Super Sound 12 inch woofer

[heater]

On a whim I just picked up a cheap (30 euro) 12 inch woofer, thinking it would be good for experiment at least. Specs as follows:

"Supper Sound" 12 inch woofer 8 ohms 300 watts. (Or so it says on the back)

The shop (Bebek Elecronics, Helsinki) supplied the following measurements with it, apparently made with LMS Ver 3.61:

Re 7.5 Ohms
Fo 24.6 Hz
Zo 56 Ohms
Sd 0.055 sqM
BL 13
no 0.866%
SPLo 91.4dB
Qms 2.96
Qes 0.45
Qts 0.39
Vas 270
Cms 635.6 Litr
Mms 65.7g
Mmd 58.3g

So far so good, but when I plug these numbers into WinISD it suggests a sealed box of 119 Litr (3db down at 45Hz) or a vented box of 244 Litr. (3db down at 27Hz) Thats 1.0m x 0.6m x 0.4m

These are huge and this experiment could get very serious. So a few questions to throw around:

1. Anyone ever hear of "Super Sound", does not turn up on my googling, any good or rubbish ?

2. Is WinISD telling me the tuth here or did I slip up ?

3. Any checks I can do on this driver before I spend hours building a box for something that is totally hopeless. All I know at the moment is that it does not "scrape" when driven to large excursions. It does actually make sound.

4. How would I guesstimate it's usefull upper frequency, before cone brak up or whatever.

The real motive for this experiment is to have a go at triamping using the tweeters and mid froms a pair of Mission 761s and this woofer. Just for fun and learning.

Cheers all.

[sreten]

Hi,

WinISD is not telling you lies acccording to the parameters you've given.

The driver could be used in a smaller box and "Linkwitz transformed".

/sreten.

[Rademakers]

Also, WinISD is just telling you a possibility, as there are many other alignments that could be used, but that's up to you.

As it's a 12", by rule of thumb you could use it up to 1500 Hz or so, before beaming occurs. Because it's a subwoofer the usable upper frequency is probably much lower. Normally the Le-parameter can give a guesstimate on that.

Do you know the Xmax?

Wkr Johan

[heater]

"Linkwitz transformed" - Hmm interesting, I have to read Rod Eliots page again. At first glance it seems that I could, for example, go for the 120 Litr vented box (or even a bit smaller), then get the response of the full size box with the help of Linkwitz. Only needing a 3db or so increase in power requirements. Seems to depend on Xmax.....

The idea was to put together a three way system where the cross overs are at about 300 and 3KHz as per Rods argument about such things. So 1500 Hz looks OK.

Remind me is Le the voice coil inductance? If so that is not in the spec sheet. I could measure it with an inductance meter if that helps.

Xmax is also not in the spec. sheet. Is there a way to estimate that in free air ? Say by applying 20Hz and winding up the power until it rattles. Then backing of and observing the travel ?

[xstephanx]

That woudl tell you xmech, the mechanichal limits of the drivers excursion, not xmax (linear).

But theres a way to get a pretty good estimate, somethign to do with magnet gap length and VC winding length or air gap height. but i think for that youd need to open up the driver....thus rendering it useless!

hers my rule of thumb, build it anyway, if it starts to sound bad at loud volumes, turn it down untill it doesnt, if thats enough SPL for you, then be happy, if not, ....build a bigger or better one ....or build another(often the extra 3dbs worth of displacement will make a volume level previously with too much distortion, completely useable.

[heater]

According to my AVO LCR meter the Super Sounds voice coil inductance (Le) is 0.85mH

Still no idea about xmax.

[sreten]

Hi,

it may be possible to estimate Xmax by measuring the inductance
of the driver with the cone at various static offsets from normal.

That is measure at say 1mm increments. When the inductance
starts falling I would presume this indicates that the magnetic
gap is not completely filled by the coil, giving you the excursion.

/sreten.