My ''TB3'' mini bipole plans

Salas

diyAudio Chief Moderator
Paid Member
2002-10-08 11:31 am
Athens-Greece
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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Salas

diyAudio Chief Moderator
Paid Member
2002-10-08 11:31 am
Athens-Greece
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.
 

Salas

diyAudio Chief Moderator
Paid Member
2002-10-08 11:31 am
Athens-Greece
by all means

Do it by all means. I am here for any additional info.

For planet 10 I attach the raw bipole response normalised to 85db (there is excess midbass to mid output I kill with the notch to get mid-high up).
As you see it really goes that down, but the Tangbands are not ok for a bipole without a notch. Such a waste of sensitivity...
And a little teaser. The 4'' Euro driver bipole new model is already playing and is a killer...news from me in a few days when I will iron it out.
 

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Salas

diyAudio Chief Moderator
Paid Member
2002-10-08 11:31 am
Athens-Greece
different thing

The TB3 achieves 85dB with notch bcs it uses 2x871s per cabinet. Not bad in the end.
The forthcoming design has 4 inch pure cone area and uses a 5 inch rim driver bipole pair per cabinet. Its not a mini, its a floorstander. The drivers will set you back more than 80 Euro each. It belongs to another category.
 

Salas

diyAudio Chief Moderator
Paid Member
2002-10-08 11:31 am
Athens-Greece
some guide according to systems

Its very delicate the way a full range responds to system tonality.
I have determined for the TB3, 4 different states after much experimentation with it. All is for TB3 pair with 56cm from its back to wall.

1. Solid state amp + rather bright cabling = .27mH notch coil (safe starting point, you can always unwind it little by little).

2. Solid state amp + neutral cabling = .25mh notch coil

3. Tube amp + rather bright cabling = .24mh notch coil

4. Tube amp + neutral cabling = 0.23 mH


As you may see, fine tuning is easy playing with just the coil and can bring the wholw system to balance.

This concludes the documentation for this project.

After much listening, tube rolling, amp technology changes and cable cooking, I can safely say that this is a very responsive and entertaining mini speaker that gives much more than its financial and room space costs.
 
Salas,

I just finished these and I must say they sound fantastic. Very detailed and balanced. The bass is very good for this size cabinet (probably the best I've heard for the TB 871) and blends well with the mids and highs. I'm running these with my modded SI T-Amp. I'm using your original notch filter and may experiment with the other coils.

Thanks for a great design. Didn't even have to buy any parts - already had everything.

-Ken
 
Salas,
You seem to have good and simple design. What are the measurements for a 4" bipole that you are planning? Do you have a picture/drawing? I have two pairs of Radio shack 40-1197 (similar to FE 103) waiting to go in a decent box. My listening room is not very big and I do not want boomy speakers. I do not plan to use any notch filters with 40-1197. Is that wise? Would appreciate all help that I can get, first time project after all.
Cheers,
Raj.