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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Loudspeaker damping
Hi Mark,
after reading your 3 part series on regarding loudspeaker damping, I was hoping I could get your help. I'm building my first DIY speaker. I attached the design notes and cabinet plans. These come with pre-built cabinets just like the plans, no internal bracing. They only come with acousta-stuff for loose fill and this simple foam to line the walls:

How would you recommend to dampen these? For example, I can add dowels to cross brace. I'm also intrigued by this product. I want to retain the liveliness through the midrange. I don't mind a bit of bass warmth from the MDF's natural 250Hz and 500Hz resonance frequencies if it keeps the midrange pure and lively.
Another option is to substitute this for the foam for the interior walls:
Greg - E-mail: johnson.greg924 (at)

Hi Greg,
Thanks for giving damping material such consideration and for considering my article an authority on the subject.

I'm guessing that the 3/4 inch mdf cabinet come ready routed for the drivers. Therefore there is little mdf supporting that woofer rim, especially close to the tweeter recess. Any cabinet front (known as the baffle) movement (vibration) at this point, caused as a reaction to the bass cone mass movement, Will have a disproportionate effect on the tiny treble signal from the tweeter. This causes intermodulation distortion, a non-linear distortion which is one of the most unpleasant artefacts in audio.

Hence, task Number 1 is to stiffen that baffle with braces at that point. As you have used imperial measurements I will stick with those. Any offcut of dense hardwood (balsa is a hardwood and far from dense, so that was no tautology) like oak, beech or one of the denser maples will suffice. 1/2" X 1/2" square section is enough in this location from the cabinet top down to the top of the bass=mid unit and from just above the slot vent diagonally in toward the bass-mid aperture.

As you suggest, hardwood dowels across the cabinet void will also help and will provide support to the stuffing. Sound absorbing layers on the walls help reduce reflections back at the bass-mid driver (paper coned in this instance) up to the frequency 1/4 wavelength equivalent to the thickness of the absorbing material. The Madisound foam sheet you link is 5/8" which in SI is 0.016m from 5kHz upwards which is therefore not useful on the cabinet sides.

Acry-Tech Acoust-X Paintable Damping Material is a different proposition. It's surface texture will scatter reflections and its composition will convert some energy into heat and its mass will lower the Q and the frequency of cabinet wall vibration. I suggest a both-and approach.

Centrally supported sound absorbing material (Acoustistuff, long-fibre wool, acoustic foam) best absorbs standing waves in the cabinet. A roll of the Madisound foam sheet will also achieve this, thus avoiding acoustistuff sag. Hence a front-back dowel close to that critical baffles weakness around the tweeter and bass unit apertures is a good idea piercing a roll of the Madisound foam.. Two dowels between the sides will help equally with strong 2 pack adhesive in every case (Aerolite 606 or similar measures better than pva in this context). The roll can be between the top side-to-side dowel and the front baffle and between the bottom side-to-side dowel and the rear. A further layer of foam on the bottom face of the loudspeaker exactly below the driver will reduce an early reflection there, especially if sculpted away from the driver. Having said that, do not overdo the damping or the port alignment will change and be ineffective. I note that Seas suggest playing with damping in the port according to loudspeaker location. The true function of a loudspeaker port is not some kind of magic to conjure bass where there was none before (ye canna change the laws of physics captain) but to control the bass driver/cabinet air volume resonant peak (hence the classic reflex double impedance peak) so damp the cabinet not the port air flow.

Seas make some excellent drivers, many of which I've used over the years. The kit you have chosen is based on an OEM complete loudspeaker system that they made that was badged Dynaco A25. It dates back to the audo heyday of the Summer of Love in 1969. They shifted over a million pairs so listeners must have loved them. Fabric dome tweeters tend to sound less like a series of resonances than plastic domes to the Old Scribe ears. Paper cones tend to sound faster and livelier than the heavy bextrene cones of the classic British sound of the same period, at the expense of a little midrange colouration.

On the other hand, mdf is the most life sapping loudspeaker cabinet material ever devised by humankind. Resonances subtract (known appropriately as destructive resonances) as well as add. Bracing is therefore strongly recommended. Even better is adding a layer of 1/4" hardwood sheet instead of veneer to the outside of the sides, top, bottom and back of the cabinet instead of veneer. You could do this later so that you can hear the difference, or do it now and get it over with! As long as you round the corners of the 1/4" hardwood sheet there will be no effect on the baffle step frequency. The most available and cost-effective material I have found for this is sold as kits to rejuvenate wood flooring.

Another future-proofing idea is to connect the drive units to two sets of terminals on the rear of the cabinet. Mount the crossover on the outside so that it is not affected by the hostile vibrations in the cabinet. Later you might choose to experiment with a higher spec tweeter capacitor or even with active drive and this makes that easy.

I would anticipate that these loudspeakers will give you hours of fun making them and even more hours enjoying them. You also get the delight of saying "I made them!"

Do please keep me updated with your project progress.

Happy building and listening,
Mark Wheeler

Lenco 75 platter ringing
I just read an article on TNT and not sure what exactly was done to the platter. The picture is too small...I applied same stuff as you underneath - around inner thin (deep) rim but after placing it back on a spindle platter doesnt move :)
Where is the catch?
Thank you
Arunas - E-mail: uksminas (at)

Howdie to you too,
the most probable cause for your problem would be that the platter is rubbing on the platter brake. This is more likely to happen with an L78 due to the design of the brake however it could still happen on an L75. Especially if the material that you applied is thicker than about 2.5 mm. On an L78 the rubber brake pad can be filed or sanded down a bit to accomodate the added insulation. On an L75 it is a bit more difficult. You can try bending the brake lever which is made of a springy metal or cutting off the end to shorten it by 1 or 2 mm.
If you are having trouble viewing the photos on the web page correctly I suggest that you try changing web browser. Sometimes that has worked for me.
Enjoy your music,
Roger McCuaig

Love your site
Greetings from Jasper,
I just purchased some vintage audio kit. I am a MacHead and a collector of vintage devices. I am always enriched by the discovery of the knowledge base provided by a site such as yours. I am curious to know if there is a monthly newsletter I might subscribe to?
I have book marked your page and will be a regular visitor.
Thanks again!
Dave - E-mail: betabake (at)

Dear Dave,
we don't publish a monthly newsletter, as we update our website every weekend, with new reviews and articles! You can bookmark the What's New page and visit it regularly on weekends. You can even stay in touch with our updates via our official Facebok Page.
Glad to hear you love vintage gear! We do love good vintage components as well. Unfortunately, nowadays, everything from the Seventies and the Eighties is now considered vintage, even if it was bad sounding back in its days! From time to time we publish reviews of vintage components we love and, moreover, we have an entire section of the website, titled “On an Overgrown Pathé”, devoted to REALLY old components of the pre-LP era.
Hope this helps,
Lucio Cadeddu

Decca tonearm
Hello sirs,
searching informations on a vintage Decca original tonearm, I saw you review dating from 2008....and I thought you could maybe help me: having bought few months ago a wonderful Decca MKII stereo cartridge, I purchased just after an original Decca Tonearm.
But I don't have the "plan" to install it properly on the turnable ( a Garrard 401 )...! (it was not included with the arm). Would you know where to find the right one, very precise?
Just in case.....thanks in advance,
All the best,
J-M - E-mail: jmharari (at)

Dear J-M,
the instruction for proper tonearm installation heavily depend on the turntable where you will install it! In any case, assuming you have purchased the same tonearm I have (New in Box! A London International) these are the two pages of installation from the original manual...

[Decca tonearm installation instructions]
[Decca tonearm installation instructions]
Hope this helps,
Lucio Cadeddu

Headphones choice
Dear Arvind,
I'm Pierluigi and I've been a TNT-Audio reader for many many years. I've recently enjoyed your article about the AK OB1 DIY loudspeaker project. I found very very interesting technical aspects in it especially the open baffle design (and the fact that is diy). Great project but my question is not about the AK OB1, or maybe a quest that can be related: the AKG K 701 in your referenge gear: I was watching that headphones for some time now and I'm curious to ask an opinion to someone that have listen to them for some time, what are the strengths and the weaknesses or why that headphones are appealing to you? One of my thoughts is that being open back maybe the sound character is comparable to the naturalness of the open baffle speakers? Speaking of headphones actually my gear is: Sennheiser HD 600 for open back (21 years old now), ESS 422H for closed back, Fiio X5 gen. 3 as source (and dac) and a Fiio A5 as amplifier, I think that the HD 600 is a bit old because it starts to lack something, I remember another sound from it (or maybe I'm wrong) and I'm searching for a substitute. TNT-Audio to me is the most reliable source of information because it's not affiliated to any brand, the opinions are genuine and the authors are passionate people about hi-fi, so here I am. Please give your honest opinion about the K701, I will consider it as pure gold because for now I got only biased reviews but not a truly honest one. If it doesn't disturb you I would like to thank you for your precious time even if only for reading my words and I hope to have an answer.
Thank you very much and greetings from Italy.
Pierluigi - E-mail: wigi__ (at)

Hi, Pierluigi,
Thanks for your kind words, and glad you enjoyed the articles. See these comparison I had done a while back; see here. Subsequently, I picked up a pair of the 701s and directly compared to the Sennheiser HD650, and much preferred the AKG. Additionally, I have since acquired a pair of the Stax SR-44, and prefer the AKG's again. For as good as the AKG's are and as little as I use headphones, I have not had any more curiosity since I picked up the 701's. If I had, I'd also check out many of the newer electrostatic models.
I hope this helps.
Arvind Kohli

Digital Audio
I read the review of the DAC and I feel a headache coming on...why? The hum problem. Like you...I abandoned digital in 2007 to concentrate on Analog. Fast forward to 2021, I love analog and own the following:

Currently using a passive preamp which works really well just curious about trying the Doge 8. I will eventually get the Doge 7 D/A. I am thinking of getting back to digital. The reason why I got out of digital, I cannot get into the music with digital. I play digital for awhile but then switch back to analog and relax. I hope after a hiatus of more than 10+ years out of the digital has improved. I assume there is no way digital can sound as good as analog even in the higher sampling I wrong?
Ren - E-mail: renantebarroga (at)

Well I see that you have lots of toys to play with!
You are asking yourself THE question; can digital sound as good as analog? Today, you have put the question to me,I feel the weight of the world on my shoulders .....As is the case with many of us, I have been asking myself that question too.
I believe that digital music does not sound the same as analog, and probably never will. That doesn't necessarily make one of the other better, it just makes them different. I personally prefer analog for several reasons; it is what I grew up with, I love the look and feel of the record and to experience the artwork, and of course the special listening experience of vinyl playback.
My experience, as well as some of my audiophile friends, has been that over the past few years digital playback quality has improved immensely. I believe that it is for the most part due to improvements in DAC chips. I recently had the opportunity to review a new unit that has two of the latest ESS DAC chips in it and I found it very impressive. (review to be published soon) But a good DAC chip is just the start, a digital playback device has to be designed with the same attention to detail and component quality as is given to high-end analog equipment and that means not just the DAC chip but also the analog section, the power supply, everything.
In conclusion, I would say that there are digital music components available today that can deliver anything and everything that a top quality vinyl playback system can deliver with not a trace of "digital fatigue". Some days I listen to digital music all day long played from my music server PC running JPLAY FEMTO into my Doge 7 tube DAC, but it doesn't sound the same. Nothing sounds the same as vinyl.
One cannot speak on this subject without mentionning the significant problem of digital music compression, AKA The Loudness War! Great playback equipment can't correct some of the terrible things being done in the recording studios.
So, there you have my take on the subject. Hope you get something of use out of it!
Enjoy the music,
Roger McCuaig

Dodge 8 preamp review
I liked the review of the preamp...any chance you will cover the dac? I live in Montreal and I am assuming you like in Ontario, I was wondering how your experience with ordering the Dodge 8 preamp directly from Doge. Aamy problems or concerns?
Ren - E-mail: renantebarroga (at)

[Doge 7 front view]

Hi Ren,
Nice to hear from you. I did write a review of the Doge 7 Tube DAC back in 2018. With respect to ordering from Doge, everything went smoothly for me and I had no complaints. (yes, I live in the Ottawa area) Now it is possible that the Covid situation has had some impact of their operations so I would suggest that you ask them directly what the situation is before placing an order.
Enjoy your music,
Roger McCuaig

Caps data
Dear TNT,
how does one calculate the speed V/uS for capacitors? I noticed this in this TNT-Audio article and I am interested in comparing and the equation would be appreciated. For bass applications, would it matter for the slew rate to get higher than 50V/uS?
Trevor - E-mail: tvormittiag (at)

I cannot find any data or info about capacitor speed in terms of V/us values. The values you find on high quality caps data sheets (for example are ESR equivalent series resistance Rated ripple current. ESR is easy to understand: in capacitor models there always is some resistance due to leads, electrodes and other inner components impedence: this is what is limiting the current in a capacitor (at least at audio frequencies), and is therefore directly correlated to speed.
However, a capacitor subject to a high current flow heats up, so you must limit the current if you want to assure a reasonable life time to a cap (
Calculations of speed and current in a given configuration, however, are not so simple, the only solution is simulation of the circuit (
This requires an appropriate simulation model ( for a discussion of a proper model) and a simulation environment (LTSpice or similar).
Hope this helps,
Giorgio Pozzoli

Clarifications about TNT AIRCOIL
Hello Roger,
First of all, thank you for the information, tips and articles that you wrote on TNTaudio, they are always interesting and useful!
I am writing to you to have some clarification about the cable in question, the TNT AIRCOIL, actually I followed the project that you described, in order to create an RCA - JACK3.5 cable to be able to connect a DAP to the integrated amplifier (an excellent example of NAD3020i whose tone I love), in my opinion, and without still making resistance and capacitance measurements, this cable sounds good, is neutral and transparent and has a lot of dynamics.
The comparison, by ear, is with the homemade TNT SHIELD cable. As conductors I used an AWG23 of a CAT6, but I did not find information on either the quality of the copper or the type of insulation. The cable is made up of two conductors for each channel (one for heat and one for cold) which are intertwined alternately in a single Teflon tube. On the RCA side, on the other hand, I adopted two pieces of Teflon for each channel and twisted to 2.
My explanations:

I apologize for the inconvenience caused, and for my poor school English (thank goodness that google translate exists ... hehehe) and above all for any wrong written information, I am a novice of audiophile environment, but I am trying to document and learn.
Thank you in advance, let me know if something is not really clear.
Best regards,
Dimitri - E-mail: skadym (at)

Hi Dimitri,
Thanks for your email. I have used both CAT5E and CAT6 cables as sources for the conductors used to build my Aircoil projects. I always try to find "Plenum Rated" cable as this means that the conductor insulation will be Teflon and not HDPE.(high density polyethylene) Teflon has a better dielectric constant. (less electric charge is stored in the insulation) Now there are certainly some people who would argue that, in this application, the difference is so tiny that it is of no consequence, and they may be right. My reasoning is simply that the cost difference is very small (in some cases I got the cable for free!) so why not use the Teflon insulated conductors. I did read someplace that CAT5E and CAT6 cable are made with 99% pure copper, however, I certainly wouldn't claim that to be an absolute truth. One thing is known, CAT6 UTP (Unshielded Twisted Pair) is capable of transmitting data at 250 MHz so our 20 KHz audio signal is not a challenge.
With respect to your cable design I'm sorry to say that I have not been able to fully understand your description so I will have to abstain from any comment on that. Maybe you could send me a sketch of photos?
Now for the noise problem associated with unplugging the cable from the DAP, well, this is quite common and the best advice that I can give you is never leave a cable connected to an amplifier or preamp input with nothing connected to the source end. It's not a good practice.
Enjoy your music,
Roger McCuaig

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