I'm trying to build my first ported enclosure using a Dayton UM8-22 8". I've done some modeling in WinISD to get my specs, but I end up with a very long port (24") for my box size (~.75cf). I can make this work, but I didn't know if there were limitations to the shape - or maybe path is a better word - of the port through the box.
Can the port double back on itself, like a tight S shape? What about a two L shaped ports that converge at the port opening making a Y shape? Basically, I'm trying to fit a long port into a box where a straight or L port won't be long enough and I'm curious what the best practice is in this scenario.
Can the port double back on itself, like a tight S shape? What about a two L shaped ports that converge at the port opening making a Y shape? Basically, I'm trying to fit a long port into a box where a straight or L port won't be long enough and I'm curious what the best practice is in this scenario.
Yes, but there's losses that makes the total length longer depending on how tight the radius plus can make the vent area larger to get sufficient airflow at a < ~17m/s vent mach, so really need to search for air duct calculators.
Been there, done that and for me it's lots easier to mock up vents temporarily attached to the outside of the box and don't forget to put in the same total volume in scrap temporarily or it will be tuned higher (too short) once in the box.
Note that to use anywhere near its 600 W power rating requires a vent area (Av) = driver piston area (Sd), so long that it's better to make it an inverse tapered TQWT.
Been there, done that and for me it's lots easier to mock up vents temporarily attached to the outside of the box and don't forget to put in the same total volume in scrap temporarily or it will be tuned higher (too short) once in the box.
Note that to use anywhere near its 600 W power rating requires a vent area (Av) = driver piston area (Sd), so long that it's better to make it an inverse tapered TQWT.
Putting the ports exterior to the box can work.
I'm thinking of Collo's pages and in particular a speaker he called The Blast furnace.
https://www.subwoofer-builder.com/blast.htm
I'm thinking of Collo's pages and in particular a speaker he called The Blast furnace.
https://www.subwoofer-builder.com/blast.htm
As others have said its specs really dictate a sealed box they do not model well ported or bandpass due to the port requirements or go a PR, even though they quote .35cf sealed apparently they are better off with about .5cf to 1cf for best extension, although bigger the box less the power it will take to hit its max excursion.
The idea to put the vent external to the enclosure was actually patented and if it has been serviced, it will still be in force
It's an 8" driver, so in round numbers, 1.5x (min) = ~8*(1.5)^0.5 = 10", 2x = 12"
edit: Didn't realize its Sd was so small, so 8" or 10" assuming there's no 9" available.
edit: Didn't realize its Sd was so small, so 8" or 10" assuming there's no 9" available.
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A few pointers I have found invaluable over the past four decades:
Begin the design with a port area equal to Sd and work backwards until it fits in the box. Size matters.
Port length should not exceed twice its diameter, and be at least its own diameter away from any enclosure wall.
Flow should be equalised in both directions to maintain linearity and reduce port rectification.
Port radius is most important and depends upon application - it's a bit of a 'Hoffman' situation where optimising one aspect detracts from another.
NO BENDS!
A single circular port remains optimum; slots are the worst.
Proper port design is a win-win; increased efficiency and lower distortion.
Don't fret about precise tuning - this will probably change more with temperature and playback level than any simulation anomalies.
Begin the design with a port area equal to Sd and work backwards until it fits in the box. Size matters.
Port length should not exceed twice its diameter, and be at least its own diameter away from any enclosure wall.
Flow should be equalised in both directions to maintain linearity and reduce port rectification.
Port radius is most important and depends upon application - it's a bit of a 'Hoffman' situation where optimising one aspect detracts from another.
NO BENDS!
A single circular port remains optimum; slots are the worst.
Proper port design is a win-win; increased efficiency and lower distortion.
Don't fret about precise tuning - this will probably change more with temperature and playback level than any simulation anomalies.
I don't want to state the obvious but simple solution is to reduce the diameter of the port.
Also, are you sure you're using the specs right? From my understanding WinISD omits some very basic but essential calculations.
Sorry, I can't work in old money. A 0.75 cubic foot box is 21 litres externally. Use 12mm timber and the internal volume is closer to 19 litres. The driver uses about another litre, and the huge port between three and four litres. Bracing consumes more volume. Your internal volume is closer to 14 litres - that's the figure you should use for your simulation.