# Need help with REW - can't get reasonable measurements



## Tobias (Feb 20, 2007)

Hi there 

I just bought an BFD and wanted to use REW to measure the proper filters to apply. But I can't really get any reasonable measurements. The curve acts very weird, growing linearly below 30 hz (being flat at 75 dB above 30hz), and certainly something is wrong since I have more than 100 dB at 2 hz :coocoo: 

The only thing I can think I'm doing wrong is the connections to my soundcard. I was a bit confused of which inputs/outputs to use. My soundcard got black, green, pink, blue and yellow inputs/outputs, and I came up connecting my receiver to the green one, and the RS SPL meter to the blue one. 

I then followed the manual calibrating the soundcard, and I got a completely flat curve at 0 dB as in the help file. Then I loaded the RS calibration file which I downloaded from this forum, and checked levels, setting my receivers master volume such that the sound level meter showed about 75 dB at the 80 dB setting. 
Finally I clicked the calibrate SPL button in mic/meter settings. The meter showed 75 dB and i just clicked finished without changing anything. 

Then I measured on the 512kb setting with end frequency 150 hz and tried to measure, and I got this weird curve, clearly not showing the proper response..

I'm completely new to this program and would be happy if someone could help me and try figure out what I am doing wrong? 

Thanks in advance


----------



## Tobias (Feb 20, 2007)

I just tried clicking the "SPL meter" button in REW and clicked the red circle, and if I made sounds at the SPL meter it didn't show up on the computer, it just stayed at 0 dB - I guess it is supposed to show the SPL reading on the meter?


----------



## brucek (Apr 11, 2006)

Sounds like you've done most things correct.

Set the end frequency to 200Hz.

Set your Graph Axis limits to a vertical scale of 45dB to 105dB and horizontal scale of 15Hz to 200Hz. This is the standard we usually use for most subwoofer graphs. You don't want to look at anything down to 2Hz because your meter and its calibration don't go that low.









Be sure to set the target up by selecting subwoofer and clicking the Set Target Level button (that doesn't look like a button) as the last thing you do before Measuring.









Post a graph and I can likely tell you what's wrong.

brucek


----------



## brucek (Apr 11, 2006)

> I guess it is supposed to show the SPL reading on the meter?


Yep. You did use stereo connectors at the soundcards line-in and line-out?

brucek


----------



## Tobias (Feb 20, 2007)

brucek said:


> Yep. You did use stereo connectors at the soundcards line-in and line-out?
> 
> brucek


Yeah I did 

And thanks for the quick replies. I'm gonna give it some more tries later to see if I can get something reasonable 

edit: Btw, should I unplug my main speakers, so it's only my sub playing..? Can't turn them off in my receiver, so I would have to simply unplug them, it's quite troublesome to get them connected again :thumbsdown:, so if I could skip this it would be preferred


----------



## brucek (Apr 11, 2006)

> and if I made sounds at the SPL meter it didn't show up on the computer, it just stayed at 0 dB


Have you tested the SPL meter by using a standard RCA to RCA connector and plugging it into the AUX or CD of your receiver and sing. It's a microphone. Be sure it works.



> Btw, should I unplug my main speakers, so it's only my sub playing..?


Most people do unplug the mains, so they're just looking at the sub with its crossover. Set the receiver to stereo mode, so only the mains are playing and not the other speakers. Then you'll only need to disconnect the mains (with the power off). Once the sub is equalized, add the mains to check the area around the crossover for dips or peaks.

brucek


----------



## Tobias (Feb 20, 2007)

brucek said:


> Have you tested the SPL meter by using a standard RCA to RCA connector and plugging it into the AUX or CD of your receiver and sing. It's a microphone. Be sure it works.


I tried that, and it works


----------



## Tobias (Feb 20, 2007)

I was wondering why my BFD keeps blinking lots of red dots in the display? Have I missed doing somethig or will it just go away when I am ready to add the filters (when I get the measurements to work )?


----------



## brucek (Apr 11, 2006)

> was wondering why my BFD keeps blinking lots of red dots in the display?


Those are filters that need to be turned to the OF mode before carrying on. 

Read the manual on how to turn them all off first.

brucek


----------



## Tobias (Feb 20, 2007)

Ah ok  I have turned them off now. 

But I tried to measure it all from scratch now, and when I was about to calibrate the soundcard, with the loop connected, having the output/input device and output/input set to default, I didn't get any reading on the input bar on the right in the settings window... I experienced this before, but I just tried using other settings than default device input/output etc. and I got input reading, if I then tried setting it back to default, I got a reading again..

I must be doing something wrong somewhere..


----------



## brucek (Apr 11, 2006)

> having the output/input device and output/input set to default


Don't set them to default. Set them to Line-out (speaker) and Line-in......

brucek


----------



## Tobias (Feb 20, 2007)

I get both input and output responses when I do as you proposed. But the measurement of the soundcard looks a bit odd 

Here's a graph:








edit: Even though I got some flat measurement earlier, i cannot reproduce it.. but this one I get every time I try now.. dunno what happened earlier


----------



## brucek (Apr 11, 2006)

> But the measurement of the soundcard looks a bit odd


Before running Soundcard calibration routine.

Clear C-Weight switch.
Clear microphone calibrate file.
Clear Soundcard calibrate file.

Run routine and save file.

brucek


----------



## Tobias (Feb 20, 2007)

I had no calibration files loaded, and unticking of the C weighting SPL meter in mic/meter didn't help


----------



## Tobias (Feb 20, 2007)

anyone know what could be wrong?


----------



## brucek (Apr 11, 2006)

> anyone know what could be wrong?


I suspect your soundcard software has some equalizer/tone control setting turned on that boosts the bass and treble a bit and you end up with that response. 

Is the graph you post the response of the loopback cable after running a measurement with the soundcard cal file in place, or is that the dotted line showing the soundcard cal file itself?

brucek


----------



## Tobias (Feb 20, 2007)

The graph I posted is the one I get after measuring without any calibration file loaded..


----------



## brucek (Apr 11, 2006)

> The graph I posted is the one I get after measuring *without any calibration file loaded*..


I'm a bit confused.

The chain of events should be to install a loopback and clear all calibration files and then execute the Make Soundcard calibrate file.

This file is saved.

Then a measurement is made before removing the loopback cable to ensure the inverse Soundcard calibration file is applied to get a flat response of the cable. You don't take a measure of the cable without any calibration file loaded?

brucek


----------



## Tobias (Feb 20, 2007)

Oh.. when I say measurement I mean the graph I get from pressing the "measure.." button in the soundcard settings  This is the graph I have posted.
In the REW help file they call it a measurement, so I just called it the same..


----------



## brucek (Apr 11, 2006)

OK, so that's the soundcard calibration file. It's not so bad really. Note the scale on the graph. The peak at ~25hz is only a ~1.5dB high. If you changed the vertical axis, it would look flat as a pancake. This file will compensate inversly when you measure.

So, if you then measured a loopback cable (with the soundcard file loaded) to verify everything is fine, I suspect you'll get a flat line.

brucek


----------



## Tobias (Feb 20, 2007)

So, now I tried measuring the sub.. I got this graph:









It looks like it's jumping very much up and down.. could this be the right graph, or do you think I got something wrong with the measurements? If you think it's the real stuff, what would you propose me to try changing? 
I can recognize the 45 hz peak, which I hear very clearly when I make the 100hz LFE sweep from the AVIA dvd, so that would indicate it's the real curve i get...

I think I will try make a measurement with the sub on some different locations.

And btw, would it be ok just to unplug one of the main speakers? (Since the output on the soundcard is only connected to L or R on the receiver) That would save some time since the cables I use is quite annoying to work with


----------



## brucek (Apr 11, 2006)

> It looks like it's jumping very much up and down.. could this be the right graph


Yeah, that's not too good. That's one **** of a dip between 20Hz and 40hz. Try some different spots for the sub if that's possible, just to be sure something else isn't wrong. Maybe just move the mic around to some other spot and get a good reading, so you know you're on the right track.

Looks like you took a good measure of the sub only, so I have to think you've done everything correct. Looks perfectly normal above 50Hz, but not so good below that....... You must be in some sort of null. You do have your receiver in stereo I presume (and not some 5.1 mode).....

Yeah, you can just disconnect the one main, if that's the only one playing. You just want to get the sub alone with its crossover. Always be sure those speaker cables don't short by mistake....

brucek


----------



## Tobias (Feb 20, 2007)

I just tried a quick measurement without unplugging my speakers (will unplug them later for another measurement) and moving my sub to some other location. I got this graph this time:









Haven't regulated the phase knob or gain for the new location.. but It does look better now ?


----------



## brucek (Apr 11, 2006)

Try unplugging those mains and see how the sub looks. Can't tell until you do that.......

brucek


----------



## Tobias (Feb 20, 2007)

I just unplugged it and now I got this one









When I do the measurements I notice that the input reading on the meter is a bit low - just around -24dB.. though I did setup up the volumes prior to the measurement..

What would you propose me to try do now to get a better response?


----------



## brucek (Apr 11, 2006)

> When I do the measurements I notice that the input reading on the meter is a bit low - just around -24dB.. though I did setup up the volumes prior to the measurement..


Did you?

1) Run Check Levels in the Settings panel and select Check/Set Levels with Subwoofer as circled below and then set input level properly in that routine?









2) Did you then Calibrate the SPL meter with Use REW sub cal pink noise selected as shown below?









3) Did you then Set Target Level with the button that doesn't look like a button?









4) In the Measurement routine did you set the end frequency to 200Hz as shown?









5) When you Check Levels in this routine is the Input level not correct as shown below?









brucek


----------



## Tobias (Feb 20, 2007)

When I do the check levels I can't get it above around -21dB  And that's with the input set on maximum 1,000..

edit: But I followed the other steps you listed.. or.. I had C weighting tickeed when I clicked calibrate SPL - I should't have that?


----------



## brucek (Apr 11, 2006)

> I had C weighting tickeed when I clicked calibrate SPL - I should't have that?


Yeah, you should if you use a Radio Shack meter. Mine is a flat ECM mic....



> When I do the check levels I can't get it above around -21dB


Which Check Levels?

In the Settings routine or the Measurments routine?

brucek


----------



## Tobias (Feb 20, 2007)

brucek said:


> Which Check Levels?
> 
> In the Settings routine or the Measurments routine?
> 
> brucek


Can't get it in neither of them..

But when I do calibration for soundcard (the "Measure.." button in settings) - I can get an appropriate input reading..


----------



## brucek (Apr 11, 2006)

> Can't get it in neither of them..


And are you setting the volume control level of your receiver to read 75dB on the Radio Shack SPL meter at the listening position ? and you can't get the required input level control in REW to reach high enough? makes no sense...

brucek


----------



## Tobias (Feb 20, 2007)

Yeah.. the input level is 1,000 by default when I check levels.. I then set the volume control on my receiver, so it reads 75 on the meter. edit: So if I do this, the input level is no higher than around -21dB

If I turn more up on my receiver, or turn up the output volume I can get a higher reading tho.. but then it's obviously not reading 75dB on the SPL meter any more 

Im just confused


----------



## brucek (Apr 11, 2006)

> Im just confused


I am too, because the Radio Shack meter puts out lots of level and the soundcards line-in usually has to be turned down quite a bit to stop it from being in the RED of the VU meter.

You are using an RCA connector on the Radio Shack meter and you tried it as a microphone into your receiver and say that was fine, so why is the level not high enough into the soundcard.

You say you connected the stereo adapter to the Blue input on the soundcard. That is usually the line-in, but how do you know which channel is the correct one? Did you select the other channel other than the one you're using?

brucek


----------



## Tobias (Feb 20, 2007)

brucek said:


> You say you connected the stereo adapter to the Blue input on the soundcard. That is usually the line-in, but how do you know which channel is the correct one?
> brucek


Yeah I connected the RS Meter to the blue one.. I came up doing this based on some small icons on the back of my soundcard. There was two icons with an arrow down, one with a microphone, and one with an arrow up (I'm not sitting at my computer now, but I'm quite sure this is right).. I assumed the arrow up (the blue one) was the one to use for input. The green one had an arrow down, and I assumed this was the one to use for output - also considering that I would connect my PC speakers to this one.

What do you mean by: 


brucek said:


> Did you select the other channel other than the one you're using?
> 
> brucek


Are you talking about selecting left or right? 
If so, I have been using the right one, but actually I'm not sure if it's the correct one.. should it have any difference since I apparently have only one input on my soundcard (two outputs though)?

I can't remember if I tried selecting left instead of right..

Btw thanks for all your nice answers  It's really nice that you can help me this much


----------



## brucek (Apr 11, 2006)

> Are you talking about selecting left or right?
> If so, I have been using the right one, but actually I'm not sure if it's the correct one.. *should it have any difference since I apparently have only one input on my soundcard (two outputs though)?*


Don't you remember earlier I asked if you were using stereo connectors at the soundcards line-in and line-out and you replied yes?

The line-in and line-out are stereo connections. 

Each connection has a left and right channel. But REW only uses a single channel from the microphone.

You need to use a stereo plug into a stereo jack, but select only one channel (right or left) that you have your single cable connected to the meter and receiver.

You 'break out' the connection at the soundcard with a stereo to mono adapter. There are two types (shown below). These stereo plugs go into the line-in and line-out *stereo jacks* blue and green. The heavier type is a bit clumsy, so many use the wire type.


















So my question above was, "are you using the same channel in REW that you have connected at the soundcard?".. It's hard to tell with the adapters which is Left and which is the Right channel (without an ohm meter), so I wanted to be sure you selected the channel in REW that you had the cable of the microphone connected to, right or left channel?

brucek


----------



## Tobias (Feb 20, 2007)

Ahh this might clear something up 

I do use the adaptor (the first picture of yours).. but as the two channels on the adaptor didn't have any markings, I just assumed (possibly a stupid assumption ) that the two were identical.. so I actually just used one of them randomly.. I thought the input selection in REW corresponded to which input you used on the back of the soundcard.

Since I can't tell the two channels apart (and I don't think I can find a wire type - would have to buy one then).. should I just try with R and L respectively, and see if I can get a nice input response with either of them?

And what about output ? Is it important which channel I use for this one?


----------



## brucek (Apr 11, 2006)

> should I just try with R and L respectively, and see if I can get a nice input response with either of them?


Yes.......



> And what about output ? Is it important which channel I use for this one?


No, REW actually outputs the mono signal from the line-out jack on both its Left and Right channel for convenience. What you're selecting with the Left or Right button in REW is the input line-in Left or Right channel. What happens sometimes, is that people select the wrong line-in channel for where they have the cable connected, and the crosstalk between channels gets over to the other channel and that's the signal they receive, albeit very low....... could be your problem..

brucek


----------



## Tobias (Feb 20, 2007)

Hm.. when I switch to left I just get -86dB in input when it displays 75 dB, but -21 dB when I use right channel. This is the "Settings" check level button.

When I have set target level and go press check levels after pressing Measurement I also get a low input reading (seems like it's a few dB lower than the settings check level)...

So this didn't really help 

Could it be that the battery in the RS Meter should be changed or something as simple as that? (The needle goes up to batt. test when I set the wheel at battery test though)..


----------



## brucek (Apr 11, 2006)

> but -21 dB when I use right channel


Too bad - no joy there I guess...



> seems like it's a few dB lower than the settings check level


Normal...



> The needle goes up to batt. test when I set the wheel at battery test though


 Not the battery then.

Bad meter.

Bad cable.

Bad soundcard.

Bad adapter - try other channel 

brucek


----------



## Tobias (Feb 20, 2007)

It couldn't be some some soundcard setting somewhere? 

If not, I'm about to give up this calibration, or go buy a new soundcard, though this would probably not help sincee the loop measurement looks fine? 

I tried replacing the adaptor connecting the RS meter to the computer with a cable, as the one you had a picture of - this didn't help.


----------



## brucek (Apr 11, 2006)

> It couldn't be some some soundcard setting somewhere?


I don't know if you've told me what kind it is?

Can you post the soundcards mixer settings jpg so I can see?. Some people completely remove the soundcards software and restart Windows so that Windows can recognize and then operate the card and use its own drivers without all the junk included with the soundcards own software. You can try that and see if Windows has the drivers to operate it?

brucek


----------



## brucek (Apr 11, 2006)

If Windows only is in control, then you would use the Playback and Record Mixer of Windows as shown below... (I photoshop'ed them over the REW panel)









brucek


----------



## Tobias (Feb 20, 2007)

The soundcard is called SB Live! Value.

I don't think I have any creative drivers installed, at least I can't find them  I tried earlier to go to creative's website to update them, but there wasn't any updates available - maybe because it's a bit old card.

But here is the mixer settings, play and recording control:


----------



## brucek (Apr 11, 2006)

All looks exactly correct as far as the mixer goes..........

Does the Window Control panel give you access to the soundcard software and all the SB Live settings?

Even though this thread is for the SB Live External USB card, perhaps there may be some hints in it to help you with some strange setting you have turned on?

brucek


----------



## Tobias (Feb 20, 2007)

I think the only settings available are those you can set in the windows control panel.. I can't get access to some SB live settings or something.. so I can't really get any settings up similar to those in the other thread.


----------



## Tobias (Feb 20, 2007)

Another thing I just noticed is that when I click the SPL meter button, and then the red dot to start measuring.. it reads around 56-57 dB even though there's no sounds playing? Is this normal..?


----------



## Tobias (Feb 20, 2007)

I also just trieed to switch the wheel to 70 instead of 80 and then I get higher input (-12dB) when the meter is reading approximately +5 (so 75dB) - but it's a bit hard to read since the needle is moving more around...

sorry for many posts in succession


----------



## brucek (Apr 11, 2006)

> Another thing I just noticed is that when I click the SPL meter button, and then the red dot to start measuring.. it reads around 56-57 dB even though there's no sounds playing? Is this normal..?


Yep, that's the noise floor........



> I also just trieed to switch the wheel to 70 instead of 80 and then I get higher input (-12dB) when the meter is reading approximately +5 (so 75dB) - but it's a bit hard to read since the needle is moving more around...


The meter should be set to Slow and C-Weight. I use the 70dB setting on the wheel.

Try calibrating the whole thing at 80db and maybe that will be good enough to get you proper input level.

If nothing else, any cheap sound card will work. That card of yours is quite old...

brucek


----------



## Tobias (Feb 20, 2007)

brucek said:


> Yep, that's the noise floor........
> Try calibrating the whole thing at 80db and maybe that will be good enough to get you proper input level.
> brucek


So I should set the wheel on 80dB and set receiver volume so it reads 80 dB and then just go as usual?




brucek said:


> If nothing else, any cheap sound card will work. That card of yours is quite old...
> brucek


I will probably go buy some external one, so I can use my laptop computer instead.. would this one for example be okay? (I know it's in danish, but there's a picture )
http://www.edbpriser.dk/Products/Listprices.asp?ID=253466

Or one among these:
http://www.edbpriser.dk/Products/Listproducts.asp?ID=28&Parent=2&Sort=&Gallery=&Producent=0&Rating=0&Max=500&Soegeord=usb&Equal345=&Direction347=2&Sorted347=&Direction648=2&Sorted648=&Direction1183=2&Sorted1183=&Equal349=&Direction647=2&Sorted647=&Submit.x=14&Submit.y=11


----------



## brucek (Apr 11, 2006)

You might also try moving the Balance control slider of the Line-In RECORD over to the right to increase the gain on the right channel input..........









brucek


----------



## Tobias (Feb 20, 2007)

brucek said:


> You might also try moving the Balance control slider of the Line-In RECORD over to the right to increase the gain on the right channel input..........
> brucek


I can't move it.. it's locked in the center..?


----------



## brucek (Apr 11, 2006)

> I can't move it.. it's locked in the center..?


Looks like it isn't locked in the Playback screen. Try it there.............


----------



## brucek (Apr 11, 2006)

> So I should set the wheel on 80dB and set receiver volume so it reads 80 dB and then just go as usual?


Yeah, everything will just be at 80dB instead of 75dB..................


----------



## brucek (Apr 11, 2006)

> but there's a picture


Yeah, as long as it has line-in and line-out it will be fine............. you don't need all the 5.1 ****, but if it's there you just select stereo instead....... I suspect the Connect one would be fine (I don't read Danish) 

brucek


----------



## Tobias (Feb 20, 2007)

brucek said:


> Yeah, as long as it has line-in and line-out it will be fine............. you don't need all the 5.1 ****, but if it's there you just select stereo instead....... I suspect the Connect one would be fine (I don't read Danish)
> 
> brucek


I found some specifications about it on creative's site:
http://uk.europe.creative.com/products/product.asp?category=1&subcategory=207&product=15911&nav=0

Doesn't look like it has line-out, or am I just missing something?

Would just like to be sure that I don't buy it just to find out something is missing on it


----------



## brucek (Apr 11, 2006)

> Doesn't look like it has line-out, or am I just missing something?











brucek


----------



## allredp (Feb 7, 2007)

brucek said:


> Yeah, as long as it has line-in and line-out it will be fine............. you don't need all the 5.1 ****, but if it's there you just select stereo instead....... brucek


So, does this mean that my HTPC with 7.1 Realtek AC97 needs to be set to "stereo" in the Sounds options in my XP Media Center OS?

Thanks for the help--having fun getting started with REW (am actually stuck on "calibrating the soundcard!)...

--Phil:nerd:


----------



## brucek (Apr 11, 2006)

> So, does this mean that my HTPC with 7.1 Realtek AC97 needs to be set to "stereo" in the Sounds options


Yes....


----------



## Tobias (Feb 20, 2007)

What do you think I could do to improve my response brucek? 
Maybe turn up the gain on the sub? (It's on 50% now, and it's a SVS PCi 20-39), and then make some more filters to reduce the level? If this sounds as a good idea, how would you do it? 
I mean, if I turn up and calibrate as before I will just end with the same results.. I was thinking about leaving the target curve at the lower level, and then turn up the gain and make some filters.. or something like that 

I just ordered the SB connect soundcard so I should be able to make some new measurements with it soon, but I wouldn't be so surprised if the response was quite the same as with the old card 

Btw, I tried a measurement with adjusment to 80dB, and I got a higher input, but the graph looked quite much the same.


----------



## brucek (Apr 11, 2006)

> What do you think I could do to improve my response brucek?


Move the location of your sub. It's probably simply in a very bad spot. Try some other locations.

brucek


----------



## Tobias (Feb 20, 2007)

Well, I have already tried some different locations, and actually the response I posted on the bottom of page 1 is the best I've gotten so far..


----------



## brucek (Apr 11, 2006)

> actually the response I posted on the bottom of page 1 is the best I've gotten so far..


Do a one foot nearfield measurement of the sub to ensure all is well there..........

brucek


----------



## Tobias (Feb 20, 2007)

I just tried placing the meter on the floor (still pointing the mic up ) about one feet from the woofer.. I got this graph:









Is that okay?


----------



## brucek (Apr 11, 2006)

> Is that okay?


Well, it ain't your subwoofer that's causing your wacky response. It's the room. It's hard to get a decent nearfield with a ported sub, but that sub looks great.

ltr


----------



## Tobias (Feb 20, 2007)

brucek said:


> Well, it ain't your subwoofer that's causing your wacky response. It's the room. It's hard to get a decent nearfield with a ported sub, but that sub looks great.
> 
> ltr


That's good to hear since I was beginning to think something was wrong with the sub 

I just received my new external soundcard, and tried to do a calibration. This time the input wasn't any problem, and I ended up using an input volume of 0,237.

But the measurement from the listening position is pretty much unchanged though. I think I'm gonna try some alternative positions.. I might be able to squeeze it into a corner at one of the front speakers


----------



## brucek (Apr 11, 2006)

> This time the input wasn't any problem, and I ended up using an input volume of 0,237.


Yep... that's better.



> I think I'm gonna try some alternative positions.. I might be able to squeeze it into a corner at one of the front speakers


Another thing you should try is to use multiple sweeps, which reduces noise and random noise. Try doing a 256K sweep with x4 or x8 sweeps set in the Measurements screen....

brucek


----------



## Tobias (Feb 20, 2007)

brucek said:


> Yep... that's better.
> 
> Another thing you should try is to use multiple sweeps, which reduces noise and random noise. Try doing a 256K sweep with x4 or x8 sweeps set in the Measurements screen....
> 
> brucek


Okay thanks for the tip 

I just tried placing the sub at the corner and I took this measurement:









What do you think about that response? It's a bit more dippy at 50/70hz, but don't you think it's better this way? 

And another thing I would like to ask you is how I should read off the values of the RS meter. The needle is quite often moving some dB's up and down, so I'm getting confused which value it reads. So far I have been trying to find a value where it seem to settle down a bit.. but is this the right way to read off the value?


----------



## brucek (Apr 11, 2006)

> but don't you think it's better this way?


Yep....



> but is this the right way to read off the value?


Well, the switch should be on slow to give you the best chance, but just take an average reading off the meter - use the 70 position on the RS meter dial. 

The only reading you have to actually take is setting up the ~75dB at the listening position to get the that approximate target level and then match the REW SPL meter to it. Once you hit the set target level button, REW takes care of everything else. Don't worry about an exact 75dB setting - do your best.

You've obviously been successful, because your target line is around 75dB. If you find after you hit the REW set target level button and it returns 72dB or something, just redo your receiver level and REW SPL meter calibrate until you get an REW set target level around 75dB.

brucek


----------



## Tobias (Feb 20, 2007)

I have been puzzling around with the BFD filters now, I inputted the filters as proposed by REW, and tried to experiment with a few (added an extra one at around 40hz).. I tried a new measurement:









I think it's starting to look better  The dips aren't so big anymore.. though I haven't made any filter with +gain.. so actually I think that's a bit weird, but as long as it is getting better it should be fine


----------



## brucek (Apr 11, 2006)

Here's a trick. 

Shut the filters off in the BFD (IN/OUT Green LED off) and do a normal measure of the sub.

Once the measure is done, Manually lower the target line in REW by clicking the little Target Level thumbwheel to expose more of your response peaks above the target line. 

Now hit Find Peaks etc.
See what happened. 

You told REW to make the filters see more peak above the line and the filters are more aggressive....

Enter the filters and then turn up the subwoofer amplifier gain control a bit and see how it looks with the new filters entered (IN/OUT back on).

brucek


----------



## Tobias (Feb 20, 2007)

Thanks for the tip  I'll try that soon.



brucek said:


> Here's a trick.
> Enter the filters and then turn up the subwoofer amplifier gain control a bit and see how it looks with the new filters entered (IN/OUT back on).
> brucek


Then I'll be using a measured target level right?


----------



## brucek (Apr 11, 2006)

Well, the whole point is to trick REW into being a bit more aggressive with the peaks it finds and then the filters it recommends from those peaks. You shouldn't go too far, but if you lower the target line (after the regular measurement at 75dB is finished) to end up with more aggressive filters, the result will be a smoother response (to the corrected line in REW), but the added cut will lower the overall level of the sub, so after you enter the filters into the BFD, you need to compensate by adding some gain to the subwoofer amplifier........ If you cut down to a line that you lowered by -5dB, then you would have to add about 5dB to the subwoofers volume to compensate (by turning up the subwoofers amplifier).

Once you've got a raw measure you can see for yourself how it works by playing around with the target line and FIND peaks. Clear the peaks and move the target line and Find Peaks again and see what it does...

brucek


----------



## JohnM (Apr 11, 2006)

Don't forget to use "Optimise PK Gain & Q" after assigning filters, the initial REW assignments are just starting points for the optimisation, you must run the Optimise routine to get correct filter settings.


----------



## brucek (Apr 11, 2006)

> you must run the Optimise routine to get correct filter settings.


Yeah, good point John, I should have made that clear.....

brucek


----------



## Tobias (Feb 20, 2007)

Ahr I forgot the optimization of the filters  Got to remember this next time 

Btw, when I have made a measurement and added some filters.. should I then just go set the phase and gain on the sub as usual, using for example the AVIA calibration dvd?


----------



## brucek (Apr 11, 2006)

> when I have made a measurement and added some filters.. should I then just go set the phase and gain on the sub as usual, using for example the AVIA calibration dvd?


The phase and gain on the sub is set to obtain the best transition at the crossover frequency between itself an the mains using REW.

AVIA?

brucek


----------



## Tobias (Feb 20, 2007)

brucek said:


> The phase and gain on the sub is set to obtain the best transition at the crossover frequency between itself an the mains using REW.


Yeah I know, but what do you mean by "using REW"? How should I use REW for setting the phase?  Should I do a measurement with both mains and see how the response changes as I change the phase or something?




brucek said:


> AVIA?
> brucek


Yeah, a calibration DVD with various test tones etc:
http://svsound.com/products-parts-avia.cfm

It has some test tone called warble sweep (I think that's the name) where you set the phase at the setting with the smallest dips in loudness of the test sounds.
This is what I've used sofar to calibrate the phase. Though I haven't yet changed phase after I moved the sub.


----------



## brucek (Apr 11, 2006)

> Should I do a measurement with both mains and see how the response changes as I change the phase or something?


Yes.......... add the mains to the sub measurement and look at 80Hz and switch the phase around for the best transition.

brucek


----------



## Tobias (Feb 20, 2007)

brucek said:


> Yes.......... add the mains to the sub measurement and look at 80Hz and switch the phase around for the best transition.
> 
> brucek


I should then check levels with "Main Speaker" instead of Subwoofer, and calibrate SPL meter with "speaker cal pink noise" and target level using full range target curve?


----------



## brucek (Apr 11, 2006)

> I should then check levels with "Main Speaker" instead of Subwoofer, and calibrate SPL meter with "speaker cal pink noise" and target level using full range target curve?


No, you're still checking from 15Hz to 200Hz. Leave settings as if you were checking sub only, but redo the levels check. etc...

brucek


----------



## Tobias (Feb 20, 2007)

brucek said:


> No, you're still checking from 15Hz to 200Hz. Leave settings as if you were checking sub only, but redo the levels check. etc...
> 
> brucek


Okay


----------



## Tobias (Feb 20, 2007)

I tried setting the phase as you proposed, and I came up with this graph as the best result:









I'm a bit worried about the lower end? Below 35hz the response is pretty low compared with the target level. But this wasn't what I got at the sub only measurement..


----------



## Tobias (Feb 20, 2007)

Does this indicate that the gain is too low, so I should raise it a bit? I remember now that I turned the gain a bit down after measuring the sub alone and setting the filters - but that was because it was louder than the speakers (according to the test tone (from the AVIA dvd).


----------



## brucek (Apr 11, 2006)

> Does this indicate that the gain is too low, so I should raise it a bit?


Yep, exactly...... and you may need to use a filter around 45hz too......


----------



## Tobias (Feb 20, 2007)

Hi again bruce 
I have been trying to do the calibration/setting of filters again, and I tried lowering the target curve as you proposed. But when I assign the filters the dips that where dips at the "real" target curve (and not so large dips at the lowered target curve) they become quite a bit larger when I set filters and optimize them (becoming more like the size of the dips at the "real" target curve).. ain't that a bit weird?

edit: And I keep getting the response higher than the target after setting filters..


----------



## brucek (Apr 11, 2006)

> ain't that a bit weird?


Not really. You have to do some manual filter adjustments to fine tune.

Hard to comment without some visuals....

brucek


----------



## Tobias (Feb 20, 2007)

After inputting some filters I got this graph:









This is the sub playing only.


----------



## brucek (Apr 11, 2006)

> I got this graph


Looks great to me.....

brucek


----------



## Tobias (Feb 20, 2007)

brucek said:


> Looks great to me.....
> 
> brucek


It's not too much above the target curve?


----------



## brucek (Apr 11, 2006)

> It's not too much above the target curve?


That isn't important. The fact that it tracks the target is the key. The amount it is wholesale above or below is a matter of gain offset. You can twiddle that yourself if you like using the trace offset (under trace adjustments) to realign it to see how it tracks.

Now that you know your sub tracks the desired curve, you can add the mains and set a level between the two that you like and check for any interaction at the crossover.

brucek


----------



## Tobias (Feb 20, 2007)

So this is how my response is now, with both mains playing too:









I tried doing a quick measurement turning off the sub and I got this:









Maybe I should try add an extra filter at 45Hz (though there are filters around that frequence already)?


----------



## Tobias (Feb 20, 2007)

Hi again  I have recently been thinking about buying new main speakers or amplifier, but as I read through reviews and articles I see that many recommend trying to do something about the room acoustics before buying new equipment (which sounds reasonable ). The problem is that I have not much knowledge about it and how to figure out what to do to improve on it.

So I thought I would take a measurement on a larger frequency range to (maybe?) help in figuring out how to make the improvements.
I tried measuring to 10kHz, but I was in doubt wether to use check levels with subwoofer or main speakers, and fullrange or subwoofer for target level. I ended up using the same settings as when measuring the sub. The graph I got is very unstable at higher frequencies.. is the graph making sense or am I doing something wrong?

I hope it's okay that I ask again  

Here's the graph:


----------



## brucek (Apr 11, 2006)

> is the graph making sense or am I doing something wrong?


Graph is quite normal. Reflections cause comb filtering which makes it difficult to see the underlying trend of the response. To solve this problem (with full range measurements only), turn on some smoothing once you've taken the measurement in the Trace Adjustments section to the left of the graph. There is a selection of rates there up to a full octave.

brucek


----------



## Tobias (Feb 20, 2007)

Okay thanks


----------



## Tobias (Feb 20, 2007)

Do you have any tips on how I could figure out what to do to improve the acoustics in my room?

I've read about a method where you have someone moving a mirror along the sidewalls and then you sit in the listening position, and at the points where you can see the front speakers you should put up some material. But I don't know what material to use, or how big it should be..


----------



## brucek (Apr 11, 2006)

You should post that question in the Home Audio Acoustics section.

brucek


----------



## Tobias (Feb 20, 2007)

Yeah okay, I will try that


----------

