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MyNameIsNoob

Box Volume, Port Area and Power.

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My wheels are turning.

I've read alot and pieced together bits of information from previous topics on here, but dont feel confident I have found the answer yet...

My question is: If you needed to build another box and wanted to "fine-tune" it a bit... When it comes to box volume, port area and port velocity, how do they affect each other? 

For instance, if I only change box volume, how would it affect the port area requirements and port velocity? Or if I increase power, should I change the box volume and port area to get the best results? Etc etc etc...

I doubt there is a definitive answer to this (?) since so many variables can affect the others, but I'd love to to know any rules of thumb and hear everyones opinion or experiences. 


1996 GMC Sierra 2500........................................................... (planned upgrades below)

Alternator .............. Factory ................................................... 270A
Batteries ................ Duralast and (1) XS D925 Battery......... replace Duralast w larger XS battery

Head Unit............. Soundstream VRN 65HB

Sound Processor ..... Precision Power DSP 88R

Component Amp ... Hifonics BRX6016.4................................. (T.B.D.)
Front stage ........... (4) Crescendo PWX 6.5" (2) Crescendo FT1

Sub amp ............... Hifonics BRZ1700.1D................................ (T.B.D.)
Subwoofer ..............(1) Soundqubed HDC3 12
Enclosure ................................................................................ IN PROGRESS

Soundproofing ......................................................................... IN PROGRESS

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My favorite topic!

1. High port velocity is bad, higher port velocity causes more air resistance in your port.  This will negatively effect your output (can be quite significant) and potential cause annoying port noise.

2. Rules of thumb are unreliable.  They are all based on assumptions which may or may not be true for your situation.  This isn't to say they are useless, but you need to understand their limitations.  I avoid them entirely.

3.  Assuming you keep everything else the same, there are three things that will increase port velocity.  The three are: increasing input power, increasing box volume, or increasing the tuning frequency.  If you do any of those you will probably want to have more port area. 

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"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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1 hour ago, Triticum Agricolam said:

My favorite topic!

1. High port velocity is bad, higher port velocity causes more air resistance in your port.  This will negatively effect your output (can be quite significant) and potential cause annoying port noise.

2. Rules of thumb are unreliable.  They are all based on assumptions which may or may not be true for your situation.  This isn't to say they are useless, but you need to understand their limitations.  I avoid them entirely.

3.  Assuming you keep everything else the same, there are three things that will increase port velocity.  The three are: increasing input power, increasing box volume, or increasing the tuning frequency.  If you do any of those you will probably want to have more port area. 

4. listen to trit

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23 hours ago, Triticum Agricolam said:

My favorite topic!

1. High port velocity is bad, higher port velocity causes more air resistance in your port.  This will negatively effect your output (can be quite significant) and potential cause annoying port noise.

2. Rules of thumb are unreliable.  They are all based on assumptions which may or may not be true for your situation.  This isn't to say they are useless, but you need to understand their limitations.  I avoid them entirely.

3.  Assuming you keep everything else the same, there are three things that will increase port velocity.  The three are: increasing input power, increasing box volume, or increasing the tuning frequency.  If you do any of those you will probably want to have more port area. 

Thanks for responding! I've read a few of your posts similar to this topic n appreciate any advice or direction that I can get.

1 - Aside from the output loss and noise, will the increase of "back pressure" from the extra resistance have any kind of effect on power handling similar to a smaller box volume?

3 - Is the effect on velocity from increasing power and volume because of the extra air being displaced? 

And how does the tuning change the air speed? Is it because of the wavelengths? (Just a wild guess, that's never even crossed my mind lol)

Hope I'm not a bother, but I have this unquenchable need for understanding hahaaa

 


1996 GMC Sierra 2500........................................................... (planned upgrades below)

Alternator .............. Factory ................................................... 270A
Batteries ................ Duralast and (1) XS D925 Battery......... replace Duralast w larger XS battery

Head Unit............. Soundstream VRN 65HB

Sound Processor ..... Precision Power DSP 88R

Component Amp ... Hifonics BRX6016.4................................. (T.B.D.)
Front stage ........... (4) Crescendo PWX 6.5" (2) Crescendo FT1

Sub amp ............... Hifonics BRZ1700.1D................................ (T.B.D.)
Subwoofer ..............(1) Soundqubed HDC3 12
Enclosure ................................................................................ IN PROGRESS

Soundproofing ......................................................................... IN PROGRESS

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23 hours ago, mestapho said:

4. listen to trit

5. I hear ya :)


1996 GMC Sierra 2500........................................................... (planned upgrades below)

Alternator .............. Factory ................................................... 270A
Batteries ................ Duralast and (1) XS D925 Battery......... replace Duralast w larger XS battery

Head Unit............. Soundstream VRN 65HB

Sound Processor ..... Precision Power DSP 88R

Component Amp ... Hifonics BRX6016.4................................. (T.B.D.)
Front stage ........... (4) Crescendo PWX 6.5" (2) Crescendo FT1

Sub amp ............... Hifonics BRZ1700.1D................................ (T.B.D.)
Subwoofer ..............(1) Soundqubed HDC3 12
Enclosure ................................................................................ IN PROGRESS

Soundproofing ......................................................................... IN PROGRESS

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10 hours ago, MyNameIsNoob said:

Thanks for responding! I've read a few of your posts similar to this topic n appreciate any advice or direction that I can get.

1 - Aside from the output loss and noise, will the increase of "back pressure" from the extra resistance have any kind of effect on power handling similar to a smaller box volume?

3 - Is the effect on velocity from increasing power and volume because of the extra air being displaced? 

And how does the tuning change the air speed? Is it because of the wavelengths? (Just a wild guess, that's never even crossed my mind lol)

Hope I'm not a bother, but I have this unquenchable need for understanding hahaaa

 

Lol, you are no bother.  I'm happy to help out anyone who wants to learn!

1. Reducing port area actually doesn't increase back pressure, nor will it increase power handling.  Its a common misconception to think that you can shrink the port to get better cone control.  In practice, just the opposite happens.   Unless you are playing way below tuning where the port unloads, ported boxes actually have less cone excursion than a sealed box of the same size does.  If you reduce port area enough it will actually begin to perform like a leaky sealed box and cone excursion will increase.  It seems counter-intuitive, but that's how it works.  

2. You are correct that the increase in port velocity from increased power or box volume is from more air being displaced.  Air movement through the port is directly related to output, so more power or more box volume will both get your more output and thus higher port velocity. 

3.  Peak port velocity generally occurs at or near the tuning frequency.  So lets compare a 30 hz tone being played through a 30 Hz tuned port versus a 40 Hz tone played through a 40 hz tuned port.  When you raise the tuning frequency you are moving roughly the same volume of air through the port, but you are doing it in less time (higher frequency) so same air moving in less time requires higher air speed.  

  • Thanks (+1 Rep) 1

"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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This is good stuff. 

So I have another post, a bit more specific, about a box I'm building for 2 15" Sundown Xv2 based on their recommendations. I was going to start a few days ago, but after I did a bit of research on these subs and read about their preferences of what the subs "liked" I started second guessing my design. 

Sundown recommends 4.25 ft3 per sub and 68" of port area at 32 hz. I designed the box to be as close to this as possible, but after reading yours n others posts I changed it up slightly.

My new numbers, compared to Sundown recommendations: (rough calculations, i have no programs to be exact)

 

8.25 ft3 (for 2) volume

Sundown says 8.5 ft3

 

17 in2/ft3 and 140 in2 of port area (8.5"x16.5"x39") @ 30.5 hz

Sundown says 16 in2 and 136 in2 @ 32 hz

 

Assuming theres plenty of power to push em hard, do you think this change would be enough to matter or should I add more port in your opinion?

Edit* As a side note, any increase of port volume, in this case, will need to be traded from box volume

Edited by MyNameIsNoob
Edit

1996 GMC Sierra 2500........................................................... (planned upgrades below)

Alternator .............. Factory ................................................... 270A
Batteries ................ Duralast and (1) XS D925 Battery......... replace Duralast w larger XS battery

Head Unit............. Soundstream VRN 65HB

Sound Processor ..... Precision Power DSP 88R

Component Amp ... Hifonics BRX6016.4................................. (T.B.D.)
Front stage ........... (4) Crescendo PWX 6.5" (2) Crescendo FT1

Sub amp ............... Hifonics BRZ1700.1D................................ (T.B.D.)
Subwoofer ..............(1) Soundqubed HDC3 12
Enclosure ................................................................................ IN PROGRESS

Soundproofing ......................................................................... IN PROGRESS

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I responded in greater detail in your other thread, but I'll reply here as well.  I think your 8.25 cu box design with 140 sq in of port area should work out just fine.  

I don't know how much actual power to expect out of your friends amps but with the port area you have planned you should be totally fine.  

Edited by Triticum Agricolam
  • Thanks (+1 Rep) 1

"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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Thank you sir. I got it all mocked up today except for the birch facing and some braces inside, so hoping to finish it up tomorrow! 

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1996 GMC Sierra 2500........................................................... (planned upgrades below)

Alternator .............. Factory ................................................... 270A
Batteries ................ Duralast and (1) XS D925 Battery......... replace Duralast w larger XS battery

Head Unit............. Soundstream VRN 65HB

Sound Processor ..... Precision Power DSP 88R

Component Amp ... Hifonics BRX6016.4................................. (T.B.D.)
Front stage ........... (4) Crescendo PWX 6.5" (2) Crescendo FT1

Sub amp ............... Hifonics BRZ1700.1D................................ (T.B.D.)
Subwoofer ..............(1) Soundqubed HDC3 12
Enclosure ................................................................................ IN PROGRESS

Soundproofing ......................................................................... IN PROGRESS

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