I am using WinISD to compare some 10" and 8" subs in a vented enclsure tuned to 32 Hz. I noticed that when tuning the subs to the same frequency in the same volume enclosure that they have the same length port tubes (port tubes are 3 inches in diameter). I would have guessed that, a 10 inch sub would have a different port tube length than an 8 inch sub even though they are tuned to the same frequency. I also noticed that different brand and RMS power ratings of 10 inch subs yield the exact same port length as well.
Am I missing something here or is this normal?
Mike
No, port size is dependent on tuning frequency and enclosure volume, not what driver you use.
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Support the12volt.comOkay - so why would one choose a 12" woofer when he can tune a 10" to the same frequency or for that matter - an 8". Of course, I understand that a bigger woofer gives you a bigger sound. What I am referring to is tuning. If I tune an 8" woofer to the same specs as a 12" woofer, does that mean that the 8" woofer will be able to reproduce the same frequency as a 12" woofer? If so, what advantage does a 12" have over an 8"?
Mike
You have a good question and it seems that it is a common perception of the value of tuning a box. But when you tune a vented box to a particular frequency you are constructing a Heimholtz resonator that will add to the sound of the woofer at that frequency. You're not changing the actual sound of the woofer....you're adding to it. (...totally dependent on proper setup, of course, because you can also ruin the sound of a woofer with a box that is built wrong...)
A 12" woofer will play freqs to a lower range than will a 10", and we have to presume comparable quality of drivers in any comparison. An 8" , being smaller in area still, will not be able to achieve the frequency range of a 10". It's at the low end of the freq range where all three subs will differ. But with most music material all three subs will perform, but with diminishing authority at the low end as you decrease the size of the sub.
Tuning the enclosure to a given frequency will add about 3 db SPL to that frequency because the enclosure sound is added to the driver's output. You could tune boxes for all three size subs to 36 Hz and all three will be louder at that frequency, but the 12" sub will perform better at the lowest frequencies in the music source. But in the purest sense of tuning a box it is generally done to add SPL at a frequency where the driver is lacking SPL......at about the point of driver resonant frequency where there is a substantially greater impedance imposed. And this is done to smooth out the output curve and add to the low end.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Now I get it! Excellent post! Thanks so much. :>)
Mike
You're welcome and I'll add this visual of what the port tuning does using a little project I'm currently working on. You'll see in this graph that the driver output is represented by a black line and at one point it dips low because of driver impedance. The port SPL is represented by a turquoise line and at that same point it peaks. The combination of everything together is shown in the final result by the heavy line, which is a smooth output and an extended low frequency for this driver. The WinISD graph gives you a combined representation of output but doesn't break it down into separate responses on the same graph like this does, but you can use the WinISD program to see the same end result. This graph was generated using Unibox.
VB_Response_Infinity_TC11MG-07-04.gif
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
