| regal |
| What frequency and Q should be used when trying to model room gain on a program like ported.xls. I am trying to design a sub box with a little hum in the 30-40hz range. I am doing this because my sub will have a fixed crossover of 80hz. My mains have an F3 of 65 so by building a box with a hump at the lower frequencies I will affectively lower the 80hz crossover to the 65hz I need. I don't want to go too far with the hump because of room gain in the lower frequencies. |
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| Ron E |
The standard rule of thumb is to use Q=0.6 to 0.7 and frequency = C/(2*L) where C is the speed of sound and L is the longest dimension of your room in units that match the length units....
For a 20 foot longest dimension, use:
1130/(2*20)=F=1130/40=28Hz
for 4 meter longest dimension, use:
345/(2*4)=F=345/8=43Hz
It is difficult to say what actual room gain will be in any instance, as it depends on: 1) above the frequency you just calculated on placement of woofers and your ears; and 2) below that frequency by how solid the walls are and what amount of leakage there is.; 3) At all frequencies it depends on how much your room differs from the ideal reflective shoebox.
In a sense, it is not all that predictable, but a program which does it better than any other freebie available is found at the FRD Consortium. Look for the RRC or Room Response Calculator. |
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| paulspencer |
Hmmmmm, my guess would be your chances of getting that to be optimal or even close are similar to trying to pin the tail on the donkey blindfolded in an arena with a 30 second time limit!
The difference between simulated and measured room gain in my case has been so big, the simulations are worthless. Further, room modes are the same and complicate it further.
80 Hz is quite high for a subwoofer xo IMO, you really need to get a variable xo point at the very least. It's not difficult to achieve or expensive. |
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| rcw |
The best advise I know is just to measure room gain.
There are just too many variables to try and simulate, unless you live in a reiforced concrete box with no windows or ventilation. |
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