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Multi-Way Conventional loudspeakers with crossovers

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Old 11th January 2011, 01:35 PM   #1
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Default My DIY Active Soundbar!

Hey all! I have a week off and I'm still waiting for my ESL parts/funds/student loan to arrive. This is very boring so... made a hasty decision to make a thread showing progress as I build my first surround sound bar!

Specs:

- 5x HiVi B3N 3" Aluminum Driver Round Frame | Parts-Express.com

- 3x Dayton ND20FA-6 3/4" Neodymium Dome Tweeter | Parts-Express.com

- Approx size (HxWxD)mm: 150 x 1125 x 150

- Frequecy responce (100Hz to 22kHz)... hopefully

- Integrated analogue processor for 5 channel input

- Integrated 4x Tripath 25W stereo amps (the tiny ones from 41Hz) so total of 8, 25W channels

- Built into a sealed MDF box. Each 3" driver will be sealed off from the next.

- Oil finished White oak vaneer!

It should give surround sound to the person sitting directly on axis (me), and an ambient blur of sound to those who don't actually care and sit off axis (my fellow students! :P)

This system is targeted for use with the occasional movies and games, in a semi portable system for those who's living room has no room for rear speakers or cabling.

This will NOT replace my Hybrid ESL project, but it will push the build down into Feb slightly due to parts-express charging me more for shipping than parts _.

The design will work by using the interaural crosstalk cancellation method polk audio uses. The rear channels will be low pass filtered to around 5.5kHz to make sound appear as its approaching from the rear. (I think that's how you do it, it works for me anyway)

Will use a separate sub to deliver bass below 100Hz.

The driver will arrive this week hopefully along with some fedex tax! Meanwhile, time for me to go make the box and design the prototype crossover network

Pics coming soon!
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Old 11th January 2011, 10:09 PM   #2
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This is the proposed system block diagram:

Click the image to open in full size.

Turning out to be a hell of a lot of op-amps...

All filters are -24dB/dec Linkwitz Riley.

(Oops, *cancel with one "L" :P)

Last edited by Ridin '24'z; 11th January 2011 at 10:11 PM.
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Old 11th January 2011, 11:06 PM   #3
Pano is online now Pano  United States
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Very cool project, thanks for posting!

What will be the physical layout of the drivers?
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Old 11th January 2011, 11:28 PM   #4
kach22i is offline kach22i  United States
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Would you be better off using what they call "line array drivers"?

Won't wiring up a couple of 8 ohm drivers present more of a amp load than a similarly arranged group of 16 ohm line array drivers? Or is that a couple of 4 ohm drivers?

I'm just trying to learn, doing that by asking questions.
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Last edited by kach22i; 11th January 2011 at 11:32 PM.
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Old 12th January 2011, 03:09 PM   #5
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I'll be posting the layout soon, (it basically looks like a polk surroundbar 50, but with only two drivers each side).

I'll be driving each speaker individually, 5 Midbass drivers and 3 tweeters. So 8 amplified channels.

These are stereo amps in really small footprints, 41Hz Audio:AMP32 kit they sound very nice and pack more than enough punch for this application.

My new table saw arrived today =D so will cut the pieces at some point and post pics.

A proper line array would require too many amps and dsp channels. I'll see how this goes, might think about trying it after...
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Old 12th January 2011, 03:26 PM   #6
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Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

So far I've cut the pieces for the box, you can see the three small tweeter holes, and divides for each section. Total of five sections.

Now to screw them together and pop to the hardware store to find me a 70mm hole saw to cut the holes for the woofers! =D

*has covered his student bedroom in MDF dust*

Last edited by Ridin '24'z; 12th January 2011 at 03:34 PM. Reason: Massive picture...
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Old 12th January 2011, 09:06 PM   #7
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So now....

Holes made for woofers using a 52mm hole saw. Not shown here but I've gone round it with a jigsaw to widen it up to the required 71mm. Will use a file to make the edges bigger if required.

Click the image to open in full size.

Click the image to open in full size.

The above image shows gluing of the front face before its screwed down again. Used normal PVA glue.

Click the image to open in full size.

Having done that, all edges where planed

Click the image to open in full size.

The rear side will be put through the bench saw again to trim off the edges. The frequency response of the system at the moment falls 3dB around 90Hz (Theoretically) so the extra trimming should be a problem for the 100Hz crossover point.

Click the image to open in full size.

OMG a gap!!!

Click the image to open in full size.

Problem sorted ;-)

Click the image to open in full size.

Little rare earth magnets implanted into the face. They wont be seen under the veneer,anyone guess what they'll be for? =D

There's also some at the base of the unit, not so obvious but these will be for some small steel spikes that will allow the system to sit on a shelf rather than wall mounted.

Click the image to open in full size.

Don't think the PVA glue will be much use here, so a dab of Epoxy to stick them on [=.

Click the image to open in full size.

Well and truly stuck!

...Will continue tomorrow when hopefully the drivers will have arrived =].
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Old 12th January 2011, 09:16 PM   #8
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Here's the crossover network, It's not tuned yet, crossing over at some random frequency purely for demonstration until I've decided where a good point to cross over is. Not sure what the best way of summing the audio is but I've just used a non-inverting op-amp summing junction with a couple 10k resistors. What kind of distortion would this introduce? Here's the LTSpice file for the simulation, seems to be in working order, will prototype at some point tomorrow.
Attached Files
File Type: zip Soundbar Crossover.zip (3.7 KB, 141 views)
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Old 13th January 2011, 07:30 PM   #9
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Time for more pictures!

Click the image to open in full size.

This will again be stuck on with PVA glue. (I'm no expert at this but at the time of writing, it seems to have worked)

Click the image to open in full size.

First, lots and lots of glue. Spread it right to the edges and cover every spot. After what I've put on above, I put even more glue on.

Click the image to open in full size.

Originally I put it flat on the floor and let it dry, but I read it can be ironed.

Don't use a iron you mind getting glue on the bottom. Most irons have a non stick surface and any glue that gets on the bottom will instantly cure and peel off. Doing this veneering procedure will scratch up the bottom of the iron a little

When the glue heats up, it becomes very slippery and the veneer will want to curl up and move all over the place. Put stuff on top to hold it down and stop it curling and moving around.

Click the image to open in full size.

Wipe up any drips, but this squidging at the edges are good.

As the glue steams and the water evaporates, the glue will instantly harden, it will be stuck there and you only get one go at this.

Don't try do the whole section in one go, do bit by bit. you want the glue to stick the veneer down before it dries. the edges need a lot of pressing down to get it to stick and give minimal curling. The wood may crack in many places, but that's fine for now.

Don't worry if the edges are unstuck by the end of it, we will be glueing them again later.

You want to trim the edges with a hobby knife.

Click the image to open in full size.

Do this all the way round.

For the holes, I got a pair of nipper and chopped through the middle. Make sure the veneer doesn't come off where it shouldn't.

Press down on the edges and the veneer should snap at the edges.

Click the image to open in full size.

Click the image to open in full size.

more glue...

Now once it's all done, you want to put glue in all the gaps that you can see and iron it on. Once every thing is stuck down, leave it for a while.

You'll notice bubbles forming everywhere. These can be smoothed down with steaming. It will crack where the bubbles are. These cracks should be filled with PVA glue and ironed flat. You want to give several coats of watery pva glue. This will cause the cracking lifting process again that you will have to fill with glue and iron down. Keep a sanding block and some coarse sandpaper at hand to clean up the edges.

A neat trick I've found is, if there's a little veneer (1 - 2mm) at the edges, they can be covered in glue and pressed around the edges with an iron. this will make it stick to the veneer in the next face. Once this is sanded flat, it'll look seamless around the edges.

Once you are sick of doing that, it's ready to sand the holes for the woofers!

I used one of these massive sanding drum things for the woofer holes:

Click the image to open in full size.

And a little one for the tweeter holes:

Click the image to open in full size.

Look what arrived! =D

Click the image to open in full size.

Trying them for size...

Click the image to open in full size.

Now that you've determined the veneer wont lift or curl anywhere. You can start filling in the cracks with some wood filler

Click the image to open in full size.

Once this is done, the long sanding process can begin...

*p.s. The little stick was made from a lollipop stick, but I found it's easer to spread the filler on with fingers :P*

Last edited by Ridin '24'z; 13th January 2011 at 07:36 PM.
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Old 14th January 2011, 11:23 PM   #10
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A quick little update, I've tuned the Midbass to high crossover to just over 8kHz. This is just before the woofer's frequency response starts to fall very steeply. The tweeter is happy from around 1kHz. I have to determine how much to attenuate the inverted L and R channels by to stop them being too loud while cancelling the sound to the respective ear.

In terms of box design, today was spent doing more ironing and lots of sanding. Lots and lots of sanding... and ironing.

There where bubbles to iron down this morning when I took a look at the thing. Gave the big bubbles some steam, put some glue on and held the iron on the wood until it was flat. It takes a few seconds of holding the iron there but as soon as the glue is hardened, the wood will stay flat and will be rock hard.

I used some very coarse wet/dry sandpaper to get all the gluey bits off and flatten the material. Aluminium oxide paper is good also. Normal stuff didn't last long at all. Using the coarse paper I also gave the edges a small radius. As you sand, you wont notice when the veneer has been sanded right through to the MDF. Keeping a vacuum cleaner handy to take the dust off the material, you will start to show the MDF underneath. I gave about a 3mm radius. A sensitive fingertip and a good eye in daylight helps here.

Next I put more PVA glue on! On all the edges that you've sanded. It's important to keep the edges well glued else a bit can rip off and take a load of the veneer off. As I found out many times. PVA glue and an iron are your friends here, and will fix all. Once you've spread glue on the edges and ironed, you can sand the entire thing free of extruding glue. Use a sanding block but the bits that wont go away can be done by rubbing the sand paper over it with a finger, or the careful use of a small hand plane.

I then put wood filler in all the gaps and big cracks. The stuff I used didn't fill the pores of the wood but smoothed over cracks very well it looked to fit straight back into the grain again. Then sanding and the occasional PVA glue when something looks like it could be chipped off.

Tomorrow I'll give a quick sand with some medium grade sandpaper and give a few coats of gloss black spray paint.

Will post a couple of today's pictures tomorrow =].
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