port length

[tald]

I built a speaker with 14.6L volume.
The tuning should be 40Hz.
The drive is SS8545-00
I put a port length 11CM and after that made
calculation that the port length should be 7.3CM for 40Hz.
11CM port is suite for 33Hz.
Would this mistake will have negative affect on sound ?
Thanks.

 

[TheSeekerr]

Yes, the lower tuning will cause your low frequency response to have a peak, then a dip, rather than a smooth rolloff. You should double check your calculations, then trim the port to the appropriate length.

 

[Ron E]

I built a speaker with 14.6L volume.
The tuning should be 40Hz.
The drive is SS8545-00
I put a port length 11CM and after that made
calculation that the port length should be 7.3CM for 40Hz.
11CM port is suite for 33Hz.
Would this mistake will have negative affect on sound ?
Thanks.

Attached is a picture that compares the two alignments, using the parameters found here (if this isn't your woofer you need to post the parameters): ScanSpeak 18W/8545 7" Paper Cone Woofer from Madisound

I think there are a few versions of that woofer - as you see, there is no peak and dip Of more importance is your port diameter - you don't state it, but to give a 33Hz tuning in a 14.6l box it must be about 3cm - this is way too small and your port velocity will be way too high and it will be making lots of nasty noises. Your port should be 5-8 cm in diameter, depending on how loud you like to play your music.

 

[tald]

Internal port diameter is 3.6CM.

 

[tald]

I don't hear nasty noises but i do feel that sound is
sometimes dip. then i moved the speakers from the back wall and its sound
much better but i fill it's sound little strange.
I must say that my room acoustic is very bad.
The XO is from here:
http://www.speakerbuilding.com/content/1021/net_draw.gif

 

[TheSeekerr]

Oops - ignore me, I'm way off the mark today.

How far away from the wall are your speakers? What side is the port on?

 

[tald]

The port is on the back side.
The speakers are about 35 cm from back wall.

What should i do ? trim the port to 7CM length
or replace it with 4.6 port diameter (11 cm length) ?
I see in many sites that minimum port diameter
should be 5CM.

 

[Inductor]

For some design considerations/choice (when needed, more wood work, etc.) you could add a second port, let's say on the front or bottom, instead.