Nice finger joints. Dogged determination, for sure.
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Like you, Mike, I was joking. I wouldn’t have a chance trying to change your point of view.
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That statement was probably incorrect. Apologies to Mijo. But I still don’t think he should attempt it before acquiring a thorough understanding of RIAA.
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Whatever you decide, my advice would be not to try to introduce the filtering externally with your digital filter device. It has to happen in conjunction with transduction of the cartridge signal.
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Thanks, Ralph. All Atma is saying is that a strain gauge needs a little EQ in order to correct for the RIAA pre-emphasis standard used to cut all LPs. I don’t know whether the SS SG phono stages account for this but I’d be surprised if they don’t incorporate some corrective filtering in the 500 to 2000Hz region.
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Dear Raul, That’s a very interesting article. The author makes a good point that using the term "fast" when describing a woofer is specious, because the "speed" required to reproduce very low frequencies accurately is within reach of any well designed woofer. But then he goes on to say: "There are reasons to use lighter, lower-mass woofer cones. They just happen to be different reasons than the ones you’ve read in print. Smaller woofers don’t make faster bass, but they do reproduce higher frequencies than larger woofers can reproduce, and this is all important when it comes to speaker design. You want the midrange driver and the woofer to integrate with sublime symmetry, with perfection and with nary a single problematic interaction throughout their overlap zone. This is why you want smaller, lighter, "faster" woofer cones -- not because they lead to faster bass. That overlap zone is so amazingly critical to your perception of bass speed that there is little or no tolerance for error." Note also that your expert does allow for the idea that some woofers are "faster" than others; he has only re-defined the term in a sense with which I do not disagree. By the way, no one "told me" anything about this. My conclusions are based on real world experiences that I had maybe 35-40 years ago when I was playing around with woofers to supplement ESLs that I then owned. So, I am expressing my personal independently arrived at opinion.
So perhaps I can be faulted for my choice of the word "fast", but what your authority wrote above is what I had in mind. Now if Mijostyn is using an 80db/octave crossover, on both high and low pass filters, then perhaps the capacity of his woofers in his system to produce higher frequencies is moot. On the other hand, all of his audio is passing through the digital domain afforded by his digital filter. That does not appeal to me.
Mijostyn, Along the same line of reasoning, you wrote, "Lastly, there is no such thing as a "fast subwoofer" when a woofer is not fast enough it’s high frequencies roll off." I hope you see the internal contradiction there. If there is no such thing as a fast woofer, then there is no such thing as a woofer that is not fast enough. But to both you and Raul, I would concede that I was guilty of sloppy semantics. When I say "fast woofer", I am thinking of the woofer and its enclosure as a whole. And I did not make that clear. You could put a small, i.e, "fast", woofer in an enclosure that limited its speed by virtue of what happens to the back wave, and it wouldn’t sound so fast, which we can define here as able to integrate well with an ESL panel. Like I responded to Raul, perhaps with an 80db/octave slope you need not worry about the capacity of your woofer enclosures to deal with frequencies above your crossover chosen point.
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Mike, You sure get up early in the morning. More important or at least as important in conceiving a supplementary woofer or subwoofer is the cabinet design. The choice of cabinet type would affect the choice of woofer, I would think. So what are you going to build, acoustic suspension, bass reflex or other ported design, open baffle, or what? (I can't be sure from your photos what type of cabinet you are presently using, either, and I don't see 4 woofers. Where are the other 3?) For me, I don't care much about frequencies below 30Hz. I much prefer a "fast" woofer that can mate well with an ESL around the crossover point. A seamless blend is hard to come by, even if using an 80db/octave slope, or especially so if using such a very steep slope. I have no dog in this fight; I'm just curious to learn. I long ago decided on a fast, smallish woofer in a Transmission Line enclosure as my ideal for mating with a full-range ESL or an ESL that needs help at low frequencies. If I wanted more oomph (as in SPLs) I would use two or more of such agile woofers per channel.
By the way, I agree with you, everything can be measured. But sadly, once you've done that and technically perfected the frequency response in room, I have yet to hear a system that was obviously benefited by such contouring. (On the other hand, in the past several years, I have not auditioned that many systems other than my own.)
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Mijo, I took a look at your system page. You do have a beautiful and comfortable looking listening room, and you are obviously a highly skilled woodworker. It's always good when one hobby supports the other. Seeing where your TT is located, on a shelf set into a wall with a shelf above, I do have to wonder whether moving your TT, just experimentally, would be worth a try. I get it that you don't want to radically reposition the TT to a permanent new location, but just for diagnostic purposes, it would be worth moving it temporarily, so that it is not against a wall and in a shelf. In lieu of moving the TT, you could also remove the dust cover when playing LPs.
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Yep. Audiokinesis and Duke Lejeune. Woofer array.
The question of whether the resonance has anything to do with Helmholtz is somewhat relevant, because if it were due to the Helmholtz phenomenon, then you could live on with your prior conviction about the unalloyed benefits of the dust cover. You point out that there is a pathway for air to exit the space enclosed by the sealed dust cover and plinth, downward around the platter evidently. But if that constitutes a Helmholtz Resonator, then sealing the space between the edge of the dust cover and the plinth ought to have changed the resonant frequency. Sealing the dust cover to the plinth changes both the area of the aperture and the net path length across the aperture, and those two parameters are in the equation for resonant frequency of a Helmholtz Resonator. Face it; dust covers are not all good. If you admit that, I will admit they are not all bad.
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Golly! I am so glad to be instructed by you after only 50 years of messing about with audio. First, I wouldn't argue for a moment that my SL experience would be improved if I were to add SUBwoofers to the Sound Lab system. (In other words, woofers that come into play at below 50-60Hz and never above those frequencies.) You are absolutely right about that. I already explained to you privately that I have made a choice not to do it, partly because the system is in our living room, which is already too dominated by audio equipment. But if I did do it, I would never add a woofer that comes in at 120Hz; there is too much real music at that frequency and down below to 40-50Hz. Your 12-inch electromagnetic woofers, impressive and loud though they may be, can never match the speed and articulation of an ESL at 100Hz. But that's just my opinion based on some prior experience. The only woofer I would even think of pairing with an ESL at those frequencies would be one based on a transmission line enclosure using a much faster woofer than average. With the Beveridge system (in my basement), I am not constrained by decor, and the 2SWs do require woofer supplementation; that's how they were originally marketed. There I do use KEF B139 woofers in a large and ungainly TL cabinet that I built myself decades ago. But even there, the crossover, as determined by Beveridge and not me, is at 80Hz. Likewise, the slope of the hi-pass filter is Beveridge, 18db/octave. Consequently, I use an outboard electronic crossover for the woofers that has a complementary 18db/octave slope. If I had my druthers, I would use the Linkwitz-Riley slope of 24db, because that maintains phase between the high an low frequency reproducers. The woofer x-over has controls for level and frequency, but I keep it around 80Hz. Finally, there is no free lunch in audio. Every electronic x-over I have ever heard has a "sound". I've never heard a digital x-over, but I am sure it has a sound too, not to mention the extensive amount of digital room correction that you have chosen to incorporate. I admit to being almost too pure a purist, but I like to avoid x-overs, both passive and electronic, if it makes sense. This is all fine. The goal is to satisfy onesself. I would never be so bold as to sit here and tell you what you are hearing over there. Perhaps you should adopt the same approach. Sorry for the very long digression, but you raised my hackles. I didn't know I had hackles.
Helmholtz Resonator. Every definition I can find, including the one on Wikipedia, states in one way or another that you need a closed container with a large hole at one end and a small outlet at the end of a narrow neck at the other end. Apparently Helmholtz built several of different sizes to demonstrate how size of the enclosed volume of air, neck length, and aperture area all determine the frequency heard at the small outlet. Based on what you wrote, it seemed to me that your problem persists after you seal the dust cover to the plinth surface. Thus there is no pathway for air to go in or out. So, you cannot have a "Helmholtz Resonator". For sure, you do have a resonance problem, just not the one envisioned by Dr Helmholtz. Where have I gone wrong in this reasoning? I think you may have the forme fruste of "dust cover blues", as you so aptly put it in the first place. In other words, you have an extreme and unusual problem that nevertheless falls under the category of why some of us eschew the use of a dust cover when playing LPs.
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You say this whole problem came to light while you were listening to Herbie Hancock’s "Secrets". How does that square with your inference that my own preference for jazz ("old" and new) limits the demands I place on my systems? I also listen to classical orchestral and chamber music, big band jazz, latin or afro-cuban jazz which is usually big band with lots of drums of all types, and I love R&B, which I do like to play "loud", also to certain pop artists where the sonics can be very demanding at low frequencies if you want to feel satisfied. I would also say that dynamics of any kind of music, not just heavy duty bass notes, are what places stress on our audio systems and is a real determinant of how close the system can come to sounding real. But I admit, I will never ever want to listen to "Soundgarden’s Badmotorfinger" at any SPL, let alone 100db.
You also wrote, "Now for the juicey part. I put felt strips under the dust cover to seal it when closed and..... the feedback got worse. I hate when that happens:-( " So much for the Helmholtz Resonator theory, which I couldn’t buy in the first place.
My speakers are 4 inches wider according to you; I don’t know the dimensions of your SLs, so I cannot comment. But if the difference in size between your panels and mine is only 4 inches in width, that would equate to a nearly 400 sq in per channel difference in surface radiating area, since my panels are 8 feet tall (96 inches). If your panels are also that tall, I was not aware of that. If they are less than 8 feet tall, then the difference in surface area between mine and yours would be greater than 400 sq in by that height difference factor. I also use tube traps and wall-mounted absorbent panels tuned to low frequencies behind each speaker, in order to absorb as much as possible of the rear radiation, so as to minimize bass cancellation. Furthermore, I have 100 lbs of lead weight sitting on each SL backplate, so as to minimize the tendency of the panel to sway when asked to reproduce low bass. The positive effect of those weights was immediately noticeable in terms of bass definition. (This is why I completely disagree with anyone who wants to put soft spongy feet or springs under any speaker.) Anyway, you don’t need huge panels because of your predilection for electromagnetic woofers (not "subwoofers" if used up to 120Hz). I am not for one second claiming that my SL system can compete with yours for bass SPLs that can blow your head off below say 40-50Hz, but I do claim that my SL speakers get all the music at low frequencies.
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Partial retraction. OK, I see that if it were the movement of air in the room, caused by your woofers, that was inducing the Helmholtz effect, then shutting down the woofers would possibly reduce the SPLs sufficiently to ameliorate the Helmholtz resonance of your dust cover/TT. I guess I just find it hard to believe that your subwoofers blow around enough air to do that, but I have not been there, as you have. Still, I would take a look at your room frequency response correction devices at the suspect frequencies.
Your microphone test for proving the utility of a dust cover. Isn't that highly dependent upon the room, the speakers, and the proximity of the TT to the speaker? In other words, you could prove it for yourself and your system, but not universally for all situations. I'd move my turntables before employing a dust cover to shield the tonearm/cartridge from SPLs. In addition, what do we know about the importance of the effect you observe, in terms of ultimate fidelity?
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Man! You really like to turn it up. Most people that come into my listening room where the 845PXs are located (otherwise known as "our living room") complain to me that I listen too loud. My sound labs probably go lower in the bass region than yours do without subwoofers, because of greater square area of radiating surface, but I do realize that with subwoofers you’re probably getting deeper base than I do. on the other hand I am hearing wonderful continuous bass down as low as I think there is any important music.
You once had an issue due to your room frequency response correction paraphernalia. Could it be that the same circuitry is boosting the bass in the problematic region, thereby either exacerbating the problem or actually causing it? Also, if the problem is caused by the Helmholtz Resonator mechanism, wouldn't you expect that shutting down the subwoofers and running the ESLs full range would not so much cure the problem (as you observed) but only reduce the intensity and clarity (because now the ESLs are straining to deal with the still present spurious LF input). The Atma-sphere amplifiers can certainly get down that low and lower. The Helmholtz hypothesis is happening at the turntable, so shutting down the subwoofs per se should not "cure" the problem. (By the way, if you are crossing over at 120Hz, I would call them "woofers", not subwoofers, but that's semantics. I think of a true subwoofer as a woofer that comes in at below 50-60Hz, to choose an arbitrary cut-off.) In my Beveridge system, I cross over to my home-made TL woofers at 80Hz, with an 18db/octave slope. Have you entertained the notion that the bass energy dumped into the room at high SPLs on bass-heavy passages is feeding back to the dust cover itself, maybe setting it into motion which affects the cartridge stability in the groove? As you know, bass frequencies are encoded largely by horizontal motion of the stylus/cantilever.
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If you cut off your subwoofers does the problem persist?
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Leaving aside our differences regarding to use or not to use a dust cover, I am thinking about your hypothesis that right now your turntable/cover are together acting according to the principle of a Helmholtz Resonator. The idea does "resonate", but so far as I can tell from my reading, a Helmholtz Resonator requires air (or whatever fluid is resonating) to be put into motion. Energy has to be put into the system for that to happen. In your conception, what is the source of energy? I would offer an alternative hypothesis, for good or ill. Could it be that energy being emitted by the cartridge body, the same energy that is heard as "cartridge noise" is bouncing around under the cover which is by chance tuned to resonate at a low bass frequency, which is why it is excited only when you play certain LPs with low bass frequencies and at a certain SPL above some threshold that causes the whole thing to get excited and re-enforce itself via positive feedback? That is what I meant when I remarked that you are experiencing a problem that I associate with dust covers per se. I put this out there for discussion, not to antagonize or criticize. In my own experience, when I played LPs with dust cover down, inevitably the dust cover itself could be felt to be vibrating, I always thought sympathetically with cartridge vibrations.
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In your first paragraph you describe the very reasons why I never use a dust cover. Also, I think you might be kidding yourself about the benefits, but I wouldn't argue that point. What you're observing is nothing special or out of the ordinary in terms of the problem with a dust cover. It's more or less the argument I posed to you long ago.
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Good idea, tvad. And it allows Mijo to reduce his tranquilizer dose. But we know that any remedy that leaves the cover in place is working because the resonance has been altered in frequency. The resonant energy generated by the presence of the dust cover is still "there", at some other frequency.
Mijo, what pictures? Did I send you one of my mug shots?
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Nature abhors a vacuum, I always say.
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"Cognitive dissonance". But Mijostyn is smart enough to change his ways, without a therapeutic intervention.
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Duh!!!
You demonstrated for yourself that your problem goes away when you lift the dust cover, yet your excessive fear of dust and static electricity and feedback induce you to want to change anything else but removing the dust cover during play.With all due respect, don’t you think that is a bit silly?
Not to mention the fact that there is static electricity buildup even with a dust cover down, and the moment you left the dust cover the LP becomes a magnet for dust.
Kudos to you, however, for having the cojones to admit to this human frailty.
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