Measured vas = 232l. what's wrong??

[zafira1981]

Hi

Sorry about opening so many threads..

I have a new question, Im trying to measure t/s parameters for a 10" speaker.

Fs is OK, 25hz.

But when I try to find the F for the VAS, it's 75hz.

That values gives Vas=232 liters with the excel spreadsheet.

can anyone tell me what's wrong?

Red line is in free air. Purple line is the driver in a 30cm x 30 cm x 30cm box (27 l)

[CLS]

Let me guess, 75Hz is the fb of that 27l test box?

[Ron E]

Below is a naive calculation, not quite right, but on the order of magnitude for a check.

Fc/Fs = sqrt(Vas/Vb+1)
3 = sqrt(Vas/27+1)
(9-1)*27=Vas = 216 Liters

A driver with a high Vas would be rather compliant and the cone would move in and out rather easily. It is not an unheard of number, even for a 10" driver. I had a 12" driver with a Vas of 400Liters.

[GM]

Greets!

Are you sure you have accurately accounted for all the air trapped in the box plus that trapped in the driver? Note that even a pinhole leak can affect it. Regardless, if this is a vintage doped accordion surround driver it's not uncommon to have a very high compliance. For instance, Altec had an ultra-wide BW 10" 'woofer' with a 263 L Vas........

GM

[zafira1981]

Originally posted by CLS
Let me guess, 75Hz is the fb of that 27l test box?

that's correct.

Originally posted by Ron E
Below is a naive calculation, not quite right, but on the order of magnitude for a check.

Fc/Fs = sqrt(Vas/Vb+1)
3 = sqrt(Vas/27+1)
(9-1)*27=Vas = 216 Liters

A driver with a high Vas would be rather compliant and the cone would move in and out rather easily. It is not an unheard of number, even for a 10" driver. I had a 12" driver with a Vas of 400Liters.

The problem is that with that value of VAS, the recomended enclosure volume (WinISD) is about... 1300 liters!!!

Originally posted by GM
Greets!

Are you sure you have accurately accounted for all the air trapped in the box plus that trapped in the driver? Note that even a pinhole leak can affect it. Regardless, if this is a vintage doped accordion surround driver it's not uncommon to have a very high compliance. For instance, Altec had an ultra-wide BW 10" 'woofer' with a 263 L Vas........

GM

After checking the "hermeticism" (does that word exists?) of the enclosure, I found that air is going out of the box in small holes, so I will use something to ensure the hermeticism of the box and re-check the Fb.

thanks for the help!

[GM]

You're welcome!

I'm curious, what brand/model driver is this and what are the rest of its specs?

Indeed it is: http://dictionary.reference.com/browse/hermeticism?r=75

GM

[zafira1981]

Originally posted by GM
You're welcome!

I'm curious, what brand/model driver is this and what are the rest of its specs?

Indeed it is: http://dictionary.reference.com/browse/hermeticism?r=75

GM

The brand is "Ucoa", an ooooooold brand of Argentinan speakers. In fact, the only thing made in argentina about these speakers are the sticker. They import some speakers and put the new sticker on them.
I think that the original brand is "Jensen", and they may be made on years 1970 - 1980. I bought them from a friend some years ago for about u$s10 with the cabinets. They were broken, and I gave them to an old man that used to repair speakers. He repaired both of them and were my speakers for lot of time. I think they have a really good bass response compaired to another speakers that I had.

I only have the parameters of the .zip attached on my first post. that is, Qms, Qts, Qte, Re...

greetings.

[GM]

If true, the Vas should be 'in the ballpark' WRT the Jensens I'm familiar with, especially considering the rest of its specs fall in line with their open back guitar amp models in that time frame.

Interesting, I initially ignored the zip file since for some unknown reason I can't open them from only this site, so wanted you to post them, but just to say I tried, I did and for the first time AFAIK I succeeded. Sure wish I knew what made yours different (he asks rhetorically).

GM

[zafira1981]

According to your experience with the jensen speakers, the measures I made and the Fs, around what values do you think that the vas of this speaker sould be?

Of course I will measure it again being sure that no air can come out from the test box.

thanks and sorry about my english...

[GM]

You're welcome! Why? Yours as well as many other foreigners who post on English speaking forums is better than way too many public schooled Americans.

Anyway, ~8 ft^3 (~226.54 L) for lead guitar, organ or other OB/IB prosound apps. For vented alignments, ~4-5 ft^3 (~113.27-141.58 L) with ~0.35-0.4 Qts. Note that in the good old days driver size was mostly irrelevant since they designed them to mount in 'one size fits all' alignments by just using baffle cutout adapters, juggling its effective motor strength and compliance specs (what we now call Qts, Vas) to get a good enough match to the cab.

GM