My First REW Measurement with PB13

**gskinusa** · **01-24-09, 10:06 PM**

Hi
I just bought the PB13 ultra sub and this is my first proper sub (previously was using bose acoustimas module as the sub). I tried configuring the sub without any proper tools and was some what satisfied with the results. I just bought the Radio shack SPL meter and so decided to do the REW test. I have to say that as I am new to this it took me a long time to have the computer sound card configured and ready for measurement. I have the first measured graph but I have no idea how to interpret it. Can some one please help me understand the graph that REW tool spit out. Please help me through this to set the sub properly for optimal enjoyment.

The test was done with default values except went for the 1MB Length. Not sure what additional details, I have to provide but please let me know if I have to identify any other details.

Thanks for your help.

**Wayne A. Pflughaupt** · **01-25-09, 07:44 AM**

Welcome to the Forum, and congrats on that new sub! I'm moving your thread to our dedicated REW Forum, where you're sure to get better answers to your REW/sub tweaking questions.

As for your graph, it looks like your level (for measuring) is way too high.

That said, your response isn't too bad. You might be able to improve it by experimenting with different locations, if that's an option for you.

Regards,
Wayne

**gskinusa** · **01-25-09, 09:15 AM**

Thank you very much for the reply and for moving the thread. Only after posting the questions I realized I should have done it in REW forum.

I agree with your observation. I also felt the same while I was taking the measurement but as I do not have the basics, I could decide what to do to reduce it. Particularly, while checking the level, the REW documentation says that, I should adjust the speaker volume so that the SPL reading is 75 db but then it says, I have to adjust the input volume to have the input level between 12 to 24 db (I think thats what it is) and the ideal is 18 db but I was confused with which one is input level. Is that the one on the top of the left & right vertical response bars (next to the output vertical bar) which was called peak value during other tests or the one below it. But, I tried aligning both and could not get any one of them properly around measure 18 db without increasing the receiver volume and input volume and the sweep level (I had the sweep level around -10 db). So, I truly appreciate any help in helping me understand how to take better measurements. If I do not do that I get the message that the level is low when I do checl level upon clicking the Measure button. I do not know how low is allowable like it was saying its around -30db and still called it as low and the lowest value I was able to get was around -29 db.

Regarding the position of the sub, currently I have it in between the mains as I do not have space between the mains and their respective walls. I think, I can move it behind the listening position or to one of the side walls but those are options I can try.

I did take a few more measurements after I did the first the post. I will try to get them posted also but all those were plagued with the same problem of increasing the volume somehow higher to get the input value between the ranges suggested in the documentation. If any one can provide some help with this I will be a happy camper

Thanks again for your reply.

**brucek** · **01-25-09, 10:15 AM**

Quote:

I was confused with which one is input level.

The value located under the REW input VU meters is the RMS value and is the one you would be shooting for. The value located at the top of the VU meters is the Peak value and you need to be sure it isn't over -3dB. If it is, you would need to lower the RMS value a bit. That's why the range given is ~-12 to -24dB.

Quote:

I tried aligning both and could not get any one of them properly around measure 18 db without increasing the receiver volume and input volume and the sweep level

If you have your Radio Shack meter dial set to the 80dB range, then the voltage that reaches the line-input of the soundcard should be suffice (assuming you have ~75dB on the RS meter needle), and enough to get at least -18dB RMS on the input VU meters.

Once the input level is set, be sure to run the Calibrate routine to tell the REW SPL meter what value the RS meter is at....

Your response is OK, but you have a peak between 20-30Hz you'll need to deal with either through EQ or placement.

brucek

**gskinusa** · **01-25-09, 10:46 AM**

Thanks for the reply. I tried aliging it like you said.

I had the Radio shack meter set to 80 db
I did the check level in the "Settings"
Adjusted the receiver for the reading to show 75 db
I tried adjusting the input volume and sweep level but could not get the value higher than -28 db. So could not get to the -18 db level. I rechecked all connections and there was not lose connection or anything like that.

I am posting one graph I took based on the feed back. Please let me know whether anything else I have to do with the software. I will now start moving the sub to a different position from the front between the mains and will come back with what I have.

Thanks again for the help.

**brucek** · **01-25-09, 11:02 AM**

Quote:

I tried adjusting the input volume and sweep level but could not get the value higher than -28 db.

OK, you will have to trick REW a little to get the level you require. With the RS meter dial at 80, adjust the receiver to show 80dBSPL at the listening position (rather than 75dBSPL). That should be suffice to get the required voltage to the soundcards input. Then, run the REW Calibrate routine and cheat the level by setting the REW SPL meter in the routine to 75dB.

For subwoofers, always use the standard Vertical graph axis of (45dB - 105dB) and the Horizontal graph axis of (15Hz - 200Hz) using the Graph Limits button in the top right corner of REW. You're being extremely kind to yourself with the scaling that you are using in your graph.

brucek

**gskinusa** · **01-25-09, 11:44 AM**

Thanks for the quick reply. I apologize for the scale difference. I hit zoom and did not scale back. I followed your suggestion of increasing the receiver volume to reach 80 db and then setting the value as 75 db while calibrating the meter. I was able to get the input value to -19 db to -20 db but the peak was around -9 to -11 db and I could not get that to -3db.

I also did move the sub to a new position and here are the graphs for both old and new position with the same measurement process identified above.

The graph in green is the new position aligned to the left wall from the listening position.
The graph in red is the old position with the sub in between the left and right main speaker in front of the listening position.
Added:
The graph in blue is another new position aligned behind the listening position.

Based on what I have learned so far the new left position does not seems to work as there are too many variations when compared to the old one. But, the one with the sub behind the listening position (blue graph) seems to be much better but need your opinion on whether I am reading these properly and what do you recommend.

Thanks

**wackii** · **01-25-09, 12:26 PM**

yup, the blue graph looks the best. Do you have any type of EQ for your system?

Al,

**gskinusa** · **01-25-09, 01:27 PM**

Thanks for the reply. I had to remove a shelf that was close to the subwoofer. So here is the new measurement with the shelf removed. I think this one is better than the previous blue graph. Please let me know your thoughts.

I do not have any EQ. Does an EQ help my situation better?

**brucek** · **01-25-09, 02:19 PM**

Quote:

EQ help my situation better?

Nope, I wouldn't change it from there - it's fine....

brucek

**Wayne A. Pflughaupt** · **01-25-09, 02:27 PM**

A shame that your best-measured position is behind you. I don't care for that personally, but certainly it's better than what you were seeing before. Any way you can re-arrange the room?
Regards,
Wayne

**gskinusa** · **01-25-09, 03:17 PM**

I don't think I can rearrange the room because of the room layout. Its a relatively small room (20x10 with a 10 ft ceiling). One side I have the TV and the mains and to the right of it I have the opening to the living room. Behind the listening position I have a window that runs the entire width of the room. I would love to have more space but dont have enough budget to create a HT room in the basement. So for now have to live this one I guess. I will try to post the room layout picture and if any of you think a better way to fit in I will try it

After I had the sub moved, I had the yamaha calibrate the things through YPAO and now its better than before. I can feel the difference in the bass as now its lot more smoother. Going to watch a movie to see how it feels.

Thanks again for each one of you for your time and suggestions.

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