Bass Cab

[petetexas]

Hi,

I have just got hold of a 4x12 speaker cabinet , and 4 Celestion BN 12 -300 S Neo magnet speakers.

The internal volume of the cab is about 4.8 cu ft.

Any idea what size and how many ports to put in ?

Pete

[Mr. Foxen]

[quote name='petetexas' post='689179' date='Dec 19 2009, 04:30 PM']Hi,

I have just got hold of a 4x12 speaker cabinet , and 4 Celestion BN 12 -300 S Neo magnet speakers.

The internal volume of the cab is about 4.8 cu ft.

Any idea what size and how many ports to put in ?

Pete[/quote]

For ports, 1 flared round one in such a position they you can't see the back of the cones through it is best. However it is not practical. Need to figure where you can put ports first. Download Win ISD to figure the right length once you have figured where you can fit them. I think the rough rule was a port aread of about 1/9th of the cone area.

[petetexas]

[quote name='Mr. Foxen' post='689192' date='Dec 19 2009, 04:41 PM']For ports, 1 flared round one in such a position they you can't see the back of the cones through it is best. However it is not practical. Need to figure where you can put ports first. Download Win ISD to figure the right length once you have figured where you can fit them. I think the rough rule was a port aread of about 1/9th of the cone area.[/quote]

Hi,

Thanks for reply, have already looked on Win ISD - does not have celestion speakers in, thats where my problem started.

Pete

Edited December 24, 2009 by petetexas

[alexclaber]

Hi Pete,

You need to find the T/S parameters for the Celestions and load them into WinISD (Pro is better). Then find the max power handling and then find the port air speed for that power input, and then adjust the port area to get the air speed reasonably low. Once you're settled on a tuning frequency and port area then you can get the port lengths. Test the actual tuning vs predicted tuning with a sine wave generator and some salt on the cone - minimum movement at the tuning frequency.

Don't forget to ensure the cab is sufficiently braced and damped before you reassemble it.

Alex

[petetexas]

[quote name='alexclaber' post='689221' date='Dec 19 2009, 05:06 PM']Hi Pete,

You need to find the T/S parameters for the Celestions and load them into WinISD (Pro is better). Then find the max power handling and then find the port air speed for that power input, and then adjust the port area to get the air speed reasonably low. Once you're settled on a tuning frequency and port area then you can get the port lengths. Test the actual tuning vs predicted tuning with a sine wave generator and some salt on the cone - minimum movement at the tuning frequency.

Don't forget to ensure the cab is sufficiently braced and damped before you reassemble it.

Alex[/quote]


Thanks guys,

This is far more complicated than I thought ! ! ! ( The cab is all ply, and braced front to back )

I have sent the info ( volume and type of speakers ) to Celestion, asking for their suggestions.

Will keep you posted.

Thanks again

Pete

[petetexas]

Hi Guys,

Had a reply from Celestion.................

Use two tubes 100mm dia x 125 mm long - but experiment with the length - longer will give more bass, shorter will give more punch.

Thanks guys , for all the help......

Will let you know how I get on.........

Pete

Edited December 21, 2009 by petetexas

[petetexas]

[quote name='petetexas' post='690468' date='Dec 21 2009, 10:56 AM']Hi Guys,

Had a reply from Celestion.................

Use two tubes 100mm dia x 125 mm long - but experiment with the length - longer will give more bass, shorter will give more punch.

Thanks guys , for all the help......

Will let you know how I get on.........

Pete[/quote]

Hi Guys,

Now fitted and wired up the 4 speakers, linned the inside of the cab, awaiting the two plastic ports to go in back panel.

Tried it with my Hiwatt 200 Valve head, with the back panel fitted ( no ports ) sounds very `restricted`.

Cant wait till I get the ports fitted.

Keep you posted

Pete

[petetexas]

[quote name='petetexas' post='692918' date='Dec 24 2009, 01:02 PM']Hi Guys,

Now fitted and wired up the 4 speakers, linned the inside of the cab, awaiting the two plastic ports to go in back panel.

Tried it with my Hiwatt 200 Valve head, with the back panel fitted ( no ports ) sounds very `restricted`.

Cant wait till I get the ports fitted.

Keep you posted

Pete[/quote]

Update,

Have now fitted the two 100 mm dia ports, and left them 180mm long as bought.

Got a tech guy to feed a sine wave, using a signal generator, into my HIWATT 200 Valve Bass Head and the cab, and

found that the cab `vibrates` at 22 / 24 Htz.

The rest of the time there is is no vibration .

The sound is really even and smooth across the fretboard, no particular notes are `booming`.

Does this mean the cab is tuned to 23 Htz ?

Pete

[Mr. Foxen]

[quote name='petetexas' post='701592' date='Jan 5 2010, 01:53 PM']Does this mean the cab is tuned to 23 Htz ?[/quote]

No, but some panels have a resonant frequency of 23hz. The cab tuning is to do with the length and area of the ports, its gives a bump in the response at that frequency, you aim to have that bump where there is already a drop off in the natural response of the cab.

[stevie]

[quote name='petetexas' post='701592' date='Jan 5 2010, 01:53 PM']Update,

Have now fitted the two 100 mm dia ports, and left them 180mm long as bought.
Got a tech guy to feed a sine wave, using a signal generator, into my HIWATT 200 Valve Bass Head and the cab, and
found that the cab `vibrates` at 22 / 24 Htz.
The rest of the time there is is no vibration .
The sound is really even and smooth across the fretboard, no particular notes are `booming`.
Does this mean the cab is tuned to 23 Htz ?[/quote]

No, you've probably got a vibrating joint somewhere. If your measurements are right, your cab is tuned to around 35Hz, which is too low. Either follow Celestion's advice or put a third port in there, which will tune the box to just over 40Hz. I'd definitely add another port, as two 100mm ports isn't really enough area for 4 12" drivers.