Effect of enclosure volume deviation on vent tuning?

rxwilson · 6th January 2007, 04:30 PM

Hi everyone,

I have a Peerless 850146 driver in a 70.3 L sealed box, but I want to change it into a vented enclosure, if possible.

The problem is that the box is a bit too small for a SBB4 alignment. According to the design charts in Dickason, the volume needs to be 78.3 L (Qts = .35, alpha is 1.84 assuming QL of 7 from the design chart, Vas = 144 L).

So my questions are: what would be the effect of just using the slightly smaller volume, assuming I calculated vent length based on the actual enclosure volume? Would it be disastrous? Or alternatively, is there any way that I can artificially increase the box volume, or are there other design tweaks that would be helpful in this situation? (I know that for a sealed box, adding stuffing increases the effective volume but I don't think the effect is the same with a vented box). Any help or suggestions would be much appreciated.

Thanks everyone

Ron E · 6th January 2007, 05:02 PM

the ~10% volume difference doesn't matter much - the vent output will drop this much: dB=20*log10(70/78)

Just do it.

Geoff H · 7th January 2007, 10:18 AM

As Ron says, just do it.

The smaller volume will increase the res freq of the enclosure. You have lowered it back by adjusting the port length. The result is you will be somewhere between two alignments.

You will still get the lift in the bass, with a faster roll off, compared to sealed. If it gets lumpy, you can dampen the port, or block it up again.

Geoff.

6th January 2007, 04:30 PM	#1
rxwilson diyAudio Member Join Date: Jan 2007	Effect of enclosure volume deviation on vent tuning? Hi everyone, I have a Peerless 850146 driver in a 70.3 L sealed box, but I want to change it into a vented enclosure, if possible. The problem is that the box is a bit too small for a SBB4 alignment. According to the design charts in Dickason, the volume needs to be 78.3 L (Qts = .35, alpha is 1.84 assuming QL of 7 from the design chart, Vas = 144 L). So my questions are: what would be the effect of just using the slightly smaller volume, assuming I calculated vent length based on the actual enclosure volume? Would it be disastrous? Or alternatively, is there any way that I can artificially increase the box volume, or are there other design tweaks that would be helpful in this situation? (I know that for a sealed box, adding stuffing increases the effective volume but I don't think the effect is the same with a vented box). Any help or suggestions would be much appreciated. Thanks everyone

6th January 2007, 05:02 PM	#2
Ron E diyAudio Member Join Date: Jun 2002 Location: USA, MN	the ~10% volume difference doesn't matter much - the vent output will drop this much: dB=20log10(70/78) Just do it. __________________ Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan* Science is a way of thinking much more than it is a body of knowledge. --Carl Sagan

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7th January 2007, 10:18 AM	#3
Geoff H diyAudio Member Join Date: Oct 2006	As Ron says, just do it. The smaller volume will increase the res freq of the enclosure. You have lowered it back by adjusting the port length. The result is you will be somewhere between two alignments. You will still get the lift in the bass, with a faster roll off, compared to sealed. If it gets lumpy, you can dampen the port, or block it up again. Geoff.

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