August 8, 2010

Golden ratio rooms for bass

Do golden ratios work for bass? I must admit I'm more than a little skeptical. Talk of golden ratios has always sounded like nonsense to me, the kind of thing that often turns out to be silly when you actually start measuring. I'll investigate this here with some simulations with the FRDC room simulator.

Here is a golden ratio room - 4.8 wide x 7.8m deep x 3m ceiling.

Image courtesy of Cardas Audio
This is just one implementation of Golden Ratios, but could be applied to rooms of different sizes.

Listening is in an equilateral triangle spaced 2.1m from the front wall and 1.3m from side walls. Speakers are 2.1m apart and listening position is the same distance direct from each speaker.

The result is suprisingly good. The bold line shows the bass transfer function of the mains. It is very good! If you actually got that out of a normal room, it would be something to dance around the room about like a nutter. It is flat +/- 5db! 15 - 20 db is more typical.

The purple line is a corner sub combined with the mains. On it's own, the sub is flatter, except for a nasty dip at 60 Hz. Using this setup as a starting point, an excellent result could be achieved easily with a little tuning.

Is it a fluke?

Let's find out what happens when we start breaking the golden rules ...

If we move the listening position back further away, the reponse gets progressively worse, until we see a broad dip centred at 50 Hz at 2m further away.

If we move sideways half a metre, the midbass imrpoves slightly but we see a nasty dip around 120 Hz.

If we move the speakers back but keep the same listening position, so that the speakers are 1m clear of the front wall, we get a narrow dip at 60 Hz.

If we make the room much wider, as if it were now a living room adjacent to a meals and kitchen area (10m), it's not so bad. Finally a change that we don't get punished for!

If you can't beat 'em, join 'em!

I'm surprised to admit that there appears to be something in these golden ratios!

Actual results will vary. The room simulated has a lot of damping and reflects either a lossy room, or one that is well treated for bass absorption.

So if you are building a room you plan to use for audio, and you were going to build a typical 5 x 7m room with 2.7m ceiling, consider this option. Change the dimensions a little, and set up the room a little differently than you might have. Try to stick to it as close as you can. It seems you can get away with changing some things and not others. The beauty of this option is that you can get to a good result very simply. In fact, most will be happy with a simple plug and play setup. A pair of stereo speakers placed as per the ratios with no EQ or special room treatment. All this assumes a lightly constructed room with no concrete or bricks in the enclosing space.

If this doesn't work for you then you will need to work a lot harder for good bass.

More reading

Cardas Audio - Golden Cuboid Listening Room Diagram

Cardas audio - Setting Up Speakers In A Rectangular Room>

1 comment:

  1. Paul,

    Just wanted to say that you have a great site. You explain many difficult audio concepts in a very clear way. Keep up the great work. You and Sigfried Linkwitz are my favorite audio sites.

    The golden ratio makes much sense to me as I follow Elliott Wave patterns in financial markets. This principle seems to govern many natural processes in our universe.

    All the best, Mike


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