Need help with REW - can't get reasonable measurements

[Tobias]

brucek wrote:

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 wrote:

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]

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]

brucek wrote:

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]

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]

brucek wrote:

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]

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

sub_right_corner_with_bfd_and_mains_1.jpg

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]

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]

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]

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]

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]

After inputting some filters I got this graph:

sub_with_bfd_1.jpg

This is the sub playing only.

[brucek]

I got this graph

Looks great to me.....

brucek

[Tobias]

brucek wrote:

Looks great to me.....

brucek

It's not too much above the target curve?

[brucek]

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]

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

sub_and_mains_bfd_2.jpg

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

mains_1.jpg

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

[Tobias]

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:
15hz_to_10khz_2.jpg

[brucek]

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]

Okay thanks

[Tobias]

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]

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

brucek

[Tobias]

Yeah okay, I will try that