[Danny Richie]

If you take the mass of the driver diaphragm and coil and divide by the area of the driver diaphragm, one should be able to compare any two drivers.

The MFW-15 Turbo driver has .252 g of moving mass per sq cm.
The GR-Research SW-12-04 driver has .283 g of moving mass per sq cm.

It doesn't work that way. You don't get meaningful data dividing the moving mass by displacement.

If you want to look at it that way then a Mini Cooper is heavier than a bus. So the bus should be able to stop faster. No, the bus is still much heavier and much harder to stop.

And a heavier driver will always have more stored energy. It has a higher mass in motion.

Now lets take a heavy driver, the FI SP4 18D1 18" driver. It has .478 g of moving mass per sq cm. That is almost double the other subs. A waterfall chart accurately shows the settling or decay time of a driver. It shows how fast it returns to rest after the signal is removed.

You can see that the heavier driver returns to rest across the frequency range a little faster than the Rythmik driver with its servo control. The reason is that the motor of the heavier driver is so much stronger that the weight increase is easily overcome and doesn't affect the settling time.

This is data taken in a way as to not give any meaningful or accurate results. Measuring a csd below 500Hz or so is very difficult. It really needs to be done in an anechoic chamber and at distance. There is no industry standard in making these measurements and they can easily be manipulated with distance and power levels.

The only thing you can really conclude from those measurements is the frequency response. One is very linear and on is not. That's very obvious.

[Danny Richie]

Again, thanks for all the great feedback, everyone. The OB dual sub option is starting to appeal to me more and more, especially if I could enlist the help of some locals in the build. I'm not finding any kits or instructions on the GR Research website. Danny, or others, could you direct me to the designs/instructions, or to where I could order flat pack for the cabinets?

One of my local buddies is Wayne (WGH), and he makes some really fine fancy doors for a living. I bet he could help me gussy up an H frame with some great veneer, maybe even some local mesquite.

If you look at the bottom of the page for the SW-12-04 then you will see a couple of different cabinet plans and a link to some pictures of the sand box during assembly.

If you look at the bottom of the SW-12-16FR driver page you will see plans for an H frame and a W frame open baffle design.

[genjamon]

Thanks for the guidance to the plans, Danny. Didn't realize I needed to get I to the driver pages to find the pans for cabinets.

As for the debate between the large driver/large magnet vs the lighter driver/probably lighter magnet issue, it seems to me we're talking past each other a bit. While I agree, buses in general are not going to have comparable stopping distances to a Mini Cooper, what if the bus had the same breaking resistance to mass ratio as a Mini Cooper? And the tire surface areas were equivalent as well? Wouldn't the bus be able to stop just as quickly? So, if the heavier driver also has a heavier-duty magnet, wouldn't that give the heavier driver similar performance to a lighter driver with lighter magnet structure?

The Turbo MFW has a 43lb 15" driver that ha reportedly very overbuilt. Wouldn't this compensate for the mass issue?

That said, I appreciate the nearly complete consensus among those who have heard both the MFW Turbo and Rythmik designs that the Turbos are not as refined for music.

[Danny Richie]

As for the debate between the large driver/large magnet vs the lighter driver/probably lighter magnet issue, it seems to me we're talking past each other a bit. While I agree, buses in general are not going to have comparable stopping distances to a Mini Cooper, what if the bus had the same breaking resistance to mass ratio as a Mini Cooper? And the tire surface areas were equivalent as well? Wouldn't the bus be able to stop just as quickly? So, if the heavier driver also has a heavier-duty magnet, wouldn't that give the heavier driver similar performance to a lighter driver with lighter magnet structure?

The Turbo MFW has a 43lb 15" driver that ha reportedly very overbuilt. Wouldn't this compensate for the mass issue?

As to your last question the answer is NO.

And in this case braking force is not increased in proportion to the mass.

Hanging double the magnet on a driver does not double control by any means. It might also have double the distance in the gap to reduce field strength. Check the Bl factor. The Bl is its force factor. That's its magnetic strength. It is basically it's ability to put the mass in motion.

And if anyone can point me to the T/S parameters of the Turbo'd 15 we can put real numbers to it.

Now look at the Q numbers. Here is what they mean.

Q: This refers to the relative damping of a loudspeaker.  This is the “Q” that is in the other Q parameters. The damping is the effect that reduces the amplitude of oscillations within the subwoofer

Qms: This is the subwoofers relative damping (Q) at the resonance frequency  (Fs), including mechanical losses.  Also called the mechanical damping of the subwoofer.  This unitless measurement usually varies from 0.5 – 10.

Qes: The subwoofers relative damping (Q) at the resonance frequency (Fs), including electrical losses.  Also called the mechanical damping of the subwoofer.  The unitless measurement usually varies from 0.5 – 10.

Qts: This is the subwoofers relative damping (Q) at the resonance frequency  (Fs), including all dimensionless losses.

Also look at the Qtc or what the Q is in the box. The box adds damping too.

Now add servo control and it can change all those numbers on the fly. It can make a low Q driver play low and a high Q driver stop really fast. It can add driving force to maintain a linear response curve. So the driver doesn't have to be as heavy and have a low Fs to play low. Then it can electrically reverse the polarity to the driver to apply breaking force. So Qms constantly changes.

[genjamon]

Thanks, Danny, for the short lesson on subwoofer technical parameters.  I knew the bus/Cooper analogy broke down at some point. 

Others know much more about the Turbo driver being used than I do, so maybe one of them could look up the parameters and share with us all?  I'm not sure where to look for that, and don't even know the name of the driver being used.

[Danny Richie]

Thanks, Danny, for the short lesson on subwoofer technical parameters.  I knew the bus/Cooper analogy broke down at some point. 

Others know much more about the Turbo driver being used than I do, so maybe one of them could look up the parameters and share with us all?  I'm not sure where to look for that, and don't even know the name of the driver being used.

And don't get me wrong. I am not knocking that driver. It is a great driver, and it will play low and hit high SPL levels. But the objectives that went into designing it are very different than what I am trying to do with the servo drivers.

[genjamon]

Understood, Danny, and thanks for your help.  Given the prices, looks like around $1K per side for dual left and right H frames if I did the cabinets on the cheap.  That just might be do-able.  And I could have something working soon, while I then maybe work with WGH on that solid-mesquite set of cabinets to swap over to later... 

And a couple guys had asked about my room via PM, so here you are:

[Danny Richie]

Those main speakers should play down low enough for a mono sub. So you could lay the sub on its side using two or three of the 12" servo subs in an H frame, and sit it in the middle of the room between the speakers.

[genjamon]

Hmm, that's an interesting concept, Danny

[Danny Richie]

Hmm, that's an interesting concept, Danny

And you'd just need one amp.

[Tomy2Tone]

And you'd just need one amp.

I like that idea too!!

Go for it Ben!

[Captainhemo]

Jay (Captainhemo) is going to be offering flatpacks for three driver H-Frames but he may also offer some for dual driver H-Frames

Mike

Yes, we'll  have CNC cut options for both duals and triples.   As I menioned in another trhead, I'll start a thread soon. just  trying to finalize  some details on another  project then will get to these

jay

[bdp24]

Yes, we'll  have CNC cut options for both duals and triples.   As I menioned in another trhead, I'll start a thread soon. just  trying to finalize  some details on another  project then will get to these

jay
Panles wil

Jay, will you be offering dual and triple H-frames for only the 8" woofer, or for the 12" as well? I had been planning on getting a pair of dual 12" frames from Ruben, but looks like he's not making anything for GR kits anymore.

[Captainhemo]

Jay, will you be offering dual and triple H-frames for only the 8" woofer, or for the 12" as well? I had been planning on getting a pair of dual 12" frames from Ruben, but looks like he's not making anything for GR kits anymore.

We hadn't even been thinking of the 8's  yet, just 12's  (duals/triples ) to start.  I'm sure 8's could easily follo

jay

[genjamon]

Could be a good option for sure. Rough timeframe of availability?   Rough price range?

[Captainhemo]

Could be a good option for sure. Rough timeframe of availability?   Rough price range?

Well , luckily these will be a much simpler project to  get going so  I don't for see a huge delay if  someone needed some in say early to mid Jan.    Just give me a littl emore time for pricing (these will be 1.5" MDF panels and 1" MDF bafle and braces).

jay

[bdp24]

Well , luckily these will be a much simpler project to  get going so  I don't for see a huge delay if  someone needed some in say early to mid Jan.    Just give me a littl emore time for pricing (these will be 1.5" MDF panels and 1" MDF bafle and braces).

jay

Will the frames use dowels for lining up the panels, or dadoes (where the baffle and brace shelf meet the inside surface of the four outside panels---the top, bottom, and two sides) and perhaps rabbets (where the top and bottom meet the sides), instead of butted together? Will you be offering a grill frame, perhaps inset into the front cavity for a flush look (1960's style, like vintage Klipsch)? Is there a set size you're thinking of, something like 16" wide and 14" deep, roughly? I've been spreading the word about the OB/Dipole Sub on Audiogon, where hardcore audiophiles are looking for subs to mate with their Magneplanar and ESL panel speakers. You might be getting a lot of interest in these frames! 

[Captainhemo]

Let's move the flat pack talk over here and  free up 
genjamon 's thread...apologies for the hijack

jay

[Nick77]

My room is very similar to OP with dual flanking subs in the corners 14x18. Will single OB servo's work in the corners? Would more like 2' from wall work okay?

[genjamon]

Let's move the flat pack talk over here and  free up 
genjamon 's thread...apologies for the hijack

jay

No worries, Jay.  It's relevant in my opinion, and I'm interested in the discussion.  I feel like I've gotten plenty of input about my original question and would be fine to let the thread evolve.  That said, if there's another thread dedicated to the flat pack, maybe it makes sense to focus discussion there rather than having it sprawl over multiple threads.

Also, I don't see a link to the flat pack thread in Jay's post, so I think this is the one he's referring to: http://www.audiocircle.com/index.php?topic=139480.msg1485708#msg1485708