"Book shelf" speakers put on speaker stands = less bass??

[Confused]

On 5/22/2021 at 8:12 AM, fas42 said:

 

Of course there are room modes - but our hearing adapts to them ... a real grand piano being played by a real person in a real, relatively small room, doesn't sound boomy - when the bass notes are being forcibly played ... at least, I have never heard such an instrument irritate me with 'resonances'.

 

So, a simple question: why is a piano OK - but a recording playback setup needs all this, umm, fiddling?

As others have pointed out, a piano will sound different in different rooms, and indeed will sound different depending on where you stand in a room.  There are many different techniques for recording pianos, and it is well established that different locations for microphones etc. will yield very different results in that recording.

 

As for real instruments exciting room modes, I mentioned the effects of the room on an unamplified bass drum in an earlier post.  In addition, I also recall one occasion where a bass guitar hit a room resonance mode with spectacular effect, and I mean truly spectacular, it is like it increased in volume about six or ten times.  Of course, this does not really count as an example of a "real" instrument, because it was an electric bass and it was the stage amp hitting the mode, which is not really different to a hifi system doing it.

 

I think it will be much harder for a piano to hit a room resonance mode than a hifi system reproducing the piano.  When you have a hifi in a room with a known resonance mode, you can usually find some dimensional evidence as to why.  Lets say you have a resonance at 50Hz and a null at 100Hz.  This equates to wavelengths of about 6900mm and 3400mm respectively .  You will probably find some aspects of the setup have relationships to these wavelengths.  So you might have your speakers 850mm from the rear and side walls, as it happens this is exactly one quarter of your null frequency wavelength, so your speaker location exacerbates the natural effects of the room null.  The same thing works with the peaks, so you might find that the back wall is 3450mm (half 50Hz wavelength) or maybe 6900mm (full 50Hz wavelength) from the speakers.  Then similar relationships with the speaker distance from the ceiling, the distance between speakers, other walls and so on.

 

So you have these very complicated interactions between all the room dimensions, which in themselves will naturally lead to resonances, peaks and nulls at different frequencies, and the specific location of the speakers.  It is here that a piano in a room is very different to a stereo system in a room.  With a stereo you quite probably do have your speakers placed identically distanced from the floor, ceiling and back wall, possibly to millimeter perfection., and these speakers are producing the sound almost as two single points in space, which exacerbates these effects in a way that a piano will not.  Consider that a piano is big, and the sound does not come from one point in space, not even close to this.  The sound is created by vibrations of a very long string, the soundboard, and the entire body of the piano acts as a resonator, together with the lid.  This is a huge dispersed area which is working together generating the sound, not the entire sound from one point.

 

There is perhaps a parallel to this with audio.  One technique for getting very even bass in a given room is to use a large number of subwoofers, or a "subwoofer swarm" as some might call it.  The idea here is not to have lots of subs to get lots of bass, but rather to have the subs located asymmetrically to the room and to each other, so each one will have different interactions and create different peaks and nulls, which will then tend to cancel out, and can be then be brought to a very even bass response, probably with room correction to prevent the overall level of bass being excessive, but at least there will be limited nulls, which are otherwise difficult to "fill" or correct.

 

This is why a piano is less likely to hit a pure room resonance than a stereo speaker, it is effectively generating the same effect as a subwoofer swarm.

 

 

[Confused]

17 hours ago, Racerxnet said:

I was looking for a dispersion pattern of the piano vs a speaker to help illustrate the interaction. 

I presume you could not find anything?

 

The link below might be interesting.  It is not exactly what you were looking for, but it does serve to illustrate that a piano does not behave like a speaker.

 

Modeling and simulation of a grand piano. (inria.fr)

 

[Confused]

8 hours ago, fas42 said:

 

This is the most plausible explanation, looking at the situation conventionally.

 

 

If the large body of the instrument is part of the answer, why not make the subwoofer large in effective area too - the Bose 901 concept - lots of small drivers spread over a large surface area? I certainly know it doesn't work in the purely vertical mode - the Steinway Lyngdorf  Model D system I heard once was the most awful rig I had listened to in a long, long time - massive, booming bass, that was quite absurd, of a recording of a piano!

The key thing is asymmetry.  This is why the subwoofer swarm technique works.  With the Bose 901 the drivers are more or less the same distance from the front wall, back wall, and the variance in distance to the side wall is small enough to be more or less insignificant.  The Bose is also considerably smaller than a piano.  The Steinway Lyngdorf  Model D system will have identical distances to many room surfaces also.  The Steinway Lyngdorf  Model D system you listened to may well have been suffering from an unfortunate interaction with the room, maybe room treatment or correction via DSP would have improved things.

 

With multiple subwoofers, or even one subwoofer, the ideal location(s) will most likely be some distance removed from the main speakers.