Look at the sub at What is inside a $700 subwoofer - Bose acoustimass 300 subwoofer disassembly - YouTube.
An 11" cube enclosure, and an overly long port of about 30" with port resonance at about 113Hz.
No problem?
An 11" cube enclosure, and an overly long port of about 30" with port resonance at about 113Hz.
No problem?
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So, 113Hz port resonance is not a problem. The port occupies most of the box volume, there is hardly any volume left for the bass reflex alignment, probably less than 15 ltrs.
Apparently a 113 Hz resonance is not a problem for Bose 🙂.
The first resonance point is likely to be a little lower than that, as it's dependent not only on the dimensions of the vent, but also the dimensions of the box.
The first resonance point is likely to be a little lower than that, as it's dependent not only on the dimensions of the vent, but also the dimensions of the box.
Definitely a bit of an odd design. Crazy pricing when you look at SVS, HSU, Rhythmik, etc. I suppose size would be the deciding factor for most in this situation.
Bose is more concerned with the style and ability to hide their components than with the sound reproduction.
That isn't a subwoofer for starters it's a bass module, it has to cover everything up to about 250hz to meet the cubes. And Bose isn't afraid of applying heavy EQ to make cheap parts do what they want. These things don't work half bad for the $50 in components they contain... LOL!
^^ Thats where you might be off the calculations.
This is a modified port, where porous aluminium sheets are placed to reduce the resonance. Thought the port length might be right, the resonances are difference due to that.
This is a modified port, where porous aluminium sheets are placed to reduce the resonance. Thought the port length might be right, the resonances are difference due to that.
The first mode of a pipe with two open ends occurs at 1/2 wavelength, so for a 30" or 76 cm port it occurs at 225 Hz.
+1, The grey windows are located at approx. 1/2 and 1/4 port length, which coincides with pressure maxima of the lowest (in frequency) modes of the air column within the port. Therefore they seem to be added to introduce damping to the first modes. I have read about drilling holes in a port to the reduce port resonance years ago, but never seen it been used until now. 🙂
I do not think they will alter the resonance frequencies that much, because the windows have a small area, compared to those of the port ends. In addition, they are covered by flow resistive material.
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Reviving an old thread. A lot of time has gone by. Can anyone correctly explain. It doesn't seem so simple. Given the fact it is done by Bose, they would have done everything possible for their ultimate aim of compactness.
Warm Regards,
WonderfulAudio
Warm Regards,
WonderfulAudio
This is a helmholtz resonator, so not exactly a quarter wave resonator. The port resonance is at about 220 Hz (wavelength of resonance = 2 * port length). I suppose 220 Hz is above subwoofer pass band.
If the long port was a tuned 1/4 wave pipe (TQWP), it would resonate at ~113Hz, not useful as a subwoofer.
Appears to be a parallel sixth order band pass (BP6) enclosure, each of two chambers with their own ports.
With such a small cabinet volume, a low ( ~40Hz?) tuning with a large cross sectional area requires a very long port.
The long curved port exits at the bottom to one side of the amplifier compartment:
The upper port(s) exit through the upper slots:
The upper chamber is rather small, a good portion of it's volume is the woofer cone's concavity.
Art