Check the 3rd paragraph if you just wanna read the question and skip the background. I recently bought a 06 Rio Yellow, I love the car, and want to upgrade the stock sound. I've been 'shop hopping' listening to different speakers, amps, head units.

I really like the Boston Acoustics SL60 Speakers. They are rated at 80watts rms, 220 peak. I also plan on adding a head unit, and I'm waffleing between Alpine, Nakamichi, and Eclipse. I'm pretty careful with the volume and amp gains, so unless anyone has a reason why I shouldn't, I'm going to add an amp with a slightly higher power output than the rating on the speakers. I'm looking at the Boston Acoustics GT-24 and GT-40 amps. The 40 is a 4 channel amp that can provide bridged power of 140 watts rms *2 @ 4ohms. The 24 is a 2 channel amp that can provide 120 watts * 2 @ 4ohms. I wouldn't hesitate and buy the 2 channel (120 seems like plenty) but the 4 channel amp is 150$ cheaper!

So my questions is, is there any issue with sound quality when bridging a 4 channel amp to 2 channels? Would it be better to spend the extra $ on the weaker 2 channel amp, or just go with the cheaper/stronger 4 channel bridged amp?
Also is this way way too much power for these speakers (i.e. will I blow them even if I'm relatively careful)? There is also a 2 channel * 75 watt amp avaliable from BA, would this be a better choice?

 

You can get the 4 channel amp. Just turn the gain down and tune it right and they'll be fine.

 

*nods*

the GT-40 is a fine amp and as long as you're careful setting the gains, you shouldn't blow anything.

there are some theoretical reasons why you'd want a 2 channel over the 4, but they are really outside of the realm of practical application (imo), and not worth worrying about.

 

Thanks!

 

what's cool is that the SL60s are bi amp capable. You can run a separate feed to the mid and the tweeter, dropping the load to 2 ohms. This way, you could even get a smaller amp--say, the GT20 (runs 80w x 2 at 2ohms) and have more money left over for a dedicated sub amp, if that's a possibility for you.

edit: Forgot to mention, if you really wanted the GT40, could run the amp at 4 ohms, non-bridged... it's 45w x 4, so you could run each channel to a speaker (bi-amp setup) and it would be about 90w per side on your components.

 

I already have a dedicated sub amp and sub. No box yet, still designing it... unless someone knows where I can get a 3/4 MDF box that fits a 12" sub in the tool well and has >.93 cubic feet of air for a reasonable price...

The GT-40, and SL60s are already on their way...

So as far as the speakers/speaker amp goes I can either
bridge the channels and have 2*140 watt with 4 ohm lines,
or I could
run the speakers bi-amp and have 4*70 watts with 2 ohm lines.

From my understanding the 2*140 would have a better distribution of power between the tweeter and mid range speaker because of the included BA box?
However the 4*70 setup allows me to skip bridging the amp...
Which is the better setup in my situation?

 

Let me see if I understand. You will have one pair of SL60 components, right? not two?

If you only have one pair (left and right, in the doors) then you will not be running a 2 ohm load. You can run 4 ohms, which will give you 45w x 4---45w to each tweeter, and 45w to each mid. Running in 4 ohms will allow the amp to run cooler and gives you lower THD anyway (though I doubt your ears could tell the difference). I don't think running bridged will give you better power distribution--technically, if the speakers are the same impedance, they'll get the same amount of power anyway (somebody please tell me if i'm dumb for saying this)? And the included BA crossover actually physically splits (see link to manual below) so it blocks low freq's to the tweeter and blocks high freq's to the mid.

http://www.bostonacoustics.com/manuals/SL60Man.pdf

 

Yes, 1 pair of speakers. The speakers and amp just arrived, and I'm even more confused now!
So what you are saying Will, is that if I wire the speakers in "Bi-amp" mode, I will click the amp switch that sends the 'front amp input' to both the 'front and rear speakers'. Then to each mid-range I will send the 'front speaker' outputs from the amp, and to each tweeter I will send the 'rear speaker' outputs from the amp.
However, this is NOT what the diagram in the speaker instruction manual shows. (In the instruction manual "Bi-amp mode" is running both crossovers in parallel from a SINGLE amp 'speaker output'....)

 

I just got my SL60s tonight also. It does appear that the internal crossover has higher impedance for the tweeter (about 5 ohms) than for the mid (about 1.5 ohms)... weird...

So I thought of something I didn't notice before--you don't want to bridge the amp to run these speakers. Why? Because when you bridge you are bridging the right and left channels, eliminating stereo sound. You're converting to mono. You'd have to hook the front channels to one component set and the rears to the other. I don't know how it would sound but i'm guessing like crap. Not to mention you'd be at almost double the rated power for those speakers, so you'd have to turn the gains way down. But how far? You won't know for sure.

If I already had the amp and speakers, like you, I would just use the front channels--leave the rears disconnected and leave yourself open for connecting some rear speakers in the future if you want--and run the front channels at 2 ohms using the bi-amp setup. You'll have 70w running to each side, it will sound great, and you'll be happy.

 

thought about it some more, and I still think this would work fine. run it exactly how you described, and again, somebody correct me if I am wrong, but the higher impedance on the tweeter crossover will limit the power going to that speaker and the lower impedance on the mid crossover will allow more power to go to the mid. All in all it should allow for the equivalent of 90w x 2.