Sean...The original (sealed) Bose speakers are the only ones that I ever thought sounded good. All speakers generate output below the driver resonance, and many use equalization, but designers usually try to get resonance down as much as possible so as to minimize operation below resonance. The Bose idea was to deliberately push the resonance up, and equalize the hell out of the signal. I think that the speakers we are talking about here take somewhat the same approach, but not in such an extreme way as Bose.
Again I note that Bose's objective was not bass extension, but rather smoothness of the response curve because of the inherent smoothness of the drivers response when operating below resonance. LF roll off was taken care of by the drastic LF boost. |
I had original 1st series 901's back in the 1970's. Harry Pearson stated that the 901's are the only speaker that has gotten worse with each new generation. I guess that means that he thinks that the 1st were the best. I would tend to agree.
As a side note, i've still got all of the drivers from those 901's. Those used nine 8 ohm drivers wired in a series-parallel circuit to achieve a nominal 8 ohm impedance. To be specific, they used 3 parallel banks of 3 drivers wired in series. The second series and up used nine 1 ohm drivers all wired in series. If you blew a driver with the first series, you could still use the speakers. If you blow a driver with any 901 after that, one driver takes the whole speaker down, kind of like old style Christmas tree lights. Sean
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Sean,
Sorry, I was unclear about the "loss" of 10dB at the speaker. I should have said "reduction" instead. In other words, the average music SPL that the speaker is able to deliver is almost 10dB less when used with the BOMB. This is, of course, due to the extra excursion needed with the boost. In other words, you cannot turn the volume knob up as high with the BOMBs in the system, because the drivers are now excursion-limited to a greater degree than previously. This naturally has the effect of simultaneously limiting the (average) allowable power input to the speaker from the amp. So while the spectral distribution of power is shifted, its maximum allowable value is not significantly increased overall, and may even be reduced depending on the program material. Of course, the overall system efficiency is reduced also, again depending on the program material. Hope this makes sense.
I mean no offense by my use of the term "sane". Trust me, I've always been a bit crazy myself, and have been known to dial the volume to 11 on more than a few occasions. I was only trying to make the point that not many people listen at 90dB average SPL. Most of them don't even own SPL meters, so wouldn't even know. I trust that you have one and have used it on a variety of program material, and so know what levels you listen at. (If you truly exceed 90dB average regularly, the physician in me would advise you to turn it down a little, for your ears' sake. This means you are likely running peaks in excess of 110dB, and there's no question about the long-term effects of that practice. Again, no insult intended, merely caution.)
I would also guess that if you took a wide sample of audiophiles, the vast majority of them would show a continuous average SPL at the chair of 80 +/-5 dB. I certainly don't know many folks who exceed this regularly.
Sheesh, being compared to Bose 901's. Now that really hurts.
Best Regards,
Karl Schuemann
AudioMachina |
Thanks for your very up-front response Karl. As fine of a speaker as you have been able to produce, your comments varify what i and several others have stated. That is, obtaining extreme low bass out of a smaller driver comes at the expense of some other area of operation. I applaud your honesty and integrity, both in your responses here and in the design attributes of your product.
As a side note, neither Mr Dartford or myself were actually making an "apples to apples" comparison between your speaker and the 901's as much as we were discussing the various manners that technology can be applied and how it is actually used in various products.
I do have one question for you though. Have you ever tried running these actively crossed? I'm curious as to what your thoughts / experiences were in this regards IF you tried that.
Other than that, i do remember you posting positively about sealed box designs in the past and contributing some excellent information / comments in various threads. I knew that i always respected your opinions and now i know why. That is, we basically agree. At least on this specific issue : ) Sean
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Sean,
When you ask if I've tried them actively crossed over, I assume you mean to a sub on the low end. The answer is that I haven't. It is my opinion, having played with this stuff for a long time, that putting any crossover on the low side of the midrange drivers, anywhere but in the low bass, causes more problems than it solves. The transition from woofer to midrange is always audible.
Many people (and I would guess that you would be in this camp) would rather run subs with active crossovers on both high and low sides, primarily for the reason we have been discussing: limiting excursion in the midrange drivers. But there is another way that is superior, in my opinion.
First of all, I will state that a subwoofer should be crossed over as low as humanly possible, for all kinds of reasons. 100Hz is way too high, and 80Hz is pushing it. Given that this is the case (and I would be very surprised to hear anyone disagree with this, if they've had experience in this area and have good ears), then it makes far more sense to let the speaker itself provide the high-pass function. In the case of the UM, its natural rolloff is essentially equivalent to a 12 dB/octave Butterworth at just under 70 Hz. Of course, this only works with a sealed-box monitor, which is self-limiting in the deep bass, but of course that is exactly what I intended from the start.
This approach is exactly equivalent to an electrical solution, but with the advantage of no added electronics and their inevitable colorations. It allows perfect compatibility with the RELs and other similar subs which are designed for exactly this approach. In my experience, this is the only way of connecting a subwoofer that actually achieves the goals of making the transition sonically invisible and causing no sonic degradation to the main monitors.
Best Regards,
Karl Schuemann
AudioMachina |
Karls...As sean said, noone is comparing your speaker's sound to that of a Bose 901. (How could I...never heard yours). But, there seem to be some similarities with the design concepts of the ORIGINAL 901. Did you ever hear original Bose 901's? Not to be ridiculed, especially for 35 years ago. That's why your effort to develop the technology is of interest to us old farts. |
C'mon guys, I was kidding, honest. It just struck me as funny, given the status of 901's as the reigning poster child for how not to make a high fidelity speaker.
Best Regards,
Karl Schuemann
AudioMachina |
Karl: I wasn't talking about supplementing the bottom end of your design with an actively crossed sub, but about using the existing design with an active crossover and bypassing the internal series crossover. I understand that you have several different circuits ( impedance compensation, notch filters, etc... ) that would have to remain.
I also have other questions about series crossovers for you, but that is neither here nor there : ) Sean
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Karls...Is there a way to hear your speakers in New England? |
Sean,
I haven't tried active crossovers, no. It's not really designed for this, because as you probably know, series crossovers only use one set of binding posts. There's no such thing as biamping. So there's only one set of posts on the speaker, and no way to easily add another one.
One of the interesting things about series crossovers is that they work like sh** unless you have everything, and I mean everything, exactly right. This means both drivers flat in frequency response, impedance, and phase, along with perfect time alignment. But once you accomplish this, it's simply a matter of punching the numbers on a calculator to get the correct values for C and L, and it will work perfectly every time. This was a revelation the first time it actually happened, but it makes perfect sense when you think about it. That, in a nutshell, is why almost everyone uses parallel crossovers. They're easy to "fudge" if you haven't done your homework. Not so with a series.
This is a long way of saying that the "other stuff" is by far the most important, not the primary C and L. And as such, there isn't much benefit to making them active. All the usual problems with passive crossovers, such as impedance and phase anomalies, have already been dealt with, and since it is only a two-way with a high crossover point, it can use small, high quality C and L, which effectively eliminates (or at least minimizes) the other argument for active crossovers.
Eldartford,
The marketing side of this project really hasn't started in earnest, but hopefully next year. So there are no dealers yet, but we do make demo systems available to people if they're interested enough to pay the shipping, and offer very good pricing on the demo systems if they decide to keep them.
Best Regards,
Karl Schuemann
AudioMachina |
Karl: My experience with even very high grade "passive parts" placed smack dab between the amp and drivers is that they drastically reduce sound quality. One can use even a lower grade electronic crossover and get better results than if one used very simple passive crossovers of the highest quality. At least that's been my experience.
My Brother argued with me about this for quite some time. That is, until i gave him an old electronic crossover that i hadn't used in years and he tried it out. Pulling even a single cap from his tweeters made a HUGE difference in terms of sonics. Why one can get away with running a MUCH more complex circuit at line level without near as much sonic degradation is beyond me, but i'm guessing it has something to do with the current levels involved.
After studying the circuit lay-out of a series crossover, i've often wondered how much more "low frequency leakage" there is into the tweeter as compared to a standard 1st order "parallel" crossover? I've also wondered about the differences in power handling between the two. Have you ever compared the two with identical designs? Sean
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PS... Thanks again for your taking the time to clarify your comments and respond to further comments / questions. |
Sean,
I'm aware of the advantages of actives, but again it becomes an issue of the overall design compromise. As few people would be interested in a $15k/pr monitor, only a tiny fraction of them would even take a glance if it required biamping. Besides, using really high quality parts makes a huge difference, and keeping it simple helps perhaps even more.
The tweeter power handling (from LF leakage) in a series crossover is a function of the DCR of the woofer inductor. The tweeter attenuation "shelves" at some point, and the lower the DCR, the lower that point is.
The power handling in our case isn't even close to being an issue. The inductor is small with very low DCR, the crossover point is fairly high, the tweeter is padded down, and on top of all that, the response is designed to fall like a brick below the tweeter resonance, which is more than two octaves below the crossover point. So in this particular case, it is more than bombproof. But that isn't always the case.
Best Regards,
Karl Schuemann
AudioMachina |
Karls...In a SERIES crossover, a WOOFER inductor? You need to explain this. |
El: Series crossovers consist of the opposite components one would use in a parallel crossover. While "common" crossovers are called "parallel" designs, they really are closer to a series circuit by their very nature. Some newer speakers ( and old ones like Fried and Koss ) use what is called a "series" crossover, which is really like a parallel circuit. You can see a diagram of a basic "series" crossover here at Karl's website. The terminology is quite confusing and i can understand why this baffles people. As a side note, i was doing a search and ran across Clement Perry's comments about Karl's speakers. You can read it by clicking on the link to Stereotimes CES coverage. Sean > |
Sean: Series crossovers consist of the opposite components one would use in a parallel crossover I think that's what El was asking about: how come the woofs are looking, so to speak, at an inductor rather than a cap... |
Yep Gregm.
In a series crossover you first put the woofer and tweeter in series. That would, of course, pass all frequencies through both drivers, briefly until the tweeter burned out. To avoid this you put an inductor across (in parallel with) the tweeter, so that LF signal bypasses the tweeter. Similarly, a capacitor across the woofer keeps HF out of that driver. The value, mH, of the inductor, together with the inductance of the driver determines the high pass frequency of the tweeter.
In summary, the inductor relates to the tweeter, not the woofer.
Perhaps the terminology just got mixed up, but, I wonder... |
The terms "series" and "parallel" describe the basic topology of the circuit, and refer to the connection arrangement of the DRIVERS. Look at the diagram link from Sean above for the first-order "series", and note the difference in driver connection compared to a "parallel".
But regardless of whether it's "series" or "parallel", the main inductor is still in series with the woofer, and the main capacitor is still in series with the tweeter. If you don't understand how this can be, it's time to do some homework. I'll give you a hint to get you started: Always think about where the CURRENT flows at a given frequency, because that's what makes the driver move. It follows the path of least resistance, just like water.
Best Regards,
Karl Schuemann
AudioMachina |
Karls...Having messed around with crossovers for more than 40 years, I don't need your schematic to comprehend a series network.
Let me ask you...which driver's crossover frequency does the inductor determine? Shouldn't we call the inductor by the same name as the driver it serves?
The way I regard a series crossover is as a series connection of two elements...(1) Tweeter/Inductor parallel pair and (2) Woofer/Capacitor parallel pair.
(And, to Sean's point, a "parallel" crossover is a parallel connection of two series-connected elements).
Makes sense to me, but you evidently have some other way of looking at it. There is more than one way to skin a cat, which we can perhaps agree is a good idea. |
Eldartford,
If you want to learn a new way of thinking, perhaps you would do well to listen to what I said, and not continue to insist on thinking about things the way you have for 40 years. I will give you another hint, and perhaps this time you will listen and actually do some thinking.
In a simple two-way parallel crossover, there are two possible paths which the current may follow. At low frequencies, it follows primarily one path (the one through the woofer), and at high frequencies, it follows primarily the other path (the one through the tweeter). In the crossover region, it goes some through one and some through the other.
In a simple two-way series crossover (such as that shown on our website), there are four possible paths which the current may follow. I leave it up to you to (1) figure out what those four paths are, (2) figure out which two paths it primarily follows, one at low frequencies and one at high frequencies, and (3) compare those two paths to the two paths in the parallel case.
Hopefully, after you have done so, you will begin to understand what I was trying to tell you. The analogy between electrons and water is an old one, but still invaluable.
As far as your question of "which" element goes with "which" driver in a series crossover, the short answer is: they don't. Both elements affect both drivers, as a cursory glance at the circuit will tell you.
Karl Schuemann
AudioMachina |
The current trend towards 6" drivers (or smaller) has been going on for quite some time...and i do think it is a good trade in relation to the large 10" drivers and cabinets of yesteryear...the gain in transparency and involvement of small two-ways at the expense of deep bass is a fair trade in my estimation...small speakers are capable of very good bass extension...especially in small rooms... |
Karls...Stop pontificating!
Of course LF energy flows through the inductor to the woofer. That's why it doesn't flow through the tweeter, so that the tweeter tweets and doesn't woof.
Suppose that you change the inductor value: make it smaller. The frequency at which its impedance equals that of the tweeter goes down, which means that the tweeter carries energy at lower frequency. Its crossover frequency has been changed. Now, has the woofer been affected? I don't think so, except for possible second order effects. Some current that formerly flowed through the inductor now flows through the tweeter, but a full range signal arrives at the woofer. Same as before. Now the capacitor across the woofer provides the low impedance path for HF and keeps it out of the woofer.
This whole silly discussion is about how to name the inductor. I claim that it should be called the "tweeter" inductor because it determines the tweeter crossover frequency. You like to call it the "woofer" inductor because it carries the spectrum of signal that is routed through the woofer (by the capacitor I might add).
Let's change the subject. Why do you think that a series crossover is superior to a parallel one, assuming that both are properly designed and optimized for the driver characteristics? I know of no reason why one should be better than the other, and I suspect that the recent flurry of series designs may be a marketing ploy. |
Eldartford,
I'm not pontificating at all. It's just that things aren't as cut-and-dried as you would like to assume. The crossover point in a series crossover is a function of both the inductor and capacitor. If you want, you can change them both, and yet still keep the crossover point the same. If you don't believe me, look it up. It's not that hard to find.
In order to carry this conversation further, you are going to have to dedicate some effort to learning the actual math behind the problem, starting with the concept of transfer functions. It is in most college junior-level electrical circuits classes.
The advantages of series crossovers are real, but again require some mathematical background to understand. The two that in my mind are the most beneficial are:
1. It guarantees a constant-voltage transfer function. This is theoretically possible, but by no means guaranteed, by the parallel.
2. It is essentially insensitive to tolerance variations in both the drivers and reactive elements, thus giving a much better chance of good performance in the real world compared to the parallel.
To this can be added the additional benefit, stated in one of my earlier posts, that the series topology forces you to do everything exactly right. While this is also theoretically possible in the parallel, for all practical purposes it NEVER happens in the real world. Almost every speaker you look at with a parallel network has grossly obvious and serious flaws, simply because the designer didn't want to spend the effort necessary to make it perfect. Thus it is a final "test" of the design, ensuring that there is no "fudging" going on and compromising the end result.
What I'm saying is that if a parallel is done exactly right, there is no reason, at least theoretically, it can't be as good as a series. But in the REAL world, it never is.
Karl Schuemann
AudioMachina |
Karls, nice of you to condescend to explain to us filter theory! Math is nice, but understanding English is even more important. Semantics do mean something. (tongue in cheek, of course).
Listen to Eldartford's explanation and perhaps you will grasp what he is saying. I thing that he used at least grade 12 English. |
inpepinnovations:
That, unfortunately, is not a useful contribution to this discussion. Of course semantics mean something, but when it comes to filter design, math rules, whether you like it or not. If you were to put a hundred filter design experts, none of whom spoke the same language, into a room with a chalkboard, they would still be able to communicate perfectly well on the subject of filter theory. But ask a hundred English majors who know nothing of filter theory to design you a crossover, and see how far you get.
I understand Eldartford's explanation perfectly, but what you haven't figured out is that my way of thinking is a very useful intuitive approach to figuring out any electrical circuit, not just crossovers. As such, it was my hope that Eldartford would grasp it and come to see that series and parallel are two sides of the same coin, to mix a metaphor.
It is not just an issue of semantics; it is an important equivalence rooted in (gasp! horror!) mathematics.
Karl Schuemann
AudioMachina |
And to Eldartford:
I was too quick to jump on you in my last post, got my hackles up I suppose. I don't like to think of myself as a pontificator, but I do sometimes get a bit hardheaded when it comes to trying to get people to see what I'm saying. My apologies, and I agree with your assessment that we are only differing in how we name the elements. I think of the series and parallel forms as being equivalent, since the equations are the same, but I must admit that my calling it a "woofer" inductor could raise some eyebrows.
Peace,
Karl |
It's more than 40 years since EE101, and although, as an aerospace systems engineer (not an EE) I worked with a lot of fancy circuits since then I never actually designed a crossover network except at home for audio. I went to the only reference that I have handy at home to read up on series networks, Dickason's Cookbook, but I drew a blank. He says that the parallel configuration is "definitely preferable" and therefore does not discuss series further.
I have always been a "contrarian", so if everyone else is using parallel configuration I would probably look at series, as you have done. However, when you take the contrarian path you must be prepared to strike out a lot. But the grand slam HR makes it worth while. Your bases are loaded.
Peace
Ed |
Eldartford,
My apologies again for yesterday's outbreaks, it was a pretty rough day and I'm not the best at being calm anyway. A good night's rest helps a lot.
To try to explain what I was after:
In the parallel case, you have two separate filters, LR and CR, which both have Butterworth responses by default (maximally flat, Q=0.7). You can change L or C, and it will change the corner frequency but not the Q of the filter, and it does not affect the other filter at all. On the other hand, it does affect the voltage sum of the two drivers, which affects the summed frequency response.
In the series case, you have the equivalent of an LCR loop, which is a resonant circuit. (It's not the simplest form of LCR, but it's a loop nonetheless.) Now if you stick to Butterworth values for L and C, you have an equivalence to the parallel case, and everything works the same. However, in an LCR loop, the resonant frequency is singular and is determined by the product of L and C. In addition, the loop has a resonant Q which is determined by the ratio between L and C. What this means is that you can double one, and halve the other, and end up with the same resonant frequency but a different Q. So it doesn't behave the same as a parallel except in the case where you use standard Butterworth values. Also in contrast to the parallel network, the series network by its very nature maintains a constant voltage sum across the drivers, which maintains flat frequency response despite the variations in the components.
Of course, there are a lot of assumptions built into all of this, such as equal resistive drivers, equal amplitude and phase response, constant voltage source, etc., none of which are really achieved in the real world. That is why I view the series as being superior to the parallel, because it automatically minimizes the effects of at least some of these "non-perfect" conditions.
Best Regards,
Karl |
Here is a link which has a downloadable .doc file (as a .zip) by John Kreskovsky, which is an excellent primer on series crossovers. Note that the damping which I referred to as "Q" is called "zeta" here.
http://www.geocities.com/kreskovs/Series-1.html
Best Regards,
Karl |
Karls...Thanks, I guess :-)
How many continuing education credits do I get for this?. Will there be a final exam? |
Ken...original Meadowlark Kestrals...or Vandy 1c... |
