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Feb 16 2014

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Jensen 1071 – Let there be SOUND … and there was SOUND

Today was a big day, in terms of my audio system.  Today there was Sound. My DIY speakers  gave first voice today. A design called “Jensen 1071″, by Mr. Troels Gravesen:  http://www.troelsgravesen.dk .

P1090746 b P1090745 b

What a happy day.  The monsters awoke and gave their first breath of life. And the walls shuddered. Mind you – not the furniture.  The walls themselves. The sheer depth of the bass was … frightening, albeit pleasing.

I had some hard time making decisions with regards to the length of the bass reflex tunnels.

Initially, I tested the “full length” of the pipes, as they come from Jantzen Audio, i.e. a pipe with internal diameter 68mm and a length of 220 mm.  The original project actually calls for 162 mm length, which I finally adapted. But mind you, for reasons that are not fully comprehendible to me, the 220 mm depth tunnels also gave a very authoritative nice bass.

The most funny part about it – as I tested the set with some reference signal frequencies, … it turns out that with the 220 mm length – the bass seems to extend even “lower” in the lowest possible registers … albeit at the cost of being less “pronounced” in the overall bass-mid-highs mixture.

I had a hard time deciding as to should I cut / shorten the tunnels, or leave them as is. Financially, not a problem – can order a new set for peanuts, but the lead time would be unnerving, and I want some good sound ASAP.  NOW.

I finally chose the “shortening” option and went for the “as designed” 162mm. obviously, theres is now a much more authoritative “slam” or “groan” or wall shaking “breath of the BEAST” kind of feeling now, which I like.  But the down side of this option is that the lowest registers are sort of “cut off” a bit higher …

So speaking of personal preferences … which one of the following scenarios would YOU choose ?

tmp pio consult 2 tmp pio consult tmp pio consult 3

To complicate the picture even more, I added a bit more damping material on the internal walls of the woofer cabinets, which sort of departs from the original design. Actually, the whole geometry is a bit different, due to the triple thickness of the front panel and the double thickness of the other panels.  The walls are a sandwich of MDF (18mm ),  Birch plywood with finely cross layered filaments (18mm ) and HDF (3mm).  The front panel has an additional layer of MDF, totalling 57 mm in thickness.

The increased thickness of the walls implied that the geometry and outer sizing needed to be changed slightly, so as to maintain the 80 Liters inner volume.


Together with the transducers, as purchased at http://www.audiotransducers.com the whole setup totals something like 110 kg per channel. This may change a bit, as the woofer box spikes will be added as a finishing spikes, and also some alternative woofer coil, that I will make by myself.

The coils that I currently have are “core based” – but in the final version, I will go for an air coil. Here are some photos of the existing woofer cross over, as currently implemented.

P1090744 b P1090741 b P1090742 b P1090743 b

Actually, I already purchased 6 kg of copper wire, the one with a rectangular cross section (2mm x 3,5mm totalling 7mm2  cross section).   The intent is to create two woofer coils, 3kg each, with an inductance of 5,2 mH and a DC resistance of no more than 0,08 ohms (give or take – we shall see how it turns out after implementation).

The photos as below – are views of the mid-tweeter cross overs, currently  laying on the top of the speakers, as I’m still fiddling with some resistor fine tuning of the overall mid-high balance.

Most probably, I shall “skip” the initial 0,47 ohms resistor at the entry of the midrange cross-over. Yes, I know that the design “calls for it” being there, but … I simply like the sound better without it.

All other resistors are hand made, DIY, … I suppose that you already know about my “resistor” make preferences.

What needs to be determined is whether to “stick” with the 1,8 ohms resistor in series with the tweeters, or skip them too.   I will need to listen to a few albums so as to gain a better impression of the overall tonal balance.

But generally, if you ask me, was it worth building 220 kg of speakers, after the initial listening experience, workshop mode, without spikes and granite support plates and proper positioning and all, the preliminary answer is … definitely YES.

P1090747 b P1090748 b P1090749 b P1090750 b P1090751 b P1090752 b

The whole internal wiring, all the “leads” as can be seen – are actually DIY leads. They are a self made litz, 32 strands of 0,5mm dia silver-copper wire, each strand dipped for a brief second in wood varnish and dried, prior to doing anything else with it.  Then I assembled the 32 x 0,5 mm litz, and pulled on some lavishly sized sleeves of insulation.

Aha, for all of you “expensive capacitors for the cross-over” freaks – yes, these are not top of the trend caps that I use there.  I am not excluding the possibility, that some day, when I get some extra free cash on hand, I shall splash out for some renown brand of caps, say Jantzen Z-Cap superior, or the Mundorf EVO, or yet something else.   But for the time being, these that I have in here are very good in terms of what I am listening to.

The multiple parallel connection of caps and the mix of various technologies obviously does the trick, at least for me.


The 110uF serial in midrange crossover consists of:  4x 20uF SEL MP (Bosch Licence for Italy) + 10uF Paper in Oil, Polish army stuff, + 5uF Epcos MKP + 7x 2,2 uF ERO Roederstein MKP1339 green series + 1uF ICEL MKT + 0,22 Russian FT-3 Teflon  …   the total fine trimmed with a capacitor meter device.

Some say that this is a no-no … but I like what I am listening to right now ….

So, let there be sound. Now I shall need to break these beasts “in” for at least 72 hours, let them swing around a bit, let the caps settle, and we shall see where we shall go from there.

Cheers, from a very happy



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