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In Reply to: RE: Optimal Set up for KEF 105 Speakers posted by Bill P on November 26, 2007 at 11:28:24
I own the 105.2s. Some comments on different things:
1. The castors:
My speakers are directly on hardwood floors, and I found it was essential that I decouple them from the floors as much as possible, or else the lower midrange would sound a bid muddy or congested. The casters were bad, as they directly transmetter speaker vibrations to the floor. I did a lot of experimenting. In the end I removed the castors and placed sorbothane spacers between the bottom of the speakers and some heavy bucther block squares squares I got at Ikeya. I put felt pads under the butcher block so I could move the speakers around. The lower midrange inproved considerably. A simpler solution, perhaps even better, would be to used Subdudes made by Auralex under the speakers; they give superb damping and isolation. However, since you are on a carpet, maybe that is enough to de-couple you from the floor., and you could get by with the casters. The ones that came with it are nothing special, and cheap ones from a hardware store would be just fine. My first house did have thick carpets, and I could easily move them around on the casters. You do have to avoid transmitting cabinet vibrations to the wood floor
2. The crossovers.
The stock crossover contains a lot of electrolytic capacitors. These can degrade after 20 years or so. You might consider replacing them or upgrading them to polyproplyene ones, which I did. The latter changed the sound a bit, making it more resolving and somehow cleaner sounding, with perhaps a bit less richness.
3. Amplifier.
I found that the big woofer benefits from a powerful SS amp, which can really control the woofer and tighten up the bass. I got the best sound from them with a Plinius with 175 w/ch.
These are very fine speakers. When they orginally came out, some reviews ranked them among the best in the world, and they still can hold their own if the crossovers are in good shape and they are properly driven.
Best of luck.
Joe
Follow Ups:
What did you do with the three 120uf non polarised electrolytic capacitors inside the bass cabinet? Did you try eliminating the high pass filter into the woofer altogether?
I don't have the circuit diagram with me right now, so I'll have to check. It was a while ago, but I remember debating whether to do something about some input caps that were there for woofer protection or some such thing; my mind is now hazy on the matter. There were two slightly different versions of this crossover. I did a replacement for every cap, but for the biggest ones, I used a combination of an electrolytic plus a smaller-value p-p in parallel to keep the cost down and make the sizes manageable. I did disable the S-stop circuitry (I think that was what it was called).
I didn't mean to dump on you about this. It's just that the 105's were the only world class speaker system I have ever seen that had a high pass filter into the woofer. When I saw that the first time I couldn't believe it. I figured it had something to do with making all the drivers operate in a bandpass filter to control phase. However, if you run the numbers assuming that the composite series cap is half of a 12db high pass filter into an 8 ohm load, then the -3db point is at 39hz. Below that it will roll off electrically at -12db and ostensibly another -12db for an acoustical rolloff. Sort of a brick wall at 40hz. Now that's okay if you're running records and want to minimize the chance of turntable rumble, but in a digital age, that seems meager to me. And when you run into speakers that are cutoff in that way, you wind up hearing comments about how much better the speaker sounds once you put 200 watts into it. Well, power won't actually change anything in this case.
That's too bad, because apart from the limitations in the extreme bass, the 105 is a stellar performer. I love the performance of that oversized tweeter. I would guess the wonderful frequency response is a consequence of the fact that though the tweeter is a dome, it isn't really a hemispherical dome. It's tremendously flattened out which extends the flat response and broadens the operating surface, or to put it a different way, the tweeter doesn't stick out very far from the surface of the baffle. That's a really good idea. The output at the center of the dome isn't fighting the output at the edge. -
Anyway, I have had friends who have owned 105's and both of them had to have their woofers replaced. A rather expensive proposition. Both of them attempted to 'fix' the bass problem by using bigger amps. It doesn't work. It just burns up the woofers.
I was just wondering whether anyone simply bypassed that high pass filter. It would be a gutsy thing to do. Simply bypass the three 120uf caps and disconnect the parallel coil and reverse the leads for the woofers. That should put the woofer in correct phase again. You might try it sometime. I don't know what it will do. Maybe nothing. Probably it will just soften the brickwall at 40 hz.
I still haven't had time to check the diagram, but I remember it did not have three 120 uf caps on the woofer circuit. Maybe it was two 200 uf, but doing the same thing. I do remember debating removing them altogether, but I was told they were there to protect the woofer in case of a malfunction of the amp. Since I have never had or even known anyone to have that kind of a malfunction, I wasn't worried. In the end, I decided to leave in the big caps.
After careful comparison to what I heard at concerts, I decided the biggest thing lacking for me in the 105.2s was the extreme low bass. I added Hsu subwoofers that were down 3 db at about 40 Hz and dropped 12 db/octave above (as I recall), and they made the low bass very nice. The subs were flat down to 20 Hz. I now only use these speakers as rear surrounds in a five-channel SACD system. They are an OK match in this use for the Vandersteen 5s I have for fronts. The 5s are simply in a different league from the Kefs.
Joe
about your comments around the premises that a lot of power does not improve the bass performance with these speakers. If you have lived with them as I had for many years, you will come to realize that powerful amp does make a difference in controlling their bottom end. Mind you not just any run of the mill powerful amp it has to be a quality powerful amp such as the Krell KSA 150 or the ARC D-250 of which it took control of the bottom end from the beginning of the Rush’s Tom Sawyer note to the end. As far as I am concerned the x-over caps replacement did not make a heck of a difference as much as the ARC D-250 or the Krell KSA 150 did to the overall sound characteristics. Of course YMMV.
BTW, it took Martin Logan Monolith III speakers to replace it in my listening room.
If a thing's worth doing, it's worth doing well
(Proverb)
I think we're talking at cross purposes. You think of bass as sustained low frequency energy. Most people do. I am talking about extended low frequency response. Certainly, having the many paralleled output devices and high capacity filter caps can offer great benefits for sustained low frequency response. What it won't do is give you extended frequency response when the woofer, in this case, has a 360uf capacitor blocking those frequencies. The filter I'm talking about does exactly the same job as the filter which blocks midrange frequencies from a tweeter. I don't think you would say that you can get much better midrange frequencies from a tweeter if you just give it more power, would you? That's the problem in the KEF 105, and in my experience it is the only speaker I've seen that puts a high pass filter in front of a woofer. In order to compensate for the electrical and acoustic rolloff represented in the KEF 105, you would have to set all the frequency controls on one of those consumer grade 10 band equalizers in the minimum position, except for the band for 30 hz. That band you would set to the maximum setting, giving a maximum difference of 20db. I'm not advocating doing that, I'm just saying that the deviation from flat response is that severe. Now if the series filter cap and parallel coil were taken out of the circuit, one could cut that deviation in half, but most people don't do that. They buy a bigger amp.
Bypassing or replacing the standard caps in the 'actual crossover' part of the circuit can be a benefit. However, KEF was trying really hard on the 105's, and I would guess that the most you could hope for would be achieving a different sound. Certainly, one could compare the differences of the caps by their equivalent series resistance and see whether or not there could be benefits.
I did not go to a high power amp in order to drive the bass response lower or to increase it. I found that different amps seemed to have different abilities to control the woofer. I'm talking about the lower midrange, not the deep bass. The Plinius gave the cleanest, tightest sound in this region of the three to four amps that I tried over the years. It also was the best with my Spendor SP 100s in the same frequency region and in general. Lower power amps couldn't handle my large room with these inefficient speakers. The TT I had at the time I bought the Kefs had some very low frequency rumble, and I never knew it at first . It didn't make it through them.
Joe
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