How many channels required for 3-way comps?

[nrgy]

I just got to thinking, I recently purchased a JBL P80.4 four channel amplifier for my stock 3-way comps, using all 4 channels. Besides the amplifiers crossovers, the only other crossover is the tiny one built into the wiring going from the 4" mid to the 1" tweeter.

I plan on upgrading to Boston Pro 6.5 3 ways. Is the 4 channel amp that I have, or two 2 channel amps required to run these speakers? Or is it possible to run 3-ways off a 2 channel amplifier? If so how? The reason why I ask is because I could have purchased the P180 which delivers 90w @ 4 ohm per channel.

Alrighty, thanks.

[n2audio]

Component sets just need 2 channels. The in line crossover will split it into 3 frequencies.

[nrgy]

Doh! I wished I would have figured this out earlier, this would have offered me many more options. Oh well, there is always eBay

Just a few more questions to be crystal clear this time. Right now, with the stock speakers I think I did need a 4 channel amplifier, since it doesn't use crossovers. Instead the two front channels go to the 4" mids and 1" tweeters, and the two rear channels go to each 5.25" woofer.

But when I upgrade to a 3-way system, if I stuck with the 4 channel amplifier, I still would only be able to use 2 of the channels because of the crossover, correct? So in this case, a 4 channel amplifier would be a waste since I could get a more powerful 2 channel amp for the same price, right?

Sooo, if I get a more powerful 2 channel amp like the JBL P180 rated at 90w per channel @ 4 ohm, since the frequencies are being split to 3 different speakers, and I would assume the power as well, how many watts would each speaker actually be receiving, assuming all were 4 ohm speakers.

Also, right now I have two sets of rcas going from the head unit to the amplifier, one for the front and one for the rear. A two channel amp only requires one set. So what does this exactly mean? Will this make my stereo system mono? Or will I just lose the fader control, which I don't need anyhow.

Thank you!

[Fabulas]

Yeah, there are a lot of ways to work it. The easiest would be to bridge the amp to 2 channels and use the passive xovers. You can get much better sound and flexability if you get a 6 channel amp and use the individual built in xovers and gain settings to give much more tweaking abilities. But then that is more costly so you might want to just go with the first method.

[nrgy]

Ahhh, I completely forgot about bridging. This would seem like a much better option since I could keep the amp I have now. The only thing I'm still confused about are the power ratings. The amp I have right now is rated at 40w/channel. So if I bridged the system I would have around 80w going to each crossover, right? But would a particular set of speakers receive more power this way then how I currently have them set up?

I guess to put things in more simpler terms, would bridging a 4 channel 40w/channel amplifier for a 3way system with passive crossovers be the same as buying a 4 channel 80w/channel amp and running the 2 front channels to the 4" mids and 1" tweeters, and the 2 rear channels to the 6" woofers?

I'm just confused on whether or not I would be getting more power to 3way comps by bridging the 4 channel amp. How much power is my current setup receiving, and how much power would an aftermarket set of 3way comps with passive crossovers receive in the bridged setup.

Ahhh Hope my questions made sense.

[Fabulas]

Yes you would probalby get about 80 watts bridged. The advantage is unless you have multiple inputs on your passive xover, you will probalby only be giving your entire set of comps 40 x 40 watts ( as you can only use two of the four channels of the amp) You could bridge it and give it 80 x 80 and it will sound a world of difference. You would not benifit by a 4 channel amp on a 3way system, unless you have some unique passive xovers that are bi-ampable or tri-ampable. Hope I made sense.

[nrgy]

Ok, I think you made sense...but just to clarify.

You are basically saying that if I didn't bridge using a 4 channel amplifier, I would only be getting 40w to each set of comps since I could only use 2 of the channels, and thus wasting 2 channels. However if I do bridge the channels, turning it basically into a 2 channel amplifier, I will be getting more power to the comps and making full use of the amps capabilities. So in other words I'm good to go with my JBL amp?

Heh, this raises a few more questions. Assuming the components are 4 ohm speakers, what type of load will they be receiving by bridging? Would they see a 4 ohm mono load? If I bridged, then would the components be in mono?

And lastly, the Boston Pros I am interested in are 3 ohm. Would this be a problem? The reason I ask is because I think I read somewhere most amps are only stable in a 2 ohm stereo or 4 ohm mono load.

[Fabulas]

All car stereo amps are at least bridgable to 4 ohms. By bridging a four channel amp you would be recieving left to one side and right to the other side, giving you 4 ohm stereo. The 3 ohm thing probalby won't be a problem(amp might heat up a little).

[n2audio]

Assuming your amp is of decent quality...a 40x4 @ 4 ohm stereo amp should put out 160x2 bridged, not 80x2. Not all amps exactly double thier 4 ohm power when driven into 2 ohms, but most good ones are in that vicinity.

[Fabulas]

Originally posted by n2audio
Assuming your amp is of decent quality...a 40x4 @ 4 ohm stereo amp should put out 160x2 bridged, not 80x2. Not all amps exactly double thier 4 ohm power when driven into 2 ohms, but most good ones are in that vicinity.

You're right, it would be about 160x2.

[nrgy]

Yes, I just realized the 160 x 2 also. Wow, even more power than I expected...all the better. But ok, I think I am finally clear on this now. So by bridging the left front and left rear together, and the right front and right rear together, this will still be in stereo, since I have a front sound stage. Therefore the 3 ohm speakers should be ok? They would be getting more than enough power so I wouldn't need to crank it up anyhow.

Thanks again, I'm finally understanding all of this.

[BostonJLman]

YES EXCELENT CHOICE!! with the boston, i have those myself, and you only need two channals for them. if you hhave rear speakers then you would need at least a 3 but most are 4. I have the 500/5 powering them now with 100 watts and they sound unbeleivable, but JL just came out with the 450/4 and i have a down payment on it now, Tweeter over here cant even get one in for display until mid march so i have to wait. But another good choice is the current 300/2 for the front two alone or the 300/4. If you wanted to know how to wire it, just connect the crossover that you get with the speakers to the amp then from the cross over wire your mid your 4 in and your tweet, you will have to play around wtih the settings to get it right though. good luck.

[rpeAMP]

Great choice for speakers. The Bostons will take every watt of clean power you send them, however since you are technically underpowering them, be absolutely sure that your gains are set correctly, or the amp could clip and damage those nice speakers of yours.

FYI- Boston is great about replacing speakers. I have had maybe one out of numerous speakers I have bought from them that had a crack in the cone, and they had a new one out to me the next day FedEx Express 1-day after I sent them the picture. I don't even think that the speaker was under warranty at the time (was an RX47).

Good luck with the install and since I have a similar system, feel free to e-mail me or PM me with any specifics you may wonder about.

BTW- Boston states 3 ohm, but that's the "nominal" impedance. No rating is exactly correct, and you will not damage or continually drive your amp into protection mode as long as you understand the limits of the amp and set the gains accordingly.

[nrgy]

Cool, thanks everyone for the feedback.

I think I'll stick to the Boston's then. I was worried about running the 3 ohm Bostons with a bridged amp but it sounds like everything will be ok as long as it is properly set up. I was about to change my selection to MB Quart Premiums just to be safe, but no longer.