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Class D Switching Power Amplifiers and Power D/A conversion

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Old 20th March 2012, 12:30 PM   #11
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Quote:
Originally Posted by dangus View Post
I have a suggestion: visit a few car audio dealers and see if they have any "pulls" from installs in recent model cars. I found a pair of 6x9 OEM speakers at a thrift store recently: they had tiny neodymium magnets and composite frames, which made them incredibly lightweight (made in Mexico, 4 ohms, 20W, no brand name, just various part numbers which don't come in Google searches). (I haven't ~listened~ to them yet, but they seemed ideal for a portable system, possibly mounted in the sides of a thrift-store picnic cooler.)
Thanks for the advice. I heard that car speakers aren't suitable for outdoor Boomboxes because they are designed for small rooms like a car.

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Originally Posted by Boscoe View Post
So do you now what enclosure size you need yet? Are you going ported or sealed? Can you get hold of any other drivers? How loud are you expecting it go? Do you want bass or is this just for casual listening? Does your amp use a single or dual supply (as in it has a positive and negative input or just positive?
Sealed design. For a ported design I would need much more volume I want to keep it as small as possible.
I haven't ordered any drivers yet so yes but I don't want spend much more money than 25€ per driver.
As loud as possible
Yeah casual listening.
Single supply it runs from battery.

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Originally Posted by gmarsh View Post
The /4 and /8 speakers might have different TS parameters, make sure you take that into consideration with your box design.

Whatever one you go with really depends on how loud you want the stereo, and how long you want the batteries to last. Your options basically are:

- Least loudest / most efficient: Use a 2 channel amp, and wire 4 ohm speakers in series for 8 ohms.
- 3dB louder / less efficient: 2 channel amp, 8 ohm speakers wired in parallel for 4 ohms.
- 6dB louder / least efficient: 4 channel amp, 4 ohm speakers.

I'm eager to see how this turns out. I'm building a full-sized Boominator but also want to build a smaller one. I was considering Eminence Beta-8A's but if I can build even smaller with Monacors that'll be excellent.
Thank you very much, exactly what I needed!
I think the 2nd one is the one I'll use. What about the tweeters what do I do with those? Are they gonna play louder than the monacors if I just parralel them?
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Old 20th March 2012, 03:14 PM   #12
gmarsh is offline gmarsh  Canada
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Put resistors in series with the tweeters (if you're using piezos) then parallel them with the Monacors.

Lots of discussion in the main Boominator thread on the choice of resistors.
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Old 20th March 2012, 05:29 PM   #13
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Well I'm not using piezos .
I planned to use the Dayton ND16FA-6 5/8 tweeters.
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Old 7th April 2012, 11:53 AM   #14
craler is offline craler  Sweden
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How's it going with the build?
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Old 10th April 2012, 06:19 AM   #15
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How's it going with the build?
Sorry for the late answer I've been on a holiday trip for easter.

All drivers arrived and I got everything I need to start. I'm using two MP-60/8 per channel in parallel configuration.

My problem now is that I don't know how to cut the holes for the 4inch speakers.
They didn't have 9mm or 12mm birch plywood at local diy-market so I bought cheap plywood. Cutting holes with a "circle cutter" for 9,5cm failed because the wood splintered.
Do you have suggestions how I can make nice 10cm wide holes for the speakers?
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Old 10th April 2012, 07:22 AM   #16
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Do you have suggestions how I can make nice 10cm wide holes for the speakers?

It is possible to saw clean cutouts in plywood. There is always some splintering, but it can be minimized. First, tape up the outline of the area you plan to cut with masking tape before cutting or marking (both sides). Then mark your exact circle on top of the tape. Use a jigsaw with a fine-tooth plywood blade. Run the saw at a moderate speed and take your time. You should wear safety glasses as you need to get right on top of the line to see it clearly with all the sawdust flying around.

The masking tape, though it only has a weak bond with the wood surface, is usually enough to keep the plywood from splintering. (Duct tape can also be used.) This is a generally useful technique for all types of sawing as well as routing.

The fine plywood blade can turn on a very small radius and, with a steady hand, cut intricate patterns--certainly 5-inch circles.

To finish the holes, carefully hand sand with sandpaper. You will probably have a few chipped out areas that will require filler, but these should not be a big deal.
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Old 10th April 2012, 07:46 AM   #17
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Originally Posted by ChicagoJTW View Post
Do you have suggestions how I can make nice 10cm wide holes for the speakers?

It is possible to saw clean cutouts in plywood. There is always some splintering, but it can be minimized. First, tape up the outline of the area you plan to cut with masking tape before cutting or marking (both sides). Then mark your exact circle on top of the tape. Use a jigsaw with a fine-tooth plywood blade. Run the saw at a moderate speed and take your time. You should wear safety glasses as you need to get right on top of the line to see it clearly with all the sawdust flying around.

The masking tape, though it only has a weak bond with the wood surface, is usually enough to keep the plywood from splintering. (Duct tape can also be used.) This is a generally useful technique for all types of sawing as well as routing.

The fine plywood blade can turn on a very small radius and, with a steady hand, cut intricate patterns--certainly 5-inch circles.

To finish the holes, carefully hand sand with sandpaper. You will probably have a few chipped out areas that will require filler, but these should not be a big deal.
Thank you very much! That was a nice explanation ... I'll try that method later.
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Old 10th April 2012, 12:56 PM   #18
gmarsh is offline gmarsh  Canada
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Pretty much repeating what ChicagoJTW said - use a jigsaw with a fine toothed blade and take your time. Also make sure the side of the plywood you want on the outside is facing down when you're cutting, as that side will splinter a lot less - the blade will tend to draw splinters towards the wood, keeping them in place, instead of pushing them out.

Normally I'll use a 1/8" round router bit to clean up cuts when I'm done, especially if they'll be visible on the outside.
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Old 9th May 2012, 12:44 PM   #19
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Update!

Click the image to open in full size.

This is a prototype made out of cheap cottonwood-plywood. Everything is just screwed toghether and it's already pretty stable and I think there won't be a problem with birch-plywood in the final build.

I wasn't very satisfied when got the lepai amp first, but after bypassing the tone control and op-amps it sounded ok.

I also like how loud those speakers can be. Loud enough for my use ... I would't sit near them longer than a few minutes if you turn them up. The sound though is still good imo. (I'm not an audiophile at all though)

Greets
nano
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Old 10th July 2012, 12:45 PM   #20
matros is offline matros  Denmark
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Do you have some measurements for that cabinet? I am planning on building one myself with the same drivers, a little different tweeters.
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