Different port lengths with lspcad and Unibox (1 Viewer)

[Kyle Richardson]

I'm just a touch confused. I'm entering in the same numbers in both programs but they are giving me different port lengths!

283 liters

22Hz tuning

3ea 4" ports

Ql=15

Qa=100

Unibox says 47.91cm and lspcad says 33.7cm for each port length. Why such the large difference?? I tend to believe Lspcad more but I was wondering what you guys are coming up with.

Thanks

Kyle Richardson

Acoustic Visions

 

[Jack Gilvey]

I get pretty much the same result, Kyle. Don't know what's up.

 

[Patrick Sun]

One of them is doing the multiple ports calc wrongly.

 

[Pete Mazz]

With WinSpeakerz, I get 40.6....go figure!

Pete

 

[Jack Gilvey]

The new WinISD Pro alpha (pretty cool, actually) gives me 45.7cm. No way to input losses, stuffing, etc., though.

 

[Kyle Richardson]

Well, its good to see I'm not crazy. Now I just need to find out which one is correct.

Kyle Richardson

Acoustic Visions

 

[ThomasW]

Don't know about UniBox I'm too cheap to upgrade my Excel-97 to a newer version....
But the most recent subs I've built using LspCAD have been dead on. The single 1503 modeled to a tuning of 18Hz, when we actually measured the sub the tuning was 18.4Hz

 

[Achim Eilers]

Just ran your numbers in BassBox:

41.54cm 1 flush end

44.08cm 2 flared ends

hope that helps

Achim.

 

[Pete Mazz]

Maybe all the sims are based on the "magic 8 ball" port length calculator!
Pete

 

[Greg Monfort]

Assuming the vents aren't flared and using an early formula that's worked well for me over the decades, I get a vent length of 40.386cm, very close to Winspeakerz's 40.6cm.

Anyway, there's always some variance in the system and why you should always cut them a bit long and fine tune them if hitting a particular frequency spot on is desired. Even if not, tuning a bit low (longer vent) is a good idea for high power apps as the system Q goes up with VC heating and the lower tuning offsets it some if it wasn't factored into the design.

GM