Low freq. from small drivers? Is it possible

Ken...original Meadowlark Kestrals...or Vandy 1c...

Karls...Thanks, I guess :-)

How many continuing education credits do I get for this?. Will there be a final exam?

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

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

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

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

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

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.

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...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.

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...

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

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.

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

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...

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...

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
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Karls...In a SERIES crossover, a WOOFER inductor? You need to explain this.

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

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
>

PS... Thanks again for your taking the time to clarify your comments and respond to further comments / questions.

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

Karls...Is there a way to hear your speakers in New England?

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
>

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

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.

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

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
>

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

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...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.

Michael: I simply posted comments in agreement with others that had taken the time to share both their personal points of view and / or scientific data pertaining to the situation at hand. Sorry if that offends you.

Karl: Thanks for taking the time to post a response. As i mentioned, it is quite obvious to me that a lot of love and thought went into this product. I hope that this was abundantly clear in my original post.

1) I am aware that they've made great advances in terms of reducing distortion byproducts as excursion increases, but as a general rule, longer excursion still equals more distortion. Some designs are obviously better at this than others. The laws of physics still apply and we can't yet get something for nothing. As you mentioned, there are trade-offs involved in every aspect of speaker design. The end product becomes a balancing act based on what the engineer was willing to sacrifice in order to achieve their desired goals.

2) "I pointed out that while there is a 10dB boost at the amplifier, there is also nearly a 10dB loss in maximum output at the speaker".

What do the losses at the speaker involve? From what i know about such designs, the losses are incurred due to inefficiencies in power transfer below the point of resonance. The end result is a high percentage of power being dissipated as heat. As you stated, the end result might sum to a neutral response, but at the expense of much higher thermal stress.

3) According to your post here, anybody that listens above 90 dB's is "insane". Call me and dozens of other audiophiles that i know "crazy" then. Especially if you are talking about 90 dB's at 1 meter. As far as i'm concerned, spl levels should be taken and compared at the listening position, not at 1 meter. Readings taken at 1 meter are only handy for sake of sensitivity or efficiency ratings, and even then, they don't tell the whole story due to differences in dispersion patterns.

El: The original and second series 901's were a sealed design. The curve for those EQ's is different than that for the series III and all those after that.

Bose obviously had to run the drivers below resonance as the drivers were run full range. Karl is doing the same thing in principle but limiting the top end of the drivers being EQ'd and using a fancier circuit. Due to the fact that the 901 drivers resonated higher in frequency, and they were applying X amount of db's to compensate for the roll-off per octave, the total boost figure for the 901's would be much higher than Karl's design. In the long run, the use of equalization below the point of resonance is nothing new. The end result is that one can increase bass extension by appr half an octave at the expense of increased power requirements, increased power dissipation in the drivers and a lower maximum spl for the same percentage of distortion. It is really a tough balancing act to do correctly and requires very close production tolerances, both in the speaker itself and the correction circuitry being used.

As a side note, Bag End makes use of bass extension technology via a calibrated EQ curve in their subs. They chose drivers that resonated above the intended band of use and then EQ it for flat response below that point. This is a very lossy method and quite out of the ordinary, but has many advantages. Woofers and sub-woofers especially are the only drivers in most speakers were "resonance" or "break up" are considered normal and acceptable, yet most engineers / designers try to avoid that circumstance like the plague with mids and tweeters. Bag End took the high road, but in this case, the efficiency and power requirements of the system was what they were willing to sacrifice to achieve their desired goals. Sean
>

Karls...Thanks for the info. For your sake I hope there are enough people willing to spend $20K on speakers to make your effort worthwhile. If they go for multichannel you have it made.

You cite 10 dB as the boost. When Bose did it I seem to remember that the "inverse transfer function" (to use your technical jargon) was about 40 dB. Bose operated the drivers BELOW resonance because of the smoothness of the response in that range. I think he had driver resonance at about 200 Hz. Do you operate (mostly) below resonance?

Eldartford,

One more comment, about your statement that "it costs too much". While it is undoubtedly a very expensive system, that is not the whole story. In my opinion, and that of many others who have heard it, it significantly outperforms any of the well-known floorstanders in the range of $20-30K, when it comes to actually recreating the full and complete illusion of "live music" in a typical listening room at typical listening levels. Viewed in this light, and if one is able to close one's eyes and simply listen, it is actually quite a bargain. Not inexpensive by any means, but still a bargain compared to other choices which cost much more but don't deliver as much musical satisfaction.

It is only the obsession with size so prevalent in the USA that keeps many people from being able to take it seriously. Somehow, they feel that their dollars should be spent buying units of mass or volume, not units of quality. I don't share that view. In fact, many of the best qualities of this system are attributable precisely to the fact that it was made as small and simple as possible. The fact that it is expensive on a $/lb or $/cuft basis is merely a byproduct of the necessities of its design philosophy. It says nothing about its $/performance ratio.

While many will question the sanity of anyone who would spend $10K+ on a speaker system (see Sean's post above), there are nonetheless many people who are willing to spend that kind of money, simply for the joy it gives them in return. We all share the same obsession; it only varies by degree. Any outsider would still shake his/her head in wonder that we aren't perfectly happy with a Bose(R) system like everyone else has.

Best Regards,
Karl Schuemann
AudioMachina

Hi Eldartford,

Basically, it is possible to describe the low-frequency acoustical rolloff (transfer function) of a sealed-box speaker as a second-order high-pass electrical filter. This is an "equivalence" in the mathematical sense. Because of this, it is also possible to create the inverse (transfer function) of the speaker's rolloff, in the form of an electrical filter, and apply it anywhere in the reproduction chain.

Now, this is very hard to "get your mind around" on first glance, but the result of appyling this inverse filter ANYWHERE in the chain (in our case, typically it is prior to the power amp), is identical. In other words, you have to consider the mathematical product of the transfer functions of the BOMB, amplifier, and UM all at once.

What this achieves is not only to totally flatten the rolloff out, but to exactly cancel its associated phase shifts as well. This is simply the mathematical result of multiplying a transfer function by its inverse: unity. In other words, it is a virtually perfect solution in both frequency and time domains, within the limits of tolerances on the speaker drivers and electrical components.

Now, if that is all you did, you would end up with perfectly flat response to DC and infinite driver excursion. So one must also insert a new rolloff (at a lower frequency) into the transfer function as well. The Linkwitz Transform accomplishes these two tasks in a single step, by what is known as a pole/zero transformation, using a single op-amp section. The new rolloff can be chosen for any frequency and system Q, but in this case was optimized for the best compromise between driver excursion, music SPL's, transient performance, and frequency extension. It has a -3dB point (anechoic) of 32Hz and a system Q of 0.7. This is about all that can be done with drivers of this size if one wishes to retain reasonable output capability. Fortunately, it gives a very satisfying overall result for typical listeners in typical rooms.

Best Regards,
Karl Schuemann
AudioMachina

Karls...Can you explain what the "Linkwitz Transform" is. What I got from your website is that it is an equalization curve, of unspecified characteristics.

I guess Dr Bose beat Linkwitz by about 20 years. I described the concept as a "neat idea". I do not consider it a bandaid.

After more than four decades as an aerospace engineer, involved with manufacture of precision electromechanical equipment I assure you that I am not "completely ignorant" about NC milling machines. Also I never suggested that your aluminum slab was a bad idea. I like it, but it costs too much.

Lots of luck. :-)

Hi Sean,
To respond to your main points:

1. It is a mistake to make a blanket assumption that increased excursion per se is a serious problem, provided that the linear limits are not exceeded. While in an ideal world, excursion would be kept to zero, that obviously would require a driver with infinite surface area. The point I tried very hard to make in my post, and which was apparently lost, is that there are many, many other issues in loudspeaker design, all of which are extremely important. While it would certainly be nice to minimize excursion, that automatically requires doing others things that, in the final result, are far more detrimental to the overall performance of the speaker. I will repeat: the recent development of highly linear motor systems has not eliminated, but HAS substantially mitigated the problems caused by high driver excursion. The proof is in the listening.

2. Regarding power handling, you did not read what I wrote about the BOMB very carefully. I pointed out that while there is a 10dB boost at the amplifier, there is also nearly a 10dB loss in maximum output at the speaker. It is actually somewhat less than this, but the implication is that in the final analysis, the speaker does not receive significantly more power with the BOMB than it could take without it. In fact, on a lot of music, the argument could be made that the average power delivered to the speaker is actually more limited with the BOMB in place, due to the linear excursion limits of the drivers. In addition, thermal compression effects are far more important on an instantaneous basis than on a long-term one. In other words, when one is speaking of thermal dynamic compression, it is not a significant issue to dissipate heat from the driver chassis into the outside world. Certainly the aluminum baffle helps in this regard, but the primary concern here is with effects that are measured in nanoseconds, which the baffle doesn't help in the slightest.

3. Again, as I tried very hard to point out in my original post, it is useless to discuss "deep" and "loud" without having defined those terms, because it varies so much from one listener to the next. The UM/BOMB system, properly set up in an "average" room of, say, 4000 cubic feet, will be able to achieve an average continuous SPL of 90dB on typical rock/pop/jazz/folk recordings, extending flat to about 30Hz and being 3dB down at about 25Hz, without audible strain. Now, I will make the assertion that very few people who value their hearing will ever exceed this level. It is MUCH louder than most sane individuals ever listen. However, audiophilia is a diverse crowd, and there are certainly exceptions. Again, as I pointed out in my original post, that is why the UM is designed to integrate so well with high-quality subs such as the RELs. The combination of a pair of UM's and Stentor III's, when properly integrated, is something to behold.

To Eldartford:
If you have read our website, it is clearly stated that the Linkwitz Transform was developed over twenty years ago by Dr. Siegfried Linkwitz. And I am eternally grateful to him for having published it, for it is by far the most elegant solution I have ever seen to this particular problem. The BOMB is most emphatically NOT a "band-aid", as you seem to imply, and has nothing to do whatsoever with having chosen "too small a box" (it is, in fact, exactly the right size), but rather is an integral part of achieving a level of performance that is well outside of the experience of most audiophiles.

Secondly, your statement about the ease with which the baffle can be made on a CNC machine betrays a complete ignorance about manufacturing techniques and production costs. As someone who has over a decade of experience with state-of-the-art CNC production machining and several decades of experience in advanced composite construction, I can tell you categorically that you have no idea whatsoever what you are talking about. If I had any sense at all when it came to minimizing cost (and making a profit), I never would have chosen this manufacturing approach. I would have banged out the enclosure from CNC-routed MDF or Corian or phenolic laminates, or laminated it from pieces of solid wood, or at the very least made it from extrusions and flat slabs of aluminum ala Krell, which would have been 1/10 the effort and cost (this is not an exaggeration, believe me). But this speaker was never meant to be a "me too" design. It was intended as an all-out assault on the state of the art, and its success is in large part due to the extraordinary effort put into the cabinet.

To Metralla:
Thanks so much for the kind words. It was indeed an honor to have Stan Ricker in the room, and a delight to hear his comments. One of the highlights of CES for me, to be sure.

Karl Schuemann
AudioMachina

Thanks for that input Metralla, I am in complete agreement with that assesment from how they have perfomed in my system.
Qualifier-IMO

Michael,

That would be "Karl Schuemann".

I was at CES when Stan Ricker auditioned the AudioMachina monitors. As many of you know, Stan plays the double bass and has decades of experience listening to the reproduction of recorded music. Not an easy fellow to impress, one would think. His praise for the way the monitors nailed the bass lines on music he knew well was effusive, unrestrained and unsolicited.

Regards,

In case of a knockdown, go to a neutral corner.

Too early in the morning. I meant Dr. Carl Schuemann and Dr. Ken also, Sheesh.

I apologize to Dr. Ken Schuemann because it is most unfortunate that such a great product has been clouded by this unnecessary rhetoric.

Sean and Michael
Thank you for your essays.
I'm shure it did not help Dr Ken much.
Blue Bull

Sean
You said it yourself:"if properly done" and "midrange response should be improved"I have found that it sometimes is not done,actually ,most of the times.I still like a well designed two-way.

Thanks for turning what started to be a very friendly and uselful discussion on speakers into another pissing match of an unrelated topic. You did it here and you also managed to do it in the following thread on speakers.
Dear Mr. Speaker Designer - What I want...
Which by the way, no longer shows up on the discussion.

I for one,,, am sick of your flaming and have made a formal complaint again to Audiogon.
Thanks for all you have tried to do for me.
Cheers,
Michael

Michael: Based on the information provided, it is possible to tell that someone invested a lot of time and research into these speakers. Whether or not they do everything well or suitable for a given installation is another matter. The more spec's that the manufacturer provides, the more that one can interpret just how well they might fit their specific needs and desires. Sean
>

PS... Thanks for the kind words. I hope you have a pleasant week-end too : )

Sean, it is so good to see that you took time out of your busy schedule to go through the above posts and do your typical blessing and discreditdations. In the future, please try to wordsmith your responses to shorten them. Really it is much easier on the reader to not have to spend so much time reading just to realize that nothing constructive or informative was really said.
"this speaker lacked the spec's that one really needs to properly judge a speaker on paper." Absurd, statements like this belong in Audio Asylum under the NEWBIE section.
"Your level of involvement / personal emotions seem to be clouding your response on this one. Then again, that seems to be a common situation when it comes to products that you endorse." Dr. Sean I will try to make an attempt in the future to run my posts by you prior to posting, so that you fully understand their intent and meaning, Furthurmore, its good to see that you have kept track of all my personal enodrsements.

I want to highlight two of your statements. Here's the first one: "Drew: very nice posts that are based on both common sense and science. Those two factors rarely meet when it comes to audio and audio forums. I applaud the efforts that you put forth in your post. He just said that this speaker lacked the spec's that one really needs to properly judge a speaker on paper"

Here's the other statement that i think requires further commentary / clarification: "Other than that, this looks to be a very well designed speaker."

If there is not adequate published specs on the speaker, how can you say it is a well designed speaker? It would appear that your level of involvement / personal emotions seem to be clouding your response on this one. Then again, that seems to be a common situation when it comes to commenting on anything topic.

I gather that the BOMB speaker utilizes heavy electronic equalization to flatten the response of drivers mounted in a too small enclosure. This is a neat idea, and one that Dr Bose came up with about forty years ago. I hope that patent issues have been resolved. The requirement for a powerful amplifier is less of a problem now than it was back then.

I am unimpressed by the reported difficulty of making the massive aluminum baffle (or whatever it's called). A numerically-controlled milling machine could knock these off at high speed to tight tolerances. Probably cheaper than a fine furniture grade wooden enclosure.

Sogood51: I liked your post. The comment about ports adding quantity but lacking quality is right on the money. The analogy of a smaller woofers vs bigger woofers and the boy / man comparison was also quite good.

Drew: very nice posts that are based on both common sense and science. Those two factors rarely meet when it comes to audio and audio forums. I applaud the efforts that you put forth in your post.

Michael: Drew never said that other speakers weren't deficient in providing usable spec's. I'm quite certain that he feels that most manufacturers don't provide anywhere near the amount of info that they should about their products, especially speakers. He just said that this speaker lacked the spec's that one really needs to properly judge a speaker on paper.

Given the claims being made for this speaker and the amount of technology that supposedly went into it, one would think that the manufacturer would want to "testify" to the actual performance of the product as much as possible. Your level of involvement / personal emotions seem to be clouding your response on this one. Then again, that seems to be a common situation when it comes to products that you endorse.

Karls: I want to highlight two of your statements. Here's the first one: "It still can't break the laws of physics, but if used within its linear excursion limits, will give extraordinary performance regardless of volume level or frequency".

The only way to maintain "extraordinary performance" with this speaker contradicts the "regardless of volume level or frequency" part of that sentence. That's because as either frequency is reduced or volume is increased, excursion also escalates. As such, what you've said is that "this speaker kicks ass / remains quite linear so long as the volume is kept to a reasonable level and one doesn't expect the deepest bass". As a few posts have pointed out above, you can't maintain high spl's and / or deep bass extension with lower levels of distortion without resorting to larger drivers.

Here's the other statement that i think requires further commentary / clarification: "The issue of the extra power required by the BOMB is more of a problem for the amplifier than for the speaker. The reason for this is that there is surprisingly little energy (on a continuous basis) in the deep bass. But when it appears, it can make very heavy transient demands on the power amplifier. The BOMB has a maximum boost of 10dB at 24Hz, which equals a factor of 10 in amplifier power".

The added power requirement of the amp is most definitely a problem that the speaker shares too. That is, the 10 dB increase in power that the amp must generate has to be dissipated. ALL of that dissipation takes place within the speaker itself. I think that this is why Drew mentioned thermal compression and power handling coming into play more rapidly with this approach than when using a larger driver with less requirement for EQ.

As a side note and to somewhat respond to Drew's comments, my thoughts are that the effects of thermal compression would be somewhat reduced with this design. This is due to the design of the driver itself and the fact that it will make use of the 2" thick metal baffle acting as a heatsink for the basket of the driver. While it is true that the voice coil & coil former are doing most of the dissipation in a driver, the basket and magnet structure also enter into the picture in this area. Given that the basket is mounted to a metal structure that should be quite excellent at dispersing heat, it probably has a sizeable advantage over other designs.

Other than that, this looks to be a very well designed speaker. I remember looking at it previously and thought it was pretty nice, but also way too costly. I do understand that there is a LOT of custom machining taking place here, but $10K for a "little" speaker is still a LOT of money. Then again, $10K for a "big" speaker is still a LOT of money in my book. I do applaud your efforts and appreciate the fact that you didn't try to push some type of bass reflex design on the public in the name of "more is better" bass response.

Bluebull: Actually, if properly done, relieving the midrange driver of the longer excursions necessary for low frequency reproduction, midrange response should be improved. Given that many two ways are a compromised design, it stands to reason that the same engineers would be even more confused when adding another driver, two more crossover points and a lot more parts to the equation. Sean
>

Eldartford.....the reason many enthusiasts buy 3 way speakers is for "good bass" ,not for good midrange.Misconception, of course.A point I think we would agree on.

Bluebull...Actually, the reason for 3-way speakers is good midrange: not good bass.