Mini desktop speaker build

mattkhan

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I built a sub in Mini sub for computer system to go under a desk so now I need some speakers to go on the desk to complete a 2.1 setup. The constraints here are;

- they will be positioned fairly close to the wall
- must be narrow (maybe 10cm or so), can be fairly deep, are preferably quite tall with the driver nearer the top
- need to extend to ~100Hz or so to allow a clean handover to the sub
- don't need to go beyond 90dB at 1m at this is a desktop system

The width constraint places a hard limit on the size of the driver to probably 3" and so I've decided to try my hand at a full range speaker to avoid having to stuff a crossover into a tiny box & because a 2.5-3" driver is used in quite a few full range designs. These often seem to be transmission lines so I've decided to go down this route and build a mass loaded transmission line (MLTL) which is basically a TL with port.

The drivers are 2½" SB65WBAC25-4 :: SB Acoustics which look like this in real life, mug of tea for comparison. Tiny little things!

upload_2016-8-17_10-9-36.png


I'm using Transmission Line v3.6.3.5 | Leonard Audio for modelling purposes which is a really easy to use piece of software, shame it's not maintained anymore but it seems to do the job nicely.

My current design is a tapered folded MLTL which gives a response like

upload_2016-8-17_10-11-17.png


first attempt at folding

upload_2016-8-17_10-11-49.png


I need to revise this though as I hadn't really accounted for the path length along the bends and I think there might be a better way to maintain the line length and driver/port positions while fitting it into a box.

Here's the line itself with driver (D) and port (P) positioned marked

upload_2016-8-17_10-14-16.png


I'm not sure if a TL is really worth it over a port but I figured that modelling a quarter wave design & learning about folding is probably a good thing to learn about :)
 
I reckon this will do it

upload_2016-8-17_23-49-44.png


basically a box 32cm tall, driver near the top, and ~160mm deep. Add an inner divider angled at 8 degrees and then an extra bit on the back angled at 5 degrees and you have your TL. Stick a port on the back 15cm from the end of the line to make it a mass loaded TL. Add a couple of reflectors to shade the corners off the folds to avoid dramatic expansion in cross sectional area and bobs your uncle (he says optimistically).
 
I think this version, which is an ML-TQWT because the taper goes in the other direction (fat to thin, port at fat end), should work a little better. The response is slightly better and it is a bit squatter (deeper but not as tall).

upload_2016-8-20_19-22-25.png
 
having built the desk, this design is a non starter as it is too wide. I'm going to change tack with this and try a v shallow wall mounted design which hangs on the wall like picture and which folds the line perpendicular to the baffle (like looking down on a maze if you get what I mean)
 
made a start on this today, didn't get as much done as I'd hoped for as cutting all those dados was a right faff. You can see how they line up on the front/bottom/back in this pic

upload_2016-10-16_19-52-40.png


Of course it was only once I was lining up my router guide for the 500th time that I realised I could have cut one big piece of wood, run a single dado for each one and then chop the piece of wood into slices :facepalm:

anyway I've got them all cut now and they seem to basically line up (I think 2 of them need an extra 0.5mm width on one piece to get it to fit) so just need to get the braces cut & then cut out the port & driver holes.

On the plus side, I got to try out my shiny new tracksaw which means I can actually cut straight lines quickly and reliably now without covering the entire shed in dust. This contrasts to my old circular saw which a) had the world's worst dust extraction, and b) had protrusions that made it really awkward to line up against my heath robinson guide system.
 
If it's to go behind a monitor, can you bolt a VESA mount to it and use that to hang the monitor off? If you wanted to get nerdy, build a channel up the middle for cabling? ;)

already got a monitor arm but not a bad idea at all, I suppose you'd need to beef up the speaker though to make sure it's strong enough though.
 
I can finally say goodbye to annoying/tedious/crufty straight edges and jigs.

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I probably would have saved some money if I'd just lashed out the cash at the start :)
 
Did the black fitting that fits onto the router come with your router or was that a separate purchase?
 
Thanks!!
 
I've decided against rear mounting the driver and so I was considering whether to try to mount them flush, shape is slightly awkward though so not sure what the best way to do this is. I guess I could do it as a series of straight lines if I'm careful, seems a fairly easy thing to go horribly wrong though :) any other ideas?

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Router it, the straight lines using your guide as close to the corners as you can, draw round the driver first then take out the middle free hand then sharp chisel the corners
 
made a bit of a mess of that effort, just not straight really, probably should have had a practice run first, fail :blush:

need to think of a way to cover it up or just leave as is as a reminder of my terrible handiwork in future :D (probably make a grill, seems like it would save me from doing much finishing work as well)
 
Last edited:
got the box together, ran a quick test with no stuffing (sim suggests I should stuff the 1st 2/3 of the line)

upload_2016-10-28_21-23-52.png


upload_2016-10-28_21-25-3.png


listened to a few tracks in mono, seems pretty decent tbh, certainly good enough for the intended purpose anyway.
 
That looks a neat approach, never thought to do it that way. I just stretched it over and stapled, without glue.
 
finally got round to putting this on the wall, sounds pretty good too. Now I really need to get that sub amp built....

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I've built a few more in this style using a slightly bigger driver in a bigger enclosure

upload_2018-4-21_22-18-21.png


the driver is a 3.5" full range effort which you can get for a tenner :)

TC9FD18-08 Peerless by Tymphany | Audio Products | DigiKey

it's a MLTL again but the bigger driver and enclosure lets me push the tune down to ~55Hz

this is the sim with the grand total of 10W fed to it, 90-95dB

upload_2018-4-21_22-23-40.png


I cranked this up today and it does go properly loud, with a nice clarity to it and a reasonably meaty bottom end for music. Not bad for £20 of drivers and some appropriately sized offcuts.
 

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