Room Optimisation (pt 2)

Does that mean that ' Bohemian Rhapsody ' is sounding as it should ?

And pretty much everything else!

What are you using to take the measurements and generate the graphs?

Can I take these measurements from my iPad ?

Microphone is a miniDSP UMIK-1

Software is Room Equalisation Wizard (REW)

Sort of, in a limited way, and with much reduced accuracy.

If you play a white noise signal and use a Real-Time Spectrum Analyser (aka a RTA) then, to some degree you can determine the in-room frequency response, but the accuracy of the iPad microphone is no where near as good as a calibrated instrument.  This is how I started out before getting the UMIK-1 though.

OK, a little more information on the room layout

The room is 4.25m x 3.75m x 2.02m.  The walls are plastered stone 600mm thick.  The ceiling is plasterboard, the floor is timber boards on 150mm joists with a thin carpet.  So fundamentally its an acoustic nightmare, with resonance peaks at the room modes in excess of +27dB.

The main speakers fire across the short dimension but can't be place symmetrically in the room.  Their locations (ref to the front and side walls respectively) are  L: 880mm, 900mm  R: 880mm, 750mm.

Behind each speaker, extending into the corners and floor to ceiling, are four broadband pressure mode absorbers.  These absorbers use a lightweight damped membrane that absorbs 35Hz-200Hz (with a reduced absorption up to 500Hz).  They consist of glass wool within a plastic membrane that's (almost completely) sealed on all six sides.  The absorbers are 450mm x 450mm x 1.2m each.  On the opposite wall are two more absorbers in one corner.  There are two more absorbers on the side walls near the back corner.

The sub is on the rear wall about half way along:  This gives the best balance between reduced excitation of the 40Hz and 44Hz modes and the dip 100Hz - 200Hz

Adding each absorber near a corner reduces all the 40Hz - 45Hz and 80Hz resonances by about 1-1.5dB depending on it's precise location.  The cumulative bass absorption effect is about 15dB on all the fundamental room modes.

The absorbers are made by Knauf insulation and are described as "DriTherm Cavity Slab 37", used still in its packaging.  Cost: £15 per item.

Finally, the working copy of the audio files has had a -5.5dB correction applied at 42Hz and 80Hz using the batch processing capability of Audacity.

Looks good!

What kind of bass traps are you using?

H

"...

These absorbers use a lightweight damped membrane that absorbs 35Hz-200Hz (with a reduced absorption up to 500Hz).  They consist of glass wool within a plastic membrane that's (almost completely) sealed on all six sides.  The absorbers are 450mm x 450mm x 1.2m each.

..."

"

...

The absorbers are made by Knauf insulation and are described as "DriTherm Cavity Slab 37", used still in its packaging.  Cost: £15 per item.

..."

There are 12 of them!

Those response curves.... that much data in the FFTs below 100Hz? Really? *Really*? Hmmmm

what software are you using?

REW as previously stated.

It analyses a logarithmic frequency sweep rather than a FFT of a constant noise signal, so yes there is an even amount of information in each octave band.  It also uses 1/12 octave smoothing, so that helps to suppress noise in the analysed data.

Hi Huge,

What kind of correction can Audacity perform.? Is it parametric equalisation or something more sophisticated? I'm using parametric equalisation in real time(*) with Audirvarna and really pleased with the results but always happy to find out if there is a better solution.

* - not quite real-time, Audirvarna applies the equalisation whilst reading each file into RAM, then plays the pre-loaded and equalised file from RAM.

Allan

Audacity can has both graphic and parametric equalisation (along with adjustable HF & LF slopes).  However in batch mode it can only apply one parametric filter (other frequency filters have to defined using other tools).

After further listening, and given that I've been listening to the same speakers for 29 years, I think ' Teo Torriatte ' is equally appropriate!