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Old 5th January 2014, 05:55 AM   #1
RyanD is offline RyanD  United States
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Default Mobile/garage MP3 sound system

Over the past couple months I've been working on this little speaker project spawned from a conversation over drinks. I'm a long time lurker and found little interest out there on this type of setup. I figured I would post the build for those that may have a similar idea for a different purpose than I.
I have a small group of friends that participate in a large bicycle social gathering that hit the streets every few weeks. During the ride we took notice of several bicyclists that built custom pull/carry sound systems similar to the ones seen below.

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I suspect their intentions were to help with the cadence and offer a bit of entertainment during the average three hour ride. This is accurate in at least one case but most of the sound systems are a constant stream of distortion. One evening, after a long ride listing to a system equivalent to a plastic kazoo, I decided to design and build something of substance. I also had an ulterior motive. I've been itching to build something I can listen to while working in the garage, grilling in the backyard or entertaining by the pool.

I wanted the system to satisfy the following criteria:

1. Battery powered - I haven't narrowed down the exact battery but most likely be a true deep cycle type (two Trojan T-105s or similar). I expect the power payload to be around 70-120 lbs.

2. Play loud and clear - it's a social ride, approximately 1500 riders. I would like to extend the sound to maybe 100 to 150 riders directly behind me.

3. Has to include some low end extension - The box design has to be optional, sealed or ported, and the port length has to be adjustable. I have some old subs from AV123 (the ones with the spider issue). I'm going to test run these subs and update to something else later. I need the flexibility in tuning for that reason.

4. Simple looking - I wanted it to look like a large docking station. A simple box with an mp3 player sitting on top.

5. Easily serviceable.

This is where I'm at:

two (2) pyle horn driver with exponential horns
four (4) 6.5" woofers
two (2) 12" subwoofers
one (1) 4 channel amp
one (1) mono amp

Box measures about 26 inches square. I have not cut the baffle and I'm still trying to work out the port details. Photos of the construction and some of the components are below. Fire away with any questions and/or suggestions.

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Old 5th January 2014, 07:21 AM   #2
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Hi,
since it's one big unity, you may want to place ( and to make a triangular base baffle , in order to support them ) the two tweeters as much as not-very-coincident, being facing at 90 each other the maximum allowed . And so the mid-wf's. The thing may be suspended from the enclosure that would serve for the subwoofer volume. Optimally, each piece of the stack should be free from interaction ( vibration caused ) from other pieces.
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Old 5th January 2014, 03:22 PM   #3
RyanD is offline RyanD  United States
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Pico,

I have a 3d model of the box on my work PC that I'll post up soon. I do agree that a triangular baffle is preferred, but I was planning on a flat baffle for the following reasons.

I've heard rumors of bicyclist with sound systems being pulled from the ride by local authorities. Reason being was noise pollution and their sound projecting near orthogonal to the street. I suspect that the home owners in the residential areas they ride thru are reporting the noise. I thought to play it safe and project the mids and highs reward parallel to the route.
Path of least resistance. Though not optimal, it's much simpler to fabricate a flat baffle than a triangular.
The 6.5" woofers utilize the small volume to the bottom left and right of the box (2 on each side). This volume is sealed independent to the sub volume. I haven't taken a close look at the horn drivers. If those are vents at the back of the driver than I guess I will need to separate them from the sub as well.
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Old 7th January 2014, 04:39 AM   #4
RyanD is offline RyanD  United States
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Old 26th January 2014, 12:42 AM   #5
dangus is offline dangus  Canada
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It looks heavy...

I'd be inclined to use very sensitive (efficient) drivers. That's just a win-win-win situation: less amplifier power needed, less voice coil heating and thermal compression, less battery capacity required. Some kind of curved enclosure could achieve stiffness with light weight. Or, use picnic coolers which are lightweight and dirt cheap from thrift stores and yard sales.
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Old 27th January 2014, 01:49 AM   #6
RyanD is offline RyanD  United States
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Quote:
Originally Posted by dangus View Post
It looks heavy...

I'd be inclined to use very sensitive (efficient) drivers. That's just a win-win-win situation: less amplifier power needed, less voice coil heating and thermal compression, less battery capacity required. Some kind of curved enclosure could achieve stiffness with light weight. Or, use picnic coolers which are lightweight and dirt cheap from thrift stores and yard sales.
I attempted to go efficient with the horn drivers and 6.5s, at least within budget. Those are the only components that I purchased new for this project. Not including the amps and subs, which were collecting dust in the garage, I'm about $300 deep (plywood, screws, wires and the highs/mids).

The subs weight in at 26lbs each. These will be the first be replaced. These subs were part of the AV123 liquidation years back. I bought them for $25 each not knowing that they have a major spider issue. At about 10mm excursion they make a mechanical popping noise.

A curved enclosure is a good approach but not easily constructed unless your good with fiberglass. I did see one guy with a decent sonotube build.

I put sound and appearance high on my priority list. To save a little weight I chose to use plywood instead of MDF. Not to mention the issue with MDF and humidity. I guess two large coolers stacked and sealed would serve the purpose. As long as your OK with the appearance.
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Old 27th January 2014, 03:05 AM   #7
RyanD is offline RyanD  United States
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More to the build log. I'm going to use an AC/DC server rack mount power supply to power the system while listening in the garage. I plan on wiring a few relays to auto switch between battery and power supply converter. When plugged in the power supply will kick in and the battery will charge. When unplugged the lead acid battery will be utilized.

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