Sub Graph. What do I do now.

Mike-M

Active Member
I've generated a graph on REW but don't know how to export it so I can post it on here and get some advice on where to go from here. It doesn't look like any I've seen on here so I've more than likely done something wrong but I've followed all the instructions correctly as far as I can tell. So how can I get it posted here.
 

chrisgeary

Well-known Member
you should see a disk symbol in the corner of the graph somewhere (cant remember which corner). i think thats the export button
 

bob1

Well-known Member
You seem to have recorded the frequency response of an F-15 from one meter. :)
Could be, but i bet he didn't calibrate the levels correctly.
 

Mike-M

Active Member
I don't know if your taking the :censored: or not lads. I know I've more than likely done something stupid, but your not helping.
 

mattkhan

Distinguished Member
I don't know if your taking the :censored: or not lads. I know I've more than likely done something stupid, but your not helping.
if you post the method (by which you arrived at that graph) in order then some comments may follow. Hopefully you don't experience the site through a screenreader as based on that graph you have no ears left :suicide:
 

Mike-M

Active Member
I believe I followed the instructions from the help files to the letter. Obviously I've done something very wrong. I don't have chance to try it again over the weekend so I'll try next week, make a note of exactly what I do and see how that goes.
 

Nimby

Distinguished Member
It seems obvious that you did not calibrate your levels when you started.

The only other explanation I can think of is that you scrolled your mouse once you had your sweep graph showing.

Start your next session of REW by getting the sound level to show 75dB on your SPL meter. Then ensure this is matched by the REW SPL (dB) readout on your monitor screen as the calibration pink noise signal is played by your subwoofer.

The next important step is to set your graph limits to 45-105dB vertical scale and 20-200 Hz horizontal scale and click on Apply.

Make sure you test only your subwoofer with your speakers muted.

The SPL meter should be at ear level at the listening position.

Small changes in microphone (SPL meter) position may affect the results depending entirely on the room.

Save your graph as a JPEG using REW by clicking on graph at top left and the Save graph as JPEG.

Upload the graph image to a free hosting service like Imageshack, Photobucket etc. If you use REW's default image size it will show as a decent sized image when you post it here. To post an image on the forum you paste the direct link given to you by the hosting service in the box provided by clicking on the little postcard symbol just above the post composing box.
 

Mike-M

Active Member
Well I've had another go at this and the results are attached. I am sure that the SPL and Soundcard are callibrated correctly. I have repeatedly set checked and double checked the sound level and am sure that it was correct but the resulting graph tells me different. I'm beginning to think life is to short for all this. Nimby, I know the graphs scale is not what you said it should be but I had done it before seeing your post. I may have another go if/when I can work up the enthusiasm.
 
F

fullthrottleric

Guest
Thats more like it ...ish, now the levels look seinsible :smashin:

Now you need to apply 1/3 octave smoothing to the curve to get rid of all that noise.

You also need to adjust your graph limits, you need the vertical to be 45db minimum and 105db maximum, yours is currently 0 and 90. Next you need to set the horizontal to 20Hz and 200Hz, currently your's is 20 and 20000.

Don't forget to set the graph to log instead of lin too :thumbsup:
 

kick ass sub

Standard Member
heh, through some great help from the guys at HT shack I managed to get a few steps further in the proces of calibrating my sub.

I'm not sure I'm doing the right thing here and I don't know very well how to interpret the graph. First I connected the soundcard to my receiver with my left speaker integrated and set it to cd mode (as the though coax dvd mode it didn't work). I did the checking levels routine and got to 12db both on the input and output VU meter while my SPL meter pionted to 75db. But during the measurement routine the headroom indicated that there was some clipping during the proces of the sweep sound. So I'm not sure if I did the measurement at the right level, although the level seemed to be fine during the pink noise rumble.
I did about 4 sweeps and first set to played in one minute and later over 20 seconds as it didn't made any difference.

graph_soundcard_4.jpg

The result made me feel even more confused. If I interpret this graph correct then it seems that between 20hz and 30hz there is a dip. I find hard to believe as during a lot of bassy scenes beneath 30hz I sence a boom. especially during the WOTW scene just after Tom Cruise says "it's freezing" there is this long continues boom that goes louder and louder.

graph_measurement_1.jpg

I also didn't expect the 40hz peak. I'm almost sure that the booming sound is located around 25Hz.

anyway, I tried to set some parametric filters for the 40Hz peak but I though I should try to set a filter for 20Hz of about 0.5 octave wide. The result was that the boom was much less, I still felt the bass beneath 20Hz but still missed a bit of punch above 20Hz.

Can someone help me and say if I did the measure properly and where I should best set the filters?
 

Nimby

Distinguished Member
I am at a loss to know why you cut at 20hz.

40Hz and 75Hz seem the obvious frequencies to start cutting to get a flatter response.

A boom below 25Hz would be all but unnoticeable as it lies on the threshold of inaudibility where the infrasonics start to take over.

A 10dB peak at 40Hz would be very noticeable. You might get away with the 5dB peak at 75Hz since it lies close to the crossover and the speakers might affect things.
 

AngelEyes

Distinguished Member
you really need to keep the graphs top the same scale so we can all see what is going on more easily. As nimby says the boom is pretty obviously the 40hz peak. just because a scene has 25hz effects doesn't mean there isn't also sound at 40hz, so the peak there is causing the boom.

I think the reason the boom was reduced when you crushed the 20hz area is because it was a wide enough cut to pull down the 40hz peak a bit but as mentioned your changing the scale doesn't help make things clear ;)

Tame the 40 and 70ish peaks and that should sound a lot better.

Adam
 

Nimby

Distinguished Member
40Hz is a harmonic of 20hz.

Reducing 20Hz with a filter may actually reduce 40hz if your sub produces lots of harmonic distortion.
 

kick ass sub

Standard Member
I've been testing and tweaking a lot the past few days and got rid large 40 peak and 60ish and 70ish peak. I also slightly pushed the 50Hz dip to get a bit more punch there.

And you're right, the 20Hz reduce wasn't necairly at all so I deleted that filter. The scene with the tripod coming out of the ground is now without the terrible boom but still has that fantastic punchy kick I needed. It immediatly brought a grin on my face. So there's defently an improvement.

I emidiatly started playing all demo scenes from my dvd collection like Master & commander, saving private ryan, Pirates of the carrebean 2 and even Die Another Day. Saving Private ryan also had a terrible boom with deep explosions before but now is more controled and nicer to listen at and even the canon fire in Master and commander (witch didn't really cause much boom) sounds more controled and let's it presence feel more then hear now. But the scene that surpriced me most was the intro of Die Another Day. When 007 surfs on the gaint roaring waves there was also a terrible boom before. But now it's just plain controled bass with much weight to it. Also explosions are much more controled and tighter.
This BFD really is a great tool and something that can't be missed when having a descent sub as the PB10. Bass is much more controled now and much nicer to listen at without getting a headake. But mostly the bass tones in music scores are easier to follow without the muffled boomy bass tones that I had before. I also have the feeling I can turn the sound up a few db's louder.

I still wonder if it's worth of getting rid of that wide dip between 21Hz and 34Hz and if that would be healthy for my sub? I read somewhere that increasing the bass for such deep tones can bottom a sub and it's better just to place the sub better, but for me that's curently no option. After all it's only a dip of about 3db too low.
 

AngelEyes

Distinguished Member
I am glad you are hearing improvements. Can you post your new graph so we can comment?

Thanks

Adam
 

kick ass sub

Standard Member
final.jpg


This is one of the most recent graphs I took. My graph now would probebly look the same exept that I reduced the 75Hz peak a bit more and pushed the 50Hz - 55Hz dib up by 2db at 0.5 octave. As you can see the 40Hz peak is as good as gone. Only the small but wide dib between 22Hz and 34Hz is still here.
 

AngelEyes

Distinguished Member
You could increase the subwoofer level (raising the whole line by 5db) and bring the dip to the target line then cut the 'new' peaks between 35 - 50 hz. This should be better than boosting a trough, although I would personally leave the 20hz peak as it will give a little boost to the really low frequencies :)

I hope that makes sense...


Adam
 

AngelEyes

Distinguished Member
I have to say I am somewhat jealous of you, I can't get Rew to work properly with my sound card, I just get stupid readouts which is really annoying as I really want to have another fiddle :mad:
 

Nimby

Distinguished Member
I'm not convinced that boosting the gain overall and then cutting peaks isn't much the same as boosting troughs.
It may actually take more power from the sub's amplifier possibly increasing the chances of clipping.

Which soundcard are you using? Any chance you can pick up a USB external card like the Creative SB Live! ?
This card has proved popular and is well supported by REW and the HT Shack's specialist REW forum and its help files.
 

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