Bluetooth Cello, Junk Making Music Again!

About: I'm an actor/tech/IT/graphics/editor/writer kind of guy. I do a fair share of voice over work and have the full time gig at Bard College at Simon's Rock. While waiting for machines to do things, I hit the ...

This all started with electronic recycling day, and someone turned in an old set of speakers.

Somewhere on line I had seen someone who had added speakers to an old upright bass, creating an amazing work of art.

From there I started looking for an upright bass, but instead found a musty old plywood cello.

Here are the materials:
Old set of speakers with crossovers
Beat up student cello
Bluetooth 100watt amp
Speaker mounting foam tape

Drill and bits
Soldering iron
Heatshrink tubing
Heatshrink gun
tape measure

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Step 1:

So here are the speakers, an old set of Marantz.  The front panels were shredded by a cat and they sounded kind of weak. The speakers were built out of particle board so I figured I would salvage the parts.  Upon inspection, one of the mid range speakers was ripped.

I ordered up a set of mid-range Dayton's from, while I was there I picked up some 5.25" Woofers as well, since the cello didn't have space for a 10" woofer.

At this point I thought the project would be passive.

Step 2:

So, this cello.  It came from my brother-in-law.  A student model that was missing a few pieces.  No bridge, no strings, and a cracked neck.

It had been in the basement for 20+ years and had this sort of... smell. That, family of mice kind of smell...

I used a light mix of water and bleach to kill the stink.

Step 3:

Ok, time to start planning out speaker placement.  I cut out some paper circles in the sizes needed.

From there I used a compass to mark out holes.

Step 4:

Here is where cello players or luthiers should leave the room!

I drilled holes then used a jig saw to rough out the holes.

Once the holes were roughed out, I used a Dremel Tool with a sanding drum to smooth out the holes to the compass markings.

Initially I was planning on having the speakers rear mounted, but without a smooth circle, it just wouldn't look right. So we were going to surface mount.

Step 5:

At this point we did a test fit.  Initially the squarish speaker frames bothered me, but I got over it.  The gold finish on the tweeters however did bug me.

So I used a paper cup to mask off the cones and sprayed the frame black.

The cello is curved, I used some speaker mounting foam tape to fit between the speaker frames and the cello, then tighter things up till it was snug, careful not to warp the frame.

Step 6:

On the back of the cello I cut an 8" access hole. This allowed me to reuse the crossovers from the Marantz speakers.  Using a bit of hot glue and some screws, these were mounted inside.

Good solid capacitors and coils. Say what you will about the late 70's, they had some great audio gear.

Step 7:

THEN sends me this email. A 100watt BLUETOOTH amp is now available.

Oh man.

It was more than I wanted to spend, just about $130.oo bucks, but the project would jump to a new level of coolness.  Audio from my iPhone via Bluetooth to my cello speaker.


Step 8:

ok again, more ripping into the cello.  For those luthiers and cello players still reading.. fair warning.

The best way to say this, is I hogged out the hole.  Due to the proximity of the neck, and the thinness of the material, and then the supporting material where the neck connected to the body of the cello needed a combination of techniques.

Basically I used an xacto blade to cut through the thin material, then the Dremel Tool again to smooth and gouge out the rest.

The scrapes in the finish will sand out.

The end result was the amp sliding right in with a compression fit.

Step 9:

The 8" hole in the back was then re-installed.  I used a couple of scrap pieces of plastic from old laptops, and secured them just inside the cello.  Which gave me tabs to re-attach the chunk from the hole.

Step 10:

So, how does it look?  GREAT!

Big question, how does it sound? Sweeeet!

The original speakers were rated for 200watts, the new amp is 100watts, so we're safe there.

The ability to fire up my iPhone and play some jazz without having to connect to a cable is very cool.  I'm already thinking how this could be used in a stage performance production.

The student cello could have been repaired, probably, but it will get used now, verses being a nice looking mouse house. The plan is it will lean in the corner of the office, and the computer speakers on the desk will disappear.

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    25 Discussions


    3 years ago

    How would I make this exactly the same but then passive thus without the amp?

    1 reply

    Reply 3 years ago

    Follow the same directions, just put connections on the back so you can plug into it.

    I would disassemble a set of old speakers, use the wiring and crossovers and go from there.


    Reply 4 years ago on Introduction

    I was lucky on this one and it was in a basement tag sale, (garage sale) for $10.00 with the broken neck.

    It's amazing what you find when you mention out loud you're looking for something. An upright student bass that's been water damaged, or even a pair of student violins for bookshelf speakers. Ask a grade school music teacher or the local music store what they have that's damaged in the rental department.


    4 years ago

    One last question, the amp that I purchased also has a port for a subwoofer. Could I add a 50 watt subwoofer too? I'm attaching a pic of the back of the amp. Can I be greedy and add a 50 watt subwoofer too?

    15, 4:40 PM.jpg
    1 reply

    Reply 4 years ago

    I think a subwoofer is a great idea, as long as you can control the volume of it. You don't want to overpower the cello and create all sorts of excess vibration that will tear it apart.

    A little goes a long way.


    4 years ago

    Or can I stay with the 120 watt Sony SS-B1000 5-1/4-Inch Bookshelf Speakers that are 8 ohms?

    I appreciate you simplifying this for me.

    1 reply

    Reply 4 years ago on Introduction

    I would stay with these if you're going to use the 250watt amp. Since that amp is probably putting out 125watts per channel. Once you dial in the 8ohm speakers, that should be a good match without much fear of blowing the speakers.


    4 years ago

    You are the best!! I found an amp that is 250 watts and 4 ohms. It has been purchased. I found some bookshelf speakers that are 4-8 ohms and 75 watts each speaker. It lists both numbers in the description. (Micca MB42 Bookshelf Speakers with 4-Inch Carbon Fiber Woofer and Silk Dome Tweeter, Black on Amazon).

    Will these work better? Or should I just look for car speakers that run 4 ohms? For all this trouble, I don't wanna blow the speakers!!


    4 years ago

    Can you explain your paragraph on the power output? The speakers I want to use are 120 watts (8 ohm). The amp I plan to use can handle 600 watts (4 ohm). How much volume will I lose?

    My current sound system is only 30 watts.

    1 reply

    Reply 4 years ago on Introduction

    I'll try, without getting too math geeky on ya.

    So you have speakers that are rated at 120watts with 8 ohms of resistance. The amp puts out 600watts, probably 300watts per channel when it sees a 4 ohm load. So will your 120watt 8 ohm speakers survive? Probably not. Even with the increase in resistance, the 300watts pounding into would be to much. If they were rated for 250watts, they would have a chance.

    So you'll lose some volume, but if you crank it to 11, the speakers will give out shortly.

    I'm sure I could dig up a formula on wattage, resistance and such, but if you're going to go through the effort, either get a smaller amp, (600 is a lot!) or invest in some speakers that will handle that power.


    Reply 4 years ago on Introduction

    Question: Are you using 8 ohm speakers with that 4 ohm Lepai amp? And it still works?

    I'm going to do the same thing with some Sony speakers and a motorcycle amp. But the speakers are 8 ohm and the amp is 4 ohm. Aren't the ohms supposed to match? And if they don't can I still do this? What are the side effects of unmatched ohms?



    Reply 4 years ago on Introduction

    The side effect is lower volume.

    Power output (10% THD): 2 x 160 watts into 4 ohms, 2 x 120 watts into 6 ohms, 2 x 100 watts into 8 ohms.

    It works great and is loud enough for my room, I rarely can crank it to full volume without having a neighbor complain. :)


    I'm a university student studying project design and we're doing a similar project that revolves around a cello. We're having some problems with creating holes in the cello and I was hoping you could give me some more detail into how you created the holes in the cello for example, drill size, whether you punched before you drillled, and how you stopped the material from cracking under pressure? Thanks!

    2 replies

    Sure thing. The top of the cello is a very soft wood. So I used a sharp drill bit, slightly larger than my jigsaw blade. I drilled inside of the compass line and also cut inside the line. The jigsaw blade was a fine tooth blade, what one would use for metal as opposed to the normal wood blade. The finer teeth take a few moments longer to cut, but leaves a cleaner, crack free, chip free edge. If you need to expand the hole from there, I would use a Dremel tool with a sanding drum mounted, it makes quick work of the wood and doesn't crack things.

    One thing I've done since the build, is add some material under where the screw holes are. This adds strength to the mounting points. This was simply done by re-using the material from the holes, cutting it to shape, and gluing it on the inside of the cello.

    This cello has been a big hit and has been featured in at least one art show so far.