Aura Sound ns12-794-4a 12" sub

[npdang]

A big big thank you to Werewolf for donating this driver!

Aura is famous for their low distortion, lightweight compact neo radial motors. It consists of an underhung design with copper faraday rings above and below the pole, as well as a ring of neodymium magnets. It's time to put one to the test and see how this driver performs.

First look shows a solidly built driver with an attractive aluminum cone and large vents both under the spider and through the pole in the back. You can also see the copper ring atop the pole piece and grilles to prevent debris from entering the motor.

Unfortunately, you can also see that the neo magnets appear to be nickel plated... not such a good idea with the magnets facing in toward the gap and high temperature in that area during operation. During Klippel testing the plating bubbled and shorted against the coil at about +100 K temp. change and ~200w, causing a nice display of sparks to fly from the driver and a very nasty rubbing sound. I managed to open up the driver and remove the bits that had fallen into the gap and chip of the remaining pieces that were still stuck to the side. Luckily, the motor was easy to disassemble and repair.

http://diymobileaudio.com/pics/aurans12/aura1.JPG
http://diymobileaudio.com/pics/aurans12/aura2.JPG
http://diymobileaudio.com/pics/aurans12/aura3.jpg
http://diymobileaudio.com/pics/aurans12/aura4.jpg

Klippel results:

http://diymobileaudio.com/pics/aurans12/bl.JPG
http://diymobileaudio.com/pics/aurans12/cms.JPG
http://diymobileaudio.com/pics/aurans12/le.JPG
http://diymobileaudio.com/pics/aurans12/dist.JPG
http://diymobileaudio.com/pics/aurans12/ts.JPG

Overall excellent results. Good symmetry, flat extended plateau, and an LE much much lower than most 7" drivers! T/S parameters look well suited to either ported or sealed enclosures.

For the $500+ that this driver costs, it's perhaps not the best bargain out there in terms of displacement. However, there's no arguing that it's certainly a very high performance driver. The powerhandling is a bit of a concern, but keep in mind Klippel testing is quite demanding with a heavy duty cycle. Aura rates this driver for 400 watts and with music that shouldn't be a problem at all. The low inductance is also something that's unique to a driver with this kind of output capability. This is nice, in that most drivers with an inductance over 1mh tend to have a noticeable bump in the frequency response between 60 and 120hz... something noticeably absent in the Aura sub.

[kappa546]

awesome. i hear these can be driven up to 500hz with no adverse effects whatsoever. finally results are posted on this gem

[bdubs767]

makes me feel good abotu buying one :) How hard is it to take that consmetic piece off to make sure the motor is fine? Just take those simple set screws out?

[werewolf]

You know, thanks to our kind host's recent tests, i've developed a new-found interest in understanding subwoofer thermodynamics a bit more. And it's not just because he comes dangerously close to burning up every sub i send him ... LOL !! :D

I recently downloaded JBL's patent on the WGti technology, hoping to read more about the distortion properties of the "differential drive" technology. Instead, the patent talks primarily about the thermal benefits ... very interesting stuff!

A sub's electrical and sonic performance don't amount to much, if it dies an early death due to poor heat dissipation :(

[npdang]

Yep, just remove the screws.

[werewolf]

... and btw, heat is no friend to neodymium :(

[npdang]

You know, thanks to our kind host's recent tests, i've developed a new-found interest in understanding subwoofer thermodynamics a bit more. And it's not just because he comes dangerously close to burning up every sub i send him ... LOL !! :D

I recently downloaded JBL's patent on the WGti technology, hoping to read more about the distortion properties of the "differential drive" technology. Instead, the patent talks primarily about the thermal benefits ... very interesting stuff!

A sub's electrical and sonic performance don't amount to much, if it dies an early death due to poor heat dissipation :(
It's quite a sight to see... literally fire coming out of the back of the motor :) Thankfully, the coil was still in perfect condition and it just required a bit of cleanup work to remove all the little metal pieces in the gap.

I forgot to mention the magnet finish blew out on 3 separate occasions... after that I set the temperature limit to about 100k and it was fine with that, although I wasn't able to get past ~50% bl as you can see.

[bdubs767]

hmmm...w15gti when do you want it? This is looking to be a show down between gti and aura ns :o


Since I now own both an Aura NS 15" and JBL W15GTI MKII I may have to do a subjective showdown....which IMO means jack compared to dangs objective testing but hey...Ill give what I can.

[kappa546]

so the w10gti is up next. cant wait for that.

[werewolf]

It's quite a sight to see... literally fire coming out of the back of the motor :) Thankfully, the coil was still in perfect condition and it just required a bit of cleanup work to remove all the little metal pieces in the gap.

I forgot to mention the magnet finish blew out on 3 separate occasions... after that I set the temperature limit to about 100k and it was fine with that, although I wasn't able to get past ~50% bl as you can see.

I'd like to request a new addition to your Klippel tests of subs ... you gotta take videos and post them on youtube !!!!

[legend94]

It's quite a sight to see... literally fire coming out of the back of the motor :) Thankfully, the coil was still in perfect condition and it just required a bit of cleanup work to remove all the little metal pieces in the gap.

I forgot to mention the magnet finish blew out on 3 separate occasions... after that I set the temperature limit to about 100k and it was fine with that, although I wasn't able to get past ~50% bl as you can see.

are you ready to test my GTi1200? if so ill send it to you if you wont set it on fire :)

[technobug]

It's quite a sight to see... literally fire coming out of the back of the motor :)

SWEET!

FIRE!...HEHEHE:D

I wanna hang a pair off the bumper of my truck. Should add to my famous smokey burnout show.:p

[technobug]

I'd like to request a new addition to your Klippel tests of subs ... you gotta take videos and post them on youtube !!!!


YES!
X2

Let's grenade my WGTi and get it on video! :D

[SteveLPfreak]

Great info and review. Can't wait to see the WGTI's. Thanks for all your work, NPDang.

[cajunner]

I'm not sure how hard it is to get neo unplated, but I have a sneaking suspicion it's mainly used for corrosive protection, I was wondering if the plating is the shiny bright nickel or the black high emissive type, could make a difference. I imagine the cost cutters had to make a call if the engineers couldn't see a difference, magnetically, but I believe the raw neo iron substrate is subject to high corrosive formations due to the temp variance in the automobile.

I don't think the pro driver 18 has this thermal remanence snafu, perhaps it's indicative of a different ring mag mounting or if there's some faraday work there that's absent at the 794 and 99? levels, and the 5?? levels on the order of a copper sleeve or aluminum heatsinking, or maybe just better venting, I know my MR's have holes in the cone, and I play the crap out of them in an old diesel with no deadener, and they just won't keel, sometimes for hours and you can tell when the sound starts it's fade it's not just your ears, but it takes a concerted effort to get there.

I always wondered what would happen if the neo radial structure was put on a flat honeycomb of suitable thickness and used in the resonant profile of a vehicle, I understand the wave propagation off a piston to be more conducive to recreating the perfect profile, bass-wise, but it would have to be hella big to raise efficiency... now with a dual geometry like JBL, or the LMS, or even the XBL advances, is it really advantageous to have the neo-radial bug?

I guess what I'm asking is if the neo-radial design has an inherent flaw in it's thermal properties when asked to pass kw's to pressurize a chamber? Due to the neo being right up against the coil?

[cajunner]

hahaha, I never wait for graphics on this cell modem connect, but now I see the shiny nickel plate....

I hate to say it, but couldn't they have made it better?

[colt45]

Nice review!
Does anyone know if it's possible to run this driver without the magnet cap on the back?
If so, how much mounting depth would be saved without the cap on?

Thanks
Steve

[thadman]

Am I reading the distortion graph right? (severe distortion above 150hz). I thought these were able to be used quite high in frequency, or is that capability only possessed by their little (less xmax) brothers?

[Tommythecat]

Look at the graph again - its a time based distortion test with no clear input. It can basically show you which factors (bl, kms/cms, le variation) are causing relative amounts of non-linear distortion.

[npdang]

You're reading it wrong :) The x axis is not freq. it's time.

[thadman]

You're reading it wrong :) The x axis is not freq. it's time.

I looked in your guides to interpreting data and that specific graph type wasn't mentioned. I'm lost to some extent...how does the value of time add anything substantial? 600 seconds is 10 minutes. I hate to feel like I'm wasting your time on something obvious and fundamental, but I'm having difficulties with it at the moment. How would I interpret that?

With that said, I see no distortion graphs vs frequency. How high can you take this driver before distortion starts to creep in for critical listening (I've heard this driver's distortion decreases as frequency increases...which is the inverse of most available drivers). How far does this trend extend in frequency in the non-linear and linear distortion department?

[werewolf]

by the way .... 100 degrees K is pretty darn chilly in my book ;) :p

[thadman]

by the way .... 100 degrees K is pretty darn chilly in my book ;) :p

Yeah, isn't 0* celsius = 273* kelvin?

Were you measuring it at night on Mars? Ahah

[werewolf]

actually, the report is at a 100 degree K temp change (probably from room temp), which is equivalent to a 100 degree C temp change ... which is equivalent to something in degree F .... :)

EDIT : 100 degree K temp change = 100 degree C temp change = 180 degree F temp change (had to refresh the aging memory)

[Abaddon]

EDIT : 100 degree K temp change = 100 degree C temp change = 180 degree F temp change (had to refresh the aging memory)

= 180 °R change

:P

[werewolf]

seriously, it's no secret that i absolutely love these Aura subs, but ...

This wonderful little driver has a 1 layer coil, with 15.4mm of winding length. We know the coil DC resistance is 3.5 ohms ... which means the wire gauge, total mass and total area can be calculated (OK, it's a 79.4mm diameter coil so the area part is easy to calculate :) ) ... bottom line, this coil will probably have some trouble dissipating lots 'o heat :(

And it seems that 200 Watts input raised the coil temp by 100 degrees C/K ... under perhaps some extreme conditions (meaning, i don't know the duty cycle, or thermal time constant of the coil assembly).

But it is interesting to note a rather large number of drivers, including the newer Aura subs, with multi-layer coils (i think the newer Auras have 4 layers, kinda seems to be "all the rage" nowadays). Now i know, heat dissipation involves more than the coil mass ... different formers are better at conducting and dissipating for example. And, more layers means more mass and probably not as tight a gap.

Guess the conclusion is that monster power handling is not this sub's forte. I wonder if McIntosh is having any field failures in their new flagship/statement line arrays? :)

[thadman]

With all that said, how high can you take these?

[npdang]

I looked in your guides to interpreting data and that specific graph type wasn't mentioned. I'm lost to some extent...how does the value of time add anything substantial? 600 seconds is 10 minutes. I hate to feel like I'm wasting your time on something obvious and fundamental, but I'm having difficulties with it at the moment. How would I interpret that?

With that said, I see no distortion graphs vs frequency. How high can you take this driver before distortion starts to creep in for critical listening (I've heard this driver's distortion decreases as frequency increases...which is the inverse of most available drivers). How far does this trend extend in frequency in the non-linear and linear distortion department?
I don't know... you'd need a distortion vs. freq. plot which I don't have. It's kinda tricky getting an absolute distortion measurement for a sub.

[the other hated guy]

With all that said, how high can you take these?

the question should be ....why do you need to cross it over higher than 80-100hz?

[kappa546]

home audio.