TNT-Audio Readers' Corner
Monthly section devoted to your letters, positive and negative feedback about everything related to Audio and HiFi.

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March 2015

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Dear dr. Kohli,
I've just read your inspiring review of supertweeters on TNT-Audio, and was wondering whether the beneficial effect you experienced with your Quad may be obtained with Magneplanar 3.7 too. I guess the answer is a firm yes, as these loudspeakers suffer from the same roll off at high and low frequencies.
I am tempted to follow your path and purchasing a pair of Dayton AMPTPRO-4, but my incertitude concerns how to mount them. Can you provide me with guidelines? Shall they be connected straight to the amplifier? Do I need a crossover? How to install them? On top of the Magneplanar? Fixed in which way?
Any suggestion would really be appreciated.
Thank you in advance,
Roberto - E-mail: fregarob (at)

Hello Roberto,
The supertweeter will need some kind of hi-pass filter ... and the slope on that filter will depend on where you current speaker rolls off and how you want the tweeter to contribute to the overall sound.
Here you need to consider 3 factors in designing your filter in terms of mating with the main driver - rolloff frequency, steepness of the slope and sensitivity.
Most supertweeters will use a very small amount of current and in most cases be driven by the main amp.
You'll want to experiment with placing the tweeter on top or the sides, and aiming it generally at the ears.
Good luck.
Arvind Kohli

Compression drivers
Hello again Mark,
I read you thoughts about B&C compression drivers. This is the medicine I needed. Be patient here with my ignorance.
I understand a compression driver in a coaxial loudspeaker is designed to reproduced the mid-range and high frequency. Do you feel a good quality compression driver can smoothly produce mid-range and high frequencies?
This is precisely the system I am considering. A single pro-audio 12" coaxial driver that I'm told is slightly modified with a 'different' spider. I don't understand any of this. I am interested in what 4-5 people have stated about a specific pro-audio coaxial brand. Apparently with a specific cabinet design, bass is not a concern either. I have a feeling you like pro-audio drivers and I'm tired of the worn-out, gasping for air home audio industry entirely.
Joe - E-mail: juniperedge (at)

Hey Joe,
"The old scribe couldn't resist that pun!" heckle plebs, stage left, "He's so predictable"

Good to hear from you again. I'd love to see Maine in Spring and Autumn light; a friend used to visit every year and indulge in large format film photography. Here in Derby at the Format Photography Festival this week there was some lovely work from Maine.

Like most things, there are no constant rules regarding pro-audio compression drivers in relation to domestic audio. What they can do much better is controlled dispersion (using cleverly designed horns) and they suffer from far less dynamic compression than the tiny tweeters in domestic loudspeakers. This is because they are MUCH BIGGER. So the coil does not get so hot so quickly and they do not have to move as far to make the same amount of noise. Being bigger they will tend to beam and fall apart off-axis if not connected to a horn. One of my favourite domestic tweeters, the Focal inverted dome range, are also working like a driven cup driving a wavefront. The shape, other factors being equal, tends to remain more rigid under pressure than a simple cone or dome. However, the compression driver is so called because it is designed to force the wavefront through a narrow throat, thus behaving like a smaller source and better matching the driver moving mass to the equivalent air mass at the wavefront. The choice of horn connected to the other side of the throat determines this impedance match. It also determines dispersion more predictably than a direct radiator. So compression drivers with horns suffer far less dynamic compression and have fewer integration problems with the other drivers in the system if the designer has thought this parameter through

The downside is coloration. For the same reason that front mounted drivers usually sound much cleaner and clearer than rear mounted drivers, cavity effect, the wrong choice of horn profile can be either be coloured or ineffective. Colouration, of a nasal or cuppy character, is not uncommon with pro-audio horns because accurately defined dispersion is more important on a horn to be used in an array on a PA rig. The acoustic lens, designed to achieve a similar purpose, on some horns, is comparable to wavelength (obviously, or it wouldn''t work) and therefore behaves like a diffraction grating sounding phasey like a flanger on a low depth setting.

The B&C compression drivers were good enough in a domestic setting, but would be even better if they were coupled to specially designed domestic horns, like those used by Japanese audiophiles, and would be interchangeable with vintage Altec, JBL or Vitavox units. All compression drivers suffer one problem which is that their high frequency response drops suddenly when the frequency exceeds that which can correctly couple to the horn. Tannoy mitigated this problem with their elaborate phase plug, on their Reds and Golds. A supertweeter is needed above this frequency (and there are slot radiators and ribbons available for this purpose). As in pro-audio, I strongly recommend active crossovers.

Bass response is a function of the interaction between driver and cabinet, as here. Pro-audio drivers are designed for high-efficiency (to make most of the power they are fed) and therefore often have rising responses due to big magnets. This produces extended tuneful but lightweight bass. Big cones offer big dynamics at the expense of directivity and colouration. I use 30cm (12 inch) cones for bass, modified from pro-audio, Focal Audiom 12VX2 (in 3-way) or Hammer Dynamics Super 12 (in 2-way). It depends on the Thiele-Small paramaters and the type and size and construction of box. Please let me know how you get on.

BIG drivers (with sensitivity above 95dB/W) will not leave you gasping for air, they'll blow your socks off.
Happy building and listening,
Mark Wheeler

Just appreciation
Hello Lucio,
I enjoy your website, TNT. Thank You. TNT is a refreshing change from all of the nonsense of the mainstream audio industry.
With kind regards,
Joe - E-mail: juniperedge (at)

Dear Joe,
thanks for the appreciation, our only reward!!! In a world that is mostly money-driven we are proud to offer a different approach to audio reviewing.
Stay tuned for more audio fun,
Lucio Cadeddu

Mains Power Switch
I am sorry to bother you.. but I do not seem to be able to direct my mail to anyone .. but yourself the 'Higher up'
I am in need of finding a manufacturer for a High Quality On-Off switch DPST rated at 6A max
I have found two manufacturers and am currently using one of them a Lorlin, but it is cheap at 2 Euro and so is the alternative product a similar.
Please can you recommend at least one company where I can purchase a quality on/off switch for my DAC ..
A switch of Seiden standard or similar would be excellent, it would please me a great deal if you could.
Brad - E-mail: bradgreen (at)

Hi Brad,
I can only suggest that you trawl the catalogues of Farnell, RS, or RAPID, to see what they can supply. It's also worth keeping an eye out on Ebay. The bottom line is that we at TNT-Audio are private individuals like yourself, and don't have any special access to exotic components.
How high quality does this switch have to be anyway? It's easy to get fixated on a particular component when it may not have the sonic impact that we think it does.
Nick Whetstone

M-Audio BX8 question
Sorry to bother you. My name is Juan and I'm from Argentina. I was going through your M-Audio BX8 review and I have a question to ask.
See, I borrowed these speakers for a weekend to mix a song for my band. Had to do it in a rush and ended up sounding like shit (here it is: I'm going to mix the song again, so I would like to know what aspects should I consider when mixing with this speakers (example: do they tend to exagerate the low end, etc.)
Also any suggestion on the mix would be awesome.
Sorry again for taking your time, and thanks for reading.
Juan - E-mail: pdg.juan (at)

Dear Juan,
the sound of this track is - dare I say it? - horrible :-) Dynamically compressed, distorted and with no highs or bass to speak of. Anyway, it is impossible for me to give a reasonable advice, not knowning how the band sounds and which kind of sound do you wish to achieve. Perhaps this is the result you're aiming to, I don't know. All that I can say is that the M-Audio BX8 active loudspeakers are pretty neutral and trasparent so they reproduce what they receive, without adding much of their own. Moreover, I'm no expert of mixing techniques, I can only judge the final outcome. Just one suggestion: avoid heavy equalizations and compressions, as they ruin the very essence of music. Keep everything as simple as possible.
Lucio Cadeddu

Audiophile Linux
Hi Nick,
I enjojed your review of audiophile linux. Are you familiar with the other versions of linux for audio Daphile and Vortexbox?
It would be interesting to know which gives the best sound. Although to be honest if they were all more or less the same quality I would choose on the basis of the user interface. Its annoying that audiophile linux does not seem to support dual boot.
James - E-mail: j.hamilton (at)

Hi James,
I have not tried Daphile or Vortexbox, so can't make a comparison with APL. I'm sure that you appreciate it's difficult to try all these systems unless we constantly install and uninstall them, and that's quite a lot of work. Once I have something up and running, I am reluctant to undo it all again.
I agree that the user interface is important, as well as the sound quality. In that respect, APL 3 with Cantata probably gets my vote (even though I had to buy a new computer to put it on - something which I still don't regret doing)!
I agree about the dual boot issue with APL. Marko Lerota has supplied APL 3 as an image which makes it much easier to install, particularly for users new to Linux. But of course, that makes it near impossible to run it on a dual-boot system.
Nick Whetstone

Strange loudspeaker
[Strange loudspeaker]
Hello! I am looking for information on this speaker, do you know anything about them? I bought them secondhand in Norway. Some of my friends think they are made in England.
Vidar - E-mail: vidar.harkestad (at)

Dear Vidar,
I have no idea...the principle is similar to the one used on Duevel loudspeakers, just uglier :-) I hope some of our readers might give some useful suggestion.
Lucio Cadeddu

Re: Question about Victrola needles
Dear David,
aActually, the label on the underside of the lid says it's model #615... which may make it even rarer than the 611, as I have not been able to locate a model #615 anywhere online. As I know next to nothing about these things, that could also mean that it was just one in a line of 600 models, and not special enough to mention. Either way, Al Bowlly sounds GREAT on it!
As for the Crosley/not Crosley conundrum, just remember that along with vintage looks, one of the main things is that it's portable and doesn't have separate speakers that have to be attached by wires. I live in a seriously tiny cottage, and I really, really don't have room for a stereo system turntable with all the geegaws.
So. Pretty, speakers embedded, and plays 78s. Those are my main guidelines. As always, your wise counsel is always welcome and appreciated. I will hold off on buying anything for now, and see if you come up with a silver bullet that hits all the marks.
Heide - E-mail: hhoegl (at)

Dear Heide,
Could that be 613 by any chance? The 613 was introduced a couple of years later (1928) and closely resembled the 611 except for having as pair of doors, with flower decorations, swinging right and left instead of the single door dropping down. It was priced at $100.
My book has no entry for a no. 615, but then, it also indicates that Columbia was not terribly consistent or systematic with its model numbers.
Happy listening!
David Hoehl

Pluto speaker review
Hi Lucio,
I write to you because I am perplexed with the last review of the Pluto loudspeaker + amp. What's the point on reviewing a speaker, when better and cheaper alternatives of the same design are already available? I quote from Siegfried Linkwitz himself:

In the past I would have recommended to build PLUTO 2.1 instead of the LX521, but now the LXmini will exceed what PLUTO 2.1 had to offer and be a true alternative to the LX521, except for the bigger speaker's extended bass.
The cost of the LX mini is 105$ for the plans + the kit from Madisound or magiclx21.
In both cases an amplifier is not included but anyway it all comes down to a fraction of the cost of the reviewed item. Obviously the Pluto Speakers are very good speakers but that's not the point. I came to know all that because I plan to order an LXmini. Why I say that? Well, you know...I understand you just reviewed the Pluto, but, what do you think, would it be possible sometime in the not so distant future to see a review of the LXmini? I think many of your readers would be interested. That would be nice. But if that is not possible, ok again.
Anyway, I read you many years now and I have to thank you for your fine work that embellishes our Saturdays. On a personal level Lucio, since we are geographically neighbors, if you ever want to come by and need an opinion, don't hesitate to ask me. I was a skipper and I know a thing, or two, about our islands.
Greetings, joy and harmony!
Yannis - E-mail: neanterdal (at)

Dear Yannis,
we review what is available, nothing more, nothing less. When one of those KITs will become available (I mean: shipped right to our door) we will be glad to test it. I understand you'd like to know which is the best way to spend your money on, but there are too many fishes in the sea, so many that is impossible to test everything, compare everything and give you a precise idea of what's best, provided that such best does really exist. The Pluto system is readily available, it is not a DIY kit, so you can't directly compare it with the ones you listed.
Lucio Cadeddu

Audiophile Linux review
Great article. A couple of questions if I may. First do you have to operate it with a monitor and keyboard, or can you operate the computer headless with say an iPad?
Second how do you rate it against Jriver and if you have tried it, JPLAY?
Ian - E-mail: studley593 (at)

Hi Ian,
I'm glad you found the article interesting. Marko Lerota uses some sort of mobile device to control his APL v3, but he does it through another computer that is connected to the APL machine via an Ethernet cable. This means that no wi-fi is involved with the APL computer. I'm sure Marko can help you further with that.
JRiver is simply music playing software for Windows. APL is a complete operating system. I have used JRiver but only on an older computer running Windows XP, so I couldn't make a meaningful comparison. JPlay has always worked well for me (see my review on TNT), and one of its features is to load a track into RAM and play it from there. I can tell you that APL does exactly the same thing, so in effect, APL v3 brings you many, if not all, the same features as you would have with Windows 8, JRiver, and JPlay (but for free).
Nick Whetstone

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