Running Subwoofer with Accelerometer and Servo Feedback Disconnected

[Data10]

I have an old IRS Beta woofer system, which uses a servo and accelerometer. The standard setup is the preamp output is connected to a servos. The servos audio output goes to the amp, and the amp is connected to the woofer system. The woofer has accelerometer feedback that goes back to the servos. I believe the servos uses this feedback to make EQ adjustments.

Preamp Audio Out -> Servos Audio Out -> Amp Audio Out -> Speaker Accelerometer Feeback -> Servos EQ

I believe my servos is malfunctioning in such a way that the subwoofer output is ~20dB lower than it should be. I've confirmed that I get the expected output with a different servos+amp+speaker setup, so I think the preamp is fine. I've also tried swapping out an amp and saw the same ~20dB too low, so I think the amp is fine. And both of 2 speakers connected to the servos are ~20dB too low, so I don't think it is a single bad speaker or single bad cable. This leads me to suspect the servos.

To confirm the servos and hopefully resolve the issue, I was thinking of connecting the preamp output directly to the amp without servos like below: The speaker has accelerometer feedback outputs, which is no longer connected to anything. Is this a safe way to run the system, or do I risk damaging speakers since I am not using the intended feedback loop?

Preamp Audio Out --> Amp Audio Out -> Speaker

 

[TLS Guy]

I have an old IRS Beta woofer system, which uses a servo and accelerometer. The standard setup is the preamp output is connected to a servos. The servos audio output goes to the amp, and the amp is connected to the woofer system. The woofer has accelerometer feedback that goes back to the servos. I believe the servos uses this feedback to make EQ adjustments.

Preamp Audio Out -> Servos Audio Out -> Amp Audio Out -> Speaker Accelerometer Feeback -> Servos EQ

I believe my servos is malfunctioning in such a way that the subwoofer output is ~20dB lower than it should be. I've confirmed that I get the expected output with a different servos+amp+speaker setup, so I think the preamp is fine. I've also tried swapping out an amp and saw the same ~20dB too low, so I think the amp is fine. And both of 2 speakers connected to the servos are ~20dB too low, so I don't think it is a single bad speaker or single bad cable. This leads me to suspect the servos.

To confirm the servos and hopefully resolve the issue, I was thinking of connecting the preamp output directly to the amp without servos like below: The speaker has accelerometer feedback outputs, which is no longer connected to anything. Is this a safe way to run the system, or do I risk damaging speakers since I am not using the intended feedback loop?

Preamp Audio Out --> Amp Audio Out -> Speaker

That is hard to answer. It is possible and even likely, that the electronics did have some type of high pass filter, to limit cone excursion below 25 Hz or so. I suspect that unit is a sealed sub, but I'm not familiar with it. If you want to salvage it, then you need to measure the FR without servo, and find F3. Then add a boost of 12 db per octave below F3, and put in a 12db per octave high pass filter around 25 Hz. That should pretty much make your sub perform as it did before.

Servo is just another way to Eq a sealed sub, and doing what I propose is just another way of going about this correctly.

If you don't have measuring equipment and don't want to invest in it, then it will be simper to replace the sub.

 

[Data10]

The Infinity servo is a fully separate device from the sub, which is pictured at https://tmraudio.com/old-products/infinity-irs-servo-control-for-beta-gamma-delta-speakers/ . It has a high pass filter control that can be set to off, 15, 22, 30, and 40. I could try adjusting that high pass filter control and see how/if it influences the speaker output.

So it's unclear whether running from preamp to amp to speaker without the servos and accelerometer feedback is safe? Or risks damaging the woofer?

 

[TLS Guy]

The Infinity servo is a fully separate device from the sub, which is pictured at https://tmraudio.com/old-products/infinity-irs-servo-control-for-beta-gamma-delta-speakers/ . It has a high pass filter control that can be set to off, 15, 22, 30, and 40. I could try adjusting that high pass filter control and see how/if it influences the speaker output.

So it's unclear whether running from preamp to amp to speaker without the servos and accelerometer feedback is safe? Or risks damaging the woofer?

I had completely forgotten about that EMIT speaker system from the eighties. What are you driving it with? It has a really low impedance around 1 ohm and was designed for AR tube electronics. It s a biamped system, so I assume you have two amplifiers. This system is so complicated I doubt we can trouble shoot it at long range. Frankly I very surprised it is still working.

There are 8 woofers, so I doubt you will damage them. However to make that system work correctly you will have to see if you can find someone to repair that equalizer box.

I think that system has had a good innings and may it is time to consider retiring it. I would have to wonder how close it is to original specs given what a lash up that unit was.

 

[Data10]

I have 2 sets of IRS Betas. Each set includes 2 woofers, 2 mid/tweeters, and a servos. I use one set for the front speakers, and one set for the center + subwoofer. So I have 4 woofers -- 2 for the fronts that begin at <110hz and 2 woofers for the standard subwoofer output. The subwoofer set is the one with the servos problem. I tried connecting the 2 subwoofers amps directly to the subwooufer preamp output withthout the servos, and the setup worked well. The subwoofer output was the level I expected and no longer 20dB too low. As far as I could tell, the sound quality was good without accelerometer feedback and EQ adjustment, although I was only feeding low subwoofer range, making it difficult to identify minor differences in quality. This strongly suggests that the servos is decreasing the output level. Searching around, I see that some other Infinity IRS owners have reported this type of problem with the servos, so not entirely unexpected.

While older, I think the speaker set is still a great system. Until ~1 hour ago, my front speaker setup had the best 2-channel + woofer sound I have ever heard in a home system. It was a shining start of my home theater. There is also a decent external market for them. They sometimes go used for as much as $10k. I'd like to continue using the system if possible.

I used past tense and said "until ~1 hour ago" due to a series of major issues while doing the test above in which I moved cables from servos to preamp, leaving me in a worse position than when I started. The RCA cables outputs from the servos have a screw lock mechanism. You need to unscrew to release or attach. My preamp didn't like this screw output system. I initially attached the fronts woofers cables to the preamp rather than the subwoofer cables. I realized the error before turning it on, but could not get the front woofer cables off the preamp. I believe the cables were too close together on the preamp, and the pressure from the angle kept the screw lock on. After ~30 minutes of unsuccessfully trying to unscrew with hands, I resorted to getting a good grip with a plier like tooi and turning at unnatural angles. I eventually got the cables off the preamp, but I may have damaged the connector in the process. A picture is attached. After reconnecting, now I get a low hum from one of the front woofers all the time. The hum is at exactly 60Hz and too loud to ignore. Muting, changing the volume, or unplugging the preamp does not influence the hum. Turing off the servos where the suspected bad cable begins eliminates the hum. Turning off the amp where the suspected bad cable ends also eliminates the hum. Swapping out the amp with another does not eliminate the hum.

Edit -- The 60Hz hum mentioned prior to the edit seems to be a ground loop. If I connect the amp and front servos to the same power outlet using a 25 foot extension cord the hum disappears. I'm not sure why swapping and replacing RCA outputs, would cause a ground loop; but at least I have a solution for the hum.

 

[TLS Guy]

I have 2 sets of IRS Betas. Each set includes 2 woofers, 2 mid/tweeters, and a servos. I use one set for the front speakers, and one set for the center + subwoofer. So I have 4 woofers -- 2 for the fronts that begin at <110hz and 2 woofers for the standard subwoofer output. The subwoofer set is the one with the servos problem. I tried connecting the 2 subwoofers amps directly to the subwooufer preamp output withthout the servos, and the setup worked well. The subwoofer output was the level I expected and no longer 20dB too low. As far as I could tell, the sound quality was good without accelerometer feedback and EQ adjustment, although I was only feeding low subwoofer range, making it difficult to identify minor differences in quality. This strongly suggests that the servos is decreasing the output level. Searching around, I see that some other Infinity IRS owners have reported this type of problem with the servos, so not entirely unexpected.

While older, I think the speaker set is still a great system. Until ~1 hour ago, my front speaker setup had the best 2-channel + woofer sound I have ever heard in a home system. It was a shining start of my home theater. There is also a decent external market for them. They sometimes go used for as much as $10k. I'd like to continue using the system if possible.

I used past tense and said "until ~1 hour ago" due to a series of major issues while doing the test above in which I moved cables from servos to preamp, leaving me in a worse position than when I started. The RCA cables outputs from the servos have a screw lock mechanism. You need to unscrew to release or attach. My preamp didn't like this screw output system. I initially attached the fronts woofers cables to the preamp rather than the subwoofer cables. I realized the error before turning it on, but could not get the front woofer cables off the preamp. I believe the cables were too close together on the preamp, and the pressure from the angle kept the screw lock on. After ~30 minutes of unsuccessfully trying to unscrew with hands, I resorted to getting a good grip with a plier like tooi and turning at unnatural angles. I eventually got the cables off the preamp, but I may have damaged the connector in the process. A picture is attached. After reconnecting, now I get a low hum from one of the front woofers all the time. The hum is at exactly 60Hz and too loud to ignore. Muting, changing the volume, or unplugging the preamp does not influence the hum. Turing off the servos where the suspected bad cable begins eliminates the hum. Turning off the amp where the suspected bad cable ends also eliminates the hum. Swapping out the amp with another does not eliminate the hum.

Edit -- The 60Hz hum mentioned prior to the edit seems to be a ground loop. If I connect the amp and front servos to the same power outlet using a 25 foot extension cord the hum disappears. I'm not sure why swapping and replacing RCA outputs, would cause a ground loop; but at least I have a solution for the hum.

Somehow I suspect you damaged a ground in that mishap.