Sub driver selection - Rythmik F12 (Al) vs F12G (Paper)

[KEW]

I have scoured the internet looking for solid information to assist me in selecting which model. At this point, it looks like the F12G is right for me, but any additional comments would be appreciated (and would help anyone wondering the same decision).

The Rythmik site offers:

The main performance difference is in the drivers. F12G uses a paper driver designed by GR Research. The paper driver is lighter than our standard aluminum drivers and has a more extended response. It can handle a higher crossover point, however, this is only significant when crossing above 80 Hz If a higher crossover point is desired, F12G is the subwoofer of choice. Please note: when crossing this high, localization can become an issue and dual subwoofers are recommended. Regarding the lower mass, this results in slightly better dynamics at low to moderate output levels. The downside with the paper cone is that it is not as stiff as our aluminum drivers.

GR Research also has the following comments in their ad copy for the paper cone driver:

The SW-12-04 gives new meaning to the terms fast bass. Fast bass has been a debatable term but really refers to a drivers ability to return back to a resting position. Any other sub must rely on the suspension alone to allow it to return back to a resting position. Any sub capable of playing down to the 20Hz range will also need a very heavy cone and a really low Fs. The heavy cone and its stored energy from the inertia of its movement make it difficult to quickly return to the resting position. The Direct Servo controlled sub can make use of a much lighter weight cone as the servo system will virtualize the parameters and add output as needed to maintain a flat response to below 20Hz even with a light weight cone that has a higher Fs. Not only does the light weight moving mass minimize the inertia but the Direct Servo control system effectively slams on the brakes electrically to much more quickly bring the woofer back to its resting position.

Here are the specs on the F12 Driver:

Model DS1200
Enclosure size 2 cu ft sealed
3-4 cu ft vented
fs 26 Hz
BL 11.24
VAS 88 L
Qms 7.42
Qts 0.472
Sd 530 cm2
Re 2.80 ohms
Le 1.0 mH
Cone finish Anodized aluminum

Rythmik Audio servo subwoofer 12" F12

Here are specs on the F12G driver (note that enclosure size is not the same):

Enclosure size 1.5 cu ft sealed
fs 21 Hz
BL 13.7
VAS 137 L
Qms 4.308
Qts 0.279
Sd 490 cm2
Re 3 ohms
Xmax 16 mm

Here are additional specs from GR Research for the F12G driver:

SW-12-04 parameters:

Mechanical Parameters:

Fs = 21.3 hertz
Qms = 4.308
Vas = 4.849 cu.ft or 137.3 liters
Cms = 0.071 in/Ib
Mms = 4.903 oz or 139 grams
Rms = 9.495 Ibs/sec
Xmax = 18 mm
Sd = 76 sq.in or Dia = 9.83 in or 250 mm

Electrical Parameters:

Qes = 0.298
Re = 3 ohms
Z = 4.0 ohms
BL = 13.7
Pe = 200.0 watts (conservitive rating)

Combination Parameters:

Qts = 0.279
Sens = 88.4 dB (2.83 V)

SW-12-04

Some questions I have are:
1) The main advantage of the Al driver is it's stiffer. How/when does that effect sound/music?
2) It is surprising that these both use foam surrounds instead of rubber. Has the life expectancy of foam surrounds improved? Any idea why they chose foam? What is typical life expectancy for foam surrounds?
3) Am I correct in thinking for music only in a small room, the paper cone is a no-brainer? I do not expect to cross-over higher than 80Hz, but assume the lighter cone will still offer benefits in articulation.

Thanks,
Kurt

 

[Swerd]

Some questions I have are:
1) The main advantage of the Al driver is it's stiffer. How/when does that effect sound/music?
2) It is surprising that these both use foam surrounds instead of rubber. Has the life expectancy of foam surrounds improved? Any idea why they chose foam? What is typical life expectancy for foam surrounds?
3) Am I correct in thinking for music only in a small room, the paper cone is a no-brainer? I do not expect to cross-over higher than 80Hz, but assume the lighter cone will still offer benefits in articulation.

1) As far as I know, aluminum (or other metal alloy) driver cones allow a driver to be stiffer than softer materials. This allows a mid woofer cone to maintain piston-like motion at higher frequencies before going into breakup (loss of piston-like motion). All other things equal, a metal mid woofer achieves a more detailed sound than a similar mid woofer of paper or plastic.

Whether this has anything to do with a sub woofer is a good question. At 80 Hz or less, you will be operating well below its break up frequency. And I have never heard someone talk about a sub woofer's detailed sound.

Perhaps in sub woofers, the advantage a metal cone has over paper is that it may allow higher excursion travel – and higher volume than with a paper cone. But maximum speaker excursion is determined by more factors than cone material.

2) Foam surrounds are made from polyurethane foam. They are light, flexible, and allow speaker cones to be more compliant than heavier & stiffer surrounds. The trouble with polyurethane foam is that when exposed to sunlight (UV light) and/or oxygen, it gradually decomposes in about 15 or 20 years. More recently, polyurethane has been made with a UV light absorber compound added to it, kind of like sunscreen. That apparently allows polyurethane to last longer. I don't know when that became standard practice, and I don't know how much extra life that gives to speakers.

3) Paper seems like a good choice to me too.