2ohm Bridge Mono

E

Eric Simna

Sophomore
Jan 12, 2011
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Cleveland, OH
www.a440sound.com
So. I'm looking for experiences. Has anyone that has own the Crest VS1500 run them down to 2ohms in Bridge Mono? I'm trying to plan ahead. Currently I have a pair of the amps, and 4 SRX728s. I don't necessarily want to run that way. But sometimes you gotta do what you gotta do.

BTW. Typically I'll only need 2 of the 728s.
 
Re: 2ohm Bridge Mono

Driving two ohms or lower (two ohms bridged is lower than two ohms) is best reserved for emergencies after something breaks.

If you can tolerate not working every night if something breaks, go for it.. if you want some safety margin to keep the show going no matter what.. keep some thermal head room in reserve.

JR
 
Re: 2ohm Bridge Mono

Eric Simna said:
So. I'm looking for experiences. Has anyone that has own the Crest VS1500 run them down to 2ohms in Bridge Mono? I'm trying to plan ahead. Currently I have a pair of the amps, and 4 SRX728s. I don't necessarily want to run that way. But sometimes you gotta do what you gotta do.

BTW. Typically I'll only need 2 of the 728s.
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You would probably only need two total if you powered them properly. One side of a Crown iTech 6000 (3000w @ 4ohms) is about a perfect match for the 728's. That being said, your amps will not last long running 2 ohm bridge, if you got a couple of minutes runtime out of it on subs before it overheats I'd be surprised. Run one box per channel so every thing is at 4 ohms and keep the amps out of clip.
 
Re: 2ohm Bridge Mono

Craig Hauber said:
2-ohm bridged is the same as 1-ohm per side if running in stereo mode, not recommended for anything other than old crown MA series -and even then they have to be configured right. Also if working correctly the draw on the AC line would be really high and breakers that normally don't may trip under those conditions
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Macrotechs are designed to run in parallel mono for low impedance loads, which effectively doubles the impedance each side of the amplifier sees. The only amplifiers that I know of designed to be run into stupid low impedances are the old 10kW class amplifiers from Crown and Crest. The Crown MA-10000 in particular is rated for operation down to .5 ohms, with maximum output into a load of .85 ohms.
 
Re: 2ohm Bridge Mono

Chris Gruber said:
You would probably only need two total if you powered them properly. One side of a Crown iTech 6000 (3000w @ 4ohms) is about a perfect match for the 728's. That being said, your amps will not last long running 2 ohm bridge, if you got a couple of minutes runtime out of it on subs before it overheats I'd be surprised. Run one box per channel so every thing is at 4 ohms and keep the amps out of clip.
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I would only say perfect match if the limiters are set right. Anything short of that, and you are asking for a trip to the recone shop. Fast.
 
Re: 2ohm Bridge Mono

The crown K2 was advertised to be stable into 1.66 ohms per channel (until crown changed the advertising). Not many pro audio amplifiers can handle the excess current, so they simply shut off. The only amps that can do bridged at 2 ohms or 1 ohm etc are high dollar competition car audio amplifiers.

Besides, if you bridge a powerful pro audio amp to low impedances and it happens to actually work, you will probably melt your speakon connectors due to excess current.
 
Re: 2ohm Bridge Mono

Eric Simna said:
And that's all I needed to hear. Didn't think it would work. But thought I'd ask.

And an IT6000 would be nice. But completely cost prohibitive right now.
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Eric, how did you end up with a slew of high-power pro subwoofers but yet you have old, low-power amps? As was said above, if you properly powered only one or two of those subs, it would most likely outperform all four on the small Crest amps you have, no matter what configuration you set the amps up in.

@Graham, I have used IT8000s with SRX718s extensively, and even with the limiters set, the amp almost always clips before the limiters kick in. So in most cases (aka, NOT EDM), the limiters would not matter much for the lesser-powered IT6000. (I am obviously assuming that the clip limiter will always be engaged.)

When I was young and stupid (wait a minute...), I was able to melt two SRX718s with an IT8000 after running EDM for three hours with no limiters.

@Tim, if an amp is capable of exceeding 50 amps continuous output (the rating of a Speakon), then you're either supplying it with camlocks, or the breaker is going to trip long before the Speakon melts.
 
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Re: 2ohm Bridge Mono

Silas Pradetto said:
@Graham, I have used IT8000s with SRX718s extensively, and even with the limiters set, the amp almost always clips before the limiters kick in. So in most cases (aka, NOT EDM), the limiters would not matter much for the lesser-powered IT6000. (I am obviously assuming that the clip limiter will always be engaged.)
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I haven't clipped the IT8000 with 2 or 3 SRX718s hanging off each side. I also have Limiters set and they've engage themselves well before I clip or trip a breaker. I've tripped a 20amp breaker with 3 SRX718s per side when I was working with a Go-Go/Hip-Hop band; limiters hitting -10 dBs when hitting the sampler pad (not me driving the rig) and tripped breaker.
 
Re: 2ohm Bridge Mono

Silas Pradetto said:
Eric, how did you end up with a slew of high-power pro subwoofers but yet you have old, low-power amps? As was said above, if you properly powered only one or two of those subs, it would most likely outperform all four on the small Crest amps you have, no matter what configuration you set the amps up in.
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One of the other guys in town is a friend and he picked up the subs. And then he was deployed a year earlier than expected. So I've got the subs. He didn't have a chance to pick up amps for them before leaving. This was what I could afford at the time. And really, the VS1500s put out 2k @ 4ohm bridge. So while not ideal, not the worst case scenario either.

The plan right now is to get Macrotechs, once we can afford them. But sometimes, you just have to make do. I will NOT be running these into the ground. It was an idea I thought 'maybe?' And figured I'd ask. Better to ask and be told I'm stupid than to do it and blow something up and really regret it.
 
Re: 2ohm Bridge Mono

Eric Simna said:
The plan right now is to get Macrotechs, once we can afford them. But sometimes, you just have to make do. I will NOT be running these into the ground. It was an idea I thought 'maybe?' And figured I'd ask. Better to ask and be told I'm stupid than to do it and blow something up and really regret it.
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Your “small” 49 pound vs1500 amps may deliver more actual sub power than others rated at far more power.

Though the Crest vs1500 is only rated for 70.7v RMS, it is rated for 200V peak, which would be 10,000 watts at 4 ohms.

Current limiting would keep the amp from delivering high peak power at impedances below 4 ohms, so obviously a 2 ohm mono load, equivalent to a 1 ohm load will just cause the amp to pump (or "sound like ass" as Bennett so precisely puts it).

Doubling the speakers gives you a real 3 dB, doubling power seldom gives a real 3 dB increase at high power levels due to thermal compression.

Easy test to do, pick a track with a lot of slamming kick and bass, play it in to a pair of the SRX 728 run up to flashing the clip lights, then compare the output to one SRX 728 bridged mono with a dB meter set for fast response.

I’d be willing to make a small bet that two SRX 728, one per side of your Crest vs1500 will have quite a bit more actual peak SPL output (at least 4 dB more) than one run bridged mono.

I’d also bet the Crest vs1500 will make more actual sound come out of your subs than many amps rated for twice the RMS power, do an A/B amp comparison before you finalize your plan to buy Macrotechs.

I was a bit surprised when I actually tested a variety of amps in the fashion I suggest above, as I mentioned in this review:

http://www.soundforums.net/live/threads/1315-SpeakerPower-Torpedo-SP1-4000-Plate-Amp

Power specifications for amps used for subs don’t necessarily dictate real world performance, especially with less than perfect AC mains voltage.

Art Welter
 
Re: 2ohm Bridge Mono

Silas Pradetto said:
Eric, how did you end up with a slew of high-power pro subwoofers but yet you have old, low-power amps? As was said above, if you properly powered only one or two of those subs, it would most likely outperform all four on the small Crest amps you have, no matter what configuration you set the amps up in.
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So Silas, how about a single EV P3000 bridged into 4ohm per sub? Will that make you happier? Now my limit is just the power available.

Now where's my back brace?

P.S. If you haven't figured out who my partner in crime is yet, I'm shocked.
 
Re: 2ohm Bridge Mono

Eric Simna said:
And that's all I needed to hear. Didn't think it would work. But thought I'd ask.
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Oh, don't get it wrong... it will "work", and I doubt you will seriously damage anything. Even though sound will come out, that amp will heat right up and be ready for baking cookies before too long. However, as has been mentioned, it will sound like total ass. Like Art mentioned, one sub on each side of this amp will do a surprisingly good job as long as the AC mains power is solid. You can get mad current out of the old Crest amps. I've got a stack of old school Pro 01 series here that I love to use just for stuff like this.

So the moral of the story is, you COULD do it and it would make noise, but you'd have much better success with one of these amps for each pair of subs. and just run them in stereo or parallel mode, NOT bridge mode.
 
Re: 2ohm Bridge Mono

@Tim, if an amp is capable of exceeding 50 amps continuous output (the rating of a Speakon), then you're either supplying it with camlocks, or the breaker is going to trip long before the Speakon melts.
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Define "continuous"...

I have melted many speakons with an XS1200 bridged at 4ohms. The funny thing is, the contacts inside the speakon welded themselves to the cable and the surrounding plastic inside the housing melted, the nose of the speakon connector did not melt.
 
Re: 2ohm Bridge Mono

Tim Duffin said:
Define "continuous"...

I have melted many speakons with an XS1200 bridged at 4ohms. The funny thing is, the contacts inside the speakon welded themselves to the cable and the surrounding plastic inside the housing melted, the nose of the speakon connector did not melt.
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That means your terminations were arcing and therefore creating heat. A bad wiring job is the problem, not the amplifier.

I just did a show with a pair of IT5000HDs bridged into some SRX728S subs, slamming them hard all night. No issues.
 
Re: 2ohm Bridge Mono

Eric Simna said:
So Silas, how about a single EV P3000 bridged into 4ohm per sub? Will that make you happier? Now my limit is just the power available.

Now where's my back brace?

P.S. If you haven't figured out who my partner in crime is yet, I'm shocked.
Click to expand...

Eric, I don't know you or your partner in crime personally, at least, that I know of.

Feel free to PM me with details. :D~:-D~:grin:
 
Re: 2ohm Bridge Mono

Silas Pradetto said:
That means your terminations were arcing and therefore creating heat. A bad wiring job is the problem, not the amplifier.

I just did a show with a pair of IT5000HDs bridged into some SRX728S subs, slamming them hard all night. No issues.
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Connections need not be arcing to melt connectors. An improperly made crimp connection (or loose screw terminal) can have the same effect. Remember that power is I^2R, so a 1 ohm connection with 10A through it needs to dissipate 100W of heat.
 
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