small boombox speaker selection and port design

[52592]

I have had a look at the mission 760i's - they look good, but I'm wondering if the size of the tweeter can be reduced?

 

[Buckapound]

@Buckapound

That box looks like it's made from some carbon fiber/aluminum honeycomb material which I've read about, but never seen for sale. Is that what the material is and would you mind sharing where you sourced it?

Thanks,
_Ben

Yes, it's a sandwich of panels made from fiberglas/carbon fiber/fiberglas, with a core of phenolic resin-soaked nomex fiber honeycomb, about 1cm thick. Super-strong aerospace stuff, must have been for helicopter floors or something. Ugly green, and a bit rough, though, which is why it's covered with a skin of decorative carbon-fiber in epoxy, glued to the structural panels with polyurethane caulk.

I wish I knew where I could get some more, but it was a one-shot deal on eBay. I paid US$70 for a sheet just big enough to build the box.

--Buckapound

 

[Buckapound]

Yes please Buck, Looks almost steampunk, really cool!!! Id like to fing some of that board too!
Thanks,
Dave

Thanks, my aesthetic was to think if Cold war era B-52 crews carried a boombox, what would it look like? Fortunately, that's easy to do with available/surplus electronic parts.

The carbon skin came from a seller on eBay I wouldn't recommend, as the surface finish was far from perfect. Just search for "carbon fiber sheet" and you'll find a number of choices, It can be cut with scissors or metal shears and glued onto wood, MDF, or anything for a durable, decorative finish.

You could use stock case corners and aluminum angle to bind the whole thing and protect the edges.

--Buckapound

 

[52592]

progress update

I managed to score a pair of mission 760i speakers off ebay for 7 pounds! Rigging that up to the TK2050 board produced some promising results.

So I've sketched up the enclosure and added the speakers.... The challenge now is to come up with a suitable porting (if at all) design. I was thinking I could have some removable 'plugs' that fit into the holes so under certain circumstances they could be removed. Any thoughts?

I need some guidance on port sizing and direction if anybody could offer advice?

I have the original foam lining the mission 760i's so I'll probably re-use this on the inside

 

[52592]

mission 760i cross-over question

I've had the speakers apart - one of the capacitors was not connected to anything and was of a different brand to the other two. One of the other two was glued with what looked like original glue. So what happened? Has somebody had these apart and replaced both capacitors, INCLUDING all of the glue? Just for comprehensiveness, I have attached a photos with values below

 

[chris661]

Having taken ours apart, the disconnected cap is the original, the smaller one just above it is a replacement. TF202 has value 4.7uF in ours.

The design you've drawn up: I'm not sure if having two tweeters is a good idea, because of comb filtering. When the distance between two point sources approaches a wavelength, they will start to cancel when off-axis. So, if you put it on the floor, you won't have much treble. It's difficult to explain, so here's someone that can...
Phase, Time and Distortion in Loudspeakers

Chris

 

[52592]

Thanks for your comments Chris, I understand what you're getting at. I had considered that arrangement (and buying a center speaker instead) but I wasn't sure what to do with the cross-over side of things. I guess my choices are:

1/ Run a mono signal into the amp, run two channels through two cross-overs and into the two mid's. Run one tweeter off one of the cross-overs.

2/ Run a mono signal into one channel of the amp, then going into one cross-over driving the two mid's in parallel (giving half the impedance, twice the power provided it doesn't mind driving 3 ohms) and one tweeter.


The cross-overs have a high pass of 4500hz so approx 7.6cm, the tweeter centres are 91mm apart. Advice would be really appreciated!

 

[Cal Weldon]

Since we are now into multi-way, I'll move it here.

 

[chris661]

Thanks, Cal.

Oil,
I would run a mono signal into each channel of the amp. One channel, run one woofer and the tweeter (you'll need to play with the series resistor to bring the level back up), use the other channel for the second woofer.
I expect this would be about the best (especially in terms of amplifier loading). Just remember to de-solder the wires from the second tweeter - you don't want them shorting...

Hope all goes well
Chris