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Making a portable stereo ... should I port it?
I'm making a stereo that is to be mounted on the back of my bike.
It's in a box that has internal dimensions of about 12" x 6" x 6" and inside this you'll find a T-amp (it's rated at 100 watts/channel, but I'm not going to power it anywhere near that high) and two 7 Ah lead acid batteries. Input will come from an iPod that's outside the box. It uses two Polk Audio db651 6.5" car speakers, one on either side. I know it's not a good speaker design, but sound quality is one of the lesser considerations (weight, size, battery life are also important) -- and really, it's not that bad. But I'm wondering if I should port it? As I see it, there's a few advantages for porting -- -- better low frequency response -- make it more efficient -- use less power for the same volume (the power limited is limited, so this is a concern.) -- if the batteries do vent some hydrogen when charged, it gives it an easy place for it to escape. It also lets the amp cool a bit easier, though it's so efficient and the power relatively low so I don't think that's a big concern. But the stuff on calculating port size is quite confusing. I imagine I could calculate the frequency of the box (though the batteries and amp inside the box are likely to confuse that calculation) and guess at the Xmax values and go from there. I could just guess, put in a port that's about as large as I have room for, though if I understand it correctly, I want to tune the diameter/length so that the wave coming out of the port is in phase with the wave coming out of the front of the speaker -- so it *does* matter. But wouldn't this calculation only be valid for a specific frequency? The calculators I find online talk about calculating things for woofers and subwoofers. I guess the main speaker *is* a woofer. But when the calculators as for a frequency ... is it the Helmholtz resonator frequency for the cabinet I should use? Maybe I just need to bite the bullet and find a book on speaker design -- since it seems that that's exactly where I'm headed. -- Doug McLaren, -- Doug McLaren, The dandelion swayed in the gentle breeze like an oscillating electric fan set on medium. |
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