Ultraportable PA system

[joecarrow]

Hi all, I was originally going to post this in the thread titled "CHEAP, High Efficiency Open Baffle", but I thought a new thread was more fitting.

My concept for a project has been cooking for a little while, and may not come to fruition for a while longer- but I thought it would be an interesting discussion due to some recent technological developments, chiefly neodymium woofers, class D amplifiers, and lithium batteries.

The overall goal of the project is to produce a PA system that is:

1) Ultra-portable
a) Lowest possible weight, with 50 pounds being an upper limit.
b) Fits into a compact space for transit.
c) Contains a minimum of parts.
d) Able to play autonomously for at least an average DVD.

2) High quality PA sound
a) Wide enough bandwidth to cover majority of instruments.
b) Controlled directivity
c) Capable of high SPL with low distortion

My idea is to use the EminenceKAPPALITE 3015LF NEO for bass, and the 41 hz Amp 9 for amplification, and either lithium ion or NiMH batteries.

The reason this thread is tangentially related to the linked thread is that I haven't ruled out dipole bass. With two of these woofers on a wide baffle (think folding wings), it wouldn't be impossible to hit 50 hz at 115 db. Keep in mind- that's with just over 20 pounds of woofers, costing about $300.

Any thoughts?

[augerpro]

Read JonM's reply to my thread. His advice is probably even more appropriate (as far as bass reproduction) to your system since I assume you want to use this outside?

[joecarrow]

Yes, this will be for outdoor use. As I said, I'm not married to the idea of dipole bass- just infatuated with the idea of not having to carry around 5 walls of a cabinet.

Most pro sound PAs are fairly limited below 40 or 50 hz. A bass drum contains little energy below 50 hz (unless you're in a small intimate room), and the lowest string on a bass is 40 hz. As long as I can play 40 hz loud and clear, that's more than enough.

I'll do some modeling; it may be that I can do far better with a ported box, and I'll be able to make it a fairly small ported box with lightweight materials. Thanks for the feedback, though.

[ThomasW]

As long as I can play 40 hz loud and clear, that's more than enough.

Battery powered, lightweight, and play for the length of a DVD?

Sorry but this is a pipe dream.

[joecarrow]

A few years ago, it definitely would have been a pipe dream. I'm not sure if it is anymore, that's why it interests me- there is new technology available, and someone's got to be the first to put the pieces together into something new. Here's why I think this may now be possible:

-94 db efficiency should be doable. It might rule out dipole operation, but that just means I need to get creative with a light bass reflex box.
-Count on 85% efficiency from the amp- a reasonable figure.
-At 110 db average, that's only about 50 watts, requiring about 65 watts from the batteries.
-Call a DVD 2.5 hours long, so the battery requirement is about 160 watt-hours.
-A battery made from 20 Li-Ion 18650 cells would weigh about 2.1 pounds, and would have a capacity of (2.2 amp-hours x 4 parallel) x (3.6 volts x 5 series) = 158 watt-hours.

Battery pack safety and low bass seem like the main problems.

[Dennis H]

One thing about an outdoor speaker is your open baffle size isn't limited like it is indoors. You could have a small baffle and huge, folding or detachable wings made of about any light material -- foam, cardboard, whatever. I imagine a 10' wide baffle would give some pretty decent bass (as long as the wind doesn't blow ).