Advantages of a servo subwoofer

DonH50

Member Sponsor & WBF Technical Expert
Jun 22, 2010
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I have two Rythmik F12's in my media room. I spent a lot of time emailing and talking to Brain (the owner/designer behind Rythmik) before getting them. I was certainly somewhat influenced by the fact that his design and patent mirrors my own first servo subwoofer, a DIY project in college when I needed a sub to match my Magnepans. My sensing coil was the second (lo-impedance) coil of an Infinity IRS woofer (they used two different impedance coils and a more complicated crossover to provide flatter, lower bass response in the IRS and my IRS II's). Obviously, I should have patented the idea back then... :)

Controlling ringing and delivering excellent time response was my big reason for a servo sub, then and now.
 

Gregadd

WBF Founding Member
Apr 20, 2010
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Metro DC
Don will keep us informed.
 

GaryProtein

VIP/Donor
Jul 25, 2012
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I never had a servo problem with my IRS-V.

The servo circuit in the IRS is built into the woofer amplifier, not the crossover.
 

garylkoh

WBF Technical Expert (Speakers & Audio Equipment)
Sep 6, 2010
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Seattle, WA
www.genesisloudspeakers.com
The issue I hear about servo control from other sub designers is reliability.

Do they say what aspect of reliability it is about? Is that comment from sub designers who don't design servo-subwoofers?

My biggest problem is that customers expect the loudspeaker to last forever, but don't realize that there's an amplifier built-in (with electrolytic capacitors that may leak or dry up). We are still supporting customers of the old Genesis and their 20 year old speakers (with built-in servo-control) and the Class D amplifiers die before the servo or the speakers die. And on those amplifiers, the part that usually fails is an IC chip that is now obsolete.

With these failures coming more often, I'd designing a new Class D amplifier/Power Supply module that can drop in, but the repair cost might be more than the 20 year old pair of speakers is worth.
 

JackD201

WBF Founding Member
Apr 20, 2010
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Manila, Philippines
I had the pleasure of using a pair of Rythmik subs in a show last year where one of our goals was to dispel the still popular notion that subs are a bad thing for audio. One feature that came in very handy was a secondary set of parametric EQs in that particular model. I think every sub should have this, it is really useful.
 

DonH50

Member Sponsor & WBF Technical Expert
Jun 22, 2010
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Monument, CO
I never had a servo problem with my IRS-V.

The servo circuit in the IRS is built into the woofer amplifier, not the crossover.

Hi Gary,

I may be mis-remembering, or getting mixed up, or just senile...

My IRS-II used the dual voice-coil woofer with a passive crossover. I remember it pretty well, and it most certainly did not have an amp built in. The crossover used both coils to help smooth out the impedance hump most speakers have in the low bass region. This was NOT the big IRS system, but the smaller single-cabinet (per side) system that was one step down from the top of the line IRS.

I do not recall if the original IRS used the servo circuit (in the amp, of course, you can't servo passively) or it was added later. In any event, my DIY design used the IRS woofer so I could use the second voice coil for feedback in my servo circuit (and I got it fairly cheaply since I worked for an Infinity dealer at the time).

Sorry for the off-topic'ness - Don

p.s. I have not heard of servo reliability issues in decades. There were some issues with some early implementations, but AFAIK any recent reliability problems are related to the amplifiers as has been stated. Again AFAIK the amps aren't any more or less reliable than any other amp; the servo circuit does not add much complexity. Probably the biggest issue with powered subs, any of them, is that they tend to get stuck where convenient and then hooked uop with long cables to the rest of the system. The problem isn't the cables but fact that the sub usually ends up on a different outlet, causing a ground loop. At least that is what I seem to see the most posts about on various fora.

p.p.s. That little single-band EQ is extremely useful to me. My Pioneer does not EQ the sub, and that Rythmik PEQ allowed me to tame the first room mode peak nicely. The other nice feature for me is the continuous phase adjust knob, which alllowed me to match (time-align) my subs with my main speakers. I run the subs in parallel with the main L/R speakers, after an active crossover, instead of using the LFE output and AVR's bass management. I had some problems with bass management in a couple of ealry AVRs, though most seem to have it right now.
 

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