How flat should the frequency response be in a room?
However for a fast start you can read the guidelines of Nyal Mellor of Acoustic Frontiers http://www.acousticfrontiers.com/audio-projects-acoustic-design/. We had a nice thread on it at WBF.
"Flat" needs a definition otherwise it's impossible to say yes or no to it. Here's my definition of flat:
Consistent frequency response, within 2-5db (at least 1/12 octave smoothing) across the spectrum, and good impulse response as well, from multiple 3D points inside the listening area tailored to the listener's preferences. The definition must include both frequency and time info because time can affect perceived frequency response.
"At Least" 1/12 octave smoothing?? That's ONE NOTE in the chromatic scale. Why would you need 1/24 or 1/36 octave. All you will see with that on the graph is a mess of squiggly lines resulting from comb filtering that really won't tell you anything useful about your room, besides, you'll get a different graph if you move the microphone an inch or two. It may even obscure what you want to see in your graph. This is a case where a little less is more.
I think the 1/12 octave smoothing you mentioned is actually ideal.
Ok from what I read 1/3 represents about where we hear, so wouldn't you want to use that? Or 1/6 to expose a few hidden bumps and dips that the 1/3 wouldn't show?
It depends. You would want unsmoothed for certain things like DSP operations. You would also want unsmoothed to help find exact location of boundary interference and even better seat/speaker position. That's how I would use it. OTOH, 1/12 octave is all one really needs to generally describe system accuracy to determine whether they have achieved their goal of linearity or to generally show someone else that's interested in their system response. However, no magnitude response alone can fully describe how a system sounds. (That was for Myles). However, crappy response does mean a system is subpar for sure. My point is that you can hide a lot of warts in a 1/3 per octave smoothed graph that are very audible even if it's better than a previous 1/3 octave graph.
Here are two examples of my room, one is flat the other is after some eq. The target is 72db in the eq measurement, this is just the mains no sub.
The problem with smoothing even at 1/6 is that you can't really see whether there's a true boundary interference contributing to that loos of energy or something else. With unsmoothed, an SBIR dip will be very obvious. If an SBIR is really there, then you can use math to figure out which boundary is causing the SBIR.
It would be a very narrow V shape, assuming the boundary is a bare wall or concrete floor; something solid and untreated. This also assumes we are only looking at a single listening position measurement.And what would that look like as opposed to a room modal issue?
It would be a very narrow V shape, assuming the boundary is a bare wall or concrete floor; something solid and untreated. This also assumes we are only looking at a single listening position measurement.
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