Mismatched amp/speakers: What can I expect from a Limiter?

[K2000]

How robust can a Limiter be (specifically, on the Behringer DCX2496 or CX3400) and will heavy limiting have a negative effect on my sub's sound?

I have a subwoofer rated at 3 ohms, that the manufacturer rates at 200 watts RMS, and 500 watts peak. The manual suggests sending no more than 20 volts to the cab.

I need to power this sub safely... I will probably buy a Behringer DCX2496 or possibly the CX3400. I currently have an available channel in my Carvin HD1800 amp, but I'm worried that it's way, way too much amp for this sub. The Carvin amp ratings: 900 watts @ 2 ohms, 600 watts @ 4 ohms. (so at 3 ohms, I assume 750 watts, all things being equal). The Carvin amp currently powers a BFM Omni 212, with just one channel being used. Perfect match of ratings there. If I can run the low power sub in the Carvin's other channel, I'll save money and there's less to carry.

Do I need to buy a less-powerful amp, or can I run my sub safely with my current amp and a good Limiter, and sound good?

(Since I have your attention, the alternate amps I'm looking at are):

QSC RMX850 (430 watts @ 2 ohms, 280 watts @ 4 ohms)
QSC MX700 (350 watts @ 2 ohms, 270 watts @ 4 ohms)
Carvin DCM 1000L (500 watts @ 2 ohms, 325 watts @ 4 ohms)

(It seems hard to find an amp that runs at 2 ohms, that is also relatively low-powered.)

[wallywally]

A limiter will work with any size amp. It limits the input voltage. An amplifier simply amplifies that input voltage. Search and read on how to properly set a limiter up. Also read gain structure.

[K2000]

Thanks.

To be more specific, can the DCX's Limiter limit a 900 watt amp to 20 volts? And do it without narrowing the frequency response, or degrading the audio quality? Would I be better off if I had a less powerful amp to begin with?

[wallywally]

I don't own a DCX so I'm not positive of it's capabilities. No limiter will narrow freq response. Limiters only degrade audio quality when it's deep into limiting(it will remove all dynamics). A limiter is meant to protect your drivers from unintended overpowering. During normal operation of your system, the limiter should not activate (occasionally is OK). If you are frequently turning it up so much that you get into the limiter....you need more speakers. No problem with an amp being overpowered, it will limit down just fine.

[Bill Fitzmaurice]

If I can run the low power sub in the Carvin's other channel, I'll save money and there's less to carry.

The problem is that you won't be able to hear that sub. What it will do with 20 volts the OTop probably will do with 2.

[K2000]

Here's my setup (I posted about this originally in the THT forum)

Omni 212 crossed over at 100hz (mids/highs)
Two Bag End SE 18 subs

I just found a Servodrive Contrabass (cheap) so I decided to try it. I'm thinking that I will cross the Contrabass over around 50hz (initial guess) just to reinforce where the Bag Ends drop off. This is the cab I'm asking about powering (takes 20 volts, but within a narrow, low freq. range... I don't know if that makes a difference).

As described above, the Carvin amp is a good match for the Omni212 (600 watts at 4 ohms, perfect) but a poor match for the Contrabass (the Carvin is 900 watts at 2 ohms... the Contrabass is 200 watts @ 3 ohms). But there is an unused channel on the Carvin, so if it can be used safely for the Contrabass too, that's "winning" (or something).

The Omni 212 is never going to see the frequencies that the Contrabass does, so they will not compete. The Bag Ends will see some of those frequencies, but are inefficient at reproducing them.

Can I safely use the Carvin amp for the Contrabass with the limiter in the Behringer processor? Does robust limiting have a negative effect on low freq. sound quality? What are the (er...) limits on what a Limiter can do? Am I better off starting with a less powerful amp? That would mean another purchase, and less headroom for the Omni212 (or use separate amps for everything... kind of a pain).

[Bruce Weldy]

I think you missed Bill's point. What he is saying is that with your sub getting it's maximum amount of voltage - it can't even come close to keeping up with the Omni 212.

In other words.....build or get a sub that can handle more power or else you will blow it trying to keep up with the tops, or you'll never hear it if you keep it at 20 volts.

[DJPhatman]

K2000, are you running an Omnitop 212, or an Omni 15 with the 2x12 driver option? Even a low resolution cell phone pic of the cab would answer a lot of questions.

[K2000]

It's an Omnitop 212.



I'm not sure why that's relevant, but there it is. (I didn't build this cab -- I am not able to build anything currently -- the seller told me it's an Omni 212)

Just pulled up the original email, it's rated at 500 watts not 600.

29" H
22" W
18" D

[K2000]

I think you missed Bill's point. What he is saying is that with your sub getting it's maximum amount of voltage - it can't even come close to keeping up with the Omni 212.

In other words.....build or get a sub that can handle more power or else you will blow it trying to keep up with the tops, or you'll never hear it if you keep it at 20 volts.

I'm sure that's true. But will I be able to run the cab using the Carvin amp and a DCX's limiter, just to test it? Nobody can answer the basic question?

[Bruce Weldy]

I think you missed Bill's point. What he is saying is that with your sub getting it's maximum amount of voltage - it can't even come close to keeping up with the Omni 212.

In other words.....build or get a sub that can handle more power or else you will blow it trying to keep up with the tops, or you'll never hear it if you keep it at 20 volts.

I'm sure that's true. But will I be able to run the cab using the Carvin amp and a DCX's limiter, just to test it? Nobody can answer the basic question?

Yes, you can run that sub with that amp. Will the Behringer be able to limit it enough? Should be able to. If not, turn the volume knob on the amp down until it tops out at 20 volts.

The point everyone is trying to make in a roundabout way is that running that sub with those tops is a giant waste of time. You will not be happy with the balance of the system - everything over 100hz (the OT212s) will be screaming. Everything under 100hz (your sub) will be whining.....if you can hear it at all.

Keep the amp and build a couple of BFM subs that can keep up with the tops. Those tops are way loud and will require a minimum of two subs - maybe more depending on what type of material you are going to put through them.

[Gregory East]

I'd be very surprised if you can't get the DCX to limit enough to choke the amp back to 20V output.

You will have to hold the 212 way back to get a balanced sound. Nothing wrong with that except it's a giant waste of the capability of the 212.

Same deal in reverse with my auto sub, the rear speaker set is 16W each. It's plenty loud enough for me, ymmv.

[Radian]

Do I need to buy a less-powerful amp, or can I run my sub safely with my current amp and a good Limiter, and sound good?

The DCX2496's limiter threshold can be set as low as -24dB of the incoming signal. With few exceptions, most "stout" pro audio amps typically support ~26-30 dBW of signal gain. In your worst case, limiting the input signal of a an amp reportedly capable of 29 dBW driving a 2 ohm load, would leave 5 dBW still available. That's 2.5V in that case. So, yeah, the DCX would still have you well covered.

[BrentEvans]

Do I need to buy a less-powerful amp, or can I run my sub safely with my current amp and a good Limiter, and sound good?

The DCX2496's limiter threshold can be set as low as -24dB of the incoming signal. With few exceptions, most "stout" pro audio amps typically support ~26-30 dBW of signal gain. In your worst case, limiting the input signal of a an amp reportedly capable of 29 dBW driving a 2 ohm load, would leave 5 dBW still available. That's 2.5V in that case. So, yeah, the DCX would still have you well covered.

That said.... you don't want to be pushing the snot out of your limiters. It will sound like crap, and you can still theoretically heat up speakers with too much current over long periods of time... as you push the limiters the waves end up with more and more current (area under the curve of the wave) and even though you won't blow the speaker by overextending it, you can still melt the VC.

However... if you set your gain structure so that you just barely tickle the threshold of the limiter, you'll be in good shape.

And.... sell your subs and get your hands on some Titans!