speaker enclosure gurus: port questions

[oddgrowth]

I run 2 mesa 1x15s (TL606 cab) recently loaded w/enimence kappalite 3015s (+a Mesa M2000) - incredible.

I have 2 old marshall JCM 800 bass series cabs. A 2x15 & 2x10,1x15. These are typical 4x12 dimentions but +/- 4" deeper.



I am wondering about loading the kapplites into the marshall 2x15.
It's interior volume is approx 6.5' which falls around the internal volume of 2 TL606 cabs.
My question is about the porting and how the differently built ports effect the cab's performance.

The port in the marshall is 5.75 in diameter.
I had a mesa 2x15 box and do remember 2 round 4" ports. How do different sized surface ports effect performance?

2nd question: the 2x10, 1x15 marshall cabinet, same dimentions, it has 2 inputs for bi-amping or 1 for full range.

I have a mesa 2x10 with the same type of porting as the TL606.

I was wondering about loading a kappalite 15 + the 2-10 ev(s)from the mesas into the 2x10, 1x15 marshall. The port appears a bit larger maybe 7".

In a full range cab where speakers share the same air space and ports, does one speakers usage of the space effect the other?

I have a Marshall DBS 7400 I want to run with 1 - 4 ohm Marshall cabinet. I'm also wondering which cab would perform better. opinions?

bonus question: back in the early 80's did marshall just build these cabs the same as the guitar 4x12's for looks - and hope for the best by deepening them and adding a port? or did they actually calculate the enclosure size and performance?

thanx!

[billfitzmaurice]

Originally Posted by oddgrowth

The port in the marshall is 5.75 in diameter.
I had a mesa 2x15 box and do remember 2 round 4" ports. How do different sized surface ports effect performance?

The port area must be adequate for sufficient airflow, or you'll get chuffing noise. The usual minimum diameter is 6 inches per fifteen inch driver.

In a full range cab where speakers share the same air space and ports, does one speakers usage of the space effect the other?

Never have different drivers share the same chamber. The official technical acoustical engineering term for doing so is AFU.
Each driver type must have its own chamber, properly sized and tuned.

[oddgrowth]

Originally Posted by billfitzmaurice

The port area must be adequate for sufficient airflow, or you'll get chuffing noise. The usual minimum diameter is 6 inches per fifteen inch driver..

So I can add another 6" port and be ok. It had no lining also. Will fix that.

Originally Posted by billfitzmaurice

Never have different drivers share the same chamber. The official technical acoustical engineering term for doing so is AFU.
Each driver type must have its own chamber, properly sized and tuned.

Strange this was how the cab was sold, stock...I thought it didn't make sense. It's an early 80's IBS series.
So I could chamber up the 2 halves...nah sounds messy and futile.

and I DO prefer the sound produced by identical drivers as opposed to mixing them.

the mod will be minimal to the 2x15.

thanks so much for the info.

[billfitzmaurice]

Originally Posted by oddgrowth

So I can add another 6" port and be ok.

Not hardly. They must also be ducted, the length of the ducts based upon the correct tuning frequency for the cab.

[oddgrowth]

Originally Posted by billfitzmaurice

Not hardly. They must also be ducted, the length of the ducts based upon the correct tuning frequency for the cab.

ok. I had trace elliott cabs that had cylindrical ports. I think they were 8-10" deep into a same depth cab.

the interior dims of this marshall cab are:

28.5 wide
28.0 tall
13.75 deep at the top
14.75 deep at the bottom

if there a formula to calculate the tuning frequency?

[billfitzmaurice]

Originally Posted by oddgrowth

ok. I had trace elliott cabs that had cylindrical ports. I think they were 8-10" deep into a same depth cab.

the interior dims of this marshall cab are:

28.5 wide
28.0 tall
13.75 deep at the top
14.75 deep at the bottom

if there a formula to calculate the tuning frequency?

http://www.linearteam.dk/default.aspx?pageid=winisdpro

[oddgrowth]

Originally Posted by billfitzmaurice

http://www.linearteam.dk/default.aspx?pageid=winisdpro

thanks, Hopefully I can clod my way thru it.

That's quite a cool app.

Now I can clearly see why there is so much love for Bill here.

+1 to your fan base bill...your knowledge/info is greatly appreciated.