Bass Reflex Question? - AVS Forum
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post #1 of 5 Old 04-02-2009, 04:45 AM - Thread Starter
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Hi,

I hope some of you audio conneisseurs can help me out with a couple of points. I'm designing some Desktop 2.0 speakers and would like to know:

1. In a Bass Reflex enclosure why is the bass vent located at the bottom? Is this purely because bass is directed at the lower area of the body?

2. Can a Bass Reflex system work if there is a vent located above and below the driver (as illustrated)? If not, what would be the outcome?

Bear in mind that these are small desktop 2.0 speakers so I don't believe bass, mid and high frequency positioning would be such an important factor here.

Thankyou
LL
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post #2 of 5 Old 04-02-2009, 06:49 AM
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Quote:
Originally Posted by mrplaydo View Post

Hi,

I hope some of you audio conneisseurs can help me out with a couple of points.

You don't want a conneisseur, you want someone who has made audio *wine* starting with growing, picking, and stomping the grapes! ;-)

Quote:


I'm designing some Desktop 2.0 speakers and would like to know:

1. In a Bass Reflex enclosure why is the bass vent located at the bottom?

Probably to put it as near as possible to a room boundary. BTW, I know of many counter-examples.


Quote:


Is this purely because bass is directed at the lower area of the body?

No, bass tends to be non-directional. You can point a vent anywhich way you want to, and the low bass will go everywhere.

Quote:


2. Can a Bass Reflex system work if there is a vent located above and below the driver (as illustrated)? If not, what would be the outcome?

You can have as many vents as you want to. The things to worry about vents is that they are the right size to tune the driver and the enclosure to the right frequency, and that they don't have excess turbulence at low frequencies and make chuffing sounds.

Quote:


Bear in mind that these are small desktop 2.0 speakers so I don't believe bass, mid and high frequency positioning would be such an important factor here.

The usage "desktop 2.0" speakers is new to me. I think that you mean 2-channel speaker without external subwoofer.

I'm familiar with this type of speaker as "near field monitors".
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post #3 of 5 Old 04-02-2009, 09:13 AM - Thread Starter
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Hi Arnyk, thanks for the reply.

Quote:


Probably to put it as near as possible to a room boundary.

I take it you are referring to the floor?

Quote:


No, bass tends to be non-directional. You can point a vent anywhich way you want to, and the low bass will go everywhere.

If so, then it doesn't matter if the bass vent was as near as possible to a room boundary or not?

Yes I'm referring to a 2-channel speaker without ext. subwoofer.
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post #4 of 5 Old 04-03-2009, 06:37 AM
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Quote:
Originally Posted by mrplaydo View Post

Hi Arnyk, thanks for the reply.

I take it you are referring to the floor?

Right.

Quote:


If (bass is very nondirectional), then it doesn't matter if the bass vent was as near as possible to a room boundary or not?

Not very much. Of course how non-directional the bass is depends on how deep the bass actually is.

I think of bass as being sound below 100 Hz or so, but with these desktop speakers, their "bass" could be as high as 200 Hz or even higher.

There might be a slight advantage to putting the port as close as possible to the nearest large, flat surface.
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post #5 of 5 Old 04-05-2009, 05:29 AM
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Desktop speakers are designed to look cool. That defines their vent placement. My Altec's "vent" is actually fake. They are sealed. (now well sealed, damped and stuffed. )

Best acoustic practice is to point the vent AWAY from the listener so any midrange reflections coming out the ports will not interfere. Same as with standard speakers. If it is too close to the driver, it can cause some phase canceling. Easy on a tiny desktop speaker.
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