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My diy speakers are 6 1/2 2-ways use high quality crossover parts and components including the often used Vifa AG25. Although I use a very nice front end, highly modded cd player -> DACT passive attenuator -> Musical Design D75 ss amp -> speakers, I'm still getting a bit of sizzle around voices. Piano, violins, brass instruments, etc sound great:) Any ideas on how to smooth out this sizzle? Keep in mind it's not horrible, just there at times when it shouldn't be. Any suggestions on using another tweeter (maybe a soft dome or cloth dome type). My crossover is a 1st or 2nd order type. Overall, mine is a nicely revealing system that just needs a little bit more smoothing out. I'm not an audiophile but I have a real good pair of ears and listen critically. Smoooth and revealing is what I'm after. Because of this problem, the speakers still call attention to themselves at times. I know a fix can be found without spending a fortune. I'm almost there. Thanks for any help you may be able to give me.
Follow Ups:
Do you have a Zobel across the tweeter?If not, make a zobel by placing a 5 uf capacitor and a 6 ohm resistor in series with one another, and then connect the zobel across the tweeter terminals.
The diffusor mod Charlie mentions will tame the top end of the tweeter, but one of the trade offs is that the tweeter will be more beamy at the top of its range. Might still be a good tradeoff.
Mr. Joseph,One again I'm amazed to receive a response to my tweeter question from someone as respected in the field of high-end speaker design as yourself. It does not appear from the crossover layout diagram that this design has the Zoebel circuit you're referring to. On the tweeter side, it shows the following from the positive input: poly caps (2.5 & 1 values) wired parallel ---> a pair of 5 ohm resistors wired parallel ---> (+) side of the D25. From the (+) of the tweeter there is a 10 ohm resistor back to GND. That point goes out to the (-) side of the tweeter. That's it. Would you still suggest the Zoebel perhaps in place of the 10 ohm resistor? Please let me know. Like I said on my original post, the overall sound is not that bad, but it's just not completely smooth either (just enough gritty, sizzle, digititus, whatever)...to call attention to the speakers and be irritating. I'm confident it's not my electronics. Is this tweeter difficult to tame? Do you think I should get away from using a metal done tweeter in the future? Would you suggest another tweeter like the D27TG05 or any other? I would truly appreciate your opinion. Thanks very much for your help.
Sounds like the circuit is just a 3.5 uf cap with a L pad of
2.5 ohms and 10 ohms shunt.I'd just put the zobel across the tweeter terminals. You can also reduce the tweeter level by either increasing the 2.5 ohm resistor or reducing the 10 ohm shunt resistor.
We did use the D25AG35 on some early RM20s. And the D27 on the original RM7si. They're good tweeters, but I think the Seas ones are better.
The cause of this "sizzle" is the series of plastic rings in front of the dome called a "phase plug" or a "diffusor". It is neither of those. It is in reality a Helmholtz resonator (just like blowing into a soda pop bottle) tuned to 15 kHz or so.It is this acoustic resonance that is causing the "sizzle" you are hearing. The solution is simple. Get a *sharp* pair of diagonal cutters (dikes) and snip the sucker out. You will be a happy camper...
What sheer luck it is that I found the answer for my question without asking it!
I have a pair of PMC FB1 speakers, which have the same D25AG-05-06 tweeters as mentioned and I have always wondered about those plastic ring in front of it. I have already replaced the whole crossover (outside the speaker now) and the internal wiring. The only remaining tweek I could think of was the removing those plastic rings, but I was unsure about their role.
Thanks for clarifying it!I was wondering however, if it is worth adding supertweeters (such as at the link below) to compensate for the lost frequencies at 15kHz?
Thanks!
Zozo
Thanks very much for your insight and comments regarding this problem. If you're right, then this may be a relatively easy fix. However, I need to better understand what you are suggesting. Are you saying that I should cut out all those plastic guards in front of the tweeter? Remove the whole thing? Since you are in the audio business (Ayre Acoustics), I assume you must have some experience with metal dome tweeters of this design. It seem strange to me that a company like Vifa would produce this tweeter with such a glaring flaw. But it's worth a try. Can't really hurt anything by doing this. I'll get back to you on the results. Does *sizzle around voices* sound like a tweeter problem rather than a mid driver problem? I don't claim to know all that much about speaker design. Thanks for your help.
If I'm thinking of the correct tweeter, the "diffusor" is molded from the same plastic as the front mounting plate itself. Once you cut the "diffusor" out, you can't put it back. Now these tweeters aren't super expensive, so it's not the end of the world. But I would be surprised if you didn't prefer the sound without the "diffusors" in place.I used to design speakers for Avalon Acoustics. We were the first US manufacturer to use metal dome tweeters. The first time I heard one, I was astounded at the improvement over soft domes. But I also heard a "hardness" or "metallic" quality that bothered me. I happened to meet Martin Colloms at a CES around 1986 or 1987 and mentioned this to him. He suggested removing the "diffusor", and it worked like a charm.
Nearly all metal domes use this "diffusor" for two reasons. First, the steady state frequency response is slightly flatter above 10 kHz with the "diffusor" in place. (It's down a couple of dB if you take it off.) Second, it provides some physical protection for the easily-dented dome. A very few companies use a simpler protection device (eg, a single metal rod in front of the dome) for better sound.
I guess most companies *like* the feeling of icepicks in the ears. Nothing like a good high frequency resonance to induce a quick case of listener fatigue...
Charles,If I'm not totally mistaken, Vifa does sell just the faceplates for its tweeters so it would be possible to buy a pair of soft dome faceplates (no diffusor / phase ring) and simply swap them on the ag35's. I've done sim. swap w/ SEAS and Audax tweeters. Also, have you ever tried the tuf-film fix on metal domes?
Pete S
If nature loathes a vacuum then why do vac. tubes sound so natural???
you want to cut the three "spokes" as close as possible to the faceplate itself. Be careful not to dent the dome (although this won't really affect the sound). I usually cut two of the spokes, then bend the "diffusor" away from the dome and hold it while cutting the third spoke.
Thanks very much for your help, Mr. Hansen. How could I not value your expert opinion. I read an interview you did with Stereophile about your preamp (sorry, can't recall the model). One of the things you pointed out was that it used a stepped attenuator which, of course, is far superior to a volume pot. Although your design was somewhat exotic using pure silver contacts and more steps than any design I'm acquainted with, I do recall that being a big plus in your design. I use a DACT series stepped attenuator which, when used between my wonderfully modded cdp and amplifier, has brought me closer than anything else to the world of high-end audio that I can't afford. I plan to install a pair of Caddocks at the inputs in a shunt circuit which should yield even better results. (a poor guys high-end preamp or Placette) Excellent when only using a single signal source. Of course, it's all about synergy. Anyway, I will do the tweek to the Vifa tweeters. I hope it does the trick. Otherwise, I'll be trying a different model. It's a privilege to have you respond to my post.
What's your crossover point? If you're using the D25AG-35-06 tweeter, and your crossover point is over 3kHz, then you're ok for that tweeter. If you're using the D25AG-05-06, it has a resonant frequency of about 1500Hz so you'd better start your crossover point above 5kHz with a 1st order filter. You may also need a resonance trap filter for the tweeter, depending on the crossover point. In addition, you may not have enough baffle step compensation for the woofer which makes the high frequencies brighter than they should be. My advice would be to re-evaluate the crossover design as I suspect that's the root of your problem.
Thanks for your input which obviously indicates that you know much more about speaker design than I do. The Vifa tweeter is the D25AG with the open back, not the 35-06 which I would rather have now. I'm sure you're comments about the crossover design are valid. I'm thinking the crossover point is about 3,000hz. I don't admit to knowing all that much about it, but I'll email you a drawing of it if you would like. I'd be glad for you to look at it and give me some advice. One other thing, in my post I mentioned that I hear "sizzle around voices." Most everything *above* the vocal range sound pretty good. Since most vocals fall into the midrange part of the frequency spectrum, could the problem be related to the mid/bass driver I'm using? With my ear close to the speaker, that sizzle around some voices *seems* to be coming from the mid driver which is the AC7 from Audio Concepts. Years ago they sold drivers and kits, but they've gone more toward the upper end market these days. The AC7 is not an expense driver but has been used in several designs...non of them very notable. I would appreciate hearing back from you and anyone else who wishes to weigh in on this problem. Surely I'm not the only one who has had this experience. Thanks.
I haven't heard the AC-7 mid woofer. I am inclined to think there's a peak around the crossover frequency that's causing the emphasis you hear. First off, try increasing the size of the woofer inductor about 50%. This will add baffle step compensation and flesh out the lower frequencies. It will also amelioriate the possible peak around the crossover frequency. You might also contact ACI and see if they recommend a crossover point and/or a zobel circuit for the woofer.
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