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Old 4th June 2006, 11:26 AM   #1
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default An easy and fairly inexpensive DIY Mini Monitor with a Fullrange Driver

Konnichiwa,

This whole story was blogged out in a little more posts detail and all over at the DIY-HiFisupply Forum. But I figured it may interrest some of you.

A good while ago Brian Cherry started the development of a moderatly small, high tech (Neodymium Magnet among other things) full range driver called for some inscrutable reason NeoFone. I had some minor peripheral involvement with this and hence have know about this for a while. While I'm not allowed to say much, the designer behind this driver is one of greats for "small drivers" and has quite an impressive trackrecord (but wishes to remain incognito on this).

Click the image to open in full size.

In the end got a pair of the final drivers to make up some speakers for the bedroom which where meant to be a little prettier than the current ugly but good sounding ones with C37 lacquered japanese 6.5" Alnic Fullrange Drivers. Quick listening tests in open air confirmed that the driver had good potential.

Brian had also picked up a good deal of surplus Foster Leaf tweeters with "lens" attachment (these are the same as found on older Legacy Speakers such as the Whisper or Focus 20/20) so I got a Pair of these too to use as super tweeter. I had previously worked out with Brian that these work very well in that role with the NeoFones when used straight with just a 0.68uF series capacitor, nothing else.

Due to time commitments at work and with other projects the Speaker simply stalled untill last week when I came in the local Woolworth across something that looked just like a solid wood Minimonitor Speaker enclosure to me. It was actually a wooden breadbox!


Click the image to open in full size.

It was pretty dead to a knuckle rap and what resonance was there dissipated rapidly, giving a pretty dry overall sound, except for mthe bottom, which is fairly thin. Anyway, I made off home with two of them and a pillow, to be torn apart to yield some polyerster batting.

Afterwards I popped in (pausing at home only to measure the inside dimensions of the breadbox) to the local B&Q Builder/DIY Merchant. There I got me a pair of 18mm (3/4") MDF Baffles cut to be glued in against the bottom to reinforce it. I had decided to use the slightly inset bottom as the "Front" of the speaker. I figured the drivers should beam enough at the frequencies these edges are obstacles that edge diffraction would not be an issue and it looked overall better to me.

I also picked up some junction pieces and short pipe pieces in 40mm inner diameter up from the plumbing section. The advantage is that you can easily extend your port and even add ellbow joins to extend it an angle using this stuff and it's cheap.

As I had quite a bit of offcut from the smallest sheet MDF I could buy I also got a pair of shelf braces cut that left around 38mm (1.5") between the rear panel and the shelf brace (plus some other pieces for another project).

I glued the baffle in using "Evostic Resin W" Weatherproof wood glue, I also used this to glue the back on after putting the shelf brace in according to the golden ratio. Golden ratio bracing works by dividing any dimension to be braced by 2.618 and placing the brace at the indicated distance. Thus each dimension is subdivided into a 1 & 1.618 long part and any remaining resonaces are spread out.

Serendipitously I also found two suitable 38mm wooden blocks which I adhered to the rear pannel and which in turn reinforce the center of rear panel, which used to be the breadbox lid and connect read and front panel via the shelf brace.

I flew to the Munich HiFi Show after gluing everything, so by the time i came back all glue was bone dry and resulting enclosure turned out quite light, very rigid and with not much resonance remaining and what remained most crucially sounded very dry indicating low energy storage and quick lossy decay.

During the week I was tied up, but yesterdays weather was lending itself to woodworking in the garden, so I got the tools out and cut the various holes using drill & holesaw for the NeoFone Driver and port and a jigsaw for the irregular cutout needed for the Foster Ribbon Tweeter.

In order to mess up the finish on the front panel with the jigsaw's base I used a bunch of waste A4 paper (unprinted side down) between it and the wood.

As my shelf brace was placed according to the golden ratio and left only a moderately deep slot at the back, in effect subdividing the enclosure. I cut the holes with the port and Foster ribbon in the smaller upper chamber with the port on the back and the NeoFone in the larger lower chamber on the front (of course).

I used a some pillock, ahhm, pillow stuffing (around a quarter pillow) stuffing in the lower chamber, the upper is empty. I used bare 1mm silver wire for connections, together with these chinese WBT copy binding posts ("charming music connectors"). The "hot" connector was sleeved in some 5mm diameter glass fibre sleeving to prevent the wires from shorting.

The Foster Ribbon is connected using thinner enameled silver (I find myself using a lot of silver these days, I have it around and at hand, copper I'd have to dig out!)....

As my big drill just broke (when I was finishing cutting the second NeoFone holes with a big hole saw) I did not do my usual trick of drilling out the center of the binding post and running bare wire through the binding posts so that the binding posts are effectively bypassed.

As I used piping from the plumbing section I had a 40mm Port 80mm as the minimum, with the option to extend it by plugging in another piece (and another, untill I get bored). I ended up with a similar tuning as Brian by leaving just the 80mm long piece.

According to WinIsd using the T/S Parameters from Brians Site this gives a tuning at 54Hz with -3db @ 50Hz. My own Spreadsheets accounting for room positioning somewhat place the -6db point at 40Hz and subjectively this seems born out.

To roll in the Foster Ribbon I used a compound capacitor of 0.69uF. I did not seem to have any 0.68uF around so I looked into my junk, ahhhm, project box. I found a pair of 0.47uF Solen MKP (I know, I pooh pooh them at any convenient occasion, hence they where in the junk box not in gear - but I figured okay for supertweeter duties) and some Multicap PPFX 0.22uF, making 0.69uF.

I could have dug around in all the various places I keep components for a single 0.68uF instead, but I figured .69 gotta be more fun than .68, if ya know what I mean....

Well, that was the speakers complete, I dropped them into the big system instead of my normal fieldcoil equipped Transparence open baffles with Visaton TL16H Supertweeters and a dual 12" Subwoofer.

Click the image to open in full size.

With the speakers having the 54Hz tuning and being literally used as Bookshelf speakers (see photo) close to rear walls the bass is proportionate, if missing the lowest octave, on a lot of music it makes sense. I listened so far mostly to rock & pop and the speakers sound well balanced, with a bass that next to open baffles is a little boxy and lumpy, but quite tight and precise. Also, the amount and depth of the bass is surprising for a miniature, at least placed as I did.

The midrange and treble is clean and in proportion, quite well detailed and brilliant, untill you really crank the system up and things fall apart. Again, imaging is pretty good and stays stable up to high SPL's.

Classical is fine with a great and delicate string tone and loads of air only really big stuff leaves you wishing for more and perhaps for a subwoofer. Notably, the strings have a silkiness and smoothness few affordable fullrange drivers manage. The Woodwinds too sound great with a natural tone, the brass section blareds as it should.

I'm driving them right now with my triode wired (good for around 30W) Shanling SP-80 Monoblocks which also had their solid state preamp section removed, a Music First Audio Passive Magnetic Preamp and a CD Player I'm not allowed to say much about yet (Vinyl is as before).

In my reviewers days I used to refuse any offers of "MiniMonitors" with a simple "It's a minimonitor and thus disqualified from High Fidelity" and sadly the NeoFone does not change that. It makes for a really good small speaker though and maybe with a subwoofer and very low frequencies cut off it can manage good fidelity in small rooms with the full range of music.

So, it's a "MiniMonitor" that is really good for the genre but does not break out of it's limits. That said, if you want a small box and have a small room and at least 20 - 30W amplifier power available this little box can be good fun and it is fairly inexpensive and easy to make.

I have no other small monitors here for direct comparison, so I'll not indulge in claiming it outperforms this or that, it simply is a good speaker and good enough that I feel no immediate inclination to take it out of the big rig.

So, if you like minimotors and need or want another pair, get a pair and make a "Breadbox". If you prefer Altec Voice Of the Theater and prefer 45 SE Amplifiers then look elsewhere, but just like in my case you might find a use for them in a second system.

In balance, the NeoFone is well recommended, within the limits of it's format, I think the DynaFone (Brians Subwoofer) as woofer, NeoFone as Midrange and the Foster Ribbon build as a full three way speaker into a nice big floorstanding enclosure would make the best out of the NeoFone and let it be really good at what it does well (midrange and lower treble) and help add scale and dynamics with a full range bass. But that would be a very different speaker to what I build.

Sayonara
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Old 5th June 2006, 10:18 AM   #2
bcherry is offline bcherry  Hong Kong
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Default Thanks for sharing the project (nt)

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Old 5th June 2006, 11:11 AM   #3
EC8010 is offline EC8010  United Kingdom
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Nice idea. I think I've seen similar boxes in Tesco or Sainsbury's. Time to investigate...
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Old 5th June 2006, 12:51 PM   #4
Colin is offline Colin  United Kingdom
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You're not restricted to playing David Gates tracks, then?

The wonders of 'found' speaker boxes. Looks like a good alternative to the ceramic plant cubes I've been playing with (Homebase).
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Old 5th June 2006, 02:17 PM   #5
MuaDibb is offline MuaDibb  United States
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I recently purchased a set of these Neo-Fones on e-bay, and while I haven't planted them in the BIB's I've built, they sound quite nice just sitting on my desk tilted back. The gentleman I bought them from had this to say :

The Neo-Fone was one of the few drivers that I didn't run distortion curves on. While I did run a frequency response measurement, it was not saved since I used it only to notch-out minor resonances with the Behringer EQ. The driver, as I recall, was much better damped than the Seas Magnesium Excel drivers we have (W15's) and vastly superior to the aluminum L15's, sonically. I didn't compare the frequency response measurement with the online version, but I remember it being fairly smooth. The Neo-Fone cone did not impart too much of its sonic character on music, unlike the strong sonic character imparted by many metal or paper cones.
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Old 5th June 2006, 05:02 PM   #6
fred76 is offline fred76  Philippines
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Hi KYW/T,

That's a sweet bread box there.

BTW, for those intrested, here's dims for a Neofone BIB enclosure done by Scottmoose:

"As per a request for the neophone, here's one.
Line length 128in.
Zdriver 25.75in
Sm (or Sl if you are so inclined) 55in^2."


Could be a slender small footprint but tallish cabs for corner placement/loading.

Terry Cain's BIB -why does it work and does anyone have those Fostex Craft Handbooks?

http://www.zillaspeak.com/bib.asp
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Old 5th June 2006, 07:42 PM   #7
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Hi

nice review, thanks!

btw. how come that you're quoting Strugazki in your signature - in german?


best, LC
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Old 6th June 2006, 07:31 AM   #8
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Konnichiwa,

Quote:
Originally posted by lovechild
btw. how come that you're quoting Strugazki in your signature - in german?
I love their writing (I read/read much of it in german translations, some also in English). I would have used the quote in russian, but I cannot really get kyrillic to work here and my attempts at an english translation quite frankly sucked.

Sayonara
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Old 6th June 2006, 11:49 AM   #9
westend is offline westend  United States
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Quote:
Originally posted by Kuei Yang Wang
Konnichiwa,



I love their writing (I read/read much of it in german translations, some also in English). I would have used the quote in russian, but I cannot really get kyrillic to work here and my attempts at an english translation quite frankly sucked.

Sayonara
Babelfish also sucks but here is that translation for those inquisitive minds that only understand English: "I heard, this way lead to the ocean of death, and turned around half-way. Since that time detours stretch, desert and bent before me"BTW, nice job on the minimonitors. The serendipitous nature of it adds to it's value, IMO.
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Old 6th June 2006, 12:59 PM   #10
KT is offline KT  United States
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KYW,

Great review. Thanks!

The breadbox is in the true spirit of DIY. Very cool.

I've been curious as to how the NeoFones sound since I first saw them on Brian's site. Seems like a decent driver for a good-sounding fun project.

The obvious question is how do they compare to the CSS FR125/WR125 or the Jordan drivers?

I'm sure we'll find out soon as more folks get a chance to compare.

Best,
KT
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