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port question


tat2jerry

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13 hours ago, tat2jerry said:

Ok so I don't have enough free space for 4 6" ports that long.

And since you seem to know what you're talking about, if I run 7 cubes, what port area for a square side port at 35hz

Based on those specs 85 sq in of port area would be the minimum.  More would be better up to around 115 sq in.  

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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13 hours ago, mothra said:

 

explain how low port area is not desirable? large ports are just cosmetic. in a ported enclosure the port takes over musical playing when the sub/speaker can no longer do so, when they overlap that's where the db gain comes into play. so if you tune low, it's the port that's playing those notes. complementing that with a higher port velocity allows that port to move similar air as a large speaker. having a low port velocity will cause the port to not play notes through, it'll have air settling in the port especially when you have a large port area. since we are in his forum, I guess that Steve has too little port area and too high of a velocity too. he didn't rip that phone book to shreads b/c he has a low port velocity. he ripped it b/c it has a high port velocity. 

 

OK, so high port velocity isn't the only way to get large amounts of sound energy out of the enclosure.  The volume of air getting moved is just as important as the velocity.  When it comes to sound energy you can move a small volume of air at a high velocity, or a large volume of air at a lower velocity, both accomplish the same thing and this is what happens with small area port and a large area port.  The difference is when you have high air velocity but low air volume you lose more energy to air resistance compared to when you have a large air volume but lower air velocity (such as with a larger port).  Its similar to how electricity works, you can produce the same watts with 100 amps at 10 volts or 10 amps at 100 volts, both give you 1,000 watts of energy.  The difference is for the 10 volts at 100 amps you will need a MUCH larger wire or you will lose a bunch of energy to resistance in the wire. A small port is like a high amperage electrical circuit trying to go through a small wire.  

As far as Steve shredding the phone book with his port because he has high port velocity, you are certainly correct to some degree.  However when it comes to the boxes I build I am much more concerned with them getting as loud as possible, not with how well they will shred a phone book and I do the best at getting loud with lower port velocity.  I don't know what all the specs are on Steve's system and I am not going to speculate as to why Steve chose the box specs he did, so its up to him if he wants to comment on that. 

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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15 hours ago, Triticum Agricolam said:

Based on those specs 85 sq in of port area would be the minimum.  More would be better up to around 115 sq in.  

thank you sir

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