Bridging Fronts

[bradl79 10+ year member]

ok so i have Rockford Fosgate T165s Comp. Speakers 80w RMS @ 4ohm, can i use my 4ch apline mrp f300 to bridge them and just get a mono block for my sub, the rms for bridging is 150w rms @ 4ohm, will that hurt the speakers or amp?

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[bradl79 10+ year member]

anything?

 

[RicksI30 10+ year member]

As long as you set the gain, and hpf correctly you will be fine.

 

[calebkhill 10+ year member]

You'll be fine. Like the above, be easy on the gains, and set your hpf.

Idk if your amp is stable at 2ohm bridged, it'll run hot probably, but if you be easy O the gains it'll be ok.

 

[bradl79 10+ year member]

So would I still set the gains accordingly using a dmm like if my amp is 150 RMS @ 4ohm bridged that sets the voltage at 24.49. Do I still set it at that ?

 

[calebkhill 10+ year member]

So would I still set the gains accordingly using a dmm like if my amp is 150 RMS @ 4ohm bridged that sets the voltage at 24.49. Do I still set it at that ?

The amp isn't 2 ohm stable bridged. I run the same amp. Its going to run hot. You'll be okay as long as your conservative with those gains.

You could use dmm but go easy on the amp.

 

[black05alti]

Adding some fans would help too

 

[keep_hope_alive Premium Member]

The amp isn't 2 ohm stable bridged. I run the same amp. Its going to run hot. You'll be okay as long as your conservative with those gains.You could use dmm but go easy on the amp.

doesn't have to be 2 ohm stable for a single pair of 4 ohm comps. i think you are assuming front and rear in parallel. if he has a pair of 4 ohm speakers up front, he bridges channels 1&2 to the front left @ 4 ohms and bridges channels 3&4 to the front right @ 4 ohms.

the key is making sure gain is equal for all channels. so use a DMM and a test tone to set within a tenth of a volt or better.

usually set gains for the speaker RMS rated power. but leave yourself head room for the recording level of various artists.

 

[Buck 5,000+ posts]

You'll be good. Make sure you set your HPF high enough where you don't blow your speakers from the bass passing through. You can blow a speaker really quick with bass, ask my Bostons //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif

 

[calebkhill 10+ year member]

doesn't have to be 2 ohm stable for a single pair of 4 ohm comps. i think you are assuming front and rear in parallel. if he has a pair of 4 ohm speakers up front, he bridges channels 1&2 to the front left @ 4 ohms and bridges channels 3&4 to the front right @ 4 ohms.
the key is making sure gain is equal for all channels. so use a DMM and a test tone to set within a tenth of a volt or better.

usually set gains for the speaker RMS rated power. but leave yourself head room for the recording level of various artists.

I thought when you bridge you cut the impedance in half . So a 4 ohm speaker bridged is now a2 ohm load.

 

[zako 10+ year member]

So would I still set the gains accordingly using a dmm like if my amp is 150 RMS @ 4ohm bridged that sets the voltage at 24.49. Do I still set it at that ?

You don't have to set speaker gain with DMM. Just don't do stupid things like trying to experiement "how hard your speakers hit". Besides, there is no good verification that the speaker will handle the rated power. Just use them to enjoy the music. Personally, I wouldn't mind running the components without bridging. Most of components with very high power ratings will still bottom out (hit back plate) on their rated power or often less unless you set your high pass to an unusually high frequency. The F300 is rated for 4x50watts, but I have seen tests showing they're underrated and will give you something like 4x65watts at 4ohm with 14.4V. Even if your voltage is lower, it's guaranteed that you should get at least 50clean watts on each channel without bridging. On the other hand, like I said, there should be no harm done when bridging. I don't like bridging class A/B amps as many run a lot hotter, but i believe F300 is class D, so it should do fine.

 

[Buck 5,000+ posts]

I thought when you bridge you cut the impedance in half . So a 4 ohm speaker bridged is now a2 ohm load.

It cuts the ohm load of your amp in half kind of, not your speaker.

If an amp is 2 ohm stable in 2 channels, and you bridge those two together, now both together are only 4 ohm stable. They usually put out the same amount of power as the 2 channels at a 2 ohm load. So say each channel is 100w @ 2 ohms, bridged total would be 200w @ 4 ohms.

Same thing works with strapping sub amps. If you have (2) 1 ohm stable sub amps and you strap them together, they can only handle a 2 ohm load.

 

[calebkhill 10+ year member]

It cuts the ohm load of your amp in half kind of, not your speaker.
If an amp is 2 ohm stable in 2 channels, and you bridge those two together, now both together are only 4 ohm stable. They usually put out the same amount of power as the 2 channels at a 2 ohm load. So say each channel is 100w @ 2 ohms, bridged total would be 200w @ 4 ohms.

Same thing works with strapping sub amps. If you have (2) 1 ohm stable sub amps and you strap them together, they can only handle a 2 ohm load.

Got ya. So the load is still 4 ohm.

So basically you can only bridge 4 ohm speakers, not 2 ohm speakers.

as long as the 2 channels are 2 ohm stable to begin with.

 

[calebkhill 10+ year member]

Another thought i've had.

No oscope.

So why not set your hu atty 3/4, then just up the gain until you hear either clipping or distortion, given you aren't overpowering your mids.

Clipping is obvious at 1khz.....

 

[Buck 5,000+ posts]

I would never recommend setting gains with DMM for speakers. Just do it by ear.