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Subwoofers that reach below 20 Hz are often a problem in regular rooms with plenty of room gain. This is a dilemma when aiming to construct a perfect subwoofer.
A subwoofer thatīs linear all the way down to 20 Hz is perfect in theory, but in practice it only works in very large rooms or rooms with very high energy absorbtion ratios. All normal rooms suffer from room gain as a result from decay time. Basically this means an general amplification of bass frequencies and standing waves that can cause severe problems for the sound to be reproduced accurately.
General explanation of room-gain:
Frequency range is normally measured as direct sound from a subwoofer (within a narrow time window). In a room, sound waves bounce before eventually being absorbed by walls, building up standing waves at resonant frequencies. This gives a higher energy level at these frequencies compared to the direct sound from the subwoofer at a given place in the room.
How much more energy depends on the rooms dimensions, the material used in the walls and how much, the subwoofer placement and so on.
All normal rooms have a certain degree of room gain (decay time). Since room gain is a result from reflected sound bouncing back and forth, slowly decaying later than the direct sound, this can also cause some "delayed" phenomenons and consequently "slower" bass character. This can very well be a reason for one of the everlasting discussions in the HiFi business, concerning "slow" or "fast" subwoofers. Many people that experience "slow" bass come to the conclusion that itīs the driver or amplifier that doesnīt keep up, which would normally be incorrect. The real cause can be the degree of room gain being very high at some frequencies.
If the subwoofer reaches very deep and the room suffers from extensive room gain, the result may very well be a slow bass reproduction, constantly "dragging" behind the music. The ideal solution would of course be rebuilding the room and cure the problems, but this would normally cost lots of money.
Another solution is to suppress the lowest frequencies to equalise the subwoofer according to the rooms frequency response. Since all rooms have some degree of room gain, and at different frequencies, itīs obvious that a subwoofer cannot be designed to fit all rooms. We look at our concept using DSP (99 W12 DSP) as the best olution with the least compromises.
When a consumer replaces his "slow" subwoofer with a new "faster" one, itīs in other words not the subwoofer technically being faster, but rather not as deep frequency response which would reduce the effects of room gain.
Once again, the art of compromising "rules". Research shows that a subwoofer with a -3 dB point of 30-40 Hz often is a good compromise in a regular room, and with the room gain included results in a good coverage down to about 20-30 Hz.
Conclusion:
A subwoofer producing a flat frequency response to 20 Hz usually means problems in a regular room. The room gain problem is more obvious in the lower part of the bass region, causing "slow" bass character. A subwoofer not reaching as deep is often said to be "faster" as the effects of room gain are not as obvious.
Read more about room gain, and a series of measurement with very interesting results! Read more >
What is room modes?
Room modes occur when resonances end up in convergence together with the direct sound, forming a pattern of spots where resonances are in phase with each other.
Mode = resonant frewquency of the room
Node = a spot where resonances are in antiphase with each other, causing near zero amplitude
Anti Node = Top, or a spot where the amplitude reaches its maximum
Standing wave = Two or more waves converge, creating a new bigger wave. If there is only one wall, there are no room modes, but still standing waves.
Explanation of tops and dips
Two waves in antiphase cancel out, which is desirable. If several frequencies or their multiples end up in phase tops or dips are formed. If a severe dips or tops are discovered during a measurement they can be impossible to compensated for. In this case moving the listening position, speakers or even re-arrange the entire room might be necessary. A "node" shows as a "dip" in the Room Analyzer.