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In Reply to: Critique this list of "rules of thumb" for SET/Speaker Interface posted by RioTubes on December 28, 2006 at 09:44:18:
Excellent post.
I'd add to the watts per dB requirement that multi-driver speakers need to be much more sensitive than single driver speakers. A 95dB single driver speaker is probably an easier load than a 105dB efficient 3 way horn. At loud listening volume you will probably get less distortion with the 95dB-er single driver, than with the 105dB 3-way, with SETs less than 4W. (Beyond 4W I have no experience.)BTW, I am building a DIY driver just for curiositys sake, using a 13kGauss neodymium magnet 1in diameter with 88lbs pulling power. It's 7in paper cone, 8R copper vc, vc+cone: 6 grams total. The cone is glued with elmers glue, the vc attached with superglue. No surround nor spider so far. The thing is not too sensitive, I have to listen to it from 2in with 1W, but it has an unbeleivably clean sound I never heard anywhere. (Although it plays pretty loud with 20W, but with heavy bass the cone starts breaking up.) Like squeezing your ear to a magic hole that opens to the land of hobbits, and you hear the sounds of living miniature beings from the other side. Most spooky experience I had with audio so far.
Long live DIY,
Janos
Follow Ups:
"I'd add to the watts per dB requirement that multi-driver speakers need to be much more sensitive than single driver speakers. A 95dB single driver speaker is probably an easier load than a 105dB efficient 3 way horn. At loud listening volume you will probably get less distortion with the 95dB-er single driver, than with the 105dB 3-way, with SETs less than 4W. (Beyond 4W I have no experience.)"I don't think this is really true, at least not all the time. I do have experience with 95 dB single driver speakers (direct radiated Fostex), 110 dB single driver speakers (front loaded Lowther/AER), and 105 dB 3-way speakers (Avantgarde DUOs).
The Avantgardes are designed such that there is no significant dip in impedance below the nominal 8 ohms. This is due in part to the midrange that uses no crossover except by mechanical means - the driver plus horn frequency response. The tweeter does have a simple crossover, however, and the bass units are high impedance active drivers (okay, so the amp is really driving a two-way here, but let's go with it :)
Anyway, the Avantgardes are great with small amps like a 2-watt 45 SET. The Fostex sounds good with 2 watts, too, but is WAY more limited in what you can do with that, and it sounds more distorted when pushing them. It won't play Van Halen to full level in your 20' x 20' garage with any amp. But the Avantgardes are much louder and cleaner with that amp or one with more power and will be quite satisfactory with any of them.
Now with the front loaded Lowther/AER drivers at 110 dB sensitivity I dialed down the bias level such that my 45's only put out 0.75 watts because that's all I ever need on those speakers and I want to save my 45's for as long as they can last. Some Lowther/AER drivers are wasted on amps over 1 watt in my opinion because over this level and there is considerable distortion. Newer high end units have upped the level for acceptable low distortion, however, since I got mine.
Kurt
Hello Kurt,
"The Avantgardes are designed such that there is no significant dip in impedance below the nominal 8 ohms."
In that case, they should be truly much more efficient than a 95dBer single driver. I'm glad to hear they are built tht way.
I was thinking about very hard to drive crossovers with big dips below nominal impedance, that make it actually much harder for the amp than what their high sensitivity suggests.I use a Fostex FE204 (95dB) Voigt pipe, and I agree with you, below 2W they are not easily driven. A Double DC Darling amp (around 1W in my case)can drive the pipes based on how many appliances the neighbors use. Eventually, in case the line AC is poor, the sound is shrill, thin, and sounds a if clipping very early on. When the line AC quality is excellent, the 1W-er can drive them with unbelievable power (for an 1Wer). Beethoven symponies can be enjoyed to full extent. However, normally, during daytime, even chamber music can suck.
As most of the time the line AC is poor, my original conclusion was that 1W is not enough to drive 95dB. Then I noticed that the flea-power amps react to poor ac with a complete loss of power and tone, and the higher power amps sound only "fades". They have different reactions.
I beleive very low power amps as super sensitive to line AC. What you feed is what you get. With higher power the bigger amps loose this utter sensitivity to poor line AC.
I did not have the chance to hear very sensitive speakers with benign xovers. You made me curious!
out of curiousity, with such a light cone and large flux density, why wouldn't the driver be more efficient? sounds like you have the makings of a special driver. Also, thanks for chipping in regarding the impact of multi way vs single drivers. My current speaker uses a 95db wideband 8" fostex augmented by ribbon supertweeter with just one cap. I like this format.
I beleive that I made the voice coil too tight, and it rubs slightly on the magnet. When the elmer's glue dries, it makes the paper shrink. Quite a bit.
I hope with slightly larger diameter voice coil that won't be a problem, and I get the desired efficiency. I can increase efficiency by doubling the number of turns (and turning it into a 16 ohms driver instead of 8R). That makes a slight increase in total mass, and a quadrupling in inductance - a significant increase in sensitivity.I also use a 8in 95dB Fostex. (FE204). :) I like it so much, that I do not intend to replace it. I am making the DIY driver for a mono setup, that I want to make as DIY as possible. I don't know if I can turn out a DIY cartridge, but it will use DIY tonearm, TT, coupling caps, and some diy resistors and transformers, chokes.... I'm doing this out of curiosity. Will take a while to build.
I like his website too. Good luck with the driver. Let us know how it turns out.
Thank you for the link. I see he updated his site quite a bit. My mentor has been telling me about old folks using very long balsa arms before the dawn of ages, and he was urging me to try it out. I was refraining from wooden arms, until I saw the Altman site. Made a "copy" of the RB300 arm first, from pine. (That is, 12in long arm.) It is slightly more elaborate than the Altman arm, carved, and painted with shellac. I was purely shocked by its sound. The RB300 sounds like a broken metal can in comparison.
since then I went through a couple different wooden arms. A flat (also carved) 18in pine arm, and others. The best arm was a yard long arm (I used an old yardstick!) That arm had unbelievable bass and detail. On organ recording I could hear the wind whistling past the mike that was suspended somewhere high in the cathedral. After 6 mo the long arm started to bend, but ultimately I had to dismantle it, as it was definitely not cat-compatible. Now I use a "short" arm again, a mere twofooter, as it fits into the cabinet with the TT... but it does not sound nearly as good as the yard-long version. Cart (and cat;) compatibility with arm is a very finicky business.Long (arm) live DIY!
Janos
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