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Old 13th May 2005, 04:13 PM   #1
Salas is online now Salas  Greece
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Default My ''TB3'' mini bipole plans

This is a nice and relatively full sounding bipole for its size. Its really mini, very good for small rooms (15-25sqm), when listening in relatively polite levels. About 85dBSPL/2.83V is its sensitivity @ 4 Ohm.
It uses 2 Tangband W3-871S per speaker so its cheap to make. The notch filter is integral to the design and I dont recommend running the speaker raw.
The TBs do not behave optimally in a bipole without a notch. It also needs about 50cm from its back to the backwall as a minimum. More distance (up to 1m) can be used if you can allow for it.
In the FR plot (3rd octave smoothed) you can see it going low enough for its tiny drivers and only 3 litres cabinet. The TBs exibit deep recession in the presence range when in an unfiltered bipole, so I had to keep that to a minimum by using a sloping response with fatty low-mids and a finally acceptable -2.5dB recession in the presence range. This is about a Harbeth BBC LS35/A type of balance. Polite enough, transparent, and full.
Please refer to the attached images for the cabinet drawing, notch filter and FR plot. The bass reflex slot I use is aluminum made but you can make it from little wooden panels or even convert it to a tube with 10-12sqcm mouth. Just keep the depth 9,5cm. Just use wool felt on the inside walls. Only one pad per side, top and bottom.
You can combine a MKT 15uf cap and a Poly 10uf cap in parallel to get the 25uf notch filter cap. This saves cost, and the better 10Uf cap dominates sonically.
A 10W MOX or other low inductance resistor is worthwile along an aircore coil of no less than 1mm wire. More is better.
All in all I am quite pleased with this mini and I recommend you try it in situations where budget and space is not sufficient for bigger projects.
I hope that by next month I will be contributing a new bipole design (floorstanding column) with a very nice 4'' Euro driver that looks quite promissing for quality and good sensitivity. In the meantime I have to photograph this TB mini one I guess and post it here. It looks pleasing enough too :-)
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Old 13th May 2005, 04:14 PM   #2
Salas is online now Salas  Greece
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Default notch filter

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Old 13th May 2005, 04:16 PM   #3
Salas is online now Salas  Greece
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Default FR plot

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Old 14th May 2005, 09:45 PM   #4
Salas is online now Salas  Greece
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Default photo

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Old 27th May 2005, 08:37 AM   #5
kenev is offline kenev  Greece
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salas,

That's an interesting design.

I tried to send you an e-mail but there is a restriction.

What I was to ask you is where did you find birch plywood in Athens. Please, if you would like, send me an e-mail to discuss about this.

Evangelos
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Old 27th May 2005, 08:58 AM   #6
Salas is online now Salas  Greece
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Old 27th May 2005, 09:31 AM   #7
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Neat little design... that is quite a low bass response for the 871! How did you measure it?

The FR plot is with the filter i assume. Do you have one without for comparison?

dave
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Old 27th May 2005, 10:25 AM   #8
Salas is online now Salas  Greece
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Default conditions

Speaker was facing 5m to front wall, open balcony to the world at the back, side walls were at 1,5m and 2,5m.
Mic @ 1.5m. MLS window 180ms. Checked the bass extention with 3 calibrated mics.
Yes it can be heard also. No big pressure but the 50hz region can be followed quite easily by ear when playing music. It did not detract much from same closed box power handling.
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Old 27th May 2005, 10:38 AM   #9
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My first post!!

Salas: Im having troubles seing the images, frustration when I have been looking for bipol surrounds and have a couple tb3 lying around.
Your design maybe exactly what Im looking for.
Is there a way to fix this?
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Old 27th May 2005, 11:15 AM   #10
Salas is online now Salas  Greece
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Default they open up ok

The images open up ok in my browser. All others see them.
Can you explain what you dont see exactly?

The FR plot is with notch filter, I will post a sans filter one during the day (P10)
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