Straight thru or bridged?

[RJP56]

I'm installing 4- 75 watt tower speakers which are being run off of a 75x4 channel amp. Is it better to pull 4 sets of wires thru or would it be alright to pull two thru and run the for speakers bridged? What are the advantages/disadvantages?

[TravisFling]

RE: Straight thru or bridged?

Kind of depends what ohm the speakers are and what ohm load the amp can handle. do you have any information on the amp and speakers? If you run two wires through you can either bridge the speakers, basically giving you more power, but increasing the load on the amp, or you can run them in series, which would give you less power but be easier on the amp. If the amp can handle it, and the speakers can handle it, then yes!!! YES!!! YES!!! Bridge the snot of out 'em and crank it up!
www.bcae1.com

[RJP56]

The speakers, 75rms or 150 peak are 4 ohms. The Amp is 75rms x 4 at 4ohms or 180rms x 2 at 4 ohms. Would I also have to up the wire gauge from 14awg?

[TravisFling]

well, if you're running two speaker wires up the tower then how would you bridge those? You could run a set of wires from speakers 1 and 2 and tie them together to the tower wire 1 and then speakers two and three and tie them together to tower wire two, which would net a 2 ohm load to the amp, and you'd only be using two channels of the amp, so that would leave two channels open to run something else off of, like the bow speakers. What kind of boat are we talking about?

[RJP56]

It's a 2001 Air Nautique. Wouldn't bridging them at the Amp use all four channels? I think it's the standard set-up. Clarion XMD1 and four speakers in the boat.

[Hollywood]

So you are talking about running 2 sets of parallel speakers (essentially a pair of 2 ohm speakers) off a bridged amp....

Sounds ok to me? Be careful I'm thinking you can blow them pretty easy this way though. Lots of power, little resistance. 14 awg is fine.

[EarmarkMarine]

RJP56,

If you run your tower speakers in series and bridge the amplifier you'll get 300 total watts, which is the same as running in the four channel mode. The series/bridged combination has the advantage of being able to use your existing tower harness. And, the 14-gauge is fine for what you have.

Parrallel and bridged is definitely an unsafe combination where your amplifier will quickly thermal or go into protection. Very few amplifiers can be bridged into a two-ohm load. Plus, those few exceptions wouldn't last long when mostly driven near full capacity. As is usually the case with tower speakers.

David
Earmark Marine

[Hollywood]

Can you show us the math on that?

[MHayes]

Can you show us the math on that?

I'd be curious to see that as well. With the speakers wired in series (2 on each side), you have an 8 ohm load for each of the two channels when bridged. The OP stated that the amplifier in bridged mode will put out 180w x 2 at 4 ohms. So how did you get to the 300w total bridged at 8 ohms, not knowing exactly what amp the OP is talking about?

[RJP56]

The Amp is an Infinity 475a and the speakers are Rockford Fosgates mounted in an Audioformz tower can.

[RJP56]

Sorry... Rockford Fosgate t162c's in an Audioformz can.

[EarmarkMarine]

Here's the basics.

When you bridge an amplifier you are 'effectively' halfing the measured impedance related to power output and stability. So, on an amplifier with an unregulated power supply the total two-ohm stereo power will usually be equivalent to the total four-ohm bridged power.

Similarly, the total four-ohm stereo power is typically the same as the total eight-ohm bridged power.

As a side note, once you approach the limitations of the amplifier's power supply section, you can toss ohm's law out. Theory only applies when you have unlimited current. Plus, amplifiers are not linear devices as their efficiency will change into different loads. While the math generally holds true there are numerous qualifications when put to real world application.

David
Earmark Marine

[MHayes]

Thanks for the explanation David.

[Andrew]

stick an ohm meter on the leads and it will be pretty obvious rather quick like....

[Mikeski]

I hate trying to explain how to do this, nobody seems to get it, but here goes anyway. You can save wires by wiring each pair of tower speakers in series then hook them up to a pair of bridged amplifier channels. This is exactly the same load and output as wiring each speaker to each amplifier channel, as David states in his first post.

Doing the math, no need the internal connection is already done inside the amplifier rendering 4 of the 8 wires of a 4 pair wiring virtually useless.

In a typical amp your layout is: L+, L-, R+, R-

The L- and R+ are the same conductor within the amp as long as it is setup for bridging. As long as your speaker impedence is balanced there is no reason to run the redundant wires.