edison dance reproducers - just hype?

[FellowCollector]

I have been monitoring the responses on this thread with interest. My experience with the Edison Edisonic reproducer as well as the Dance Reproducer is that they are definitely louder and clearer when rebuilt properly as compared to the standard Edison DD reproducer. I have rebuilt my own and I also have several Edisonics as well as standard Edison DD reproducers that were rebuilt by the late Bob Waltrip. Without a doubt, for my hearing, the Edisonics and the Edison Dance reproducer sound noticeably louder than my rebuilt standard DD reproducers. My hands down favorites are those rebuilt by Bob Waltrip. His work on reproducers was superb. He experimented with a ton of different materials for diaphragms until he settled on a unique type of styrofoam (according to my telephone conversations with him years ago). I have one particular Edisonic reproducer in the nickel finish that Bob rebuilt for me at least 17 years ago that still sounds as great as it did on the day it arrived in the mail. Interestingly, Bob always cocked the DD reproducer "cup" (the bottom part of the DD reproducer) so that it more closely matched the grooves of the disc. I asked Bob about why he cocked that portion of the reproducer that way and he told me that he felt that the stylus and weight would be more compliant with the disc grooves with the bottom turned like that. Seemed hokey to me but who knows. I do know that my reproducers sounded fantastic when he was done with them. I wish that I had the presence of mind back when he was still living to have more of my reproducers rebuilt by him.

[gregbogantz]

John, you and others that are confused about this, I think are misinterpreting the purpose of the tracking weight. Ideally, the fulcrum of the stylus bar should be held stationary during record play. This allows all the motion of the stylus tip to be transferred to the diaphragm thru the pivoting stylus bar. The only reason that a tracking weight is used at all is because the stylus tip must be allowed to move globally over a fairly large range to accommodate warped or eccentric records. If records were perfect, the stylus bar fulcrum could be fixed to the reproducer, the tracking force would be determined by a micrometer adustment that carefully positioned the stylus bar such that a fixed average amount of diaphragm dishing or bias would be produced, and no tracking weight floating assembly would be required at all. In other words, the reproducer would be a fixed mechanism running on a feedscrew much like modern record cutters. They have no tracking weight and no floating assembly aside from the suspension of the entire mass of the cutter above the recording blank.

But records are not perfectly flat or concentric, so the floating tracking weight/mass is required to address these imperfections. Still, the fulcrum of the stylus bar should not be allowed to vibrate. The mechanical lever advantage of the stylus bar causes there to be mechanical amplification of the diaphragm motion relative to the amplitude of motion of the stylus tip. This mechanical "gain" is a result of the leverage ratio of the length of the back end of the stylus bar (fulcrum to link attachment loop) to the length of the front end of the bar (fulcrum to stylus tip). If these lengths are the same, the ratio is 1-to-1 for a net gain of 1 or no actual gain at all. But the Edison DD and diamond amberola stylus bars (also true of most other cylinder reproducers) have the back length considerably longer than the front length - the ratio is about 2.6 for a DD stylus bar and about 1.8 for an amberola stylus bar. So these designs produce mechanical amplification if the fulcrum is held steady.

The primary purpose of the tracking weight is to provide a large MASS coupled to the stylus bar FULCRUM to prevent it from being vibrated during record play. Any motion of the fulcrum caused by sound vibrations will lessen the amount of energy transferred to the diaphragm and a consequent loss of loudness. So, maximum efficiency of the system depends on sufficient mass at the fulcrum as well as sufficiently low mechanical load by the diaphragm so that it responds to all the vibrations. If the diaphragm is too stiff (low compliance), it will load the linkage with too much mechanical restraint, causing the energy to be partially transferred to the fulcrum, causing the fulcrum to yield and vibrate under the energy from the stylus tip. In this case, the stylus tip motion amplitude is not affected, but the fulcrum vibrates, and less amplitude is delivered to the sound chamber above the diaphragm, causing loss of loudness. The solution for this problem is to either increase the diaphragm compliance (less stiffness) and/or increase the mass of the tracking weight so that the fulcrum does not vibrate while playing the record. When playing loud records, the early Edison designs had insufficient tracking weight mass to keep the stylus bar fulcrum from vibrating. Thus, the Dance and Edisonic designs were developed which have an increased tracking weight mass. When playing softly recorded records, there is little energy being produced by the system, the diaphragm compliance is not being heavily stressed, the fulcrum is not vibrating significantly, and you will notice little difference in reproduced loudness from either the early or later reproducer designs. But when playing loudly recorded records, the stresses are greater on the diaphragm which will cause it to more heavily restrict the motion (this is a classic definition of nonlinear distortion) which will then cause the fulcrum to vibrate. Consequently, you will hear the early reproducers sound a bit less loud than the later, heavier ones when playing these loud records.

But in addition to these effects, the lesser mass controlling the stylus bar causes the stylus tip to come under rapidly varying instantaneous tracking force. This results in the tip bouncing up out of the groove for a fraction of a wavelength, depending on the signal frequencies and the several mechanical resonances and dampings of the diaphragm, stylus bar and other mechanical interactions in the linkage. This causes mistracking distortion as the stylus tip is not perfectly following the groove shape at every instant. This, too, will cause a bit less overall loudness to be perceived but with the addition of noticeable mistracking distortion, typically heard as "blasting". The solution to this problem is, again, to increase the compliance of the diaphragm and/or increase the mass at the fulcrum and/or increase the tracking force. The larger tracking weight of the later designs addresses both the increased mass and the increased tracking force needed to calm the spurious vibrations in the linkage.

The problem with increasing the tracking force in a vertical reproducer such as the Edison designs is that the nominal (average) tension on the linkage caused by this tracking force during record play causes a constant average tension or bias on the diaphragm which causes it to be deflected or dished (strained) from it's unstressed condition. The diaphragm is, among other things, a round leaf spring. The more a flat, disc spring such as this is deflected from its rest position, the more restriction it produces to counteract the stress. In other words, its mechanical "spring constant" is far from ideal - it is not at all constant but varies substantially with the stress that tries to dish it away from its unstressed shape. So, the force required to move the diaphragm FARTHER into its already stressed dish shape is much greater than the force required to move the stylus back toward its unstressed shape. This results in a very nonlinear stress/strain response from the diaphragm, centered on its average stressed shape during record play. This results in assymetrical loading response to the linkage depending on whether the diaphragm is being forced up or down from its average position. This is a classic cause of assymetrical waveform distortion which produces even-ordered harmonic distortion products.

The Dance reproducer was designed to try to address this assymmetrical diaphragm loading. The original Dance design includes a spring attached to the TOP of the diaphragm to bias it in an upward position. The purpose of this being to counteract the downward stress produced by the tracking weight and linkage during record play with the intention of causing the diaphragm to have little net average stress which would lead to less nonlinear behavior, resulting in less distortion. Apparently, Edison decided that this extra spring was not effective as he eliminated it again in the later Edisonic design.

Congratulations, if you've managed to read this far into this epistle. Long story short(er), if you have a sufficiently low mass and sufficiently high compliance diaphragm, the difference in the loudness of the earlier Edison reproducers compared with the later ones will be minimal. That's because the stylus bars have the same mechanical gain. And if the stylus bar fulcrum is not vibrating due to the optimum diaphragm design, there is no difference in the net diaphragm motion, regardless of the extra tracking weight. Since it is not possible to make an acoustic diaphragm with vanishingly low mass and infinite compliance, there will still be some net difference in the undesirable fulcrum motion of the stylus bar when comparing the low versus the high tracking weight designs. But the difference will be less with better diaphragm designs. As some of you readers have mentioned, you don't notice much if any difference in loudness between the early and later Edison designs. This is consistent with the theory of operation.

[pughphonos]

Greg, I've just read your essay here as I was referred to it in connection to my question about the capabilities of the Edison dance reproducer of 1926 vis the Edisonic of 1927-29. I can't claim to understand it all, but it has helped a good deal. Understanding the weight on an Edison disc reproducer as primarily a stabilizing influence (to facilitate goove adherence and prevent excess vibrations from reaching the diaphragm) seems to be key.

Do I understand correctly, then, if I think that the extra weight on the Edisonic does NOT mean extra record wear? Or DOES it--but it's unavoidable if one wants to play the loud records of the late 1920s without distortion?

Ralph

[gregbogantz]

Congratulations, Ralph, on wading thru my previous dissertation on Edison reproducers. It's kinda heavy lifting (couldn't resist the pun), but it does explain in mechanical engineering terms the physics of these systems. Yes, the extra weight of the larger Edisonic and Dance reproducers DOES increase tracking force on the stylus tip which WILL cause increased record wear. But the advantage of using the heavier weight is to reduce tracking distorion when playing records with high modulation levels (i.e. loudly recorded). The primary benefit is to reduce distortion.

The fact that some people hear an increased loudness from the heavier weight is due to two factors: (1) as mentioned earlier, the reduced distortion means that the stylus is stying in contact with the record groove surface more reliably. Compared with what happens with the lesser tracking force which allows the stylus tip to momentarily lift away from the groove surface, this will result in greater amplitude of vertical motion at the stylus tip which will result in increased energy transfer to the diaphragm which will be perceived as increased loudness. This would be the case if the rest of the reproducer was the same, that is no change in the diaphragm stiffness or resonance or damping or changes in the mass or stiffness of the linkage. This perceived loudness increase is relatively minor, but the difference in distortion is much more noticeable when playing loud records. (2) The original Dance reproducer and maybe the Edisonic designs use different diaphragms from that used in the conventional DD reproducer. Among other things, the Dance reproducer has a different resonant frequency and probably less damping. THIS is what causes the Dance to sound "louder" - the frequency response is purposely peaked in the midrange so make it sound louder there (as if the original design wasn't already peaky enough). Apparently, Edison thought that this would be a sales gimmick to entice people to buy the newer product. I can only assume they did this on purpose so that they could advertize it as playing louder than the earlier design. Turns out that extra loudness is maybe only 2 or 3 dB increase at only SOME midrange frequencies which is by no means "twice as loud" (which would require a 6dB increase at all frequencies to be a technically accurate statement). But that extra loudness comes at the price of the intentionally peaky frequency response. The increased peakiness occurs in the frequency range that emphasizes the sound of the brass horns (primarily saxophones) that were popular in the dance orchestras of the day. But this is why some listeners prefer the less peaky and more accurate design of the earlier Edison diaphragms for playing chamber or symphonic music that have a wider variety of instrumentation.

So, the bottom line is, the best and most accurate sound that you can get from any Edison reproducer will be provided by a diaphragm designed with high compliance, low moving mass, properly designed mechanical resonant frequency, and proper damping. With these characteristics in place, you will not hear much difference in loudness when using it in either the earlier reproducers or in the newer Dance and Edisonics. The reason being that there is much less distortion with this kind of diaphragm even with the smaller weight and lower tracking force. So increasing the weight and tracking force accomplishes less improvement. Again, with a good diaphragm design the most improvement that you will get with the heavier weight is less distortion, not significantly louder playback.

[pughphonos]

Greg, I can see, therefore, why there has also been a good deal of discussion about diaphragms in other posts. Right now I own two Edison reproducers (an Edisonic and a Long Play), both rebuilt for me by the folks at the Victrola Repair Service in Vermont. I trust they're up to speed with the best materials/builds currently out there. If I go ahead and buy a Standard reproducer it will probably be sent off to them too.

One more question, Greg. You mention that the lighter Standard reproducer is "thrown" (my term) a bit when playing the louder records. Wouldn't that uneven posture in the grooves lessen any wear advantages it would have as against the Edisonic (when playing louder records?)

This is the moral of the story for me right now: own a Standard reproducer (rebuilt) for softer records (mostly pre-1925) and go ahead and use the Edisonic for post-1925 or post-1927. Sound reasonable?

[Valecnik]

This is the moral of the story for me right now: own a Standard reproducer (rebuilt) for softer records (mostly pre-1925) and go ahead and use the Edisonic for post-1925 or post-1927. Sound reasonable?

It can get more complicated than that. A Standard reproducer with an original diaphragm and one of the excellent new diaphragms like Greg's will sound different on different records. For late acoustics I generally favor the original diaphragm. For earlier recordings the new diaphragms seem do do better imho. Then there are those records, generally later acoustics and electrics in NOS condition that I would only play with a new electric turntable tracking at a couple grams.

Oh and if you are going to switch frequently between Edisonic and Standard, get an extra turntable felt you can lay over the existing felt. The dance and Edisonics track closer to the platter with less clearance so when you put on a standard it helps to raise the record up a bit or the limit pin will tend to hit the loop. The other option is to adjust the height of the horn which is easy to do but if you need to do it often it's a pain.

[gregbogantz]

Mistracking can cause record damage. When the stylus tip is bounced out of contact with the groove momentarily, it then slams back down against the groove just milliseconds later. In so doing, it momentarily presents the groove surface with an added accelerated mass as the stylus tip hits the groove surface. This results in a momentarily very large increase in groove pressure which can cause more permanant groove damage than using sufficient tracking force to prevent the stylus tip from ever leaving contact with the groove. This happens with all types of analog records, and is often seen when playing vinyl records that have been subjected to mistracking during previous plays. Whenever you hear grunginess, distortion, or "blasting" during the playback of high level sound passages, the record has either been damaged by previous mistracking, or you are presently destroying it as you are playing it.

Golden ears are particularly guilty of this transgression. They worry and fret so much that they are not using too much tracking force ("I've used my hyper-micro-accurate $1000-dollar digital scale to set my $2000-dollar SuperOrgasmotron moving-coil cartridge to exactly 0.788496 grams because I read in StereoPILE magazine that even though it's rated by the manufacturer to track at 1 to 1.2 grams that this is really the minimum that you can use") that they end up using too little force and damage their records from mistracking. I've actually witnessed this kind of behavior among golden ears. It's a classic case of knowing just enough about something to be dangerous - to their equipment and to their bank accounts.

Anyway, I wouldn't worry about it too much because record wear is a fact of life when tracking records with ancient technology acoustic reproducers. ALL of them will cause record wear because they are unsophisticated devices. When they mistrack, they do even more damage. If you really value your records, play them with modern cartridges that can perform well at low tracking forces. Reserve the enjoyment and demonstration of your acoustic players (and the crappier electric players) to playing records that you aren't afraid to wear.