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Re: 18" Sub Tunning

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Posted by Dave Rat on January 30, 2002 at 22:23:09:

In Reply to: 18" Sub Tunning posted by Tim Moss on January 29, 2002 at 08:40:38:

Hello Tim,

Here is a some info that may be helpful.

We use about 8 cu feet per 18 in our subs.

20 cu feet per 18 is quite large and not really practical for most portable systems.

5.5 cu ft per 18 may be a bit small and in order to toune low your port will be smaller than is recommended Small ports sealed sealed enclosures can be quite hard on the speakers.

On the bright side:

We thrive on undersized, under ported enclosue designs.

Some speakers handle it better than others and don't have much real world experience with the JBL's you have.

You lose efficiency when you "undersize" an enclosure, you can make up for it some what by making sure you have ample power and excellent protection.

All in all you should see:
a clear increase in SPL in the 50Hz to 100Hz region if you double the speakers and the power as well.

Some level drop in the "below 40 hz" region.

If you buget restrains you from building new boxes, adding the extra speakers sounds like a nice stepping stone to get you into more 18"s, then more amps and somewhere down the road build new boxes and move the 18"s over.

I always use quite a bit of insulation in subs and though "theory" says its not necessary in well designed cabinets, I prefer the way a well damped sub sounds, especially in the highly reveberant environments we so often find ourselves doing in.

Dave Rat

: I have four single 18" subs. The cabinets are
: 48' X 24" X 24" apx. 11 cubic ft. internal. Need more low end. I know JBL recommends 20 cubic ft per box for thier dual 18" 4719 sub. I am on a low budget and am contemplating adding an additional 18" JBL 2241H to each cabinet. I realize that I am short about 8 to 9 cubic feet on each cabinet. I thought I would add insulation to effectively increase my internal volume.
: What do you think is the downside of doing this ? Will I notice an audible increase in low end, get spl or am I just waisting my money. Thanks for your expertise

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