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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April 2007

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Loudspeakers damping
Hi Mark,
Does rigid 1" extruded polystyrene foam from the hardware store in 4'x8' sheets for home insulation have acoustical sound/vibration damping qualities suitable for use in loudspeaker cabinets?
I have a vintage Bozak rebuild project this summer and wanted to consider alternate sound/vibration damping choices. Also thought about 1" soft foam from local Army/Navy store. Manager tells me it can be used as acoustical foam.
Appreciate your thoughts and suggestions for my infinite baffle tower design project.
Paul - E-mail: pmt1954 (at)

Hi Paul,
Without inspecting the products in question, and preferably seeing their acoustic specification data (absorption at various spot frequencies is commonly available for building materials, although by the 21st century one would have expected full spectrum graphs to be available) I can not make any useful comment.
I do know that here in the UK, for example, that rockwool slabs are normally specified at a certain mass per square metre for the UK building regulations minimum 75mm wall cavity, but that they also supply a 100mm higher density version (RS80) that is recommended for acoustic applications, as well as improved thermal insulation properties.
The only material I am familiar with that sounds like the type you describe is known in Britain as Styrofoam Floormate, and is used to insulate between the cold ground surface and the cast concrete slab commonly used in the ground floor construction in UK newbuild houses. That material would not be suitable on its own as it would probably be very frequency selective.
It is ironic that you ask me this now as I am writing (among 8 other current loudspeaker articles in preparation and many other pieces too) "Get stuffed" on this very subject.
In short, the stuffing pitfalls are:

  1. Too much stuffing reducing the internal volume
  2. Too little stuffing failing to attenuate standing waves and reflections back through the cone
  3. Stuffing the wrong place failing to attenuate low-enough frequencies
  4. Stuffing too tight & dense that simply reflects rather than absorbs
  5. Stuffing too loose that slows rhythm by random movements
  6. No stuffing at all, as recommended by Deflex when their acoustic panels are deployed, does not work for me either. I do use surface treatments (like deflex panels, wood beading laid side-by-side to diffuse reflections, rubber wedges like an anechoic chamber, and sculptured foam) combined with minimal stuffing.
I prefer long fibre wool (as specified for Bailey transmission lines) in minimal quantities combined with internal surface treatments. The correct amount is critical. In a recent 44litre reflex box I found: This is very little stuffing because the internal surface treatment and brace arrangement combine to minimise standing waves. The wool is teased out and supported by the central brace where it has the most effect and some on the bottom surface.
I hope this helps, and good luck with your project; resurrections are great fun.
Happy listening,
Mark Wheeler

DIY cables 1
Hi there,
i was reading on TNT-Audio for quite a while now and i am a huge fan of your site. although i don't experience soundstage an imageing that often because i rarely listen to acoustic music i really like your reviews and articles - they are understandable and i like the down to earth viewpoints on it. thank you for that.
I would not consider myself an audiophile. i am a home dj that likes vinyl and good detailed sound. the reason why i am writing to you is the following: i have a fairly good home dj stereo setup with an allen and heath mixer and b&w 602 s3 bookshelf speakers. i use tara labs prism 500 interconnects and monster speaker wire. i listen to mostly electronic dance music (techno, house, electronica). if i listen to rock music on my system it often sounds a little dull but mostly kinda exhausting to me.
do you think it is worth trying out your diy cable projects to improve the sound of my stereo? i am willing to spend a few bucks and some time on such a project. last time i went to my local hifi store ( music lovers in berkeley) and asking them the same question, they suggested transparent speaker cable for 800 dollars a piece telling me it would improve the sound a lot. well that would be more than my speakers and my amplifier togheter (marantz pm 7000). my uncle who is an audiphile with a pretty nice system doubts that i will really improve the sound because i listen to electronic music mostly, so there is no soundstage and imaging and so on. from reading your article it sounds like its worth a try.
what do you think? is the type of music one listens to (electronic versus acoustic) a factor or can you improve sound with a better cable no matter what you listen to?
and last but not least a question that you probally got asked a million times already: the cat5 cable you use for your diy cables, does it matter if the outer shell is pvc as long as the inner on is teflon? with the tnt star and mains cables: is that cable stranded or solid conductors. so far i had no luck finding a shielded mains cable here in the usa, california. in particular one with solid conductors.
Thanks for your time.
Stefan - E-mail: vincevice (at)

Dear Stefan,
the reason why you don't like the sound of your set-up has nothing to do with cables, I'm afraid. Oh yes, you can build some of our DIY designs (TNT Star, the one to start with) but don't expect miracles, considering you already have decent wires.
Speakers set-up and room acoustics might have a far better influence here. Also, the B&W's you have aren't exactly soft or warm. Their mid-high range can sound irritating and fatiguing, on certain set-ups. Since you're after rock and electronic Music, please consider auditioning a pair of Klipsch Reference series speakers, of the floorstanding variety. I'm pretty sure rock will sound much better, provided you place the speakers not too close to rear and side walls.
Finally, to answer to your last questions about our DIY cables: yes, our mains cables and TNT Star loudspeakers cables use stranded copper wires. FFRC and others use solid core wires. The outer sleeve of the cables is not all that relevant. Use only unshielded CAT5 cables. Try sourcing all of them online, perhaps even at Radioshack, Maplin or RS.
Hope this helped somehow,
Lucio Cadeddu

DIY cables 2
Dear Lucio,
I'm a relative beginner in DIY audio. I'm involved in several speaker designs (mostly as a tester), and also in the designing and evaluation of a high precision DAC to improve the sound output capabilities of PC's.
I have already built an UTP based speaker cable, now I'm trying it again to build it according to the FFRC plan. My current cable is a monowire config with two UTP cables per speaker (1 for each polarity) and it has already beaten my moderately expensive speaker cable by a huge amount. Sound is much cleaner, less mushy, featuring more dynamic lows and much more defined, precise highs. If only there were a little less mids, they are a bit too obtrusive.
My first two questions regard cable types to buy for the FFRC:

  1. Does it matter if I get Cat5 or Cat6 cable (100Mhz vs. 250Mhz)
  2. Does it help (or make it worse) if I get foil shielded (FTP) or foil/braid shielded (STP) cables? They are available from 600 to 1500Mhz.
  3. Finally, in theory, how should a braided 3 cable configuration per speaker (FFRC monowire) improve sound compared to my current setup? I'm not really familiar with cable physics.
Thanks for your help!
Your site is a great inspiration. Thanks for all the hard work!
Greg - E-mail: gkovacs (at)

Dear Greg,
you can use both CAT5 and CAT6 cables but please avoid the shielded variety. According to the original designer (T. Loesch) shielded ones would sound worse. If you wish to experiment different approaches, why don't you give our Triple T cable a try? There are many options you might find interesting.
Keep us updated!
Lucio Cadeddu

Naim IBL upgrade
Hi Lucio,
I found your piece on IBLs on the net and thought you were the first person to turn to for advice!
I have a pair of Mk1 IBLs made in August 1989. I am considering having them upgraded to Mk2 status (at considerable cost) and wonder if you might be able to tell me what I might gain.
My system is Naim CD5 with hi-cap, nait 5 with flat-cap, the other half of which powers a stageline. Existing speakers are Epos M12.2 on Epos ST12 stands. Cable is Chord Rumour 2. My room is 5x3m with 2.5m high ceiling, and has little furniture and a wooden floor on top of concrete. I live in a flat with neighbours above and below, so I don't play massively loud.
My view is that there is something very attractive about the IBLs but they do sound thin, as you suggest in your article. I have already tried borrowing a nap 200, which helped but probably needed a nac 202 to develop it's full character.
Might the upgrade improve the IBLs in such a way that the nait 5/ flat-cap would drive them happily and with a more even tonal balance? In other words, so that I no longer have to consider spending 3000 on a 202/ 200 to get an acceptable result!

This evening I have re-read your piece on TNT-Audio and made a few changes:

I did everything all at once apart from the last, and you know what, they sound a whole lot better! I would still appreciate your comments however. I should add that the IBLs have always fired down the long axis of my room. The wall behind them is solid.
I have also experimented with the hi-cap. I have used it to power the Nait with the flat-cap powering the CD5 and the stageline. This has the effect of making records and FM radio sound better and CD sound worse, as we might expect with a source first approach. But FM does sound especially good with this configuration.
You may like to know that Naim have quoted "approximately" 610 inc vat [!] for the replacement of the mid-bass units with a further 200 inc vat [!] for the tweeters. These figures are not mis-prints. They say they "believe [these modifications] to be a considerable improvement, with the Bass units being the biggest improvement" but they were unable to say how, hence my original question to you.
Best wishes,
Chris - E-mail: chris.moorhouse (at)

Dear Chris,
for sure, I wouldn't shell out 810 UKP for improving the IBL's that way!!!! There's a wiser thing you can do: buy a NAP 250 power amp (second-hand), even one of the oldest chrome-series. It would be a VAST upgrade! And your mkI IBL's will thank you forever. Eventually add a 32.5 or a 72 preamp. You won't regret this move.
Hope this helped somehow,
Lucio Cadeddu

Concordant Excelsior
I bought a Concordant Excelsior via E-Bay. My expert technician asked me for schematics about this pre. He is a very experienced technician in the field of Tube amps but with the aid of schematics............ Do you know something about schematics about this Pre ???
At last: Ernest Ruiz wrote in his article about a 6CG7 tube, my pre has five ECC83s; is there something wrong ??
I would be very pleased about an helping hand.
Kind regards
Robert - E-mail: rdszopinski (at)

Hi Roberto,
There does seem to be some confusion about which tube goes where, and there were some changes during production. There should not be five ECC83 (or Golden Dragon E83CC for that matter) in the Excelsior.
One correspondent reported substitution of the psu valve with the shared triode in the audio circuit, but this would be wrong, refer to my article and other letter replies for the full story.
I would dearly love to have a schematic (circuit diagram) for the pre-amp and psu. If your technician will do it, I will make it presentable to put onto TNT audio. I do not have time to undertake this task myself.
Do replace all the electrolytic capacitors, they are well beyond their service life by now. I'd recommend a Cerafine (if you can still get one) in the psu. I've always been happy to use Solen SCR to replace smaller electrolytics, but some people find them metallic sounding. They're much cheaper than Black Gates. OScons are OK too.
I sued to love Wondercaps, but I do not believe I can hear any improvements with the newer Infinicaps, which, being much more expensive have dropped off my bang-for-buck radar (I spent a fortune on them in my SET300B and couldn't hear any significant difference over the NOS Wondercaps they replaced).
Where did your Excelsior come from? I see you are in Germany and I did not know many had been exported.
Stay in touch,
Mark Wheeler

Wood is good
I am currently building the so called TNT Sand Box for a platform and just read your article on box clever, wood is good and I am most intrigued, but you wrote about rf screening with copper sheet and star grounding it what is star grounding?
I have only found the TNT site a week ago and already have read most of it though not necessarily understood everything, this is a very good, maybe the best site I have visited.
Jon - E-mail: Azura (at)

Hi Jon,
You will certainly hear the effects of the sandbox, so good luck with the project.
Noise in audio systems is what really separates many of them, and there are many sources of noise and non-linear distortion. One of these is electrical noise caused by the so-called zero-potential reference point of the system (ground or earth in various parts of the Anglophone world) being more or less zero-potential in different parts of the system. When this is wildly different on two sides of an amplification stage we hear the well-know 'ground loop hum', a loud hum at 50Hz or 60Hz (depending on which side of the Atlantic we're suffering the problem) and its multiples (for you 100Hz, 150Hz, etc).
Most earthing, or grounding, is carried out by an earth bus. This is a thick wire or copper bar through a piece of electrical equipment, to which each active stage is connected to achieve a common zero-potential (0 volts with respect to the earth under our feet) point for the whole piece of equipment. Voltage simply measures the difference between two points, and the easiest way to define a universal point is to say that the ground is defined as zero volts.
Hence the impedance Z (resistance ohms, capacitance Farads and inductance Henries combined so that the actual resistance at any given frequency can be calculated) between any part of an audio circuit and the defined ground zero needs to be equal at any part of the circuit to minimise noise. If we plug our audio system into different sockets in the room and connect them with long interconnects we have just introduced multiple connections to earth (in the UK the so-called neutral wire is usually bonded to earth near our electricity meter) with different impedance characteristics for each, thus introducing a noise generating circuit.
Within the whole system something approximating star-earthing can be achieved by using a multiple socket for the hifi system with a same-make same-length mains cable from each socket to each audio component. Better yet is something like the hydra-headed connector Naim used to take to hifi shows with a clutch of cables and IEC plugs emerging from one 13A plug (Maplin supply an ideal plug for this).
If you are qualified and technically competent to rehouse your hifi components or build DIY from scratch, you can arrange the internal wiring such that all zero-potential connections are taken to one central earth point in each case. This can be connected to a central star-earth point (Russ Andrews is so convinced by this arrangement that he makes a product to enable this). Thus all supposedly zero-potential points in your audio system are the same electrical distance from the zero-defined point that is the earth we stand on.
Spookily an article about this is due to appear on TNT-audio soon, I'm just waiting to get it checked by an electrician. Do not attempt any electrical work unless you are suitably qualified, competent and sober at the time.
Thanks for the kind words about TNT-audio, I believe we're the best because we have no commercial ties.
Happy listening,
Mark Wheeler

Preamps for NuForce
I very much enjoyed your review on the NuForce REF9's Monoblocks, please could you recommend any preamps either tube or solid state that work with these amps? I was thinking of using Audible Illusions Modulus 3 Preamp, I would be using Technics SL1200 with Origin Live Silver tone arm, with Sumiko BluPoint Special cartridge or Cartridge Man Music Maker 3.
My speakers are Rogers LS7t using Epos open frame stands from the early eighties. My current amp is Musical Fidelity A1000 which has some nice attributes but also sounds veiled and dull at times only the Sumiko livens it up a bit. Any information would be greatly appreciated.
Kind regards
Nick - E-mail: nike (at)

Dear Nick,
the Audible Illusions might be a nice match with the REF9's but if you want to preserve their transparency please consider a Spectral preamp, they are not rare in the second-hand market. Still solid state and also quite easy to find second-hand, consider Mark Levinson 26 or 28. As for tube, Audible Illusions aside, I have a couple of friends who use the REF8's and 9's with Audio Research preamps, even from the old SP series.
Hope this helped somehow,
Lucio Cadeddu

Ikea Hol table
Hi Mark,
In your review you mentioned that 'hol' is meaningless in any European language. Well, in my mother tongue Afrikaans which is derived from Dutch it means 'hollow' and I'm pretty sure that it means the same in Dutch. Since Dutch, Afrikaans and the Scandinavian languages all have some words in common, I'll wager that it means the same in Swedish.
Jan - E-mail: JVanderWesthuizen (at)

Hi Jan
I only suspected that Hol is meaningless, and I didn't check with my Dutch speaking friend. I admit I made the assumption because I wanted to believe that this team of linguists is employed to coin entertaining neologisms!
I do know car manufacturers employ teams of language experts to check whether there are any secondary connotations to any model names they plan to introduce. There is the famous example in the 1970s of the Japanese car manufacturer who planned to name their new prestige model the "Cedric". The story goes that the company who planned to become the Australian importer had the following conversation at a motor show:
Australian: "This new 'Cedric' model, we have a problem with the name"
Manufacturer: "What's is the problem? Cedric is a fine old English name"
Australian: "Yes, but in Australia the word 'Cedric' is also a term for homosexual"
Manufacturer: "Are there many homosexuals in Australia?"
Australian: "Of course there are"
Manufacturer: "We sell many Cedrics then"
Given that Britain was invaded by the Scandinavians for hundreds of years (first Vikings, now Ikea) I'll bet that's the derivation of our own words hollow and hole. You are the first to spot my mistake. We're all much more connected than different. Thanks for letting me know, I'll take the trouble to check as thoroughly as I check audio facts in future.
Happy listening,
Mark Wheeler

Many thanks...
...for if TNT depended on subscriptions or adverts it could never have been as open and honest as it is now.
Many thx for all you did for us all that love music
Takis - E-mail: tsozou (at)

Dear Takis,
thanks for the feedback! Your appreciation is our only reward. Ok, ok, sometimes reviewing can even be amusing :-)
Stay tuned!
Lucio Cadeddu

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