Theoretical room - possible to create a frequency response? - Home Theater Forum and Systems - HomeTheaterShack.com

Old 04-30-12, 05:58 AM Thread Starter
Shackster

Join Date: Apr 2011
Location: Leeds, UK
Posts: 34
Theoretical room - possible to create a frequency response?

Can REW be used to create a frequency response for a theoretical room?

It seems like it would be able to as it has the ability to add modal peaks one by one to create an overall frequency response.

I guess it would only be useful in the design stage - when you can actually set the room dimensions - and even then it'd only work for cuboid shaped rooms (at first at least) - but even that would still be useful for loads of people.
pitchtwit is offline

Old 04-30-12, 10:07 AM
Senior Shackster

Nathan

Join Date: Mar 2009
Location: Lincoln, UK.
Posts: 110
Re: Theoretical room - possible to create a frequency response?

Yes, if they're cuboid.

You supply the room dimensions, absorption factors for the boundary surfaces along with your speaker position and your listening/measuring position, and it gives you a simulated response. As far as I can tell, that includes all the modes and the quarter wave frequencies from the back wall (or knowing JohnM, all the walls ).

John is considering (well if I lobby him hard enough) putting mode annotations as an overlay over these response graphs -real and simulated. The math gets much harder for non-cuboid rooms.

You've just reminded me, I didn't ask for quarter-wave frequencies in the FR!!

>
planetnine is offline
Old 04-30-12, 03:00 PM Thread Starter
Shackster

Join Date: Apr 2011
Location: Leeds, UK
Posts: 34
Re: Theoretical room - possible to create a frequency response?

That's great news I'll look into that. Do you know what technique the maths is based on? I know of one technique that appears in Kuttruff's book - Room Acoustics 5th edition - equation 3.10 or 3.16, and then I've recently read of two other newer techniques outlined by Trevor Cox, Peter D'Antonio and Mark Avis in their paper, 'Room Sizing and Optimization at Low Frequencies' (2004). I'm interested to see how REW does it.
pitchtwit is offline
Old 04-30-12, 03:16 PM
REW Author

John

Join Date: Apr 2006
Location: UK
Posts: 6,296
Re: Theoretical room - possible to create a frequency response?

REW's modal simulator is a simple tool to generate axial mode responses, it was made to produce test data for the modal analysis tool rather than accurately simulate a room. I have a version that uses the image source method to produce a complete modal simulation response, but it is much slower and I haven't enabled it in the released builds - don't have anything to validate it against.
JohnM is offline
Old 04-30-12, 03:25 PM Thread Starter
Shackster

Join Date: Apr 2011
Location: Leeds, UK
Posts: 34
Re: Theoretical room - possible to create a frequency response?

Ah okay, so it's based on axial modes only - that's good to know - and obviously that's fair enough - it's not what the program was intended for after all. How about empirical validation?
pitchtwit is offline
Old 04-30-12, 03:29 PM
Senior Shackster

Nathan

Join Date: Mar 2009
Location: Lincoln, UK.
Posts: 110
Re: Theoretical room - possible to create a frequency response?

Build a concrete box!!

>
planetnine is offline
Old 05-01-12, 02:48 AM Thread Starter
Shackster

Join Date: Apr 2011
Location: Leeds, UK
Posts: 34
Re: Theoretical room - possible to create a frequency response?

I just have a couple of questions on the settings I can input on the 'Modal Simulation' section.

1) What does Noise level (%) mean?
2) What do the filter responses represent and how are they used?
pitchtwit is offline
Old 05-01-12, 02:50 PM
REW Author

John

Join Date: Apr 2006
Location: UK
Posts: 6,296
Re: Theoretical room - possible to create a frequency response?

The noise control is to add noise to the signal - for testing the modal analysis routines in the presence of varying amounts of noise

The filters are to allow a subwoofer's response shape to be emulated, with a 12dB/octave lower cutoff at the sub's lower limit and a pair of upper filters to give 24dB/octave high end roll-off akin to a bass management low pass.
JohnM is offline
Old 05-02-12, 04:41 AM Thread Starter
Shackster

Join Date: Apr 2011
Location: Leeds, UK
Posts: 34
Re: Theoretical room - possible to create a frequency response?

Ah - that's simple enough, thanks for that

Are there any plans to add tangential and oblique modes at any point? Just out of interest.
pitchtwit is offline
Old 05-02-12, 03:08 PM
REW Author

John

Join Date: Apr 2006
Location: UK
Posts: 6,296
Re: Theoretical room - possible to create a frequency response?

As I mentioned above, I have a version that uses the image source method to produce a complete modal simulation response, but it is much slower and I haven't enabled it in the released builds - need a way to validate it and some time to turn it into something more useful. The time is the harder part to track down
JohnM is offline

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