BL configurations?

[TRANSDUCEReng]

Anyone can help on BL configurations for transducers?
In overhung voice coil topologies Xmax=v/c winding Length - plate thickness/2
Increasing the winding length increases the Xmax at the loss of BL product as the magnetic gap falls off rapidly out side the gap also making it vunerable to Bl distortion.
On the other hand increasing the plate thickness does help to increase the BL and gap size but reduces the Xmax available.
i don`t no much about underhung voice coil .Thanks in advance..

[kelticwizard]

Perhaps this will help a little.
http://ldsg.snippets.org/motors.php3

[Ron E]

Xmax is always |Gap height-VC length|/2 the || stand for absolute value.

Off the top of my head:

Overhung motors typically have a higher B because the gap is shorter.

Underhung may have a heat transfer advantage because there is more material near the coil.

Underhung becomes impractical at long excursions, unless it is a NdFeB magnet system, and then it is sensitive to temperature, etc.

Overall, Overhung coils give the best set of features, and are cheaper for the same Bl, so they are used more often.

Do a search on the forum for "DIY dynamic driver" and you will find a very simple transducer design spreadsheet I made in Excel. It is useful as it gives you an idea how fundamental parameters affect T/S parameters. You need to supply Bl, so you have to design your magnet system in FEMM (freeware).

[John Sheerin]

I am not sure about overhung being best... What you normally see is a BL curve that has no flat point - it's always changing, unlike an underhung which can be very flat (so lower distortion) around the zero excursion point. Granted overhung is what probably 99.9% of woofers out there are, but that may be more driven by the demands to make smaller cheaper woofers with more xmax in smaller boxes with some semblance of linearity, not by ultimate sound quality concerns.

Also, unfortunately FEMM is no longer free. It is $4k for one year of support, and the program comes with that support contract. There is still a demo version available, but it is limited to a 1000 node mesh, which is pretty coarse.