# When does a $50 sub sound like a $600 sub?



## Patrick Bateman (Sep 11, 2006)

In another thread I was discussing what it takes to reduce distortion in a subwoofer. For instance, you can put a shorting ring in the motor, use an underhung motor, or use a split gap motor like the Adire Audio XBL^2.

Here's a neat trick that I stumbled across a few years ago. I had a friend who wanted a couple of subs, but had a VERY small budget. So I picked up a pair of hideously cheap JBL subs from Fry's Electronics. We're talking about $30 or $40 each.

The subs required a VERY large box, so I just put them in an infinite baffle in the trunk.

Lo and behold, it sounded as good or better than my own subwoofer, which was much more expensive, and was in a big heavy box.

Here's what I *think* is going on here. Bear with me - I might be wrong on this. Anyways...

When you buy a $600 subwoofer like an underhung model from AuraSound, or a $200 XBL^2 sub from creative sounds, they're using an exotic motor type to reduce inductance.









In this cross section of the Aurasound, you can see it has an enormous voice coil for high power handling, along with a very expensive underhung motor geometry.








Here's an Adire XBL^2 motor.

And you can see from their spec sheets that these exotic motors are effective. For instance, the Shiva-X2 12" with an XBL motor has an Le of less than 1mh, with an Re of 3.8.

So if you've made it this far, you can see that low inductance is A Very Good Thing in a woofer. When I'm looking for a clean sub, it's probably the first spec I look at. (Xmax is important too.)

Now let's compare the Shiva to a Polk subwoofer that costs the same. Polk has a 12" model that costs $220, or ten percent more than the Shiva. The Shiva has an inductance of less than 1; the Polk has an inductance of 3.0mh. Or over 200% higher!

Pretty amazing huh? So even though the cost is comparable, you can see that Polk has focused on power handling and cosmetics.

Now here's where I am going to throw you a curve ball.

Remember how I said that a cheap infinite baffle sub, with JBL 12s, sounded a lot better than it should? Well lets take the CHEAPEST subwoofer you can buy from Crutchfield. That's an Infinity REF1252W. We look at the spec sheet and find that the Infinity has an inductance of 2.24mh.

Crazy huh? While we don't have distortion specs for that crappy woofer, I'd be willing to bet that the crappy Infinity sub has lower distortion than the $220 Polk Subwoofer.

Of course the Shiva trumps 'em both. But again, I think people assume that higher power handling is always a good thing. It's not - high power handling contributes to high inductance, and that leads to distortion.

*So why does the $50 P.O.S. sub have lower inductance than the $220 sub?*

Here's what's going on. If you want to increase the power handling of a woofer, it raises the inductance. It's just like using a big inductor; the bigger it is, the higher the inductance. So the Infinity can't take as much power as the Polk, but that gives it a big edge when it comes to inductance. And generally, woofers with lower inductance have lower distortion.

So let's say you have $400 to spend on a subwoofer and the amp. You could buy the Polk for $220, and $180 on an amp and build your own box. Or you could spend $150 on three of the Infinities, throw them in an infinite baffle, and enjoy much higher efficiency and dramatically lower distortion than a single twelve.

Weird huh?

Here's the links to the specs, you can review the Le and Re yourself.

Infinity 1252W $49
http://manuals.harman.com/INF/CAR/Boxes and Parameters/1252W.pdf

Polk MM1240SVC $220
http://www.polkaudio.com/downloads/manuals/car/MM2008_Sub_WebMN.pdf

Shiva - $198
http://www.diycable.com/main/pdf/ShivaX2.pdf


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## Boostedrex (Apr 4, 2007)

This very post is the reason I dislike the popular trend of 1+KW capable subs with massive amounts of excursion. Bring back the old days of car subs. I'm talking early to mid 1990's. The SS Velvet Hammer is still one of my favorites of all time. Or the first JBL GTi series with the grey cones.


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## ANT (Oct 15, 2005)

Graet post!
Glad you are a part of the DIYMA forum.
So many of the old times are gone now. It is nice to have new & thought provoking blood on the site.

I do have a question though, and please forgive my ignorance, but is the inductance linear?
Will it change with box volume or power or anything else?

I ask because I am wonder about higher power rated subs that are fed less power than their rating.
The Brahma for example had a decently high power rating but could easily reach full excursion without getting close to its thermal limit and sounded great with tons of power on it. 
If inductance changes with other variables would the same conept apply to a higher power sub that was reaching full excursion with less power?
If so, then wouldn't the distortion you talk about be reduced as well, and in the end, we would have a higher power rated sub that sounds great, but might cost more money!?


Not sure this is coming out right...

ANT


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## Brian Steele (Jun 1, 2007)

Boostedrex said:


> This very post is the reason I dislike the popular trend of 1+KW capable subs with massive amounts of excursion. Bring back the old days of car subs. I'm talking early to mid 1990's. The SS Velvet Hammer is still one of my favorites of all time. Or the first JBL GTi series with the grey cones.


The first GTis had grey cones? I thought I had two of the first model - see image below:










I do agree though - more subs = less excursion to meet same SPL = less distortion.

BTW - the 1200Gti had an inductance of 0.98mH and a 4" coil - and this was the days before shorting rings and the like .


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## Boostedrex (Apr 4, 2007)

Brian, the GTi with the "pro audio" style surround is the one I was thinking of. Maybe they didn't have grey cones after all. It has been over 10 years you know.  I would LOVE to have a pair of those old school GTi 12's.


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## Brian Steele (Jun 1, 2007)

DIYMA said:


> I do have a question though, and please forgive my ignorance, but is the inductance linear?


Le is measured @ 1kHz. It's actually a bit of a fudge, as yes, it does vary (not with box volume (well, not directly), but with cone displacement and frequency (it goes down as frequency increases).

I think what's important is not just Le, but the variations in Le that happen when the cone is moving. Lower variation = less distortion.




DIYMA said:


> The Brahma for example had a decently high power rating but could easily reach full excursion without getting close to its thermal limit and sounded great with tons of power on it.


The Brahma had basically a flat BL curve for a good portion of its excursion. I suspect that's one of the main reasons why it sounded so great.


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## Luke352 (Jul 24, 2006)

You've made some good points, just out of interest I was looking this site Option Audio - Car Audio, In-car Entertainment, Sub Woofers, Speakers, LCD Screens just to see what they offered, since they have become quite popular with the ricer and young boom boy crowd in Australia now, so we get quite a lot of questions about there gear on the Australian Forum I'm on so figured I should check some of there stuff before commenting on it. I knew most of the stuff they sell is rubbish anyway, they've actually admitted there component speakers are from the same people who make the Focal fakes.

Anyway I was checking the specs on there subs and came to the conclusion there entry level one is the only one I would even consider worth anything as it's Inductance was only 2.19mh I think, whereas the two higher models are up around 25mh which is so high they'd be almost useless.


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## Brian Steele (Jun 1, 2007)

Boostedrex said:


> Brian, the GTi with the "pro audio" style surround is the one I was thinking of. Maybe they didn't have grey cones after all. It has been over 10 years you know.  I would LOVE to have a pair of those old school GTi 12's.


Yup - that sounds like my 1200Gtis - they had a three-fold linen surround, like you find on many pro audio subs. In fact, it's actually based on the same motor that JBL uses for one of its pro audio subwoofers, the JBL 2206H. See Parts-Express.com:JBL 2206H 12" High-Power LF Driver | 2206h jbl lf driver pa woofer low frequency speaker. Notice the similarity? Add some mass, a stronger cone, and replace the coil with a 4 ohm one and you've got a 1200Gti .

They were damned good subs, 'cept for two things IMO: dustcap dry-rot and cone-sag.

I wonder if anyone's ever tried the 2206H drivers in a car audio install?


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## bassfromspace (Jun 28, 2016)

Are we talking measured distortion or distortion you hear?

The W7 appears to have extremely low distortion with huge excursion.

How does it buck the trend?


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## ItalynStylion (May 3, 2008)

Patrick, you're suggesting that LE has a direct relationship to distortion? I'm confused as to why something like the DIYMA R12 would have L(e)= 2.03 mH. Seems high for the conversation at hand considering its reputation. LE is largely a parameter I don't fully understand so I'm still trying to get a grasp on it.

EDIT: I also want to add that the Tang Band 6.5" subs I use have an LE of 0.34mH. Maybe I'm not that crazy after all.


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## Patrick Bateman (Sep 11, 2006)

bassfromspace said:


> Are we talking measured distortion or distortion you hear?


Subs produce gobs of distortion. Check out Mark K's blog - he publishes the data the manufacturers don't want you to see. Even with a single watt you can see 10% 3rd harmonic distortion. And it just gets worse as the excursion goes up. So distortion is measurable and audible.



bassfromspace said:


> The W7 appears to have extremely low distortion with huge excursion.
> 
> How does it buck the trend?


The W7 has shorting rings and a split gap, if I'm not mistaken. And that's why it's so expensive.

But if you're on a *budget*, sometimes two or three cheap woofers will outperform one woofer that's modestly priced.

Here's another example:

I have a friend who had a box with dual twelves in her trunk that was ripped off. She came to my house the other day, whining that she needs bass. Her amplifier is about 150 watts RMS. I asked her what her budget was, and she said $75(!)

Now if she walks into an electronics store, I'm sure they're going to tell her that the Polk is a better choice for her, and the Infinity is a $50 POS. But in this case, _it's not true._ The Infinity has lower inductance, and she'll never need the higher power handling of the Polk with her 150w amp.
Most importantly, the use of two or three raises the efficiency dramatically, which is great when you only have 150watts to play with.


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## Niebur3 (Jul 11, 2008)

Patrick Bateman said:


> Subs produce gobs of distortion. Check out Mark K's blog - he publishes the data the manufacturers don't want you to see. Even with a single watt you can see 10% 3rd harmonic distortion. And it just gets worse as the excursion goes up. So distortion is measurable and audible.
> 
> 
> 
> ...



Can you help me with what shorting ring in the motor, an underhung motor, or a split gap motor looks like so I know what to look for?


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## chad (Jun 30, 2005)

Brian Steele said:


> Yup - that sounds like my 1200Gtis - they had a three-fold linen surround, like you find on many pro audio subs. In fact, it's actually based on the same motor that JBL uses for one of its pro audio subwoofers, the JBL 2206H. See Parts-Express.com:JBL 2206H 12" High-Power LF Driver | 2206h jbl lf driver pa woofer low frequency speaker. Notice the similarity? Add some mass, a stronger cone, and replace the coil with a 4 ohm one and you've got a 1200Gti .
> 
> They were damned good subs, 'cept for two things IMO: dustcap dry-rot and cone-sag.
> 
> I wonder if anyone's ever tried the 2206H drivers in a car audio install?


The coil is just the "G" coil, and there is a set of VGC 15's up for sale now with the same motor as the 1500GTi, they are the 2226, freshly re-cones and at a ridiculous cheap price.


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## gymrat2005 (Oct 4, 2009)

Not to get off the OP's point, but I had some of the original JBL Automotive subs when they first came out. Their whole line was the "T" series. The 12's were called T120's and they sounded so dang good. The had that same "Aquaplas" coating. The GTi series came out right after those.


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## Brian Steele (Jun 1, 2007)

Niebur3 said:


> Can you help me with what shorting ring in the motor, an underhung motor, or a split gap motor looks like so I know what to look for?


All of those are product differentiators. If the driver has any of them, the manufacturer is likely going to make a point of advertising that.


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## trevordj (Feb 22, 2009)

Niebur3 said:


> Can you help me with what shorting ring in the motor, an underhung motor, or a split gap motor looks like so I know what to look for?


I had the same question. This read helped me quite a bit. Someone please correct me if I am wrong, but I believe a shortening ring is synonymous with a faraday ring. 

OP: Thanks for the write up, very informative.


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## Patrick Bateman (Sep 11, 2006)

ItalynStylion said:


> Patrick, you're suggesting that LE has a direct relationship to distortion? I'm confused as to why something like the DIYMA R12 would have L(e)= 2.03 mH. Seems high for the conversation at hand considering its reputation. LE is largely a parameter I don't fully understand so I'm still trying to get a grasp on it.
> 
> EDIT: I also want to add that the Tang Band 6.5" subs I use have an LE of 0.34mH. Maybe I'm not that crazy after all.


I've never played with a Dumax or a Klippel. NPDang had one - if he chimed in on this it would be great.

I honestly don't know why drivers with lower inductance have lower distortion. There's a strong correlation for it - all of the measurements of exotic motor types demonstrate a reduction in inductance and distortion. If I had to take a stab at it, and this is seriously just a wild guess, it's that there's no way to electronically filter out distortion. So the inductance in the motor filters out the fundamental *but the distortion remains*. For instance, let's say you're listening to your sub and a big drum beat hits at 60hz. The third harmonic distortion is at 180hz. _There's no way to electronically filter out distortion._ So that distortion at 180hz is heard, no matter where you set your crossover. Now if the inductance is 4mh instead of 0mh, the sounds that's *supposed* to be coming out of the woofer will be filtered by the inductance in the coil, and the 3rd harmonic will be audibly louder. (Since there's less of the "real" signal to mask the distortion.)

Again, total stab in the dark. Dan Wiggins, where are you? 

The thing that piqued my curiosity is that there are other ways to reduce inductance besides using a split gap or shorting rings. Simply using a smaller motor will reduce inductance.

Some of the most natural bass that I've ever heard came from an Emerald Physics speaker, which uses six extreeeeeeemely low-tech fifteens.










If you wire four of these fifteens in series parallel, you wind up with a subwoofer that has the cone area of EIGHT twelves, and an inductance of less than ONE millihenry, for $240. You can buy it here:

Parts-Express.com:Eminence Alpha-15A 15" Driver | alpha-15a 15" guitar speaker 15" keyboard speaker pa driver 200 watt driver

So I think the Emerald Physics guys know what they're doing. These look like cheap crummy subs, but they outperformed every sub I heard at CES. (There's no replacement for displacement...)

Here's some reading on the inductance versus distortion thing:

http://forum.soundillusions.net/dan-questions-driver-t55762.html?t=55762


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## pwnt by pat (Mar 13, 2006)

It's been said that inductance is the SOLE parameter that dictates how quickly a woofer will respond to an input signal. In fact, this principle was pretty much the entire basis for the SI magv4. XBL2 for lower distortion over greater cone distances, low inductance for quick response, big voice coil for power handling, and a shallow profile.

http://stereointegrity.com/docs/WooferSpeed.pdf


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## ItalynStylion (May 3, 2008)

pwnt by pat said:


> It's been said that inductance is the SOLE parameter that dictates how quickly a woofer will respond to an input signal. In fact, this principle was pretty much the entire basis for the SI magv4. XBL2 for lower distortion over greater cone distances, low inductance for quick response, big voice coil for power handling, and a shallow profile.
> 
> http://stereointegrity.com/docs/WooferSpeed.pdf


Fantastic read, thanks for the link. I always like to find a good read and learn something.


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## thehatedguy (May 4, 2007)

I don't think the W7 has a split gap. Seem to remember Manville saying it was a really long coil in a long gap. Not sure if there are shorting rings either.

I do love my IDW15s, they were about 1 mH Le way back before shorting rings and such too. Just a 3" coil...but low Le probably because the coil was so short.

Really one of the people you should ask about the correlation (if any) to low Le and distortion is John Janowitz at AE. His published Le numbers are magnitudes lower than nearly anything on the market.


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## Mless5 (Aug 21, 2006)

ItalynStylion said:


> Fantastic read, thanks for the link. I always like to find a good read and learn something.


x2. 

+ 

Where is my "bow down" smiley?!


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## thehatedguy (May 4, 2007)

Maybe I'm reading the data wrong in the link, but the conclusions being drawn aren't being shown by the stated data.


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## cubdenno (Nov 10, 2007)

looks like it was labeled wrong. Or I a reading it wrong.


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## mikey7182 (Jan 16, 2008)

chad said:


> The coil is just the "G" coil, and there is a set of VGC 15's up for sale now with the same motor as the 1500GTi, they are the 2226, freshly re-cones and at a ridiculous cheap price.


Thanks for the plug  They did sound amazing, as I heard they would. They took a bit to break in, which is something I normally don't subscribe to, and once they did, it was very hard to tell them apart from the current W15GTi, sans about the bottom half octave. Brian- I know of someone working on a pair of 2206, but not sure if his install is done.

Patrick- great info as usual. So the new goal is to find a cheap sub with low inductance and buy 4 or 5 of them as opposed to a single expensive sub (as long as you have the room) and you'll have higher efficiency AND SQ to boot.


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## Xander (Mar 20, 2007)

Patrick Bateman said:


> I honestly don't know why drivers with lower inductance have lower distortion. There's a strong correlation for it - all of the measurements of exotic motor types demonstrate a reduction in inductance and distortion. If I had to take a stab at it, and this is seriously just a wild guess, it's that there's no way to electronically filter out distortion. So the inductance in the motor filters out the fundamental *but the distortion remains*. For instance, let's say you're listening to your sub and a big drum beat hits at 60hz. The third harmonic distortion is at 180hz. _There's no way to electronically filter out distortion._ So that distortion at 180hz is heard, no matter where you set your crossover. Now if the inductance is 4mh instead of 0mh, the sounds that's *supposed* to be coming out of the woofer will be filtered by the inductance in the coil, and the 3rd harmonic will be audibly louder. (Since there's less of the "real" signal to mask the distortion.)




I agree that there is no way to electronically filter distortion that is created by the driver, since it is created in the process of converting the electrical energy to acoustic energy.

But when the voice coil, which is just a low pass filter, reduces the output of the fundamental frequency BEFORE it is converted to acoustic energy, doesn't it by nature reduce the eventual output of the harmonic distortion by the exact same amount?

I'm not trying to argue here, only add my opinion, so please take it as only that. I really appreciate the intelligent discussion here and some of the great info offered.


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## ItalynStylion (May 3, 2008)

thehatedguy said:


> Maybe I'm reading the data wrong in the link, but the conclusions being drawn aren't being shown by the stated data.


The first graph is right I think but i believe the 3rd one is wrong. I was thinking the same thing when reading it. I think the labels just got mixed up.


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## Boostedrex (Apr 4, 2007)

ItalynStylion said:


> Patrick, you're suggesting that LE has a direct relationship to distortion? I'm confused as to why something like the DIYMA R12 would have L(e)= 2.03 mH. Seems high for the conversation at hand considering its reputation. LE is largely a parameter I don't fully understand so I'm still trying to get a grasp on it.
> 
> EDIT: I also want to add that the Tang Band 6.5" subs I use have an LE of 0.34mH. Maybe I'm not that crazy after all.


Where did you get Le = 2.03mH for the DIYMA R12? The spec I got from NPDang a couple of years ago was Le = 1.319 mH. Just curious.



thehatedguy said:


> I do love my IDW15s, they were about 1 mH Le way back before shorting rings and such too. Just a 3" coil...but low Le probably because the coil was so short.
> 
> Really one of the people you should ask about the correlation (if any) to low Le and distortion is John Janowitz at AE. His published Le numbers are magnitudes lower than nearly anything on the market.


IDW15... Is this anything like the B&C 15NW100? Here's a link to that driver.
B&C 15 NW100 is a lightweight very high power 15" woofer for speaker subwoofer systems. B&C 15 NW100 Speakers - B&C 15" 15 NW100 high power speaker for speaker subwoofer systems. B&C 15 NW100 high power speakers available now.


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## Brian Steele (Jun 1, 2007)

Luke352 said:


> Anyway I was checking the specs on there subs and came to the conclusion there entry level one is the only one I would even consider worth anything as it's Inductance was only 2.19mh I think, whereas the two higher models are up around 25mh which is so high they'd be almost useless.


Something's got to be wrong there - it's highly unlikely that the inductance on those drives is actually as high as that.


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## Oliver (Jun 25, 2007)

Boostedrex said:


> Where did you get Le = 2.03mH for the DIYMA R12? The spec I got from NPDang a couple of years ago was Le = 1.319 mH. Just curious.


I believe these are demoed with Diyma  YouTube - Grandmas Hands Demo 3


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## WLDock (Sep 27, 2005)

Great post. This is the type of thinking many SQ types have had for years. While good output is always the goal of a sub system, many find that they have to fight with the enclosure rather it is ported or seled to get great sound. Some have found that surface area in an IB install produces about as accurate bass as one can hope to get in a car.
There are no magic boxes but IB can sound VERY good in many installs.

Myself, while having to recently sell off my entire system due to major repair issues with my car. Now, I am stuck with am OEM system that I did not want to go into another FALL/Winter season with. SO....I have a Blupunkt THw 1200 sub laying around that I payed $40 for,also a set of Phaze Audio mids, Eclipse CD8443 deck, Aura tweets, and an old amp that I am not sure who it is made by? 

I think I will throw this system in and see how good I can get it to sound for cheap. And YES! I plan to mount the sub IB because this THw 1200 sub need a large sealed box (1.5-2.0 cu ft). This is a shallow sub so it is going to be very cool to not take up a ton of room in the trunk. Will see if I can improve upon the OEM sound.....


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## stoeszilla (Jul 9, 2007)

Brian Steele said:


> Yup - that sounds like my 1200Gtis - they had a three-fold linen surround, like you find on many pro audio subs. In fact, it's actually based on the same motor that JBL uses for one of its pro audio subwoofers, the JBL 2206H. See Parts-Express.com:JBL 2206H 12" High-Power LF Driver | 2206h jbl lf driver pa woofer low frequency speaker. Notice the similarity? Add some mass, a stronger cone, and replace the coil with a 4 ohm one and you've got a 1200Gti .
> 
> They were damned good subs, 'cept for two things IMO: dustcap dry-rot and cone-sag.
> 
> I wonder if anyone's ever tried the 2206H drivers in a car audio install?


This guy seems to support the theory of using pro-audio type speakers as he sells this:
DECWARE / PRO SPL WOOFER
what looks to be a rebadged Eminence pro audio driver (http://www.parts-express.com/pe/showdetl.cfm?Partnumber=290-426 ...takethat for what it's worth.


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## 12vTools (Jan 15, 2009)

Those aren't the same speakers that Winslow has at the shop for his car.




Boostedrex said:


> IDW15... Is this anything like the B&C 15NW100? Here's a link to that driver.
> B&C 15 NW100 is a lightweight very high power 15" woofer for speaker subwoofer systems. B&C 15 NW100 Speakers - B&C 15" 15 NW100 high power speaker for speaker subwoofer systems. B&C 15 NW100 high power speakers available now.


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## Boostedrex (Apr 4, 2007)

I wasn't thinking so g0a, but I had heard people refer to those B&C's as IDW15's and had always wondered why.


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## bassfromspace (Jun 28, 2016)

Boostedrex said:


> I wasn't thinking so g0a, but I had heard people refer to those B&C's as IDW15's and had always wondered why.


If I'm not mistaken, there was a new IDW called the Neo to be released based on that driver.


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## Brian Steele (Jun 1, 2007)

stoeszilla said:


> This guy seems to support the theory of using pro-audio type speakers as he sells this:
> DECWARE / PRO SPL WOOFER
> what looks to be a rebadged Eminence pro audio driver (Parts-Express.com:Eminence Kappa Pro-10A 10" Cast Frame Driver | kappa pro-10a 10" cast frame driver 10" pa woofer 10" bass guitar speaker 500 watt 10" speaker ...takethat for what it's worth.


He was off to a good start - then suggested putting the driver in a small sealed box. Just under 5mm Xmax? That's not how I'd use it. EBS more likely.


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## ItalynStylion (May 3, 2008)

Boostedrex said:


> Where did you get Le = 2.03mH for the DIYMA R12? The spec I got from NPDang a couple of years ago was Le = 1.319 mH. Just curious.


I had looked for the specs on the R12 and the only thing I was able to find was a post by Patrick on DIYaudio.com where he said he measured the woofer himself.

EDIT: Found Here Tapped Horn meets Bandpass Sub - diyAudio


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## Neil (Dec 9, 2005)

The W7 does not have shorting rings, nor does it have a split gap.

The W7 uses a long voice coil; typically, the longer the voice coil, the higher the rest inductance (must be cautious to distinguish between rest inductance and inductance with a change in coil position or change in amperage through coil). To combat this, JL uses less layers on the voice coil (I believe it's a 2 layer coil instead of the more typical 4 layer). This helps lower inductance at rest, and in turn the inductance variation (with current and position) is less offensive (so long as it does not vary wildly, which it doesn't).

As for the BL linearity, the modifications are fairly simple. First, the majority of the BL curve is achieved simply by paying close attention to coil and gap ratios, the type of insight that is gained through FEA. You can make pretty good plain-old overhung drivers just by extensively simulating multiple scenarios. Second, the pole piece has several holes drilled in it in the region that is parallel to the gap. By removing steel from where the coil rests, the available flux (B) is lowered; this means that BL is lower at rest than it would be otherwise, but translates into a smoother BL curve, which translates to less BL distortion (though it simultaneously decreases efficiency). This also has the benefit of creating more convection in the region where the coil oscillates the most (at +10mm to -10mm displacement), which helps improve power handling, which would otherwise be sacrificed by the lower number of layers on the coil mentioned above.


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## thehatedguy (May 4, 2007)

Those B&C drivers were looked at by Image a few years back as a possible updated new IDW. But for whatever reason Image decided not to pursue them further. I am aware of one person getting a set calling them neo IDWs, and then later selling them as such. But there was never really such a thing as a neo IDW.


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## thehatedguy (May 4, 2007)

It wouldn't really surprise me that the Adire sited papers had some issues with the data...they were known to be "creative" with their published numbers of their drivers and tested drivers referenced on their website.


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## TREETOP (Feb 11, 2009)

a$$hole said:


> I believe these are demoed with Diyma  YouTube - Grandmas Hands Demo 3


After watching that, I was expecting to hear the triangles from The Pink Panther next.


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## Boostedrex (Apr 4, 2007)

thehatedguy said:


> Those B&C drivers were looked at by Image a few years back as a possible updated new IDW. But for whatever reason Image decided not to pursue them further. I am aware of one person getting a set calling them neo IDWs, and then later selling them as such. But there was never really such a thing as a neo IDW.


Cool, thanks for the clarification Winslow. I actually ended up with the drivers in question. I traded off some gear for them. They now reside in my DIY bass guitar rig.


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## WRX/Z28 (Feb 21, 2008)

Great post. This was something that i've always done. I have had people looking at these so called "super woofers", and when determining their needs, found out that they didn't care too much about trunk space. Once this was determined, i'd almost always suggest a multiple of moderately priced woofers setup over a single "super woofer". It always yielded better results, and would have the guys friends coming in saying "how did you get his car to sound better/louder with those cheap subs than my car with the megaswoofer?" This was even in a sealed box. 

Displacement is definately a good way to gain efficiency. IB is a good way to eliminate the trunk space problem from the equation. 

I was already looking to go IB to save weight/space and gain efficiency. This probably pushed me over the edge. Thanks! Great post!


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## stoeszilla (Jul 9, 2007)

So if a person were to run three of these IB it would set you back about $90: Parts-Express.com:12" Dual Voice Coil Subwoofer | 12" subwoofer Dual Voice Coil Subwoofer DVC sub car sub home theater poly cone eminence sealed box subwoofer marcato DVSSUB090109 

If we look at the specs: (Specifications: *Power handling: 200 watts RMS/400 watts max *VCdia: 2" *Le: 1.73 mH *Impedance: 4 ohms *Re: 2.78 ohms *Frequency response: 23-800 Hz *Fs: 23 Hz *SPL: 88 dB 1W/1m *Vas: 5.66 cu. ft. *Qms: 9.43 *Qes: 0.44 *Qts: 0.42 *Xmax: 7.0 mm *Dimensions: A: 12", B: 11", C: 5-1/2". Note: All specifications are with voice coils connected in parallel.) 
So we have an LE of 1.73 mH (seems low in a good way) but a Qts of 0.42; I always thought a higher Qts was desired for IB (like 0.6 or higher) or is that wrong? What am I missing?


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## lucas569 (Apr 17, 2007)

you know, i needed a new sub recently and after all these years i never tried mtx....

cause i heard so many bad things about them just being spl oriented but let me tell you i bought a 12" 9500 series and imho it sounds GREAT! i have 700 watts mono going to it and it blends very well with my front speakers.

anyhow my car buddys really liked the sound of them so i sourced 2 more pairs for their cars (all less than $100 off ebay) got a 5500 series and a 7500 series good clean sub bass... 

its weaird what sounds good from person to person butim kicking myself in rhe butt for not trying this line sooner. 

my spring time plans were to get a morel ultimo 12" or maybe a JL 12w6/13w6 but this mtx 9500 sounds damn good for the time being! imo just as good as my last 10w6 it replaced.


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## Megalomaniac (Feb 12, 2007)

a$$hole said:


> I believe these are demoed with Diyma  YouTube - Grandmas Hands Demo 3


That video has a SI Mag v3 in the trunk not a diyma r12. Also the video really does no justice, i dont think my digital camera can pick up the foot stomps in that song.


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## blamus (Mar 9, 2009)

stoeszilla said:


> So if a person were to run three of these IB it would set you back about $90: Parts-Express.com:12" Dual Voice Coil Subwoofer | 12" subwoofer Dual Voice Coil Subwoofer DVC sub car sub home theater poly cone eminence sealed box subwoofer marcato DVSSUB090109
> 
> If we look at the specs: (Specifications: *Power handling: 200 watts RMS/400 watts max *VCdia: 2" *Le: 1.73 mH *Impedance: 4 ohms *Re: 2.78 ohms *Frequency response: 23-800 Hz *Fs: 23 Hz *SPL: 88 dB 1W/1m *Vas: 5.66 cu. ft. *Qms: 9.43 *Qes: 0.44 *Qts: 0.42 *Xmax: 7.0 mm *Dimensions: A: 12", B: 11", C: 5-1/2". Note: All specifications are with voice coils connected in parallel.)
> So we have an LE of 1.73 mH (seems low in a good way) but a Qts of 0.42; I always thought a higher Qts was desired for IB (like 0.6 or higher) or is that wrong? What am I missing?


How about 3 of these 

Parts-Express.com:JAMO 20392 15" Paper Cone Woofer | JAMO 20392 15" Woofer Treated Paper Cone driver speaker bass

oh wait, even "IB" in the average car won't be enough space as a sealed box for 3 of these lol.

In the home however, I wonder if a few of them IB will be good, according to patrick's Emerald Physics 4x15" subs argument.


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## Rare177 (Sep 7, 2009)

very good read, but im curious about one thing.

depending on the level of power compression on a coil, wouldn't this raise the inductance? if this were the case, it's very hard to judge what driver is going to have lower inductance.

for example, your infinity subs you mentioned vs a 1000wrms driver.

how high is the power compression going to be between both drivers from say 300 watts? is it going to effect the infinity sub that much that inductance raises higher than the 1000wrms driver from such small amounts of power?

this is something i've always been interested in..


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## BLD 25 (Apr 13, 2007)

So the idmax with an inductance of 2.9 mH is just cosmetics then? Why is it the best subwoofer I have ever heard? I have owned:

infinity reference
3 different infinity kappas
(120w.br, 120.1se, 120.3)
infinity Kappa Perfect
Infinity kappa VQ
JL Audio W0
Oz Audio ME
SI BM
SI Claw Mag
Diamond Audio TDX 
ED 130v.2
ED 12k
ED 13kv.2
ED ehqs8
soundsplinter RL-P12
Idmax 12

Why is it considered one of the best subwoofers you can buy by many many people?


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## WRX/Z28 (Feb 21, 2008)

bld 25 said:


> So the idmax with an inductance of 2.9 mH is just cosmetics then? Why is it the best subwoofer I have ever heard? I have owned:
> 
> infinity reference
> 3 different infinity kappas
> ...



Maybe the distortion is not always perceived as a bad sound? The same way a flat RTA curve doesn't necessarily sound good.


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## Rare177 (Sep 7, 2009)

bld 25 said:


> So the idmax with an inductance of 2.9 mH is just cosmetics then? Why is it the best subwoofer I have ever heard? I have owned:
> 
> infinity reference
> 3 different infinity kappas
> ...


i think this may come down to what i said earlier.

i also dont think Le is the only attribute to a good sounding driver, how well a driver can keep its motor strength over the stroke also plays a huge part in low distortion.


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## bassfromspace (Jun 28, 2016)

What exactly is a "good sounding" sub?

They go "boom...like so".


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## Electrodynamic (Nov 27, 2007)

Patrick Bateman said:


> I honestly don't know why drivers with lower inductance have lower distortion. There's a strong correlation for it - all of the measurements of exotic motor types demonstrate a reduction in inductance and distortion. If I had to take a stab at it, and this is seriously just a wild guess, it's that there's no way to electronically filter out distortion. So the inductance in the motor filters out the fundamental *but the distortion remains*. For instance, let's say you're listening to your sub and a big drum beat hits at 60hz. The third harmonic distortion is at 180hz. _There's no way to electronically filter out distortion._ So that distortion at 180hz is heard, no matter where you set your crossover. Now if the inductance is 4mh instead of 0mh, the sounds that's *supposed* to be coming out of the woofer will be filtered by the inductance in the coil, and the 3rd harmonic will be audibly louder. (Since there's less of the "real" signal to mask the distortion.)


Low inductance alone does not always equal lower distortion. The exotic motor types that you mentioned use lower inductance coils vs. their traditional motored counterparts which achieve the same, if not higher, levels of linear excursion. Those particular motors have lower distortion because they provide more BL over stroke, which is what lowers distortion. Distortion heard by our ears still lies primarily in the motor (Xmax is 70% of BL by most measurements, Klippel is close to 80%), followed by the suspension, inductance variances and/or levels, etc.

Now when it comes to how much inductance change/variation can you hear, it all depends on a lot of variables such as bandwidth, power, and the amount of change in the system. In terms of bandwidth, classical/traditional crossover filter theory suggests a self-inductance F3 of at least one octave above your bandwidth of interest. For a 3.5 Ohm DCR at 100 Hz, that would be 2.75 mH. Ideally you should have an inductance lower than that, and many long voice coil drivers are considerably higher. 

But you need to address lower inductance from the source – the voice coil. Lowering inductance through shorting rings is a good way to lower (and some times balance) inductance, but hitting the nail on the head in the beginning is a solid start since you’re really after looking at inductance and position and power and frequency (it’s really a 4D space you’re looking at). You can definitely over-sleeve a motor which creates a sharp spike in inductance at a certain frequency, which causes it to ‘hang up’ at that area. 

PS: The W7 does not use a multiple gap motor. They achieved the extra one-way BL plot by manipulating the pole piece. It does have a really clean suspension though. 

PS again: You need to look at Le vs. Re. For instance, our new BM mkIII's have an Le of 2.4 mH at 8 Ohms with the coils wired in series, which is 1.2 mH per coil, or 0.6 mH when wired down to 2 Ohms.


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## bose301s (Dec 8, 2008)

This little part about the Lambda motor from Acoustic Elegance helps explain inductance, what it does and why reducing it helps.
AE Speakers --- Superb Quality, Unforgettable Performance, Definitely.

I also think this poster from Klippel which John from AE showed me is great, it helps explain a lot and shows the biggest sources of distortion in a typical electrodynamic driver.
http://www.klippel.de/download/Nonlin/Klippel_nonlinearity_poster.jpg

Basically from my research and from listening experience any source of nonlinearity hurts a drivers performance substantially, another large factor that has not been mentioned however is power compression. Drivers that use smaller coils will generally suffer great power compression which up the impedance and has a direct affect on Le as well. Personally my favorite motor structures that I have seen and have had experience with are the XBL^2 motors and the Lambda motors from AE. They both offer extremely low Le and help stabilize the B field in the motor reducing distortion from a moving magnetic field.


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## Rare177 (Sep 7, 2009)

bose301s said:


> This little part about the Lambda motor from Acoustic Elegance helps explain inductance, what it does and why reducing it helps.
> AE Speakers --- Superb Quality, Unforgettable Performance, Definitely.
> 
> I also think this poster from Klippel which John from AE showed me is great, it helps explain a lot and shows the biggest sources of distortion in a typical electrodynamic driver.
> ...


read up


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## BLD 25 (Apr 13, 2007)

these last few posts were my point. Thank you guys! Inductance is important, but there seems to be a lot more involved. For example, after reading this, I looked up some different drivers in partsexpress, and the goldwood Poly 6.5" driver has an inductance of like .3 mH. Interestingly enough, I thought they sounded like poo. I will be the first to admit this t/s parameter is one that I don't know much about, but there has to be more involved than just that.


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## western47 (Nov 17, 2008)

I would urge people to look at some of the newer data regarding smooth bass response. In any pressure vessel; a car, home, barn; the more sources that you have in different locations the more even bass response you will have across the board. Every environment is a little bit different but a good general rule of thumb is to have as many bass sources in different places in your environment as possible. The caveat to this is that you would like to be able and control their output levels individually as some will excite certain modes more than others. I urge people to look at the works of Geddes and Welti as nothing differs from the home environment.

The other thing that needs to be considered is our ability to hear distortion at low frequencies. There is plenty of data to support that distortion at low frequencies is really a non-factor.


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## stryke23x (Jun 22, 2007)

Rare177 said:


> depending on the level of power compression on a coil, wouldn't this raise the inductance? if this were the case, it's very hard to judge what driver is going to have lower inductance.


Keep in mind that it is not the overall inductance value, but the ratio of inductance to resistance. Power compression occurs as the coil heats and resistance goes up. At the same time, inductance also goes up but the proportion stays mainly the same.

Someone asked what defines a woofer as a "good sounding" woofer. My thought is that the woofer shouldn't sound like anything itself, it should only reproduce what is input to it as close as possible. Obviously any distortion of the signal is not reproducing the original accurately. However to our ears there are components to distortion that are more audible than others. The higher the order the distortion, the more audible it will be. A 2nd order harmonic is much closer on the frequency scale to the fundamental than a 5th order harmonic for example. The 5th order harmonic is separated from the fundamental much farther so it stands out much more. 

Also realize that these harmonics are created by the fundamental frequency being played and will NOT be filtered out by any crossover. This is particularly problematic in midrange drivers. While you can cross the driver over with a steep order xover to get the electrical response down, any physical resonance in a cone, dustcap, surround, etc can still be excited by the harmonics that are not filtered out. This is why even with steep xovers many drivers tend to sound harsh.

We also need to look at where these distortion components come from to better understand. Specifically we'll look at in the motor as that is the main factor in a woofer at least. As Bose301's posted, Klippel makes it easy to see which non-linearities affect which distortions. Non-linear Bl for example affects only the sound pressure domain, meaning difference in volume level with difference in position. Non-linear inductance has 2 components due to variance with position of the coil, and flux modulation created by the coil. IMO and in many others, the inductance issue has much more significant effect on how a woofer sounds than the BL linearity as it effects both sound pressure and current domains(and time domain as a result).

Le(x) causes a change in the impedance curve and as a result change in the response curve of the driver from the inward to outward stroke. The larger the difference in response curve from one position to the other, the more distortion is created. This can be minimized in a few ways. Since the coil acts as an inducter, the first is to keep the "core" the same at all excursions. Keep in mind that in a woofer, not only the pole on the ID makes up the "core" but also the top plate on the OD. A long pole extension past the top plate, and thick top plate are 2 things that are the basic starting point in keeping the core the same. Regardless of this, the inductance will still vary with excursion to some extent, but this is the starting point. The other thing to do is lower overall inductance with a properly done shorting ring. Properly done being the key. This will get rid of nearly any inductance variation. You can see here impedance curves done by Augerpro of our TD15X at +/- 13mm. Notice that even out to 20KHz there is almost no variance in inductance even at the extremes of it's excursion.

Le(x) (drivervault)

Compare that to measurements with some of the other drivers on there and you will see how effective the shorting ring is when done properly. Now, the impedance curve determines how much power is applied at any given frequency P=I^2R. As resistance changes so does the power applied. This means varying amounts of power get applied at different points during the stroke. This greatly distorts what the driver can output.

Le(i) is flux modulation. As the coil is an electromagnet it has it's own magnetic field. As it moves through the gap this field modulates or moves the fixed field around. The more power applied and the more windings there are, the worse the effect becomes. Any symmetry that was originally designed into the motor is nearly thrown out the window once the field is moved. The first way to reduce the effect is with smaller coils. Less coil means less electromagnet and less flux modulation. The larger and heavier the coil, the more effect it has. This is why people often think drivers with heavy Mms sound "slow". It's not the physical Mms that is the problem, it's the fact that it comes from a big coil that creates more flux modulation and affects the time domain. Adding physical mass to the cone for example has no effect in the time domain and doesn't make things sound "slow".

Old alnico motored drivers were and are regarded as very good sounding for a reason. They higher flux density in the alnico and it's resistance to be modulated lower the effects of flux modulation. Again the shorting ring is extremely effective (if done properly) to reduce the effect of flux modulation, even more so than alnico. Ideally both can be done, alnico and a shorting ring. With the shorting ring, any flux modulation creates eddy currents that are shorted out keeping the flux from moving. Again position and thickness of the shorting ring are key to making this work well.

Eliminating any non-linearities is good, and should be worked at in good driver design. Linear Bl is a good thing. Having soft parts that lead to linear compliance is a good thing. The effects of non-linear inductance though contribute to the most distortions of any one given source.

John


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## stryke23x (Jun 22, 2007)

bld 25 said:


> these last few posts were my point. Thank you guys! Inductance is important, but there seems to be a lot more involved. For example, after reading this, I looked up some different drivers in partsexpress, and the goldwood Poly 6.5" driver has an inductance of like .3 mH. Interestingly enough, I thought they sounded like poo. I will be the first to admit this t/s parameter is one that I don't know much about, but there has to be more involved than just that.


One of the big things is the variance in inductance. A driver like that may have .3mH at rest, .1mH on the outward stroke, and 1mH on the inward stroke as the core of the VC changes. The short Xmax adds other distortions and many physical issues with soft parts may be present as well. 

The way to see the real effects of inductance is with 2 drivers, one with and one without a shorting ring. This gets all the other variables out of the way and lets you concentrate on one to see its effects.

John


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## BTA (Nov 5, 2005)

A good sounding sub is a sub in the proper enclosure with the proper power for the car it's being installed in. Tuned properly.

Regardless of price.


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## thehatedguy (May 4, 2007)

John, would a neo motored sub be able to get more flux in the gap that even an alinco driver?


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## Rare177 (Sep 7, 2009)

thanks for that John, its great to see a guy with as much knowledge on driver design as you posting such posts, great read, so i thank you for your time on that.

i've always wondered why the really good SQ subs have such low BL, and i've always thought that more BL = a bigger change during the stroke of the driver, but is there not a way to keep BL even over the stroke, regardless of the amount?

thats probably a stupid question because if it were possible it would be done.


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## trojan fan (Nov 4, 2007)

A lot of great info....thanks


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## T3mpest (Dec 25, 2005)

Rare177 said:


> thanks for that John, its great to see a guy with as much knowledge on driver design as you posting such posts, great read, so i thank you for your time on that.
> 
> i've always wondered why the really good SQ subs have such low BL, and i've always thought that more BL = a bigger change during the stroke of the driver, but is there not a way to keep BL even over the stroke, regardless of the amount?
> 
> thats probably a stupid question because if it were possible it would be done.



isn't that what xbl^2 and split coil designs attempt to do? Keep BL constant right up until xmax, which is why the curves arent' parabolic.


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## Rare177 (Sep 7, 2009)

T3mpest said:


> isn't that what xbl^2 and split coil designs attempt to do? Keep BL constant right up until xmax, which is why the curves arent' parabolic.


well xmax is where BL changes 70% of its original value, so im not exactly sure if thats how it works, can some one chime in on this?


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## BassAddictJ (Oct 1, 2009)

interesting info.



its still fun throwing 3kw to a woofer that'll take it and laugh


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## T3mpest (Dec 25, 2005)

Rare177 said:


> well xmax is where BL changes 70% of its original value, so im not exactly sure if thats how it works, can some one chime in on this?


yes and on a normal woofer the bl drops as excursion increases pretty much the entire time. On an XBL^2 woofer you have an extended flat line for your BL "curve" that simply drops sharply at a relatively high value. It seems like an XBL^2 woofer with an xmax of say 25mm has more constant BL all the way up like 22mm or so. At say 22mm it simply drops like a stone hitting 70% at 25. A normal parabolic curve hits 70% at the same value, but is lower at every other point and more constantly changing at xmax values that you would actually use. BL linearity is the main goal in the designs. I think tc sounds actually gave a 1% linearity figure if I'm not mistaken. Their LMS was good to 20mm with only 1% variance IIRC, as much xmax as many drivers have period! Granted the xmax was 38mmish so the other 29% came relatively quick obviously. 

Now here's a question I have? Why aren't manufactures using the various BL methods and combining them with faraday rings to lower the inductance? We have nice LE based designs like AE speakers offering and then we have split coil and xbl^2 style BL based approaches. Why not build say a speaker using say a 3" xbl^2 style coil with a tight gap and full aluminum sleeve? Even with the lowered amount of coil due to xbl^2 the fact that the gap tolerance is low and sleeve would dissapate heat I'd bet you a coil like that could still handle 1500+watts no problem. Combine that with a quiet suspension capable of say 35+mm excursion and you'd have a winner in my book.. Basically what I'm saying is AE speakers should go get a liscense to use xbl^2 coils lol.

anyway here are some dumax reports of various woofers from adires site (si reposted them)
http://stereointegrity.com/technical2.php


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## Oliver (Jun 25, 2007)

Some Alnico magnet woofers

ToneTubby Speaker Specs

ToneTubby Speaker Specs


> The only # missing is Le, and I came up with .177 and .191mH.
> 
> Regards,
> John
> ...


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## Patrick Bateman (Sep 11, 2006)

T3mpest said:


> yes and on a normal woofer the bl drops as excursion increases pretty much the entire time. On an XBL^2 woofer you have an extended flat line for your BL "curve" that simply drops sharply at a relatively high value. It seems like an XBL^2 woofer with an xmax of say 25mm has more constant BL all the way up like 22mm or so. At say 22mm it simply drops like a stone hitting 70% at 25. A normal parabolic curve hits 70% at the same value, but is lower at every other point and more constantly changing at xmax values that you would actually use. BL linearity is the main goal in the designs. I think tc sounds actually gave a 1% linearity figure if I'm not mistaken. Their LMS was good to 20mm with only 1% variance IIRC, as much xmax as many drivers have period! Granted the xmax was 38mmish so the other 29% came relatively quick obviously.
> 
> Now here's a question I have? Why aren't manufactures using the various BL methods and combining them with faraday rings to lower the inductance? We have nice LE based designs like AE speakers offering and then we have split coil and xbl^2 style BL based approaches. Why not build say a speaker using say a 3" xbl^2 style coil with a tight gap and full aluminum sleeve? Even with the lowered amount of coil due to xbl^2 the fact that the gap tolerance is low and sleeve would dissapate heat I'd bet you a coil like that could still handle 1500+watts no problem. Combine that with a quiet suspension capable of say 35+mm excursion and you'd have a winner in my book.. Basically what I'm saying is AE speakers should go get a liscense to use xbl^2 coils lol.
> 
> ...


I can't speak for Dan Wiggins, but I believe the reason that many of the XBL^2 woofers do not use shorting rings is that they're not intended to play above 500hz. For instance, the CSS full ranges use shorting rings AND XBL^2, but that's because they're designed to play to 20khz.


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## stryke23x (Jun 22, 2007)

thehatedguy said:


> John, would a neo motored sub be able to get more flux in the gap that even an alinco driver?


The amount of flux in the gap is really a factor of several things. The traditional alnico motors had a slug of alnico in the pole and just a little steel cap on top. This piece of steel would be fully saturated, and then magnet with even higher flux density was very close to where the coil would be. If the alnico was moved farther away, the amount of steel in the path would be increased and that region would be more susceptible to flux modulation. In theory if you could get the neo very close to the coil you would have good results. The Aura NRT motors are very good in this right because the coil is right next to the radial neo.



Rare177 said:


> i've always wondered why the really good SQ subs have such low BL, and i've always thought that more BL = a bigger change during the stroke of the driver, but is there not a way to keep BL even over the stroke, regardless of the amount?





T3mpest said:


> isn't that what xbl^2 and split coil designs attempt to do? Keep BL constant right up until xmax, which is why the curves arent' parabolic.


Getting Bl linearity in a 2d model or to show it in a klippel test is fairly easy to do. There are many variations on gap design to get flat BL curves and get near perfect symmetry. The problem is when you apply current to the coil and start moving it. As mentioned this will modulate the field generated by the permanent magnet and things change. The lower the density of the flux field, the more it can be moved. As a result, flux modulates more in air than it does in steel, and more in steel than it does in the magnet. You also want to keep the flux density in the steel as close to saturation as you can around the gap. Keeping the gap tight is key. It keeps the flux density in the steel high, and keeps the air gap to a minimum. While XBL and split coils and LMS all will flatten the static BL curve, they introduce other issues in the current domain. Flux modulation is more irregular and less predictable. A static 2d BL curve may be flatter, but in many cases under real world use it has a lot of variance.

John


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## Patrick Bateman (Sep 11, 2006)

bld 25 said:


> So the idmax with an inductance of 2.9 mH is just cosmetics then? Why is it the best subwoofer I have ever heard? I have owned:
> 
> infinity reference
> 3 different infinity kappas
> ...


If cost is no object, I would personally use a woofer which uses a split gap, shorting rings, or both. But if I was helping someone on a tight budget, I think that arrays of inexpensive subwoofers have a few advantages over a single subwoofer of "average" pedigree.

For instance, three cheap twelves in an infinite baffle will often outperform one average subwoofer in a box.

A lot of this has to do with the IB alignment. If you actually built a box for three cheap twelves, the size would be prohibitive.


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## stryke23x (Jun 22, 2007)

T3mpest said:


> yes and on a normal woofer the bl drops as excursion increases pretty much the entire time. On an XBL^2 woofer you have an extended flat line for your BL "curve" that simply drops sharply at a relatively high value. It seems like an XBL^2 woofer with an xmax of say 25mm has more constant BL all the way up like 22mm or so. At say 22mm it simply drops like a stone hitting 70% at 25. A normal parabolic curve hits 70% at the same value, but is lower at every other point and more constantly changing at xmax values that you would actually use. BL linearity is the main goal in the designs. I think tc sounds actually gave a 1% linearity figure if I'm not mistaken. Their LMS was good to 20mm with only 1% variance IIRC, as much xmax as many drivers have period! Granted the xmax was 38mmish so the other 29% came relatively quick obviously.


The 2d models definitely show that XBL would have flatter BL curves up to a given point. However, figure though that you have extra air gap between two gaps. You have a shorter coil(good for lower inductance) with much less area to dissipate heat(bad for power compression). It makes very inefficient use of flux in the gap, much like an underhung driver as only a portion of the gap is being used at any time. Under dynamic conditions(real world) where the coil is energized and actually moving, you'll have much more variance to the BL curve than the static 2d model predicts due to flux modulation. 

LMS has all kinds of issues with flux modulation and varied inductance with excursion. You constantly have a different amount of windings in and out of the gap with more or less air gap depending on position. The wide air gap requires massive motors(expensive) to get the steel close to saturation and BL high enough. Again, it is a situation where flux modulation will affect the Bl curve under real world situations and it won't be nearly as flat as claimed. The more power applied, the more the curve is altered and distortion increases exponentially. 



> Now here's a question I have? Why aren't manufactures using the various BL methods and combining them with faraday rings to lower the inductance? We have nice LE based designs like AE speakers offering and then we have split coil and xbl^2 style BL based approaches. Why not build say a speaker using say a 3" xbl^2 style coil with a tight gap and full aluminum sleeve? Even with the lowered amount of coil due to xbl^2 the fact that the gap tolerance is low and sleeve would dissapate heat I'd bet you a coil like that could still handle 1500+watts no problem. Combine that with a quiet suspension capable of say 35+mm excursion and you'd have a winner in my book.. Basically what I'm saying is AE speakers should go get a liscense to use xbl^2 coils lol.


The problem is that XBL is already inefficient in the use of flux as mentioned. To take off more steel on the pole and add a sleeve would greatly lower the motor strength. It would be extremely high in cost as the motor size would have to be increased. As i mentioned originally, non-linearities in BL affect only the sound pressure domain. Meaning things get quieter as the BL drops. The levels drop equally at all frequencies. BL non-linearity does not however affect the current being input to the driver or the impedance and as a result response curve of the driver like Le non-linearities. This is where things get to be a mess as some frequencies are affected more than others. This Le non-linearity is a nightmare for passive crossover implementation.

The thick gap plate, and long extended pole on the TD woofers give a nice broad BL curve. Yes, the BL does decrease with excursion, but it decreases predictably. It also stays the same as power is increased. There is little flux modulation and in reality at high power the TD motors will have MORE linear BL curves than most of the "linear" motor type drivers claim. 

Yes, something like XBL with a full copper sleeve on the pole could be even better possibly. Would it be worth the cost though? Figure the cost of something like a TD15 would have to be up-sized from a 2" coil to a 3" coil at minimum and would now be double in cost. A pair of the standard TD15's would still be lower distortion than one of these new drivers by a substantial amount, have twice more output capability, and cost the same. 

John


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## stryke23x (Jun 22, 2007)

bld 25 said:


> So the idmax with an inductance of 2.9 mH is just cosmetics then? Why is it the best subwoofer I have ever heard? I have owned:
> 
> infinity reference
> 3 different infinity kappas
> ...


Out of all the drivers listed above, I don't believe any have done anything other than a standard overhung coil. I don't believe any of them use shorting rings. They are all just standard overhung drivers. Someone correct me if i'm wrong on that. 

The old IDMax woofers that were very highly regarded had underhung motors. If you look at our paper we actually mention how underhung are ideal in many ways. Nearly flat BL curves as the coil never leaves the gap until high excursion. The core stays the same at all times so Le stays linear. Tight gap means flux modulation is cut to a minimum. However the flux still does move. Our Dipole woofers use an underhung motor with the full copper sleeve. The Lotus Group uses them in their Granada speaker which you can see here as well as reviews from this years Rocky Mountain Audio Fest.

The Granada Loudspeaker

The only drawback is that underhung is inefficient and you can't easily get a high motor strength woofer this way.

The new IDmax i don't know much about. What I can do is point you to a couple people who had them as well as other drivers who have put in our IB15's.

http://www.diymobileaudio.com/forum...ivic-lx-sedan-build-thread-36.html#post685715

http://www.diymobileaudio.com/forum...e-ib15-4ohm-car-version-idmax-comparison.html

John


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## sqshoestring (Jun 19, 2007)

Great post. A few years ago I had people telling me I was nuts for liking IB but it seems to be coming back. I can run quad cheap subs, never get to their xmax, and use low power to get pretty nice SQ using little space. Low xmax gets you out of so many driver issues, can use more efficient drivers long as they get low enough for you, and with that much cone area the output is not bad they can get kind of loud and reach deeper than many subs. 

I'll admit my quad 12s are a little bit too much, and too heavy with the infinity 1252s. I could have used a cheaper driver, but that just depends on what max output you need. These infinity sounded way too tight for me in a recommended sealed. While the qts is a little low they do perform well otherwise, just have to EQ the bottom up more. Inductance is 1.12 on these.
http://manuals.harman.com/INF/CAR/Boxes and Parameters/1252W.pdf

I love how crutchfield says no IB and in the manual Infinity says half of rated power for IB, duh. Half is 150rms, that seems right I can't get to xmax clipping on 100rms each. (what is power compression? LOL) That is far more output than my four doors can make even with the rears turned up, and they are EQ'd to get low, under 50hz to 20.

On the other hand I don't lend a lot of importance to distortion in the sub section in a car. Sure I don't want any, but a lot of specs for home audio just don't affect anything close to typical car audio. On top of that I like subs to play around 50 and lower so they don't localize, then it means even less. Can't always do that of course.

In a simple sense, if you don't push the sub they work much better just like not clipping an amp. The issue I run into is if you want to get 20Hz you need a lot more capability to move air. If you can't use multiple drivers/large drivers you will have to go to an expensive sub with big xmax and good specs. As I posted elsewhere, at times I ran 4 or 6 pyramid subs, the really cheap paper ones but I don't see them for sale anymore.


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## spork (Jul 1, 2008)

There have been some GREAT sounding cheap subs lately - I guess the cost of the more expensive ones is (like mentioend previously) more xmax, more power handling, etc.

The funny thing is, often times, a few of the great quality cheaper subs is usually louder, just as clean sounding - and overall cheaper than one nice sub.


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## thehatedguy (May 4, 2007)

Just FYI, IDMax motor hasn't changed designs and isn't underhung.

I'm glad to see someone in the industry finally saying XBL^2 isn't the best thing since sliced bread.


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## sqshoestring (Jun 19, 2007)

I found a lot of the pyle subs are low Fs and high Qts, good for IB, just not sure if I want to try one or not. They even have an 18".

Sometimes if you have good cabin gain a cheap and more efficient sub can really thump on lower power and still get low...I should say sub*s*. The pyramids I used were not the lowest Fs, they did roll off more, and seemed more capable the more I used.


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## thehatedguy (May 4, 2007)

Well when you are using multiples of subs, you really decrease distortion and other effects.


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## ItalynStylion (May 3, 2008)

thehatedguy said:


> Well when you are using multiples of subs, you really decrease distortion and other effects.


Seems quite logical to me. It's like having a single big strong guy carry a large object or 4 average joes each holding part of the same weight. The strong guy can do the work on his own but he's gotta reach a limit that's not likely comfortable. But 4 guys can do the work without breaking much of a sweat.


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## sqshoestring (Jun 19, 2007)

Low excursion = low distortion is what I find.


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## stryke23x (Jun 22, 2007)

thehatedguy said:


> Well when you are using multiples of subs, you really decrease distortion and other effects.


Yes, this is one of the best ways to lower distortion. Woofers have to move much less which keeps them working in a more linear range. This means lower variation of inductance, less variation of Bl, etc. The other big factor is that power is reduced to each woofer individually. This lowers thermal issues and even more importantly less current in the coil = less flux modulation.



sqshoestring said:


> Low excursion = low distortion is what I find.


There is some merit to this, but not just because you have a low excursion driver. Again flux modulation is probably the most critical cause of the more audible order distortions. Low excursion woofers will have small coils. The smaller the coil, the less the windings, the weaker the electromagnet the coil will become when energized and the less it can move around the permanent magnetic field. A lower excursion driver also has less power required to reach the limits. So a small coil with low power applied means flux modulation is lowered. 

John


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## Boostedrex (Apr 4, 2007)

thehatedguy said:


> Well when you are using multiples of subs, you really decrease distortion and other effects.


Exactly why I use multiple subs even though I don't ever ask for more output than a single sub could provide. I think that people need to play their drivers (especially subs and midbass) in a *REALISTIC* passband. That would eliminate lots of problems right there.


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## thehatedguy (May 4, 2007)

What, playing 6s down to 30 hertz is a bad thing?


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## chad (Jun 30, 2005)

thehatedguy said:


> What, playing 6s down to 30 hertz is a bad thing?


awww come one man :laugh:

What fun are you? :surprised:


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## thehatedguy (May 4, 2007)

That was with a 6 dB slope...lol.


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## chad (Jun 30, 2005)

you should have let them "naturally roll off" it's more pure.


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## Boostedrex (Apr 4, 2007)

thehatedguy said:


> What, playing 6s down to 30 hertz is a bad thing?


Exactly Winslow.  Haha, how did I know that you would chime in on that comment.


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## thehatedguy (May 4, 2007)

I had to use a 6 dB slope because it's the audiophile thing to do. :toff:



chad said:


> you should have let them "naturally roll off" it's more pure.


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## ItalynStylion (May 3, 2008)

thehatedguy said:


> What, playing 6s down to 30 hertz is a bad thing?





Boostedrex said:


> Exactly Winslow.  Haha, how did I know that you would chime in on that comment.


Are you guys talking about midbass's or subs? I've never had a problem with my 6.5" subs. I like mine 

Will be doing it again soon. I already have the subs in my room just waiting.


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## thehatedguy (May 4, 2007)

Midbasses


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## ncv6coupe (Oct 25, 2009)

Question for the more well informed here, What is the deal with sub manufacturers posting Spl numbers when they measure it a 1khz frequencies and don't post frequency response graphs? With that little info they give us we are forced to go by peoples opinions of what REALLY goes deep at the specified S.tupid P.ressure L.evel +or- whatever through its frequency response?

damn all that amplifier talk has me buzzing


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## chad (Jun 30, 2005)

speakers don't have a S/N ratio.


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## Boostedrex (Apr 4, 2007)

ItalynStylion said:


> Are you guys talking about midbass's or subs? I've never had a problem with my 6.5" subs. I like mine
> 
> Will be doing it again soon. I already have the subs in my room just waiting.





thehatedguy said:


> Midbasses


It was actually pertaining to both Steven. I was commenting on people who expect too much out of their midbass drivers (not everyone Winslow, just a lot  ) while not expecting enough out of their subs.


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## bassfromspace (Jun 28, 2016)

stryke23x said:


> Yes, this is one of the best ways to lower distortion. Woofers have to move much less which keeps them working in a more linear range. This means lower variation of inductance, less variation of Bl, etc. The other big factor is that power is reduced to each woofer individually. This lowers thermal issues and even more importantly less current in the coil = less flux modulation.



Two questions for you.

1. How does one standardize "linear range" across a variety of subwoofers?
The linear range for a W7 is different from a Pyramid Super Blue.

2. Does reduced distortion in the sub-range even matter due to increased distortion and a lack of sensitivity at these frequencies?


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## stryke23x (Jun 22, 2007)

ncv6coupe said:


> Question for the more well informed here, What is the deal with sub manufacturers posting Spl numbers when they measure it a 1khz frequencies and don't post frequency response graphs? With that little info they give us we are forced to go by peoples opinions of what REALLY goes deep at the specified S.tupid P.ressure L.evel +or- whatever through its frequency response?


A 1w/1m SPL figure is actually not a measured number at all. It is a calculated parameter based on measured Qes, Fs and Vas.

Efficiency is given as n0 = 9.64 * 10^(-10) * Fs^3 * Vas / Qes

Then 1w/1m SPL = 112 + 10 * log(n0 )

What this gives you is an SPL number based on the electrical parameters of the driver. Anywhere above where the cabinet rolloff begins and before the electrical rolloff due to inductance occurs, the driver will perform at this level. This doesn't however take into account things such as cone breakup, resonances, etc that may alter the efficiency over a short band.



bassfromspace said:


> 1. How does one standardize "linear range" across a variety of subwoofers?
> The linear range for a W7 is different from a Pyramid Super Blue.


Unfortunately there is no real industry standard or anything. Everyone does their own thing so nobody can really compare numbers. Klippel is one of the best options but still doesn't tell you everything. It can show where BL curves and compliance curves get outside a point where distortion should become audible based on fairly accepted "standards". It can measure distortion curves under some conditions based on excursion and frequency. Those curves give you somewhat of an idea, but don't necessarily tell a lot either as that doesn't represent how a woofer works under real world situations. 

In the real world you have various frequencies playing all at one time. The excursion created by a hit on the kick drum for example can make some huge changes to a note being played on a bass guitar higher up in frequency at the same time. To really see what is going on we'd need to look at the waveform of the kick drum and bass guitar first. Then record the wave that comes out of the woofer and compare the two. That will give you a real look at what is going on due to all the effects. You can measure distortion based on Bl non-linearity, flux modulation, inductance non-linearity, all under static conditions, but when you take them all into account under a measured situation you get a full picture. The amount of distortion is often magnitudes more than any of the models would predict.



> 2. Does reduced distortion in the sub-range even matter due to increased distortion and a lack of sensitivity at these frequencies?


It depends on the amount the signal is distorted. We have a local guy with a bunch of our TD18's. He previously replaced some really nice B&C 18TBX1000 with them. For fun he did a side by side comparison. Same exact enclosures, but different woofers. Keep in mind that Bl, Qts, Vas, etc are all very close as they were designed to fit the same need. We played one of the demo tracks I use a lot. Duende by Black Light Syndrome. Amazon.com: Black Light Syndrome: Bozzio Levin Stevens: Music At the beginning there is a short section where Terry Bozzio pucks some quick notes on the bass. Fundamental frequencies in the 40hz range I'd have to guess, while the overtones are going to be up towards the top end of where the subs cover. The B&C's reproduced the tones loudly, but you could not here any notes individually being played. It was like a rumble that changed frequency from note to note. The TD18's clearly reproduced the signal much more accurately. You could hear each note being plucked individually. 

One of the things that is going on is that they both reproduced the fundamental frequencies fairly accurately. However, the excursion created by these fundamental frequencies creates high levels of flux modulation in the case of the B&C as it has no shorting rings. This flux modulation completely distorts the waveform of the upper frequencies. While you could run a distortion sweep of the driver and get satisfactory numbers, in the real world the results aren't good.

An easy example we use for midrange drivers is to play a vocal track over a sine wave. Example would be a 60hz sine wave at high excursion over a male vocal being sung. With high inductance variation with excursion, Bl variation with excursion, and high flux modulation you will hear very clear modulation of the vocals. They get quieter and louder each time the driver goes in and out. You also hear other distortion effects. The same would apply to a woofer with high excursion on the low end and the upper bass region being greatly distorted.

John


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## npdang (Jul 29, 2005)

Aurasound sub was the only ones that have caught on fire when I Klippel tested them 
Seems like the metallic paint/coating they use in the gap heats up, bubbles and connects with the voice coil and ignites.

I maybe making this up as well, but I also believe that if you take a nearfield measurement (put the mic right up to the sub) of a sub and it doesn't have a "hump" between 60-120hz, then it has very low inductance (not to be confused with having a stable inductance vs. x). Quick way to verify.

I also recall that inductance isn't a large contributor to overall distortion performance in subwoofer frequencies... therefore not all that relevant. Very relevant for midrange performance though! Linkwitz and Klippel both wrote some wonderful stuff on this. I seem to remember that those old Lambda drivers with super thick copper sleeves and ridiculously low Le numbers weren't that great distortion performers, and the sensitivity was awful. 

Honestly, people IMO worry way too much about their subs. It's not a very substantial part of the music spectrum and generally we aren't that sensitive to distortion in that region either. What is horrendously difficult and what I would concern myself with are room interactions. Good quality bass is always about controlling the room (and not so much the sub). Most high quality subs today are cheap, work great (distortion performance sufficient for realistic/high spl levels), and can easily get the job done.

It mostly just comes down to budget and enclosures when picking your sub. My 2 cents.


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## bassfromspace (Jun 28, 2016)

stryke23x said:


> A 1w/1m SPL figure is actually not a measured number at all. It is a calculated parameter based on measured Qes, Fs and Vas.
> 
> Efficiency is given as n0 = 9.64 * 10^(-10) * Fs^3 * Vas / Qes
> 
> ...


Great info.

Thanks.


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## thehatedguy (May 4, 2007)

I'll have to check out BLS...Terry Bozzio is one of my favorite drummers.


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> I'll have to check out BLS...Terry Bozzio is one of my favorite drummers.












there's a lot of, uh, "talent" in the family


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## stryke23x (Jun 22, 2007)

npdang said:


> I also recall that inductance isn't a large contributor to overall distortion performance in subwoofer frequencies... therefore not all that relevant. Very relevant for midrange performance though! Linkwitz and Klippel both wrote some wonderful stuff on this. I seem to remember that those old Lambda drivers with super thick copper sleeves and ridiculously low Le numbers weren't that great distortion performers, and the sensitivity was awful.


I have a feeling you're talking about something substantially different than the Lambda drivers if you are talking about low sensitivity. They are known specifically for high sensitivity, high bandwidth, and low distortion. The TD15X,S and H are all right around 94dB1W range for example, much higher than most any other 15" "woofers" on the market. Augerpro recently did a bunch of testing on various pro audio drivers including various Lambda woofers and they did extremely well compared to all the high end drivers on the market.

Home (drivervault)

Overall inductance numbers are not necessarily important for a woofer. If you had high inductance but could keep the value stable and eliminate the flux modulation issue, the inductance alone would be a non-issue. You can EQ the response flat and correct for the time domain issues and everythign would be fine. 

The variance with excursion IS important especially if the inductance is high enough. As an example take the HE15 that we used to have made by TC Sounds. It was their standard 3HP motor. Very high inductance. Very long Xmax so it could move a lot of air but was also very high distortion. Inductance varied greatly with excursion. You can see the two extremes from high to low inductance over a given stroke plotted here.










From 70-80hz the change in inductance contributes to a 3dB difference in that range from the inward to the outward stroke. Therefore the driver moving at high excursion due to a lower frequency tone, creates this upper frequency fluctuation. Looked at another way, this inductance change is effectively doubling and cutting the current applied in half over and over with every stroke to create this 3dB difference. The distortion measured in a swept sine wave won't be effected because there isn't much excursion at those upper frequencies to give that fluctuation. However, do a swept sine while playing a 20hz sine at high excursion and the distortion goes up exponentially. 

Real world I can show you many examples of how inductance and the resultant effects in a woofer can give some very audible effects. The Black Light Syndrome track is one I have demo'd for many people. With cabinets right next to each other they don't know by looking which one is playing but can clearly pick out which one sounds better every time. A recent customer made the same comments on his AVS post here:

_The usual "Im hearing things I never heard" applies here. For example ,in Queens "We Will Rock You" everyone is familiar with the signature "Bump Bump - Thwack" beat of the song. Man I never realized there were tones and textures to the "Bump Bump" ! LOL It has always sounded like just a super dead single note before._

First Look - TD-18H+ - Page 2 - AVS Forum




> Honestly, people IMO worry way too much about their subs. It's not a very substantial part of the music spectrum and generally we aren't that sensitive to distortion in that region either. What is horrendously difficult and what I would concern myself with are room interactions. Good quality bass is always about controlling the room (and not so much the sub). Most high quality subs today are cheap, work great (distortion performance sufficient for realistic/high spl levels), and can easily get the job done.


I agree that the room is a big issue. No woofer/speaker can correct for issues in the room. If only I could get all the churches, recording studios, concert halls, etc that I work with to understand that. I see places spend $50,000 on a sound system only to put it in a large rectangular room with nothing but drywall and tile floor and then wonder why it doesn't sound good. 

As far as a woofer covering only a small range, I wouldn't go that far. We hear much closer to logarithmically than we hear linearly. That means that the 20-100hz range is just as big as 200-1KHz or 2KHz to 10KHz. It is in reality about 1/4 of the range we hear. The extent of content below 100hz is greater than the extent of content above 10KHz in most all recordings. Not only that, but consider what the content is in that range. Of course it depends on what you listen to, but a kick drum is primarily in that range except for the attack from the striker which is much higher. Toms, snare, tuba, trombone, bassoon, cello, bass guitar, harp, keyboard, piano, all have content below 100hz. Keyboard, bass guitar, and piano being the most critical. 

John


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## npdang (Jul 29, 2005)

John, my memory fails me these days... but for some reason I seem to recall that the Lambda drivers I had were not very efficient at all. I could certainly be wrong as it's been quite some time since I ordered from Nick... but I still remember how eager I was and how I couldn't stand how long it took him to build the drivers  I believe I still have distortion plots somewhere on my computer from years ago and from what I remember they were a bit better than some Focal subs I had, but did not come quite near to the comparably sized TC driver at the time. In fact I believe your own drivers do significantly better nowadays.

From my own experience, I'm still not a big believer that inductance variation is any significant contributor to distortion performance. Many Klippel tests show typically less than 10% contribution IIRC. Some of the best designs that I've tested and owned tended to have negligible mechanical noise, long stroke, and no shorting ring.

True as well, that we do distinguish sounds "logarithmically." However, I would not focus on how we separate the range of frequencies we hear so much as I would on where the bulk of the musical content typically lies. In that respect, the frequency range played by most subwoofers is really only a very small part of most music.


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## Nidec (Jan 31, 2009)

Hi dudes, i'm new here and quite interested by this subject.
From what i've understood, coil inductance non-linearity affects intermodulation distortion more than harmonic distortion. Perhaps this could explain why most measurements make high-Le woofers look better than they might be? Do Klippel tests rely on harmonic measurements only or IM too?


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## thehatedguy (May 4, 2007)

I'm not a speaker engineer, but I would want a speaker that was smooth and predictable outside of it's pass band. I would think the better it is outside it's operating band, the better behaved it would be inside. Maybe that's why I like for my subwoofers to be able to play midbass.


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## ItalynStylion (May 3, 2008)

thehatedguy said:


> I'm not a speaker engineer, but I would want a speaker that was smooth and predictable outside of it's pass band. I would think the better it is outside it's operating band, the better behaved it would be inside. Maybe that's why I like for my subwoofers to be able to play midbass.


Agreed. I think we're on the same page with regards to that.


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## bassfromspace (Jun 28, 2016)

npdang said:


> Honestly, people IMO worry way too much about their subs. It's not a very substantial part of the music spectrum and generally we aren't that sensitive to distortion in that region either. What is horrendously difficult and what I would concern myself with are room interactions. Good quality bass is always about controlling the room (and not so much the sub). Most high quality subs today are cheap, work great (distortion performance sufficient for realistic/high spl levels), and can easily get the job done.
> 
> It mostly just comes down to budget and enclosures when picking your sub. My 2 cents.


My sentiments exactly.

Music genre also plays a large part in this equation.


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## T3mpest (Dec 25, 2005)

thehatedguy said:


> I'm not a speaker engineer, but I would want a speaker that was smooth and predictable outside of it's pass band. I would think the better it is outside it's operating band, the better behaved it would be inside. Maybe that's why I like for my subwoofers to be able to play midbass.


Yup slopes aren't magic brick walls that stop sound. Even when crossing your sub relatively low alot of ppl would be suprised how much higher frequency contest is still audible.


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## sqshoestring (Jun 19, 2007)

T3mpest said:


> Yup slopes aren't magic brick walls that stop sound. Even when crossing your sub relatively low alot of ppl would be suprised how much higher frequency contest is still audible.


And can be a real pita with more efficient subs IB. They will blow over the LP badly.


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## DS-21 (Apr 16, 2005)

mikey7182 said:


> Thanks for the plug  They did sound amazing, as I heard they would. They took a bit to break in, which is something I normally don't subscribe to, and once they did, it was very hard to tell them apart from the current W15GTi, sans about the bottom half octave. Brian- I know of someone working on a pair of 2206, but not sure if his install is done.


I think a characteristic of good subwoofers is that they should converge sonically. And from my own listening, I can tell that when EQ'ed for equivalent response (verified by spatially averaged measurements) I can't tell the difference between the "supersubs" I own (and use at home - not in a car because that much capability isn't needed in a car), the Aura NS12, Exodus Maelstrom-X (Mk. I, which seemed to have much lower inductance than later models, though I've not heard or even seen one other than mine from any era), and JBL W15GTi, up to the limits of the driver with the smallest Vd. (The Aura, obviously.) If I ever get time, I'll re-run the test at higher levels, because now I also use an Aura NS15 at home.



Neil said:


> The W7 does not have shorting rings, nor does it have a split gap.
> 
> The W7 uses a long voice coil; typically, the longer the voice coil, the higher the rest inductance (must be cautious to distinguish between rest inductance and inductance with a change in coil position or change in amperage through coil). To combat this, JL uses less layers on the voice coil (I believe it's a 2 layer coil instead of the more typical 4 layer). This helps lower inductance at rest, and in turn the inductance variation (with current and position) is less offensive (so long as it does not vary wildly, which it doesn't).


The W7 also has very high inductance - almost to the levels of the old TC Sounds for Stryke HE15. And it sounds like it, too, unfortunately.



western47 said:


> I would urge people to look at some of the newer data regarding smooth bass response. In any pressure vessel; a car, home, barn; the more sources that you have in different locations the more even bass response you will have across the board. Every environment is a little bit different but a good general rule of thumb is to have as many bass sources in different places in your environment as possible. The caveat to this is that you would like to be able and control their output levels individually as some will excite certain modes more than others. I urge people to look at the works of Geddes and Welti as nothing differs from the home environment.


Well, sort of. The main benefit to multiple sources is smoothing out response not in the ULF, but in the modal region. In a typical car, that means below maybe 200-250 Hz. But I do think that a typical car with a bunch of good small sealed subs - say, 4-5 CSS Trio8's randomly distributed in three dimensions within a cabin - should have much smoother mid/upper bass performance than a typical car does. And it's in the 50-500 Hz range where cars sound so awful. The ULF performance is typically astounding even with crappy woofers.



Patrick Bateman said:


> I can't speak for Dan Wiggins, but I believe the reason that many of the XBL^2 woofers do not use shorting rings is that they're not intended to play above 500hz. For instance, the CSS full ranges use shorting rings AND XBL^2, but that's because they're designed to play to 20khz.


So far as I know, all of the modern ones currently available do have shorting rings. All of the Exodus ones do, and I know the Trio8 from CSS does, as well as their SDX15. The SI ones do too, I believe.


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## cvjoint (Mar 10, 2006)

This was a top notch discussion...continue...


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## Oliver (Jun 25, 2007)

What's it a l l mean , I'm so confused 


We can't get some people to tie both of their shoes and we would hope that they can read all of this and revel in the information :laugh:


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## Mack (Jul 27, 2007)

I'm glad someone brought this thread back from the dead as I've learned quite a bit from it. I've got to read through it a few more times to get my head around a few theories, but this is why I love Diyma!


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## Chaos (Oct 27, 2005)

Threads like this are what set this forum apart.


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## DonutHands (Jan 27, 2006)

Was just looking at the PDF files, the infinity says it has a LE of 1.12 but the post says 2.24. 

How does that work?


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## fish (Jun 30, 2007)

internecine said:


> Was just looking at the PDF files, the infinity says it has a LE of 1.12 but the post says 2.24.
> 
> How does that work?


I asked a similar question on another forum & this is the answer I received.

Well inductance is always a function of the resistance.

Let say you have 1 mH of inductance per coil and each coil is 4 ohms.
You will have 0.5 mH of inductance in parallel and a 2 ohms resistance.
You will have 1 mH of inductance if you wire a single coil and 4 ohms resistance.
You will have 2 mH of inductance in series and a 8 ohms resistance.

It's similar, inductance stays always in the same proportion versus the resistance, so don't worry, be happy ! 

Yes the inductance raises when you wire in series, but so does the resistance, so in the end you end up with the same thing.simon5 

Posts: 2058
Joined: Thu Dec 02, 2004 2:49 pm 
Private message


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## 60ndown (Feb 8, 2007)

im sure iasca will see a lot of $50 subs as a result of this awesome thread.


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## stryke23x (Jun 22, 2007)

cajunner said:


> I keep saying cobalt alloys, Permendur, Hiperco, etc. could bring the amount of flux density up towards the end of stroke, and you'd have several advantages that aren't expressed in the reduced B scheme


I looked into the options of using Permendur/Hiperco50, etc for the poles in some of our drivers. It is unfortunately not a practical option. First it is expensive. To do a standard pole for one of our 2" coil TD woofers would cost over $800 just for the Hiperco50 rod alone. Add in the fact that it's nearly impossible to machine and you'd have multiple hours on an OD grinder to get the pole to tolerance. Figure just the pole alone would be upwards of $1000. 



> you could adjust the curve simply by adjusting where the most flux passed... so if you have a lot more flux at the bottom of the gap in your standard design, instead of having a shorting ring you just put more flux on the top of the gap at the pole to compensate?


Keep in mind that these materials are only a medium for flux to travel through. They don't create any of their own flux. You could put the Hiperco50 at the top of the pole which would allow for more flux density in the material at that point than regular steel. In most cases though, the steel is never even saturated in the pole, so more density isn't going to change anything. Putting a more magnetically permeable material there doesn't change the flux density without other changes. The flux has to come from somewhere. The flux will have to travel all the way up through the pole which is still low carbon steel. Flux in the Hiperco50 could never be greater than the amount of flux that is in the steel around it. The biggest benefit of Hiperco50 is in the reduction of flux modulation because it is less electrically conductive. 

John


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## bassfreak85 (Jul 26, 2009)

double post...


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## bassfreak85 (Jul 26, 2009)

stryke23x said:


> I looked into the options of using Permendur/Hiperco50, etc for the poles in some of our drivers. It is unfortunately not a practical option. First it is expensive. To do a standard pole for one of our 2" coil TD woofers would cost over $800 just for the Hiperco50 rod alone. Add in the fact that it's nearly impossible to machine and you'd have multiple hours on an OD grinder to get the pole to tolerance. Figure just the pole alone would be upwards of $1000.
> 
> 
> 
> ...


i have a easy solution to saturate the pole peace easily and practically without increasing cost by much..
i firmly believe that its not a motor topology problem in high powered woofers its power compression.. the next huge leap will be to find a way to A keep the coils cool as possible and find a way to increase power handling in the drivers.. the next step is how to increase xsus without sacrificing linearity or integrity/stiffness.. 

also important is keeping the flux focused where you need it and keeping the lines of magnetism perpendicular..
another thing that is becoming increasingly important is inductance and its variance in these high powered high xmax drivers(ESP in mid range and mid bass drivers).. adding shorting rings will only do so much.. hence if we can get a glue to beable to withstand temps of 1000f you could effectively use a coil much smaller to reach a give output.. SQ is no longer at 100DB.. we are push the boundaries and very soon speakers will be in a new era of design and maybe even function..

while power compression on first look only limits output capability its clear it goes much deeper than just output.. as the coils heat up the impedance as well as inductance rises and the L or potential strength from the coil goes down.. so no matter how linear you physical motor strength is if the coil is too hot to reach those physical limits its about as good as buying a gun and not being able to buy bullets..


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## bassfreak85 (Jul 26, 2009)

honestly its much cheaper to use 1008 and neo i promise you i cna get any pole peace saturated with neo or alnico magnets..

also as for under 100hz your barin can be trained.. just most poeple do get to experence it often but any well seasoned competitor will disagree.. strangely enough after years of SPL competition i have an ear for ever the slightest changes whether it be closing in on 20khz or 20hz.. in fact its been proven some people can hear as low as 3hz.. and its not uncommon for people to beable to hear as low as 10hz with 130+db..


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## bassfreak85 (Jul 26, 2009)

cajunner said:


> some of this is contradictory, we're talking about inductance distortion, not inductance in and of itself, the magnetic field moving in response to the coil's field is inductance-related, as is illustrated in several threads on this site.
> 
> Having flux in the gap modulate due to the moving field of the coil, is where it all comes together. You control the gap, saturate the pole and it's much harder to develop all those intermodulations that arise due to a non-static flux field.


well i wanted to explain what inductance is and is responsible for..
inductance simply limits how fast the can can saturate and vice verse..

modulating flux is most often a problem with stray flux fields like those outside the gap hence using faraday rings that exceed the length/height of the gap greatly reduces modulation.. you can limit this as you said by offering a tight gap and smaller gaps as well.. but its alot more complex that simply that..
im not sure waht you mean by thats where it all comes together.. as in the EMF generated is a by product of inductance and flux saturation(ie B and more specifically L?) the key to a great woofer is using as much b as is necessary is simply because of the motor strength we can achieve now IE you can have less inductance for a give motor strength by increase flux saturation.. any time you have 2 magnetic fields your not going to get perfectly perpendicular flux fields as your going to have tiny "air gaps" where the flux isn't ideally out of phase 90 degrees.. its hard to explain without a pic.. this is where the faraday rings takes those out of ideal phase forces and absorbs them..


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## cvjoint (Mar 10, 2006)

Well there are two schools of thought. On the one hand we have Klippel and his experiments which show inductance distortion is third most important. Than on the other hand we have the 'flux is always important' claiming there are other dimensions we're not looking into. 

IMO, there is sizeable proof that above 50hz inductance management becomes important. The inductance variation will be exhibited in inward/outward stroke variations, and overall inductance will act as a LP filter. This SHOULD be relevant for 99% of the car audio setups. SHOULD is key, because car audio users heavily underestimate how hard it is to get adequate output down to 50hz from drivers up front. A minimum of a pair of 10" drivers and a very sturdy baffle will do it. 

Secondly, while there is not a lot of material sub 100hz, it is very cherished by the listener. I would say the average subwoofer is asked to keep an output level that is 10db higher than the midrange. Even if you roll off the sub at 50hz 24db slope it will still bring in lots of higher end punch. 

Then you have the Dayton reference. Why on earth would they created the HO and HF versions, reducing the coil mass in the HF? Not only does it have shorting rings, and lots of it, Dayton feels the need to reduce coil mass on top of it. It seems like a ludicrous thing to do considering higher chance of overheating/warranty issues etc, unless of course it does matter.


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## bassfreak85 (Jul 26, 2009)

look up howard johnson permanent magnet motor and read some of his ideas..


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## bassfreak85 (Jul 26, 2009)

you can treat the voice coil as a load and the permanent fringe field as a line.. a motor(electromotive and magnetic) is different because you creating a constant flow between your north pole and south pole(think water flow) an the coil acts like north only or south only(monopole via electron flow in one direction or multi pole if alternating)..

not only to you have inductive lag/lead you have magnetic lead lag as well but thats another story.. point is you cannot just look at the inductor and its flux field but both..
what i meant is when you get those alterations because you have a electromotive field it has to be accounted for.. IE the faraday helps absorb those weaker fields produced by the coil(via induction) while they so little to address magnetic induction its not a issue in the frequency bandwidth but it can be of importance..
and the weaker field that do escape the permanent flux field are also adsorbed as well.. but what i was gettng at is once in motion you line of flux are going to remand 180 degrees out of phase the phase will change causing problems.. this is what the fardays help address as well as back EMF even in-between signals can create havoc on transient response.. when a signal is player ideally you want the driver to return to rest fast as possible while not sending the amp a signal.. 

plain and simple the lower the inductance and its variation the better.. although i might add a properly design amp will require more feedback so to speak for a give amount of distortion..


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