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When porting a cab, do you...?

m.oreilly

m.oreilly

Jul 5, 2006
1,192
12
Ukiah, CA
#1
...go by the driver's free air resonance, or it's 'usable' low frequency? also, is it better to use one large port over two or more smaller diameter (round port) ones? i'm just about to do some cutting, and needed to know before i went too far
:confused:
 
#9
m.oreilly said:
...or a 6" at over 2" for a res of 60hz...like i had originally. so what should one tune for? the free res or the 'usable' lowest frequency???
Click to expand...

Neither is what you go by.

What you do is, you model a lot of different tunings, looking at the frequency response curve and excursion-limited power handling while maintaining sufficient port area to avoid chuffing at high levels, all while keeping build-practicalitiy in mind. Programs are written for round ports; as you move to other shapes that have larger perimeters relative to their cross-sectional area (like a rectangular slot port), the port lengths predicted by the program become less reliable; the actual required length is reduced, though I'm not sure why.

Any tuning you choose will be a juggling of tradeoffs, a compromise among several factors (some of which are mentioned above). Overlook or over-emphasize one factor and the result can be poor performance.
 
#10
Duke, what program would you recommend to calculate excursion-limited power handling? WinISD is a nice utility but doesn't seem to have that feature. I don't know if WinISD Pro provides this but it locks up on my PC running Vista (aaargh, hate that OS).
 
#12
DukeLeJeune said:
Neither is what you go by.

What you do is, you model a lot of different tunings, looking at the frequency response curve and excursion-limited power handling while maintaining sufficient port area to avoid chuffing at high levels, all while keeping build-practicalitiy in mind. Programs are written for round ports; as you move to other shapes that have larger perimeters relative to their cross-sectional area (like a rectangular slot port), the port lengths predicted by the program become less reliable; the actual required length is reduced, though I'm not sure why.

Any tuning you choose will be a juggling of tradeoffs, a compromise among several factors (some of which are mentioned above). Overlook or over-emphasize one factor and the result can be poor performance.
Click to expand...

what do i look for in the winisd chart?
here is what i get with the 6" duct for 53hz:

[Invalid or Expired Link Removed]

and 60hz:

[Invalid or Expired Link Removed]
 
#13
M.orielly, I don't use WinISD. You can look at those curves vs other tuning frequencies to see what gives the shape curve that will best suit your needs. But, that will not tell you the whole story.

Without knowing what the excursion-limited power handling is, I would suggest you tune somewhere in the 42 to 48 Hz ballpark, as that usually works pretty well. 53 Hz is pretty high unless it's a relatively small enclosures, and the result can be premature fartout if you don't use a highpass filter to protect the woofer from over-excursion. 60 Hz is quite likely to result in early onset of fartout without a protective high-pass filter set pretty high. So in this case, my off-the-cuff suggestion is to lower the tuning frequency down to 48 Hz or maybe even a little lower. You lose some meat in the 60 to 120 Hz region, but in exchange you gain some real-world headroom, and imho end up with a better balance of characteristics.
 
#15
m.oreilly said:
what do i look for in the winisd chart?
Click to expand...

The box is too small. Let the program calc the ideal configuration, per driver it will give 2.16 cu ft /50 Hz.
WinISD Pro provides this but it locks up on my PC running Vista
Click to expand...
Run it in Windows 98 compatability mode.
 
#16
WinISD Pro Alpha? It's easy to calculate excursion at various frequencies, varying amounts of power, etc., what different tunings do to the low end, port air velocity, what applying eq will do, etc. Translating what your ear wants to hear to what that looks like on paper is the kicker sometimes.

It is good for predicting what will happen in the lows. As far as what the mids/highs will do, consult the spec sheet for the driver. It will figure it out for you but consider that the "technically" best box for the speaker may result in something that's too big to be practical or tries to reach deep lows that aren't needed to make a bass guitar sound good and could be traded off for more real power handling where it counts.
 
#18
Having No Port Chuffing is important & must be under 0.16 to no whistle...
Having one big port over two smaller ones wont make much difference, this is what ive been told anyway.Main thing with them is the ports shouldnt be more than about 5-10% shorter or longer than calculated so it must be done properly to get the right tuning.
I definitly had problems with tuning at first but after it was set proper i got the sound i need.I found out the hard way that you cant just stick speakers in a cab & off you go.
My rig now fills out all the bass needed to get the job done @ any volume basically....Anyway
I went for 42hz tuning with the BP102.
Who said the 102 is no good ??
 

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