initial Frequency Response - Now what?

You do not need any HF absorption. If you are going to add panels, make them thick and with a reflective skin. Same for the bass traps.

+1. That's quite a bit of HF roll-off. What are the room dimensions, and what sort of furnishings/coverings/rugs now?

Does your receiver have eq? There is a tad to much 50 hz, but your low end is really good actually. Turn up the treble a LOT. You're about 20 db down at 20khz. What kind of speakers? It'll be hard to bring up that much high frequency.

Oh and how did you measure? It's possible your mic is off above 10 kHz making it look worse than it is.

And toe in your speakers if you can.

If the mic is pointed straight up, aim it at the speaker you are measuring. Measure each speaker independently. Measure the sub by itself, and then measure the blend at the crossover.

Yes, but the graph you showed is misleading. For assessing low frequency response you do not want to use third-octave averaging. That just hides all the detail. Below is a graph showing the exact same measurement with 1/3 versus 1/12 octave smoothing. This article explains the best way to display the various graph types (and many related topics):

Room Measuring Primer

--Ethan

That may explain the roll off of high frequency. Try pointing the mic straight towards the tweeter and see how it measures assuming your speaker height is set so that the tweeter is at ear level when sitting down. Also try different toe in angle of speaker to see how it changes the high frequency response.

To me that looks pretty good except for the 40 Hz null. That null is most likely a room mode, and bringing it up will be difficult. Lots of bass traps will help, though there's fairly low. It may be easier to move the furniture to get out of the null.

Peaks and nulls are caused by sound waves bouncing around in the room. A peak is when they add, and a null is where they subtract. Because of other factors, like vibrations in the walls and ceilings, peaks rarely exceed 10 - 20 dB and can usually be brought down by EQ. Nulls are harder to handle since the signals can cancel quite well, making a very deep (and thus difficult to correct) valley.

If you can't move the listening position, then you could bring the subs out so you are near-field. Note that at 40 Hz a wavelength is about 28 feet; you may need to move a couple of feet to see a big difference. For starters, measure at spots perhaps 2' forward and back of your first set and see what happens.

You should also follow up with Ethan about bass traps -- you may be able to make a significant improvement by investing in (or building) some good bass traps.

HTH - Don

You really don't want to do that (it'll sound unnaturally bright) and don't want a flat reverberant field.

The problem here is that your ears are looking at the direct sound, similar reflections that are coming later, and combining their spectrums with some sort of time-based weighting to determine timbre. They expect some roll-off in the reflections at high frequencies because those are more readily absorbed in natural surroundings and have higher losses with distance (listen to what happens to highway noises as you get away from one - you hear more low frequencies when you get distance and things like trees between it and you).

The microphone is just adding all the reflections together equally (apart from its pickup pattern, which we'll ignore to simplify the discussion).


Leave the high frequencies alone unless you have room problems you can't address acoustically (speakers in a big room with lots of sliding glass doors, tile floors, etc. A cut helps but doesn't work as well as fixing the problem). Don't make fine grained corrections.

Low frequencies are different. Your ears need a cycle to pickup the tone and are picking up reflections before they're done with a full wave of direct sound. Perception seems to have more to do with the steady state measured response.

You just want to consider what's going on when you want multiple "good" seats, where the interactions of room modes can be radically different (even 6" away) and aim for the best average corrections.

Try putting one sub on top of the other at the front and see what happens. Try both left and right location for this and pick the flattest bass response. Also, I would turn up the sub just a little.

post waterfall plots (0-300hz)

flat freq response is only one side of the story --- the time domain is equally important, as it will show modal ringing.

also, you may not need "HF absorption", but you would still benefit from absorption at the first order/early reflection points. side walls + ceiling.

That looks better now. I think the sub level looks good, but bass level can be a little personal. I don't like my bass cooked.

Try putting the sub xo back to 75 or 80 and change the subwoofer phase until the xo null is gone. Then you get the advantage of a lower xo and keep it flat. 100 works because it's in phase is all.

You can put pieces of rubber or felt pads at 3 or 4 spots. If it's only temp, just use a sheet of thick fabric or rug. Stacking is to use one best spot for room response while maintaining the output of 2 subs.


Yes, if they are both at the same location such as stacking.

Use the Distance setting for the sub in your receiver. It's a better tool for setting the relative delays between the speakers and sub than a phase control.

Craig

I like having a phase (or distance) knob on the sub for these situations. If you have one sub output from your AVR, or just one sub processor even if there are two outputs, you need some way to adjust the phase of each sub independently if they are not co-located, or at least equidistant from the listener.