Installation guide

In the Limits tab the ‘Full Range’ line and the ‘Desired Response’ line are shown. The Full Range

is the measured response of the whole speaker, incorporating digital crossovers if you have

included these.

The Desired Response is the theoretical calibrated response of the speaker, having regard to the

effective frequency range of the correction and the boost and cut limits. The effective frequency

range and the boost and cut limits can be adjusted. In the figure above the frequency range of the

correction has been set from about 200Hz to 20kHz.

Setting the correction limit for low frequencies:

In the diagram above, notice that the bass frequencies roll off below about 200Hz, suggesting

that this 2-way speaker will later be incorporated with Subwoofers. Notice also that the correction

zone (within the blue box) only starts above 200Hz. As noted above, the time delay from the start

of the impulse to the room’s first reflection in this case was 4.8ms, which is the time it takes

sound to travel about 5 feet (sound travels roughly one foot per millisecond).

The longer the delay for the first room reflection to arrive relative to the time it takes for direct

sound to reach the measurement microphone, the more bass information can be gleaned. A

minimum target would be 3 milliseconds, which will limit measurement usefulness to frequencies

above about 400Hz. Doubling this to 6 milliseconds for example, achieves an additional octave of

bass resolution: down to about 200Hz, which is the lower correction limit used for this case. In

this example, if you attempt to correct below 200Hz phase distortion will be introduced to the filter,

which will make the resulting sound dull and flat - worse than the uncorrected speaker.

Methods to maximise the effective delay before the first room reflection include:

1) Placing the microphone closer to the speaker baffle. For example, if the baffle-to-

microphone distance was originally 1M and the first reflection reaching the microphone

occurred 3ms later than the speaker’s direct sound, then by halving the baffle-to-

microphone distance to say 0.5M (keeping the microphone’s height from the floor the

same) this will increase the ‘relative’ first reflection delay to 6ms, achieving one octave

improved bass resolution - down to about 200Hz instead of 400Hz.

2) Absorbing the floor reflection: Alternately, if keeping the baffle-to-microphone distance at

one metre but entirely absorbing the floor reflection with suitable absorption materials

such as 1ft high mound of pillows and/or woolen bed coverings (on floor between the

baffle and microphone) while ensuring that the next closest reflective surface (walls,

ceiling or cabinet surface etc) is a minimum of 2 metres away to the microphone, then

this should also achieve a 6ms delay.

3) Placing mic height at half room height: If the speaker can be lifted from the floor so that

the tweeter/midrange driver mid point is on-axis to the microphone which is set at half

room height, and where the nearest reflective surfaces are at least also half-room height

distance away from the microphone, there is no advantage using absorption materials

because the reflection from the floor and ceiling will arrive at the same time. This will

typically not provide a 6ms delay, but usually in the order of 4 to 5 milliseconds.