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11 minutes ago, Primare Knob said:

Yes, that is correct. I have a small gap between the wall and the sub, and placed the mike there close to the floor.

There will be variations between the same positions, as I did it by hand. My intentions are to find possible locations to place pressure based traps.

So, the highlighted results on your charts, are not the ideal places for traps.... They're just higher because they are very close to the source.

 

You don't need to measure anything to know where to place it.    If you are targeting (for example) 100Hz.... then you work out which path lengths in the room correspond to the 100Hz mode .... and then you put that trap where it will be in that path.

 

 

http://www.hunecke.de/en/calculators/room-eigenmodes.html

 

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5 hours ago, davewantsmoore said:

but you also have a quite low decay time now (how much absorption surface area is there in the room now?) .... and so I would probably want to put something in front of them to prevent non-bass frequencies from being absorbed so much  (although that is personal test to some degree).

I just went back and looked more closely at the RT times posted earlier - I hadn't taken enough notice of the "Y" axis - I agree with Dave - any more absorption needs something in front to reflect higher frequencies...

...but IMHO based on that RT graph the low bass is "nearly there" also! if not good enough already

 

I take back my comments above regarding the need to clip/channel/gyprock!

 

As an experiment I would wrap your existing Superchunks in builders' plastic (ugly but cheap and quick).

The low frequency performance should improve and reduce high frequency absorption.

You want to get the RT times a bit more consistent across the frequency bands - and a small increase below 50Hz or so is expected.

Note sure if I've posted the Acoustic Frontiers "Measurement Standards for 2 Ch Rooms" in this thread already?

http://www.acousticfrontiers.com/wp-content/uploads/2011/10/acoustic_measurement_standards.pdf

 

You may get to sufficient low freq absorption just with the plastic on your existing traps, but some more "similarly" sized absorption traps (also wrapped in plastic) should get there.

You can always put some slats over the plastic later in a 1D BAD pattern to get some diffusion (or fancy 2D masks).

 

Muck with speaker/sub position/EQ from there...are you trying to get smooth bass across multiple seating positions? Something like Multi Sub Optimiser (MSO) may assist (a free tool) if you have the ability with DSP to apply delay and EQ individually to subs.

 

cheers

mike

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31 minutes ago, almikel said:

I just went back and looked more closely at the RT times posted earlier - I hadn't taken enough notice of the "Y" axis - I agree with Dave - any more absorption needs something in front to reflect higher frequencies...

...but IMHO based on that RT graph the low bass is "nearly there" also! if not good enough already

 

I take back my comments above regarding the need to clip/channel/gyprock!

The chart doesn't show below 60, and is 1/3 smoothed  ;)  

Quote

As an experiment I would wrap your existing Superchunks in builders' plastic (ugly but cheap and quick).

Maybe, but I would like to see the before/after data for the 'superchunks'.... I know whether it was them which made the decay so low .... or what is going on.    I just can't say anything useful without more info.

 

 

Judging my the excess group delay.... I'd just be using EQ only  .... or at least I would be forcing the response to be flat with EQ, before I looked at any decay charts, or distortion charts, or anything.

http://www.acousticfrontiers.com/201163hard-proof-that-equalization-kills-room-modes-html/

 

Then you will get a clear idea of what room effects need to be solved.

 

1.  Put subwoofers in their places, selected by the flattest measured response (if you have multiple subs, then the flattest sum)

2.  EQ the subwoofers to be flat (and then apply low pass filter)

3.  Look at the decay of the woofers ..... and perhaps install bass traps to fix it

4.  Repeat

 

 

... by doing the above, you do certain things:

  • You only look at solving room issues, which need to be solved  (ie. after the speaker is setup properly)
  • You are never comparing A and B, where they have different frequency responses.    Every single chart you ever produce will be a "flat" (or close enough to) frequency response.    (This is really really important)

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20 minutes ago, davewantsmoore said:

great link - I'd not read that before - I need to spend more time surfing their site!

I've never doubted EQ fixes both the FR and ringing for "minimum phase" regions - although I'd be wary of such narrow/hi Q cut described.

Applying narrow EQ works if the region is "minimum phase", but generally the higher the Q/narrower the EQ cut, the more position dependent it becomes.

 

As you already know, DSP and the EQ capability it brings can be used for good and evil - well implemented it is very good -  when poorly implemented EQ has the ability to make things much worse.

 

It's fantastic we have free tools like REW that show us things like "regions of minimum phase" - in these regions EQ will fix both FR and ringing in the room's response.

Outside of these "minimum phase" regions, I wouldn't use any EQ at all for room issues.

 

I bolded room issues - I still use EQ to fix the FR of a speaker (which is typically "minimum phase"), or apply broad EQ "shelves" to taste such as a room curve, or bass/treble "tone" controls.

 

cheers

Mike

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1 minute ago, almikel said:

although I'd be wary of such narrow/hi Q cut described.

Yes, you'd want to make sure you'd checked the accuracy of the measurements, and all listening positions.

 

FTR, I wouldn't be boosting any dips.... as they're total cancellations.

1 minute ago, almikel said:

As you already know, DSP and the EQ capability it brings can be used for good and evil - well implemented it is very good -  when poorly implemented EQ has the ability to make things much worse.

That's no difference from the crossover filter inside any speaker ...... "DSP" lets you have sharper filters, but I think they are rarely required.

1 minute ago, almikel said:

 

It's fantastic we have free tools like REW that show us things like "regions of minimum phase" - in these regions EQ will fix both FR and ringing in the room's response.

Outside of these "minimum phase" regions, I wouldn't use any EQ at all for room issues.

PKs data, if correct,  shows it is entirely minimum phase. 

 

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