DBX DriveRack 4800

[Jonas_h]

But the problem, and as I understand, the concern of Jonas, is to know exactly where to set the levels on the amplifiers for the different drivers.

Yes, exactly. I found this in the Crown manual though: http://dl.dropbox.com/u/10759510/ForumPics/ctsLevel.gif

If the listings are precise, I can se exactly how much I'm lowering the gain on each channel.

In regards to the "analog gain structure" function on the DBX4800 I linked to earlier, can anyone explain this? Not much info in the manual, and I am a little confused if lower or higher values are preferable. With lower output-clip values, I am able to raise the gain on the amp and be closer to the 3/4 gain setting recommended by Crown.

[1audiohack]

Oh right,, make me go back to the books!

I found in my fourth edition of the Master Handbook of Acoustics the equation you correctly quoted in the Modal Resonances in Enclosed Spaces chapter.

One thing to look out for is when formula for statistical spaces finds it's way into small room acoustics. Few of the intelectual tools of the trade for large rooms can be applied to small rooms. I am not arguing that the math is not correct, just the validity of some of it as it applies to small spaces. The 0.5 second reverb time is an indicator that this has happened.

If you look back a couple of paragraphs it is stated;

Region B is that region we have studied in detail in which the dimensions of the room are comparable to the wavelength of the sound being considered. It is bounded on the low frequency end by the lowest axial mode, 565/L. The upper boundry is not definite but an approximation is given by what has been called the cutoff or crossover frequency given by the equation;

F2 = 11.250 (RT60/V) 1/2

Where F2 = cutoff or crossover frequencyin Hz
Where RT60 = reverberation time of the room in seconds
Where V = volume of the room in cubic feet

What is often overlooked in the attempted measurement of RT60 in small rooms is that the definition of RT60 has two parts, the first of which is often overlooked or ignored;

1 RT60 is the measurement of the decay time of a well mixed reverberant sound field well beyond the Dc', or the critical distance.

2 RT60 is the time in seconds for the reverberant sound field to decay 60 dB after the sound source is shut off.

Since in small rooms there is no Dc', no well mixed sound field, hence no reverberation but mearly a series of early reflected energy, the measurement of RT60 becomes meaningless in these environments.

What becomes meaningfull is the control of the early reflections because there is no reverberation to mask them.

Finally, the formula I used comes from the Handbook for Sound Engineers, 4th edition, Small Room Acoustics chapter by Doug Jones. I have also had the good fortune to have received some formal training from him and could use a great deal more!

All the best,
Barry.