Stress on subwoofer at tuning

[timc31610]

What is the rating on the resistors? Im assuming the frequency of the tone nor the volume it's played will be a factor since you are plotting the difference?

[Triticum Agricolam]

What is the rating on the resistors? Im assuming the frequency of the tone nor the volume it's played will be a factor since you are plotting the difference?

Yeah, I've used a 1K ohm resistor and it worked fine for this, I don't think it really critical what resistor you use. If you are interested in getting a mic, this is the one I have: http://www.parts-express.com/dayton-audio-umm-6-usb-measurement-microphone--390-808

Other than the mic all you need is a laptop. For software is use Room EQ Wizard (REW), its free and does the job very well. Its also very useful for lots of other acoustical measurements.

[Triticum Agricolam]

Here is a screen shot from REW of a measurement I did.

The pink line is the output from the port, the purple line is the output from the cone.

As you can see its pretty easy to figure out what your tuning is from the graph.

[TRON]

That video...is inaccurate.

[Wicks]

To visually represent what Bkolfo has said about the impedance graph, I'll repost Wick's measurements of his XL12's with his car door open.

For the techies , here's an impedance sweep of my sub-box with the cabin sealed up:

Here's another sweep with the driver door open:

Interesting that my tuning slightly got lower with the door open and the impedance at my upper peak dropped quite a bit, from 15ohms to 9 ohms.

That drop in impedance would definitely correlate to an increase in output

Link to his build log:

http://www.stevemeadedesigns.com/board/topic/141656-wicks-e46-m3-build-1st-place-win-and-guess-who-got-a-50/page-50

Thanks for the quote Krakin

To elaborate on the statement of in-car tuning being different then on paper and therefore not what you think it is:

Here are my box specs on paper

You can see above what I'm actually tuned at. A difference of ~5Hz and would definitely be different for each vehicle being measured.

I would assume my rear window area continues to act like a port flare and lowers my tuning below (32Hz) what the box itself is actually tuned to (37Hz).

[Krakin]

That video...is inaccurate.

Is it because of him just basically eyeballing it, or are you saying the method?

[Triticum Agricolam]

You can see above what I'm actually tuned at. A difference of ~5Hz and would definitely be different for each vehicle being measured.

I would assume my rear window area continues to act like a port flare and lowers my tuning below (32Hz) what the box itself is actually tuned to (37Hz).

The way Torres calculates port length for slot ports isn't the most accurate, it will pretty much always tune you lower than what it says. What you are saying about your rear window area is probably part of why you are tuned lower too. Lots of different factors will affect your tuning.

[bkolfo4]

You will find many times a box sitting outside the car still is not tuned exactly where you calculated.

There are many issue - end correction factor not 100% accurate, bends in ports change the tuning slightly, etc.