JBL 1500 Sub enclosure

Though this has been discussed in a previous thread, there seems to have been much discussion without clear recommendations.
The options seem to be:
2 cu.ft. sealed enclosure,
2 cu.ft. sealed enclosure w/ EQ (6dB @ 30 Hz?),
4 cu.ft. sealed enclosure,
4 cu.ft. tuned enclosure.

While the first three options are clear, the question is: what port size should be used to tune the 1500 Sub to a 4 cu. ft. box for a sub woofer application?

Though I feel the 4 cu.ft. tuned enclosure will be my choice, I'd be curious to hear opinions about these four options.

Thanks for your opinions and clarifications on this.

Tom

I am using the Sub 1500 in a 5 cu ft box tuned to 21Hz. I am very happy with this tuning. I have one sub in a corner and the other along a wall.

If you want to stay with a 4 cu ft box and extreme deep bass isn't an issue you would get great results tuning it to 25Hz.

Can you tell me what the port sizes should be for the 4 cu. ft. and 5 cu.ft. boxes should be?
(using 3" and/or 4" tubes)

Thanks,

Tom

Giskard,

That was an excellent summary of the salient points of the Forum's longest thread.:thmbsup:

Quote:

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Originally posted by Tom Loizeaux
Can you tell me what the port sizes should be for the 4 cu. ft. and 5 cu.ft. boxes should be?
(using 3" and/or 4" tubes)

Thanks,

Tom

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Tom,

To explore the two vented enclosures described above, you will need to build the cabinets so that the net volume is 4 or 5 cu ft. That means you have to add the volume of all of the bracing, the driver, and the port or ports. Typically it will add between 0.4 cu ft to 0.75 cu ft.

For a 4 cu ft cabinet tuned to 25Hz you could use a pair of 4" ducts at 22 3/8" long. (Might be tough to fit in the box.)

If you use one 4" tube it would be 9 9/16" long but at high spls it might make pumping noises.

You could construct a rectangular port of 4 1/4" by 4 1/4" by 14 7/16". This would be my choice.

For a 5 cu ft cabinet tuned to 21Hz you could use a pair of 4" ducts at 26" long. (Might be tough to fit in the box.)

If you use one 4" tube it would be 11 3/8" long but at high spls it might make pumping noises.

You could construct a rectangular port of 4 1/4" by 4 1/4" by 17 5/16". This would be my choice.

If you have the time and inclination you might take Giskard's advice and build a sealed box as well and compare them. I did as I had heard them set up that way in their original Revel enclosures and was impressed with them. I found for my needs and lust for ever more I opted for the 5 cu ft vented option. The bottom line is that with these woofers you can't go wrong.

Widget

Thanks guys for the theory and some specific practical suggestions!

Tom

Does anyone know the volume of the L200 (L200 Studio Master Speaker Cabinet) I picked up a pair empty cabs on ebay and thought I might convert it for a sub1500 enclosure (temporarly to play with), and want to set up a vented enclosure (or maybe later sealed). Any hints or reactions welcome. I have been toying around with cutting out he back panel, pulling out the existing braces and building a box with 3/4 mdf inside it and bracing the crap out of it. (that is, if the original bracing doesnt look like it will handle these bad boys with out sending panels out toward my family during Independence Day landings) These seem to be in excellent condition and I love that Star Trek, 1970 look of the box. Reality checks encouraged. :nutz:

The L200/L300 are said to have an internal volume of 5.5 cu.ft.
You may find a need to increase the bracing, but...hey, try it and report back.

Tom

Thanks Tom, I calculated a little over 6 cubic feet but that was based on external published dimensions and I knew that couldnt be right.
Mr. Widget, what about using three ports in a five cubic feet enclosure, could I decrease the length of the vents, (like in my 4518 enclosure for my 2245h). I dont have box modeling software, but planned on trying the sub1500 in these L200 enclosures this weekend and thought I could throw another vent into the horn hole. I think the vents in the L200 are three inches, I could install three four inch ones, but dont know what depth. (obviously I would prefer to just have three of the ones in place but would probably have 24 inch port tubes).
Thanks, my wife is extremely excited about getting the pair of SUB1500s, and my brand new used Crown K2 pounding in our 150 ft2 living room :duck: ,
Oh well, its either speakers or the AV room addition, I dont have time for everything :thnkfast:

Quote:

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Originally posted by andresohc

Mr. Widget, what about using three ports in a five cubic feet enclosure, could I decrease the length of the vents, (like in my 4518 enclosure for my 2245h).

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Essentially as the area of the port increases the port length must increase to maintain the same tuning frequency. So if you use (1) 4" tube for 21Hz it is 11.3", (2) 4" tubes for 21Hz are each 26", (3) 4" tubes for 21Hz are each 41".

Now a hole cut into a 1" baffle with no tube would be a little under 1.75" in diameter. The problem with the smaller port diameters is that as they get smaller the likelihood of air moving through the port causing audible noise goes up.

Since JBL typically tunes in the 30Hz up range the ports are shorter in length.

Widget

The basreflex would be interesting if you anly have one or two.
Otherwise sealed box would be interesting couse it can go lower.

I dont know about the unlinjear (corect spelling) parameters
on the driver. so..

If putting it in a to small enclosure, the compressed air can get
it to be unlinear, also a to big box sealed can get it unlinear
couse the air behind would be less compressed.

Revel 47L, well i think this is at minimal.
60L would work well.

I dont know about 80L - 100L !

Also it can be interesting to alter the Q dynamicaly during playback, also the FS !

Carefull Niklas... try to keep any "theory" out of this. :p