I fully agree that TL bass is not suitable for your particular goal unless you have room for truly massive cabinetry. I’m getting what bass I want with what I have. You ignore the fact that I used HDF, not MDF, and that the cabinets are further damped and weigh about 120 lbs each. Beyond that a TL design does not absorb much amplifier energy in the first place. But again, your after something I don’t care to pursue.
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The TL is not a “sub”woofer. Nor did I want it to be. I’ve built two pair, so I’m well aware of the complexity, but I beg to differ on the woofer shaking the cabinet. Not much of that happens because the driver is very lightly loaded. Anyway, one inch thick HDF makes my cabinets very solid. Formica over that for a rosewood appearance. Nor did I need the lesson on TL design but thanks anyway.
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Mijo, In a distant way, there is a relationship between a transmission line and a dipole design, or whatever you call the type where two woofers are working in or out of phase, back to front or front to front. The transmission line is akin to an open baffle where the rear radiation is used to augment the very low frequency bass output by undergoing a phase change in the course of passing through the transmission line and out through the port at the base. But the cabinet does not damp the motion of the woofer, as in open baffle.
Raul, I was a lowly intern when I first heard the IMF Monitor at Lyric Hi-Fi in NYC. I wanted that speaker very badly but could not afford what seemed to be the stupendous price at the time, $1000 I think. I had a patient who offered me the use of his bench saw, so I bought the HDF, clamps, glue, drill, etc, and built the transmission line exactly according to the IMF Monitor, which was based on a published paper in a British journal called "Wireless World". A guy named Bailey described the TL in one issue of the journal and gave all information needed to make the cabinet using a KEF B139 woofer. Then my home-made version used a KEF B100 midrange, as in the Monitor, and RTR Electrostatic tweeters, 4 per side, that I bought from a guy in CA who was associated with Infinity, which was then making the Servo-Statik 1. The problem then was that I knew nothing about crossover design. I got some help with that from an MIT-trained engineer who worked for NSA here in the DC area. I eventually sold the speakers to my cousin, and then bought them back from him about 20 years later. I cut off the midrange and tweeters and saved the TL woofer cabinet, which I now use along with the Beveridge 2SW, as the outboard woofers.
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I think Mr Volti was a furniture maker before he went into the loudspeaker business. His cabinet work is certainly first rate.
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dogberry, No one, least of all me, is dismissing full range ESLs. That’s exactly what I listen to in one of my two systems, Sound Lab 845PXs, with no subwoofer. One reason for no subwoofer is my disinclination to clutter up the listening room any further, since it is also our living room where we entertain guests after dinner in the adjoining dining room. Three turntables, front end electronics, the huge 845PXs, and two large monoblock Atma-sphere chassis’ are enough. Other reasons for no subwoof, related to the first, are my own cheapskate nature, the wonderful deep bass I get from the panels with no augmentation, and the fact that I believe I would have to spend quite a lot of money to find a subwoof that can keep up with and blend with an ESL. However, I do not argue with those two guys who describe the putative benefits of a subwoof. In principle, they are correct. However, I take exception to Mijo's endorsing Doppler Distortion as a compelling mechanism for crossing over at a relatively high frequency (100Hz or higher). Because I doubt "Doppler Distortion", which is a real thing but not really due to the Doppler Effect, is much of a factor with a huge planar speaker that has a much shorter excursion than does a dynamic speaker and spreads the frequencies among a myriad of unitary panels of different sizes so as to distribute resonance.
Jonwolf, I heard the Volti Audio Rivals at the Capital Audiofest. I thought they were excellent, far better than many much more expensive speakers that I heard at the show. In fact, in many ways I thought they were better than the older big brother Volti speakers at $20K, which were owned by my neighbor and which I heard at length at his house. Good choice.
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Mijostyn, I appreciate your unequivocal convictions on nearly all things audio, but don’t you think you’re a bit over the top or around the bend in subwoofers? The ONLY worthwhile design is the dipole??? Really? I do like the idea of the dipole though for its potentially compact form factor. What do you recommend? Have you ever heard a really correctly built full size transmission line woofer? For me that’s the fastest and lowest distortion bass for mating with an ESL. But can be very large. Also, if a subwoofer is palpably vibrating, could that possibly mean it’s playing bass tones, not distorting? Or do you think a sub should play bass without moving at all? I’d like to see that.
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We once calculated that my speakers have about 400 in.² greater radiating area then do yours. Perhaps that’s where our results differ, because my speakers are not perceptibly distorting in anyway at 100 Hz. And there is the added value of coherence and continuity with higher frequency music. Now you are saying there is no point in reproducing music below 40 Hz, because there is not much information. Isn’t that contrary to your previous assertions about your system going down to 15 Hz or thereabouts? Why do you bother to be concerned about frequencies below 40 Hz, if they are irrelevant? I say this Not as someone who believes that frequencies below 40 Hz are irrelevant.
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SL used to make and sell a single huge ESL woofer panel to be placed in between a pair of their largest speakers, then called the A1. They also made add on wings for the A1, to attenuate the back wave and reduce cancellation. That becomes less necessary with their current curved arrays. I get wonderful chest thumping bass out of my 845PXs, and if I were to add subwoofers I would crossover way below 100Hz. But that’s just me. I am not offended if someone else wants to do differently.
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As a 25 year user of an Atmasphere OTL, I can tell you that with these amps a failing tube signals its demise rather gently. But keeping them in open air for ventilation and in plain sight is a good idea.
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In the DIY community, Nichicon electrolytics are very highly regarded. Not a compromise at all compared to Vishay or CD. I use them and if I thought there was a better brand for a particular application I’d use that brand over Nichicon. The cost differential among different brands of electrolytic caps is trivial, now that Black Gate and Cerafine are defunct.
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Raul, You are right. I apologize to you and any others who were offended by my and Mijostyn's going off topic. It seemed to be permissible because no one else was trying to change the subject, back to the actual subject of the thread. But, dear sir, please also keep in mind that you do the same from time to time.
Mijo, I will take our conversation private from here on out.
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If memory serves me, you felt in the end that you had burned up your brilliance control because your equalizer was boosting the signal by 10 or 12 db at a frequency that was traveling through the brilliance control. So that was in medical parlance iatrogenic. A problem you can easily get around by ceasing to cause it. anyway, I am sorry to learn of the demise of Plitron. They made good stuff. Sowter is also a very good company, and I am sure they can do a good job as well. To my knowledge they make only EI type transformers. Is that still correct? My other point was that you are taking a shot in the dark as to whether a single transformer with a 1 to 100 step up ratio can adequately drive the panel at frequencies as low as 100 Hz with vigor to satisfying levels. I wonder about this because Although I did not measure the frequencies involved, my memory tells me that when I tried to drive the panel full range with my 1 to 90 transformer the response was unsatisfying at frequencies that went well above 100 Hz, at least up to 200 or 300 Hz or so However, one could argue that because you are taking the onus of driving very low frequencies away from the ESL transformer, perhaps it will perform better at the higher frequencies (above 100Hz) that will be required. Anyway, you will find out if you do this experiment. I personally would not add a tweeter to Soundlab ESL or any othe high quality ESL, but that’s just me.
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What do you mean by "power"? I get that you want to play at high SPLs, but if you are going to use bass and high treble supplementation and probably roll off the response of the SL speakers with very steep slopes, given your penchant for digital crossovers, then why do you anticipate needing the transformer to take lots of power? Have you evaluated the specifications of the Plitron toroid, so as to form a basis for your belief they cannot be driven hard, or what? Anyway, I have no compulsion to dissuade you from your aim to use Sowter transformers. (1:100 would be technically more correct than 100:1, BTW.) Sowter certainly is well regarded, although I did not associate them with making audio step-up transformers to drive ESLs. Sure, go for it. My recommendation of Plitron was solely based on the idea of your driving the speaker with two transformers (one for bass and the other full range) and dumping the RC network in the process. However since you are venturing into the unknown, you might want to find a way to experiment with using a single 1:100 step-up before investing in a custom build of two of them. (Acoustats are not identical to SLs in terms of stator to diaphragm spacing and bias voltage, although using separate bass and treble transformers was originally the idea of Acoustat, borrowed by SL in the late 90s or so.)
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Mijo, You wrote, with reference to our SL speakers: "I went back to Sowter and they will make custom transformers. I drove the Acoustats with 100:1 transformers from 125 Hz up and it worked well. Right now I am crossing out of the stats at 100 Hz. I also am thinking about getting RAAL ribbon tweeters too cover 12 kHz up. I wonder if the bass transformer would handle that range or should I have 100 or 150:1 transformers made. The Plitron is too small."
My questions are with reference to your last two sentences. What range are you talking about that you wonder whether the bass transformer could handle it? If you are thinking about, say, 100Hz to 12kHz, I would say no. One reason for my opinion is that when I measured the OEM bass transformer, it rolls itself off at or around 2kHz, probably due to self-inductance. Another reason is that you need to keep in mind the effect of the ESL step-up on impedance seen by the amplifier is the converse of using a SUT with a phono cartridge. The impedance seen by the driving amplifier is the intrinsic Z of the screen with no transformer divided by the square of the turns ratio. So as you go up in frequency, a 1:250 turns ratio is going to result in a very low impedance for the amplifier, except as the self-inductance of the transformer seemed to dominate when I measured Z with the bass transformer alone driving the speaker. Anyway, I would not be hopeful that this is a good idea.
And what makes you say the Plitron audio transformer is too "small"? Have you ever seen the audio step-up transformers used by Martin-Logan and some other companies? They ARE tiny, but SL use substantial transformers, and the Plitron 1:75 full range step up appears to be about the size, at least, of the OEM SL toroidal transformer they use for treble. Or is it the turns ratio (1:75) that you think is too small? To that I would only say that 1:90 of my Australian sourced transformer is excellent. 1:75 in terms of voltage is not that different, and because of the effect of the turns ratio on impedance (see above), Z at higher frequencies will be a bit higher than what I observe with a 1:90 ratio. So it might be a trade-off with no untoward effects on perceived efficiency. Anyone, like Intact Audio, who actually knows transformers is welcome to correct me on these generalizations.
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Wow! Raul's speakers sound wonderful in those Youtube videos. I'd love to hear a pair in person.
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jayctoy, No one would argue with the positive experience you had listening to your friend's system, but in my opinion the system as described is very pedestrian for its day (late 90s to early 2000s) or any day, actually. For one thing, my buddy owned an LS2B. We both thought it was one of the least good sounding preamplifiers ever made by ARC. That's the nicest way I can put it. I can say this to you I hope without personal insult, because it was not your system. But this just goes to show us that there is pleasure to be had from even a set-up that would be considered mediocre at best by most.
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Mijo, This is perhaps not the place to discuss it, for fear of boring a few others, but I have been there, done that, when it comes to audio transformers for the SL speakers. First, a single transformer with a 1:100 step-up ratio does not cut the mustard for good bass response from the panel. Of course, since you are subwoofer supplementing, perhaps you could get away with some compromise, but so far as we have been able to find out, the bass transformer on our speakers is 1:250, or something close to that range. (SL will not divulge the information.) And you do not want a full-range trans with such a high step-up ratio, because that will produce very low input impedance as frequency goes up. (Remember that an ESL is naught but a giant capacitor.) For the full-range transformer in my speakers, which I couple with the OEM SL bass transformer at low frequencies, I use a 1:90 ratio in a very hefty step=up that was made in Australia. Unfortunately, that model is discontinued but the same company may make a suitable substitute. Anyway, I tried driving my SLs with the Australian transformer full range without any bass transformer, and the bass to low mid-range was very anemic, totally unacceptable in fact. So, there’s a reason that SL uses two transformers to achieve a robust full range response. I use a single huge air core inductor to roll off the OEM SL bass transformer somewhere in the low midrange, in parallel with the 1:90 Australian transformer running full range with no RC network at all. In theory, you’d think that might present problems. In fact, the first time I heard it in my home, it brought a tear of happiness to my eye. If I were to do this today, and if the Australian company don’t have a suitable substitute for the discontinued units I use, I would consider the full-range 1:75 toroidal transformer made by Plitron. A small benefit of that unit would be slightly higher impedance at high frequencies, compared to what I’ve got. But you are way too concerned about the Z at high frequencies, in my opinion. You once mentioned that you boost response by 6db per octave above 12kHz. That probably contributes to heating up your crossover. But more than a decade ago, some SL users found that the higher the power rating of the R in the treble RC network, the better was the sound. Guys were using humongous resistors that did not even fit into the backplate. (I was one of them.) But real happiness is no RC network at all.
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Much of the energy used to drive the Sound Lab is soaked up by the passive crossover, because SL (for other compelling reasons) chose to use a resistance in the RC network that comprises the high pass filter that is much lower than the natural impedance of the panel itself, sans RC network. Thus the amplifier is expending more energy to drive the resistor than to drive the panel. With RC network removed, the big SLs are remarkably efficient and present an impedance in the 20 to 25 ohm range (never below 20 ohms) from about 100Hz to 5kHz. Impedance goes up below 100Hz and down between 5kHz and 20kHz. This gets rid of the midrange impedance issue that Ralph alludes to. And of course it’s favorable for an OTL tube amp. I daresay that a 50W amplifier is sufficient; my Atma-sphere amps with about 100W are coasting. Of course, you also have to replace the treble audio trans with a suitable full range audio trans. They’re not easy to find.
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“In another room “ stories are absolutely irrelevant. When the source is in another room with respect to the room inhabited by the listener, the ear and brain are deprived of several cues used to distinguish live from reproduced music. Phase and bandwidth included. When it’s an unaccompanied vocalist or single instrument, it becomes plausible that you’re hearing a live musician, until you check it out by entering the space containing the source.
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No need to say more. I’m sorry I opened up yet another can of audiophile worms.
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henry53, In a small club listening to a vocalist backed up by a small jazz group or to a small jazz group alone, you certainly can hear a degree of "realism" not easily replicated in the home. In that sort of set-up, some of the instruments and a vocalist typically will be electronically amplified, but if you're sitting within about 20-25 feet of the performers, the PA system typically does not really pollute what you hear to a great degree. To demonstrate the difference between that sort of live listening and your home system, ask a professional musician to come by your house and play a few tunes in your listening room, preferably standing between your two speakers. Concerts in large halls are a whole different ball of wax, up or down.
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So that takes us down a different road of inquiry. A never ending contentious one. We can all agree that sometimes the live experience is not so great, because of room acoustics, ambient noise, noisy audience, bad amplification, etc but live instruments don’t lose their dynamics, even then. I was more responding to Mijostyn’s post advocating digital intervention, to artificially flatten the frequency response in the listening room, and enormous woofers (the way I think of the dynamics of live music has little to do with thunderous bass). I do agree with him that crossovers are often the enemy of verisimilitude.
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When you say “improve on live sound”, what does that mean?
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Very few if any audio systems can capture the dynamics and amplitude of live music in an intimate setting. That’s a worthy goal to pursue as you grow your system. Otherwise what’s the question?
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