Servo Truth ? You Tell Me ? Good Experiment.

jparkhur · « **on:** 28 Nov 2012, 02:32 am »

I noticed after some rearranging that one half of my 8 servos were being over driven and sounded muddy. I switched amps, RCA cords, other stuff and it kept hitting the right speaker. Dug a little further and noticed I had pulled the return series wire from my neutrik connector. Fixed and we are back to control. Why am I saying this???? The amp was just doing what I told it to do but I failed on the servo control- is this what life is like without a good servo? Thoughts. Take one side, by accident, and let it go, chaos began and I could hear it loud and clear. I am now under tight servo control. Thank you Brian and Danny.

jparkhur · « **Reply #1 on:** 28 Nov 2012, 02:35 am »

Ed VB · « **Reply #2 on:** 28 Nov 2012, 03:08 am »

Jon

So what kind of bass are you getting out of the three servo sub's compared to the V series?

Are you using a sub for the last octave?

jparkhur · « **Reply #3 on:** 28 Nov 2012, 03:18 am »

Ed, right now the are covering everything below the FS of the Dayton in OB. Three 8s is almost ~ to 2 twelves when looking at area of cone. I ran some stereophile test tones and turned off the filters, good strong in to very low 20's with my room. The sure load the room differently than sealed subs. If u are asking about Super V with H baffle, I would need another 8. Ian actually going to pick up four more 12's and put them in an H to see what the sideby side sounds like. Also, this baffle is slightly different. I need more room.

JohnR · « **Reply #4 on:** 28 Nov 2012, 03:25 am »

Quote from: jparkhur on 28 Nov 2012, 02:32 am

The amp was just doing what I told it to do but I failed on the servo control- is this what life is like without a good servo?

According to Danny, the amp is unstable if you disconnect the servo. Which makes sense. So all this demonstrates is that circuits don't work properly if you don't connect them up right.

jparkhur · « **Reply #5 on:** 28 Nov 2012, 03:40 am »

Yes John, but the question is on control, speed and quality. My point, maybe buried, was that over powering drivers or using an amp without good control of a woofer can really be demonstrated by this. Yes the amp will still drive the speakers but without the servo circuit it does not do it well- actually terrible. After looking at the last sub show down on another forum area I noticed that the non industry participants noted the servo controlled sub had more unique qualities when it came to sound quality. I am not speaking of overall SPL but rather mimicking what the music is telling it to play. Thanks John, my circuit was not connected but my fault in wiring gave me and others a simpler way to look at things- maybe.

I have had the following subs in the last 30 years and these are by far the best. Velodyne 18 and 15 ULD II, MK 200, MK 80, Klipsch 12, ACI Titan, Titan II, and Maestro, Dayton Titanic III, and a few others. We need to do another double blind sub test in the Midwest. Who's hosting???

JohnR · « **Reply #6 on:** 28 Nov 2012, 04:18 am »

Quote from: jparkhur on 28 Nov 2012, 03:40 am

Yes John, but the question is on control, speed and quality. My point, maybe buried, was that over powering drivers or using an amp without good control of a woofer can really be demonstrated by this.

OK, so if the amp is underpowered or unstable, then it won't sound good. I'm not why anyone would contest that or why the point needs to be made...

jparkhur · « **Reply #7 on:** 28 Nov 2012, 04:24 am »

John. Your on fire this week. Just breath and look at the learning possibilities that are in front of us. You for one post here to learn and grow. We can all do that on many levels some just need more time. It's like when I experimented with my kids using Tullio's Phenomenon. Nothing like some good old fashion nausea and vertigo on minors. Sound familiar.

we should all use this.

jparkhur · « **Reply #8 on:** 28 Nov 2012, 04:25 am »

Must sleep and listen to Pink Floyd live at MPLS with Sony DAT 8 and Nak mics.

JohnR · « **Reply #9 on:** 28 Nov 2012, 04:26 am »

Jon - I'm just pointing something out that you seem to have missed.

jparkhur · « **Reply #10 on:** 28 Nov 2012, 04:32 am »

The pot and the kettle are friends. I was, and was also trying to explain how others are learning too. You missed that. I'm not all knowing, just want to show progress. I like you John, you ask great questions and I can see how you want to share what you know with others. Thank you for your time and input to all these great forum areas. I want to inspire, learn and show others I make mistakes but hopefully learn from them. And to all a good night.......... Jon

John you didn't need to erase your last post, I'm a big boy, I know you mean well.

Also. I will win the Powerball.

Danny Richie · « **Reply #11 on:** 28 Nov 2012, 05:08 pm »

John, I am sorry if I left the wrong impression on what would happen when one unplugs the sensing coil. I didn't say the amp becomes unstable. The amp works fine. It just has an erratic response. In fact I used the word erratic, not unstable. It no longer had the linearity that it maintain with the servo system engaged. It fluctuated, and the output level kicked up.

I don't know for sure if the amp was looking for the feedback or if the response was the result of the shelving circuit minus the servo control system or what.

I can measure it again to show you the difference if you want, but I still don't recommend my customers simply unplug the sensing coil or the level will shoot up too high.

I'd have to ask Brian what really happens to the amp when the sensing coils are unplugged.

richidoo · « **Reply #12 on:** 28 Nov 2012, 10:29 pm »

If these 8" drivers are like the 12" GR paper OB servo drivers then they have high Qts, which will sound as you describe, warm and muddy without the servo. I think this high Q of Danny's OB servo drivers is how they can play at higher freq than the other servo drivers. Less mechanical damping makes them easier for the amp to correct. Easier to accelerate means accuracy at higher freq. Just a guess..

jtwrace · « **Reply #13 on:** 29 Nov 2012, 12:28 am »

Quote from: richidoo on 28 Nov 2012, 10:29 pm

If these 8" drivers are like the 12" GR paper OB servo drivers then they have high Qts, which will sound as you describe, warm and muddy without the servo. I think this high Q of Danny's OB servo drivers is how they can play at higher freq than the other servo drivers. Less mechanical damping makes them easier for the amp to correct. Easier to accelerate means accuracy at higher freq. Just a guess..

See more here http://www.audiocircle.com/index.php?topic=111452.0

richidoo · « **Reply #14 on:** 29 Nov 2012, 02:36 am »

Thanks Jason...

JohnR · « **Reply #15 on:** 29 Nov 2012, 03:51 am »

Quote from: Danny Richie on 28 Nov 2012, 05:08 pm

I didn't say the amp becomes unstable. The amp works fine. It just has an erratic response. In fact I used the word erratic, not unstable.

You did say erratic... I'm afraid I'm not seeing what the distinction is. An amp that is "erratic" is not working fine...! Presumably, with the feedback coil disconnected the servo "thinks" the cone is not moving and will then drive the amp harder to try and make it move. Right? By disconnecting the feedback coil, Jon is not comparing servo with non-servo, but "servo working properly" with "servo not working properly"...

Danny Richie · « **Reply #16 on:** 29 Nov 2012, 02:11 pm »

Quote from: JohnR on 29 Nov 2012, 03:51 am

You did say erratic... I'm afraid I'm not seeing what the distinction is. An amp that is "erratic" is not working fine...! Presumably, with the feedback coil disconnected the servo "thinks" the cone is not moving and will then drive the amp harder to try and make it move. Right? By disconnecting the feedback coil, Jon is not comparing servo with non-servo, but "servo working properly" with "servo not working properly"...

I didn't design the amps. I'd have to ask Brian to respond with the correct answer.

rythmik · « **Reply #17 on:** 29 Nov 2012, 07:09 pm »

Quote from: JohnR on 28 Nov 2012, 03:25 am

According to Danny, the amp is unstable if you disconnect the servo. Which makes sense. So all this demonstrates is that circuits don't work properly if you don't connect them up right.

The servo uses a combination of current feedback and sensing feedback. When the sensing feedback fails, there is still a current feedback. It is a feature of so called graceful degradation. We wouldn't be even make it into a DIY product if it is not unconditionally stable. The problem Danny described is there is a huge gain at the resonance peak point with only current feedback. That may be what surprised him when he did the music or sweep. But this is designed as complete package so even in that scenario, the driver should be ok. I have experienced several time worse scenario in that sensing coil is connected out of phase and it caused a loud oscillation. If acted adequately fast to turn off the power, the driver will survive that type of torture.

jtwrace · « **Reply #18 on:** 29 Nov 2012, 07:16 pm »

Brian

What's the max amperage draw from the wall on the A370?

rythmik · « **Reply #19 on:** 29 Nov 2012, 07:19 pm »

Quote from: jtwrace on 29 Nov 2012, 07:16 pm

Brian

What's the max amperage draw from the wall on the A370?

6A if you put it into full power worst load 10hz. The draw is much less at impedance peak of the driver/enclosure system and with F12 that you have, it is at 35hz.