Looking for advice on porting a LE15A in a L300-like enclosure

[tjm001]

As seen in the picture I am building L300-like enclosures for my LE15As, LE85s and 077/2405s. I’m about ready to glue on the baffles, but before doing this I wanted to make sure I had the correct hole size for the porting for the LE15A. I realize the physical characteristics of the LE15A are not the same as the 136A for which this enclosure was originally designed for. So I’ve been looking at the 1975 JBL Transducer/ Enclosure Porting Information table in the JBL Library to try to figure out what to do before I glue the baffles on since it will be easier to make any changes now. http://www.lansingheritage.org/images/jbl/plans/1975-kit-plans/1975-porting.gif

(http://www.lansingheritage.org/images/jbl/plans/1975-kit-plans/1975-porting.gif)

According to my math the volume of L300 enclosures allowing for the transducers and bracing falls into 4.1 to 5.0 cubic ft. column of the table. If I am interpreting this table correctly that column seems to be in line with the 4 inch port hole of the L300 when using the 136As. That is, a 4 inch diameter hole is right around 13 square inches. I am not sure what the actual length is of the port in the original L300 enclosures is, but the table says it should be 4.5 inches. Anybody know?


Any way the table says the port for the LE15A should be 26 square inches and a length of 7 inches. This equates to a diameter of about 6 inches for the hole. I’d like to get your informed opinions/advice on how to proceed. It would be much appreciated. Thanks.

Tom
67753

[4313B]

The 4331/4333/L300 volume was ~ 5 cu ft with the fiberglass installed. It was tuned to around 32 Hz. For the LE15 you want to tune it higher up around 38 Hz so shorten the duct. You might want to use two ducted ports to cut down on vent noise.


Any way the table says the port for the LE15A should be 26 square inches and a length of 7 inches. This equates to a diameter of about 6 inches for the hole. I’d like to get your informed opinions/advice on how to proceed. It would be much appreciated. Thanks.Yeah, just use two 4-inch diameter ports instead of a single 6-inch diameter port?

[macaroonie]

Assuming the box to be 120 ltr ( 5 cu ft ) and allowing for the components.

Win ISD beta suggests 2 ports @ 102mm dia 265mm long or 1 port @ 102mm dia 95mm long or 1 port 140mm dia , 217mm long.

The first option gives the best air velocity result with a nice curve

Tuning is at 34 Hz

You could probably sneak it a bit lower but would not gain much.

Win ISD is a free bass modelling program http://www.linearteam.dk/?pageid=winisd , it's worth spending a little time getting to know it.

[tjm001]

Outstanding and quick responses. Thank you! Two holes it will be.

Tom