Interesting 12" woofer with adjustable Qts

[Pete B]

I often check the moving mass and Rvc when looking at new woofers and noticed that this 12" has a cone mass of 119g and Rvc of 2.8 ohms. The cone mass is slightly higher than the AR-3a woofer but this should compensate for the slightly stiffer suspension since it has an Fs of 23.2 Hz. Rvc is also close enough to the AR-3a woofer. It has nearly 3 times the Xmax with 18 mm one way making it a very significant upgrade. It also has a curvilinear cone to provide a smoother response in the pass band but of course actual measured response will determine if they achieved this goal. It has a second smaller voice coil that provides an amount of damping dependent on the resistance loaded across it. These will not fit in any of the applications that require the side flats but they might fit the AR-9 or a from scratch copy or new design. Here's a link:

http://www.ascendantaudio.com/Atlas%2012.htm

I'm certain that there's an error in their measurement of T&S parameters and I've (PB2) started a discussion about it here:

http://www.diyaudio.com/forums/showthread.php?threadid=56552

The extra voice coil wastes some magnetic gap energy and I question if this is the right way to go, it is interesting to look at in any case.

Pete B.

[Pete B]

They seem to be rebuilding their site, here's the archive:

http://www.ascendantaudio.com/archive/Atlas%2012.htm

[soundminded]

These look like some really fine drivers to me. Especially intriguing was the 18" Avalanche in a 7.5 cu ft enclosure. I just happened to be in Home Depot in South Plainfield yesterday and they had 2' x 4' 1/2" and 3/4" mdf precision precut for cheap. You could easily build an enclosure of this size from five of them around a frame of say 2" x 2" quickly and cheaply or double up on the 1/2" mdf for a really stiff cabinet (the 1/2" were about $7.50 each. so ten would run $75.) Of course it would weigh a ton. Looks like a project you'd build in the basement and keep in the basement. I wasn't clear if the response curves were for a ported or a sealed enclosure, I assume it was sealed and there was an error on the web page with the link. It is only down 7db at 20 hz from about a 90 db output at 100 hz (midband for this driver) hinged at about 40 hz. This should make one hell of a subwoofer. Would it equal or outperform an AR9????? Maybe. Any thoughts Pete?

http://www.ascendantaudio.com/archive/Aval...led%20graph.htm

BTW, AR9 woofers do have truncated flat sides just like the other AR 12" drivers so this 12" is really no more of a drop in substutute for that speaker than any of the others. Price is about the same. Also looks like another really fine driver. How do you think it would compare with the Tonegen 1259?

[Pete B]

New issues with the company:

http://www.diyaudio.com/forums/showthread....&threadid=56659

[Pete B]

Yes I do think one of those 18s would outperform the pair of 12s in the AR-9. I'm not sure if you'd plan for one of these 18s for each side? That would be a lot. I do like stereo subs and to have them close to the main speakers. I'd probably go with a pair of the newer very long throw 15s for a wall shaker sub, since I've been trying to reduce the size of my latest speakers.

7.5 cuft is huge I see that you say it'd be a basement speaker and I agree. Yes precuts are a nice idea especially for a quick prototype.

Is there a physical obstruction that requires the flat sided 12" with the 9s? That would be unfortunate.

Most call it the NHT 1259 even if it is made by Tonegen. The 1259 is a dated design, however some say that it is "better" in practice than some of the competing 12s that look better on paper. I think this driver is probably better but one would have to measure and listen. The Shiva 12, also a dated driver, was outperforming the 1259 in specs and measurements many years ago. But I always like to give a listen, in A/B comparisions because it's hard to predict the perceptual weighting of different measurements, especially distortion.

Pete B.

>These look like some really fine drivers to me. Especially

>intriguing was the 18" Avalanche in a 7.5 cu ft enclosure. I

>just happened to be in Home Depot in South Plainfield

>yesterday and they had 2' x 4' 1/2" and 3/4" mdf precision

>precut for cheap. You could easily build an enclosure of this

>size from five of them around a frame of say 2" x 2" quickly

>and cheaply or double up on the 1/2" mdf for a really stiff

>cabinet (the 1/2" were about $7.50 each. so ten would run

>$75.) Of course it would weigh a ton. Looks like a project

>you'd build in the basement and keep in the basement. I

>wasn't clear if the response curves were for a ported or a

>sealed enclosure, I assume it was sealed and there was an

>error on the web page with the link. It is only down 7db at

>20 hz from about a 90 db output at 100 hz (midband for this

>driver) hinged at about 40 hz. This should make one hell of a

>subwoofer. Would it equal or outperform an AR9????? Maybe.

>Any thoughts Pete?

>

>http://www.ascendantaudio.com/archive/Aval...led%20graph.htm

>

>BTW, AR9 woofers do have truncated flat sides just like the

>other AR 12" drivers so this 12" is really no more of a drop

>in substutute for that speaker than any of the others. Price

>is about the same. Also looks like another really fine

>driver. How do you think it would compare with the Tonegen

>1259?

[tysontom]

>I often check the moving mass and Rvc when looking at new

>woofers and noticed that this 12" has a cone mass of 119g and

>Rvc of 2.8 ohms. The cone mass is slightly higher than the

>AR-3a woofer but this should compensate for the slightly

>stiffer suspension since it has an Fs of 23.2 Hz. Rvc is also

>close enough to the AR-3a woofer. It has nearly 3 times the

>Xmax with 18 mm one way making it a very significant upgrade.

>It also has a curvilinear cone to provide a smoother response

>in the pass band but of course actual measured response will

>determine if they achieved this goal.

>The extra voice coil wastes some magnetic gap energy and I

>question if this is the right way to go, it is interesting to

>look at in any case.

>

>Pete B.

Aside from the incompatibility in mounting this Atlas 12-inch woofer in any of the AR flat-side speaker enclosures -- which run from the AR-1 up through the AR-9 and beyond -- the big problems seem to be: (1) it is a purpose-built subwoofer driver, and is probably not optimized to go up into the 500 Hz range without difficulty, (2) the Fs is actually 1/3 to 1/2 octave higher than the standard AR woofer, so that the unequalized system resonance would therefore be higher than the standard AR-3a rendering the speaker a "bass-thin" character compared to the standard woofer. Even though it migh have lower distortion, the FR would likely be all over the map and very difficult to optimize to the AR-3a crossover without coil changes and so forth. The "curvilinear" cone really has little to do with smooth band-pass response, but more to do with keeping the diaphram rigid, "piston-like" for low-frequency excursions. It might keep the Atlas response cleaner down in the subsonic region, but probably little else. As you noted, one would have to see the frequency response to see how well it performs at the higher bass frequencies.

The idea of gettin a woofer to provide longer excursions and potentially greater bass output and less distortion is certainly appealing. I went through this same ordeal with the NHT 1259 driver in the AR-303a. With great promise, it fits fine, has approximately the same resonance as the standard 303 woofer, but would not optimize to the speaker enclosure and crossover. Although the NHT 1259 has over twice the Xmax as the standard 303 woofer, the net result was a much better balance with the original woofer. It was going to require a re-design of the crossover, but even then the woofer was not as smooth above 200 Hz. as the original, and in my experience the improvements in the lowest octave were not even audible unless you ran the speaker to very high levels.

--Tom Tyson

[soundminded]

The AR9 cabine has its sides routed to allow the AR 12" driver to sit recessed with its front lip flush with the cabinet but the grillcloth is mounted externally and even has a 12" round opening so an adaptor to allow a 12" round driver to be mounted in it would not take much effort or be an eyesore. There is also sufficient clearance and no frame molding as with AR3 or AR3a to prevent a slightly larger woofer frame from being used. AR9 crosses its woofers over at 200 hz so the lack of any response above that frequency would not be a problem either. There may be electrical differences requiring modification or even abandonment of the AR woofer crossover section but again this should not be a problem. In fact it's easy because the speaker system is set up for bi amplification so an outboard woofer crossover or even an active electronic crossover is very feasible. Perhaps this is one driver you could try Pete for your own version of AR9. Personally, if I ever had to replace one of the drivers in my AR9s, I'd go for an exact replacement. The bass performance of this speaker continues to amaze me. It's absloutely room shaking when the program material has suitable low frequency content. I sometimes wonder if I haven't gone a little too far equalizing it. When you consider that this design is nearly 30 years old, that the principle is fifty years old, and you listen to the competition, they are nothing short of pathetic. I just can't understand why they haven't caught up.

The AR woofer has an effective cone diameter of 8 inches making the pair of woofers in an AR9 have an effective surface radiating area of 32pi square inches. Even if the Avalanche 18" woofer has an effective cone diameter of only 14", that would give it an effective radiating area of 49pi square inches so a single Avalanche woofer would displace half again as much air as an AR9 for the same excursion. A single 18" woofer per channel would be more than adequate for most installations. Whether to mount it on the front or side is a different question. Reading Tim Holl's explanation of how the phase cancellation problem in the crossover region between the woofer and lower midrange in AR9 was solved makes a strong case for side mounting. I agree Pete that having one subwoofer for each channel and keeping it close to the main speakers makes far more sense than only one for an entire system. With only one, I don't see how it is possible to avoid serious phase interference and therefore frequency response irregularities in the crossover region.

[Pete B]

>The AR9 cabine has its sides routed to allow the AR 12"

>driver to sit recessed with its front lip flush with the

>cabinet but the grillcloth is mounted externally and even has

>a 12" round opening so an adaptor to allow a 12" round driver

>to be mounted in it would not take much effort or be an

>eyesore. There is also sufficient clearance and no frame

>molding as with AR3 or AR3a to prevent a slightly larger

>woofer frame from being used.

Thanks Soundminded now I understand why it doesn't drop in, looked like it would.

Pete B.

[Pete B]

Well Tom I wondered how long it would take for you to join in with your usual it can't possibly work attitude. I'll offer a few comments but this is getting tiring:

>Aside from the incompatibility in mounting this Atlas 12-inch

>woofer in any of the AR flat-side speaker enclosures -- which

>run from the AR-1 up through the AR-9 and beyond

I already stated this and was thinking possibly the AR-9 as Soundminded clarified.

-- the big

>problems seem to be: (1) it is a purpose-built subwoofer

>driver,

Yes, it is purpose built to be GENERAL purpose, the parameters that are not adjustable AND ARE IMPORTANT are close to the AR values.

and is probably not optimized to go up into the 500 Hz

>range without difficulty,

The manufacturer states that it DOES have a smooth upper range, your guessing again, I'll wait to see measurements.

(2) the Fs is actually 1/3 to 1/2

>octave higher than the standard AR woofer, so that the

>unequalized system resonance would therefore be higher than

>the standard AR-3a rendering the speaker a "bass-thin"

>character compared to the standard woofer.

Have you ever simulated the low frequency response of a woofer, your statements suggest not. Fs is not a strong indicator of in box performance in high alpha systems. I suggest that you simulate before jumping to conclusions. The driver has variable Qts allowing Qtc to be adjusted to avoid a "bass-thin" response.

>Even though it

>migh have lower distortion, the FR would likely be all over

>the map and very difficult to optimize to the AR-3a crossover

>without coil changes and so forth.

This is alarmist speculation.

>The "curvilinear" cone

>really has little to do with smooth band-pass response, but

>more to do with keeping the diaphram rigid, "piston-like" for

>low-frequency excursions. It might keep the Atlas response

>cleaner down in the subsonic region, but probably little else.

I suggest that you do some research, the truth is the opposite of what you claim.

Here's a quote from the web site:

"What makes this possible is the curvi-linear cone profile. Due to its shape, we can use a lighter cone that still remains very stiff. The shape also pushes unwanted breakup modes further out of the driver's bandwidth."

> As you noted, one would have to see the frequency response to

>see how well it performs at the higher bass frequencies.

>

>The idea of gettin a woofer to provide longer excursions and

>potentially greater bass output and less distortion is

>certainly appealing. I went through this same ordeal with the

>NHT 1259 driver in the AR-303a. With great promise, it fits

>fine, has approximately the same resonance as the standard 303

>woofer, but would not optimize to the speaker enclosure and

>crossover. Although the NHT 1259 has over twice the Xmax as

>the standard 303 woofer, the net result was a much better

>balance with the original woofer. It was going to require a

>re-design of the crossover, but even then the woofer was not

>as smooth above 200 Hz. as the original, and in my experience

>the improvements in the lowest octave were not even audible

>unless you ran the speaker to very high levels.

Did you measure as you demanded for my AR-2ax experiment?

Voice coil inductance is very different between the two drivers and yes the crossover would have to be adjusted, not a complete redesign. Off course you'd have to drive it hard or use very low frequency test source material to hear the difference because these are situations where the long throw is needed.

Pete B.

[ar_pro]

WACFA !

Three questions, Petey:

1.)Did you get pushed around alot in school?

2.)How much do you want to buy back our introduction to you?

3.)"If yer so smart, why ain't you rich?"

[Pete B]

Mark, how long do I have to put up with this "person"?

>WACFA !

>Three questions, Petey:

>1.)Did you get pushed around alot in school?

>2.)How much do you want to buy back our introduction to you?

>3.)"If yer so smart, why ain't you rich?"