Port length for shiva? (1 Viewer)

[DorianBryant]

I built a 85 liter Shiva with a 4" port. I must have ordered the wrong port from Parts Express or they sent me the wrong one. The one I received is 11.5" totall length and flared on both ends. The numbers i came up with indicate the port length should be 13.87" to tune to 20-22 hz.

Does this sound right? I tried the 11.5" port but it seems to be a bit boomy.

Should i get the longer port? I tried to plug the port but it really effects the output. It somewhat tighter though.

What length 4" port should i be using?

 

[Stephen Hopkins]

Sounds like they sent you their clearance 3" x 11.5" port. I would send it back and have you send the correct 4" port because that's what you paid for or refund you the difference. That said, the 3" x 11.5" port is giving you a tune of around 21.5hz which should give a prety gradual rolloff w/ an F3 of around 25hz. What you're perceiving as boominess is probably due to room peaks or nulls. I would experiment with placement to see if you can minize this, or it may be neccesary to add some kind of EQ to combat the peeks.

 

[minhG]

just to be clear, is that 11.5 with the flares or only the center section?

 

[DorianBryant]

Actually it is a 4" port with flares on both ends and a total length of 11.5".

I have gotten conflicting results from a couple of different programs. Thought I would pose the question to those in the know. Since the hole is cut, what length 4" port should i use to get down in the 20's? Does 13.87 sound reasonable?

I may look into an EQ. Most seem to be using the BFD.

I was also using a 120watt RMS amp which may or may not have a bass boost. I sold it and will be getting a 250 watt amp from PE without a boost.

when i demoed the sub upstairs in my living room i played around with placement but was getting some serious resonance from the windows. I want to get the port length and amp straightened out first.

Thanks for the help.

 

[Ryan Schnacke]

Not particularly. I assume you mean 13.87 inches TOTAL (including flares). This would get you to around 26-27Hz tune with about 1.5dB bump around 40Hz.

In 85L even using the full 18" length of the 4" flared port you'll only tune it down to about 23-24Hz. So I'd want to use at least this much. And perhaps you could mate some other 4" tubing to the flares to get more length. You'd need 25-26" total to achieve the "Adire alignment" and get 20Hz tune.

 

[Dennis Gardner]

It took a 19" long 4" port to get a 17 hz tune for my 142 litre box. I run dual Shivas with 320 watts.

 

[DorianBryant]

yes, 13.87" inclusing the flares. 11.5 seems just too short. hopefullt this, and a better amp will allow me to ge the performance I am looking for.