"Referring now to FIG. 8, there is shown a cutaway perspective view of an exemplary electroacoustical Waveguide system according to the invention. The waveguide system of FIG. 8 uses the implementation of FIG. 6, With the FIG. 8 implementation of the elements of FIG. 6 using common identifiers. In the implementation of FIG. 8, Waveguide 11 has a substantially uniform cross sectional area of 12.9 square inches and a length of 25.38 inches. The acoustic volumes 24a and 24b have a volume of 447 cubic inches and 441 cubic inches, respectively, and the acoustic drivers are 5.25 inch 3.8 ohm drivers available commercially from Bose Corporation of Framingham."
Using this information, I think it's possible to put together a Hornresp sim that will approximate the response of the Bose LSPS bass module up to the frequency at which the distance between the two entry points of the driver chambers into the path approaches 1/4 wavelength. At longer wavelengths, the separate driver chambers can be modeled as one chamber container located at the midpoint between the two entry points.
From the description and diagram, the entry points are separated by 32.34 cm, so from that we have:
So, at frequencies below 264 Hz, we should be able to model the separate driver chambers as one chamber container located at the midpoint between the two entry points and get good results. Other information in the patent suggests that this entry point should be 0.25*L, where L is the length of the TL's path, so we end up with the following:
Vtc = 447+441 = 88 cu.in. = 14.6 L
S1 = S2 = S3 = 12.9 sq.in = 83.23 cm^2
L = 25.38 in = 64.47 cm
0.25*L = 16.12 cm
L12 = 16.12 cm, L23 = 64.47-16.12 = 48.35 cm
As for Atc, required to complete the model, I estimated from the diagram that it's about 2*S1 = 166.4 cm^2
From those parameters, we get this:
Which in turn predicts this:
However, this model is incomplete, because it doesn't include the impact of the stuffing in the driver chambers.
To do that, we can convert the model into a stubbed horn, treating S1-S2 as the "stub" and the driver chambers as part of path with a discrete change between the new S1-S2 and S2-S3 segments. With David's help with the model, we now end up with this:
L12 = 14551.7/166.46 = 87.42 cm
Path
S1 = S2 = 166.46 cm^2
S2S = S3 = 83.23 cm^2
L23 = 48.35 cm
Stub
S5=S6 = 83.23 cm^2
L56 = 16.12 cm
With that info, we end up with this:
As for stuffing, I cheated a bit and adjusted the stuffing in the L12 section until Fb was a close match for the measured Fb of the Bose LSPS subwoofer:
Comparing this against a rough FR test I did last night, the sim'd response looks like a pretty decent match to the measured response from 30 to 200 Hz:
Using this information, I think it's possible to put together a Hornresp sim that will approximate the response of the Bose LSPS bass module up to the frequency at which the distance between the two entry points of the driver chambers into the path approaches 1/4 wavelength. At longer wavelengths, the separate driver chambers can be modeled as one chamber container located at the midpoint between the two entry points.
From the description and diagram, the entry points are separated by 32.34 cm, so from that we have:
| 1/4L | = | cm |
| L | = | cm |
| c | = | m/s |
| F | = | Hz |
[td width="64px"]
32.24
[/td][td]
128.96
[/td][td]
340
[/td][td]
264
[/td]So, at frequencies below 264 Hz, we should be able to model the separate driver chambers as one chamber container located at the midpoint between the two entry points and get good results. Other information in the patent suggests that this entry point should be 0.25*L, where L is the length of the TL's path, so we end up with the following:
Vtc = 447+441 = 88 cu.in. = 14.6 L
S1 = S2 = S3 = 12.9 sq.in = 83.23 cm^2
L = 25.38 in = 64.47 cm
0.25*L = 16.12 cm
L12 = 16.12 cm, L23 = 64.47-16.12 = 48.35 cm
As for Atc, required to complete the model, I estimated from the diagram that it's about 2*S1 = 166.4 cm^2
From those parameters, we get this:
Which in turn predicts this:
However, this model is incomplete, because it doesn't include the impact of the stuffing in the driver chambers.
To do that, we can convert the model into a stubbed horn, treating S1-S2 as the "stub" and the driver chambers as part of path with a discrete change between the new S1-S2 and S2-S3 segments. With David's help with the model, we now end up with this:
L12 = 14551.7/166.46 = 87.42 cm
Path
S1 = S2 = 166.46 cm^2
S2S = S3 = 83.23 cm^2
L23 = 48.35 cm
Stub
S5=S6 = 83.23 cm^2
L56 = 16.12 cm
With that info, we end up with this:
As for stuffing, I cheated a bit and adjusted the stuffing in the L12 section until Fb was a close match for the measured Fb of the Bose LSPS subwoofer:
Comparing this against a rough FR test I did last night, the sim'd response looks like a pretty decent match to the measured response from 30 to 200 Hz:
I'd think it has more to do with the bass module having to reach up to ~200 Hz where the "Jewel Cube" speakers used in these systems crap out.
Also, Bose probably had plenty of the 5.25 inch mid-bass drivers already available..
They could have done that with basically any decent bass driver. The response above 200 Hz or is largely influenced by the type of alignment that they chose anyway and the amplifier includes some EQ.
I'm curious though if these 5.25" drivers were used in any systems prior to the LSPS bass module.
I'm curious though if these 5.25" drivers were used in any systems prior to the LSPS bass module.
