Jbl Sub1500 15" Subwoofer 4 Ohm

[MJC]

Despite previous claims that there is no connection between group delay and real time in playback, I do not think having subwoofers back in the corners behind the speakers (as I have seen in many system photos in these forums) is a very good idea. I'll refer to Drew's suggestion that subwoofers be centered between the main speakers and forward of their plane if possible. Can't hurt to try it. I believe that JBL is now suggesting midway along the sidewalls now in some of their literature.
David

But using the newer pre/pros or receivers, like the H/K AVR 635, that has the auto eq you can set the distance of all the speakers, including the subs, from your seated position. And I do have my two 1500s in the front corners, in sealed 2.5cuft boxes. They sound great for both music and HT.

Although when I first built the boxes, using two layers of 5/8" mdf, I built them in a way that I could attach an eight inch deep open ended extention and just repositioned the back. This gave me 4cuft boxes, but I couldn't hear any difference. Guess I could try them again with a port for HT and then plug them for music.

[MJC]

This thread has been idle long enough!

I have been using Sub1500s since March 2004... during that time I tried 1.5 cu ft sealed boxes and ported 5 cu ft boxes. In my large bass hungry room I found the big ported numbers to be preferable. For the vast majority of their life I have used these wonderful woofers in my HT system and the results are simply staggering. The sound of a building coming down or a mid-air collision is quite enveloping as the room pressurizes with the impact of the subsonic noise.

Most likely I will build a pair of 2.5-3.0 cu ft sealed boxes for a pair to be used with music and continue using another pair in the big ported boxes. For now I am using the patented Zilch magic port stoppers (otherwise know as a 4" plumber's plug). Here are plots comparing the frequency response change and the group delay changes between the two. Realize these are simulations and do not show any room gain.

Widget

What length did you make the 4" port. Or more to the point, what length would I need to put into my extended 4cuft boxes, that I mentioned above?

[Mr. Widget]

You may need an elbow... I have mine tuned to 21Hz. For a 4" ported 4 cu ft box it should be ~15.25" long. Ideally you should have two 4" ports to reduce port noise, but for movies it isn't a problem. Two 4" ports would need to be ~33" ea.! This is why all of those small subs use PRs... there is no way to tune them low and physically fit a port.


Widget

[MJC]

The 8" extentions makes the boxes 25" deep x 19" wide. So I could go either way, one port of 15.25" or two 33" long using elbows. But in either case I'd plug the ports for music.
Thanks.

[Zilch]

Proprietary plumbers' port plugs proliferate!

[Heh, heh.... ]

[Mr. Widget]

Proprietary plumbers' port plugs proliferate!

[Heh, heh.... ]

You know, while they do work well... they make my thumbs sore tightening them down. Seems like there must be a better solution. Something with lever action rather than a twist.


Widget

[Zilch]

Called "Quick Snap Test Plugs," they have a camlock lever; look like the old soda bottle sealers.

Cost more, is all, the 4" version is $29.04 at McMaster-Carr, 3" is $26.61.

You can also "Hotrod" the cheap ones with a teflon washer and larger "T" knob to replace the wingnut for a couple of bucks.

Another option: Use a hexnut and box wrench.

Usage tip for the low profile big rubber washer ones: After loosening, give them a couple of minutes to "relax." They'll fall right out, then. You'll soon learn just how much to loosen not to have them literally do that, tho.

I use the low profile ones 'cause they grab right at the cabinet baffle and don't stress the ID of the port itself....

[MJC]

http://www.partsexpress.com/pe/showd...number=268-352

Has anyone tried these? If they work as described, I'd only need one per box.

[pangea]

http://www.partsexpress.com/pe/showd...number=268-352

Has anyone tried these? If they work as described, I'd only need one per box.

Yes I'm using curved ports like that and yes they are very good.
When using those, you should also put a curved flange inside the speaker, because the air is pumping both ways.
I've also read somewhere that it is important to have at least a W/H 2x2 inch "baffle" mounted on the flange inside the speaker!

If memory doesn't fail me, the length of the port is measured at the middle point on the curved flange.

BR
Roland

[Mr. Widget]

Flared ports are superior to standard ports in that they are quieter and they also couple with the air better. When using flared ports the effective length is increased. (You need a shorter flared port for the same tuning.) With flared ports you really should measure the tuned frequency electrically and determine the ultimate length that way.


Widget

[pangea]

Flared ports are superior to standard ports in that they are quieter and they also couple with the air better. When using flared ports the effective length is increased. (You need a shorter flared port for the same tuning.) With flared ports you really should measure the tuned frequency electrically and determine the ultimate length that way.


Widget

Hi Widget!

How much shorter would you say roughly?
Could you please describe how that is done electrically and what equippment is needed?


Could I use a tone generator or test CD and could I use an RTA like in the Behringer Ultradrive?

BR
Roland

[stevem]

Flared ports are superior to standard ports in that they are quieter and they also couple with the air better. When using flared ports the effective length is increased. (You need a shorter flared port for the same tuning.) With flared ports you really should measure the tuned frequency electrically and determine the ultimate length that way.


Widget

I've used the 4" version of these ports, and if I remember correctly, you have to ADD and inch to the overall port length to compensate for the flares. I agree with Widget that you should measure the resonant frequency to determine port length.



Be aware that the ABS used here is much thinner (flimsier) that that found in ABS or PVC drain pipes that many people use for ports

[Mr. Widget]

I've used the 4" version of these ports, and if I remember correctly, you have to ADD ...

Are you sure? I haven't used them myself, but I thought they reduced the needed length... the mind is a terrible thing to loose...


Widget

[Mr. Widget]

Could you please describe how that is done electrically and what equippment is needed?

If no one else pops in I'll get back to you with a method. There are several. I have to run...


Widget

[stevem]

I went to their website: http://www.psp-inc.com/

The installation instruction page states the following:

"The Precision Port™ should be 1" longer than Lv when assembled"

I know what you mean about the mind!