Black arts of Driver Constructrion

[fr0st]

I've been following the DIY parthenon thread with eager eyes but I don't want to attemp such a large project without any experience and lack of knownlage (or clog the thread with questions).
I'm mainly interested in creating a sub of maybe 10-12 inchs so its not too small to physically create and that the bass spectrum intrests me the most.
If anyone can post any links or show examples of what they've done it would be greatly appreciated.
Firstly... How are voice coil gaps signifigant in the design?
Relating to size and location mainly. In the JBL tech notes cross section they show, the gap is level with the top plate but the magnet is recessed in relation the the toplate (further away from the pole piece/VC).
I'm assuming that its used to concenatrate the magnetic field on the voice coil spot to maximise effientcy, but why not along the entire length of the VC instead of what looks like half?
Also in the tech not it shows a copper and aluminium shorting ring, the copper one looks like a faraday ring... wats the purpose of the aluminum one?

Also, what are the ways to make the speaker excel in different aspects (e.g greater sensitivity, lower resonance and the ability to suit the driver to a certain type of box) ?

Thanks all

[Vikash]

The LDSG should answer some of the basic questions.

You may also find this thread interesting, and here's a link to my diy transducer diary.

the gap is level with the top plate but the magnet is recessed in relation the the toplate (further away from the pole piece/VC).
I'm assuming that its used to concenatrate the magnetic field on the voice coil spot to maximise effientcy, but why not along the entire length of the VC instead of what looks like half?

Motor design is really interesting. The magnet position, plates and pole thickness, and shape etc. are chosen to create a circuit that saturates the gap with flux. Among other things, the goal is to produce a symmetrical field in the gap, and minimise stray fields. I would recommend FEMM to model magnetic circuits.

but why not along the entire length of the VC instead of what looks like half?

Thes simple answer, the larger the gap, the more difficult it is to concentrate flux in it. See overhung vs underhung topology in the LDSG link.

Also, what are the ways to make the speaker excel in different aspects (e.g greater sensitivity, lower resonance and the ability to suit the driver to a certain type of box) ?

As dictated by the TS parameters. i.e. sensitivity is dictated by the mass vs motor force, or mms vs BL (perhaps) Resonance will probably be mass vs suspension compliance (Qms). For people that require a driver built to spec, they can use SpeaD and Reverse SpeaD which will produce designs based on the T/S parameters you require.

[fr0st]

Thankyou for the link, it was extremely helpful!
I came across that site before but completely missed the part on motors

Your diary never mentions how your driver sounded with the latest cone and basket attatched.... how'd it do?

For comparitive purposes, for say 1kg of ferrite, what would be the equivilant mass of neodynium for the same magnetic field?
I havn't yet seen a sub thats used neodynium (probably because the companies are trying to save a quick buck)

i.e. sensitivity is dictated by the mass vs motor force, or mms vs BL (perhaps)

Is motor force increased by the raw size of the magnet? (among other things)
So the more flux you have in the gap, the more the voicecoil moves for a given voltage ...?

Thankyou for your time
Its very much appreciated

[Vikash]

Is motor force increased by the raw size of the magnet? (among other things) For comparitive purposes, for say 1kg of ferrite, what would be the equivilant mass of neodynium for the same magnetic field?

Read this intro. This flux density calculator may help answer your question.

I havn't yet seen a sub thats used neodynium (probably because the companies are trying to save a quick buck)

Were the pics of the Parthenon not convincing enough for you?

Your diary never mentions how your driver sounded with the latest cone and basket attatched.... how'd it do?

It's yet to be put together. The current motor isn't good enough so I plan to restart with a new motor - then I can build upward from it.

If you want sleepless nights, then attempting to design your own transducer is the way to go.

[hunter audio]

hi

first of all thats a huge effort vikash

1

i have replied to a few inquiries on shorting rings in my thread _ transducer manufactured by me in india , its in the trade section

i have not followed the diy partheon

if you tell me where the shorting rings are or ,
any inquiry on shorting rings used in any transducer design
i will attempt to explain its working and purpose

2

neodynum is used in woofers / pro audio drive units which employ ferrofluid cooling

this is necessary as though neodynium is wonderful and far superior it tends to de magnetise with rising temperature

where cooling has been addressed neodynums have been used - speacially in set ups where the company is designing the amps , enclosures and driver , like Myers

in this approach there is not much possibility of company reputation being hampered due to a mistake on the part of the customer in using the drive units

suranjan

transducer design engineer