Miniscule monitors

( NB I'm cross-posting this from PFM only because it's totally the opposite end of the scale to Dev's and especially SpeedySteve's recent DIY speakers..! It involves no serious measurement or attention to detail and only requires one key piece of info from the driver datasheet - the recommended box volume.

Everything else is glue and fun, proper kitchen-table DIY audio )


I lashed-up a new pair of speakers yestoday, and can't believe what I'm hearing for the lack of effort involved.

The drivers I've had in the cupboard for years, Bandor 50mm fullrange drivers. Now I've played with them before - one evening some years ago MarkW and I fabricated some conical horns. More accurately ...we taped together some leftover bits of foamboard in the caricature of a horn for fun. 15minutes of careful engineering and we had two of these:


And several hours of listening followed easily, like this:


(yes of course there was beer involved)

Later the horns went into the bin, and the drivers were put away.



Mooching through Habitat's closing sale yesterday lunchtime I saw a nice bamboo utensil pot and another silly idea struck. So I bought two - cheap!

It turns out the recommended loading for the Bandor 50s is a sealed, stuffed enclosure of 1.5litres. And that's exactly what I have now. No pics of the build because it is so desperately simple - drill some 4mm sockets in the (base) of the tub, two lengths of wire to link them to the driver, I stuffed the box full of spare mineral wool batt offcuts and glued a baffle in the front (top) to carry the driver. Like this:


OK these things are really tiny. Sat on the H2s they look a bit lost:



Expecting nothing but sinkplunger-y cone movement and thin sound, I fed them Dexter Gordon's One flight Up and laughed out loud. Then a good dose of Kruder & Dorfmeister and giggled some more. The sound is astonishingly coherent, and there's even bass - not loud, but great grip and clarity and tone and all the way down. For 6" cubes that simply must roll-off below100Hz they sound so full there's a bit of a cognitive disconnect at work.

These things are thoroughly insensitive - somewhere around 78dB/W I reckon - but in this room they go loud enough, and after a couple of hours of trying different genres I'm simply amazed. The 'speed', clarity, tonal rightness and coherence bears comparison with the ESL57s I had. Not bad for £15

NB after a day of listening - yes there's no serious bass energy, but there's something very right about the protrayal of rhythms. And no risk of annoying the neighbours late at night!

 

Thanks Rob.

Looking through the bits box(es) I have some Eminence Deltas, some 7.5mH chokes, and some 100uF polyprop caps spare. If my ballpark maths is right, that little lot will give me pretty much a 200Hz crossover to pass duties onto some bigger drivers plonked in an open baffle (- which may still need padding-down )

But really the point was to try these small, no, tiny fullrange drivers in conventional if easy closed-boxes; and to encourage others to try similar! Afterall you can find small paper-based FR drivers really quite cheap. I have to say the result has greatly exceeded my expectations - these may be either the world's finest PC speakers, or just very large headphones...

 

just discovered this excellent thread
I recall the cardboard mock up being posted but not the cubes.

I think The equivalent Jordan units are around 86dB & same volume needed
made up as linear array from 2 to 4 to 8 drivers is where they excel

bandor make up a bandpass bass unit sub without crossover
it looks like a small coffee table

 

Jordan's JX92s are 100mm cones and yes, reasonably sensitive; twice the diameter = 4x the area, so +6dB sensitivity ...rather makes my in-room estimate and yours agree.

But there's no way around the problem posed by a 'full-range' driver less than 2" across. These toys require at least 100degrees more vol pot rotation than my H2s for similar impression of loudness at conversational levels, beyond which deep bass notes make the cones hit the end-stops!

They are proving really quite good though. Despite the published curves, it is obvious they roll-off gently c.15Khz ish unless you are exactly centred on- axis, and that's not a bad thing - it nicely balances the lack of bottom-end weight and the result is still, really, surprisingly listenable and satisfying with almost any material. Drums, snares etc really have a good 'startle' /presence quality; so dynamics, within the driver's modest envelope, are excellent.

While I could use more units/side I really cannot see the point - it'd address neither the sensitivity nor extension issues adequately. The 'bass-augmented wideband' approach above is almost certainly going to do that a lot better - and much cheaper! These shiney things new are well over £1.50 per mm of diameter...

Anyway - I'll get a second opinion from MarkW on Friday; after which we might think up something even sillier

 

Hello Felix

I was referring to the Jordan 2" driver at 86 dB (actually the newer version is 89dB) see the Best Midrange thread & look up the link

Off axis listening is the big plus with Jordan units 2" & 4" but they need a severe toe in to work best your photo shows them at too wide an angle

I've been using the linear array for a good few years but its the100mm which is my favourite & sounds meatier

 

Actually they are toed to cross well ahead of the listening position as advised in that pic (the result otherwise is rather obviousley 'phasey ' I found)

86db/W I simply do not believe. I'll measure my pair properly tomorrow...
Thanks.

 

Felix - different manuf's not the same but similar ancestors

More info on this thread plus pics (albeit poor quality).

http://www.lencoheaven.net/forum/index.php?topic=3235.15

Ted J recommended 60 degree toe in from rear wall plane spaced 2 - 2.5m apart with hot spot 1m back from their crossing point. The linear array he used were wall mounted & bass units laid on floor. With this set up the hotspot was less critical allowing off axis listening. You can walk right up to one speaker & still retain central image.

I find the more you widen the spacing and/or angle the more you need to move back. My office layout dictates I sit in line with the left speaker & I'm pretty happy with the central image preserved. (it is better centre though)

As far as I understand Bandor units & their cones were older technology than the Jordan ones I have. As far as specs go I'd trust Ted J's measurements & claims of that time. My toe in varies between 60 & 70 off the rear wall plane.