Axiom Home Page Forums General Discussion Home Theater Fred's Excellent (hopefully) Calibration Adventure

The ears are well broken in, I've lost the perma-grin and I'm up to date on my movies.

Its time to play!

Over the last couple of months I have been doing a lot of reading on the 2nd most important influence on the quality of sound: the room. I have become convinced that there are reasonable things one can do to significantly improve the sound quality of any audio system.

The starting point is of course, figuring out exactly what your speakers are putting out. For the last few days I have been playing with a program from the folks at hometheatershack.com called Room Equalization Wizard (REW). I gotta say this is a pretty slick program! These days everyone has a computer, and for the cost of a few extra cables and an spl meter (which we all have anyway right?) this program is a no-brainer.

Here is what I have so far.

The layout:



The surrounds are now where the two Xs are. With the FR speaker being blocked by the couch this channel is boosted by about 2-3db to compensate.

The Sub:



The good news is that I am getting extension down to 22Hz. Not bad considering the posted specs list the -3db point as 28Hz and the sub is not corner loaded. The bad news is the huge dips around 40 and 70Hz. Yuck.

By the way, I had never level matched the sub until two days ago. It seems I was running the sub a little hot. I turned it down from about 1:00 to around 10:00, about 15 'clicks' on the dial!

Sub waterfall:



Everyone probably already knows this, but the waterfall plot shows how fast each frequency decays. The Z axis on the graph it time, so wherever you see a ridge extending out for any significant time, that frequency is being reflected around the room.

For fun I also plotted the sub + mains:


I did not db match during pre-sweep level checks, so the dbs for each trace are different, but you get the idea.

What surprised me here was the big boost at 37Hz. I know the M80s reach low, but with the high-pass roll off I didn't think the mains would contribute much this low. I bet there is a room mode at play as well, but still...

It’s interesting how some frequencies are boosted and some seem tamed. The 52Hz area does not look quite as bad with the mains in, but yowzers! Look at 80Hz.

I didn't upload the waterfall for the sub+mains sweep, but it looks like I get my boom from 37, 52 and 80Hz. I'm also missing a lot between 38 and 70Hz or so. Maybe thats why I wanted to turn the sub so high.

Once REW is set up, measurements are a snap. Set up the spl meter, check to make sure the meter is calibrated to REW test signals, check levels for the chosen location and measure. I spent more time waiting for my fridge to turn off than making measurements.

Those dips you have are very severe, You may want to play around with phase and placement to see if you can get rid of them. You'll probably be surprised how much of a difference it can make. I have my subs and M80's hooked to a Behringer DCX2496 which is an active crossover and eq among other things and had been playing around with REW for a while. A few tweaks later I am able to get a pretty flat response, It definetly is a handy program

I forgot about adjusting phase. I definately plan to play with placement, though my options are limited.

Nice work Fred. Someday I hope to have some spare time to do what you are doing. I have had REW downloaded on my hard drive for over a year and have yet to fire it up!

I actually considered this stuff fun for awhile too, until it became clear that I wasn't able to do anything about my "valleys and nulls" that didn't involve a general contractor! I never used that program though....maybe someday I'll give it a shot!

One thing to note, however: I'm not really familiar with waterfall graphs but will will mention that lower frequencies will always have a much longer decay due to their much longer wavelengths....

Still, it's nice to see somebody else' semi-sucky room to start my day off with a smile!

Evil for the month of September, remember?

Fred - I'm sure you remember I went through the same fun (I think?) with my own poor room modes when I first picked up the EP600.

This was what my raw output looked like where I first had my sub:


I had some ugly dips at around 35 and 60 hz. I ended up getting the Behringer Feedback Destroyer (fondly known as the BFD) to smooth responses, but what I found was that these types of dips (-20 dB or more) weren't correctable through any other means than moving furniture or moving the sub itself. The best I could do in that position, even with the BFD, was to get the curve to about -12 dB at 60 Hz (and other ugly problem spots as well), which was still way too much of a drop off for me to be happy with.

Fortunately in my case better results were achievable without moving walls.

Now take a look at what happened just by moving position of the sub, this is still before using the BFD in the new position:



Moving the position caused the response to move from +/- 40 dB to +/- 10 dB (and my satisfaction level with my EP600 to go from 0 to 100).

Then, finally, I applied the BFD adjustments to my curve and achieved the flattened curve I was looking for:



The moral of this long story filled with squiggly lines and charts? Even though I know you've said you have a tough room, definitely experiment with different locations for the sub to see if you notice a difference (primarily with your ears, but also with the REW curves). Also, like you said, adjust the phase options to see if it makes a difference, though in my case even phase adjustments in the first position were not terribly helpful. It was just a very bad location in the room. In the second position though, and especially after adding a second sub, the phase adjustments became critical to smoothing response throughout the room.

Have fun, keep us posted!

Jason

And I thought I was bad. I've had rew downloaded for a couple of months now. I have spent a lot of time reading up on the various options for taming my room though.

Semi-sucky? Semi-sucky!! I'll have you know that I am surrounded on 4 sides by concrete! My room is mondo sucky. Its the KING of sucky.

Jason. I do remember you went through some fun. For some reason, the second and third graphs in your post are not showing up.

I expect it may take a while for me to get through this. As has been mentioned by several people, my options include adjusting phase, moving the sub, adding a sub, moving furniture and one not mentioned, bass traps.

I have already checked a position about 1.5 feet closer to the front of the room. That would put the seating position at about 35% of the way from the back of the room. I seem to remember this as being the 'magic' spot. That helped a little with the 37Hz suck-out, but its still ugly. Moving the couch forward is the only furniture moving option.

For moving the sub, I only have two other places: the back corner or between the right speaker and the TV.

Edit: Hmmm. Looking at the room layout, I could also try the sub in the other 'not quite' back corner. I bet that would do funky things to the bass in the Kitchen!

I will probably try corner bass traps at some point, but I don't think they are very effective down below say 100Hz. I expect my room will need help in the 100-500Hz area where corner bass traps are more effective.

Fred, well at least you've been able to make Mark Johnson feel better! On the sharp dips shown, one point to keep in mind is that both the positioning of the sub at a null and the microphone(or your ears)at a null can result in such dips. For example, someone sitting in the middle(horizontally speaking)of a 15' wide room would experience a dip at about 560/15 or 38Hz. Your room dimensions plus sub and ear positioning will change these effects.