Setting up house curve??

[cruzmisl]

Hi All,
I have my sub response withing +/-3dB. The response looks great but it sounds lifeless. I did some research on the room curve and think that's what I need. PRoblem is I am unsure of the best way to set it up. My QSC DSP 30 has a shelf filter (or multiples if necessary) so I'm wondering what the best way would be to achieve the curve I want.
Thanks,
Joe

[Wayne A. Pflughaupt]

House curve: What it is, why you need it, how to do it

See Part 1, scroll down to “An easy way to determine the house curve you need.” Adjust a cutting shelving filter so that it reads 0 dB at 30 Hz, and the amount of cut you decide you need at about the crossover frequency, or slightly higher. If you’re using a boosting filter, 0 dB would be at a bit above the crossover frequency, and the amount of boost you need at 30 Hz.

Regards,
Wayne

[cruzmisl]

That's where I'm confused. My shelf filters allow for frequency, Q and gain adjuststment. Where should the increase in dB start (frequency)? Also I read that it should remain flat below 31Hz. What's the best way to achieve that?

This thread, http://www.hometheatershack.com/foru...use-curve.html shows what the repsonse should look like which is helpful. I am thinking setting the filter at 30Hz but the Q is what is confusing me a bit. I can have it rise sharply or more of a gentle slope. Any suggestions or is it preference?

Thanks,
Joe

[Wayne A. Pflughaupt]

Also I read that it should remain flat below 31Hz. What's the best way to achieve that?

Hmm... That statement tells me there’s some confusion as to exactly what a shelving filter is. Maybe this picture will help.

As you can see, the shelving filter will automatically flatten response below 30 or so Hz, if it’s adjusted right.

That's where I'm confused. My shelf filters allow for frequency, Q and gain adjuststment. Where should the increase in dB start (frequency)?

If you’re going to use a boosting shelf, then the starting frequency is where you want the rise to begin. Typically this is the crossover frequency, or slightly lower (not above as I mentioned before – sorry ‘bout that). The reason you might want to start slightly lower than the crossover frequency is because the signal is typically down about 3dB at the crossover frequency:

So if you’re using the test tones to figure out how much of a slope you need, the exact crossover frequency might not be the best reference point. Make sense?

I am thinking setting the filter at 30Hz but the Q is what is confusing me a bit. I can have it rise sharply or more of a gentle slope. Any suggestions or is it preference?

I’ve never used a shelving filter with adjustable Q, or the DSP-30, so I can’t help you there. You’ll just have to play with the Q, frequency and boost values until you get the slope you want – i.e., 0 dB @ 80 Hz, +8 dB @ 30 Hz, or whatever you’re shooting for. As you can see from the shelving filter graph above, the actual frequency setting will be somewhere between the high and low points (i.e., shown as the "Cutoff frequency").

With the Behringer EQ, the Velodyne SMS-1 and a few other parametrics, you can do your tweaking “real time” in REW; unfortunately, the QSC is not one of the equalizers REW “supports.”

It might be simpler to ditch the QSC’s shelving filter and create your own with a regular filter, using the “brucek method” discussed i the house curve article. That you could do on-screen with REW and see the results “on paper” before applying it.

Ultimately, it may be easier to load a house curve calibration file into REW and re-equalize from scratch.

Regards,
Wayne

[Fred33]

That is some great info Wayne. Love the graphs since I am a visual learner.

[cruzmisl]

Thanks Wayne, I'll play around with it a nd see what I come up with.

[cruzmisl]

OK, I played around with the DSP-30 and as you wrote, the level remains constant once it reaches the max dB. I thought it continued to rise. I just need to play around with the Q since I can have 0dB at 80 using a frequency of 50Hz or the same using a frequency of 30Hz, depens on the Q I chosoe. I'm thinking a bit more of a gentle slope may be preferred but we'll see.

Thanks,
Joe

[Mark Seaton]

Hi Joe,

Just now catching up on many things (owe you some e-mails as well).

The QSC's shelving filter is typical of many other DSP's, but it does allow a range of "Q" for the filter. The Q is simply how fast the transition is from one level to another, with higher Q providing a faster/steeper transition. The gain defines the difference between the levels at high and low frequencies and the frequency is the center of the transition range.

In my experience with the SubMersive I usually prefer to keep the 25-35Hz range within 3-8dB of the 70-100Hz region. +5-6dB is where I would start. You can then adjust the levels and crossover frequency to make sure the <100Hz range is a few dB above the 500-2kHz range (the range of common test tones in a receiver or test disk). While the scale is rather small on the frequency response display, if you input larger numbers and at higher frequencies (multiply ferq. by 10 for example) you can get a good idea of what each filter is doing as you change the parameters.

Hope that helps some.

Cheers,