Inspired by another thread today, I've made some quick measurements to compare the effects of both EQ and acoustic absorbers on specifically decay times. The comparison used Dirac Live (but just a single measurement point) and two Rockwool corner bass traps (one 1200 x 600 x 600 mm and the other 1200 x 600 x 300 mm). The responses shown is using a Power Sound Audio S1510 subwoofer crossed over to a pair of Edifier S300 Pro main speakers at 110 Hz.
With no EQ or bass traps, I measured the following response at the listening position. (For those not familar, this is a waterfall plot, showing frequency left-to-right and time front-to-back. At each frequency, the further forward the signal still shows, the slower the decay.)
Applying EQ just up to 180 Hz and re-measureing at the exact same position gave the following result:
The effect of the EQ is seen not only in terms of the initial bass response (back of the graph) being much smoother but also how the bass notes don't persist at high levels for so long compared to the higher frequencies. The rate of decay of bass notes hasn't actually decreased but they get to lower levels sooner purely by virtue of being lower to begin with.
What is needed to genuinely increase the rate of decay is absorption. Putting my bass traps back into position, making a measurement to generate a different EQ correction filter specific to this situation but with the same target curve, I got the following:
Comparing this to the blue plot above, the added benefit of the bass traps on the decay is seen most clearly between 50 and 100 Hz, although there are smaller reductions at higher frequencies too. The initial response is also slightly smoother with the bass traps in place due to there being a little less for the EQ to try to compensate for.
For completeness, here's what the response looks like with the bass traps in place but without any EQ:
In this particular example it's pretty clear the EQ has the bigger effect, but the bass traps I have offer a further, and different, improvement. More money and space for acoustic treatments could I'm sure make this a closer 'fight' though. The above is all just at a single point as well, whereas another benefit of bass traps is to reduce the variation in response with position.
With no EQ or bass traps, I measured the following response at the listening position. (For those not familar, this is a waterfall plot, showing frequency left-to-right and time front-to-back. At each frequency, the further forward the signal still shows, the slower the decay.)
Applying EQ just up to 180 Hz and re-measureing at the exact same position gave the following result:
The effect of the EQ is seen not only in terms of the initial bass response (back of the graph) being much smoother but also how the bass notes don't persist at high levels for so long compared to the higher frequencies. The rate of decay of bass notes hasn't actually decreased but they get to lower levels sooner purely by virtue of being lower to begin with.
What is needed to genuinely increase the rate of decay is absorption. Putting my bass traps back into position, making a measurement to generate a different EQ correction filter specific to this situation but with the same target curve, I got the following:
Comparing this to the blue plot above, the added benefit of the bass traps on the decay is seen most clearly between 50 and 100 Hz, although there are smaller reductions at higher frequencies too. The initial response is also slightly smoother with the bass traps in place due to there being a little less for the EQ to try to compensate for.
For completeness, here's what the response looks like with the bass traps in place but without any EQ:
In this particular example it's pretty clear the EQ has the bigger effect, but the bass traps I have offer a further, and different, improvement. More money and space for acoustic treatments could I'm sure make this a closer 'fight' though. The above is all just at a single point as well, whereas another benefit of bass traps is to reduce the variation in response with position.
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