I'm using two Visatron FRS 5X-8 Speakers in a project. The amplifier being used is a Dayton KAB-215. Powering the whole thing from my power supply at 12V, I see a current draw of ~50 mA even at full volume. I'm a bit confused by this result.
My math suggests that for the two 5W RMS (8W Max) speakers I should see around 10W of power draw or ~.8A @ 12V. While I realize they may not operate continuously at this power during music, there is a big spread between 600 mW and 10W.
It seems like both the power supply (150W) and the amplifier board (2X 15W @ 8 Ohm) have tons of headroom here, so I don't really understand the low power draw. The bluetooth board doesn't have a volume knob on it currently, which the datasheet indicates should result in "full volume" on the amplifier side. My phone volume is maxed (when testing), and yet the power draw is super low. The speakers are fairly loud but not insanely so. I do have SPL measuring equipment that I can use to try to validate if the output is close to what it should be, but I'm still a bit perplexed.
I look forward to your thoughts on what is limiting the current draw, and whether this is a surprising result or not.
I tested this with a couple other devices, and agree that it my phone bluetooth output is quite low.
Source: Galaxy S10, Via Bluetooth, "Audio Tools" App 100 Hz Sine Wave
Drivers: 2 Visatron Drivers, one in a 3D printed enclosure, one with no enclosure
Power Supply: In constant voltage mode at 12V, supplying power to both speakers Voltage: 12 V Current: .313 A
Single driver measurements + output: Voltage (Measued with true RMS meter in AC mode): 4.1V Driver impedance from datasheet: ~22 ohms Volume: 81 db @ (roughly) 1m, measured via the same phone app
I'm not quite sure how to translate the AC voltage at the speaker into wattage, given that the impedance is likely complex (right?). I read this post, but didn't gain a lot of insight from it.
The more I work on this the more I realize I don't understand, but I suppose that's part of the process. I also have a better measurement mic/setup, but I feel like I'm chasing bigger issues rather than small optimizations. I'm going to trace the graph, put it into WinISD and see what it expects from an SPL standpoint. I think that probably I just don't have that much input voltage from the bluetooth chip, and that everything else is behaving as expected, but I also don't understand the system well enough to conclude that.