Now I’ve decided upon construction of a 3D Printed Transmission Line enclosure I need to figure out just how….
Lets start on google – and…
Some Speaker Stuff (copied from …..Speakerboxlite.com )
Presumably, this lot means something which will help to figure out the optimum enclosure-y stuff ‘n thingies.
|Number of coils||1|
|Reference efficiency η0(%)||0|
Some more googling on just what this lot means and it’s relationship with Transmission line design brings up a couple of parameters of note…Great website by Eminence right here –
- FS(Hz) – 119.8 – This is the Resonant Frequency that the speaker works at
- SD(mm.2) – 2830 – This is the speaker’s surface area…..
Transmission Line design………
Transmission line lengths are designed to 1/4 of the wavelength of the Fs / resonance of the speaker..
Lets find the wavelength – A quick way – Using this online calculator
- FS = 119.8 Hz =
- Wavelength = 2.96327 Meters (at 40 Degrees C)
- Wavelength = 2.863105 Meters (at 20 Degrees C)
So, a 1/4 Wavelength is somewhere between 71.6 cm and 74cm depending on air temperature (at sea level)
Room temperature (when the missus isn’t home playing with the heating) is typically around 20 degrees centigrade so around 72cm seems a good length to settle on
- QTS = 0.72
I’ve been told by a few people that this is a ‘bit crap’ , way too high and really, given the size of the speaker cone – 28.3cm2 (6cm diameter, AKA Tiny!), there’s absolutely no point in bothering trying to get Bass from this, just shove it in a box and be done………..
Surface Area of the Speaker and Transmission Line
- SD(mm.2) – 2830 –
To work effectivley, Transmission Lines have an area of least SD. To work best, they must be much larger. Googling suggests anywhere from 1.5x upwards depending on the required volume of the enclosure
Lets settle on 2x to start
- 2 x 2830mm2 = 5660mm2
- Which works out at 8.5cm Diameter
First steps to design
Create a pipe of 8.5cm diameter and 72cm in length in Fusion! and fit it into as small an enclosure as possible
if we ‘fold’ the transmission line a few times then we can get a fairly compact enclosure –
that 72cm long line, split 4 times becomes 18cm…….. see the above quick model for the idea – the block at the front is the speaker cutout , the cylinder below is the port and the curvy bit’s the transmission line……..Early days yet…..