Axiom Subwoofer Blog

[gtpsuper24]

http://www.axiomaudio.com/blog/home-subwoofer/

Doesn't really answer any questions or state facts seems to be more marketing hype mumbo jumbo.

Just though it would be a good read for all those that like to discuss subwoofers.

 

[gene]

Unfortunately there is no real substance here to discuss. It's a marketing piece that ironically rejects 3rd party measurements of products and tells the readers to just rely on listening. I can see the appeal to this type of article for a layman, but to reject objective 3rd party measurements and analysis just doesn't jive with the NRC gospel they always preach. It seems counterproductive to me. Very strange

 

[MinusTheBear]

There is nothing to that article to discuss. It's vague and offers no technecial explanations on how to design a subwoofer. Like Gene said, it's looking to impress the layman, but there isn't any substance to the article because they do not back a single thing up.

One of the things I do have to point is about this quote "the Axiom DSP also keeps a ported subwoofer from making any significant port noise". I remember in a few subwoofer comparisons (one against an SVS) one of the biggest complaints of the EP600 was significant and audible port noise during the same scenes where the SVS wouldn't break a sweat.

 

[MinusTheBear]

Here is one persons description of the port noise made by the EP600 which is a DSP subwoofer. There is another comparo against an SVS subwoofer that shows this too.

"Playing test tones, especially down in the 30-20hz range the EP600 makes soo much port noise that it almost drowns out the bass. I actually thought my audioadvisor catalog was going to get sucked up into the cabinet when I held it over the port. The airspeed coming out of it seems really high."

http://forums.audioholics.com/forums/435100-post80.html

 

[Ricci]

Not much there about design at all really.


Might as well rant about something though...

Many times you may see opinions from people that harp on "loud" speakers or subwoofers and seem to insinuate that you cannot have a powerful or loud speaker without sacrificing the sound quality to some extent. The old 8" woofers are faster or higher fidelity than 15" or 18" type myth. Nothing could be further from the truth. In fact output headroom is one of the most important aspects of performance that allow for pristine reproduction. I'm not talking about bandwidth limited or peaky speakers here that sacrifice bandwidth and damping, but well designed large, efficient and powerful mains and subwoofers. These are some very important attributes to have:

1. Wide bandwidth, smooth response
2. Low distortion
3. Large dynamic headroom
4. Maintain basic bandwidth uniformity with increased output
5. Good damping

Let's take a small 10" subwoofer versus a much larger 18" based subwoofer, assuming drivers and designs of equivalent quality to utilize them, the 18" easily performs better in the first 4 categories due to basic physics. The 18" has nearly 4x the piston area which requires 1/4 the cone excursion for the same output as the 10". Technically for the same output level yes the 10" is faster. That is because the cone has to travel 4X as far over the same time period to reproduce the signal. If the 10" is traveling 2" peak to peak to reproduce the signal the 18" will only be traveling 0.5" peak to peak. The 10" may be technically moving faster but which one do you think will be starting and stopping easier with less distortion and mechanical noise the driver cone traveling 2" round trip or 0.5"? Also the 18" in the larger enclosure will be more efficient as well which results in it also needing less input power applied to the voice coil for that same output. Both of these will result in lower distortion and coloration for the 18". If we assume the same stroke is available from both drivers then the 18" should be capable of 10dB or more total headroom past what the 10" can provide as well which means that it will easily outperform in bandwidth uniformity and bass extension at useful levels, the smaller 10" driver. Everyone has probably heard a subwoofer being driven at or near it's limits. Not exactly the epitomy of SQ. You might say "Well you shouldn't be overdriving the 10" like that and if you let it operate in it's comfort zone it very well might sound better than the 18"." Doubtful since the 18" will be driven that much less hard as well.The less power used and stress on the driver the better and more accurate it is likely to sound. If the comparison is changed to 3 or 4 10" drivers versus 1 18" things become much more interesting.

Obviously there is a lot of generalization going on here and variation in quality of units, but if we consider a good representative from each the above holds true.

 

[FirstReflection]

Yes, it's a poorly worded title since there really isn't anything of substance in regards to subwoofer design. I also think the introduction saying that there are only two schools of thought when it comes to subwoofer design is off the mark. It's basically saying there are "one note" subs and "true to life" subs, but nothing in between, which certainly isn't true.

I'm not entirely sure where Gene is inferring that Axiom is saying to reject an 3rd party measurements though I didn't read anything in that blog post about measurements at all. All I saw was some vague advice to listen for stand-up double bass runs, which is fine. I didn't see anything indicating to reject measurements though. Measurements weren't mentioned. If it were actually an article about subwoofer design (which it isn't, again, poorly worded title), then measurements ought to be talked about. But I think Gene is inferring something that was not stated or implied in that blog post when he says that Axiom is saying to reject objective measurements. I didn't get that message at all from the text itself

It's just a blog post, written by Amie, and clearly just some musings on really basic design goals that a speaker maker might aim for at the outset of designing a new subwoofer. There's nothing wrong with the notion that a subwoofer maker might be aiming for smooth, linear, articulate bass, even if it is not as immediately impressive due to not being as loud as another sub or because a sub with a mid-bass hump will immediately stand out for its "hit you in the chest" tactile impact. But that's not the design of a sub, it's just a basic sort of goal that a subwoofer maker might set out to try and achieve at the very beginning of the process. It's got a poor title, but I don't think anyone here should be coming at it with any sort of scorn. If it simply had a more appropriate title, nobody would think anything of it.

 

[gene]

Yes, it's a poorly worded title since there really isn't anything of substance in regards to subwoofer design. I also think the introduction saying that there are only two schools of thought when it comes to subwoofer design is off the mark. It's basically saying there are "one note" subs and "true to life" subs, but nothing in between, which certainly isn't true.

I'm not entirely sure where Gene is inferring that Axiom is saying to reject an 3rd party measurements though I didn't read anything in that blog post about measurements at all. All I saw was some vague advice to listen for stand-up double bass runs, which is fine. I didn't see anything indicating to reject measurements though. Measurements weren't mentioned. If it were actually an article about subwoofer design (which it isn't, again, poorly worded title), then measurements ought to be talked about. But I think Gene is inferring something that was not stated or implied in that blog post when he says that Axiom is saying to reject objective measurements. I didn't get that message at all from the text itself

It's just a blog post, written by Amie, and clearly just some musings on really basic design goals that a speaker maker might aim for at the outset of designing a new subwoofer. There's nothing wrong with the notion that a subwoofer maker might be aiming for smooth, linear, articulate bass, even if it is not as immediately impressive due to not being as loud as another sub or because a sub with a mid-bass hump will immediately stand out for its "hit you in the chest" tactile impact. But that's not the design of a sub, it's just a basic sort of goal that a subwoofer maker might set out to try and achieve at the very beginning of the process. It's got a poor title, but I don't think anyone here should be coming at it with any sort of scorn. If it simply had a more appropriate title, nobody would think anything of it.

One thing I often find confusing and somewhat amusing are reviews claiming one subwoofer “outperforms” another without any explanation as to what that might mean. By outperform do we mean a sub plays louder than another, and if so, at what frequency? With all types of music and movies or only with specific CDs?

It's pretty clear to me that they are saying reviewers don't qualify with measurements why one sub is better than another. Also the whole tone of the article is to trust your ears over anything else using music, and of course you can't compare subs unless its done blind, which again is ridiculous.

 

[MinusTheBear]

The whole article is a playbook out of Bose. It's quite sad actually because when I was first introduced to them I thought they were actually a serious, technical audio company.

I don't think most people would have a problem with it but Axiom always claims cutting end research and technology, yet can't provide or have anyone reproduce consistent results with their products. They seem to live in their own audio la la land.

It's always:

1) Reviewers don't know how to measure products
2) They don't have the proper equipment
3) People don't understand measurements - the irony is Axiom doesn't understand comb filtering measurements. Their view doesn't jive and is taken out of context with Floyd Toole's research which shows that some of their driver complements are actually detrimental to accurate loudspeaker reproduction.
4) When asked for measurements, use your ear. When judging Axiom products vs. a product someone subjectively likes better, you can't verify which is truly better without proper testing, measurements and double-blind conditions.

 

[gene]

3) People don't understand measurements - the irony is Axiom doesn't understand comb filtering measurements. Their view doesn't jive and is taken out of context with Floyd Toole's research which shows that some of their driver complements are actually detrimental to accurate loudspeaker reproduction.

Interestingly enough, their whole jargon about being part of the research at the NRC with Dr. Floyd Toole isn't even accurate. All of that research was done by Floyd and his team years before Axiom ever entered the NRC. I was told this directly by Floyd himself!

 

[gtpsuper24]

Marketing company that just happens to make speakers? Its the ID version of Bo$e, I bet Axioms products have a HUGE profit margin built in, I would guess probably more than any other ID brand out there.

Isn't it easier to just make a great product, instead of having a PR dept. defend the products and make them out to be something there not? Produce a product you can be proud of not hide been smoke and mirrors and fooling people.

 

[MinusTheBear]

Marketing company that just happens to make speakers? Its the ID version of Bo$e, I bet Axioms products have a HUGE profit margin built in, I would guess probably more than any other ID brand out there.

Isn't it easier to just make a great product, instead of having a PR dept. defend the products and make them out to be something there not? Produce a product you can be proud of not hide been smoke and mirrors and fooling people.

I don't have a problem with companies making money. If they take in huge profit margins, congratulations to them. The parts quality used in Axiom speakers are inexpensive (woofers, tweeters, crossover parts) and are foreign manufactured. However, they do have domestic labor for cabinet building and assembly so it might offset a bit where you have other speakers with more expensive parts and exotic cabinets with nicer finishes being employed but all manufactured and assembled with foreign labor.

I was under the impression for ID companies, the going profit margin is 5 times the total cost built into producing a single speaker.

 

[gtpsuper24]

Sure I have no problem with a company making a profit, but with Axiom it seems that they take so many shortcuts and really low quality parts to make a profit.

 

[MinusTheBear]

Gene. You should come up with in-depth educational article exploring the world of comb filtering - why some forms of comb filtering is more detrimental than others. I know you have touched on comb filtering and the listening environment but how about comb filtering effects and their potential audibilty occurring among driver layouts of a loudspeaker themselves.

 

[gtpsuper24]

Gene. You should come up with in-depth educational article exploring the world of comb filtering - why some forms of comb filtering is more detrimental than others. I know you have touched on comb filtering and the listening environment but how about comb filtering effects and their potential audibilty occurring among driver layouts of a loudspeaker themselves.

My VP150 is probably the best example of comb filtering to the extreme. It seemed alright at first but really became a nusance after listening and I found myself using my system less and less, until I purchase Arx speakers. Cheaper and head and shoulders above Axioms.

 

[MinusTheBear]

I own a VP150 as well.

What's happening within the driver complement of the VP150 is actually acoustical interference which is a form of comb filtering but not the comb filtering that is referred to as offering "spaciousness". The destructive interference (large dips) that occurs within the loudspeaker within the dual spaced horizontal tweeters can be detrimental and its degree of audibility will depend on many factors including listening distance to the speaker, on-axis vs how far off-axis, speaker placement and room acoustics. Other driver complements such as the WMTW VP160 which they are currently bringing to market and with a properly executed crossover design should be a big step up over the VP150 and should offer more consistent performance from room to room with better intelligibility across a more wide range of seating positions. One of the main goals of a WMTW center channel which Floyd Toole points out in his book is it's ability to combat acoustical interference occurring within the drivers, which makes it a much superior design to MTM, TMMMT ect.

If you listen to a lot of peoples opinions on this center channel there are VERY EXTREME opinions on both sides and perhaps both are correct due to the reasons I posted above. But that shouldn't be the goal.

 

[gtpsuper24]

Audessey has the hardest time figuring out what to do with the VP150 from my experience. Usually its sets a 200hrz crossover for it, and distance is usually way off too. I wouldn't count on Axiom properly designing a Xover for the VP 160, thats what will make or break the VP 160, but I think theres so much dislike of Axiom on most of the forums that I doubt it will be a hit on here or AVS.

 

[MinusTheBear]

The crossover points are very important. You also don't want to run the midrange "full range" like they do with the tower.

 

[gene]

Gene. You should come up with in-depth educational article exploring the world of comb filtering - why some forms of comb filtering is more detrimental than others. I know you have touched on comb filtering and the listening environment but how about comb filtering effects and their potential audibilty occurring among driver layouts of a loudspeaker themselves.

In part 4 of our "Identifying Legitimate High Fidelity Speakers" we discuss this topic in some detail. I may also write or co-author a more in-depth article on this as its a rather fascinating subject. It's also quite complex topic to turn into an editorial with supplementary graphs and diagrams to make it easier for the average reader to digest.

We are almost ready to post part 3 which discusses "crossovers" so stay tuned...

 

[gtpsuper24]

Well finally got a response to my question a few weeks ago in Axiom's current Newsletter.

[Question of the Month: What Is a High Pass Filter?
Q. Please explain why the response of the EP400 falls so rapidly below 20Hz. It looks like a brick-wall filter - should it not be a gradual roll-off?

A. All Axiom DSP subwoofers have either a 48 dB or a 36dB per octave high-pass filter set to the frequency below which there is no useful information that the particular model is capable of producing. For an EP800 that is 12Hz, an EP600 is 15Hz, an EP500 is 18Hz, and an EP400 is 20Hz.


http://www.axiomaudio.com/archives/images/EP400Graph.jpg

EP400 Frequency Response Graph. Click to see larger version.
The above graph is the current production model of the EP400. 36dB per octave means if you set the target frequency for 20Hz and you had an output of 100dB at 20Hz, then once you got down to 10Hz the output would be 64dB instead of 100dB - that is, 36dB less.

Every time you go down or up an octave, it's either a halving or a doubling of the frequency. So in the case of the EP400 it will be down 36dB at 10Hz and 72dB at 5Hz.

If we used a more gradual roll-off below 20Hz you would simply have too much output at frequencies where it was not desired. For example, a 12dB per octave high-pass filter at 20Hz would leave you only 12dB down at 10Hz and 24dB down at 5Hz. This would not be a steep enough roll-off to keep the subwoofer from producing audible extraneous noises when pushed hard at those frequencies. Further, you would not be preventing the sub from sucking up a large amount of the available amplifier power trying to reproduce frequencies well below the linear operating range of the subwoofer.

We need to keep in mind that if your subwoofer can produce cleanly say 120dB at 25 or 30Hz it will be rendered useless if information at 10Hz is causing your subwoofer to make obnoxious noises at an earlier volume level. In the real world of listening you can only turn it up to a point below which audible distortion would be created at any frequency.

So in answer to the specific question; our high pass filters are not brick-wall filters, which would be full output at 20Hz but none at 19Hz, but rather they are designed to be as gradual as we determined would be required to optimize the overall subwoofer performance of each model. And at those frequencies where you may have less than 2 octaves to 5Hz that means pretty steep.

-- Andrew Welker, Axiom R&D]

 

[gene]

Well finally got a response to my question a few weeks ago in Axiom's current Newsletter.

[Question of the Month: What Is a High Pass Filter?
Q. Please explain why the response of the EP400 falls so rapidly below 20Hz. It looks like a brick-wall filter - should it not be a gradual roll-off?

A. All Axiom DSP subwoofers have either a 48 dB or a 36dB per octave high-pass filter set to the frequency below which there is no useful information that the particular model is capable of producing. For an EP800 that is 12Hz, an EP600 is 15Hz, an EP500 is 18Hz, and an EP400 is 20Hz.


http://www.axiomaudio.com/archives/images/EP400Graph.jpg

EP400 Frequency Response Graph. Click to see larger version.
The above graph is the current production model of the EP400. 36dB per octave means if you set the target frequency for 20Hz and you had an output of 100dB at 20Hz, then once you got down to 10Hz the output would be 64dB instead of 100dB - that is, 36dB less.

Every time you go down or up an octave, it's either a halving or a doubling of the frequency. So in the case of the EP400 it will be down 36dB at 10Hz and 72dB at 5Hz.

If we used a more gradual roll-off below 20Hz you would simply have too much output at frequencies where it was not desired. For example, a 12dB per octave high-pass filter at 20Hz would leave you only 12dB down at 10Hz and 24dB down at 5Hz. This would not be a steep enough roll-off to keep the subwoofer from producing audible extraneous noises when pushed hard at those frequencies. Further, you would not be preventing the sub from sucking up a large amount of the available amplifier power trying to reproduce frequencies well below the linear operating range of the subwoofer.

We need to keep in mind that if your subwoofer can produce cleanly say 120dB at 25 or 30Hz it will be rendered useless if information at 10Hz is causing your subwoofer to make obnoxious noises at an earlier volume level. In the real world of listening you can only turn it up to a point below which audible distortion would be created at any frequency.

So in answer to the specific question; our high pass filters are not brick-wall filters, which would be full output at 20Hz but none at 19Hz, but rather they are designed to be as gradual as we determined would be required to optimize the overall subwoofer performance of each model. And at those frequencies where you may have less than 2 octaves to 5Hz that means pretty steep.

-- Andrew Welker, Axiom R&D]

Cool so they changed the HPF slope of their subs since V1 versions. Kudos to them, especially in taking the time to formally respond in an article format to your queries. Too bad they don't show how the limiter behaves when the sub is driven at higher output levels though