Prahnisteur feat. Sound Cart

My brother and I like to use our synthesizers to hang around each other and create long sequences of music together. Usually we do this once a year around easter and this year we decided to go for the ultimate test: We decided to leave our cozy home studios and to confront the masses. This is about the equipment we used and the things we learned.

Some guy in a park

My brother testing the rig in our chosen location

We were sure that we wanted a fairly mobile setup with its own power supply and enough oomph to be heard throughout a small park. The chassis we chose was a bicycle cart that doubles as a hand cart when no bike is attached. We are located in two different cities roughly 100km from each other and so what was planned as one mobile operation turned out to become two operations: Before we could move our contraption through Berlin, I had to get my stuff there. And for historic reasons it was my brother who had the cart.

So I decided to design a rack to be mounted on my brother’s cart and that can be converted to a wheelbarrow to carry my stuff to Berlin. Or at least to the train station. Without access to the exact dimensions of our carrier vehicle the design had to be flexible enough to accommodate these unknowns.

A heap of wood in front of a heap of concrete

The transforming rackbarrow has arrived in Berlin

The first steps were to come up with a concept and then to get as many dimensions off the internet as possible.





Engineering is Educated Guessing
Yay! Paper!

Dimensions of the Rack, the cart and a shopping list

The dimensions of the cart are part manufacturer’s information and part guesswork. I determined the diameter of the tubes from the difference of the inner and outer dimensions of the upper frame. The height of the inner frame was estimated by closely looking at how it relates to the known diameter of the wheels (This means ‘guessed’).

Then it was time to shop for some lumber and immediately cut it to pieces.

A Professional Working Environment is Essential

This is how we do it.

Measure once, cut twice

Here I’m going for the first cut in what totally is a professional woodworking shop. Even though it looks like my hallway.

Yes I did most of the work in my flat and predictably ended up spreading sawdust everywhere. I still find that stuff in some of my socks even directly after pulling them out of the laundry. On the other hand: A short commute is priceless.




It’s all about Precision

Now that I used what was supposed to be the Alt text as title, I no longe know what to write here.

Brace yourselves, a hinge is coming!

This is seriously overdoing it. The hinges are so loose, that  I didn’t really need to bother with precision (which I didn’t at any other point of this build anyway).

I case you’re wondering, this is the top of one of the A-frames of the rack. The lumber is 44×44 mm planed pine.



Limping on

This is no longer the hallway

No legs without feet

Here you see the other end of the A-frame getting its foot attached. Again this is high precision work. I used 5×70 mm screws from IKEA that I sunk 2 cm into the foot part. At this point I had moved to the kitchen, mostly because the hallway was full of sawdust.

(The real reason is that my hallway completely lacks working surfaces with proper cushions on them)


Getting my Shit Together

In the upper left: Mr. Soft Owl's sister

There’s a lot going on here

Here you see one of the finished A-frames and the completely undocumented floorboard right before drilling the holes for the bolts. The floor is 8 mm birch ply reinforced by two lengths of 22×44 mm lumber that have been glued and screwed into place (3×40 mm Spax, a lot of them)

The vertical board is 60×18 mm and will later distribute the weight of the rack to the reinforcing rails of the floorboard.

BTW: Costruction now has reached new territory

As the previous picture, this takes place in my living room

This may look simple but when working without a drill press I strongly suggest that you clamp all your parts together exactly the way you want to position them in the end and then drill all holes in one pass. Your holes will not be straight but at least they will match. Also consider using a drill bit that is half a millimeter larger than your bolts or at least to thoroughly ream the holes after drilling so your bolts will go in nicely. This is also a great way to get sawdust all over your living room.

Getting Support

Overengineering at its best

Aaand back in the kitchen

Why use bolts when you have clamps?

I really like my one hand adjustable clamps a lot

Here you see the the bars that will later support a table for my equipment and on the other side carry my brother’s Roland JX-305. I attached doorstops, figuring that whatever is sturdy enough to stop doors will be able to handle that beast of a synth. They’re screwed into place with fierce 5×50 mm wood screws, the lumber is 32×55 mm pine.

The next picture shows the fitting of the supports for the table and my brother’s synth. I placed two of the bolts where they would be needed later, so only two additional holes would be required when adjusting the rack to the cart. Note that I’m using the ‘clamp your stuff together and then drill your skewed holes’ technique mentioned above.

Cutting Edge Technology

This is cutting edge technology! Ba- Dumm Tsss

Cutting straight lines

While we’re at precision work with handheld tools: Jigsaws are inherently unsuitable for straight cuts, use some kind of guide to literally keep them in line. The part you see there is the bottom of the cart in wheelbarrow mode, one of two parts that don’t serve a purpose after transforming into rack mode.

Getting There



Fuck Pareto and his principle

Mostly assembled

This is the Wheelbarrow mostly assembled. The side panels are 4 mm poplar plywood with rails made from 22×44 mm lumber that has been attached with wood glue and approximately two thousand 3×40 mm screws. The panels will become the place for the mixers and other hardware.

The sack barrow that is supposed to lend its wheels to the contraption is still held in place by bungee cords. While quite a professional solution in itself, I wanted some more rigidity at that point.



Adding Wheels

Insert butt plug joke here

A Tight Fit

The 22×44 mm lumber proved to fit surprisingly well into the frame of the sack barrow so in it went after some minor adjustments. Shout out to Duckworks Magazine for bringing the Shinto Saw Rasp to my attention, it is a great tool for such applications.

This and a second block were bolted into place at the underside of the floor board after adding a crossbar with special elastomer pads to each. The crossbars hold the sack barrow firmly in place.

To my surprise the sack barrow coupling turned out to align perfectly with the inner frame of the cart and they worked great as anchors for the floor board.


Yup, that are some skewed holes

Last appearance of the bungee cords

Yeah, right

Crossbars wit ‘High Tech Elastomer Padding’™

Autobots, Transform!

...seriously, Im running out of ideas

Half way there

As said above, the floorboard with the barrow coupling was a perfect fit for our cart with zero wiggle in x direction. The frames are mostly supported by the spreader boards that rest on the reinforcement rails of the floor board that nicely distributes the weight over the whole cart. The feet of the A-frames lock into the outer tube of the cart frame and prevent the rack from tipping over.

The arms for the big Roland are not yet fully attached and the second instrument panel (former side panel) is not in place.

The last picture shows the rack fully assembled (sans beer holders, they got lost in the mail).

In the background: The one of our duo that actually knows something about music

The assembled rack in its natural habitat

And how did it all turn out?

It was fun and we learned a lot 🙂

Our power supply, consisting of two parallel 80 Ah car batteries is grossly overdimensioned. When designing the power supply I drew inspiration from a soundsystem on a cargo bike that is used to blast large audiences with stereo sound for eight hours flat. That system runs on a 120 Ah battery and we decided that we needed a similar amount of power. As it turned out, our Mackie Thump 12 is vastly overpowered for street music applications and we ran it at some 30% when we wanted to get heard. Most of the time we stayed around 20% so one battery would have sufficed.

Playing in front of an audience is scary, things got much better as is became dark and I could no longer see all ten of them. We will add lights to the rack because there was a phase where I had trouble finding the buttons on my drum machine. The flashlight on my phone helped, but some discoblinkies would solve the problem in style.

We wanted to have guests participating but fucked up the invitations. We were kind of unhappy with ourselves until something amazing happened: Random people stopped to sing into our mike. That was awesome and plotted out the way we want to go with this project. We will add a second mike and mark the keys for our preferred tonalities on our keyboards to let people from the audience participate. Perhaps a netbook running Imitone could also be added.

For increased mobility (the current sound cart is heavy and the weight is poorly distributed) we will split the system into two carts, but we will continue looking for people to play with us.