The choice of the amp and power supply will depend on what you you're trying to accomplish, the exact model of wireless mic and it's power requirements, etc. You didn't mention whether the speakers are cones or horns (but I'll assume they're horns), or what you're attempting to call in, but I would suggest that 40 amps on a horn is probably overkill for anything other than crows.
You're really talking about two different amps and power supplies. Good news is it's all modular (or at least it will be unless/until you bolt all the components into a hard sided case).
To fully drive that 40 watt speaker you're contemplating is going to require an amp of similar wattage, which is going to necessitate one heck of a battery and is going to generate a lot of heat. These issues can be dealt with, but the caller won't be very portable (more like portage-able. Expect this caller to weigh 10-15 lbs or so!). There are a lot of choices of auto amps in the 40 watt+ range. You're probably going to need at least a 5 amp-hour battery for a caller like this; you should be a be to find a sealed lead acid (if you can't find one locally try McMaster-Carr Supply Co) or motorcycle battery that'll do the job. Just don't accidentally fire it up at full volume in your basement or garage or your eardrums will be bleeding.
If on the other hand you want something highly portable and are satisfied with a reasonable level of excess volume, you can power a small 15w horn to a very loud level with a 5 or 7 watt amp, keeping the package compact by powering both a Nady 151/351 mic and Velleman 7W amp with a 10.8 volt pack of 8 AA 2500 mah NiMH batteries; these are now commonplace and can be fast charged in as little as 15 minutes.
Such a caller using an MP3 player for the call storage and remote can weigh in at just couple of pounds. (If you need more excess volume, swap out the batteries for a 12 volt one, if you're wireless mic runs at 12vdc) .
On the other hand some of us choose cone speakers instead of horns for their better high and low frequency response. But even a 6" coax can be driven to a volume sufficient for most of my purposes with a 7W amp and an 8 cell AA pack.
LionHo
