Rythmik Audio Subs

[richidoo]

I have sent out an invite to Brian from Rythmik to join our little group here and offer up his two cents. 

Thanks John!!!

[Carlman]

I sent him an invite a couple of days ago... It might've gone to spam so, thanks from me too.
-C

[Black Sand Cable]

I just heard from Brian. He will be here later on today.

[bpape]

Excellent.  I'd love to hear more from the horse's mouth about his products.  Like I said, I've heard a lot of good things about them.

Bryan

[richidoo]

http://www.rythmikaudio.com/

I have read the website, it is very interesting!!

Any advice on using direct servo drivers in an open baffle speaker? I want ultra clean 95dB at 20Hz for organ and dance music. I think I would need at least 2 12" drivers per side to achieve this without direct servo, but with your improved accuracy with high excursion, maybe one is enough??? I know there is math to figure this, but that is just so daunting...  I bought some Peerless XXLS but not used them yet. They are Fs 21Hz, pulp cones.

Can your drivers in OB play flat to 20Hz without resonance aberrations? I guess that is a lot easier with servo... But is it really just as clean through resonance as in the clear? What is the Fs of your driver? With metal cone, I guess it is way low so not an issue?

I have a digital external crossover (DCX-2496). Can I feed its signal to the direct servo amp, so that my crossover is used to crossover to midrange driver up to 300 Hz knee?

My mid driver in OB will roll off at about -12dB/oct I think... so if your bass driver is as fast and accurate as you claim I would probably like to steepen up the crossover slopes as much as I can get away with to bring the full range driver down as low as possible. I can boost it some at 200Hz without a problem. So 150Hz is probably the lowest crossover frequency I can do. If I wanted a LR2nd order crossover at 200Hz would that be possible with your direct servo amp?
Thanks a lot Brian,
Rich

[rythmik]

http://www.rythmikaudio.com/

I have read the website, it is very interesting!!

Any advice on using direct servo drivers in an open baffle speaker? I want ultra clean 95dB at 20Hz for organ and dance music. I think I would need at least 2 12" drivers per side to achieve this without direct servo, but with your improved accuracy with high excursion, maybe one is enough??? I know there is math to figure this, but that is just so daunting...  I bought some Peerless XXLS but not used them yet. They are Fs 21Hz, pulp cones.

Can your drivers in OB play flat to 20Hz without resonance aberrations? I guess that is a lot easier with servo... But is it really just as clean through resonance as in the clear? What is the Fs of your driver? With metal cone, I guess it is way low so not an issue?

I have a digital external crossover (DCX-2496). Can I feed its signal to the direct servo amp, so that my crossover is used to crossover to midrange driver up to 300 Hz knee?

My mid driver in OB will roll off at about -12dB/oct I think... so if your bass driver is as fast and accurate as you claim I would probably like to steepen up the crossover slopes as much as I can get away with to bring the full range driver down as low as possible. I can boost it some at 200Hz without a problem. So 150Hz is probably the lowest crossover frequency I can do. If I wanted a LR2nd order crossover at 200Hz would that be possible with your direct servo amp?
Thanks a lot Brian,
Rich

There are different recommended xover limits for different drivers. DS12 is about 100hz max, DS1500 is about 80hz, Danny's SW12-4 and SW12-8ohm are 120hz. Danny's OB driver will be able to play up to 150hz (LR max is 150hz). If you want to crossover to 200hz, you need to set the xover to max, and uses phase control to add delay for phase alignment. For me, the true contribution from LR is that they pointed out the most important issue in xover is phase alignment at xover point.  After they published their paper on AES, the later investigation from Dr Toole confirms that dispersion pattern is far more important than FR flatness. To get the best dispersion pattern, the phase has to be aligned so that it gets not only the widest, but also a symmetric dispersion pattern. 

One thing one needs to note though is OB is a very physically demanding system. It is not power hunger, but it needs to physical asset  such as excursion to perform. So you really need more drivers. My calculation is that if you have design the wings to be large such that the loss does not happen until 80hz, you would lost about 12db when you reach 20hz. That means you need 4 of them to achieve the same output as a single "boxed" 12" driver.

 

[richidoo]

That makes sense. Thanks. I figured 4 drivers last time I looked at it.

Is there a physical limitation of the drivers or amps that prevents playing higher frequencies?

With 3 of the GR SW12-FR16 drivers in parallel, I wuld need one of your 4 ohm amps, right?
Thanks for your advice Brian!
Rich

[rythmik]

All of our amps are 4ohms rated. So for 8ohms, it can drive two, and for 16ohms drivers, it can drive four.  So we uses amp servo controller to drive multiple drivers, all drivers need to be in close proximity.  So the drivers need to in a cluster. The amp can be located 12' or 20' away from the driver cluster. 

[richidoo]

Makes sense, and that's how I would use it in cluster of 2-3 per speaker.

Hey Brian, can you help me understand a little better the limitations on crossover frequency? What is limiting me from playing frequencies above the built in crossover filter? If I turn it to max I still only get 200+Hz, right? Then I have to deal with the built in slope too. Can the built in crossover filter be disabled in favor of an external crossover? I want some flexibility in the xover frequency.
Thanks
Rich

[rythmik]

Makes sense, and that's how I would use it in cluster of 2-3 per speaker.

Hey Brian, can you help me understand a little better the limitations on crossover frequency? What is limiting me from playing frequencies above the built in crossover filter? If I turn it to max I still only get 200+Hz, right? Then I have to deal with the built in slope too. Can the built in crossover filter be disabled in favor of an external crossover? I want some flexibility in the xover frequency.
Thanks
Rich

The xover is a natural roll-off due to the inductance. We would like to stay away from the area that inductance becomes a significant part of the impedance curve. That is where the cone control becomes more difficult. Inductance is esentially an isolation between the motor and amplifier output.  Even though voice coil resistor has similar effect, inductance is worse as its impedance goes up with frequency.   Some may ask why the nonservo does not this limiation?  They are in a different operation mode.  Servo has such a strong cone control that the effective voice coil resistance is 1ohm or lower.  This arrangement gives us the best cone control ability.  I can loosen up the control such that it is close the nonservo configuration. But that defeats the purpose of having a servo control.  And you can trust me that our dirvers have the lowest inductance that I can achieve.   

The internal xover is 250hz max. I can put a jumper to bypass that stage. However, the roll-off would still occur at around 160hz for SW12-16 model and even lower for other models.  So far that has played pretty well because a sub is a sub. They are not designed to play into upper bass.  If you would like to do that, you really need a driver that more resembles midrange driver, not the one with oversize surround which is a problem when play into higher frequencies.

 

[richidoo]

OK that makes sense. I can try boosting my "full range" driver to get it lower, but otherwise mid driver it is! No shortage of nice ones.

Thanks very much for your thorough and insightful replies Brian! I look forward to hearing it. I will buy them from Danny to get his expertise on OB usage. There is a nice long thread in his AC circle on these drivers too.

Am I correct that his drivers are paper coned where the normal Rhythmik drivers are aluminum cones?
Rich