# Low measurement with REW?



## exojam (Oct 28, 2006)

First let me apologize if my graph is not formatted correctly in regards to the db levels (but that me be my issue).
I went through the help files and believe I have calibrated the sound card and SPL meter correctly. I loaded the digital cal file for my RS meter.
I ran the output of my soundcard to the DSP1100P (in bypass mode) to the amp of my sub.
Running a Sonotube TC2000 15".
Calibrated the SPL to 75.
Ran the measure and the "response" line is way down in the db range. Does it appear that maybe I set something up wrong? Thanks for any help that can be provided.


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## brucek (Apr 11, 2006)

Did you Set Target Level with the button in the target Settings panel?

and if so, did it return a value around 75dB?









brucek


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## exojam (Oct 28, 2006)

I had not done that. Just ran and did it. It came back as 74.8db. Ran measurement again and got back the same response line.


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## brucek (Apr 11, 2006)

OK, under Settings pull-down, select Delete Settings and Shutdown.

Restart REW and go through a setup and see if it still does it.........


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## exojam (Oct 28, 2006)

I went through and deleted the information. Redid the setup. This time I removed the BFD from the loop and ended up with the below information. First shot is of the information from calibrating the sound card and than SPL. The second is the measurement of the sub. I am wondering if the BFD was causing something weird to happen. It was given to me by a friend and I thought I had successfully cleared it memory.


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## brucek (Apr 11, 2006)

Looks quite normal now. With the BFD, to temporarily turn off the filters, simply push the IN/OUT button so that the green LED is off and the signal should just pass through the BFD with no filters. The filters are engaged when the green LED is on.

Either way, for the BFD program that you will be using, be sure to go through and turn each filter to 'OF' and save it. Then you can add your own filters from there.

brucek


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## exojam (Oct 28, 2006)

Sounds good. I am now manually going to attmept to laod some filters. Thanks for your time and help.


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## exojam (Oct 28, 2006)

Well here is my first attempt at tweaking the sub with the BFD. I have a dip around 60 but cannot get it any better. I made the below filters for it. Not sure if I can clean the dip around 60 up any better. If anyone with more expereince with the BFD has any advice on this that would be great.

20 + 2
25 + 2
40 - 3
63 + 13 
80 - 7


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## brucek (Apr 11, 2006)

> advice on this that would be great


Looks good except for that gain filter of +13 at 60Hz. Best to simply remove it. Gain reduces dynamic range and a dip that narrow will not be noticed...

It's usually best to EQ the sub alone first, then add the mains to tweak any problems around the crossover area.

brucek


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## exojam (Oct 28, 2006)

Sounds good. Will do.


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## adogand6kids (Jul 29, 2006)

Also, please notice that your measured sub (green line in graph) response is mostly found below the "target level" (blue line on graph). With this situation, the REW program sees all of this (mostly everything up to 60 Hz) as dips in the frequency response and won't do anything to fix it. To make better use of the program, try turning up the volume / gain knob on your sub (not your receiver) and re-measuring the response. Once the measured response (green line) is mostly above the target level (blue line), then have REW suggest filters to cut the response at the high spot and bring everything down to a smooth level.


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## exojam (Oct 28, 2006)

I was not aware that REW could make suggestions like that. I have everything disconnected right now (measureing equiptment) but I will be moving the sub to another location, so when I move it I will rerun everything. Thanks.


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## brucek (Apr 11, 2006)

> To make better use of the program, try turning up the volume / gain knob on your sub


Or, once your measurement is done, just adjust the _target level_ thumbwheel up or down to include as much or as little as you want of your response to be considered by the _find peaks_ button.

brucek


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## exojam (Oct 28, 2006)

Bruce,

I have a follow up question for you. I do apologize up front if this is a really bad question. You had mentioned to add in the mains and do some testing. In the REW help files it shows to connect into "Aux in" if available. I have a Denon 3803 which does have analog in for 5.1. My question is, if I use these, it seems I would have to do one main at a time. Can I connect into either the analog "cd" or "phono" to get both mains at the same time? Also, I have removed the filter for "+13" at 60. Thanks.


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## brucek (Apr 11, 2006)

> Can I connect into either the analog "cd" or "phono" to get both mains at the same time?


You may be a bit confused here. 

When you connect to AUX (or CD for that matter), and place your receiver in _Stereo_ mode (with the crossover enabled), then the _sub and mains_ will be on, and the center and surrounds will be off. 

With this setup then, to test the sub alone, you remove the mains by shutting off the mains amp (if you have one) or by disconnecting the mains speaker wires. To add in the mains, you connect the speaker wires. Of course you do this disconnecting and connecting with the power off while ensuring the wires don't short.

brucek


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## exojam (Oct 28, 2006)

Gotcha. Thanks again.


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## exojam (Oct 28, 2006)

Bruce,

I have relocated the sub to it permanent place and measured again. The first graph is with no filter and the second is with two filters (40 -4db and 50 -2 db). If you don’t mind making an recommendations-comments on this. Also, I am not using a midi cable to connect over. If I did would this provide anymore functionality with other freq's not all ready in the BFD? Thanks.


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## brucek (Apr 11, 2006)

> Also, I am not using a midi cable to connect over. If I did would this provide anymore functionality with other freq's not all ready in the BFD?


The midi cables' function is simply to transfer the filter settings from the REW computer to the BFD as a matter of convenience. Without the midi cable, filters are entered manually into the BFD front panel. No difference.



> The first graph is with no filter and the second is with two filters (40 -4db and 50 -2 db). If you don’t mind making an recommendations-comments on this


You're on the right track, but you haven't really gone far enough. You need to be a bit more aggressive to remove the peak between 40Hz-50Hz. You need to increase the sub amplifier volume a bit (~5dB) and then cut the peak between 40Hz-50Hz some more......

brucek


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## exojam (Oct 28, 2006)

What I have been doing it setting the sub amp so when I run the "calibrate spl" I am close to 75. I will set it be 80 and try again. One other question, should be trying to use the "fine" to get a freq around 45 and pull it down so I am not just pulling down 40 and 50? Thanks again.


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## brucek (Apr 11, 2006)

> when I run the "calibrate spl" I am close to 75. I will set it be 80 and try again


Nope, should be 75dB... My suggestion to turn up the sub amp doesn't affect the REW calibration settings, it just makes the sub a little higher level than the mains level.



> One other question, should be trying to use the "fine" to get a freq around 45 and pull it down so I am not just pulling down 40 and 50?


You should use REW to create a set of filters from your raw measurement to create a corrected response and then enter those filters exactly into the BFD and remeasure to see how you did...

brucek


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## exojam (Oct 28, 2006)

Will do. Thanks.


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## exojam (Oct 28, 2006)

Bruce,

Please forgive my ignorance but I would just like to verify my steps are correct.

1) BFD in bypass
2) click SPL meter button
3) set sub amp so output is 75db on meter 
4) run set target level
5) run measurement 
6) find peaks
7) program filters that are shown

At anytime do I need to redo the set target level? 

Thanks again.


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## brucek (Apr 11, 2006)

After you've set the subwoofer output trim in your receiver, then use your receivers test tones to roughly match the subwoofers level with the rest of the speakers. The sub level would be set using the sub amplifiers level control.

1) The BFD should have its filters either in OF mode or bypassed (IN/OUT green LED off) to obtain a raw without filters measurement.

2) Ensure the soundcard and meter calibration files are loaded in REW, cutoff set at crossover setting (i.e. 80Hz).

3) REW Settings ICON.
- Check Levels routine, using receivers master volume control to set 75dB on SPL meter.
- Calibrate SPL routine.
- Set Target Level.

4) Measure, find peaks, assign filters, adjust filters manually to get best result. You can raise or lower the target level manually to get more of your response above the target line if you want.

5) Enter filters into BFD and then remeasure to see results. (with filters engaged)

brucek


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## exojam (Oct 28, 2006)

On step 3 I have been bypassing the receiver and going straight to the BFD so for that step I will need to get back there and hook into the receiver than to the BDF. Thanks again.


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## brucek (Apr 11, 2006)

> On step 3 I have been bypassing the receiver and going straight to the BFD


Yeah, it's better to use the receiver with the crossover set that you use normally, and put the receiver in stereo so that all the extra speakers shut off. Most people like to disconnect their mains and get a sub only measurement when equalizing the sub, then add the mains later.

brucek


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## exojam (Oct 28, 2006)

OK, here we go.
1) The BFD should have its filters either in OF mode or bypassed (IN/OUT green LED off) to obtain a raw without filters measurement.----------Led OFF

2) Ensure the soundcard and meter calibration files are loaded in REW, cutoff set at crossover setting (i.e. 80Hz).--------ALL LOADED

3) REW Settings ICON.
- Check Levels routine, using receivers master volume control to set 75dB on SPL meter.
- Calibrate SPL routine.
- Set Target Level.
------------
With sub amp turned off, ran setting using speaker pink noise. All at 75db

Took measurement of speakers only with receiver cutoff at both 60 and 80

Redid setting using "subwoofer", all 75db

Took measurement of sub with main speaker wires unplugged.

The first shot is both mains and sub with receiver crossover at 60.

Second is the same but crossover at 80.

Besides the very bad dip at 60, I don’t think it looks to bad. I am not sure if the 60 can be correct. No filters were applied at this time. Receiver is a Denon 3803. What do you think?


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## exojam (Oct 28, 2006)

Well here is my attempt with the below filters. All came from REW except 5, 6 and 7. Sorry about the graph, did not realize it was in the incorrect format till I e-mailed off my laptop.
1) 24.5 -3
2) 29.2 -4
3) 33.2 -4
4) 36.6 -4
5) 59 +4
6) 60 +4
7) 62 +4
8) 74.9 -4


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## exojam (Oct 28, 2006)

Here is my latest attempt. Now I just need to figure out the house curve stuff.

1) 20 + 1
2) 22.5 + 4
3) 25 - 1
4) 32 - 1
5) 40 - 1
6) 60 + 4
7) 88 - 5


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## brucek (Apr 11, 2006)

With all those -1dB filters (almost insignificant), I'd like to see the response without the BFD. I suspect you don't even need one............

brucek


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## exojam (Oct 28, 2006)

I will try to get one when I get a chance and post it.


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## exojam (Oct 28, 2006)

Bruce, 

Below is a shot of the graph with the BFD in bypass, than engaged and a averaged shot. Please let me know what you think. Thanks.


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## brucek (Apr 11, 2006)

What can I say. If it were my response, I'd remove the BFD.

Then I'd do the same test with a mains added, and adjust the phase of the sub to get the best transition at the crossover.......

brucek


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## exojam (Oct 28, 2006)

Bruce,

Sorry for the bad question here, but does that mean you think the responce is half way decent or is bad?


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## brucek (Apr 11, 2006)

I think the response is quite good and doesn't need to be equalized. I'm sure there are those that might find some fault somewhere, but a lot of other people go through lots of gyrations to get that very response you're getting for free.

There's a price to pay with the BFD. You have to digitize and un-digitize your signal. You have to be concerned with limiting your dynamic range and adding noise to the signal. You are adding filter specific phase changes to the signal. You are adding the possibilities of ground loops. etc, etc.

All you'll have between your receiver and sub is a cable. Lucky guy.... 

brucek


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