127A box

[Hans]

Hi, I've just got 2 JBL 127A in fairly good condition. Any of you who can help me (yes offcourse you can) with the net volume and the porting of a box to make these sound good? I would appreciate the smallest box possible.

Hans

[Zilch]

127A is one of a small group of JBL drivers, basically the vintage "Decade" woofers, well suited for closed-box alignments. EBP = 54 for 127A

BB6P suggest really big boxes >10 cuft for venting, but they run out of cone displacement at low power. Looks great, but is impractical (red).

Venting alignments <2 cuft behave like L100 - a boomy peak in the bass (orange). That's how JBL used them, typically.

BB6P's suggested closed-box alignment is 2.75 cuft, but that size pushes the cone excursion limits. Use that, or a little smaller (2 - 2.5 cuft,) if you're willing to keep the SPL under control (blue).

My experimental 127As are out for refoam right now. They'll be going into an even smaller 1.5 cuft, a true acoustic suspension alignment, without excursion limit, due to box damping (violet).

You can see from the graphs, that basically provides L100 equivalent bass without the boom. :thmbsup:

More on my recent adventures with closed boxes here:

http://audioheritage.org/vbulletin/showthread.php?t=12036

[Hans]

Thanks a lot Zilch! I follow your ideeas and build a sealed 1.5 cuft box and we will see what the result will be. Please let us be in contact to exchange the results.

Hans




127A is one of a small group of JBL drivers, basically the vintage "Decade" woofers, well suited for closed-box alignments. EBP = 54 for 127A

BB6P suggest really big boxes >10 cuft for venting, but they run out of cone displacement at low power. Looks great, but is impractical (red).

Venting alignments <2 cuft behave like L100 - a boomy peak in the bass (orange). That's how JBL used them, typically.

BB6P's suggested closed-box alignment is 2.75 cuft, but that size pushes the cone excursion limits. Use that, or a little smaller (2 - 2.5 cuft,) if you're willing to keep the SPL under control (blue).

My experimental 127As are out for refoam right now. They'll be going into an even smaller 1.5 cuft, a true acoustic suspension alignment, without excursion limit, due to box damping (violet).

You can see from the graphs, that basically provides L100 equivalent bass without the boom. :thmbsup:

More on my recent adventures in this area here:

http://audioheritage.org/vbulletin/showthread.php?t=12036

[Zilch]

Good!

We'll compare results here, good or bad, for everyone to see.... :thmbsup: