newbie question theil small

[psychosteve]

ok ive got some drivers, 8inch 50 watt rms, usable freq. 68Hz to 4.5khz. i cant get any data for the qms qes and qts, or vas and resonant freq. how can i get this without contacting the manurfacturer, (unknown) or buying expensive equipment to test them myself??? help please, steve.. ..

[BillFitzmaurice]

You can't. Sorry.

[Sandy H.]

I once used the method from the Loudspeaker Design Cookbook and freeware with a laptop soundcard as a signal generator through an amplifier for larger current.

Basically, I measured the impedance per the LSDC at 5 Hz intervals from 10-40 or 50, then 10Hz from 50-100 then 20 etc (or whatever the intervals should be) and plotted them to get a visual of the impedance curve. I then used the added mass method (you could use the sealed box method) to get the new data and used the equations from the LSDC to derive the parameters. I never did measure Bl, though as that was a different set-up.

This was a while ago, so I may well have left out a step or two, but I did just follow the LSDC. One of the equations in there (or maybe in the Weems book) was either wrong or I interpreted incorrectly. Once I found the error, the results were very close to the manufacturer's specs and Darren @PE's Clio measurements. If you're dealing with a complete unknown, I'd say its better than nothing.

You would need the LSDC, a decent DMM and a PC with a soundcard (with a freeware tone generator). A standard known resistance of 10 ohm makes calibration easier.

If there are additional comments to support or deny this as a valid method, please post them for my sake as well.

Sandy.

[goering]

Here's a link: http://sound.westhost.com/tsp.htm

I tried it but I'm not really good with math (the "sanity check" calculation would never be correct for me). Maybe you can try it and show me how you did it.

[Vikash]

Originally posted by psychosteve
ok ive got some drivers, 8inch 50 watt rms, usable freq. 68Hz to 4.5khz. i cant get any data for the qms qes and qts, or vas and resonant freq. how can i get this without contacting the manurfacturer, (unknown) or buying expensive equipment to test them myself??? help please, steve.. ..

Speaker workshop is free and a wallin jig won't set you back a lot (<£20 I think). If you want cheaper than check out the Speaker Workshop help files and it shows you how to do it. Cost will be low, but time and learning curve may not be.

[psychosteve]

cheers guys ill have to look at wheather its worth it or just pay more for some new drivers that i can find the params for. thanks again guys, steve.. ..
P.S. any one know where i can get some 8inch 30 watt rms bass/mid drivers for under £15????? lol....

[ergo]

You could tryPraxis

It measures T/S in freeware mode. It's quite easy to do as a script walks you through the steps. It support both added mass and closed box method.

Ergo

[richie00boy]

You might as well measure the ones you have. You will need (for other general and audio stuff) the things you have to buy for measuring anyway. Plus you should really measure speakers that you buy even with published specs as there is always manufacturers tolerance and some can be way off.

[psychosteve]

ill have a look at praxis, probly get anoyed and just dump them in a box and play around with ports and damping till they sound the best. cheers guys, steve.. ..

[mr_push_pull]

Originally posted by BillFitzmaurice
You can't. Sorry.

Isn't it great to be mean? I guess some of us were born with a degree in electroacoustical engineering.