Bose:Small enclosure, long port, how?

[wonderfulaudio]

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?

 

[chris661]

It's one approach. I'd just use a passive radiator.

Chris

 

[wonderfulaudio]

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.

 

[Brian Steele]

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.

 

[hv6478]

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.

 

[kevinahcc20]

Bose is more concerned with the style and ability to hide their components than with the sound reproduction.

 

[conanski]

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!

 

[TNT]

??

 

[hv6478]

??

I am both confused and intrigued by this.

 

[Cal Weldon]

It's an underwater bass unit, hence the snorkel.

 

[hv6478]

Ah yes of course, how could I not see it!?!

 

[TNT]

Just thinking "out-of-the-box" ;-D

... and yes, it can wade.

//

 

[thirumalkumaran]

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?

How that 113hz resonance is arrived?
I couldn't find anything on the video!

 

[GM]

It's a 1/4 WL pipe harmonic: ~13543"sec/4/30" = ~113 Hz

GM

 

[thirumalkumaran]

^^ 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.

 

[TBTL]

It's a 1/4 WL pipe harmonic: ~13543"sec/4/30" = ~113 Hz

GM

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.

This is a modified port, where porous aluminium sheets are placed to reduce the resonance.

+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.

Thought the port length might be right, the resonances are difference due to that.

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.