Tiny speaker build

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JimGore

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In the last thread I started, there was some interest in a small format speaker kit which tickled my fancy.  I will build and documenting the first set here on the forum so you can follow and share your opinions with me.

I have been busy doing quite a bit of research on 4" wide and full range drivers which I will import in the near future.
While that is going on, I have a couple of sets of these drivers in stock.

Mid/bass driver is a Vifa TC9FD-25.  This driver was made by Vifa for AE (Acoustic Energy), and I have a purchased some of the over-run.  Spec sheet: https://docs.google.com/leaf?id=0B-tjuI6q2pSHYjRhZGVkYjItNGE4OS00MTBjLThiNGItYTNmYWNjMjYxYjEw&sort=name&layout=list&num=50
TC9FD25-08.jpg


Tweeter is the Vifa BC25SC55.  Spec sheet: https://docs.google.com/leaf?id=0B-tjuI6q2pSHZmI0MmMwNjEtMWRiMi00NjQ0LTg3ODUtN2E0OGRhMDkxNTk0&sort=name&layout=list&num=50
BC25SC55-04.jpg


These speakers will need a small subwoofer as they will not be too strong on the bass.  The mid/bass driver is only a 3" driver, with an effective cone area of about 68mm.  What I do like alot about this driver is that it uses a treated paper cone (not plastic).  The total moving mass is only 2.0 grams!

Cabinet size is 3.0 lit internal volume, and ported at 90 Hz.  The driver doesn't have a large maximum excursion, so we will need to protect it from the low frequencies using one of two methods:  Either an active filter on your amplifier, or with a first order highpass filter at 120Hz.  This allows us to drive the little sucker a bit harder without damaging it by going into the mechanical limits of the driver.

The slightly higher QTS of this mid/bass driver allows us to tune the cabinet such that we get a bit of a bump in the bottom end of the response as you can see from the graph below.  I have opted to go for a 1.5dB bump in bass reponse, but this can be tweaked quite easily by changing the port tuning frequency.

This little driver then will give us an F3 of 100Hz in a 3 lit bass reflex enclosure, with the first order high-pass filter at 120Hz.  Not bad at all!

Predicted transfer funcion & magnitude:
Transfer%20Mag.jpg


Predicted cone excursion at 15W RMS:
Cone%20Exc.jpg


For the crossover, I am planning to use a first order filter at between 6 and 10 Khz somewhere.  That will only be decided on when I have built the enclosures and can measure the drivers.  While the mid/bass driver will reach up high all the way to 20Khz, and is quite nice and flat for most of the frequency range, there is a sudden rise in response at the highest frequencies.  Because of that I think it will be better to add a tweeter to the project, rather than try and tame the top end with all kinds of filters, etc.
 
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