So what does this all mean? REW graphs...

[davewantsmoore]

The CSD is hard for me to understand.

 

Yup.    What you are seeing in the frequency resolution reduced (what we were just talking about) in order to show you high resolution time data.

 

They're all meaningful of course, but can take practise to read.   ETC is the one I focus on for placing speakers, or other things in the room.

 

 

Editorial Note Regarding CSD by Dr. Floyd Toole:

Because of the time gating, necessary to see into the time domain, frequency resolution is sacrificed – note the smoothness of the curves. This means that energy in a high-Q resonance is spread over a wider frequency range, resulting in an artificially low level.  Besides all of this decorous displaying of data, the fact is that, except at very low frequencies, humans do not hear the ringing, we hear the spectral bump (which, ironically in these displays cannot be accurately seen).  See Section 9.2.1 in my book [1]. See also Figure 13.23 p. 246 for examples of the “uncertainty†principle as applied to waterfall displays of data.  You have a choice of seeing high resolution in time or frequency domains, not both.  They are pretty, though.

 

http://www.audioholics.com/loudspeaker-design/loudspeaker-measurement-standard/CSDsample.jpg/image_view_fullscreen

 

In perceptual terms, the audibility of ringing is substantially reduced by a phenomenon known as “forward temporal masking†– the initial sound reduces the audibility of sounds that immediately follow it.

[1] F. Toole, Sound Reproduction: Loudspeakers and Rooms. Burlington, MA: Elsevier, 2008

Edited August 6, 2015 by davewantsmoore

[Pieface]

I continue to fuss around from time to time with the microphone. A few flashes of inspiration that typically wither under the harsh glare of empirical assessment. My latest little thought trail has taken me down an interesting path...

 

 

Consider these two FR taken from the MLP with an 80Hz crossover in place. My initial reaction was that the light blue trace is superior but a little delving revealed that the light blue response was made up of the following outputs of my two subs:

 

 

Whereas the green trace (Turned it pink now somehow sorry) consisted of:

 

 

It looks to me like there is not as strong modal impact on the individual sub responses even though the combined response is not quite as flat as the alternative MLP. Does it matter?

 

Moving the microphone laterally across the couch seems to indicate it might...

 

Strong modal impact on individual sub FR:

 

 

The right seating position (red trace) cops a nasty null at 55hz.

 

less modal impact on individual sub FR:

 

 

Here seat to seat is much more uniform (yes 8dB difference between left and right seats may be a problem for some people)

 

The difference in mic positions was less than a foot closer to the front wall.

 

Conclusions:

 

Measuring at only the MLP can be misleading

Placement of subs and listening position is most important

Maybe I need another sub or two for smoothing purposes

 

Small room acoustics are very frustrating

 

 

 

 

 

 

 

 

Edited November 6, 2015 by Pieface

[davewantsmoore]

even though the combined response is not quite as flat as the alternative MLP. Does it matter?

 

 

In general I'd be choosing the listening position based on other things than this... but impossible to say without knowing the room.

[Pieface]

I hate the room, you don't want to know it I think a rectangular room would be a lot more predictable.

 

I realised I had stuffed up the graphs...too many damn measurements gets your eyes crossed! The story is still the same but the FR at the MLP are more similar than I originally posted :s All fixed.

 

Placement of the speakers and the LP (and the damn mic) in the room make such a big difference to what you see and with relatively minor positional changes too. It's quite the anti-dote to the "get dual subs and win" attitude that prevails at some AV-type forums.