slot vent and ports?

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blackcivichatch

Copper - Posts: 229

Joined: January 27, 2009

Location: Missouri, United States

Posted: January 28, 2009 at 3:20 PM / IP Logged

I have built a 3 Cu. ft, box for my cerwin vega V max 15. the box has a 1.5" by 15" port tuned to 38 hz. I Blew the CV when i upgraded to a 1000 watt Memphis class D amp. im in the process of looking for a new sub. my question is, could i add a round port to the box along with the slot vent? Im not very interrested in the SQ, i would just like more output from the box. Thanks

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DYohn

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Joined: April 22, 2003

Location: Arizona, United States

Posted: January 28, 2009 at 3:37 PM / IP Logged

Could you? Of course. Is it a good idea? No. It will only change the tuning frequency, not generate more output.

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blackcivichatch

Copper - Posts: 229

Joined: January 27, 2009

Location: Missouri, United States

Posted: January 28, 2009 at 3:52 PM / IP Logged

The thing is, the box was well built and fits perfectly in my hatch. i have plenty of PVC pipe laying around. Would it be a better idea to simply use another sheet of MDF to cover the port and make new ports with the pvc?

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DYohn

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Joined: April 22, 2003

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Posted: January 28, 2009 at 4:04 PM / IP Logged

Why do you want to change the porting?

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blackcivichatch

Copper - Posts: 229

Joined: January 27, 2009

Location: Missouri, United States

Posted: January 28, 2009 at 4:18 PM / IP Logged

Well I had the same sub in a previous, same sized box. It was my first ported box.The vent on the old box was about 3.5" by 15" and tuned at 55 hz. I now know that this frequency is way too high, thats why the new box was built. But the old box had a slighly higher output than the new one has. I also have a creative cosmetic idea for the round ports.

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DYohn

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Joined: April 22, 2003

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Posted: January 28, 2009 at 4:30 PM / IP Logged

Gotcha. Then sure, you can seal up the old port and add different ones. Just be sure you calculate properly for the desired tuning frequency.

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blackcivichatch

Copper - Posts: 229

Joined: January 27, 2009

Location: Missouri, United States

Posted: January 28, 2009 at 4:32 PM / IP Logged

Thanks a lot for the help

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blackcivichatch

Copper - Posts: 229

Joined: January 27, 2009

Location: Missouri, United States

Posted: January 28, 2009 at 9:15 PM / IP Logged

Another question: What exactly is the benefite of tunning the box to the Fs of the particular woofer?

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DYohn

Moderator - Posts: 10,741

Joined: April 22, 2003

Location: Arizona, United States

Posted: January 29, 2009 at 10:02 AM / IP Logged

blackcivichatch wrote:

Another question: What exactly is the benefite of tunning the box to the Fs of the particular woofer?

The purpose of the port is to augment the driver's output by creating resonance in the port. At fs the driver is in resonance, and it has very little ability to create sound. But a better target for turning frequency rather than fs is to determine the enclosure's f3 and port at that frequency. f3 is where the output is -3db from nominal, and the port will add that 3db back in to create a flatter response curve.

On the other hand, if what you are after is high SPL rather than a flat response, often the best results are to port for the resonance frequency of the vehicle so that you excite those frequencies. This, combined with the ways our ears perceive sound, is why the 55Hz tuning was louder in your vehicle than a 38Hz tuning, although he 38Hz tuning probably created a better overall frequency response in your system.

The real question is what is your desired result from this system? Loud or low?

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blackcivichatch

Copper - Posts: 229

Joined: January 27, 2009

Location: Missouri, United States

Posted: January 30, 2009 at 5:13 PM / IP Logged

I currently have a 12" Total Mobile Audio in a pre-fab ported box for temporary. Since I am used to listening to my 15" in an oversized box, the 12" has way too much of a high pitch for my taste. to answer the question " Loud or low?": Low. This particular application is for a Daily driven "showy" car. I guess is what im really looking for is a box to play the low sounds loudly. lol. You mentioned the resonance freq. of the vehicle... How exactly is this determined? i have a '96 Honda Civic Hatch.

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