Suitcase speaker MKIII

Mark III was a troubled build form the beginning, the original speakers I got lied to me, they were home theatre speakers and while I thought I had 6 drivers for my original design.

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Turns out that home theatre speakers are quite fond of using passive radiators to make them look more impressive while saving on cost, so I only half the speakers I thought I had once I shredded them, also the sub woofer was substantially smaller that I’d originally thought, so they got binned and replaced with a assorted speakers I’d collected over the following months since MKI,

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The middle speaker and the tweeters are from the same speaker and the  black ones on the bottom are from a different set .2016-01-11 22.04.41

Under the hood it’s powered by, a 2.1 TPA3123 powered 20w+40w amplifier

With the larger amplifier I figured it need a larger battery, so a 12v 6.2ah  SLA which is 50% larger than the MKI


instead of the rather expensive kemo battery guard I substituted a cheaper alternative sourced from ebay while fairly functional, the voltage cut off is set with dip switches at predetermined values . It does have a rather high current draw of 50 ma when active due to it using a relay rather than a MOSFET.

Even with a battery protection circuit if the user doesn’t switch off the device the protection circuit draws enough current that it can drain the battery to the point it won’t charge.

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The battery meter was a usability failure, it’s percentage reading doesn’t really match the voltage reading, it would read 40-50% charged when the battery was exhausted and the cut off circuit had disconnected the battery, also it doesn’t work when charging the battery it always reads 100% which can be confusing for the the end user. I combination of these factors and user error lead to a failure of the battery, they very problem I was trying to avoid with using a protection circuit. In spite of these failures the MKIII remains my favorite speaker I’ve made to date because of the aesthetics of the case and the extra power it packs in the bass rages.

My solutions to the aforementioned problems is to remind people to turn the speakers off once they do dead because the quiescent current of the circuit is enough to completely drain the battery.


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