port fitting difficulty, help please!

[shredder2]

Yes... it's a bit high, but the efficiency and volume savings might be worth it. It's a compromise like most enclosures, but I' do it... Round-over the entry and exit .75", lengthen the tube that amount and your volume/tune would be close.  

A big 8" would be LONG... even a 7.5" like a Sonotube, but a 6" is more area than a pair of 4", easier to do than 3 4" ports  and most likely enough for a 1000 watt amp playing music. 

Sheeit... for your power I'd look for volume and efficiency and that aero/round ought to serve IMHO.

 

[BOOMINGRANDPA 5,000+ posts]

Hmmm. I’ll have to consider that. I think WinISD put the air velocity at well over 30 m/s when I looked at 6” round port though. 

I thought with round port air velocity had to be below 40mps not 30 like slot port.. shredder said jeff said that last yr anyway

 

[shredder2]

I said that?... I suppose you're gonna quote me and try to prove a point... ok... here goes... I keep it under 115fps if I can... otherwise I specify an aero or some kinda flare. As far as compression losses go... I've really never noticed when the velocity is a bit high, chuffing either... Plus actual power delivered is usually less than most think, especially when playing actual music. 

 

[shredder2]

Using a round limits the port area available to a fixed value... sometimes sacrifices/compromises are made. Hell, most enclosures are a collection of compromises  

 

[YukonXL04]

Using a round limits the port area available to a fixed value... sometimes sacrifices/compromises are made. Hell, most enclosures are a collection of compromises  

This. That's the downside to round ports. But I like throwing a big flare on them if I'm borderline on port area.

I know that's how all my boxes go, one compromise for another. But I also try to go for the max in a given area as well...

 

[shredder2]

And nobody likes to do the work to add a bend it seems when area necessitates length (with an aero), oh you can minimize the length with added volume but that's most likely why the aero was used (space savings) plus the added volume usually increases velocity a bit in my experience. Compromise, compromise... sometimes slots just make more sense cause the added bracing and port area/bends are easier for whatever volume/tuning/area you are trying for. 

 

[BOOMINGRANDPA 5,000+ posts]

I said that?... I suppose you're gonna quote me and try to prove a point... ok... here goes... I keep it under 115fps if I can... otherwise I specify an aero or some kinda flare. As far as compression losses go... I've really never noticed when the velocity is a bit high, chuffing either... Plus actual power delivered is usually less than most think, especially when playing actual music. 

no idk where that was. yeah u said u saw jeff say that so thats what i went by., i guess aero port is best if doing that high port air.. like u said i think if people use say 800rms as system input power on a 1200rms amp and air so high they probably only really getting 500-600 watts anyway..

 

[shredder2]

Yeah... I'm still learning about this everyday.

Since increasing the area of a port quickly produces very long ports, the most effective means of moving more air is to increase the air velocity.Ports operating below about 10 m/sec generally have no problems with turbulence and compression. As velocity is increased beyond this, turbulence occurs as air exiting the port is forced to slow too quickly as it encounters the surrounding still air.Flared ports cause the airflow to expand and loose speed in a controlled fashion, allowing higher speeds without turbulence. This method targets the air in the "boundary layer", which is close to the walls of the port.Increasing velocity even further, the air in the "core" of the port becomes turbulent. Flares are unable to help with this problem, which represents the limiting velocity for the port. By this stage the port is beginning to present a different load to the system, resulting in de-tuning and subsequent loss of output, known as compression.

Area Ratio is the cross-sectional area (CSA) of the port opening, divided by the CSA of the unflared section of the port. It gives an indication of how quickly the air has to change velocity as it exits a flared port, and is a more useful measure than flare radius alone.

Gramps, any given sized aero with any real velocity will benefit from a flare is what I read above (and the bigger the flare the better)... but there is a point of compression (I use 35m/s) and compromises are made sometimes. 

Now I'm gonna get flamed by others most likely... lol

 

[shredder2]

I think it was this box...



The dual 4" ports show compression modeling it up but the OP seemed extremely pleased with the result, and no flares were used.

 

[mestapho]

Since this is active again, I'll update.  I built the box as I designed and it came out good except I f()cked up the speaker holes. boo. 

I've redesigned the box w/a higher tune and slightly smaller and it'll be more straight forward. 

Figuring out the box tune by speaker movement I think the orig. box came out tuned to between 30-32.  I feel like its not quite as punchy w/rock as my 36Hz box for my 8's was, so

with the next box I'm tuning to 35 which is SD's recommendation anyway. 

3.5 cubes at 35 Hz

https://3dwarehouse.sketchup.com/legacymodel.html?id=71a99ede-2bd9-4394-9bc0-2895de38336e&legacyredirect=backend

View attachment 2+SA+12+take+two.skp

 

[mestapho]

Got the new box built.  Much better result than version 1.  Just need to get some Duratex to finish it. 

I’m surprised at how much I can hear a difference between the two boxes.