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Mini Convertible (active DSP speaker)

edited November 2013 in Audio Projects

(Enough website work for today! Time for some fun.)

I finished up a prototype pair of these little speakers a few weeks ago:

HifiZine Mini Convertible prototype, front view

HifiZine Mini Convertible prototype, rear view

Had a few people listening to them at Terry's place in Bathurst, and Nig and Paul came over for a listen. Next up is to make a nice-looking pair from better-quality ply. And also, a pair of stands, which will make the speakers into floor-standing ported speakers.

Long technical article here: http://www.hifizine.com/2013/09/the-mini-convertible-active-loudspeaker-design/

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Comments

  • Just so so so much potential here. Just feeling I'd need a two box solution (or two stack solution) to make it work as integrated pieces of furniture. But as a system to suit any room...sweet.

  • These will fit in the house we want to buy ,cool .

  • You're gunna need a sub with that.

    2 actually!

  • I could use the tapped horns :-)

  • Some of best work so far John, can't wait to hear then with the stands.

  • Thanks guys. I need to order a couple of sheets of good ply from DMK in Brookvale and get cracking. Stoopid weather keep putting me off.

  • "Next up is to make a nice-looking pair " !!?? - guess taste is up the arse of the beholder, but I like the look of the ones above.

  • edited January 2014

    Some of you may remember that at Bathurst the two speakers were different. One had an offset tweeter, to test the theory that this will give better off-axis response curves.

    I have finally done some measurements of the offset tweeter and the results are better than I could have hoped for. These are in-room measurements, so I've applied some smoothing, and I'm assuming that is the cause of the peak at 500 Hz and the other bumps and ripples above and below that. But look how smoothly the off-axis curves change (red is on axis, green blue etc are 15, 30, 45, 60, 75 and 90 degrees):

    offset tweeter, good side

    Well, this looks stellar to me. Note that the frequency range is from 100 Hz to 40 kHz. The reason I ran the measurement to 40 kHz was because this tweeter has a big resonance at 27 kHz and I wanted to be sure I had "tamed" it with the DSP.

    Above is the "good" side i.e. the right side of the right speaker in the above photograph. Here for comparison is the "bad" side, which seems to be fairly similar, in the off-axis measurements, to the speaker with the centered tweeter (and better in the on-axis):

    offset tweeter, off side

    I'll do some more accurate outdoor measurements for an article, but for now it seems fairly clear that the offset tweeter is worth the extra time in construction.

  • G'day john

    So, do the offset tweeters need to be symmetrical?

    If so, should the tweeters be in the centre or the outer of the sound stage?

    Graham

  • Yes, they need to be mirror image. Depends on where you point the speaker. Pointed in front of you, on the outside. Pointed at you or behind you or straight ahead, on the inside.

    This is, of course, not confirmed by actually listening to it, still need to build a mirror image pair...

  • Look forward to your thoughts once you've built them.

  • Hey John I might copy your beveled edges on a small 2way were building .

    2 way cab Cheers

  • I really like the visual of the bevel edge.

    I would do all 12 edges :)

  • 12 edges ??? what about the other 4 ? Nice measurements John. Can't wait to hear them and compare (dbt) to the centralised tweeter.

  • edited January 2014

    Nigel you must be feeling a bit edgy! Graham is right....

    Mal, of course you can copy me... if I can copy you :D :-b Based on that drawing you might need to have a think about the port sizing/distance to edge.

  • JohnR said: Nigel you must be feeling a bit edgy! Graham is right....

    Mal, of course you can copy me... if I can copy you :D :-b Based on that drawing you might need to have a think about the port sizing/distance to edge.

    It looks a bit tight doesn't it .Were trying to keep tweeter height down at seating position so maybe the simple roll over might be the go . Drivers are AE TD6M & Corona plasma tweeter .The cabinet below will house a AE PB18" .

    Cheers

  • MALfunction said: It looks a bit tight doesn't it . Cheers

    I prefer it tight :)

  • I left 8mm between the driver edge and the start of the chamfer. So 26mm to the edge if the baffle was left square.

    Mal, I meant with the port, you might end up with a sharp edge where the edge of the port meets the chamfer. In the base for the mini convertible I resized the port opening to leave 9mm. However with your that might not be possible, I'm assuming it's a slot formed along the base of the speaker?

  • John, where do I buy one of them DSP stereo plate amps from?

    I want one for a centre channel I'm going to build.

    Graham

  • edited January 2014

    Twodogs said: 12 edges ??? what about the other 4 ?

    Don't drink & post

    [-X

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