Anyone know of a review of the Axiom EP-600 Sub - Page 4 - AVS Forum
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post #91 of 751 Old 02-03-2006, 04:42 PM
 
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Quote:
Originally Posted by craigsub
Yes, little one, and we will actually do some LISTENING tests in a room larger than a walk in closet first. Those tests will be done blind, as usual, and the subwoofers properly calibrated. You should try it sometime.
Now that you mention, here is my latest review. The whole last chapter is about how it sounded... ;) Too bad that you don't understand Finnish.
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post #92 of 751 Old 02-03-2006, 05:13 PM
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Gentlemen. I have company over for some HT viewing and will contribute to the thread later but can we keep it civil. Many great points being made and it would be a shame to repeat the thread closures. :)

John
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post #93 of 751 Old 02-03-2006, 05:23 PM
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Quote:
Originally Posted by craigsub
Yes, little one, and we will actually do some LISTENING tests in a room larger than a walk in closet first. Those tests will be done blind, as usual, and the subwoofers properly calibrated. You should try it sometime.
Too funny........ :D :D

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post #94 of 751 Old 02-03-2006, 05:30 PM
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Good evening gentlemen,

When I say IM distortion, I am referring to what is commonly known as Doppler distortion (apologies to anyone if that was not clear). I am not referring to BL nonlinearities or anything else. Of course we also give serious consideration towards distortion due to BL nonlinearities, why do you think we are using XBL^2 TM linear BL motor technology in our newest drivers? :)

IM (ie. Doppler in this context) distortion gets exacerbated with higher cone excursions. This is obvious to anyone who has even a basic understanding of IM (Doppler) distortion. There is no evidence needed to prove this, as this fact has already been established. Like it or not, higher cone excursions will increase IM (Doppler) distortion.

Now, in response to the comparison on page 2 of one driver with > 20mm xmax versus another driver of the same size with 8mm xmax...

This comparison really misses the point we are trying to make.

Our viewpoint is that we would rather increase cone area instead of increase driver excursion in order to achieve higher output levels at the frequencies where subwoofer output is limited by driver excursion.

The reasons for this are the same as I have already mentioned: we use a vented system with the goal of reducing driver excursion in the low bass and in turn lowering dynamic distortion in the low bass; ultra high excursion woofers tend not to be very cost-effective; ultra high excursion woofers tend to be less reliable (this should be obvious...the more a woofer is able to move back and forth, the greater chance there is for a problem to occur. In fact, we have made it known on many occasions that adding a second subwoofer increases reliability because driver excursion demands are reduced in half); ultra high excursion means ultra high IM (Doppler) distortion (whether we like it or not, IM (Doppler) distortion becomes exacerbated with higher excursions. If the goal is higher output at frequencies where the subwoofer is limited in output by driver excursion, we would prefer to increase cone area instead of increasing excursion). The audibility is something for future study, just as is the audibility of total harmonic distortion, the audibility of dynamic distortion, or the audibility of any type of distortion in the low bass.). Other problems with ultra high excursion drivers that I have not yet mentioned: they tend to be less efficient and require more power to perform optimally (this further increases cost beyond the increased cost to manufacturer the very high excursion driver); ultra high excursion will increase reactive forces, so the enclosure will have to be strengthened even more (which further adds to cost to manufacture, and adds weight which increases the shipping cost even more to the consumer).

There are some applications where I think it makes some sense to use very high excursion drivers. Mark Seaton's project is a good example of this. He is using a balanced force design and sealed enclosure with the goal of cleanly reproducing very low frequencies without the assistance of a port or passive radiator. The clean low bass his subwoofer will be able to produce per the given enclosure size should be really really impressive. However, for a vented commercial design, I feel it is much more cost-effective and makes much more sense not to use ultra high excursion drivers, since one of the main design goals is to reduce excursion in the low bass. Of course, one could argue that a ultra high excursion would come in handy when the subwoofer is variably tuned to a lower frequency. The problem with this is that, with existing methods of variable tuning, port cross-sectional area is required to decrease by 33-50% with each lower tune. So at the same time that driver excursion demands are increased, port flow capability is substantially decreased, which leads to a less balanced design in my opinion.

To put things in perspective: most commercial subwoofers today are limited most in the low bass, and they are limited by porting! In our VTF-3 HO (non turbo) subwoofer, even without ultra high excursion driver and even without ultra high powered amplifier, the porting restricts at 16Hz well before the amplifier runs out of steam and well before the driver runs out of excursion. To achieve as balanced a design as possible, we felt it necessary to substantially boost port flow capability in the low bass (with turbocharger) in an attempt to try to remove or relieve that bottleneck.
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post #95 of 751 Old 02-03-2006, 05:36 PM
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Please allow me to add that I also think that there is validity in people like Steve Callas using very high excursion drivers. Remember that Mr. Callas really does not have to limit enclosure size, limit port cross-sectional area, or limit port tuning frequency since he designed his own subwoofer. Also, he does not need to control costs other than what will fit inside his budget. A commercial designer will always have to control size and control costs, which will place some limits on those things mentioned above.
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post #96 of 751 Old 02-03-2006, 07:24 PM
 
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Quote:
Originally Posted by Ilkka
Now that you mention, here is my latest review. The whole last chapter is about how it sounded... ;) Too bad that you don't understand Finnish.
Hey, It looks like you actually listened to one disc and watched a movie. BIG step up for you. Our typical 20 hours of blind listening is looking pretty pale now ... :D

Seriously, and take ALL the time you want on this: You go find where anyone has referred to a review of Ilkka's, AVTalk's or Ed's and talked about anything but max output levels.

Find all the posts about excellent group delay or frequency response.

Correct me if I am wrong, but wasn't the BK XLS200-DF in your first shootout ?
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post #97 of 751 Old 02-03-2006, 07:29 PM
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That last post is fair and examines the topic under the right frame of mind. High excursion drivers may not be something your company is interested in due to the need to mass produce a bang for the buck commercial subwoofer. You are looking at this from the viewpoint of a sub manufacturer trying to keep manufacturing costs down as opposed to the viewpoint of the consumer who wants certain performance for a given price point.

As for your main three reasons against high excursion drivers, the same ones which have been regurgitated over and over again, and the two new ones, they don't hold any weight UNLESS you limit yourself to the afore mentioned restrictions. Even then, they only make sense if you are comparing a larger diameter driver with less excursion to a smaller diameter driver with high excursion, OR if you are comparing two subs to one. In both cases, the higher excursion driver would likely be more cost effective anyway. Also, I'm not familiar with any HSU drivers larger than 12".

When you are just comparing one single driver subwoofer to another, both which use drivers of the same diameter, more excursion is a GOOD thing performance wise and distortion wise. As Ed has stated, only considering doppler distortion is a very small piece of the puzzle - not only does it not accurately represent IM distortion, but it in no way reflects performance as a whole. It is a flawed argument and it doesn't really mean anything significant.

I apologize if that sounds a little harsh, but we need to stop living in an audio world with smoke and mirrors and start talking about the truth for once :)


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post #98 of 751 Old 02-03-2006, 07:40 PM
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Steve, I think the idea is, because of a larger surround of a higher excursion driver, that surround, effective eats up cone area give the same size of the frame.

edit: Also, as far as IM distortion is concerned, there is an interview with Dr. Hsu that points to it as being one of three types of distortion that he seems to be concerned with....not the only one.

-curtis

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post #99 of 751 Old 02-03-2006, 07:56 PM
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But as Ed has stated, excursion isn't the only thing to take into account when considering IM distortion. So in the grand scheme of things, doppler distortion does not seem all that significant, especially when you consider what you are GAINING (which seems to be ignored) with a higher excursion driver.


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post #100 of 751 Old 02-03-2006, 07:59 PM
 
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Quote:
Originally Posted by SteveCallas
But as Ed has stated, excursion isn't the only thing to take into account when considering IM distortion. So in the grand scheme of things, doppler distortion does not seem all that significant, especially when you consider what you are GAINING (which seems to be ignored) with a higher excursion driver.
You should call Dr. Hsu and see if he needs an assistant. Heck, you could probably teach him a lot ! ... :D
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post #101 of 751 Old 02-03-2006, 07:59 PM
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Our viewpoint is that we would rather increase cone area instead of increase driver excursion in order to achieve higher output levels at the frequencies where subwoofer output is limited by driver excursion.
So, larger drivers/larger cabs, multiple drivers/larger cabs, or even multiple cabinets are what you espouse as more "cost-effective" than a single high-excursion driver? Or are you recommending lesser excursion due to the smaller surround requirement, as mentioned bove?

Let's talk single-driver, 12" subs for example. You know, the kind that both companies make. Is it better to have a high-excursion driver and a bit of "doppler distortion" at a given point, or is it better to have a lesser-excursion driver and have all distortion (harmonic, dynamic...) skyrocket at that same output as it moves well out of its linear range?
In a scenario where a single driver is employed, are you claiming that a lower Xmax is better? Do you feel that the lower excursion driver is somehow more linear at the same excursion as a high-excursion driver?

Quote:
Of course, one could argue that a ultra high excursion would come in handy when the subwoofer is variably tuned to a lower frequency. The problem with this is that, with existing methods of variable tuning, port cross-sectional area is required to decrease by 33-50% with each lower tune. So at the same time that driver excursion demands are increased, port flow capability is substantially decreased, which leads to a less balanced design in my opinion.
So, given that the Turbo ostensibly alleviates this low-Fb port compression, a Turbo'd VTF3HO does need an "ultra-high-excursion" woofer to be a "balanced design" (as I alluded to earlier)?

Jack Gilvey
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post #102 of 751 Old 02-03-2006, 08:04 PM
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Quote:
Originally Posted by cschang
Steve, I think the idea is, because of a larger surround of a higher excursion driver, that surround, effective eats up cone area give the same size of the frame.
So the critique is that given say two different 12" vented subs, one having a high xmax and the other having a less high xmax (but possibly greater SD) the lessor xmax sub may have higher SPL efficiency and therefore less IM for a given high level SPL?

It seems that if we had the full T/S of the respective subs and their enclosure characteristics a straightforward analysis/modeling with UniBox or BassBox, etc. could tell us what is really going on with the respective subs.

Otherwise we are getting a lot of posturing and handwaving. Maybe we will have to do some two tone (non-harmonic) tests at a given high level (95 dB @ 20 Hz) for equivalent tuned vented subs in order to resolve this.
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post #103 of 751 Old 02-03-2006, 08:06 PM
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WOW.....just WOW :rolleyes:

the amount of misinformation in this thread is dumbfounding..... :(


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post #104 of 751 Old 02-03-2006, 08:07 PM
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Quote:
Originally Posted by SteveCallas
But as Ed has stated, excursion isn't the only thing to take into account when considering IM distortion. So in the grand scheme of things, doppler distortion does not seem all that significant, especially when you consider what you are GAINING (which seems to be ignored) with a higher excursion driver.
Understood.....it is all part of design and engineering goals. Remember, high excursion is not the whole ball of wax either.

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post #105 of 751 Old 02-03-2006, 08:09 PM
 
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Quote:
Originally Posted by ssabripo
WOW.....just WOW :rolleyes:

the amount of misinformation in this thread is dumbfounding..... :(
What are you trying to say ? Is it that you DON'T think Mr. Callas could teach Dr. Hsu a lot about subwoofer design ? :D
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post #106 of 751 Old 02-03-2006, 08:12 PM
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Quote:
Originally Posted by bobgpsr
So the critique is that given say two different 12" vented subs, one having a high xmax and the other having a less high xmax (but possibly greater SD) the lessor xmax sub may have higher SPL efficiency and therefore less IM for a given high level SPL?
That gets into the argument "is it all about SPL?" again.

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post #107 of 751 Old 02-03-2006, 08:25 PM
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Quote:
Originally Posted by craigsub
What are you trying to say ? Is it that you DON'T think Mr. Callas could teach Dr. Hsu a lot about subwoofer design ? :D

:p


hey man....don't knock on Purdue! I know the good Dr is an MIT grad, but it doesn;t necessarily mean the boilermaker couldn't come with some good counter arguments! Heck, I work with MIT grads all day, and this YellowJacket grad (yours truly) smokes them left and right.... :D

not that it means anything...... what the hell are we talking about anyways in this thread...I forgot


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post #108 of 751 Old 02-03-2006, 08:31 PM
 
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Quote:
Originally Posted by ssabripo
:p


hey man....don't knock on Purdue! I know the good Dr is an MIT grad, but it doesn;t necessarily mean the boilermaker couldn't come with some good counter arguments! Heck, I work with MIT grads all day, and this YellowJacket grad (yours truly) smokes them left and right.... :D

not that it means anything...... what the hell are we talking about anyways in this thread...I forgot
Well, it started about the Axiom EP-600. The OP ordered one, and has the good sense to stay away from this thread now ... :D

And who mentioned Perdue ?

I am sure the MIT guys are glad that you provide that service, too, not every job provides someone to handle smoking duties. That is quite the fringe benefit you are providing, Sherv... :eek: ;) :D

Edit, I am off to an all day swim meet in Ohio tomorrow. Sherv, I will look for your comeback Sunday AM. Assuming you "got" this last one, by then, of course ... ;)
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post #109 of 751 Old 02-03-2006, 08:31 PM
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Quote:
Originally Posted by cschang
That gets into the argument "is it all about SPL?" again.
ahmm yes

generally:

digging deep (<20 Hz) + high SPL + low distortion (all kinds) = $$ and/or large size

But aren't the three qualities on the left what most of us are trying to achieve?
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post #110 of 751 Old 02-03-2006, 08:45 PM
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If not, I wouldn't have this giant beast in my living room :D


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post #111 of 751 Old 02-03-2006, 08:47 PM
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Quote:
Originally Posted by bobgpsr
low distortion (all kinds) = $$ and/or large size
I think that is where I jumped in......the argument on what types of distortions exist and should be kept low.

I don't claim to know...just looking at all arguments.

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post #112 of 751 Old 02-03-2006, 09:32 PM
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Just finished watching the Island. Not bad science fiction flick about cloning humans that spend all their time posting in threads. (Kidding :) ) Nicely recorded bass heavy soundtrack in that DVD.

This digression into IM distortion has been useful but I am surprised that so many people can object to a simple physical phenomena. Why argue that drivers with large mechanical movement will generate distortion as a result of the doppler effect. What's next: prove that if we drop an apple it won't hit the ground?

There are good reasons why one would want to use a high excursion driver such as producing lower bass at higher SPLs . Designers that do can brag about low harmonic distortion and not bother with that hard to measure annoyingly high intermodulation distortion that comes with it. After all a woofer with a 3" linear peak to peak excursion should produce low harmonic distortion and thats what mainly matters to modern reviewers. So what if the high IM distortion and dynamic distortion from interactions with the amp muddy and blur the sound. Only certain diehards would ever bother to conduct a listening test to actual identify muddiness from subs with high excursion drivers.

Like I said earlier and Peter Marcks elaborated on, if one is intending to build a high quality subwoofer he must compromise the driver, amp, enclosure amongst other features to keep ALL distortions at reasonable levels. Allowing high intermodulation and dynamic distortions to be high for the sake of measuring low TH distortion seems convoluted and is bound to result in an inferior listening experience. While we have mainly focussed on IM distortions in this discussion, it has also been mentioned that the use of heavy drivers will lower efficiency with the amplifier. At peak demands the amplifier will have a greater tendency to get out of step with a heavy cone. All the more reason to have as much headroom as is practicable in the amp.

The attendants at the November 20 listening session heard the difference between a more balanced design having a driver with a lighter mass and lower excursion and one with a heavier mass and higher excursion. Yes I know this is a simplification because there were other important elements to the designs. Nevertheless the lack of clarity and detail was evident in the design with the heavier high excursion driver which I believe can be attributed to higher IM and dynamic distortion. That's yet another reason why I've always railed against the misleading use of THD measurements as a proxy for all distortion and noise.

Floyd Toole in "Loudspeaker Measurements and Their Relationship to Listener Preferences: Part 1" J. Audio Eng. soc., Vol. 34, No. 4, 1986 listed in rough order a list a list imperfections found in loudspeakers which apply just as well to subwoofers. Some of you may have seen this list before but I will list them for others using modern terms:

1. Frequency response(amplitude response)
2. Harmonic distortion
3. Intermodulation distortion and spurious noises
4. Frequency shift (FM distortion)
5. Dynamic Range compression (Power compression)
6. Transient distortion
7. Phase distortion
8. Group delay
9. Electoacoustic Efficiency
10.Power handling capacity
11.Constancy of Performance

Note the large number of distortions other than harmonic and the high priority of intermodulation and dynamic distortions. It should be clear from looking at this long list why better designers understand the importance of a balanced approach especially in matters regarding all types of distortions. It should also be clear why one cannot rely on only THD measurement to represent the many other distortions found in subs.

John
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post #113 of 751 Old 02-03-2006, 09:48 PM
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Intermod distortion is what attracted me to this thread.

After reading the thread, I wonder if any posters have a clue as to what it is. :eek:

IM(doppler) distortion? Sheesh! I apologize, Peter, but...what the heck is that?

Doppler distortion should have little, if anything at all, to do with a downfiring sub as, at 90 degrees off axis it drops to nearly zero, IIRC. Of course, it appears that Dr. Hsu, in his concern for Doppler Distortion, has overlooked this fact with the Turbo thingy model, which is direct radiating. But what that has to do with IMD has me scratching my head. :confused:

My interest in IMD arose as I designed my first Rebase Routing Processor. I was interested to know if there would be an audible difference in a subwoofer system that played the summed (RB+LFE) single signal, wherein there are many instances of a music soundtrack and LF sound effects that overlap, vs a sub system comprised of a discrete RB sub and a discrete LFE sub, as far as IMD were concerned.

But, if the discussion is actually about Doppler Distortion, and not IMD caused by a single driver attempting to play multi inharmonic tones simultaneously, I'll just stand by and observe. :cool:

Bosso
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post #114 of 751 Old 02-03-2006, 10:27 PM
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Quote:
Originally Posted by Jack Gilvey
So, larger drivers/larger cabs, multiple drivers/larger cabs, or even multiple cabinets are what you espouse as more "cost-effective" than a single high-excursion driver?
This is a good question Jack. We feel that, since we use vented designs, there will be diminishing returns by using ultra high excursion drivers. We would rather put the extra money towards something else, such as something that helps to boost porting in the low bass where we feel commercial subwoofers are most limited.

Quote:
Let's talk single-driver, 12" subs for example. You know, the kind that both companies make. Is it better to have a high-excursion driver and a bit of "doppler distortion" at a given point, or is it better to have a lesser-excursion driver and have all distortion (harmonic, dynamic...) skyrocket at that same output as it moves well out of its linear range?
Another good question. I guess it depends. Using a higher excursion woofer will be beneficial at the frequencies just above tuning where the port begins to contribute little to nothing towards boosting low bass output. So, if port tuning was 18Hz, then somewhere around 25Hz is where excursion demands would be greatest. Higher excursion driver will definitely help to boost output at this frequency. However, higher xmax driver will not always mean higher output above this frequency. Lighter cone woofers, which generally have relatively low xmax, tend to have very high mid/upper bass headroom. For instance, the STF-2/VTF-2 have quite good mid/upper bass headroom and impact, even with a relatively low excursion driver. This is one of the reasons why high excursion is a double-edged sword in subwoofer design. There is always a tradeoff.

I think that a good question to ask would be, at what frequencies do commercial ported subwoofers tend to be most limited at? This would be the lowest bass, say 20Hz and below, I think. The limitation at these frequencies with commercial subwoofers is the porting. To achieve a very low tuning while also achieving relatively large port cross-sectional area is very difficult to do even using a relatively large enclosure designed for commercial use. We felt that we could achieve a more balanced design by boosting the porting in order to boost the low bass power down to 16Hz. The driver simply needed to have enough linear excursion to not bottom out and to not have a poor power response over the range > 25Hz where the port contributes little to nothing towards output, and we succeeded in doing that. Without assistance from the porting, driver excursion demands at 16Hz would be much much higher, and then it would make more sense to use even higher excursion. Fortunately we do have the porting to assist in that range.


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So, given that the Turbo ostensibly alleviates this low-Fb port compression, a Turbo'd VTF3HO does need an "ultra-high-excursion" woofer to be a "balanced design" (as I alluded to earlier)?
Not exactly, we felt that about 2" peak to peak linear excursion was more than enough to satisfy our design requirements, the requirements being to maintain a relatively even power response without woofer bottoming. Even at maximum output levels where driver excursion demands somewhere above port tuning are highest, the woofer should not bottom out.
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post #115 of 751 Old 02-03-2006, 10:30 PM
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Bosso, I was always under the impression that IMD, where one frequency modulates another, was commonly known as Doppler distortion. Perhaps that is not quite the best way to describe it.
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post #116 of 751 Old 02-03-2006, 10:45 PM
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Originally Posted by SteveCallas
That last post is fair and examines the topic under the right frame of mind. High excursion drivers may not be something your company is interested in due to the need to mass produce a bang for the buck commercial subwoofer. You are looking at this from the viewpoint of a sub manufacturer trying to keep manufacturing costs down as opposed to the viewpoint of the consumer who wants certain performance for a given price point.
I agree with you to an extent here, Steve, although I would like to clarify and say that our decisions were not simply based on keeping manufacturing costs down. We feel that porting (and not driver excursion) is the major limitation in most commercial vented products, so we focused on boosting that area. The driver simply needed to have enough linear excursion to achieve a relatively even power response and not bottom out over the range where driver excursion demands are highest.

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When you are just comparing one single driver subwoofer to another, both which use drivers of the same diameter, more excursion is a GOOD thing performance wise and distortion wise. As Ed has stated, only considering doppler distortion is a very small piece of the puzzle - not only does it not accurately represent IM distortion, but it in no way reflects performance as a whole. It is a flawed argument and it doesn't really mean anything significant.
Trust me Steve, we have certainly considered distortions other than IMD (in this context, where one frequency modulates another). Lower distortion due to BL nonlinearity is why we are using XBL^2 TM after all! Now, I would suggest that higher xmax is a double edged sword. In fact, woofers with very light cones have relatively low xmax but tend to have very good mid/upper bass headroom. However, higher excursion drivers will definitely provide extra output at the low bass frequencies where driver excursion demands are highest, somewhere a bit above port tuning. But then again, we always come back to the notion that commercial subwoofers are limited by porting in the low bass. Generally, I do not think that it makes much sense to compare xmax at face value between two different products without considering all the other design choices and all the other tradeoffs as well.
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post #117 of 751 Old 02-03-2006, 11:02 PM
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Anyway, it should be clear why I consider the Axiom EP600 to be such a fundamentally sound design. I am quite in favor of the design choices they made with their subwoofer.
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Quote:
Originally Posted by Peter Marcks
Bosso, I was always under the impression that IMD, where one frequency modulates another, was commonly known as Doppler distortion. Perhaps that is not quite the best way to describe it.
I did some Googling and came out with this.

Doppler Distortion

http://stereophile.com/reference/1104red/

It looks to me that DD (doppler distortion) is a problem when a same diaphragm is producing both low (say 100 Hz) and high (say 3 kHz) frequencies. The speed of the cone required to produce each frequency is so different, that it causes DD. But DD and IMD are not the same, you can check the link for more information. And as site suggests, DD is NOT a problem with speakers (cones) which only produce a small range of frequencies like subwoofers (lets say 20 Hz to 100 Hz). The speed of the cone is so low and the differences between them are so small, that doppler distortion is not a problem with subwoofers. But that doesn't mean that there is no IMD present (if more than a single non-harmonic frequency is being produced).

"Doppler distortion worsens as the frequency difference between the modulating and modulated frequencies increases. This inevitably means that, for a given diaphragm size, Doppler distortion will be worst in loudspeakers that use a single, full-range drive-unit. Two-way speakers will suffer less, and three-ways with a lower bass/midrange crossover frequency will suffer less still."

Another good link regarding DD.

http://sound.westhost.com/doppler.htm

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Intermodulation Distortion

A complex form of distortion occurring when two signals at different frequencies are produced at the same time creating additional signals at various other frequencies and at various amplitudes. New signals are created at frequencies found by adding the original two frequencies, by subtracting the original two frequencies from one another, from harmonics of the original two frequencies (although this particular distortion is classified as harmonic distortion and so is not truly a part of intermodulation distortion), from the harmonics of these two newly created frequencies (the sum and difference of the original two), and from the sums and differences of the harmonics. Needless to say, this form of distortion results in a multitude of additional frequency signals beyond the original two produced, and each of these frequencies may be heard distorting the original signal.

For clarification, a harmonic is a multiple of an original frequency. For instance, a frequency of 2 kHz would have harmonics of 4 kHz, 6 kHz, 8 kHz, 10 kHz and so on with each harmonic being less powerful or of a lesser amplitude than the original signal and the harmonic preceding it. The 4 kHz harmonic would be less powerful than the original signal and the 6 kHz harmonic would be less powerful than the 4 kHz signal like a downward slope. Harmonic distortion is caused when harmonics of an original frequency are produced.

Intermodulation distortion begins with additional frequencies being produced by the sum and difference (addition and subtraction) of two original frequencies. For instance, two frequencies of 2 kHz and 8 kHz may have been produced by an audio system. Intermodulation distortion would create two additional signals at 10 kHz (the sum or addition of 2 and 8 kHz) and 6 kHz (the difference between the numbers or subtraction of 2 from 8 kHz).

Each of these new signals, the first parts of intermodulation distortion, would then develop harmonics of their own (creating harmonics from 6 kHz of 12 kHz, 18 kHz and so on while producing harmonics of 10 kHz at 20 kHz, 30 kHz and son on). To further confuse the issue and add even more distortion, these harmonics (the harmonics created from the sum and difference frequencies of the original two frequencies) would then create their own sum and difference distortions (for example, the first harmonics located at 12 kHz and 20 kHz would create a sum frequency of 32 kHz and a difference frequency of 8 kHz).

Obviously, many additional frequencies are added to the audio output creating a complex pattern of distortion. From the two example frequencies at 2 kHz and 8 kHz would come distortions (additional frequency signals) at 4, 6, 8, 10, 12, 16, and 20 kHz within the range of human hearing and many more beyond our ability to hear. Each of these tones at new frequencies are less powerful or have a smaller amplitude than the original two signals.

In the final conclusion, intermodulation distortion (IM distortion) can have a profound affect on an audio signal due to the sheer number of distortions it creates. Always look for audio components with the lowest possible distortion numbers, be it harmonic distortion (THD) or intermodulation distortion (IM).
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I trust my eyes are not reading Peter Marcks incorrectly:



"We felt that about 2 inches peak to peak linear excursion was enough to satisfy our design requirements..."

This would seem to refer to the new VTF-3HO driver.
Seems like a pretty high excursion driver for a $900 sub.

And BTW, Craig is correct about it being quite doubtful that 2 colocated '3HO + Turbos will achieve 126 db at 16 HZ. I was thinking about the 20Hz stat. Using the 20Hz measurement of 114db from Keele for the TN1220, if one '3HO + Turbo actually equals 2 1220, then extrapolating, one '3HO + Turbo = 120 db, 2 colocated '3HO+ Turbos = 126db at 20Hz.

Of course, this involves a lot of speculation.
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Quote:
Originally Posted by spyboy
I trust my eyes are not reading Peter Marcks incorrectly:



"We felt that about 2 inches peak to peak linear excursion was enough to satisfy our design requirements..."

This would seem to refer to the new VTF-3HO driver.

Would seem to be a fairly high excursion driver for a product at the $900 price point.

Anyone, please correct me if I am wrong.
2" peak to peak is around the amount what for example SVS uses, so it makes this whole conversation pretty much meaningless... :D

But I have to give credit to Peter, some of the things you said really makes sence. Thank you. :)
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