Audio project, will rechargeable batteries do?

[davewalby]

Hi there

I am currently designing a wireless audio system, hence i need to use batteries so that the system can be portable and not require a mains power supply.

However, i am using car speakers for it and am worried that batteries will not be powerful enough or last long enough.

The speakers i am using have the following spec:

Peak Power - 200 Watts
Rated Power (RMS) - 60 Watts
Sensitivity - 89dB
Impedence - 4 Ohms

Can you tell me what Voltage / Ampage etc battery i will need? And how long it may last?

Any help would be appreciated, thanks

Dave

 

[mneary]

I would use supply rails of +/- 12V, built from a pair of $22, 12V, 7AH, SLA units.

My proposed batteries would give you a total of 168 watt hours, so if it's consuming an actual 5W and delivering 2W to a speaker (a pleasant 92 db) you would get almost 4, 8-hour days.

 

[Nigel Goodwin]

Presumably you're looking at some kind of portable PA system?, in which case I suggest you look at PA speakers - car speakers aren't really much good for such use.

 

[audioguru]

Car speakers are usually a 6" x 9' oval with a built-in tweeter. They have adequate bass if their enclosure is the entire trunk (boot) of a car. If they have a small "bookshelf" size of enclosure then their resonance will be at an upper-bass frequency where they will have a boomy peak, with hardly any deep bass.

You didn't mention which power amplifier circuit you will use.
An amplifier powered from 24V and driving a 4 ohm speaker will produce a power output of only 12.5W RMS.

For a power amplifier to produce a power output of 60W into 4 ohms then it will need a total power supply voltage of about 49V or have two amplifiers in a bridge with a 27V supply.

The speaker has its sensitivity rated at a frequency where it has a peak. The average sensitivity over a wide range of frequencies is less. It is rated at a distance of only 1m like you are almost wearing them. At a distance of 2m then the sound pressure is 6dB less.

If the multi-frequency sound pressure is 92dB then the amplifier's output must be about 8W if the distance is 2m. That is for the average sound level of music. Peak levels will be 12dB louder which need a power of 128W RMS.