PDA

View Full Version : lowing the tuning on a 4645?



Doc Mark
11-07-2009, 02:24 PM
Greetings, All,

As I was working in the studio today, I got to thinking about all the stuff that is still yet to be done, in order to get my 4645 up and running with the electronics on hand. I'm hoping to have a little more time, and can start taking care of each item, one at a time. But, that reminded me that I was wondering about retuning my 4645 cabinet. The stock tuning for that box is 30HZ, and I was wondering how to retune it to 25HZ? I'm thinking about "shimming" the three ports with slightly larger tubes, inside of which, will be whatever addtional length I would need to drop the tuning that last 5HZ. Any thoughts or ideas, Folks? I'm thinking 2"-3" added on to each port should do the trick, but don't know for sure. What do you think? Thanks, very much, and God Bless!

Every Good Wish,
Doc

P.S. Of course, this part of the project load is "on hold" until I get the hum in our system traced down and eliminated, plus a few other things, as well. Thanks, again.

grumpy
11-07-2009, 09:29 PM
3 ports... Could plug one or more as another option.
I might be able to run a test tomorrow...
W/ 2242? You could dry run w/ WinISD,
trying as many methods as you like.

Doc Mark
11-07-2009, 09:40 PM
3 ports... Could plug one or more as another option.
I might be able to run a test tomorrow...
W/ 2242? You could dry run w/ WinISD,
trying as many methods as you like.

Hi, Grumpy,

Thanks for the shout. Yes, 2242 woofer in the 4645. I didn't think about plugging one of the ports, and would be interested in hearing how that works. So far, with the free program that I downloaded, I have not found any functions that let you play with porting. But, maybe I'm just not looking in the right place. In any case, yes, if you could run a test on this, that would be outstanding, and I would very much appreciate it. However, remember that, before I play with retuning the 4645, I'll be spending time trying to track down the hum in our system, then deciding if I want to keep the Ashly 4001 crossover. I seem to remember it being a bit shrill on the top end, which I didn't like too much. The old Crown VFX-2A was much more natural sounding, compared to the new Ashly. Thanks for your thoughts on this, Sir, and I'll talk to you later. Take care, and God Bless!

Every Good Wish,
Doc

Doc Mark
11-07-2009, 09:52 PM
Evening, Folks,

As I'm sure you already know, the title of this thread should be "LOWERING" the tuning, and not "lowing"..... Damn, it's hard to get old, fumble-fingered, and unable to hold my Guinness!!! :o::o::blink:

Doc (who's off to beddy-by.....)

grumpy
11-07-2009, 09:57 PM
Evening, Folks,

As I'm sure you already know, the title of this thread should be "LOWERING" the tuning, and not "lowing"..... Damn, it's hard to get old, fumble-fingered, and unable to hold my Guinness!!! :o::o::blink:

Doc (who's off to beddy-by.....)

Moo.

Doc Mark
11-07-2009, 10:16 PM
Grumpy,

THAT was hilarious!!! Thanks for the humor nightcap!

Doc

grumpy
11-08-2009, 05:08 PM
Plug one port. That will get you very close to the 25Hz figure.

I doubt port noise will bother you much when the thing is putting
out 100dB+ in-room at 20 Hz (music, not tone). Plumber's plugs,
often referred to here as "Zilchplugs" ... a naming that I'm
not sure was intended as an honor or a hope ;)... work well.

Note that you don't get something for nothing. You gain ~5dB of
sensitivity and some power handling at 20Hz... but you'll also lose ~2-3 dB
of sensitivity in the 30-50Hz range, have a non-flat anechoic bandpass
response (tapers off vs the 30Hz tuning as you go lower... which may
actually complement your room in a good way), lose some power handling
in the ~40Hz range, and marginally increase the group delay (doesn't
bother many people). ... at least that's what WinISD says :) ... I don't
have the help here to move those beasts around today.

FWIW, it looks like you would have to add ~7" to each port to keep
them all open... which IIRC, would require a bend to stay in the box.

Doc Mark
11-08-2009, 06:35 PM
Evening, Grumpy,

WOW! Thanks, very much, Sir! Once I get the hum problem solved, I will hook up the system and see how it sounds with it's original tuning. Then, I will A/B it back and forth, with one vent "Zilched", and then open, again, to see if I can notice much difference. In any case, as always, I very much appreciate your help, Grumpy. Having the proper tools at hand, like WinISD, is a good thing. Once I update my Mac computer, I'll go for something like FuzzMeasure, which won't load on this computer, and a few other speaker designing programs. Combined with my RTA and it's mike, I can then "see" somethings that I cannot see now. Thanks, again, and I'll let you know how it all turns out. If you decide to play around with your own setup like mine, please post your thoughts, too. Take care, and God Bless!

Every Good Wish,
Doc

grumpy
11-25-2009, 10:59 PM
2242H in 4645 cabinet (no suffix ... i.e., three 4" dia. ports)

using WT2:

impedance minima => 32Hz (indicative of port tuning, not exact, iirc)

one port blocked => 27Hz

two ports blocked => 20Hz

Doc Mark
11-26-2009, 07:50 AM
Good Morning, Grumpy,

Happy Thanksgiving Day, by the way!! Many thanks for posting that porting info on the 4645 cabinet! That's just what I wanted to know, and will offer a bit of fun in the subwoofer equation. Thanks, again, my Friend, and as always, God Bless!

Every Good Wish,
Doc