Now what? Please give comments

The attached files are my room layout and the center speaker REW plot. BFD or no BFD. The location of the sub is between the left speaker and the center speaker. That is what seemed to give me the best response. I put in a house curve of +5 at 30 Hz and 0 at 80 Hz. My crossover is at 100Hz and I am running bass management with an Outlaw Audio ICBM. Please give comments and be brutal.

Thanks - hope I did this right.

Attachments

	center final.jpg (48.9 KB, 197 views)
	Room1b.GIF (9.3 KB, 192 views)

Can you explain what you mean by this?

brucek

The graph is the frequency response of the center speaker using Room Eq. Wizard. This includes the subwoofer and the center speaker.

Hi Greg,

Well, we normally measure our sub response by itself -- turn off all other speakers either by cutting power to their amp, or by simply removing the speaker cables from the speakers (or at the amp).

Also, the fact that you were able to measure the center response tells me that you were using some type of audio processing mode -- perhaps DPLII or "multi channel stereo" mode. Either way, disable any of those modes and just measure the sub in a stereo mode with crossovers engaged. REW is a mono signal that's meant to be handled in a simple fashion.

What sub are you using? You're getting a very solid response to 30 Hz, and then it drops like a rock. Is that expected or is the ICBM somehow imposing that?

If you're asking whether or not you should get a BFD, I would answer that I could go either way on that. Your response looks very good in general, and most of us would be happy to have a natural response like that. On the other hand, I love the BFD, and would not be without it or its equivalent.

In general, you're on the right track. It looks like you have REW set up properly, and you're able to take measurements. Keep going!

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-- Otto

Thanks, Otto. I have a seperate preamp, an Outlaw Audio ICBM (I just use it for bass management because I have an older preamp/pro: http://www.outlawaudio.com/products/icbm.html, and a 5 channel amp. All of the channels from the preamp go into the ICBM then to the amplifier (and the sub) and out to the speakers. Here is the setup for the signal from the computer (output). I ran the output cable from the computer to the left channel of the inputs of the preamp. Then I ran the left output from the preamp to the channel that I am testing (input for the ICBM) For the graph I show in the first post, it is the center channel which includes the sub.

I have a Def Tech Super Cube II subwoofer. When I did the sub alone (as you suggest by just unplugging the speaker wires) I get a pretty big hump from about 30to 50 Hz (at least I think it's from about 30to 50 Hz - my files are on my home computer). I will go ahead and post that later today. When I connect the speaker it settles down like my graph that I have posted.

Is the drop from 30 Hz unusually steep?? When I tried adjusting the phase the dip from 50 to 60 Hz just got deeper.

The phase will only affect areas that are shared by two speakers. So, the frequencies near a crossover, would enjoy the largest effect.

The quick drop below 30Hz is a bit sharper than a natural rolloff, so it's likely cause by the room.

brucek

Maybe if I move the sub around I could get a better response below 30 Hz??

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Thanks for the suggestions, Wayne. I will try the corner placement to see if I get a better response from the low end. I also noticed that when I adjust the xover on my ICBM, I don't seem to get much change - I will have to explore that.

I suppose it would be better to use just the signal to the sub only for placement then get it tuned in with the front speakers, right?

I will try to post more graphs when I get time.

Thanks again for your help.

I did some more testing over the weekend. I moved the sub to a number of locations and still did not get much of a response from below 30 Hz. I also looked at the room modes. I got the following using the room mode calc located here: http://www.hometheatershack.com/foru...converter.html

I used dimensions of: 7 FT height, 8'10" width, and 12'8" length. I had to take some averages of the width and height.

Maybe I'm not reading this right, but if the room affects my response below 30 hz, wouldn't that mean there should be a mode around that frequency and that I would be in a null??

There is probably more going on in the room - tangential modes???

I will post more graphs later tonight with just the sub.


I was also curious about the sub itself (Def Tech Super Cube 2). Would the fact that it has one active woofer and 2 passive woofers cause some sort of cancelation? Does anybody else have any experience with the Def Tech subs and REW?

Attachments

room modes1.PNG (13.2 KB, 153 views)

Forgive me for breaking the suggested graph limits but I had to show you guys this. Here is my sub only. I did not think I was getting any response below about 30 Hz. It looks like a huge dip. Is this normal below 20 hz???

Can this be fixed with a BFD?

Incidently, my crossover has two settings - 12 dB/Octave (normal) or 36 dB /Octave (special for THX subs). I have it set to normal or 12dB/octave.

Attachments

sub only position 1.jpg (84.1 KB, 150 views)

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Well I do have a lot of headroom left. My sub is at about 15 to 20 percent of capacity. I bet I could easily boost it up to get the 15 Hz to 75 dB. But wouldn't that blow out every thing else?

No gaping holes. I do have a basement window that is in the room, but it is small (typical basement window). The window is closed, and I have linacoustic lining the walls. The position of the sub is fairly close to the corner - just the right side of the left speaker. When I move the sub around the room I get, in general, the same response.

Wayne,

Here are 50 percent, 75 percent and 90 percent in that order:

Attachments

	50 percent.jpg (77.1 KB, 148 views)
	75 percent.jpg (78.7 KB, 147 views)
	90 percent.jpg (77.2 KB, 150 views)

The information below 20hz is not actual output from the sub. As the response drops into the noise, the meter calibration file compensates (as it also drops) and applies its opposite compensation.

See in your graph where the cal file drops past 10Hz and carries lower (because C-Weight is incorrectly turned on). This offers increasing compensation, and as the actual signal enters the noise, the meter file creates the strange rising signal.

Your usable response goes a little below 20Hz.

Below I show a couple graphs of a small sub I own.

You can see from the impulse response where the signal enters the noise about ~45dB down.

Then see the associated frequency response plot (with the exaggerated vertical scale) that is created from that impulse response, and you can see where the signal is down about ~45dB, but then begins to rise. This isn't signal - it's noise.

Generally you determine where your sub signal enters the noise and set your bottom horizontal axis to that...... For most people, that horizontal scale is about 15Hz.... The LLT guys use about 10Hz....


RISING LEVEL impulse.jpg
RISING LEVEL with c.jpg

brucek

Thanks, Bruce. So based on that I should set my lower limit of frequency back to 15 and try to equalize that. You mentioned that C-weighting is incorrectly turned on - do you mean below 15 Hz? I assume I should have it on for measurements and that it is not relavant below the limit of my small sub.

Who are th LLT guys? I did not understand the reference.

From my graphs of 50, 75 and 90 percent, would a BFD help to tame things with my sub?

Thanks again for the help.

You should set the axis on your graphs to horizontal of 15Hz-200Hz and the vertical to 45dB-105dB. The third (blue) plot you show is quite good. The natural low end extension is a bit below 20hz. That's good. You can't equalize below 20Hz with a BFD. Either way, there's no upside to trying to boost below a subwoofers rolloff at the bottom end.

The C-weight check box in REW is only active outside the limits of the meter calibration file. It should be turned off.

Many members here have built LLT's. See the DIY subwoofer and Soundsplinter sections in the forum..
LLT explained

You have a very good response. I wouldn't try and equalize it.

brucek