Class D Amplifier(s) for SWARM Subwoofer System

@atmasphere  Hi Ralph. Good to hear from you. I actually do have two of those Dayton amplifiers that Duke recommends. Each amplifier runs two subwoofers in series, so the effective impedance is 4 ohms. But the output is way too low to balance my 87 db efficient mains, which are driven by VAC Phi 200 monoblocks. The JL Audio CR-1 subwoofer offer has much more flexibility… Allowing me to mix RCA and balanced inputs, and outputs, allows me more flexibility for the signal balance between the mains and the subs, and has all the controls on the Dayton amplifiers as well. This will help me greatly as I try different equipment, its universality.  it will also allow me to use some more powerful amp, and hopefully get a better SPL balance between the two, so I think it is a win all around. I have the CR-1 on the way.  Make sense?

@audiokinesis Hi Duke. I’ll reach out to you offline to discuss troubleshooting on the Daytons. I should have reached out earlier to you about this concern. I am running two balanced outputs from my VAC Signature 2se preamp, one to a pair of VAC Phi200 monoblocks and the other to the Jensen ISO-MAX PC-2XR, which converts the balanced to SE signal (and +4 to -10 db conversion). I am guessing that Ralph is doing the same, but require confirmation. I will report back on this thread as more is known. I can definitely try the LFE inputs on the Daytons.

It looks like there is no way to bridge the Daytons to get more power (since I am only using one channel per amp) - but another option would be to use both channels and run one sub per channel.

@audiokinesis Thanks for clearing that up about the Daytons!  I will get back when I set up the CR-1. 

I think the drivers are damaged.  I am in touch with @audiokinesis and hope to resolve promptly. 

I misrepresented the impedance of the subwoofers. They are each four ohms. So, running them in parallel would present a two ohm load. That will not work. Running them in series presents an eight ohm load.  

@bdgregory See the new information above.

So what is so special about these crown amplifiers for running subwoofers? I have only heard a crown integrated amplifier, and I was not impressed. But I am guessing this is a different class. What I need to be worried about the age of the amplifiers, and aging capacitors?

@atmasphere HI Ralph.  I am puzzled too!  I agree that the volume matching SHOULD be a walk in the park.  I am also using Jensen transformers to convert the balanced output from my preamp to the SE input of the Dayton amps. It is the ISO-MAX PC-2XR.  Perhaps this is the issue, from the spec sheet: "Converts +4 dB balanced signals to -10 dB unbalanced".  Maybe the Jensen is removing too many dB???

Regarding series/parallel - Duke told me that there are two versions of the Swarm subwoofers.  In one version, each sub has an impedance of ~6 ohms.  In the other, ~4 ohms.  I believe the four ohm model is meant to be set up as two "pairs" wired in series. For each pair, the "intermediate" sub has two pairs of speaker terminals, and the only resistance (3.7 ohms on mine) is b/t the two positive terminals. The other sub has just one pair of speaker terminals, also with ~4 ohms across the pair.  So the signal "passes through" the  2x-terminated sub (energizing that speaker), then passes through the 1x-terminated sub, and then back via the negative terminals of the 2x-terminated sub (which are simply strapped together)..  The two 4 ohm subs in series provide 8 ohms effective.

Regarding the Dayton amps, I had previously asked Duke why one would use two amps rather than one, particularly since you are only using one channel on each amp and the presented load is a benign 8 ohms.  His answer is below:

"There is a worthwhile spatial-quality benefit from using two amps. You can drive the two speakers on the left-hand-ish side of the room with one amp, and the two on the right-hand-ish side with the other amp, and then use the phase controls on the amps to put them 90 degrees apart in phase.  This simulates the sort of phase differential you would get at your two ears in a large acoustic space.  So in effect the playback room's inherent "small room signature" is suppressed.  This "unmasks" the low-frequency acoustic space information on the recording, so you have more of a sense of the venue acoustics on the recording (whether they be real or engineered or both)."  

The only flexibility I lose with the CR-1 is adjustable phase. I'm not sure which will be better - using the two Dayton amps with 90 degree phase  offset, or using the CR-1 with it's better flexibility paired with a pair of Hypex NC400 amps I just bought to power the subs.  I think the flexibility of the CR-1 could be fairly valuable.

Thoughts?  

@atmasphere For continuity testing, you are just saying make sure that there is continuity for each of the three pin/socket pairs, correct?  If not, I have a broken cable.  I can test, but I would be surprised to have two broken cables (2 Dayton amps, 2 XLR cable runs).  How about the possibility of a different pin layout b/t my VAC preamp and the Jensen PC-2XR?  I see there are dip switches on the Jensen for grounding.....?  Thanks!