Advice on port positioning

[Sootshe]

Hi,
Putting together a 3 way system with bass reflex 15", Altec 511 mid & JBL 2404 highs, crossover at 500/6000.
I have a design for the bass cabinet to suit my chosen driver (see attached) & it has a slot loaded port at the very bottom of the cabinet, with the bass driver mounted towards the bottom of the cabinet.
The attached cab will contain the woofer only & will have a seperate cab for the 511/2404 above this.

Does anyone see any issues with mounting the bass driver towards the top of the cabinet to locate it directly under the 511 & then move the port higher up the cabinet to position it underneath the bass driver? With issues, I mean will it alter the tuning of cabinet to any significant degree........or should I just leave it as per the original design.

Hope this makes sense.

Regards.

[Dr.db]

Mounting the bassdriver at the top of the cabinet is a smart idea, as boundary effects will be less dramatic. Midbass should sound a little tighter and less boomy.

Regarding the position of the port...
I honestly can´t tell you what´s the best choice. This has to be judged individually for every single speaker and room setup.
But locating the vents e.g. ports close to the floor definitly affects the actual tuning of the enclosure AND the coupling to the room-acoustics. Mounting the vents at the bottom of your enclosure, they remain physically the same length, but acoustically they may extend in length. Also you will encourage the room-modes a little greater.

[Don C]

It should definitely be a noticeable change. You will hear less low bass due to taking away the boundary reinforcement that the port would have.

[ivica]

Hi,
Putting together a 3 way system with bass reflex 15", Altec 511 mid & JBL 2405 highs, crossover at 500/6000.
I have a design for the bass cabinet to suit my chosen driver (see attached) & it has a slot loaded port at the very bottom of the cabinet, with the bass driver mounted towards the bottom of the cabinet.
The attached cab will contain the woofer only & will have a seperate cab for the 511/2405 above this.

Does anyone see any issues with mounting the bass driver towards the top of the cabinet to locate it directly under the 511 & then move the port higher up the cabinet to position it underneath the bass driver? With issues, I mean will it alter the tuning of cabinet to any significant degree........or should I just leave it as per the original design.

Hope this makes sense.

Regards.

Hi Sootshe,
about the port length correction may be the attached would help.
Position of the port in the box is very 'intriguing topic' for me, especially concerning the internal resonance in the box so if any member has some more info, it would be nice.

regards
ivica

[RMC]

Hi Ivica and Sootshe,

These two JBL docs should help re vent location on the box. In first doc see p.2 and in second doc see Q.8. There's a third doc I have on this issue but can't find it right now...

Richard


JBL ENCLOSURE GUIDE enclgde[1].pdfJBL FAQ speaker building q&a.txt

[toddalin]

That's a bit low to crossover to the 2405. I think the minimum used by JBL was 6,500 Hz in the L65s.

[ivica]

Hi Ivica and Sootshe,

These two JBL docs should help re vent location on the box. In first doc see p.2 and in second doc see Q.8. There's a third doc I have on this issue but can't find it right now...

Richard

Hi Richard,

Thank You for the info.
Interestingly looking the ports movements 4343 and 4344 JBL models.
Seems to me that JBL had tendency to put vents somewhere in the middle of the box.

regards
ivica

[Sootshe]

That's a bit low to crossover to the 2405. I think the minimum used by JBL was 6,500 Hz in the L65s.

Sorry about the typo.......but the tweeter is actually a 2404.


The bass driver will cross at 500 & the mid driver will hand over to the 2404 at 6000.

[Sootshe]

Appreciate all the input everyone & will keep the port at the bottom of the cab. My main reason for wanting it higher was purely cosmetic, but the best sound dictates the final positioning ........so bottom of cab it is......don't mess with a proven design.

Not sure if you guys want to see the progress of this build, as it's not exactly a JBL project, but you have provided a wealth of info already that I was unable to get elsewhere.

Thanks again.

[ivica]

Appreciate all the input everyone & will keep the port at the bottom of the cab. My main reason for wanting it higher was purely cosmetic, but the best sound dictates the final positioning ........so bottom of cab it is......don't mess with a proven design.

Not sure if you guys want to see the progress of this build, as it's not exactly a JBL project, but you have provided a wealth of info already that I was unable to get elsewhere.

Thanks again.

Hi Sootshe,

It would be nice to infrom us about the progress in your project, and the results at the end.

regards
ivica