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Air Volume Acceleration
Dear Mark,
I have a couple of questions regarding your article on Air Volume Acceleration, which was most interesting by the way!

1. What Happens to the total air volume acceleration when two drivers (say two midrange drivers for example) are connected in parallel or series with each other?
2. How can the air volume acceleration be calculated for a ribbon tweeter? Bl is not given for most ribbon tweeters I have come across.

MW
Hi Sören
Thank you for the kind words. I will deal with your questions in reverse order. It is possible to calculate neither acceleration nor air volume acceleration without information on magnetic field strength and the length over which it acts. I imagine that it is probably difficult to calculate for pleated ribbons, hence it does not get specified. However, The acceleration of typical ribbons is orders of magnitude better than moving coil devices due to their tiny mass. The air volume acceleration is quite good, although the area of a ribbon is not equivalent to the area of a dome or cone as it is pleated and moves differently. As soon as a horn is placed in front of the ribbon its air volume acceleration is multiplied by the multiplication ratio of the horn (dependent on shape, throat and mouth) so a properly horn loaded ribbon (like the old Decca London) is pretty spectacular at moving air fast, beyond most modern supertweeters but direct radiating ribbons struggle to shift much air hence their higher crossover requirements.

Two drivers wired in series have half the acceleration as one as the magnet force product is working against doubled moving mass (series must be summed - in English the letter 'S' is the reminder). They have the same air volume acceleration as the doubled cone area is cancelled by the doubled moving mass on the other side of the equation.

Two drivers wired in parallel have the same acceleration as one (two adjacent Mini Coopers accelerate at exactly the same rate as one Mini Cooper) but double the air volume acceleration. You don't get something for nothing as double the current is being drawn from the amplifier to achieve this (remember the equation is a function of current).
Do let us at TNT-audio know about your speaker building project.
Happy sawing, soldering and listening,
Mark Wheeler

Onkyo MC cartridge
Werner,
I realize it's been years since you wrote the show report, but I just ran across it doing some research on moving coil carts. I worked for Onkyo in the 70s and early 80s, Denon in the 80s until '92. I just wanted to let you know that around 1980 Onkyo DID produce a moving coil cartridge. It was the MC-100, low output similar to a DL103. It was quite good sounding, but was not a commercial success. I don't believe that more than 200 were built. There was a plan to introduce a MC-200 but it was cancelled when the 100 did not take off. I had a prototype which I sold to a gentleman in HK - for hundreds of dollars. It was only one of 4 ever made and as far as I know the only surviving sample. I recently found a packaged NIB MC-100 that I intend to put up on eBay.
Best regards,
Ken - E-mail: ken (at) furstmarketing.com

WO
Dear Ken,
I had to read back that old show report to realize that you refer to my "Actually they aren't: AFAIK Onkyo never made a classic moving coil cartridge. Or studio gear." For that thank you very much indeed as it is good to know that Onkyo did make a moving coil. I would be even more grateful if you could photograph that cartridge you have, scan its documentation, and submit all to www.vinylengine.com, the web's resource dedicated to archiving all things related to LP reproduction.
With the kindest regards,
Werner Ogiers

Miniwatt amp in the USA
Hi Nick,
I read your review in reference to the Miniwatt amp. Do you have any information where in the USA, one can be purchased? I tried one place (alo audio) and they wanted $369 US for a updated version. Thanks in advance.
Frank - E-mail: Frank.Dinatale (at) dover.af.mil

NW
Hi Frank,
I can only suggest contacting the manufacturer to ask them if they have a distributor in the USA. As far as I know, the only mod for the Miniwatt was the addition of a couple of ceramic caps so don't go paying over the odds for something that is supposedly modified. The real beauty of the Miniwatt is its low cost!
I know from reading various forums that there are lots of Miniwatt owners in the USA so Googling 'Miniwatt' may also be helpful.
Hope this helps.
Nick Whetstone

Pre amp for Miniwatt
Hi Nick, I'm an happy owner of a Miniwatt s1, and I thought a preamp would be great. Then I read your review...
Could you advice me about a suitable and not too expensive preamp that will fit my needs? My system is mac mini (lossless files) > optical/usb> musical fidelity vdac> miniwatt > axiom m3v2 speakers (92db)
Thanks a lot and have a nice day!
Mathieu - E-mail: mtornare (at) me.com

NW
Hi Mathieu,
If you can control your volume level through the Mac Mini, then I would suggest a buffer rather than a pre amp with another volume control in it. As I said in the review, a little extra gain seems to help the Miniwatt.
A lot depends on your musical taste as to whether you go for a valve or solid-state stage. There are quite a few valve buffers on Ebay ranging from 50-300 euros. The Trends PA-10 that I reviewed worked well, and is in that price range. If you are prepared to do a bit of DIY, something like the Audiodigit Tube-Pre is another good buy although you need to provide a case and transformer etc.
As regards, solid state, all my buffers are DIY except for the very good Burson Buffer that is very good but at a price of 350 euros, it may be above your budget. Looking at the TNT archives, there doesn't seem to be much in the way of budget pre amps so I can only suggest that you look on Ebay, and trawl through as many reviews as you can.
Sorry that I cant be more specific.
Regards,
Nick Whetstone

The secret home of coaxial cables?
Hello TnT,
you've convinced me! I should give up on commercial cabling and only build my own speaker cables. I have tried various types of store-bought cables over the years, from no-name manufacturers to products from the likes of Monster (yes, everyone has a Monster phase - it seems to be the entry into "high-end" cables) to Oehlbach, Ply and Virtue Audio. But the speakers cables that sounded the best so far in my system (FLAC streamed via Squeezebox, external Scott Nixon tube-buffered DAC, Kebschull tube mono amps, Monitor Audio Silver speakers, in a small-ish living room) was the FFRC using solid-core Cat 7: it had the most tight and controlled bass (deep, but not boomy and mushy) and very nice highs without being harsh. Wow.
So, now I want to to try your other cable: the Ubyte2. And here's the rub: unlike twisted-pair Cat 5/6/7 cable, it's really hard to find a source of suitable coaxial cabling. Coax with a solid copper center conductor is easy enough to find, and even silver-coated copper is available. However, I have not been able to find coax with pure copper foil shielding. Metalized mylar and aluminum foil seem to be the only materials used in coaxial cable shielding these days.
Can you give me a hint? Do you know any sources, in Europe or anywhere I guess, of coax fitting for the construction of the Ubyte2??
Perhaps there is even a commercial version of the Ubyte2... but that wouldn't in the spirit of the thing. ;-)
Greetings from Berlin!
Christian - E-mail: xtian (at) devolving.net

LC
Dear Christian,
I'm glad you are enjoying our TNT FFRC DIY speaker cables in your system. A source for coaxial cables can be found here. It seems they have a wide choice of coaxials with copper shielding. Anyway, silver coated copper isn't a bad thing :-) but, most of the times, it is only tin coated, not silver coated!
Anyway, may I suggest the fastest way to get informations and support for building our DIY designs? It is our discussion forum!.
Hope this helped and keep us updated!
Lucio Cadeddu