Maintaining the seal of your JBL cabinet

[Goldjazz]

For some time now I've not had all the screws in place in my 4343 baffle. Basically due to all the driver configurations I've tried pulling the baffle on and off and laziness to put all the screws back in.

Then my mind cast back to an original JBL label on the back of my cabinet stressing the importance of maintaining the seal of the cabinet and not to remove the screws etc. I didn't think much of it due to the huge open ports at the bottom.

So just now I found some of the missing screws put them back and plugged up a few missing screw holes with "blue tac" (the putty stuff you stick posters to the wall with). Well man I'm hearing a difference: Tighter, deeper base, punchier, better imaging.

I'm now thinking of checking all the gaskets on the drivers. I even sealed up the gaps around the l-pad knobs with the blue tac.

Anyway just wanted to share this in case it helps someone else. Moral of the story is make sure that cabinet is sealed in the way it was intended.

[Ian Mackenzie]

Thank you for posting.

It’s easily overlooked.

[RMC]

Hi Goldjazz,

In his "Bullock on boxes" book, Bullock says that cabinet air tightness is the single most important issue for bass and that this cannot be overstressed...

If you model in speaker design software some boxes but with different QL numbers (box losses) as can be done in Win ISD Pro 2016 edition, you can see easily the effect of air losses on bass response. Model a design starting with the usual QL 7 number, keep all parameters the same but then change only the QL to 5 or even 3 (more lossy boxes) and you'll see the bass response dropping. On the other hand, increase only QL to 10 or more (more air-tight boxes) and you'll see the bass response increase. So, box tight seal IS really important for low-frequency performance you are expecting from the software model.

Win ISD uses as default QL 10 which is overly optimistic. To change that number when your box is designed, click on Box tab then at the bottom of the screen click on Advanced, click QL, a window opens with QL 10 and change that number for 7 and close that window. The response on the graph should have changed. To make sure you did it right, re-do the same path up to QL number window opening to see if it shows QL 7 and if yes just close that window you're done for that and if not change the number again. SINCE MANY FORGET ABOUT THIS, ONE MUST REMEMBER TO RESET THIS EVERY TIME OPENING WIN ISD PRO SINCE THE DEFAULT IS ALWAYS QL 10. Its not over yet.

Because your on screen response design has changed a little re QL number change, then you have to re-work a little cabinet volume and/or tuning frequency to get back to the response curve you wanted initially. Don't forget that, according to that software's designer- see help files in the WIN ISD PRO software- and to John Eargle of JBL (Loudspeaker Handbook and Handbook of Sound System Design) the response modeling in software already assumes or includes ONE boundary speaker placement. So, low-frequency response seen on the screen is valid for ground/floor OR large wall placement.

In theory, this means air-tight boxes can reach similar LF response in a smaller cabinet since it makes better use of the air Inside (no losses). In practice this remains difficult to achieve as each and every POSSIBLE air leak must be dealt with, a monk's job... Since I built my boxes meticulously and chase all possible air leaks I tend to think I may reach QL 10.

Regards,


Richard

[Goldjazz]

Hi Richard, thanks for the very informative post. it's good to know there is a basis to what I was hearing. I downloaded that software and am having a play around. I've entered all the values for the 2231H. Was just playing around with that Ql value, I can see the effect that has. Very interesting, thanks.




Hi Goldjazz,

In his "Bullock on boxes" book, Bullock says that cabinet air tightness is the single most important issue for bass and that this cannot be overstressed...

If you model in speaker design software some boxes but with different QL numbers (box losses) as can be done in Win ISD Pro 2016 edition, you can see easily the effect of air losses on bass response. Model a design starting with the usual QL 7 number, keep all parameters the same but then change only the QL to 5 or even 3 (more lossy boxes) and you'll see the bass response dropping. On the other hand, increase only QL to 10 or more (more air-tight boxes) and you'll see the bass response increase. So, box tight seal IS really important for low-frequency performance you are expecting from the software model.

Win ISD uses as default QL 10 which is overly optimistic. To change that number when your box is designed, click on Box tab then at the bottom of the screen click on Advanced, click QL, a window opens with QL 10 and change that number for 7 and close that window. The response on the graph should have changed. To make sure you did it right, re-do the same path up to QL number window opening to see if it shows QL 7 and if yes just close that window you're done for that and if not change the number again. SINCE MANY FORGET ABOUT THIS, ONE MUST REMEMBER TO RESET THIS EVERY TIME OPENING WIN ISD PRO SINCE THE DEFAULT IS ALWAYS QL 10. Its not over yet.

Because your on screen response design has changed a little re QL number change, then you have to re-work a little cabinet volume and/or tuning frequency to get back to the response curve you wanted initially. Don't forget that, according to that software's designer- see help files in the WIN ISD PRO software- and to John Eargle of JBL (Loudspeaker Handbook and Handbook of Sound System Design) the response modeling in software already assumes or includes ONE boundary speaker placement. So, low-frequency response seen on the screen is valid for ground/floor OR large wall placement.

In theory, this means air-tight boxes can reach similar LF response in a smaller cabinet since it makes better use of the air Inside (no losses). In practice this remains difficult to achieve as each and every POSSIBLE air leak must be dealt with, a monk's job... Since I built my boxes meticulously and chase all possible air leaks I tend to think I may reach QL 10.

Regards,


Richard

[RMC]

Hi Goldjazz,

I'm glad the info helped you. One precision. If you saved a project box in that software and later re-open that file for further work I think the program will have saved also the QL number used for that modeling. So in that case no need to reset QL. But check value anyway. However, when the program is opened for a NEW project it will show QL 10 as default so change it. Remember to ALWAYS use QL 7 as a starting point when you model a box in software. This is the widely accepted number (not QL 10). The author of the program says in the help files he used default QL 10 because a "quality" box should reach that... But that means a damn good air-tight box! Not too many people have the patience, will or skills to get there, nor realize how important this is for the low-end. Many want a "nice piece of furniture" in the living room. I'm more interested in an acoustically correct box, not nice furniture, if it does't look as nice be it.

Richard