PDA

View Full Version : Bridging Fronts



bradl79
06-12-2013, 12:00 AM
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?

bradl79
06-12-2013, 05:21 AM
anything?

RicksI30
06-12-2013, 06:07 AM
As long as you set the gain, and hpf correctly you will be fine.

calebkhill
06-12-2013, 06:12 AM
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
06-12-2013, 04:25 PM
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
06-17-2013, 05:14 AM
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
06-17-2013, 05:16 AM
Adding some fans would help too

keep_hope_alive
06-17-2013, 02:49 PM
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
06-17-2013, 03:15 PM
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 :crap:

calebkhill
06-17-2013, 07:25 PM
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
06-18-2013, 04:09 AM
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
06-18-2013, 04:18 AM
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
06-18-2013, 05:53 AM
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
06-18-2013, 06:02 AM
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
06-18-2013, 02:46 PM
I would never recommend setting gains with DMM for speakers. Just do it by ear.

black05alti
06-18-2013, 02:47 PM
^^ This for sure

keep_hope_alive
06-18-2013, 02:55 PM
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.
yes.



I would never recommend setting gains with DMM for speakers. Just do it by ear.
never say never. i've met plenty of people that think clipping and distortion are just what loud music sounds like. let them set by ear and they would just max everything and think all was well.

it is useful to use the DMM as a check to see what RMS voltage you are getting out of the amp and if that makes sense with expectations. but you always fall back on what you hear as being your guide.

usually, speakers need much less power so gains are lower anyway.

black05alti
06-18-2013, 02:56 PM
never say never. i've met plenty of people that think clipping and distortion are just what loud music sounds like. let them set by ear and they would just max everything and think all was well.

it is useful to use the DMM as a check to see what RMS voltage you are getting out of the amp and if that makes sense with expectations. but you always fall back on what you hear as being your guide.

usually, speakers need much less power so gains are lower anyway.

Let those people learn that hard way then lol..

keep_hope_alive
06-18-2013, 03:05 PM
Let those people learn that hard way then lol..

thing is, they won't learn if you don't take the time to teach them. we cannot just say "listen for distortion" since that requires some hands-on training.

using a DMM is safer and usually quite conservative. I have no issues recommending it to a Novice as it also introduces them to Ohm's law and gets them using a DMM. the effort teaches several concepts.

black05alti
06-18-2013, 03:08 PM
thing is, they won't learn if you don't take the time to teach them. we cannot just say "listen for distortion" since that requires some hands-on training.

using a DMM is safer and usually quite conservative. I have no issues recommending it to a Novice as it also introduces them to Ohm's law and gets them using a DMM. the effort teaches several concepts.

This is true. But this is just one thing I don't about forums... I'd rather be teaching people hands on in person. I'm not the best at explaining things online.

calebkhill
06-18-2013, 03:15 PM
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; keep_hope_alive;

What about that that I mentioned earlier. Using a tone to set by ear.

Buck
06-18-2013, 07:53 PM
It's definitely worth it to develope the ear to tune anything without needed other equipment. Idk, I have an ear for EQ'ing and setting gains. If you do it enough, it's very easy to tell when something is off.

Buck
06-18-2013, 07:56 PM
You don't need a tone. Set it on the music you play, heavy music with a lot of sounds, a lot of range in the spectrum.

keep_hope_alive
06-18-2013, 08:21 PM
tones would be easier than music, because music is dynamic and constantly changing.

Autosound 2000 Disc 102 includes tones that intentionally clip for 3-4 seconds so you can hear what it sounds like. it allows you to easily set gains by ear.

keep_hope_alive
06-18-2013, 08:25 PM
This is true. But this is just one thing I don't about forums... I'd rather be teaching people hands on in person. I'm not the best at explaining things online.

likewise. my efforts in person are somewhat different than my recommendations in forums. over the years i've honed my recommendations and general rules, knowing that many more people will read my posts than will ever comment on it (many non-members). so i consider my audience to be more than the OP but the general public and people all over the world.

calebkhill
06-18-2013, 08:27 PM
tones would be easier than music, because music is dynamic and constantly changing.

Autosound 2000 Disc 102 includes tones that intentionally clip for 3-4 seconds so you can hear what it sounds like. it allows you to easily set gains by ear.
bradl79;
There's your answer.
Of course you don't need the disk. Get a tone and listen carefully, you'll tell when it clips.

And I feel like being technical right now lol, but the only thing I see going wrong with this is if your amp puts out way more than you're speakers can handle and you end up putting too much power to them before the amp clips.

Of course this probably isn't the case in most situations.

keep_hope_alive
06-18-2013, 08:34 PM
setting with tones is pretty conservative anyway. even after you set gains, you use good judgement for volume setting. or PM me for links to those tracks.

black05alti
06-19-2013, 01:18 AM
likewise. my efforts in person are somewhat different than my recommendations in forums. over the years i've honed my recommendations and general rules, knowing that many more people will read my posts than will ever comment on it (many non-members). so i consider my audience to be more than the OP but the general public and people all over the world.

That's a very good way to think about. I'll have to keep this in mind.