Crown XLS Drivecore amps & subsonic content (v. we have a problem Houston?)

Does anyone else with a Crown XLS Drivecore have an issue with subsonic content triggering some sort of undocumented "protection" mode in the amp?

I have a XLS Drivecore 1500 that I've been using to test out my new DIY subwoofers (each a 2 ohm load) until the Crown XLS Drivecore 2500 I bought arrives from the friendly UPS delivery man. I have the amp setup to run stereo and the subs are a 2 ohm load. Long story short, I discovered while playing the War of the Worlds pod emerging scene the amp goes into a temporary protection mode where the thermal lights flash and the output is muted momentarily. After a few seconds the flashing stops and output resumes. This was at -10dB on my receiver and the amp was not working that hard. (the -10dB lights were on pretty solid). Turning the volume down a little didn't solve the problem. The issue still happened even at -20dB on my receiver.

It's not a straight thermal issue since the amp will play through other extended bass heavy scenes from other movies without any issue. Further, this protection mode triggers at the same point in the scene every time regardless of whether the amp has been pounding for minutes (presumably heated up) or has been idle. When I engaged a 2nd order Butterworth HPF at 15Hz in my MiniDSP and then the scene plays fine. This leads to believe that it's not thermal protection, but something else that's not documented.

As a final confirmation test I tried playing low frequency sine waves through the amp and found it pretty easy to trigger this undocumented protection mode. The lower the frequency, the lower the volume where this "protection" kicks in.

Here's what I found.

Frequency : receiver volume where the protection kicks in
20Hz : no
16Hz : no
15Hz : -4dB
10Hz : -12dB
5Hz : -18dB

As a point of reference the amp seems to run out of power at about -4dB when audible distortion from the sub starts so I didn't push any further. My receiver was fed full scale dual channel mono sine waves (0dB?) from my PC via a digital connection (HDMI).

Are these amps just not suitable for sealed subs where no subsonic HPF is used or do I have a lemon? I sent an e-mail to Crown, but haven't heard anything back yet.

What impedance load do you have connected to your XLS 1500 and how is the amp configured?

FWIW, I should point out that I tried this with the clip limiters in the amp both on and off and got the same results either way. I also tried driving the subs with a QSC PLX2402 and it had no issues in the same in WOTW scene (BD) at the same volume.

I'm going to be unhappy if the XLS 2500 does the same thing since I bought it specifically to use on these subs since it was "silent".
Edited by Stereodude - 12/10/12 at 5:42pm

Yes, I tried my sine wave testing with the clip limiters both turned on and off and got identical results either way.

Interesting... Have you ever tried playing reasonably high output subsonic sine waves?

I only just started using the amplifier on these subs on Sunday evening so I haven't played all the usual LFE demo scenes yet. I've played some and so far only had a problem with WOTW. I'll have to step up my game and systematically go through the demo DVDs and BDs and see if there are any other scenes that cause the amp fits.

If it's just me that means somehow I always manage to get problematic gear or manage to find these sorts of problems. I'm still waiting to hear back from Crown.
If he's running 4 of the Dayton 18" HOs from a single XLS2500 he should have a pretty similar impedance load in the subsonic range heading down to ~1.7ohms per channel at DC.

Edit: After double checking, this is not completely correct. The Dayton has a DC resistance of ~3.4 ohms. The AV15-H is ~2.7 ohms so it is harder to drive.

It will be a little difficult since I put Speakon connectors on the enclosures and I need to rig up some sort of adapter to put two speakon cables in series. However, I think I have the right loose connectors to make an adapter harness though. I'll see about trying it tonight after work though admittedly I don't see why it should matter unless the "protection" thresholds are different depending on the mode of the amp.
Edited by Stereodude - 12/11/12 at 9:48am

Yes, I have a full 120V or a little more.

Not exactly. They are sealed dual opposed. If I power only one driver I end up with a passive radiator of sorts, and I'm not sure what the net effect is in terms of putting big power to a single driver. The best option is probably to rewire a single enclosure to be two 4 ohm loads. That will still take some effort to do since I'm using Speakon connectors and don't have 4 conductor cables or the internal wiring to do that, etc.

Negative, it does the same thing with them off or on.

According to the simulation results, the impedance of the enclosures does drop below 2 ohms basically at 16Hz. So, that's probably a key factor here.


Oh, I know they drop low. I just wasn't expecting this. The drivers are AE AV15-Hs and the cabs are ~165L net with walls covered with R13 fiberglass.

So after thinking this over since yesterday... (long time I know)

First, my hope is that the XLS 2500 is a little more resilient than the 1500 / has more headroom before this protection kicks in. Second, based on the in room frequency response at the listening position shown here:



It seems pretty clear there's little point in trying to reproduce subsonic content under ~13-14Hz since it should be imperceptible relative to any other sounds the system is reproducing at the same time due to the low SPL level (relatively). So, the use a complementary subsonic filter in the MiniDSP around the same frequency should significantly reduce the likelihood of this protection triggering without taking anything away from the overall LFE experience.

That's basically my conclusion also.

It would be nice though if this protection feature was documented in the manual. I was showing the subs off to a friend yesterday since I only finished them on Sunday, hadn't tried WOTW before, and got a little concerned when the amp muted the outputs and flashed the thermal lights. Thankfully he's a DIY guy also and enjoyed the ensuing testing and amp swapping that followed.

I really don't think so. I measured the response with my QSC and got the same response.

As an aside, I tested the QSC (with a different D/A from the signal chain in my great room) into a 8 ohm load and found the -3dB point to be ~2.5Hz.
Edited by Stereodude - 12/11/12 at 2:12pm