How accurate is Win ISD spl graph?

[Mustang2dakota]

Anyone who has used win isd and has actually built the same box with the same sub(s), how did the spl graph match up to your actual numbers? I know that a lot of things can change when put into a vehicle, but id like to see some comparisons. Also i do not have a Termlab or anything to measure spl; if i did i would be doing testing instead of asking you guys

[Triticum Agricolam]

WinISD pretty accurately models what the output of your sub will be, but this output is what your sub would do in half-space, IE like it was sitting in the middle of a big open field. Like you said, it doesn't account for cabin gain, which will change things quite significantly. I don't think this makes WinISD any less useful, you just have to know its limitations.

I can post some pics of a box I built modeled in WinISD and then the measured in vehicle response when I get home later.

[Mustang2dakota]

WinISD pretty accurately models what the output of your sub will be, but this output is what your sub would do in half-space, IE like it was sitting in the middle of a big open field. Like you said, it doesn't account for cabin gain, which will change things quite significantly. I don't think this makes WinISD any less useful, you just have to know its limitations.

I can post some pics of a box I built modeled in WinISD and then the measured in vehicle response when I get home later.

yea id love to see some numbers. Can cabin have a negative effect in any way? If not then that would mean that win isd's numbers are on the smaller side of what you would actually see on a termlab, correct?

[WCA Rusty]

Id say theres to many factors to base a termlab score on the win isd spl graph

[Mustang2dakota]

Id say theres to many factors to base a termlab score on the win isd spl graph

yea thats kind of what i figured. Im just more or less wondering if its even in the ball park. what i said above " win isd's numbers are on the smaller side of what you would actually see on a termlab, correct?" was more of a theoretical question

[Triticum Agricolam]

yea id love to see some numbers. Can cabin have a negative effect in any way? If not then that would mean that win isd's numbers are on the smaller side of what you would actually see on a termlab, correct?

Generally the measured response is going to be higher than what WinISD predicts, sometimes MUCH higher. However if you are having cancelation issues due to placement/reflections/etc the measured response can be lower.

Like WCA Rusty said, you can't just look at WinISD and infer what you are going to do on a TL. There is just too many variables.

Once you have measured the actual response of your vehicle you can use that info to get a rough idea of how a different enclosure/sub would do in your same vehicle. For example if WinISD says your box puts out 135 db at 40 Hz, you measured it in the car and are getting 148 db at 40 hz. Now if you design a different enclosure that WinISD says is 3 db louder than your first one, your measured in-vehicle output of that new enclosure will probably also be around 3 db more than your first one. Again there are other factors that WinISD can't account for, so it won't be perfect, but it can give you an idea at least.

[Mustang2dakota]

yea id love to see some numbers. Can cabin have a negative effect in any way? If not then that would mean that win isd's numbers are on the smaller side of what you would actually see on a termlab, correct?

Generally the measured response is going to be higher than what WinISD predicts, sometimes MUCH higher. However if you are having cancelation issues due to placement/reflections/etc the measured response can be lower.

Like WCA Rusty said, you can't just look at WinISD and infer what you are going to do on a TL. There is just too many variables.

Once you have measured the actual response of your vehicle you can use that info to get a rough idea of how a different enclosure/sub would do in your same vehicle. For example if WinISD says your box puts out 135 db at 40 Hz, you measured it in the car and are getting 148 db at 40 hz. Now if you design a different enclosure that WinISD says is 3 db louder than your first one, your measured in-vehicle output of that new enclosure will probably also be around 3 db more than your first one. Again there are other factors that WinISD can't account for, so it won't be perfect, but it can give you an idea at least.

The main reason that i ask is because i was messing around and put 4 Fi SSD 18's and compared that to 4 Alpine Type R 12's and win isd is telling me that the Type R's would be louder at almost any level even when i changed the tuning (these are just example subs and both are 1,000rms) and i would think that 4 18's in the same environment would score higher that 4 12's

[Triticum Agricolam]

The main reason that i ask is because i was messing around and put 4 Fi SSD 18's and compared that to 4 Alpine Type R 12's and win isd is telling me that the Type R's would be louder at almost any level even when i changed the tuning (these are just example subs and both are 1,000rms) and i would think that 4 18's in the same environment would score higher that 4 12's

Yeah four 18"s should pretty much walk all over four 12"s. What are the specs for the boxes you sim'ed?

I'll try plugging in the numbers and seeing what I get.

ETA: With both subs in their recommended size enclosures I show the 18"s beating the 12"s by a significant margin, as they should. Maybe you entered in some subs specs wrong somewhere.

[Triticum Agricolam]

Here is a sub I simmed in WinISD. Its a Sundown E-12 in a 1.5 cube box tuned to 26 hz.:

Here it is with approximated cabin gain added in:

And here is measured in-vehicle response from 25 - 125 hz, 6th octave smoothing:

Looks like I got a little more cabin gain than my approximation showed, but other than that is reasonably close. The SPL numbers are meaningless since I didn't take the measurement at full power, I was just interested in the frequency response.

[Joe X]

The main reason that i ask is because i was messing around and put 4 Fi SSD 18's and compared that to 4 Alpine Type R 12's and win isd is telling me that the Type R's would be louder at almost any level even when i changed the tuning (these are just example subs and both are 1,000rms) and i would think that 4 18's in the same environment would score higher that 4 12's

Definitely you need to check your data, maybe define same input power, number of subs, sensitivity.... one of those.