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Port Size and Stuffing

ani_101ani_101
in Related
I was modelling a couple of driver and like the response and box size, but ran into an issue with port chuffing. At full tilt, port chuffing is pushing 80 m/s. I am planning to have the port on the bottom of the cabinet, but assume this will still be audible. Would a heavy carpet or a pad of stuffing under the speaker help muffle some of the noise? Any other suggestion? Increasing the port size i tun into too long of a port... 

This is with 100W per driver for a max response of 106db SPL

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Comments

  • ani_101ani_101
    Modeling for more sane power and response, at the other end of the spectrum with 2.5W per driver for 90Db SPL at 1M, I get this...

     
  • ani_101ani_101
    at 10 W per driver, 96DB SPL, this is the result


  • ani_101ani_101
    Going a bit over at 20W per driver at 99DB SPL, this is the response and port noise.... This is good enough i suppose for 99% of all listening.... even for the occasional party? and XMAX is not exceeded at any frequency...

     


  • dcibeldcibel
    In WBCD I always hit the "MAX SPL" button to see where the xmax limited SPL is, this gives you a good idea of the peak SPL you can generate before you exceed xmax, then drop 6-12dB crest factor for average SPL. Design the port around the power input that generates max SPL.
    rjj45
    I'm not deaf, I'm just not listening.
  • ani_101ani_101
    Good is unibox , xmax is exceeded at f3 and lower at around 106db. Modelling at xmax requires a 3.5 inch port. A 3 inch port needs to be 20 inch in length, which doesn't fit inside the box. 

    The 2" port required around 8inches in length, much more manageable. Usually I model around xmax, but expecting a 5 incher to hit 31hz at 106 db 1m.... It does have 9" for xmax
  • PWRRYDPWRRYD
    Port compression is also a big concern, even before audible port chuffing happens.
    rjj454thtry
  • dcibeldcibel
    Ports can be bent and folded to make it fit.
    I'm not deaf, I'm just not listening.
  • ani_101ani_101
    What is port compression and can it be simulated or measured? Is it also depends on power? At low power, there should be any issues? Only when pushing it I expect things to go haywire...
  • WolfWolf
    You could run an SD215-PR per W5, right?

    InDIYana Event Website

  • ani_101ani_101
    dcibel said:
    Ports can be bent and folded to make it fit.
    Yes, definitely, but not in this case (box), hence asking how bad it would be in real world under realistic conditions and if there is anything that can be done to reduce it.

    Would love to overbuild, but the design choice asks for a compromise, would like to know how bad of a compromise it is.
  • WolfWolf
    slot port?

    InDIYana Event Website

  • dcibeldcibel
    ani_101 said:
    dcibel said:
    Ports can be bent and folded to make it fit.
    Yes, definitely, but not in this case (box), hence asking how bad it would be in real world under realistic conditions and if there is anything that can be done to reduce it.

    Would love to overbuild, but the design choice asks for a compromise, would like to know how bad of a compromise it is.
    Well, at 20W you're doing okay, beyond that you may start to be disappointed. So the question is, will you be satisfied with the SPL at 20W.
    ani_101 said:
    What is port compression and can it be simulated or measured? Is it also depends on power? At low power, there should be any issues? Only when pushing it I expect things to go haywire...
    "Port compression is a reduction in port effectiveness as sound pressure levels increase. As a ported system plays louder, the efficiency of the port reduces, and distortion emitted by the port increases" - Wikipedia

    Basically, the greater amount of air needed to squeeze through the port opening, the higher the back pressure generated by the port. Just like any fan system, a higher amount of restriction (pressure) requires a greater amount of force to overcome it to create flow, so the port becomes less effective. It's part of that whole "chuffing" issue, but when a speaker is chuffing it's not just wind velocity as a result, but loss of bass efficiency and increase in distortion. The ROT to keep velocities below 25m/s or 17m/s depending on who you talk to, is there to get at the happy result of a port that is "good enough" with reasonable dimensions. You just have to pick the power level (SPL) where that velocity occurs at.

    Simulations of any speaker performance at high SPL lack accuracy. The simulation is based on T/S parameters which are small signal by definition. The simulation doesn't take into account changes in suspension stiffness and BL over the driver excursion. For example, below 20Hz you probably show excursion sky high even at low power, yet I'm sure if you play 20Hz signal the cone won't fly across the room.


    ani_101
    I'm not deaf, I'm just not listening.
  • jhollanderjhollander
    Might consider port out of the bottom and using the bottom plate to extend the port. A slot port along the interior can also help. I personally think the lower rear port that have a flare have less noticeable port noise.

    Also consider checking the port resonance box if that is unibox so you can see where the port resonance shows up.
     John H, btw forum has decided I don't get emails
  • rjj45rjj45
    A folded slot port can usually have enough area and length to minimize air speed at a given (highish) SPL. You inevitably start to add distortion as you really push a speaker, the bass starts to sound funny, and finally you can actually hear chuffing. Not a "sound of death", but pretty high distortion due the factors that others have detailed.
    But Chahly - Stahkist don't want speakers that look good, Stahkist wants speakers that sound good!
  • NavyGuyNavyGuy
    What does your cabinet shape and internal volume look like?
  • ani_101ani_101
    20 liters, 20x6.5x10 internal dimensions, the woofers are on the front 6.5x20 and the port is on the bottom 6.5x10.
  • NavyGuyNavyGuy
    ani_101 said:
    20 liters, 20x6.5x10 internal dimensions, the woofers are on the front 6.5x20 and the port is on the bottom 6.5x10.
    Is the box already built? If you added another 1" of depth you could fit an APR10 or the 10" RSS passive.
  • ani_101ani_101
    Yes, box is built, had not simulated at xmax. Should be ok at normal volume me thinks, but let's see what it does at elevated spl.
  • 4thtry4thtry
    ani_101 said:
    What is port compression and can it be simulated or measured? Is it also depends on power? At low power, there should be any issues? Only when pushing it I expect things to go haywire...


    Hi Ani,

    Sorry for the late comment, just found this thread.  There was a Speaker Builder article published many, many years ago where a fairly experienced builder did port compression analysis using a 10" woofer and, as I recall, several port diameter sizes ranging from 2 to 6 inches.  He published several graphs showing comparative SPL compression effects at low frequencies.   I'll dig through my  SB back issues, find the issue, and bring it along to Indy.

    Bill 

    ani_101
  • rjj45rjj45
    One of the guys on DiyLoudspeakerPad on FB did a pretty comprehensive study of various port geometries and sizes, with compression and distortion measurements. Crap - it's pretty much impossible to find older posts on FB.
    If I find the PDF on my disk, I'll post a Google Drive link to it.
    But Chahly - Stahkist don't want speakers that look good, Stahkist wants speakers that sound good!
  • jr@macjr@mac
    rjj45 said:
    One of the guys on DiyLoudspeakerPad on FB did a pretty comprehensive study of various port geometries and sizes, with compression and distortion measurements. Crap - it's pretty much impossible to find older posts on FB.
    If I find the PDF on my disk, I'll post a Google Drive link to it.
    Fun group for awhile, but it got to 20,000 members and it became impossible to keep up. The Facebook timeline model is alright for getting glimpses into peoples lives and interests - but damn, clusterfuck for searchability. Hit the refresh page - and it presents an entirely new set of posts to browse. 
    rjj454thtry
    I have a signature.
  • rjj45rjj45
    It was Scot Hinson - I found some other technical PDFs by him, but I can't find the port tests. Darn.
    But Chahly - Stahkist don't want speakers that look good, Stahkist wants speakers that sound good!
  • dcibeldcibel
    Is this what you were looking for?


    4thtry
    I'm not deaf, I'm just not listening.
  • rjj45rjj45
    dcibel said:
    Is this what you were looking for?


    Yeah - that was / is it. Thanks.
    But Chahly - Stahkist don't want speakers that look good, Stahkist wants speakers that sound good!
  • 4thtry4thtry

    Ani,  Found the article that I was looking for.  It was published in Audioxpress mag Sept 2001.   It was written by Bohdan R., author of the Soundeasy software package.   Here is a link to the article:

    https://audioxpress.com/article/how-good-is-your-port

    Bill


    dcibel
  • 4thtry4thtry
    +1 on the FB comments.   Very difficult to find things there.   Does it help if you are a member?  I do not have a FB account, so I always thought that my difficulty was due to limited non-member functionality; that I could only click on the "discussion" button.    
  • Ron_ERon_E
    4thtry said:
    +1 on the FB comments.   Very difficult to find things there.   Does it help if you are a member?  I do not have a FB account, so I always thought that my difficulty was due to limited non-member functionality; that I could only click on the "discussion" button.    
    I don't think it helps if you're a member.

    Ron

  • jr@macjr@mac
    It doesn't help. 
    I have a signature.
  • 4thtry4thtry
    Sad, as there a number of good builds over there.  Some type of external google search workaround is needed.
  • jr@macjr@mac
    The whole idea is to scroll, scroll, scroll, refresh, scroll, scroll. It is formatted to enhance ad views, not the UE. 
    rjj45Gowa4thtry
    I have a signature.
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