Hi
20 Hz or less, flat?
Where does the specification come from?
The frequency range of musical instruments very rarely reaches down to 20 Hz or even below.
You will know the frequency charts like this one from gearslutz.com:
They have left out the lowest tone of the pipe organ, the subcontra c at about 16 Hz (in German it's called the humbleness pipe).
Only some pieces use that pipe, for example Richard Strauss' "Also Sprach Zarathustra".
Also room responses of concert halls don't include frequencies that low.
The famous Golden Hall of the Vienna Musikverein (if you are watching the New Year's concert of the Vienna Philharmonic Orchestra, you will know it) has a well known mode at 21 Hz. But you don't hear that as strong as a room mode in a home theater.
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If you read the papers by Floyd Toole and Sean Olive on loudspeaker evaluation, you might know that they also determined how listeners rated the bass response of loudspeakers.
The found out that there was no real correlation between listener preference and the "flat" bass extension (the usual -3 dB limit).
But they found a correlation of listener preference with the -10 dB point. The lower that was, the better were the ratings.
That means tha speakers don't really need a deep flat bass responde (@ -3dB), but a flat roll-off in order to reach a deep -10 dB point.
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There are several speakers with those specifications, also at lower prices than 10k U$.
I'm using Shahinian Obelisk peakers, they reach 28 Hz @ -3dB and have bass roll-off of -6dB/octave.
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Regarding the placement.
If one is really serious about good sound reproduction, he won't make any coompromises.
So he would first place the speakers (e.g. onto the nulls) and build up his equilateral stereo-triangle from that.
But I'm aware that in most cases one needs to make compromises in regards of the placement.
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I think it is also important to note, that only looking at what frequencies can be resproduced at which levels is not really the correct way to estimate how well the result will be for the listener.
The human ear does not work that way.
It analyses the complete sound patterns, i.e. the enevlope curves consisting of a mixture of many frequencies.
One of the important elements of that envelope are onsets. Those consist of different frequencies rising at the same time.
If one places a subwoofer far away of a speaker, the low frequency onsets arrive at different times than the higher frequency onsets.
That diminishes the onset of the envelope cuve.
Even worse, if one uses one sub that is closer to one speaker and further away from the other.
This results in different envelopes from the left and right signal, making the bass "slow".
So, if using one sub, one should place it symmetrically between the two speakers.
Cheers
Babak