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Old 5th May 2013, 11:16 PM   #1
Markgm is offline Markgm  United States
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Default Here's an Acoustic Boombox

Hi,
This all started with the idea of going to work, where I work the trim phase in building houses. The drywall is all on, and there is power every day I go to work. What I also wanted to have was desktop audio at home. So, I bought the Overnight Sensation speakers kit and a Dayton DTA-100A amp.

Then I went to the hardware store and got a nice 2' x 4' sheet of 3/4" plywood, which fits in my car, a 3' x 1" oak dowel, and a 3' stick of 1/2" thick x 1 1/2" poplar.

The thinking with this acoustic box was to leave the dispersion from the speakers open and free. I think there will always have to be more obstruction than plain stands to gain this carry-around convenience, so competing needs exist here.

The sheet of plywood provided for the box and a rack to fit around my laptop to use as a base for home desktop use. There was a little left over - about a square foot (in pic on left speaker), which is available if I want to make another shelf or something.

These are the finished pieces...
Click the image to open in full size.

Note: The first time I listened was last night, and that was without the slats - the 1/2" strips front and back that the speakers sit on. (Actually ripped material - 1/2" x 1/2") Today they are on those slats. I have to say this made an audible difference! I imagine the ability for sound to travel under the speakers and above the shelf to help? Also, those are so the speakers can be pulled forward 1/2" and they will slope upward a bit doing so.

Its all for better acoustics. The gaps in the front of the base (shelf) are to remove obstruction to the speaker outputs. There is also 2' of space between the speakers.

And here it is set up at home on the table with the laptop. Actually, there is a plus with the base unit, because light getting in and making the laptop screen unseeable is no longer an issue. hee hee

Click the image to open in full size.

I am really enjoying the acoustics with this! Next thing, I'll be blasting another new house with them tomorrow.

As for what I would do different the next time... The speakers fit snug between the triangular brackets on either side of them, and this really helps hold them in place for carrying. Also of note: I plan to add some kind of clamps to the wood behind the speakers and clamp on to the speaker wires there - to help hold the speakers in place for carrying. (These are very good binding posts) But I would make the brackets differently. I would make them arc-shaped instead of triangular, to hold the speakers more securely in place. As it is, I squeezed them to the sides of the speakers while piloting/screwing them into place.

- Mark
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Last edited by Markgm; 5th May 2013 at 11:30 PM.
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Old 6th May 2013, 01:30 AM   #2
Markgm is offline Markgm  United States
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First idea for tweaks/improvements: Replace the 1/2" slats/risers under the front of the speakers with just a couple of 1" pieces (instead of 6" strips), and move them back a half inch.

This configuration does not work entirely right with these speakers turned up loud (louder than acceptable here) because the table vibrates and the stuff on the table rattles.
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Old 6th May 2013, 01:57 AM   #3
Markgm is offline Markgm  United States
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Different angle, better light and quality of pic...

Click the image to open in full size.

I'm already starting to have new ideas about improving room acoustics of a rack like this. The speakers and center compartment could be on 3 individual shelves. There could be maybe 3 strips of wood running across the bottom of all 3 to hold them in place, and the rear strip could be mated with a strip that runs across the back, like the back of this one. The speaker wires could be clamped to the back strip, or the speakers could be screwed right onto the back - what the hey! Just wood putty the screw holes if they ever come off. That's about the best combination of acoustic considerations and easy portability I can think of.
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Last edited by Markgm; 6th May 2013 at 02:02 AM.
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Old 6th May 2013, 05:19 AM   #4
Markgm is offline Markgm  United States
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Default New slider idea!

This has got me thinking about a better portable stereo. Better acoustics - easier to carry around. Pretty solid. The only other thing is screwing right into the bottoms of the speaker cabinets.

Here is a picture of the expanding/contracting rack...

Click the image to open in full size.
Above: Top-down view of the expanding/contracting layer.
The center console is the largest square area (in the middle).
The heart at top and the upside hats at bottom are the tops and bottoms of long bolts; they are the big wingnuts and nuts on the ends of the long bolts.
There are 3 legs that slide out to the left, and 3 to the right.
As depicted the legs are all contracted.
The circles on the legs are all 1/2 to 1" spacers between legs and speakers. (Better acoustics)

Each of the legs has slots cut through their middles for 2/3rds of their length to allow them to slide in and out while the long bolts are running through them.

The wingnuts can be loosened and tightened against all same-side legs at once. This is to make it so that there will be no rattling.

In the area of the center console, the layer depicted above is topped and bottomed by a sheet of plywood to encase it. Only the top and bottom strips (closest to wingnuts and bolts) attach directly to these plywood sheets. The moving parts and the 1/3rd length spacers inside (not yet mentioned) can move freely between.

So, there could be a 12" wide center console area, and fully contracted speakers could stick out 6" on each side, and expand to 14" out on each side (with 8" of space) putting around 28" between the two speakers. The circle-spacers on the legs would be where screws go in through the legs and spacers and right into the bottoms of the speaker cabinets.

Best acoustics in a portable box I can imagine! Contracts to 2' wide by 9" deep (or however much is desired).
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Old 6th May 2013, 05:24 AM   #5
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Won't work. It's been tried many times before.

EDIT: Sorry. Should read more carefully that it wasn't a retractable/expandable cabinet but just a standard expandable speaker mount. Yeah, sure. Why not buy it though? I think they have an almost identical one in Ikea.

Last edited by Saturnus; 6th May 2013 at 05:29 AM.
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Old 6th May 2013, 05:28 AM   #6
Markgm is offline Markgm  United States
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Quote:
Originally Posted by Saturnus View Post
Won't work. It's been tried many times before.
Why, is it rickety and rattles?

Edit-add: OK, well I don't get an item for that purpose at Ikea in my first search. But I am curious as to how this type of item would handle the vibration, and how strong the clamping action would be, or if it would be strong enough.
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Last edited by Markgm; 6th May 2013 at 05:40 AM.
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Old 6th May 2013, 05:43 AM   #7
Markgm is offline Markgm  United States
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You know, when I say better acoustics with spacers, I am surprised. Spacers between speakers and the stands they sit on seem to make better sound, but I had never heard of doing this. I have done so inadvertently before, by spiking my stands, but not for the purpose of making a space between the bottom of the cabinet and the stand or shelf itself. I think it really helps.

Cheers,
Mark
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Old 6th May 2013, 05:45 AM   #8
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It's not certain they have it anymore. They had one some years ago when I was last in Ikea (maybe 10-12 years). Clamping don't have to be that strong. Friction does most of the work and there's not that many stresses on it (hopefully). For there to be rattling the speaker cabinets would have to vibrate quite a lot. No well-constructed speaker cabinet vibrates.
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Old 6th May 2013, 06:04 AM   #9
Markgm is offline Markgm  United States
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Quote:
Originally Posted by Saturnus View Post
It's not certain they have it anymore. They had one some years ago when I was last in Ikea (maybe 10-12 years). Clamping don't have to be that strong. Friction does most of the work and there's not that many stresses on it (hopefully). For there to be rattling the speaker cabinets would have to vibrate quite a lot. No well-constructed speaker cabinet vibrates.
No, but a loud, well-constructed speaker cabinet will skip a record. Of course, that's the bass coming out of the speaker, and not necessarily the cabinet itself.
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