Monacor SPX-21M

v-bro

Member
2006-05-08 1:03 pm
Built some super tiny notebook speakers not sounding bad at all! Sure, they are tiny, don't expect them to blast you from your chair, but they sound more than decent!

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Sound curve straight on the amplifier:

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The usual raised midrange from a fullranger...

I had already composed a little filter to straighten them out before having measured them... And it turned out just the thing they needed:

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The filter is a little LRC notch followed by an LR high range padding.

That is 10uF, 220uH and 13R and the LR is 330uH and 3.3R....

Box is about 0.3 liters and port 15mm diameter and 12cm length (with a bend inside to make it fit in the tiny box)
 
Interesting little speaker I had missed thus far. I think your correction is very well done, as well as the way the BR extends the bottom end.

What is the dip @ +/-1700 Hz? Standing wave in the cabinet or port resonance? 12.5 cm plus some extension at both ends could sustain a standing wave of around that frequency, and little you can do about that, except taking a smaller diameter port and shorter length. But if it is in the cabinet, it should not be that difficult to improve a bit by applying some dampening. I found thick (1cm), open felt to work very well for small enclosures.
 

v-bro

Member
2006-05-08 1:03 pm
I am still far from ready with the design and I will see what happens to the little dip there, but this was never intended to become even as good as it already has, so I am more than happy already! I doubt it has anything to do with the port as it is curved round the back and up, so it's virtually impossible to create a standing wave. Damping right now is open porous foam, but it could perhaps do better with felt, got some laying around that I could experiment with a little.

I intended to make them active, perhaps with a little TDA8920 amplifier implemented and well power controlled. These match the application voltage really well...

Am also experimenting with the somewhat more expensive SPX-20M which is also a new miniature fullranger from Monacor. Will be posting up some more measurements when that is done, but don't nag me around about it as I have extremely limited time for these things...
 

v-bro

Member
2006-05-08 1:03 pm
Is that a standard NEMA electronics enclosure? Never thought about using one of those for a speaker cabinet! Nice work, the response curve looks very nice.

No it's a rose 02.081106/P311, but I have also used metal boxes for drivers like Fountek FR88EX and FR89EX recently and many many more before...

Love the BOX G115 encolsure for a 3", and you can use two bottoms of these together to double the volume as well...
 
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im always ogling those Rose boxes on RS. Diecast IP65? With the nice o-ring gasket?
Ive often wanted to try the same as you've done. I just find the sizes a little awkward, no Golden ratio sizes that I know of. Ive got some Hammond boxes im considering putting so 2 inch widerange drivers in, im just unsure theyre thick enough?

How is the stiffness of the box?
 
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No it's a rose 02.081106/P311, but I have also used metal boxes for drivers like Fountek FR88EX and FR89EX recently and many many more before...

Love the BOX G115 encolsure for a 3", and you can use two bottoms of these together to double the volume as well...

They want $27/ea for those Rose/Bopla polyester boxes from DigiKey. I was afraid they would be expensive being electronics enclosures.

I think I will stick with Dollar store foam core...
 

v-bro

Member
2006-05-08 1:03 pm
Hammond boxes are barely stiff enough, I only use the boxes that have the IP65 seal and the G115 (or G113 if it needs to be smaller) have PCB slots which act as very nice strengthening ribs.

The rose boxes are really THICK material and super super stiff, I've even milled the area around the speaker hole from the back to become thin enough to prevent reflection problems.

To get a nice golden ratio size the G113 or 115 boxes are very nice if you use two bottoms and sand the mating surfaces down nicely and glue them together. If you drill the thread out of one bottom and drill from the back up to a certain point you can use the M4 bolts to also bolt them together. Doing that gives a superbly firm and solid box with nice sizes. Then put it on some rubber feet to stabilize it because they are a bit cake shape boxes...

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From:
http://www.diyaudio.com/forums/full-range/117698-fountek-fr88-ex-8.html

These are available for prices as low as 15 euro a piece, and then it'll be about 30 for a box using two bottoms, but they are super super nice and so immensely solid that I find it well worth it.
 
Very nice V-bro

I think a bit of PCB and epoxy could help in the Hammond boxes.......

You've got me thinking, Those are great little speaker/s, makes me think that 1st thing on Monday morning I'm going to go into work and build some speakers with the Hammond boxes and whatever else I can find in the Lab!

They want $27/ea for those Rose/Bopla polyester boxes from DigiKey. I was afraid they would be expensive being electronics enclosures.

I think I will stick with Dollar store foam core...

They aren't cheap, but over here (UK) foam core isn't cheap either!


:radar:
 
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v-bro

Member
2006-05-08 1:03 pm
I think if you get the Hammond boxes with the adhesive foam seal it'll do good enough regarding stifness for these little drivers, they aren't that powerfull.

To those who intend to order the Rose/Bopla boxes one piece of caution, you MUST mill the baffle out from the back to get the drivers in nicely as they'll otherwise have breathing/reflection* problems and the reflex port won't fit.

*Depending on whether you mount them front or back.

I've given them another listening session today, and I think these would also do really great with a sub added. They have a fairly good voice to them, though there is a slight hint of sibilance. Might do some more filter tweaking and measuring if I ever find the time...