external ports?

beetooex · 1st June 2006, 07:45 PM

Hey,

i've been doing a load of research but i've got a bit stuck...

Basically i'm trying to model my bass cabinet in winisd and all i need to do is figure out the length (depth) of the slot port.

It only extends 1 inch in FRONT of the baffle board and not at all back into the speaker enclosure. Does this length count in the calculations or is it an untuned vent?

hope this is an easy one for you!

thanks in advance

Volenti · 2nd June 2006, 12:14 AM

The length of the vent is the length of the vent, regardless if it's inside the enclosure or not.

boydon_lepasci · 2nd June 2006, 01:23 AM

I would be extremely suspicious of a 1 inch long port. It typically indicates one of the following:

- a really large box
- really high tuning
- the port is too small in area for the amount of air it will pass, thus making unmusical noises

If none of these are the case, I am curious about this design.

johninCR · 2nd June 2006, 02:06 AM

Quote:

Originally posted by boydon_lepasci
I would be extremely suspicious of a 1 inch long port. It typically indicates one of the following:

- a really large box
- really high tuning
- the port is too small in area for the amount of air it will pass, thus making unmusical noises

If none of these are the case, I am curious about this design.

Agreed. Also, with such a short slot port, figuring out the exact effective length will be tricky. Slot ports require special consideration anyway, but I've never see an end adjustment for one that is in the corner. I think that will create even more effective length, than the usual slot port adjustment.

lndm · 2nd June 2006, 03:15 AM

Yes, I would definately consider making the port longer (and correspondingly wider) for the same tuning frequency. If you put your vent inside the box, you need to make the box slightly larger to accommodate the volume of the port.

beetooex · 2nd June 2006, 07:51 PM

Cheers for the help guys, have plugged in my numbers + been playing with winisd since got home from work :-)

After measuring it properly this time (stupid mistake) the slot port is actually just over 2" long

The cab is for playing bass guitar through (driven by a 100w valve amp) and so is pretty hefty.

Dimensions are 53x53.5x25cm

the slot port runs the whole length of the bottom at 53x3x5.5cm

There's one 15" fane driver (studio 15b) I'm pretty sure this isn't original hence me trying to find out whether its suited to the cab.

Winisd reckons the port tunes to ~50Hz. (not great when the lowest open string on a bass is 40Hz) I'm sure i've read somewhere that winisd doesn't calculate slot ports accurately- Is this right in anyone's experience and does it affect the port freq?

Volenti · 3rd June 2006, 12:24 AM

Quote:

Originally posted by beetooex

Winisd reckons the port tunes to ~50Hz. (not great when the lowest open string on a bass is 40Hz) I'm sure i've read somewhere that winisd doesn't calculate slot ports accurately- Is this right in anyone's experience and does it affect the port freq?

A slot port with a ratio like that won't model correctly using conventional software, it's likley the enclosure is actually tuned slightly lower than 50hz with a more damped output (compared to round vent) from the port.

beetooex · 4th June 2006, 06:48 AM

Looks like it may not be a bad bass cab then as far as i can see.

It must be farting out because of amp clipping.

cheers for the opinions

1st June 2006, 07:45 PM	#1
beetooex diyAudio Member Join Date: Jun 2006	external ports? Hey, i've been doing a load of research but i've got a bit stuck... Basically i'm trying to model my bass cabinet in winisd and all i need to do is figure out the length (depth) of the slot port. It only extends 1 inch in FRONT of the baffle board and not at all back into the speaker enclosure. Does this length count in the calculations or is it an untuned vent? hope this is an easy one for you! thanks in advance

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2nd June 2006, 12:14 AM	#2
Volenti diyAudio Member Join Date: Aug 2003 Location: Australia	The length of the vent is the length of the vent, regardless if it's inside the enclosure or not.

2nd June 2006, 01:23 AM	#3
boydon_lepasci diyAudio Member Join Date: Apr 2005 Location: Salt Lake	I would be extremely suspicious of a 1 inch long port. It typically indicates one of the following: - a really large box - really high tuning - the port is too small in area for the amount of air it will pass, thus making unmusical noises If none of these are the case, I am curious about this design.

2nd June 2006, 03:15 AM	#5
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	Yes, I would definately consider making the port longer (and correspondingly wider) for the same tuning frequency. If you put your vent inside the box, you need to make the box slightly larger to accommodate the volume of the port.

2nd June 2006, 07:51 PM	#6
beetooex diyAudio Member Join Date: Jun 2006	Cheers for the help guys, have plugged in my numbers + been playing with winisd since got home from work :-) After measuring it properly this time (stupid mistake) the slot port is actually just over 2" long The cab is for playing bass guitar through (driven by a 100w valve amp) and so is pretty hefty. Dimensions are 53x53.5x25cm the slot port runs the whole length of the bottom at 53x3x5.5cm There's one 15" fane driver (studio 15b) I'm pretty sure this isn't original hence me trying to find out whether its suited to the cab. Winisd reckons the port tunes to ~50Hz. (not great when the lowest open string on a bass is 40Hz) I'm sure i've read somewhere that winisd doesn't calculate slot ports accurately- Is this right in anyone's experience and does it affect the port freq?

4th June 2006, 06:48 AM	#8
beetooex diyAudio Member Join Date: Jun 2006	Looks like it may not be a bad bass cab then as far as i can see. It must be farting out because of amp clipping. cheers for the opinions