markus111

Actually, I'll second the question. I picked up a pair of RF-7 tweeters a while ago for cheap. I have no idea why I bought them - maybe just to add to my growing speaker component collection Actually, I was toying with the idea of mating them to a pair of JBL woofers I have. Does anyone have the impedance curve for the tweeters, or a frequency response graph? If not, I'll go ahead and measure them when I get the time. In the RF-7's, the tweeters handle 2k to 20khz, so it may be possible to throw together a 2-way system with the components I have. Mark

As thebes pointed out, it's probably a minor problem. But to be safe, ask if he is willing to take pictures of the inside of the amp with the covers removed. Tubes, caps, and control cleaning are not that big of a deal, but a fried output is a bigger problem. If you can get pictures of the inside, look for gobs of wax on the bottom panel that would have leaked from the transformer. It doesn't necessarily mean that it's shot, but it does mean that it ran very hot for a long period of time. To get the best sound and reliability out of this amp, you are probably looking at new filter caps and coupling caps at a minimum. Probably $100 in parts, and a couple hundred in labor. These are darn nice sounding units when they are restored. Mark

Has anyone tried the crossover box from Vidsonix? It looks like a pretty quick way to try different crossover points, slopes, etc. http://www.vidsonix.com/vidsonixnew/vidsonix_audio4ind.htm Mark

I can't speak for the Beyma, but the JBL absolutely embarrases the T35. It's a very nice sounding tweeter on the K Horn, and adds tremendously to the sound. Mark

---------------- Yes! metal near an air core will mess it. Case in point: hat stupid steel crew on the AA tweeter filter inductor! Al K. ---------------- Does this include the squawker horn? Is it only ferrous metal that will mess it up? I can remember an article in Speaker Builder where the author took a pair of Advents (?) and unhooked the tweeters from the rest of the network, and unhooked the woofer. He was actually able to drive the tweeter inductor with inductive coupling from the woofer inductor! The unhooked tweeter volume was only 20db down from when it was hooked up! His point being that there is significant coupling present in some production speakers. He modded them by separating the tweeter and woofer sections of the crossovers, and he says that he could tell a difference in the sound. I wish I could find the original article - I'm pulling all of this from memory. Mark

I had a co-worker try to get me into the act. He took me to one of the meetings, and it was one of the creepiest experiences I've ever had. I couldn't get the Jim Jones cult and people drinking cyanide kool-aide out of my head. These people were clearly brainwashed, and I felt like the whole thing was designed to brainwash the newcomers like me. It took 6 months to get this co-worker off of my back, before he finally got the point that I didn't want to join. Stay away!

---------------- And! I know people who rely on crimping only, and say that it works well for them! Erik ---------------- Erik, They are very lucky people! One of the worst weeks I've ever spent was in an environmental test facility testing a new machine. We had a new tech who didn't know that he was supposed to solder every connection, as well as crimp. As soon as we got the machine on the vibration tester, it stopped working. For the next 12 hours we had to carefully solder every connection until we could get it working. While we were doing this, we were still paying $100 an hour for the testing! Even though speakers are not subject to harsh environments, they do get quite a bit of vibration. I think for as few connections as there are in a crossover, it's worth the time to solder up all the loose ends. Mark

---------------- On 5/17/2005 1:30:17 PM D-MAN wrote: ---------------- On 5/17/2005 10:07:04 AM psg wrote: some folks think that there is some edge diffraction with the 3/4 plywood motor board. PWK thought this was a non-issue." ---------------- Who in their right mind is going to admit that it increases refraction and we did it because it was cheap? Nobody who wants to sell the things... I rest my case. DM ---------------- I agree. There may be an issue (probably small) - not a big enough issue to warrent changing a manufacturing method. It's probably way up on the exponential curve of diminishing returns. You get a 0.05% increase in performance for a 3% increase in manufacturing time and cost - not worth it. Mark

---------------- On 5/17/2005 8:42:01 AM Raptor22 wrote: Markus, I have always been led to believe that for a proper solder joint the conductor should been tinned with solder first. However, if the purpose of the soldering you refer to is to encapsulate the joint rather then provide the electron path then I might defer. ---------------- Deforming and tinning provide the same basic purpose of getting through the thin layer of oxidation that exists on the surface of the copper. We found that deforming it first worked better in our application, followed by soldering to seal it. Tinning is definitely preferred at home, as most people won't have the right crimpers for every applicaton in their home workshop. We have about 30 different sizes at work. Mark

I work in the auto industry, where we had one of the most expensive recalls in history due to bad connections. We performed a 1 year study (no joke) on how to properly put a connector on a wire to achieve the best connection and conductivity. The conclusion was that you crimp the wire so that the copper wire deforms, and then solder over it. Deformation of the wire is important for greatest surface area contact. Picture a multistrand copper wire which consists of 20 or more individual round strands in a bundle. It should be crimped with a crimper that can smash the round wires into approximately hexagonal shape so that there is a high amount of surface contact, and little air space between the strands. It is important to have the right size connector for the wire diameter. Then, you solder over the connector to fill in the remaining air space. This approach was found to give maximum conductivity as well as protection from oxidation. Mark

---------------- On 5/6/2005 4:30:32 AM DrWho wrote: I think the best way to answer your question is to ask why do you want to know, or for what application do you plan to apply the information? ---------------- Dr. Who, Thanks for the detailed response. Actually, that's exactly the type of info I'm looking for. As for how I'd use it, really just to gain a more objective understanding of what I'm hearing when I listen to music and evaluating my system. I don't have an equalizer in my system, just because I've not yet heard one that improved the sound. However, I wouldn't batt an eyelash at changing a tube, or a capacitor value in my amp or crossover to get just the sound I want. I know that sounds like driving a tack with a sledgehammer, but I like building and tweaking tube amps. I have a spectrum analyzer, but sometimes the trace of the sound which is coming from the speakers appears almost identical when in fact the sound is not. It would be nice to say, "the sound of this female voice seems harsh in the upper range - I should look a little harder at the range from 3-4khz." Of course, it could be Stevie Nicks, in which case the whole range is harsh But seriously, I would just like to be able to evaluate sound in the same way a chef evaluates cooking, and to be able to speak about it in more precise and objective terms. Mark

I remember reading somewhere that 8khz was the "sibilance" region. Is there a document that describes in laymans terms how different frequency ranges correspond to different colorations of the sound? I would imagine this is the kind of thing that any self-respecting sound engineer or recording techician could spew in his sleep. Mark

Ok, after some extended listening with the 2404s, I have a bit more to add. Overall, the sound is excellent. The improvement over the T35s was well worth the price. Imaging is far better, transients are great, and there is considerably more detail. I felt that it was a bit hot on the high end, so I went ahead and measured it. On my 31 band analyzer, it is 2db up at 6khz and 8khz, but then it drops back down and remains flat out to 16khz. If I am reading John's graphs correctly, it looks like it may be worthwhile to try the filter and play with that resistor value. I've got enough spare parts lying around, so I will give that a try this weekend. Mark

---------------- On 5/5/2005 10:44:52 AM Mark Hardy wrote: Ask me how I know this! :-( ---------------- Boy, that is a drag! I thought that's what I remembered. It probably sounded great in their marketing hype - until the phones started burning off the hook. I wonder how many voice coils they fried before they pulled this from the market? Seems I remember this option from several of the manufacturers during that time. I wish I could remember what "that time" was. Was it 1982 - 1984? A mind is a terrible thing to lose........ Mark

Sorry - off meaning leave it on a/c. Mark

As I remember, this was a fad for a couple of years where they advertised direct coupled output. Don't quote me on this, but I believe it let them advertise that the response was DC (zero Hz) to 30khz, or something ridiculous like that. I remember having a discussion with a pretty knowledgable Marantz guy who said there are times when you shouldn't use it, and it really doesn't have any benefit sonically. He recommended leaving it off all the time. Mark

I just recently heard a pair of the reproductions. My modified khorns sound quite a bit better. It really wasn't a fair comparison though, because the room the hartsfields were in was way too small. I had a feeling that they should (could) have sounded a lot better than they did. The bass was truly excellent, but the mids and highs were not so great. Part of the problem was that the guy demoing them nsisted on playing them so loud that the treble cut through you like a knife. I have a feeling that in the right setting these could sound really good. They still cost $20k though, and for half that you could put together a pair of Jubilees.

If you want the best bass response that you can get, then those measurements are zero inches and zero inches It really makes a difference getting them pushed right up to the corners, and actually sealed against them to get the flattest frequency response. If you can't get them right in the corners (like most of us) they will still sound great, but they may have some peaks and dips in the bass. There are many threads on this BB about sealing your khorns to the corner, or even making false corners. They also sound best when aimed right at you. Getting them in proper corners and aimed at you can be tricky. Mark

---------------- On 4/29/2005 7:02:09 AM Frzninvt wrote: I think I am going to pull the K-77's out of my '77 Khorns and put them in place of the T350's in the Speakerlab cabinets then. I can always have a woodworker build me a new motorboard and I can mount them in the same configuration as the speakerlab K's with the tweeter mounted vertically to the one side of the midrange horn. I see these tweeters sell for $300 a pair easily. I just need to get some 100W L-Pads from Parts Express. ---------------- Do yourself a favor and build the l-pad out of resistors. I have a pair of the parts express l-pads that I'm ready to throw out. They have sounded terrible on everything I've tried them on. I haven't opened them up, but I have to assume that they are wire-wound, because they have inductance as well as resistance! When I tried them with my tweeters, they severely rolled off the top end. Mark

Yeah, we have some great banter. The engineers tell physicists jokes, and the physicists tell engineer jokes. And in both cases, that darn light bulb never gets changed...... I'm kidding about the physicists. We have a lot of great guys at work. Only one or two fall into the nutty professor category! Seriously though, this is an interesting thread and I don't want to derail it. One possible reason for bringing in an "air" guy would be to study the sources and effects of turbulence in a horn. Reading Bill Fitzmaurice's articles in AudioExpress, he goes to extreme lengths to round internal corners and make the horn folds as smooth as possible to avoid turbulence. It may be interesting to do a very detailed model of the way air moves around horn foldings. ME's may already be doing this - I have no idea. Mark

Please - don't bring in the physicists! I am an EE, and I work for physicists. The physicists I know would design the perfect speaker. It would be incredible, magnificent, sublime.... It would be the best speaker in the universe that could NEVER possibly be built by mankind.....

There was a guy on Audiogon with those Fostex horns for sale. It looked like a steal, as he was selling the fostex mid horns plus drivers, fostex tweeters, and fostex bass bins for $1400! The only catch was it was pickup only, as these babies weighed about 300 pounds a piece. Back to the 2404 - I tried padding them down with an l-pad tonight. They are the rotary l-pads from partsexpress. Man, these sounded awful! After listening for a while, I went ahead and measured the system. The tweeters were matched to the mid as far as volume, but it was severely rolled off above 16khz. There must be some inductance in those cheap l-pads. It wasn't just rolled off though, it really sounded horrible. I may pick up a pair of autoformers for the tweeters. Has anyone actually tried this yet? I know Dean and Al said they were going to try it. I was just curious if anyone has experience using the autoformers on their tweeters. Mark

That sounds great Al. Is there any concern using these for tweeters with respect to frequency response? Just curious if they roll off at the top like most transformers do. Mark

---------------- On 4/27/2005 10:11:35 AM DeanG wrote: Something that can be easily integrated is a second autoformer, which is what I'm going to do with the ALKs I'm building. If the autoformer is situated between the driver and tweeter filter, the different taps can be utilized to attenuate the tweeter without having to change any component values. Thanks to Al and UT, there is now the perfect autoformer for this, which supplies attenuation in 2db increments. I personally think this is the way to go if trying to incorporate a new tweeter into the mix. ---------------- Dean, That's a good idea - I was thinking of doing the same thing. I think you will also need a swamping resistor on the input the tweeter autoformer. If you just use the autoformer, it will raise the reflected impedance of the tweeter, which will change the crossover point. The swamping resistor in parallel with the autoformer brings the impedance back down to 8 ohms or so. Al had a suggested value for this in another thread. I think it was 15 ohms?????? Mark

Yeah, the midrange thing. I think most of my midrange woes come from the fact that the room is too small and I'm too close to the horns. I actually have a couple of 511b horns and 802-16G drivers waiting in the wings. I was going to hook them up, but I may wait and get used to this JBL 2404 in my system. It sounds so good right now, I may wait a week or so and then re-evaluate to see if there are any other changes I want to make. Mark