I have been putting off writing about acoustics issues with bass for a reason: it is a difficult subject to really get. However, once you get it, the topic seems intuitive and simple.
In most rooms there are at least two large opposing parallel reflective surfaces, like the walls, ceiling/floor, etc. These surfaces reflect sound back and forth with and can set up resonances between them at frequencies where the distance between the two surfaces are equal to the wavelength, or multiples of the wavelength, of the frequency being generated in the room.
Below is an example of a primary standing wave node where the distance between two reflective surfaces is equal to one full wavelength.
The red area is where the sound from the acoustic energy is the strongest and the white area is where the energy is the weakest. The highest energy point is called the antinode and the weakest is the node, or often the null. If you are standing exactly where the null is, there is absolutely nothing you can do electronically to make that frequency heard. Increasing the output level will make the red areas, the antinodes, louder, but the nodes (nulls) will remain absolutely silent to the ear as there is no energy at that point in the room.
However, if you are standing 3/4 of the way across the room, at the antinode point, the sound will be the loudest it can be at that frequency. if you boost that frequency to solve silence of the node, you will be boosting the antinode correspondingly. If you attempt to eliminate the antinode by cutting the frequency electronically, you will likely be forced to cut it completely and ensure you will never hear any content at that frequency on that system.
When acoustic energy is generated in a room, the inherent resonances the standing waves (called standing waves becase the nodes do not move through the room but are stationary) will start to build up at the exact frequencies where the wavelengths between the reflective surfaces is equal to the distance between the surfaces. So, if the walls in a room at exactly 20 feet apart in the example above, then the standing wave shown in that example is 56.5Hz. If you are standing exactly in between the walls and played a 56.5Hz sine wave test tone, you would not hear the primary wave (though you would hear some harmonics and other distortions and room noises).
That's at root single wavelength frequencies. What about other frequencies?
Well, the same rule applies to multiples of the standing wave frequencies. For instance, if there is a standing wave at 56.5Hz, then there will also be a standing wave at 113Hz, or two wavelengths in a given distance. The image below illustrates a two wavelength standing wave:
Again, if you are standing directly betwen the two surfaces, or the node point, then the root frequency will be inaudible. If you are standing at the 3/4 point between the walls, you are standing at another node, or null. Unlike the root standing wave where the 3/4 point is the absolute loudest, the 2 wavelength standing wave will have a null at the 3/4 point.
So, where would you want to be standing to get the most even bass?
Keep in mind that all multiples of the root standing wave will have strong nodes and anti nodes in the room. So, not just the single wavelength, but the two wavelength, three wavelength and four wavelength frequencies will all have standing waves up to the point where the room decor and other reflective surfaces start breaking up the acoustic waveform. So, in our imaginary sample room which has two large reflective walls which are 20 feet apart, you will have serious nodes and antinodes at 56.5Hz, 113Hz, and 169.5Hz. At 169.5Hz there will be 6 nodes, or nulls, spaced evenly across the room between the two surfaces.
This is simple two surface issues. Most rooms have six reflective surfaces in parallel pairs, so you have to deal with multiple standing wave issues all at the same time. So, if your head is placed directly in the center of the room, between each of the three reflective parallel sets of surfaces, you will be exactly at the node point for 3 sets of root standing waves plus all their multiples.
In most rooms there are at least two large opposing parallel reflective surfaces, like the walls, ceiling/floor, etc. These surfaces reflect sound back and forth with and can set up resonances between them at frequencies where the distance between the two surfaces are equal to the wavelength, or multiples of the wavelength, of the frequency being generated in the room.
Below is an example of a primary standing wave node where the distance between two reflective surfaces is equal to one full wavelength.
The red area is where the sound from the acoustic energy is the strongest and the white area is where the energy is the weakest. The highest energy point is called the antinode and the weakest is the node, or often the null. If you are standing exactly where the null is, there is absolutely nothing you can do electronically to make that frequency heard. Increasing the output level will make the red areas, the antinodes, louder, but the nodes (nulls) will remain absolutely silent to the ear as there is no energy at that point in the room.
However, if you are standing 3/4 of the way across the room, at the antinode point, the sound will be the loudest it can be at that frequency. if you boost that frequency to solve silence of the node, you will be boosting the antinode correspondingly. If you attempt to eliminate the antinode by cutting the frequency electronically, you will likely be forced to cut it completely and ensure you will never hear any content at that frequency on that system.
When acoustic energy is generated in a room, the inherent resonances the standing waves (called standing waves becase the nodes do not move through the room but are stationary) will start to build up at the exact frequencies where the wavelengths between the reflective surfaces is equal to the distance between the surfaces. So, if the walls in a room at exactly 20 feet apart in the example above, then the standing wave shown in that example is 56.5Hz. If you are standing exactly in between the walls and played a 56.5Hz sine wave test tone, you would not hear the primary wave (though you would hear some harmonics and other distortions and room noises).
That's at root single wavelength frequencies. What about other frequencies?
Well, the same rule applies to multiples of the standing wave frequencies. For instance, if there is a standing wave at 56.5Hz, then there will also be a standing wave at 113Hz, or two wavelengths in a given distance. The image below illustrates a two wavelength standing wave:
Again, if you are standing directly betwen the two surfaces, or the node point, then the root frequency will be inaudible. If you are standing at the 3/4 point between the walls, you are standing at another node, or null. Unlike the root standing wave where the 3/4 point is the absolute loudest, the 2 wavelength standing wave will have a null at the 3/4 point.
So, where would you want to be standing to get the most even bass?
Keep in mind that all multiples of the root standing wave will have strong nodes and anti nodes in the room. So, not just the single wavelength, but the two wavelength, three wavelength and four wavelength frequencies will all have standing waves up to the point where the room decor and other reflective surfaces start breaking up the acoustic waveform. So, in our imaginary sample room which has two large reflective walls which are 20 feet apart, you will have serious nodes and antinodes at 56.5Hz, 113Hz, and 169.5Hz. At 169.5Hz there will be 6 nodes, or nulls, spaced evenly across the room between the two surfaces.
This is simple two surface issues. Most rooms have six reflective surfaces in parallel pairs, so you have to deal with multiple standing wave issues all at the same time. So, if your head is placed directly in the center of the room, between each of the three reflective parallel sets of surfaces, you will be exactly at the node point for 3 sets of root standing waves plus all their multiples.
