Building a Bluetooth Speaker: A Step-by-Step Guide

Hello and welcome to my Bluetooth Speaker Build Log. If you've not seen it yet, have a look at my previous video where I give a quick overview and a sound demonstration. Otherwise, just continue watching to see how I built it.

I had three main goals when designing my Bluetooth speaker: uncompromised bass, loud volume, and an enclosure that can be considered portable. All three work against each other, so it was a balancing act to get it all working well. Reproducing bass requires a much bigger enclosure than would be required for just midrange frequencies. So instead of using two full-range speakers with an internal divide, I decided to use a single bass speaker that could utilize almost the entire internal volume, essentially working like a subwoofer.

In theory, this would deliver deeper bass with the same sized enclosure. The other frequencies were to be handled by smaller speakers that would have their own internal enclosures. So the first step was to choose some speakers, to which I'll refer to as drivers. Because I didn't want to spend much money on them, I decided to use some from an old set of creative computer speakers that I had lying around. While not of the highest quality, they sound decent enough for general listening.

The subwoofer was particularly suitable because it had been designed to deliver high pressure sound from a relatively small enclosure. Next it was time to make the enclosure. I used 12mm MDF sheets. MDF is dense which is great for speakers, and it's also easy to work with. Before I boxed in the midrange drivers, I added some dampening which was actually just roof insulation. Above these enclosures sit the tweeters.

Next I added the port, which was just a length of PVC pipe. I used an online calculator to make sure that it was the right length for the resonant frequency I was after. Note the white stuff along the back edges; it's silicone sealer and was added to make sure the back access panel seals well when screwed down, allowing no air to escape, which would harm audio quality. The amplifier I chose was a 15w Tripath amp. It was an easy choice to make because tripath-based amps are powerful, cheap, and sound really good.

They're also particularly efficient, which is great news for battery life. For power, I decided to use a 12v rechargeable battery pack from an RC car. It's charged by an internal battery charger that automatically stops charging once the pack is full. Multi-gang switches are used for the power and charge buttons, which simultaneously connect and disconnect various wires. This means that the unit can still be used whilst it is charging, and it also has the option of running entirely off the mains if needed.

While I've not timed the unit's listening-hours, I've found that I only need to charge the unit every few weeks or so, which is all thanks to the efficient tripath amplifier and of course the capacity of the batteries. For Bluetooth functionality, I used a cheap Bluetooth receiver from China. It runs on 5v, so I used a simple buck step-down converter to attach it to the 12v battery.

There is some signal processing going on to get even more out of the system. First, the Bluetooth module's stereo signal is mixed down to mono using two 160ohm resistors. This is because stereo won't be noticeable on a unit of this size, and having just a mono signal allows for neat double-amplification trick for the bass driver. So what happens is that the mono signal enters channel 1 of the amp through a 1:1 ratio audio transformer.

This transformer is from a cheap ground loop isolator and is there to eliminate the ground loop caused by the Bluetooth module and amplifiers sharing the same ground. The front grill is just some perforated aluminium, which is screwed to the front using some standoffsto make a small gap. Its edges were quite sharp, so I cut down the side of an HDMI cable and removed the wires from inside. The empty rubber sheathing was then slotted over the edge of the aluminium and glued in place, which makes a nice buffer and also frames the front nicely.

So, that's how I built it. If you enjoyed this video, please hit the 'thumbs up' button, and maybe consider subscribing.

"WEBVTTKind: captionsLanguage: enHello and welcome to my Bluetooth SpeakerBuild Log.If you've not seen it yet, have a look atmy previous video where I give a quick overviewand a sound demonstration.Otherwise, just continue watching to see howI built it.I had three main goals when designing my bluetoothspeaker - uncompromised bass, loud volume,and an enclosure that can be considered portable.All three work against each other, so it wasa balancing act to get it all working well.Reproducing bass requires a much bigger enclosurethan would be required for just midrange frequencies.So instead of using two full-range speakerswith an internal divide, I decided to usea signle bass speaker that could utilise almostthe entire internal volume, essentially workinglike a subwoofer.In theory this would deliver deeper bass withthe same sized enclosure.The other frequencies were to be handled bysmaller speakers that would have their owninternal enclosures.So the first step was to choose some speakers,to which I'll refer to as drivers.Because I didn't want to spend much moneyon them, I decided to use some from an oldset of creative computer speakers that I hadlying around.While not of the highest quality, they sounddecent enough for general listening.The subwoofer was particularly suitable asit had been designed to deliver high pressuresound from a relatively small enclosure.Next it was time to make the enclosure.I used 12mm MDF sheets.MDF is dense which is great for speakers,and it's also easy to work with.Before I boxed in the midrange drivers, Iadded some dampening which was actually justroof insulation.Above these enclosures sit the tweeters.Next I added the port, which was just a lengthof PVC pipe.I used an online calculator to make sure thatit was the right length for the resonant frequencyI was after.Note the white stuff along the back edges.It's silicone sealer and was added to makesure the back access panel seals well whenscrewed down, allowing no air to escape, whichwould harm audio quality.The amplifier I chose was a 15w Tripath amp.It was an easy choice to make because tripath-basedamps are powerful, cheap, and sound reallygood.They're also particularly efficient, whichis great news for battery life.For power I decided to use a 12v rechargeablebattery pack from an RC car.It's charged by an internal battery chargerthat automatically stops charging once thepack is full.Multi-gang switches are used for the powerand charge buttons, which simultaneously connectand disconnect various wires.This means that the unit can still be usedwhilst it is charging, and it also has theoption of running entirely off the mains ifneeded.While I've not timed the unit's listening-hours,I've found that I only need to charge theunit every few weeks or so, which is all thanksto the efficient tripath amplifier, and ofcourse the capacity of the batteries.For bluetooth functionality I used a cheapbluetooth receiver from china.It runs of 5v, so I used a simple buck stepdown converter to attach it to the 12v battery.There is some signal processing going on toget even more out of the system.First, the bluetooth module's stereo signalis mixed down to mono using two 160ohm resistors.This is because stereo won't be noticeableon a unit of this size, and having just amono signal allows for neat double-amplificationtrick for the bass driver.So what happens is that the mono signal enterschannel 1 of the amp through a 1:1 ratio audiotransformer.This transformer is from a cheap ground loopisolator and is there to eliminate the groundloop caused by the blutooth module and amplifiersharing the same ground.The signal is then amplified, and sent tothe midrange and treble drivers.The treble drivers, by the way, have 2.2ufcapacitors connected with them in series.This is to allow only high frequency soundsreaching the tweeters.This same amplified signal is also sent throughanother 1:1 ratio transformer, which basicallyfloats the signal completely from its source.The signal then goes through a low-pass filterconsisting of a few capacitors and resistors,one of which is adjustable and forms the tonecontrol for the bass.The signal then enters channel 2 of the amplifier,and is amplified again creating a strong basssignal which is then sent to the bass driver.While it's not a particularly elegant method,it is a quick and dirty way of getting a loudbass signal out of a single stereo amplifier.For volume control I used a logarithmic potentiometer.Logarithmic should always be used over linearfor audio applications because of the wayhuman hearing works.To finish the unit off, I glued on some texturedfabric that looks and feels a bit like leather.It resists scratches well, but is susceptibleto gouging if heavily knocked, so next timeI might use something a little more robust.Diamond eye marine base plates were used forthe hook latches on either side, and a strapfrom an old laptop bag was utilised for thehandle.The front grill is just some perforated aluminium,which is screwed to the front using some standoffsto make a small gap.Its edges were quite sharp, so I cut downthe side of an HDMI cable and removed thewires from inside.The empty rubber sheathing was then slottedover the edge of the aluminium and glued inplace, which makes a nice buffer and alsoframes the front nicely.So, that's how I built it.If you enjoyed this video, please hit the'thumbs up' button, and maybe consider subscribing.I hope I see you next time, where I'll beshowing you how to build a 100w super-brightLED light panel.\n"