maxg Posted June 25, 2004 Share Posted June 25, 2004 OK - I am now armed with the rules explained simply to me by Ami (thanks) so I think I can safely make a post without getting closed / moved / other. Nothing P/political here just an audio question - and no mention of the film that dare not speak its name either! As follows: In theory I should be firmly in the camp that uses low power, SET, amplification. I say this because most, if not all, of my listening is done at low levels (usually around 75 dB with peaks around 85-90 dB). Even on my speakers - with sensitivity around 91 dB - that is an easy ride for an amp - I shouldnt have to run more than around 5 watts - ever. But here is the thing. With my previous amps (45 wpc KT88) and with the 300B amp I tried out - the amps failed to drive the woofer properly and most certainly failed to control it. During the testing period, before buying the new amp, switching from one amp to another of the other 2 amps - both failed in exactly the same way. Switching to the newer amp, the one I eventually bought, was a night and day change. The woofers were under total control. The sound was etched, large and clear wiht bass as tight and fast as I had always expected it to be when I build the things. As this was obvious - even at the low levels I listen to - I now do not think it was merely a power issue. In other words although the new amps have an impressive 70 wpc that is not the reason they drive my speakers so much better than the other amps. The thing is - I have no idea what the reason is. Just as a matter of confirmation of my findings, in a way at least, I was talking to Tony the other night about the days he used to run the KHorns. He tried out just about every form of amplification known to man (at the time - there were no digital amps around then other than the Sharp that was too problematic to bother with). After testing about a dozen examples of amps - including Cary's, 300B's and who knows what else - he went for the Accuphase E407 SS monster integrated amp with 170 wpc. In the theory prevalent on this board that is not the obvious choice, but to him, and indeed to me when I got to hear his setup the sound was staggeringly good. He cited to me that the main change in the sound had been to the Bass and that was what convinced him. Again I doubt it was the power, in and of itself. What was it? Anyone? Quote Link to comment Share on other sites More sharing options...
edwinr Posted June 25, 2004 Share Posted June 25, 2004 I don't know whether speaker sensitivity alone determines whether a loud speaker is 'easy to drive'. I think you have to also take into account whether the speaker has an even impedance throughout the frequency range you are attempting to reproduce. Some loudspeakers may have enormous impedance swings which may unfortunately coincide with extreme bass or extreme treble - just the areas where (I'm guessing here) some SET amps and low power pp amps may have trouble. Is your x-over custom made? Perhaps there is an issue there. I thought most Klipsch products where fairly benign loads impedance wise - as far as custom speaker designs like yours go, I wouldn't be surprised that you would need to try different combinations before one worked to your satisfaction. Quote Link to comment Share on other sites More sharing options...
Audible Nectar Posted June 25, 2004 Share Posted June 25, 2004 Max: To the best of my knowledge, your question relates to "damping", or the amplifier's ability to control the motion of the speaker. Of course, higher numbers don't necessarily mean better sound, as my old MC250's quote a damping factor of 10 (a low number theoretically), where other amplifiers with a higher quoted damping factor are supposed to have better control over the speaker. I like the Mc bass better than other, supposedly higher damped designs. Translation: I listen to the amp, just like any other component, then choose what sounds best. Had this former solid state loon paid attention to the theoretical, I would have something else, since low damping factor supposedly relates to less control, but I find the Mc amps to be excellent and tuneful in the bass, so it shows you what the specs know. Edwinr: Of the impedance curves I've seen (Heritage), the curves are ANYTHING but benign......in fact, they look more like the profile of Cedar Point's roller coaster, "Millennium Force". These curves show wild swings across the range, and I believe a major reason (besides sensitivity, of course) that Heritage Klipsch have a hard time finding the RIGHT amplifier to match. The impedance runs from about 4 to 30 ohms across the range.....a very broad swing for one amp to handle. Quote Link to comment Share on other sites More sharing options...
Ray Garrison Posted June 25, 2004 Share Posted June 25, 2004 Max, Your system profile says you have custom speakers, so the rest of this post may or may not be accurate, as I don't know anything about them. Typically, when different amps provide very different listening experiences in the bass, it's because the speakers present a difficult load at low frequencies. Tube amps typcially (almost always) have a much higher output impedence than solid state amps. If the speakers have a fairly low input impedence in the bass, or a very reactive one, then a tube amp's highish output impedence will react with the speakers input impedence according to Ohm's law and cause severe frequency response anomolies. A solid state amp, having a much lower output impedence, will react much less strongly. It's not simply a question of power. A 100 watt Tube behemouth with a high output impedence driving a a speaker with a very low input impedence in the bass will sound a *LOT* different (and probably much less good) than a lower power solid state amp with a very low output impedence. If the speaker is not very sensitive or efficient, that'll make things worse, but even if the speaker has a very high sensitivity and is very efficient if its impedence is low you'll bump into the problem. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted June 25, 2004 Share Posted June 25, 2004 Yup, I would also guess that it's the damping factor, which seemingly is the realm of the SS amp more often than not. There are exceptions to every rule, of course. DM Quote Link to comment Share on other sites More sharing options...
Ray Garrison Posted June 25, 2004 Share Posted June 25, 2004 To expand for a moment on just what "damping factor" is: Damping is the ability of a power amplifier to control loudspeaker motion. It's measured in "Damping Factor", which is load impedance divided by amplifier output impedance. That is, if the speaker impedance is 8 ohms, and the amplifier output impedance is 0.01 ohms, the *damping factor* is 800. That's a simplication. Since the speaker impedance and amplifier output impedance vary with frequency, so does the damping factor. Also, the impedance of the speaker cable affects damping. Thick cables (with low AWG) allow more damping than thin cables with (high AWG). The lower the amplifier's output impedance, the higher the damping factor, and the tighter the sound is. A damping factor of 1000 or greater is considered high. High damping factor generally equals tight bass. How It Works How does an *amplifier* control speaker motion? When the loudspeaker cone vibrates, it acts like a microphone, the motion of the speaker moving through the magnetic field generating a signal from its voice coil. This signal generated by the speaker is called back EMF (back Electro Motive Force). It travels through the speaker cable back into the amplifier output, then returns to the speaker. Since back EMF is in opposite polarity with the speaker's motion, back EMF impedes or damps the speaker's ringing. The lower the amp's output impedance, the greater is the effect of back EMF on the speaker's motion. An amplifier with low output impedance does not impede the back EMF, so the back EMF drives the loudspeaker with a relatively strong signal that works against the speaker's motion. When the speaker cone moves out, the back EMF pulls the speaker in, and vice versa. In short, the loudspeaker damps itself through the amplifier output circuitry. The lower the impedance of that output circuitry, the more the back EMF can control the speaker's ringing. To prove it to yourself, take a woofer that is not connected to anything. Put your ear next to the cone and tap on it. You might hear a low-pitched "bongggg" if the speaker itself is poorly damped. Now short the speaker terminals and tap again. You should hear a tighter thump. Damping factor varies with frequency. As you might suspect, damping factor is most important at low frequencies, say 10 Hz to 400 Hz. Quote Link to comment Share on other sites More sharing options...
John Warren Posted June 25, 2004 Share Posted June 25, 2004 Damping is the dissapation of energy in resonant systems.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /> In the case of a loudspeaker mounted in a suitable enclosure, damping of the loudspeaker is provided by two mechanisms, 1) electrical dissapation, i.e. the DC resistance of the voice coil and 2) the frictional lossess associated with the conversion of mechanical motion into heat thru the flexing of the suspension and spider. The Damping "factor" of an amplifier is defind as the nominal load impedance divided by the output impedance of the amplifier. The total dissipation the sum of all three. For purposes of illustration say we ignore the suspension damping and consider just the voice coil resistance and the amplifier output impedance (the electrical dissapation). Say we have an 6.5 Ohm DC resistance voice coil, 8 Ohms nominal. Say we have an amplifier with a damping factor of 100. The amplifier output impedance is then 8/100 = .08 Ohm. So the total "system" electrical dissipation is amplifier output impedance + the voice coil resistance and that is .08 + 6.5 = 6.58 Ohms. That means the amp is responsible for .08/6.58 = ~.012 or 1.2% of the total dissapation. wow! (edited for clarity, the only contibution we are dealing with are the electrical disspative effects of which the amp output impedance contributes) Quote Link to comment Share on other sites More sharing options...
John Warren Posted June 25, 2004 Share Posted June 25, 2004 Continuing The total system damping (associated with electrical effects) is <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /> Qes = 2 pi Fs R Mms / (B L)2 where: Fs = Resonance frequency of the driver B = flux density in the magnet gap L= length of voice coil wire in the gap. R = total loop resistance R is the total loop resistance and this is where the amp output impedance comes in since R = DC resistance of the voice coil + amp output impedance + network resistances. By FAR the biggest dissapative factor is the voice coil resistance as per the post above. The other big factor is B, the flux density in the gap. (added "associated with electrical effects") Quote Link to comment Share on other sites More sharing options...
John Warren Posted June 25, 2004 Share Posted June 25, 2004 moving on, the damping associated with mechanical effects is Qms= 2 pi Fs Mms/Rms where: Fs = resonance frequency Mms = Moving mass of cone Rms = Mechanical losses associated with the suspension (in mechanical Ohms). This is what I referred to (add neglected) in my first post. The total system damping is thus Qts = Qes*Qms/(Qes +Qms) and Qes is the dominant term. So Max, to answer your question what controls the woofer? all of the above. That's a cop-out answer, I admit. What makes the "best" woofers are ones that have low values of Qes and that means lots of wire in the coil (large diameter coil) and a large flux density (large . Note that these two parameters are related, if you want a large voice coil the magnet must be very large to get a high value of B. Quote Link to comment Share on other sites More sharing options...
John Warren Posted June 25, 2004 Share Posted June 25, 2004 ---------------- On 6/25/2004 3:37:20 PM Ray Garrison wrote: In short, the loudspeaker damps itself through the amplifier output circuitry. ---------------- Ray- No it doesn't. The total loop resistance (see above) is largely controled by the DC resistance of the voice coil. Amplifier damping factor is negligible. Do the math. The DC resistance and the BL product damp the woofer electrically, the amp does "squat". Mechanically the suspension is the dominant. jw Quote Link to comment Share on other sites More sharing options...
John Warren Posted June 25, 2004 Share Posted June 25, 2004 ---------------- On 6/25/2004 2:29:33 PM D-MAN wrote: Yup, I would also guess that it's the damping factor, which seemingly is the realm of the SS amp more often than not. You geussed wrong. There are exceptions to every rule, of course. Yes, the exception is called engineering. DM ---------------- Quote Link to comment Share on other sites More sharing options...
John Warren Posted June 25, 2004 Share Posted June 25, 2004 ---------------- On 6/25/2004 5:58:11 AM Audible Nectar wrote: Max: To the best of my knowledge, your question relates to "damping", or the amplifier's ability to control the motion of the speaker. Of course, higher numbers don't necessarily mean better sound, as my old MC250's quote a damping factor of 10 (a low number theoretically), where other amplifiers with a higher quoted damping factor are supposed to have better control over the speaker. I like the Mc bass better than other, supposedly higher damped designs. Precisely! The reason why the Mc bass sounds good even though it has a DF of 10 is becasue, to your point, the DF is a meaningless parameter. ---------------- Quote Link to comment Share on other sites More sharing options...
Soundthought Posted June 25, 2004 Share Posted June 25, 2004 Great posts, John. Excellent answers, gentlemen... On a side note... This is where my belief in the benefits of bi-wiring come into play. Please. Correct me if i'm wrong. Back EMF not returned or seen through the HF section of a seperated network allows for less distortion thus giving heightened clarity with upper level harmonic information not being lost or distorted....basically. Among other theoreticals, this is what I consider to be viable proof of bi-wiring benefits. Am I nuts, or is there something to that? Regards, John. Quote Link to comment Share on other sites More sharing options...
MrMcGoo Posted June 25, 2004 Share Posted June 25, 2004 Woofers have an impedance that varies with frequency. Some amps have not only low output impedance, but also have the ability to produce the needed current to drive the lower impedances that woofers can exhibit. Another way to put it, not all 100 watt amps can drive the lower impedances as well as the best 100 watt amps. Bill Quote Link to comment Share on other sites More sharing options...
John Warren Posted June 25, 2004 Share Posted June 25, 2004 ---------------- On 6/25/2004 7:50:06 PM Audioreality wrote: Back EMF not returned or seen through the HF section of a seperated network allows for less distortion thus giving heightened clarity with upper level harmonic information not being lost or distorted....basically. The back-EMF thing is nonsense. Back EMF is just the motional impedance of the driver. It is the consequence of a moving mass passing thru a resonance. A well designed amplifier can easily handle the load. Nothing is "backwashed" to the tweeter. Look at it another way, the tweeter (say the T35) cuts in a 6kHz. The K33E has a resonance peak at 28 Hz. How much back EMF (i.e. motional impedance) do you think is generated by the K33E at 6kHz? Especially when it's low-passed at 400Hz by a series choke? Am I nuts, or is there something to that? I don't know if your nuts, but the back EMF thing is. Regards, John. ---------------- Quote Link to comment Share on other sites More sharing options...
Deang Posted June 25, 2004 Share Posted June 25, 2004 "Precisely! The reason why the Mc bass sounds good even though it has a DF of 10 is because, to your point, the DF is a meaningless parameter." I don't really understand what you are saying here John? Why would it be a "meaningless parameter" in relationship to "his point"? A DF of 10 should have some overhang -- a nice rubbery sound. Quote Link to comment Share on other sites More sharing options...
John Warren Posted June 25, 2004 Share Posted June 25, 2004 ---------------- On 6/25/2004 9:27:58 PM AK-4 wrote: "Precisely! The reason why the Mc bass sounds good even though it has a DF of 10 is because, to your point, the DF is a meaningless parameter." I don't really understand what you are saying here John? Why would it be a "meaningless parameter" in relationship to "his point"? A DF of 10 should have some overhang -- a nice rubbery sound. ---------------- Look at the loop resistance "R" in the post above. The amp output impedance affects the Qes in the 1% range. Increase the DF to 500, it makes no signficant difference when measured relative to the voice coil resistance. A change more like 250% would be necessary to change a woofer from "tight" to "rubbery" (Qts .5 to Qts 1.25) Nectar was tacitly implying that his "lowly" DF 10 McIntosh sounded pretty good and that higher DF amps do not "necessarily" sound better. He is 100% correct, as long as it is aroung 10 and up, it really doesn't matter how high it is because the DF is a second order parameter when youcompare it to the primary paramter the VC resistance. Does this mean we "ignore" it all together? No. But the DF is NOT responsible for controlling woofer motion, that is what I am trying to get at. Quote Link to comment Share on other sites More sharing options...
edwinr Posted June 25, 2004 Share Posted June 25, 2004 Great answers guys. I've had to read this stuff a few times to makes sense. But some of it is sinking in. So far what I get out of this is that there is a heck of a lot of engineering involved in getting the right sound. There are obviously electrical parameters that must have priority over others when engineering a product - in other words you need to take the good with the bad to achieve your objectives. Quote Link to comment Share on other sites More sharing options...
formica Posted June 26, 2004 Share Posted June 26, 2004 ---------------- On 6/25/2004 7:44:55 PM John Warren wrote: There are exceptions to every rule, of course. Yes, the exception is called engineering. DM ---------------- John do you mind if I borrow that?... Quote Link to comment Share on other sites More sharing options...
djk Posted June 26, 2004 Share Posted June 26, 2004 My McIntosh has a DF of 14, but it sound 'tighter' and 'hits harder' than an Adcom GFA555 with a DF of better than 250. Why? Because I added a pair of 47µF bypass caps in parallel with the main filter caps. DF is a red herring, John did a real good job explaining it. "Woofers have an impedance that varies with frequency. Some amps have not only low output impedance, but also have the ability to produce the needed current to drive the lower impedances that woofers can exhibit. Another way to put it, not all 100 watt amps can drive the lower impedances as well as the best 100 watt amps." Another red herring. Tube amps have troubles driving speakers with big magnets because of the impedance PEAKS, not the dips. Older designs frequently had larger cores than they (seem'd) to need, and an air-gap too. Newer stuff is value-engineered within an inch of its life, except the program is no smarter than the guy that wrote it, and he doesn't have any real life design experience. djk suggests trying a 15R 25W resistor in parallel with the speaker and use the 4R tap (vented designs w/big magnets only). Is my box too small? If you like SET amplifiers and small speakers, the answer may be yes. Box size in general is proportional to the square of Qts. The Qts of drivers with small magnets goes up proportionally with high amplifier output impedance. In general this is not a problem as those same small speakers are so inefficent that they are not normally used with flea-powered SETs. But to be on the safe side, always listen to the combo at home before carving the deal in stone. Quote Link to comment Share on other sites More sharing options...
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