Bridging an amp?

SPAZ5446 · #1 02-01-2011, 05:35 PM

I was recently looking at some bass heads that allowed bridging and increase power, but even after searching I still don't fully understand the concept. I've been looking for a head to power a 600 watt 8 ohms 4x10 cab, but found that getting close to even 400 watts at 8 ohms would require about a 600-700 watt head. I looked at the Carvin R600 and saw that bridged at 8 ohms gets 500 watts, but I have no idea what that really means.

To get to the point I have a few questions:
1. Is there a simple explanation for bridging?
2. Is it possible to bridge said amp to one 8 ohms cab?
3. What happens if another 8 ohms cab is added (changing the resistants to 4 ohms), how would bridging be done that way?

P.S. Sorry about the number of newbie questions I've posted in the amps category, I'm totally new to head and cab setups and have had a little 75 watt combo for the past 4 years.

RickenBoogie · #2 02-01-2011, 05:51 PM

You do not need an amp to match the rated specs of a speaker cab. Besides, that rating does not tell you what the cab can actually handle. If you own an 8 ohm 410 rated for 600 watts RMS, a 100 or 200 watt amp will work fine. Forget the numbers, find an amp you like how it sounds.

Marko5657 · #3 02-01-2011, 05:53 PM

Bridging is combining both channels of a two-channel amp.

If you bridge an amp into an 8-ohm cab, each channel will realize a 4-ohm load.

If you bridge an amp into two 8-ohm cabs, which brings the load to 4-ohms, each channel of the amp realizes a 2ohm load, which is only okay if the amp is designed to handle a 2-ohm load.

Marko5657 · #4 02-01-2011, 05:55 PM

Quote:

Originally Posted by RickenBoogie

You do not need an amp to match the rated specs of a speaker cab. Besides, that rating does not tell you what the cab can actually handle. If you own an 8 ohm 410 rated for 600 watts RMS, a 100 or 200 watt amp will work fine. Forget the numbers, find an amp you like how it sounds.

+1

ReedSpacer · #5 02-01-2011, 06:06 PM

An analogy: Imagine you have two heavy objects that need to be pushed to different locations, and two people to push them. Each person can push one of the objects and both will move towards their new locations at the same time.

Now, imagine you only have one heavy object to move, but you still have two people to move it. If one person pushes the object from behind and the other person pulls it from in front, significantly more force can be applied to the object.

Amplifier bridging is similar - two power amplifier channels are combined, with one channel working normally and the other working "backwards" (i.e. its phase is reversed) to apply more power to the speaker. The trade-off is that you no longer have two independent amplifier channels that can drive separate speakers with different signals - you're effectively down to one channel, but it's more powerful than either of the original two alone.

Amplifiers are rated for a certain minimum speaker impedance when run normally, and typically a different (and higher) minimum impedance when run in bridged mode. Check the specifications. If the specifications for the Carvin state a certain wattage at 8 ohms in bridged mode then you should be able to drive your 8 ohm cabinet without risking damage to the amplifier. The Carvin may or may not be rated for a 4 ohm load in bridged mode - again, check the specifications. If you don't see a power rating at 4 ohms in bridged mode, it's pretty certain that the amp is not designed to operate in such circumstances.

SPAZ5446 · #6 02-01-2011, 06:38 PM

Thanks guys! The analogy really put it into perspective for me.
Also the Carvin R600 is rated 4 ohms bridged at 600 watts, while 8 ohms is 500 watts.

SPAZ5446 · #7 02-02-2011, 08:06 AM

One more, probably stupid, question to bring up. With two 8 ohms cabs hooked up so the impedance is 4 ohms, would the bridged amp share the power (300 watts or so into each cab) or push 600 watts into each cab? I'm assuming it would still share power.

SPAZ5446 · #8 02-02-2011, 09:25 AM

mdogs · #9 02-02-2011, 09:32 AM

share

derridiandrift · #10 02-02-2011, 09:37 AM

Quote:

Originally Posted by SPAZ5446

One more, probably stupid, question to bring up. With two 8 ohms cabs hooked up so the impedance is 4 ohms, would the bridged amp share the power (300 watts or so into each cab) or push 600 watts into each cab? I'm assuming it would still share power.

The total power that the amp puts out is divided among all of the drivers that are connected to it. If the two cabs are identical, the total power of the amp is divided equally to the two cabs.

Two cabs that can dissipate 600 watts each can effectively dissipate 1200 watts if they are arrayed in the normal way that bass amps are connected. I'm inferring from your original post were it says that you're trying to closely match your total bridged power to the total power handling capacity of whatever cabs you have. So if you have two cabs that handle 600 watts at 8 ohms you would want to get a power amp that produces 1200 watts bridged at 4 ohms or 600 watts (per channel in stereo) at 8 ohms.

You don't need to get too hung up on the numbers, but you asked the question and there's your answer. Hope it helps.