Fullrange design help

[gaust]

I have some full range wharfedale drive units originally from the 'modus cube' speakers which I would like to put to use in a surround sound system. I have bought myself a dayton woofer tester and after testing the T/S parameters of various other small fullrange drivers that I have I am convinced that it is providing decent and believable results.

I have built various speakers to plans provided by others such as the needles and TABAQ but I thought it would be useful to start trying to understand how to go about designing some speakers myself. I have downloaded various software including WinISD and had a play with this, and I also have had a look at the transmission line alignment tables, but I think that I could do with some pointers before I start.

The T/S paremeter that I have for the wharfedale 4" units (103-84, 6 ohm) are

Re 4.8792
Qes 0.5149
Qms 2.2946
Qts 0.42052
Vas 3.082
Fs 80.48
Le 0.24936
mms 4.121
Spl 86.84

Hopefully these may be useful for others who have bought these speakers and don't have facilities for measuring themsealves.

I would initially like to make some moderately small speakers, probably of a bass-reflex design. I particulalry liked the onken-style enclosures especially the 'moon-onken' design.

Longer term I was hoping to be able to design some larger boxes for the fronth left and right channels that may be of a TL or BVR design like the Brynn design for the fostex FE127.

So my design goals to start with are to make some surround speakers, but I'm not sure how low to aim on the bass side, probably go for not being too greedy, but I was not clear when playing around on WinISD what constitutes the best response.

Secondly the Vas of these speakers is quite small (~ 3L) and so I was not sure what impact this has on the boxes you could / should design for these speakers.

Thirdly I have started thinking about baffle-step compensation. Is it possible to design this into the box, of will you always need some sort of compensation circuit.

Finally I have also bought some cheap Vifa tweeters and and played around with these and the wahrefdale units in a test box and just using a single capacitor to bring them in quite high (8-10 kHz) seems to work quite well and add a bit of extra sparkle.

Any help, advice etc that you can give would be greatly appreciated,
Cheers,
Jon

[planet10]

Can you post some pictures of the driver?

dave

[chris661]

Fantastic - that's all I can say.

I have 3 of these drivers (pretty sure it's the same ones), they sound Ok, but not brilliant. This may be related to their past - someone I know was clearing out a recording studio - most of the equipment had already gone, but I got a 15" 'blown' (long story) woofer and 3 of these cubes.
This info will definately help.

Just noticed - mine are the 1038A version.

Paper cone, surprisingly long excursion for the size of the surround, plastic basket, magnetically shielded, 8ohm, foam gasket on the front, rubber seal on the back.

Have some pics anyway - let me know if they're the same or similar.

Chris

PS - I know the pics aren't good, but the digi camera's flash can't be set to half-power, so it was a combination of zoom and covering the lamp with paper etc.

[planet10]

Here is a 1st pass sim of a Fonken-style box. The high resistance ports will lower the system Q, if you want a small speaker bump to get the illusion of more bass than they have, raise the tuning a bit (this will also shorten the port, so you have a better chance of fitting them in the box. With a box this small you will need to calculate the net volume quite accurately

dave

[planet10]

Originally Posted by chris661

Paper cone, surprisingly long excursion for the size of the surround, plastic basket, magnetically shielded, 8ohm, foam gasket on the front, rubber seal on the back

Not the old Wharfedale 4" with the giant soup can magnets. These would date from the Rank era.

With a plastic basket, there is likely a good chance they are Audax OEM units. A standard set of cone mods would probably do wonders to the sonics.

dave

[gaust]

Here are some pictures.

I have two different types, more of the unsheilded 103.84 type (left on the photos) and some of a shielded type (103.77) that I was planning to use for the centre channel.

Chris - the drivers that you have look similar but possibly more modern than the ones that I have. I'm not sure how relevant the T/S parameters would be, however the ones I measured (for the unshielded 103.84) are similar to ones that I found on the web (for the shielded version).

Thanks for your replies

[gaust]

Hi Dave,
Thanks for running that sim - so if I'm reading it right then the box volume is 3.5L (not including the ports?) and 4 vents of 0.9 cm x 20 cm in length. I have a feeling that I came up with something similar to this in WinISD where the vents were so long I couldn't work out how to fit them in the box.
Cheers,
Jon

[planet10]

3.5 litres not including ports, back of the driver & the driver brace.

4 ports 9mm wide x 20mm high x 75 mm long (i chose 9mm wide because i understand that is a common material width in the UK). They could also be 6mm wide x 30mm high. From another recent post 6mm is also common. 6mm might be best use of sheet material -- port slot spacers could be 6mm, the panels could all be 2x6mm and a 3rd layer of 6mm added to the baffle to create a rebate (with sufficient material left to probably build a 2nd pair).

When designing these kind of boxes i go thru an iterative process to get the right balance of vent height & length to fit the box.

dave

[chris661]

Originally Posted by planet10

Not the old Wharfedale 4" with the giant soup can magnets. These would date from the Rank era.

With a plastic basket, there is likely a good chance they are Audax OEM units. A standard set of cone mods would probably do wonders to the sonics.

dave

Thanks for that - by "standard set", we're talking phase plugs, ...?

I have 3 so I wouldn't mind if one went west for testing purposes.

Chris

[planet10]

Phase plugs are optional, and with small drivers you can take a hit on bass capability (very driver dependent). I've yet to find a paper cone that didn't benefit from judicial coating of "puzzlekoat", and the basket/magnet interface being shaped damped with some duct seal. These are also perfect for practising your EnABL skills on.

dave