Room Analysis case study

This is an example of a room analysis job for one of my PSE-144 customers. This client built two subs of my design - T20, intends to build multiple large 18" bass boxes along with my horn. The goal here was to figure out the best treatment scheme along with a suitable bass arrangement.

You can see there is a lot of brick in this room, which could be a recipe for disaster in the bass, if not for a large window across the left wall and some openings.

For testing here I used an old Wharfedale speaker with a 12" woofer in a sealed box, powered by a DSP amp. EQ is used to get it flat when measured nearfield:

After confirming the extension and smoothness of the test speaker, different listening positions were tested:

Listening positions: Orange: rear left, Pink: rear right, Green: middle front

Here you can see the two seats against the rear wall, with a third position with another chair in front, centred on the couch.

This measurement might lead you to think that the left rear seat is the one to choose. However, in reality much of the bass will play through both main speakers and only one is shown here. Summed mono, the combined bass is expected to even out the response.

Left (grey) and right (black) bass bins shown for the left seat

Now in the right seat, we also see the two bass bins:

Green = right bass bin, pink = left.

Again, when these are combined, we expect the dip will be smoothed out and we will see a fairly flat bass response with a hump around 40 Hz. Both of these seats end up with a similar bass response.

What we see here is that the combined bass response of the two main bass bins is expected to be good. We see no major need for a more complex multi sub arrangement.

Next we moved on to testing sub positions.

 

The results cover a 50 dB range.

The best overall sub position was the centre of the front wall (black), which is compared to the middle of the ceiling, such as may be used in an infinite baffle sub.

 Black - sub in middle front wall vs ceiling centre (green).

Below 40 Hz, the ceiling position has around 10 dB less output, and significant nulls. The main area of interest for a sub position here is below 60 Hz, as the horn in question is best operated below that point.

Basically, the central mid wall position in this room has the best mix of extension, output and smoothness.

The recommended treatment scheme here includes a little more focus on diffusion due to the dispersion control. There is less off axis energy from the horn. Hence, here I suggest retaining more of that energy in the room with a little more later arriving reflections at a lower level. This will retain some natural ambiance in the room and maintain spaciousness.