Jbl Sub1500 15" Subwoofer 4 Ohm

[Mr. Widget]

In these trying times there are concepts such as standing waves and room nodes that multiple point sources help to alleviate. If one still hasn't gotten the hint yet then feel free to just run one.

This is a really good point Giskard. I have a different system that resides in our "Living Room". For aesthetic reasons I have one 10" Velodyne HGS sub hidden in a cabinet. I have it tuned to sound right in the sweet spot, but as you walk around the room there are some nodes that are quite pronounced. At the dinning table some 15-20 feet away from the sweet spot there is a strong reinforced node that can be annoying.

Widget

[jblnut]

I thought I was a jblnut....I'm not even in the same league as you guys !

Nice hanging out with y'all just the same....


jblnut


PPS - can't you just sit in a different location if your particular seat happens to be in a non-optimal standing wave reinforcement zone? Don't you introduce more cancellation problems with multiple sound sources ? Just curious....

[Niklas Nord]

This is great guys!



There is many thing to do with room acoustics if you have,
lets say 4 sub-modules. Depending on your room measurements.
And proportions. And how the listening is aligned.

[boputnam]

Originally posted by Mr. Widget
At the dinning table some 15-20 feet away from the sweet spot there is a strong reinforced node that can be annoying.

Roomate...?

19 of them!!?? Widget - you are on VLF probation!

Now, finish-up your work like a good Widget and provide us

Originally posted by David Dryden
...conclusions on the optimum box size (sealed)?

[Ralf]

Originally posted by Mr. Widget
Damn! I've ordered a total of 19 of them. Is that overkill?

Widget

Oh Mr. Widget...you will lose your wife.

Believe me. I have also no more...

Greetings
Ralf

[David Dryden]

Please forgive my ignorance, but is a Qtc of .7 considered to be "optimally flat"?

[David Dryden]

It sure is nice having all of this knowledge available to us "rookies"! Thanks for all of the research and info! Until I get my garage built (this Spring-Summer), building speaker boxes is not the easiest thing to do - no room to work. It would be nice to be able to "get it right" on the first box! I'm anxious to fire these babies up!

[jim henderson]

I just got my pair. These things are GORGEOUS!

I can't wait to design a pair of end table/cabinets for these.

Thanks again for all your help guys!

[John Y.]

Some of you may remember that I went through a design process a while back where I intended to convert a Lansing C37 cabinet I built in 1957) to house a 2245H by enlarging the volume (extending the depth) to get 8 cubic feet. By procrastinating, I now don't have to do extensive mods.

With the PE deal, I can use a 1500 in the cabinet and, with only doubling the panels on the inside and cross bracing, I can easily get 5 cubic feet without touching the exterior. I immediately ordered two 1500's so that I can try the mod and then either duplicate the cabinet or build two new sealed boxes, if that solution seems better. I await the results of all the testing going on.

Mr. Widget, your results with the 5 cu ft tuned to 21 Hz sound great. What size duct was used for your tuning?

Thanks to the forum for the alert.

John Y.

[Mr. Widget]

Originally posted by John Y.

Mr. Widget, your results with the 5 cu ft tuned to 21 Hz sound great. What size duct was used for your tuning?


John Y.

Well first of all let me second your call for procrastination!

For my initial test I pulled a pair of 2235s out of their 5 cu ft boxes and plopped the Revel subs in there. The 2235s called for a tuning of (2) 4" dia ducts that are 11" in length. Since capping one of these ports yields a tuning of 21Hz, that was the approach I took for my initial tests. This port is not recommended for the ultimate solution as it yields a very high vent velocity which will produce audible noise at certain frequencies at higher power levels.

A 5" dia port that is 19" long will yield better results. A square port that is 4.25" X 4.25" that is 17.31" should also be satisfactory.

I hope this helps.

Widget

[John Y.]

Mr. Widget,

Would any duct (or ducts) that were 8 inches or less satisfy the 21 Hz tuning requirement for a 5 cu. ft. cabinet? The C37 cabinet has only 13 inches internal depth from the front of the speaker baffle to the rear panel. A single 5.25" dia hole (originally for the 075) and a 3 x 13.5" rectangular vent are in the baffle panel aside from the 13.5" circular driver mounting hole. If necessary, I could cut a duct hole in the side or in the bottom if I put the enclosure up on 5" wooden legs. The bottom is preferable for aesthetic reasons, so the cabinet could retain its retro effect.

BTW, how do you figure your tuning? Is it by BB Pro, or by experimental measurement?

Thanks for your help. My drivers will arrive on or about the 16th, so I have to get cracking on the design. Maybe I should alternately consider putting both drivers in the same 5 cu ft cabinet. Think that would work? If so, maybe I should order two more.

John Y.

[4313B]

"BTW, how do you figure your tuning? Is it by BB Pro, or by experimental measurement?"

There is only one way to "figure" tuning and that is by measuring it. The math programs can be quite effective at getting one close but they aren't 100% every time. Two people can build what each thinks is a 5.0 cubic foot volume and end up with different effective volumes depending on total system losses.

[boputnam]

Originally posted by John Y.
The C37 cabinet has only 13 inches internal depth from the front of the speaker baffle to the rear panel.

Hey, John...

You can put a bend in the duct, if need be. You may know that JBL often did this, for space reasons, and also perhaps to keep the duct-end a minimum of 3-in from any cabinet wall. You can use 90-degree elbows...

[Mr. Widget]

Originally posted by Giskard
"BTW, how do you figure your tuning? Is it by BB Pro, or by experimental measurement?"

There is only one way to "figure" tuning and that is by measuring it. The math programs can be quite effective at getting one close but they aren't 100% every time. Two people can build what each thinks is a 5.0 cubic foot volume and end up with different effective volumes depending on total system losses.

I too am generally obsessed with details. That said, I have discovered that in most cases being "off" by an inch or so in port tuning is readily measurable but unless you listen to test tones absolutely inaudible. In most cases I am too lazy to set up and verify that which my ears are happy with. Now if I am not happy with the outcome, that's another story. In the old days when I used inaccurate charts to "calculate" bass tuning, I often had to go back and re-tune, measuring the resonance peaks etc. Since using BBPro6, I have been very pleased with the results... so far. I have only used it with a handful of woofers, but the results have been surprisingly as predicted.

As for different 5 cu ft boxes, well there do seem to be discrepancies there. The "5 cu ft" boxes that I am using started out as 5.41 cu ft. Then I subtract out the cross bracing and ports and woofer volume. (BBPro6 suggests a 5.39 cu ft box to achieve a 5 cu ft before any bracing.)

John,

You are discovering one of the primary reasons that passive radiators exist. It is sometimes difficult to fit a port in the box. I would recommend you put the port on the bottom of the cabinet. The larger the dia the longer it needs to be. Multiple small ports would also need to be longer. I assumed you would have this problem and that is why I suggested the two ports I did. They are sort of the best compromise for vent velocity (air noise) and port length.

I still haven't gotten around to tuning the EQ of the sealed box, but with out some EQ tweaking the bass isn't quite right. The 5 cu ft solution sounds great with no EQ. Hopefully others will offer their opinions and describe how they are using theirs.

Widget

[4313B]

"unless you listen to test tones absolutely inaudible."

Ooops! There is other stuff to listen to??? What have I been missing???

"Since using BBPro6, I have been very pleased with the results... so far. I have only used it with a handful of woofers, but the results have been surprisingly as predicted."

Ditto!