Posted by emailtim (A) on April 10, 2024 at 10:26:58

In Reply to: RE: As for me posted by MarcL on April 10, 2024 at 06:36:36

I tested with 1, 2 and 3 GR Research 12" drivers before going to 4 in 3 different baffles.

The subs are air pumps. The more air displacement you have, the better. I noticed better performance as displacement increased. More air volume also extends to low volume listening.

The GR Research subs have 18mm XMAS and VD of 882.5 cm^3 (FS 28). The Dayton Audio Reference subs have 14.3mm XMAS and VD of 742.6 cm^3 (FS 31.6). Davey likes the DA drivers for OB subs.

I am in the process of trying a 4th baffle design which is a spin off of the XSD project in a narrower footprint. It is a hybrid of what I learned in the preceding OB/Dipole tests.

The H-Frame provided the most even room loading, but doesn't have the force cancellation benefits. The new hybrid baffle "should" merge those two issues (knock on MDF).

I tried the front/back and all front facing drivers in the H-Frame and didn't notice much difference. To do it right, you need to do it in pairs.

From my REW measurements, I found a stronger amp was able to set the drivers faster than the servo plate amp. This also depends on the strength of the sub's motor. I would guess if the servo used the same amp, it would have the edge.

The electronics in the plate amp also got into the way of what I was doing upstream with XO and DSP ( dueling banjos ). It was much easier to control everything in 1 place than trying to stack controls so I sold the plate amp. It is a great one size fits all Swiss Army Knife amp, but to do so, makes general purpose engineering decisions. It is great if you lack alternate control means.

One of the design goals of servos was to control the impact the back wave cabinet reflections have on the driver in boxed subs. With OB, there is no cabinet back wave, so the primary problem that servo was designed to control does not exist in this application.

With my DSP, I was able to get below 20Hz, (FS 28) F3 of 15Hz-17Hz in my room with 4 x 12". Pushing them to 500Hz in an H-Frame cabinet showed some minor distortions coming in that were resolved by changing the 13" square chase to a 13" cylindrical chase.

I have not heard the MG woofer stack, nor seen any frequency response plots on it from the various online posts/reviews so can't tell how low it goes.

X publishes his XSD plots so you can see how low it goes.

Drivers with a lower FS should play lower in X's SLOB baffle.

X selected budget drivers (FS 69, VD 42). There are more expensive drivers with both lower FS and larger VD (e.g. FS 28.3, VD 149).

The slot loading design supposedly lowers the driver's FS at the cost of HF extension.

X also uses passive XO's so it might go lower with DSP. There appears to be at least 2 ways to get his SLOB design to go lower.

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2022/03/30 Historical Records CENSORED

Edits: 04/10/24   04/10/24   04/10/24   04/10/24   04/10/24   04/10/24