Why does WinISD show my response as just a slanted line?

[Based]

I loaded up a driver into WinISD and I open it up. At first it shows a normal graph but when I change the box volume from the volume it originally put it as, the response goes from a normal looking response curve to a straight slanted line at a very low volume. Why is this? I read the help menu about how to enter driver data properly. It doesn't do this for the drivers that are already in the program.

Click to read more...

 

[shizzzon 10+ year member]

what is a straight slanted line? Paradoxial response curve?

 

[Based]

what is a straight slanted line? Paradoxial response curve?

here

 

[shizzzon 10+ year member]

the 2nd pic looks more normal for winisd because it's sealed but must warn you modeling sealed enclosures for a car is pointless.

The Environmental response will do everything but what that program is showing.

 

[Based]

the 2nd pic looks more normal for winisd because it's sealed but must warn you modeling sealed enclosures for a car is pointless.
The Environmental response will do everything but what that program is showing.

Well I wanted to see how big the box would have to be to get a certain low end response.

 

[trumpet 5,000+ posts]

Well I wanted to see how big the box would have to be to get a certain low end response.

What shizzon was getting at is WinISD does not, in the default settings given when you model a driver, account for the low-end enhancing effect or "free bass boost" that we call cabin gain. The general rule for this is a sealed enclosure rolls off at the bottom at 12 dB/octave, and cabin gain counteracts this with a 12 dB/octave gain. It will not be this exactly in your vehicle, but it's a bad idea to try to model an enclosure size in WinISD that is big enough to ever get a flat line down to 20 Hz, or whatever low end you're after.

Refer to this document for a graph that shows Out-of-Car and In-Car predicted response for JBL GT5-15.

http://static.highspeedbackbone.net/pdf/JBL%20GT5-15%20Subwoofer%20Data.pdf

 

[Based]

What shizzon was getting at is WinISD does not, in the default settings given when you model a driver, account for the low-end enhancing effect or "free bass boost" that we call cabin gain. The general rule for this is a sealed enclosure rolls off at the bottom at 12 dB/octave, and cabin gain counteracts this with a 12 dB/octave gain. It will not be this exactly in your vehicle, but it's a bad idea to try to model an enclosure size in WinISD that is big enough to ever get a flat line down to 20 Hz, or whatever low end you're after.
Refer to this document for a graph that shows Out-of-Car and In-Car predicted response for JBL GT5-15.

http://static.highspeedbackbone.net/pdf/JBL%20GT5-15%20Subwoofer%20Data.pdf

oh ok. I think I remember reading somewhere that there's some form of filter you can use in WinISD to simulate cabin gain I'm going to go look for it

 

[Based]

Oh I think I figured it out. For some reason the Vas on the sub was only 1 liter... I changed it to it's 106.5 liters and now it's good. Especially when I put a 24db/oct low pass at 80hz, a 24db/oct SSF at 20hz, then a Linkwitz Transform filter from 60hz to 20hz with a Q of 0.707. I put the sealed enclosure volume for it at 2 cubic feet which is the max recommendation for that sub in a sealed box and it's basically flat from 30hz to 60hz. Not saying that's what it's actually going to be when it's installed but at least I found my mistake lol.

 

[Jeffdachef 5,000+ posts]

oh ok. I think I remember reading somewhere that there's some form of filter you can use in WinISD to simulate cabin gain I'm going to go look for it

it does not have one. If you have android, go to an app called woofer box calculator, it gives you a rough estimate if your cabin's peak resonant frequency along with everything winisd provides and possible spl gains.