Amplifier for Audiobahn Bandpass Enclosure?

[Alien Mantis]

Originally Posted by PSYS

Well, if all the cool kids in the sandbox are using monoblocks to drive subs these days... then that's the way I wanna roll, too, dammit!
I'll be the first to admit that I'll need to brush up on my impedance / ohms worksheets. I had ASSumed that a monoblock amp wouldn't work with this enclosure due to it having (2) SVC 4-ohm subs. With the monoblock essentially dropping the impedance of the subs to 2-ohms, I ASSumed that would be bad and should not go that route.

You are wrong, but that's okay. We'll get it sorted out.

A monoblock amp can drive more than one speaker, it all depends on the ohm loading of the entire configuration.
The way you choose to wire the speakers also determines the final ohm load. You can wire speakers in series or parallel.
If you wire your two "single-4-ohm voice coil" subs in parallel, you get a 2-ohm final load. The AMP never determines the ohm load. The speaker(s) and how they are wired together determine the ohm load.
If you wire your two subs in series, you will get an 8ohm load.
Once you have your load factor determined, you can look at an amp to see what it can deliver at your particular OHM rating.
Most modern ClassD monoblock amps can deliver power to an 8ohm, 4ohm, or 2ohm load. Some higher quality amps can also supply power to a 1ohm load.
Some amps need a minimum of 2ohm load to be stable.
An amp can deliver power to an 8ohm load, but it will be LESS power.
The higher the OHM load, the less power the amp can deliver.
We try to strike a balance between power and efficiency with our amps and drivers. Most bass setups are a final 2ohm load.
Next we look at the RMS power requirements for the subs we are using, and select an amp that will deliver this power at the load rating we are using.
If a subwoofer can handle 350watts RMS max, and we are running TWO of them, then we need to find an amp that can deliver around 600-700 watts RMS.
The enclosure also plays a factor in which amp to choose.
A sealed box can control higher power. A ported or band-pass box will not control excessive power at the subwoofers. So you must be careful not to overdrive them in that enclosure.
You can always run a stronger amp than what your subs are rated at, because you can always adjust the amp's GAIN lower.
If your amp is too small for the subs you are running, you cannot simply turn the GAIN up more. This will cause clipping, and you will overheat your system.
It is safe to buy an amp that has slightly less power than the max rating of your subs. This way you can drive them hard, without worrying about accidentally overdriving them. They will run cool and last a long time.
If your two subs are rated at 300watts RMS each, and you have them in a ported box, and they are wired at a final load of 2ohms, then you can buy an amp that delivers 500watts RMS at a 2ohm load and be happy.
It will work fine. ( Especially if it is a good quality amp. )
If you want to run a smaller amp, then you need to choose subs that are more efficient, and require less power.
It helps to first decide what you are trying to accomplish, then choose ALL your components according to that master plan. Components that match and compliment each other.
Whatever you choose, always use the proper wiring.
Bad wiring can ruin good compenents. The chain is only as strong as the weakest link. Choose good components, run good wiring.