[bfs21]

Hi -- I bought a used set of GR servo subs (H-frame configuration), and they have worked brilliantly to date.

Unfortunately one of the drivers is now inactive. (Top one on the left channel.) I've tried swapping cables and servo amps, etc., and nothing gets it to move. So the driver may simply be the issue.

I'd order a replacement, but I'm not sure what kind of subwoofer drivers I have -- 8 ohm or 16 ohm. I've looked for any kind of label but no joy. Is anyone here able to tell the difference just by looking? Photos here -- https://photos.app.goo.gl/45L9t5qq5b4JosFJ9

Related question. Let's say I never get to the bottom of this, take a wild guess as to which kind I have, and just order two matching replacement woofers for the H-frame in question. Would it matter much if there was a mismatch between the left and right channels? For example, if the left H-frame had 8 ohm drivers and the right had a pair of 16 ohm drivers. I'm guessing it's not a big deal as the A370PEQ amp should be able to drive both types of drivers.

Thanks in advance for any thoughts. 

[S Clark]

I bet you can take an ohm meter and measure the resistance of each driver.  Then contact Danny Richie.   

[HAL]

Look at the back of the speaker magnet.  It has the GR-Research model number printed on it.  But I see in your case it is not.

The SW-12-16FR are typically used in the OB H-Frames and are the 16 Ohm speakers.

Measure the DC resistance of the drive coil after disconnecting them.  The 16 Ohm speaker DC resistance measures around 12-14 Ohms.  If it is around 7 Ohms it is the 8 Ohm version of the sub driver.

[Hobbsmeerkat]

Since you have the A370 PEQ amplifiers, there's a 99.9% chance it's the 16-ohm version, as the 8-ohm versions were only used with the HX300 amplifiers which could handle the lower DCR of the 8 ohm woofers running in parallel.

[mlundy57]

Since you have the A370 PEQ amplifiers, there's a 99.9% chance it's the 16-ohm version, as the 8-ohm versions were only used with the HX300 amplifiers which could handle the lower DCR of the 8 ohm woofers running in parallel.

Unless he's an oddball like me. I have the 8 ohm version with the A370 amps. 

[corndog71]

Unless he's an oddball like me. I have the 8 ohm version with the A370 amps. 

Same here.

[Early B.]

Since you have the A370 PEQ amplifiers, there's a 99.9% chance it's the 16-ohm version, as the 8-ohm versions were only used with the HX300 amplifiers which could handle the lower DCR of the 8 ohm woofers running in parallel.

Hmmmm... I have a dual servo sub that houses a pair of 16-ohm drivers powered by an HX300 amp. Am I using the wrong amp (or wrong drivers)? If so, what is the result/effect or potential problems I could encounter?   

[Hobbsmeerkat]

Hmmmm... I have a dual servo sub that houses a pair of 16-ohm drivers powered by an HX300 amp. Am I using the wrong amp (or wrong drivers)? If so, what is the result/effect or potential problems I could encounter?   

There's no problem with the HX300 with 16 ohm woofers.

As it was explained to me, the main issues is when the 8 ohm woofers are used with the A370, as the amp can have issues with impedances below 4 ohms, while the HX300 is stable to 2 ohms.. (the combined impedance is closer to 3 ohms)

It may not be the case that everyone will have issues, seeing as 2 people have that exact combo without issue, but I'm guessing it's an issue that some others have noticed in the past, leading to the change.

[HAL]

My pair of Super V's that were at the RMAF show also had 8 ohm servo drivers with an A370PEQ amp.  IIRC, that was before the 16 Ohm drivers were out and before the HX300 servo amps.  The HX300 used Hypex 300W Class D modules and no problem with lower impedance, but no longer manufactured.

The A370PEQ amp will get very warm with the 8 Ohm drivers in parallel at high LF SPL's, so they need airspace around them to keep cool.

[bfs21]

Huge thanks to everyone while I get up to speed on this. The GR community is like no other.

So -- I have an additional question...

To test the problem driver in complete isolation from the rest of the system, I took a traditional amp and a source and connected them directly to the woofer via the driver terminals. The goal was to see if I could get the woofer to play just on its own. All servo coil wires disconnected.

At first I thought there was no sound. But then as I turned up the volume, I could hear very faint output. Given the power of the amp (Parasound HCA-1000) there should have been way more output.

Would the faint output be the ultimate confirmation that my driver is blown?

[HAL]

If you have a DC resistance (Ohm) meter, check each set of terminals. 

The Driver coil should be around 6 Ohms and the servo coil should be around 20 ohms IIRC.

If the sound level is low driving the drivers coil terminals, something maybe wrong with the voice coil or lead wires.  Remember this is a subwoofer, so not much output will be audible even with full range input signal.

[Danny Richie]

Definitely put an ohm meter on it and let's see what you have.