a multimeter.

 

[crdm6]

Looks like I was right. Some of the values are close but wrong and the switch is wired wrong. Still, it works sort of. It's late for me so I'll look at it again in the morning. This could be good.

 

[crdm6]

Looking at it this morning, it seems to me that the problem is that the B200 is the wrong one for that circuit. The one you have, the SP1014, has a very high midrange level compared to the SP1039. I think the screechy you're hearing is actually the B200. If you want to test this theory, turn the L Pad all the way down so the tweeter is off. If it sounds about the same then there you go.

The tweeter section is not too bad but the 10 ohm resistor should be a 3 ohm. The L Pad shouldn't really be necessary and the fuse could be increased to a 1 Amp fast blow which is what KEF used. 1/2 Amp is a bit conservative.

The switch is a center off type which explains what happens when you have it centered.

If you want to pursue this you would need to rebuild the woofer section to accommodate the SP1014 version woofer. The KEF approved type is the SP1015 crossover. Parts Express has all the bits you'd need. I would get iron core coils for this and electrolytic caps. You will have to parallel some caps to get the correct values like a 15 and a 1 to get the 16's. You will also need to get a 6.5 ohm power resistor to put between the 2mH coil and the 16uf cap. The original KEF 2mH coil had that resistance so you need to fake it. They don't have a 1.1mH coil but a 1mH should work OK.

Do NOT buy the expensive versions of the parts. It won't make this circuit better.