Could this be right?

**raylock** · **07-25-07, 08:38 PM**

I have finally been able to attempt to take some measurements using the REW software. There are some elements of this graph which seem reasonable which I compare it to other graphs that represent different sub positions. For example large dips in one area disappear when I move the sub from one part of the room to another. The thing that makes me think that I am doing something wrong is I am not seeing a roll off at low frequencies. Any ideas?

**Otto** · **07-25-07, 09:41 PM**

Hi there, Ray!

Could you do us a quick favor and repost the graph with axes from 45 to 105 dB (on the vertical, Y axis) and 15 to 200 Hz (on the horizontal, X axis)? It'll help you compare "apples to apples".

Thanks!

**brucek** · **07-25-07, 09:51 PM**

Yeah, set the axis as Otto recommends and also set your target level to 75dB.

Any response information that is below the meter calibration file is not meaningful. Below that, the falling meter calibration waveform (which is incorrect, since you have C-Weight turned on) is exaggerating the signal that's in the noise and making it appear as though the response down low is good. I'm afraid that it's not though. Uncheck the C-Weight box.

brucek

**raylock** · **07-26-07, 10:04 AM**

OK, Thanks for your help! I have tried to follow directions

but I am not sure I like what I see. Here are two graphs prepared with the sub on opposite sides of the room. It looks like I have some problems of some kind. Maybe room, maybe sub but more probably operator given my slow learning curve here

Any further thoughts would really be appreciated

**raylock** · **07-26-07, 10:07 AM**

Sorry, I should have put these both on the same graph. Couldn't figure how to fix it once I posted it. Will remember next time.

Ray

**brucek** · **07-26-07, 10:24 AM**

Yeah, good job on the graphs......

You need to turn off all the other speakers and only check the response of the sub by itself, using the crossover frequency you would normally use. That means, using the CD or AUX input to your receiver, and then put the receiver in stereo (that way only the mains and sub are on ). Then disconnect or turn off the mains. Then do your REW check levels etc and do the response. It will reveal a lot more than what you have now. I suspect a lot of the problem will be that the mains are a lot higher than the sub in level....

Maybe post another plot when you've done that....

brucek

**raylock** · **07-26-07, 11:18 AM**

Thanks for the help. It must be frustrating answering questions from people who don't know what they are doing

Ok, receiver (Marantz 7001) set to stero, mains unplugged, using aux 1, c weight unchecked. Crossover set to 80Hz. Here's what I get. I'm back to the no low end roll off problem

Maybe I need to take a day off and just re-read (or maybe read) the instructions in the help file.

Ray

**Otto** · **07-26-07, 01:03 PM**

Hey there,

I didn't see what sub you are using. What kind of output would you expect at 15 Hz?

**brucek** · **07-26-07, 02:50 PM**

Looks reasonable (if the sub is capable - as Otto points out).

Heck of a dip at ~50Hz. Does moving the sub or the listening position have much effect on that?

Tell us the type of sub and whether you plan on getting a BFD? You need one....

brucek

**raylock** · **07-26-07, 03:36 PM**

Quote:

brucek wrote:

Looks reasonable (if the sub is capable - as Otto points out).

Heck of a dip at ~50Hz. Does moving the sub or the listening position have much effect on that?

Tell us the type of sub and whether you plan on getting a BFD? You need one....

brucek

Yes I have a BFD setting here ready to go to work

That is going to be another project. I have been trying to learn how to measure responses with the REW. Once I have mastered that I will move on to the BFD. There will probably be a whole other barrage of newbe questions. Based on my very limited knowledge of these things, it is my understanding that I will need to handle the dips with physical location and can us the BFD to tame the peaks. Does that sound correct? Moving the sub didn't seem to affect the dip much, but I really haven't had a chance to play with it much since I figured out the software issues.

Thanks again for your help.

Ray

**brucek** · **07-26-07, 03:42 PM**

Yeah, your sub measures quite good except for the dip and a few eq problems.

Generally, dips don't respond well to equalization, but sometimes they do. A small amount of gain doesn't hurt, but realize you are reducing your dynamic range somewhat when you add gain filters. Never go above 5dB of gain in a filter.

Smart idea to get a feel for REW first...

brucek

**clubfoot** · **07-26-07, 03:50 PM**

raylock, what is your room layout, i.e. dimensions, is it enclosed, can you move your seat location? If your sub is not too heavy, put it in your seating location and move the spl meter/mic to different locations and take measurements to find a good sub location.

**Blaser** · **07-29-07, 10:19 AM**

What sub are you using?

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