July 1, 2014
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.
May 31, 2014
The new measurement system is almost ready. A galvanized steel pole slots into the ground, into a steel tube with a concrete footing and a cap when not in use. Triangulated ties attach to the fascia board, bolted in place to ensure stability. The main pole is 4m high. A block and tackle is used to lift the speaker from just above ground level. The old system was a back-breaker when it came to getting speakers up onto the turntable stand.
The new system also elevates the speaker higher than the mic stand will allow. A new and more stable mic stand is coming up next, with greater repeatability in position.
Not shown above is the turning mechanism, where a lever that looks like a periscope handle is attached to the bottom of the turntable.
April 18, 2014
April 7, 2014
Which bass module would you prefer?
The speaker on top has a familiar form factor, with a dome tweeter and 6.5" midrange driver, but with a twist. It features 93 dB sensitivity, high enough to be driven by most valve amps. The bass module will feature a ported DSP powered 10" woofer, except version B which fits a larger 12" driver.
A - a simple box where the front is angled to match the front baffle of the speaker on top
B - side walls angle out to fit a 12" woofer
C - both front and back angled out
D - a simple rectangular box
April 6, 2014
PSE-144 almost maintains its horizontal pattern control down to 250 Hz, with modest midrange narrowing. At very high frequencies the pattern narrows. Around 5 - 7k one can see that there is a difference in the axial and off axis response from around 15 - 40 degrees. This is very useful data to consider in making choices about what to correct in the crossover and how this speaker should be set up in a room.
The horizontal design beamwidth is 80 degrees.
The directivity waterfall plot shows the same data in a different way. The data is shown with the minimum smoothing the software allows (1/12 octave) and here we can see the effectiveness of the dispersion control employed in this horn. The crossover point is not evident in any way.