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Boom Box: Hot Wheels South Africa’s car audio system is the smallest in the world

Manny Kightley has worked in the local film industry for around 15 years. His expertise is in building special effects props and rigs, and some of his most famous work can be seen in a few memorable TV ads, for which he built mechanical rigs. Familiar with his expertise, he was called up when it was proposed that – as a great publicity stunt at the Johannesburg International Motor Show – a car audio system be installed in a Hot Wheels die cast model.

It was only after saying yes that Manny realised what he’d signed up for.

hw_boomboxAt 1/64th the size of real cars Hot Wheels models don’t quite have the kind of internal space you’d need to fit ordinary speakers. Manny realised that his first hurdle would be finding speakers that would both fit in the toy car, as well as produce audible sound. His first attempt involved the circular drivers usually found in headphones. at around 20mm across, these would’ve needed some work to fit, but they didn’t have enough volume.

Even the original idea of using acoustic tricks to maximise sound output didn’t pan out.

“I thought that we could maybe put the car in a specific environment and maximise the amount of sound coming out of it,” he says. “Then what happened was, as we started developing and building, and taking the project forward, we weren’t getting much volume. Then I tried the acoustic tricks, and they didn’t really do anything.”

“That’s where I kind of reached the stage where I was wondering if it was going to go forward.”

Operating in unknown territory – to their knowledge, those who arranged the project have seen nothing else like this being attempted before – Manny didn’t even have a benchmark. He just wanted something that would play as loud as possible.

Mulling it over, he wondered how he’d get more volume from small speakers. It’s then that it struck him: his Nokia cellphone has a pretty loud ringer – and that’s just one speaker. With that thought, he approached a cellphone repair shop, hoping to salvage a few ringers from scrapped phones.  Fortunately, the shop referred him to supplier of cellphone speakers.

circuits

“I went to one of the China malls and got a load of cell ringers – I was assured they were loud. This was the second batch of speakers.”

But once again, he had no luck. “They were pathetic. They distorted.”

With the deadline drawing near, Manny realised that he might run out of time, luck, and speaker options. So he hit the internet and found a shop in the East Rand that had speakers. Not original Nokia items, but loud enough for the project. The next step was to select a Hot Wheels model for installing everything into – and that’s where Manny finally ran into some luck.

Hot Wheels SA gave him a selection of cars, and of those he picked one that had a huge floorpan – the area he planned to use for installing the speakers. It’s only serendipitous that the car, a fantasy model in the Hot Wheels lineup, goes by the name Boom Box. With help from an electronics expert, some calculations were done to figure out how to wire up the tiny speakers. The six drivers were wired up in a configuration to reduce impedance, so that a conventional amplifier could be used to drive them effectively. A custom printed circuit board was used to keep everything together, and wiring was run in the tiny car to hook up everything.

In construction: the Boom Box disassembled, with the six microdrivers that made it sing.
In construction: the Boom Box disassembled, with the six microdrivers that made it sing.

In reality, the Hot Wheels Boom Box on its own is just a speaker – not a self-contained audio system. An external amplifier is used to drive the speakers, and that’s hooked up to a CD player or MP3 player for music input.

boomboxrear

“[Wiring up an internal amplifier and CD player] isn’t possible at this stage,” says Manny, adding that the time constraints for this project made it unlikely to happen.

For the show, the Boom Box was hooked up to a NAD 3020 stereo amplifier. At 20 watts per channel that had more than enough oomph to power the little car’s six drivers, and music came from a CD player as well as an MP3 player. And to help the car look the part, Manny propped open the rear hatch, which showed off a leopard print-covered backboard that has a fake, miniature speaker installation. The actual speakers, mounted inside the car, faced downwards and played out the bottom.

How loud did it end up being? At the Johannesburg International Motor Show, where it was unveiled, it notched up a respectable 96 decibels – louder than a passing train (at distance), or a vacuum cleaner. The sound isn’t exactly earthshaking, but if you imagine yourself as a tiny human driving around in a Hot Wheels car, you’d be suffering some hearing damage in a hurry. And, in true Hot Wheel fashion, the stand was styled to look just like any other motor show stand – replete with two young boys acting as salesmen.

hw_plinth

There were some other challenges, too. On the show stand, playing for 10 hours a day, the car ran into thermal constraints. Pumping out music at that volume level generates a decent amount of heat and there’s nowhere for it to go. As a result the speakers started distorting and a second car had to be built to accommodate this limitation.

Nonetheless, this micro music marvel soldiered on for the whole show and drew admiration from both young and old. Asked whether it was a hit and if he got any good feedback, Manny shares an anecdote. While he was busy setting up the stand and configuring everything, two guys walked up and started musing over the little car making a lot of noise.

“Two guys in their thirties or forties. They got down on their hands and knees like children. They were absolutely fascinated. I liked that very much.”

 

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