Low freq. from small drivers? Is it possible

Can you get really low freq. (lets say 30 and down) from a small driver (~6 inch? What is the relationship between driver size and frequency? Most speakers today have went away from a large base driver (10 inches or more). Have we really come that far or is it really a compermize?

Any recomendations for smaller floor standers with good bass?


Dr. Ken
The only small speakers I have heard that had ridiculous bass, relatively speaking of course, were Royds. They are tiny floorstanders that have a weird porting design that makes them sound really full range while only having 6 inch drivers (or something close to that). They are cool but very rare in the USA.
Small drivers, like 3/4 inch headphones, are perfectly capable of LF response, but not at any volume. Because a small driver cannot move enough air to achieve useful volume at low frequency they are designed for other characteristics like mid/high reproduction. A 6 inch subwoofer is technically possible, but would be almost useless for any real audio system.
Here is the Royd homepage if you are interested: http://www.roydaudio.com/main.htm
It is absolutely possible even without a port.
Karl E. Schuemann and the ultimate monitor have accomplished this very very well, at least in my system.

Best Regards,
Michael Wolff
Yes, there are many speakers that can get to the 30hz range with those 6.5" drivers. VBT has a claimed frequency response of 18hz(-6db) with one of their subs using a 6.5" driver.

There are tradeoff though. A 6.5" driver generally can't play as loud as a 10" driver before breaking up. Second deep bass in small boxes generally means lower effeciency. So yep physics still applys.
The key is to move a large volumn of air. If long throw woofers are used then they don't need have as large diameter.
Speakers with only one 6 inch bass driver (mid-range really) are not going to move enough air for output into any room larger than a small car trunk even at 35hz.

Ported speakers only add SPL pretty much and are a poor choice for bass output IMO.

If you need (want) deep bass don't start out with a design that is compromised from the start....OR, you could say, don't send a boy to do a man's job.

I heard amazing, deep, tuneful bass down to 30hz and then some from a 6.5" woofer in the Merlin VSM-MM. And this was in an approx. 8000 cu. ft room. They really did blow my misconceptions of what a small woofer could do in a well designed speaker. It was an eye (ear) opener.

Hi - I own a pair of Avalon Eclpses, which I consider small woffer and capable of reproducing a very clean low frequency range at 35Hz and up. Be sure to position this (or any other speaker) on it{s right place to achieve the best possible bass.

The specs of small drivers can have a low cutoff - my bedroom speakers have a pair of 5.25" mid-bass drivers and are flat in-room through 30Hz.

In practice it doesn't work.

SPL is purely a function of displacement and frequency. Displacement requirements quadruple for each octave you drop in frequency, meaning excursion increases 4-fold in a sealed system when you don't change the diameter.

Play with www.linkwitzlab.com/spl_max1.xls if you want.

This has a couple of problems
1. Physics prevent reaching reasonable SPL levels with small drivers outside a car or closet environment where you have up to 12dB of cabin gain below the fundamental resonance .

2. Excursion increases 4-fold with each octave lower if you don't change diameter. Distortion is a function of excursion. My 5.25" midranges (about equal to a 6.5" driver - they have more area, but will have less excursion) double at low frequencies - the harmonics are loud enough that you hear the higher tone. IM distortion (why old transistor amps sound bad) also increases. I never got good midrange performance from drivers <= 6.5" when bass notes were also present. Adding a sub-woofer with a 80Hz cross-over always cleaned up bass and midrange in music with a bassline. I now use an 8.5" midrange, 2 10" long-throw subwoofers per side for bass below 120Hz, and add a 14.5" subwoofer for theatrical tracks where the bass is really out of hand.

If you want small speakers use subwoofers too. You can have small boxes for WAF, small baffles for minimal difraction, place the midrange+highs for their best performance, and the sub-woofers for the flattest response at your listening position.

Many people find the best integration when crossing over an octave above ported speakers' F3 point (LR4 order electrical high and lowpass) or at sealed speaker's F3 point (2nd order butterworth high-pass, LR4 low-pass).

If you don't want sub-woofers and do want full-range music (symphonic, rock, jazz with an upright bass, etc.) you need 3-way speakers with a large bass driver.

Here is the frequency response of the Ultimate Monitor from Karl Schuemann
Two way, with Scan Speak Symmetric Drive 6" and 1.1" drivers

Frequency Response
+/- 1dB: 70Hz - 18kHz
-3 dB, typical in-room: 45Hz - 20kHz
-3 dB, typical in-room, w/ BOMB: 25Hz - 20kHz

Believe when I say I hear what is written above.
Check the review on 6moons website about the Harmonic Precision Caravelle monitors.
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Where's Warren?

He's had great results with the Harmonic Precision Caravelle as well.
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Hey Tvad,

You can find out about the Ultimate Monitor and the BOMB at this link on Positive Feedback.


I am a believer in large area LF drivers. My subwoofer system sports three 15" drivers and three 12" drivers. I have some small monitor speakers that will play almost as low in frequency, but there is obviously no comparison in the impact of the sound. Large diameter (area) LF drivers have an effortless quality to their sound.
It's possible to get excellent bass by using multiple smaller woofers as opposed to fewer larger ones. The surface area works out to be about the same but the smaller drivers are generally quicker.

For example, the bass specification of the Dali Megaline is 35 HZ.

That specification did not particularly astound me until I was face to face with the designer at the London audio show. When I found the measurement was taken at center line of an anechoic chamber I was impressed.

In a typical listening room the boundary reinforcement at the floor, sides and rear wall would improve those numbers substantially.

The Dali is a line source two way (ribbon plus woofers) with twenty four 6.5 inch bass drivers to achieve the desired surface area. They are rated in excess of 131 DB before breakup.

I will try to verify when mine get past the required 500 hours and I get some serious power on them.
Smaller drivers can produce low bass IF the cone is of a high mass design and capable of long excursion. There are several problems here though. That is, why would you want to use a smaller woofer of higher mass? This reduces both transient response and high frequency bandwidth, negating much of the benefit of using a smaller driver. On top of that, a driver with more surface area reproducing the same note at the same amplitude of a smaller driver with longer excursion will produce lower distortion. The more "throw" that the driver makes, the more distortion that it produces. On top of that, longer throw woofers produce more reflected EMF, making them harder to control. On top of that, the smaller driver will have to move more air to produce the same spl, meaning that it will be producing more distortion at all times while running into Xmax ( linear excursion capabilities ) sooner than a larger driver. Obviously, there are a lot of "on top of's" in this equation : )

In plain English, this means that if you want deep bass out of a small driver, you'll have to make several compromises in other areas to get it. The only way to get low distortion and deep bass while retaining good linearity at high volumes is to use large woofers in a large cabinet or a multitude of smaller woofers in a large cabinet.

To quote speaker designer Bill Fitzmaurice: "The bottom line for speaker cabinets is that for the goals of a small box, a reasonably efficient system, and good bass extension, you may achieve any two of those goals at the same time, but not all three". Sean
hmmm, very interesting!

For example: So the base out of a twin 6.5 like the b&W Naut 804, could be good, but not great.
>Here is the frequency response of the Ultimate Monitor from >Karl Schuemann

The specs don't tell you enough to be useful.

1. They don't tell you about distortion. The mid-ranges used in my speakers are good for .3% THD @ 96dB/1 meter in their operating range with an increase to 1% at the tweeter cross over frequency where they're 6dB down and distortion should be less. Run at lower frequencies they'll have horrible distortion at much lower output levels - maybe 10% at 70dB one you reach 30Hz. This is especially bad at low frequencies where tight spacing of the equal loudness curves makes the harmonics sound louder than the fundamentals. IM distortion is even more of a problem.

2. They don't tell you what the maximum output level is at those frequencies. Using a pair of 6.5" scan speak mid-bass units (Sd = 145 cm^2, xmax = 5mm) in a sealed box the linear limits are about

88dB @ 35Hz
94dB @ 50Hz
100dB @ 71Hz

3. They don't tell you what the off-axis response looks like. At reasonable listening distances you're picking up more sound from the reverberant field than direct sound. The shape of the off-axis curves has a _huge_ effect on what you hear.

4. The don't quantify thermal compression. This is especially important where you start equalizing. The BOMB is a Linkwitz Transform which allows you to change the F3 point and Q of a speaker thus getting you lower bass extension and less group delay at higher frequencies. Low group delay means "fast bass." The problem is that your power requirements go up. The extra power increases voice coil heating and therefore resistance. That means more thermal compression and changes in the cross-over response with output level than you'd have in a speaker without equalization.

I'm sure the Ultimate Monitors are exceptional speakers although they can't break the laws of physics. If you want natural sounding bass at realistic output levels you need a 3-way or sub-woofers, the later being better because high and low frequency transducers interact with the room differently and therefore work best with different placement.
This question in analogous to asking whether it's possible to produce high horsepower from a small displacement piston engine. The answer is yes, but it's much easier, more efficient and less performance compromised if you produced the same horsepower with a larger displacement engine. Small cones in small cabinets can produce deep bass, but larger cones in larger cabinets can do it more easily. Multiple small cones in a large cabinet is a good combination, but it tends to be more expensive and complicated than an equivalent single large cone. Every design choice presents a set of compromises. None of the choices is inherently better than the others, they simply present a different set of compromises.
Onhwy61...A better analogy would be trying for high torque at low rpm from a small displacement engine. The small engine might produce lots of horsepower, but you won't win many drag races.
I'm just curious as to any speaker which is in the same price range that lists all those specifications that you say are missing on the Karl Schuemann site.
I have been searching and Wilson Watt at $20K plus does not,
Sonus Faber Stradavari does not, Von Schweikert does not,
Kharma does not. In fact, Karl gives a huge amount of information of how his speakers spec and perform.

Before pointing fingers and saying that "The specs don't
tell you enough to be useful", do your homework please.

Eldartford, what you describe is virtually impossible, whereas I recognize that you can get deep bass from relatively small cones.
Hi all,

I was forwarded this thread by Michael Wolff, and since my speakers are being discussed here, thought it would be appropriate to throw in my 2c.

Many of the above posts are correct. It is indeed possible to get good bass out of small drivers, and at the same time, as the old saying goes, there is just no substitute for cubic inches (in this case, driver displacement and cabinet volume). The answer to the original question depends almost entirely on the priorities of an individual listener. What is considered a "realistic" volume level and "deep" bass is totally different from one person to the next. Many would consider 90dB at 30Hz to be plenty deep and loud, because the vast majority of listeners will never exceed this. (It's louder and deeper than you think.) Others may not be happy unless they can achieve 110dB at 15Hz! These two things are so far apart as to make discussion utterly meaningless without first defining what you are trying to achieve.

Many of the knocks on the excursion levels of small drivers are substantially solved by the new ultra-linear motor systems developed in the last five or ten years by several manufacturers ("Symmetric Drive" by Scan-Speak, etc). This results in a drastic reduction in IM distortion, and the performance achieved by the Ultimate Monitor would not be possible without this. 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 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. That is why I recommend relatively high power amplifiers for use with the BOMB. It's not unreasonable-- 100wpc into 4 Ohms is plenty for most applications, provided it's high quality-- but I wouldn't dream of trying to pair this system with a 3W SET amp. The real tradeoff here is that you lose nearly that same 10dB in peak output at the loudspeaker end, in order to stay within the linear excursion limits. As bad as it sounds on paper, this is not a limitation for the vast majority of listeners.

Those who have heard the UM/BOMB system would likely agree not only that the system obliterates every preconceived notion they have about "small speakers", but furthermore, that for "reasonable" listening levels in "normal" sized rooms, they deliver all the volume and bass that most people will ever use, and then some. Will they deliver 110dB at 15 Hz? Not a chance. But that's why they were designed to integrate extremely well with the REL subs and similar sub-bass units.

The bottom line, with this issue and many others, is that there are always compromises. Every time you decide you want to improve performance in one area, you give up something elsewhere. Adding a column of 15" woofers is a great way to make more bass, and it's also a great way to (m)uck up the entire system. There are a hundred things that are of absolutely critical importance in the design of a high-performance loudspeaker, and deep bass extension is one of them.

In the design of the Ultimate Monitor, the goal was always to achieve extraordinary "real world" performance-- that is, to make a small speaker that has virtually no serious flaws when used in average-sized rooms at average volume levels. This is a far, far harder task than is generally realized, and drives the design compromises in directions that most speakers don't take. It's quite simple to design a 3-way ported box speaker that has a wide frequency response, if that's all you're after. It's another thing entirely to make it sound like real music.

I would encourage anyone interested in the technical aspects of speaker design to read the two articles under "tech notes" on our website, http://www.audiomachina.com. They will (hopefully) give a better understanding of the tradeoffs and necessities in any loudspeaker design that aspires to "high fidelity".

Best Regards,
Karl Schuemann
Onhwy61...Agreed. You can get deep bass from small speakers: even from the 3/4 inch drivers in headphones. However, real LF sound at high volume, such as generated by an organ, is felt as much as heard. It takes large drivers to create the total sensation.
I was talking about the SF Cremonas. You need to hear this
speaker to know what is possible with small twin 6"
Hi Dr Ken
I laugh at people who say you need 3 way speakers for good bass.The quality of the bass more important than the quantity.Stick with 2 ways ,many added benefits-timing,coherency ,imaging,simpler crossover etc.Revel M20's good example of a answer to your question.Remember my previous suggesstion in another forum regarding the Merlin's?Like I said,I ordered VSM-MM's.Read the Merlin website carefully as well as the forums on audio.Hope my opinion helps
Good Luck
Dr Chris
Bluebull...Actually, the reason for 3-way speakers is good midrange: not good bass.
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.
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

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.
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.
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 : )
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.
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.
Sean and Michael
Thank you for your essays.
I'm shure it did not help Dr Ken much.
Blue Bull
I apologize to Dr. Ken Schuemann because it is most unfortunate that such a great product has been clouded by this unnecessary rhetoric.

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.

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

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
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?
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