Does Port Length REALLY Matter?

 

New member
Username: Silby101

Kelowna, BC Canada

Post Number: 1
Registered: Oct-04
I am designing a box for 2 JL 10" subs and have a question. Does port lenght really matter? I ask this since all the things I read say that you should use the calculators or the manufactures suggested lenghts but here is the problem.

Bose wave radios work on a design which is one huge port. I have one and it's amazing. The bass that I get from these 2.5" speakers are amazing. But the port lenght is just as long as what is suggested for my 10" sub. So what gives? Does a longer port take away from the bass or enhance it? Bose gives the analogy of a whisper in a flute can fill up a concert hall with sound. Small movment but a long focusing chamber or port. What are some peoples ideas about this?

Thanks for the input!
 

Gold Member
Username: Jonathan_f

GA USA

Post Number: 2366
Registered: May-04
Yes it matters. Wave radios aren't actually a port. It is their variation of a Transmission line enclosure, and they got a huge team of lawyers to get them a patent on their rendition of an old design. Anyway, port length matters. With a ported box, length and crossarea is what tunes the enclosure, and tuning is the frequency in which air resonates inside the port, and if you don't get the length right, that frequency will change. The difference in ported and transmission line is that with a transmission line, you're making the rear port length a certain fraction of the length of the waveform that the speaker resonates at (1/4 wave is most popular), thus allowing the speaker to play lower, and cone resonance is removed because air doesn't resonate inside the enclosure. With ported, you're tuning to a frequency, and that tuning (resonance of the port) generates more output at that frequency, and anything below that point will unload and have a 24db/oct rolloff.

"Bose gives the analogy of a whisper in a flute can fill up a concert hall with sound. Small movment but a long focusing chamber or port."

That analogy is a bunch of BS and has no relation to the output of the radio. TL designs are naturally more efficient than sealed or ported, but it has no relation to a flute in a concert hall. The only reason TL is louder is because of the way the port controls the speaker cone, it's not because the port is "long and focused". You should hear the Henry Kloss radio, it sounds a lot better and is cheaper.
 

Silver Member
Username: Insearchofbass

Post Number: 895
Registered: Jun-04
you go jon bose is over rated and yes i agree they stole an old idea...i bought a pair of advent prodigys years ago for me home theater and they had an eight inch woofer and a tweeter and somehow they got the mids to play nicely out of them too. Anyway they cost me 200 bucks and before that i was looking at the bose 301s at 300 bucks. All i can tell you is the advents blew the bose away in every way for a 100 bucks less and to top it off i found out advent was a subdivision of the jensen company go figure.

ps...if i would have known the advents were made by jensen i never would have checked them out. Also i have since replaced the advents with cerwin vega dx 7s (12s with mids and tweets)
 

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 4836
Registered: Dec-03
I'll keep my Martin Logan ESLs.
yeah the bose wave radio uses a folded horn or TLS variant.
port length tunes the enclosure to a specific frequency.
this makes all the difference in the world to how the enclosure is going to sound.
tuning to 45Hz gives a boomier response. tuning to ~65Hz is ideal for SPL events usually, and tuning to lower octaves like 32Hz or 28Hz is ideal for deep bass response.
big big difference with port length.
diameter matters as well since this will affect port noise.
 

New member
Username: Silby101

Kelowna, BC Canada

Post Number: 2
Registered: Oct-04
Thanks so much for all the information. I have one last question. Does a bend in the length of the port matter. Say if my calculated lenght for the frequency that I want is longer than the depth of my box, does a bend affect that? I found this predesigned box from JL that has one, and hope that I can use this same concept in the box that I want to build. Thanks again!Upload
 

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 4911
Registered: Dec-03
you can bend the port like that as long as you calculate to keep the proper cross sectional area for the port.
 

Bronze Member
Username: Thumprms

DaltonUSA

Post Number: 41
Registered: May-04
Glass
could i just add 2 inches to all the measurements to make this box for a 12'' subwoofer?
 

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 4950
Registered: Dec-03
for a slot vented box for a 12" sub, you want 2cu ft, on average.. and you'll need to completely recalculate port dimensions for tuning.
 

Bronze Member
Username: Thumprms

DaltonUSA

Post Number: 42
Registered: May-04
how can i translate 4 x 10 3/4 pvc pipe into a slot port?
 

New member
Username: Silby101

Kelowna, BC Canada

Post Number: 3
Registered: Oct-04
From what I understand, if you make the slot area, the same as the area of the circle port, you can keep the same lenght for the slot as the port, thus keeping the overall volume for the port the same. But since I'm new, I could be completely wrong. But hey, I've gone to school and could be right!
 

Bronze Member
Username: Thumprms

DaltonUSA

Post Number: 43
Registered: May-04
cassidy where did you find that picture of the subwoofer box? Is it for a ten inch sub?
 

New member
Username: Silby101

Kelowna, BC Canada

Post Number: 4
Registered: Oct-04
I got it off the manual for the JL 10W7 (http://www.jlaudio.com/subwoofers/10w7.html). The website has recommended box sizes for all of their subs in the manuals. The image is for a 10" box.
 

Bronze Member
Username: Thumprms

DaltonUSA

Post Number: 44
Registered: May-04
thanks
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