Waterfalls

[atledreier]

That seems to somewhat contradict your general advice to use broad filters, Wayne. I use your advice with good results, but whatever works.. I'd like to know more about this.

[JohnM]

The amplitude and phase response of EQ filters is inextricably linked. What the passage says is use narrow filters to counter narrow effects, i.e. modal resonances. To counter a mode the corresponding filter needs to match it precisely, which is why smoothing should not be used when viewing responses with the aim of addressing room modes. The waterfall plot is a good indicator of whether a filter's bandwidth and centre frequency are correct to deal with a mode - it is difficult to do this with the initial response alone as the overlapping effects of the various modes can make it hard to separate them, as the waterfall progresses the strongest modes (which most need correcting) stand out as the response around them decays, making it easier to work out the filter settings needed to address them.

All that is not an argument against broader filters for response shaping, that is another tool in improving the overall response and the only one that can be usefully applied above about 200Hz as modal eq filters would only be effective over a very small area at such frequencies. Both should be combined with careful placement of speakers and listener to start with the smoothest response that can be practically achieved in the space and whatever room acoustic treatment can be accommodated, even sympathetic choice of furnishings, drapes etc can be very beneficial.

[Wayne A. Pflughaupt]

Okay, so basically phase shift and modal ringing are the same thing. So in essence what the Rane man is saying here...

In fact, it can be argued that phase shift is the stuff that causes amplitude changes. Amplitude, phase and time are all inextricably mixed by the physics of sound. One does not exist without the others.

...is that change in modal ringing (phase) from an equalizer is no big deal. I agree.

atledreier wrote:

That seems to somewhat contradict your general advice to use broad filters, Wayne. I use your advice with good results, but whatever works..

I get the impression he’s mainly talking theory more than practical application, because...

Only by adding many precise, narrow phase shift and amplitude corrections do you truly start equalizing a system's blurred phase response.

...for one, I don’t know of anyone who makes an equalizer like that – i.e., allows for numerous highly-precise filters.

Second, I assume he would know that it would be impossible to achieve this for every location in a room.

Third, from what I understand, room modes as we know them in our little rooms are not a significant problem in the large rooms you typically see in Rane’s world.

Regards,
Wayne

[Wayne A. Pflughaupt]

JohnM wrote:

To counter a mode the corresponding filter needs to match it precisely...

Am I the only one who has “repeatability” problems? A measurement I take say, today is a little different than what I got back in the summer, or even last week - different enough for REW to generate slightly different modal filters. Which are the precisely-perfect filters for the room mode?

Regards,
Wayne

[terry j]

Wayne A. Pflughaupt wrote:

Am I the only one who has “repeatability” problems? A measurement I take say, today is a little different than what I got back in the summer, or even last week - different enough for REW to generate slightly different modal filters. Which are the precisely-perfect filters for the room mode?

Regards,
Wayne

How much natural variation would you get between measurements over a period of time, given that the mic is probably not exactly in the same spot, small changes may or may not have been made in the room, different ambient conditions etc ?

I know the bass is not as twitchy as the mids and highs etc when the mic moves just a bit, but are the minor changes in the bass from different mic positions enough to account for what you are talking about?

[atledreier]

I'd say screw EQ for anything over deep bass, and treat the room! That's what I do, and I'm very happy. I do one filter at 33Hz and that's it!

[Blaser]

atledreier wrote:

I'd say screw EQ for anything over deep bass, and treat the room! That's what I do, and I'm very happy. I do one filter at 33Hz and that's it!

You are one lucky man!

[JohnM]

Wayne A. Pflughaupt wrote:

Am I the only one who has “repeatability” problems? A measurement I take say, today is a little different than what I got back in the summer, or even last week - different enough for REW to generate slightly different modal filters. Which are the precisely-perfect filters for the room mode?

Filter settings are likely to need tweaks to get the best match, the waterfall plot is helpful in assessing what tweaks are improving the result. For good results the centre frequency needs to be within 1% of the mode's frequency, the bandwidth settings is less sensitive. Once the right values have been found they won't change unless the room is changed in some way (altering the modes), or the sub is moved, or you measure at a different position.

[Wayne A. Pflughaupt]

John,

Is there any particular reason why these graphs are displayed in a 300 ms window and not some other value?

Regards,
Wayne

[JohnM]

That's just a convenient starting point that is often suitable for looking at low frequency behaviour, can dial in whatever window width and time span you find appropriate, bearing in mind that shorter windows decrease frequency resolution (the resolution is shown next to the window control).