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Step 9The fully integrated Active 12V-24V speaker
Along my quest for speaker efficiency I started thinking about Active speakers (also called Powered speakers). This is the term for when the amp is built into the speaker. Most active speakers are built for 120V wall power - it means you just plug in your active speaker and plug the mp3 player straight to it. very convenient.
I looked around for a while for an active 12V speaker - one with an integrated 12V amp - but there's really not much out there. just a few subwoofers for cars, nothing full range. so lets make one! the benefits:
inside your speaker are normally 2 or 3 "drivers" - the things that make the sound. the low-frequencies are made by the big cone, called the woofer. the highs are made by a smaller horn called the tweeter. sometimes there's a 3rd midrange speaker. the efficiency of each of the 2 or 3 drivers is not the same. in a PA/DJ speaker the woofer might have a 96 SPL rating, while the tweeter might be around 103. that's a big difference! when you have your amp outside the speaker (as in any home or car stereo setup), there is just 1 signal sent to the speaker. inside every speaker is a "crossover" circuit that splits the sound up - it sends the low frequency part of the sound to the woofer and the high frequency part to the tweeter. just doing this at all incurs perhaps a 5% or 10% efficiency loss. But - what if the tweeter is much more efficient than the woofer? if all the crossover did was split up the sound, then the efficient tweeter would play all the high-pitch sounds way too loud compared to the low-pitch sounds played by the less efficient woofer. so the crossover has a 2nd job - it equalizes the sound by reducing the volume on the tweeter. but, the way that this volume adjustment happens in the crossover is by blowing off the excess power as heat - another efficiency loss. in an active speaker we have the opportunity to fix this - active speakers use a separate amp for each driver - one amp for the woofer and one for the tweeter, and we can just turn down the volume on the tweeter's amp. that's an efficient way to reduce the tweeter volume instead of the inefficient way the crossover does it. Since our T-amps are so cheap, this also won't cost much to do, and we'll end up with our amp neatly mounted inside our speaker.
I looked around for a while for an active 12V speaker - one with an integrated 12V amp - but there's really not much out there. just a few subwoofers for cars, nothing full range. so lets make one! the benefits:
- with the 12V amp inside the speaker, you have a convenient integrated package, plus you save the weight of an extra box and wires.
- with the amp wired inside the speaker, you can wire individually to the tweeter and the woofer. this allows additional efficiency improvements. lets explain:
inside your speaker are normally 2 or 3 "drivers" - the things that make the sound. the low-frequencies are made by the big cone, called the woofer. the highs are made by a smaller horn called the tweeter. sometimes there's a 3rd midrange speaker. the efficiency of each of the 2 or 3 drivers is not the same. in a PA/DJ speaker the woofer might have a 96 SPL rating, while the tweeter might be around 103. that's a big difference! when you have your amp outside the speaker (as in any home or car stereo setup), there is just 1 signal sent to the speaker. inside every speaker is a "crossover" circuit that splits the sound up - it sends the low frequency part of the sound to the woofer and the high frequency part to the tweeter. just doing this at all incurs perhaps a 5% or 10% efficiency loss. But - what if the tweeter is much more efficient than the woofer? if all the crossover did was split up the sound, then the efficient tweeter would play all the high-pitch sounds way too loud compared to the low-pitch sounds played by the less efficient woofer. so the crossover has a 2nd job - it equalizes the sound by reducing the volume on the tweeter. but, the way that this volume adjustment happens in the crossover is by blowing off the excess power as heat - another efficiency loss. in an active speaker we have the opportunity to fix this - active speakers use a separate amp for each driver - one amp for the woofer and one for the tweeter, and we can just turn down the volume on the tweeter's amp. that's an efficient way to reduce the tweeter volume instead of the inefficient way the crossover does it. Since our T-amps are so cheap, this also won't cost much to do, and we'll end up with our amp neatly mounted inside our speaker.
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http://www.ebay.com.au/itm/230608706091?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649#ht_3755wt_907
and one of those
http://store.monkeylectric.com/ProductDetails.asp?ProductCode=XOVER1
both mounted in the box, and a 12 volt battery yet to be acquired.
any of you experts know what kind of volumes i can expect from this kind of set up?
the speaker isn't massive i know, but it's a convenient size, and i can always swap it out for a bigger one.