|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
76.173.115.53
I've assembled the following "rules of thumb" related to SET/speaker Interface that I'd appreciate feedback/corrections/comments on. Not hard and fast requirements, just general guidelines to consider. I don't yet have a firm grasp of the last two. Most of these came up while researching suitable drivers, hence there are a broad range of important issues (crossovers, phase angles, etc.) not covered here. My aim would be to revise this list with input/feedback form this board.
1. Watt requirement for various speaker dB ratings (see AA FAQ by Paul Joppa)
2. Nominal impedance >= 8ohm and relatively flat response
3. Avoid highly reactive drivers => generally larger drivers that handle high power.
4. Mass rolloff of woofer (where driver rolls off on top) = Fs / Qes helps determine suitable enclosure type (source: Bruce Edgar)
5. Woofer impedance at resonance around 50 ohm or less, and < 5-6X rated impedance.
6. The amplifier's output impedance should be no greater than the speaker impedance (and preferably less). SET Zout is usually 4-10 ohms.
7. Large magnet + light cone = low Qes. 15” light cone ~50 grams. If horn loaded then pick a driver that has a stiff cone, low Q and a very strong magnet. Forget about drivers with a moving mass above 60-70 grams for a 15"
8. High magnetic flux density (source: the late Dr. Gizmo)
9. Alnico or neodymium magnets preferably (source: the late Dr. Gizmo)
10. Very small voice coil gap (precision voice coils) (source: the late Dr. Gizmo)
11. Qms < 7 and resonant frequency relatively high (high Qms & low Qes is BAD)
12. Damping Factor = speaker impedance / amps output impedance + DCR voice coil. Generally 2-3 for SET
13. Drivers with low order distortion specs that cancel out SET amp’s distortion (Eduardo de Lima’s whitepapers).
14. Amp/speaker synergy: Driver with roll-off tailored to SET’s output transformer inductance, which forms a third-order electro-acoustic filter (source: Srajan Ebaen’s Soundstage interview with Eduardo de Lima).
Follow Ups:
The one simple summary of all that information might be that the better damped (ie. controlled) the speaker itself is the more likely that it will work well with a SET amp. Speakers with poor self control (ie. High Q bass alignment, wild impedance, high mass drivers with small motors etc.) need to get it from the partnering amp but this then introduces compromises (as we in SET asylum all know) in the circuit design that does not lead to good sound (like lots of negative feedback).
Nice succinct summary of the essentials.I'm still trying to understand:
"14. Amp/speaker synergy: Driver with roll-off tailored to SET’s output transformer inductance, which forms a third-order electro-acoustic filter"
I wonder what it is about the spec of the transformers inductance, and the nature of the driver's rolloff (steepness or freq)...that would be good synergy?
Take a look and see if this fits...power paradigm rules (opens in separate window)
That's an interesting list you have going there. I can't vouch for each line item, but the impetus that builds that list is better than the list itself. I think about all of the little things that are overlooked by people who believe in applying more power to get better speaker performance (including me with my massive 8 watts and barely "efficient" 2.5 way speakers). I like the idea of expecting more from the speaker and less from the amplifier and I try to apply that thought process when thinking about total system gain too.I think one of the best things about low powered SET is that it forces us to concentrate on the things that matter the most for home music reproduction. Thanks for the reminder.
That is the way to go I think. With higher efficiency less power (and musical signal) is wasted, and with lower power less distortion is introduced. The combination of the two results in retrieval of very lowlevel information that is lost in the sheer power avenue.Actually, it is much more complex, as every system has its fault, and the power race begun to extract more of the recorded material (plus get things mass-produced). However, low power amp with very few parts in the signal path + high eff. speakers is the best road that can reveal the harmonic content of the recordings. Other solutions might sound more hifi, or with greater perceived detail, but with an alien, unnatural feeling to it.
Janos
I wish that I would have put it that way. Thanks!
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
"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
Obviously I agree with #1! :^)Many of these are often but not always true. That's because they may be symptoms rather than a root cause. I'd like to expand on a few of them - consider this my two cents worth:
#3, 5, and 11 basically say to avoid mechanical damping. But it's really only a problem when it's significantly nonlinear. Linear mechanical damping, specifically of the surround, will reduce cone resonances and coloration, and is a good thing. But many surrounds and spiders may have anonlinear damping, specifically a hysteresis behavior which can be fairly unpleasant - like poor capacitors in the electronics.
These same points, plus #2 in part, also caution against wild impedance swings which can cause response variations with amps of different damping factor. If a speaker is voiced for SET amps with typical damping factors, then that is not a problem. By far the largest problem is speaker systems which have a minimum impedance below, say 75% of the nominal impedance. Impedance peaks cause less of a problem.
#2, 6, and 12 are also related. I don't think the nominal impedance is important, as long as the amp has a suitable impedance tap on the output. SET amps usually have a damping factor of 2 to 4, meaning the output impedance is 1/4 to 1/2 the nominal. Four ohm speakers work fine on a four ohm tap, but they hurt on an 8 ohm tap and really suck with a 16 ohm tap.
#4, QT matters, not QE, and fs/QT has to do with the bass cutoff, at least for direct radiator speakers. QE is relevant for horns because a good horn will add considerable mechanical (radiation) damping, swamping out the speaker's mechanical damping.
#7, 8, and 10 basically say that the speaker should be efficient. To get efficiency, some combination of powerful motor, light moving mass, and large radiating area is needed. But none of these parameters by itself is critical. All of them also make for poor bass extension. What really matters is efficiency and bass extension, which rep[resents a tradeoff among these parameters and the system requirements.
#9 - yes, alnico and neodymium do often sound good. A major reason is that they are conductive, which ceramic is not, so these magnets effectively have shorting rings built in to reduce distortion. But ceramic magnet systems with shorting rings have the same virtue, and should not automatically be rejected.
I am a great admirer of Eduardo de Lima’s work and would encourage anyone to read his papers if you are thinking of making an integrated speaker/amplifier system.
inter-relationships among some of these, and clarifying some of the others. Raising the tradeoff issue of LF extension vs optimizing other areas is important, an aspect that requires everyone's attention.I do not have a real handle on a few of De Lima's comments (#13-14) and would be grateful if someone could explain these in layman's terms.
Paul,Great info. I have a question. If I have a 16 ohm (nominal) speaker, would it be better to drive this with a 16 ohm tap or an 8 ohm tap from the amp.
Given that the speaker may actually have impedance below 16 ohm in its freq range, would it not be better to always have the amp at a lower output impedance than the speaker's impedance to meet rules #2 and #6 always. But then again having a 16ohm tap with a 16ohm speaker impedance gives better impedance matching. Your thoughts and commnets most appreciated.
Addicted to Tubes
Janos is right, it gets down to specifics.Some amps use a relatively low transformer impedance (relative to the tube's operating point) in order to get more power from the amp. This works as long as the speaker impedance does not drop much below nominal. Other amps may use a relatively high transformer impedance, which enables them to work well with speakers that have a more severe impedance dip. Also - a separate effect - using the higher primary impedance provides a larger damping factor, which may or may not be important for the speaker in question.
Putting a 16 ohm speaker on an 8 ohm tap will provide more damping, less distortion, and less power. Best to let your own ears choose among these. It won't hurt anything either way.
In this case it comes down to how the specific amp interacts with the specific speakers, and with the room acoustics. In one room the 8R tap would work better, and in a different room the 16R might be the optimal... it also depends on how much power the amp has, and how sensitive the speakers are.
The way the OPT is built (capacitances) also influences the selection.
Hi Janos,In my case, I have 8w 300B SET amps driving 16ohm EV12TRXB speakers which are 96-97dB.
A 300B should drive 96-7dB super easily, but I have no idea which tap will sound better. The 8R tap will probably have better highs, and the 16R tighter bass.
Hi Janos,In my case, I have 8w 300B SET amps driving 16ohm EV12TRXB speakers which are 96-97dB.
When "conventional wisdom" says otherwise? Just curious what your thoughts are regarding this.
a guideline. Compared to most SS amps with high damping factor that provide good electrical braking of cone motion, I understand that most SET amps generally have comparatively low DF (say 2-3). Consequently, a driver with a relatively light cone and a spider/surround that provides good mechanical damping becomes important in order for it to behave linearly with low reactance. At least this is my current understanding, and I encourage feedback if mistaken.
Yes, if you have a low damping factor you will need a well controlled (good mechanical damping) speaker.With most SS gear the speakers will be over-damped. That is just as bad as under damped.
It's the total system Q that matters. Total system Q includes (among other things) the room.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I think you have covered very much and hope this will decrease the number of posts ie. " Can I run 45 monoblocks with my Magnepans?". I know that interest in SET is growing fast and your post should help some novices that have these type of questions. Thank You.
This post is made possible by the generous support of people like you and our sponsors: