Jump to content

Allison effect and Bestplace program


Guest Doug Murray

Recommended Posts

Guest Doug Murray

Allison effect and Bestplace program

Hi everyone,

I have been trying out the Bestplace program by RDL Acoustics, which I got from this website.

Now, in this program, one sets the straight-line distances from the centre of the woofer to the 3 closest room boundaries, these being labelled as the front wall, the floor and the side-wall.

It struck me that there is another boundary that is relevant for the Allison effect – the ceiling. Since this distance is potentially of the same order of magnitude as the others, does anyone know if Bestplace takes the ceiling distance into account in its calculation (i.e. assumes a ceiling height and subtracts the floor distance)?

Please correct me if the 4th boundary distance is not relevant to the approximation.

My room dimensions are 6.6 m (21.65 ‘) by 4.5 m (14.76’) by 2.4 m (7.87’).

The woofer centre is 1.0 m (39.4”) from the floor, when on its stand. This gives a distance of 1.4 m (55”) from the woofer centre to the ceiling.

Bestplace with distances of Floor = 39”, Front = 31”, side = 14” gives quite a good result, with deep troughs in the low or mid-bass, and a response of +3.5 dB . If I pretend that the floor is the “ceiling” I get a -4 dB trough at 62.5 Hz. Averaged, these 2 responses complement each other quite nicely.

Am I on the right track?

Many thanks,

Doug

Link to comment
Share on other sites

Allison effect and Bestplace program

Hi everyone,

I have been trying out the Bestplace program by RDL Acoustics, which I got from this website.

Now, in this program, one sets the straight-line distances from the centre of the woofer to the 3 closest room boundaries, these being labelled as the front wall, the floor and the side-wall.

It struck me that there is another boundary that is relevant for the Allison effect – the ceiling. Since this distance is potentially of the same order of magnitude as the others, does anyone know if Bestplace takes the ceiling distance into account in its calculation (i.e. assumes a ceiling height and subtracts the floor distance)?

Please correct me if the 4th boundary distance is not relevant to the approximation.

My room dimensions are 6.6 m (21.65 ‘) by 4.5 m (14.76’) by 2.4 m (7.87’).

The woofer centre is 1.0 m (39.4”) from the floor, when on its stand. This gives a distance of 1.4 m (55”) from the woofer centre to the ceiling.

Bestplace with distances of Floor = 39”, Front = 31”, side = 14” gives quite a good result, with deep troughs in the low or mid-bass, and a response of +3.5 dB . If I pretend that the floor is the “ceiling” I get a -4 dB trough at 62.5 Hz. Averaged, these 2 responses complement each other quite nicely.

Am I on the right track?

Many thanks,

Doug

Have you read Allison's AES papers? What he did was to compute, and measure

the effects of one, two, and 3 boundaries as they reinforce the output of a typical

speaker. An Ar3? woofer only was used for the experiments, and IIRC they were

done outdoors, with the ground and concrete walls as boundaries so that there

was virtually no wall flex. The problem is simply a source summed with the "image"

source(s) provided by the boundaries. Any finite spacing causes delay in the summation

with the resulting out of phase combination at certain frequencies. These data help

a loudspeaker designer understand how the system interacts with the nearby room

boundaries. It helped to determine new placements for the woofer as is seen in the

AR-9, 90, Aliison's own speakers, and the NHT-3.3 and other similar models. The

paper that covered boundary reinforcement did not consider a real room where the

other walls come into play making it a cavity resonator. Wall flex was also not taken

into consideration which can reduce the boundary reinforcement effect.

A speaker was measured in a large number of "typical" home rooms and the responses

averaged in another paper by Allison, to determine if there were any common trends.

These would take into account the room as a cavity resonator, but this is not a feature

of the BestPlace program.

To answer your question another boundary beyond what is provided in BestPlace cannot

be handled by the program since it provides a resonance condition where there will be

standing waves between the two boundaries. There are other programs that provide

some insight into rooms as cavity resonators.

Link to comment
Share on other sites

Hi Doug,

It's been a while since I've used that program. Some members on the yahoo Allison group are technically astute for those kind of calculations and measurements, as is Pete. You could ask over there too. Have you moved the speakers around and listened (or measured) with your calculations? Every room is different. It may be fun!

JK

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...