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Discussion in 'Amps and Cabs [BG]' started by insomniac2295, Sep 18, 2008.
Say I wanted to do this to my 1x18 and 4x10 cabs. Would I be facing any major issues in doing this?
It would be the same as filling your mouth with cotton batten. Things just ain't going sound the the same anymore.
Ports are tuned into a cabinet, if they're properly designed. The plug them up would be like cutting off the bass response. That's why guitar cabinets are sealed and don't have ports. They put rear ports in stereo speakers so you can put them against the wall and the bass can bounce off the back and fill the room that way.
If you're unhappy with the sound try turning you're 18" cabinet around to face the wall. 18" speakers aren't for everyone. I find them slow moving and muddy up the mix. A well made 'ported' cabinet with a 15" JBL, EV, Guass(they still in business?) speaker should give you a tighter low/bottom end.
As far as just "covering up some ports"...Sure, anyone can do that.
Remember, typically with a ported cab, (in most cases) the inner dimensions are larger as opposed to sealed (due to the tuning of the cab, for your specific drivers), you might want to look at the dimension requirements of your specific driver specs. You could affect the performance of the driver(s) somewhat.
Keep this in mind, with your ported cabs, they are slightly more efficient, for the fact that the cab can breathe (and are tuned to a particular frequency). Sealed cabs are not as efficient, thus may need more power to achieve the same performance as your current ported cabs.
This is provided that the cabs were built to the driver's specs, which in turn I would say, Don't do it. But they're not my cabs anyway.
stuff something in the port to see what it is like. compare with and without to determine if you think that plugging the port would be useful. maybe use some socks in a plastic bag or similar.
Screw a piece of drywall/wallboard over the port and that will close it right off. Anything fabric or insulation wise will leak thru.
bad idea. the good news is you won't have to permanently mod your cabs to discover this. most drivers that work well in a ported cab don't perform well in sealed enclosures. and even then, the optimal enclosures are never the same size. it is theoretically possible that your cabs are so badly designed and mismatched with their respective drivers that sealing them up would result in a better alignment, but that is very unlikely. even the cheapest bass cab has some amount of r&d. sealed vs. ported for any given driver is one of the very first questions that has to be answered. then they go from there and figure out how best to compromise the tone in the quest for cheap.
if you're serious about this the learn to use winisd, track down the specs on your speakers, and model them in your enclosure. this costs nothing but time and will give you all the info you need to decide if the project is worthwhile.
You'll totally eliminate the low end by using drivers intended for a vented cab in a sealed cab, but aside from that, no worries.
all of the above is taking for granted that:
(a) the cab *is* tuned "properly", or failing that, tuned in a way that sounds "good" for bass. i suppose that one can be a little subjective.
(b) the mfr. wasnt trying to force the speaker to do something it wasnt designed to do, which seems at least somewhat common. "as loud as possible" is one avenue, as is the "bose method" of making it stand out in some way on the sales floor by hyping the sound in some way, regardless of what that does to the sound in a real-world application. (cough... bose cubes... cough)
i own two cabinets that came from the factory a mess. the first is an SWR bassic black combo. pretty cool amp, decent speaker, and well braced cabinet. but, the internal volume was pretty small with the amp in, and the huge 5-6" "port" (which was really just a hole cut into the back) "tuned" the cabinet pretty high. after i cooked the amp years ago, i closed up the opening with 3/4 ply screwed and glued to use it as an extension cab. removing the amp made the internal volume larger, but it was still tuned too high, IMO.
likewise, a fender HM215B cab--- this one had TWO 6" holes cut into the baffle for venting. again, a nice solid-ply cab with a reasonable amount of bracing. that one was "tuned" north of 200hz, according to my calculations. that one in particular sounded like you would expect---- a muddy, boomy mess that fell to pieces on the lower notes.
over time, i have sealed both cabinets, changed drivers, and ultimately re-tuned the cabinets to a more appropriate frequency (50-55hz for the ampless bassic black cab, and 45-50hz for the fender, allowing for error); the former sporting a 1502 BW and the latter a pair of 1505 BWs. absolutely a night and day difference. from my perspective, the vast improvements in both cabinets make me really question the so-called R&D mentioned above.
it made me realize that there were many other cabinets suffering from the same plight, presumably to make the cabs "louder". not only in bass amplification, but in PA stuff, home or car subwoofers, etc etc. its that low-mid "boom" that alot of those home-theater-in-a-box systems have--- seems impressive in the store ("wow, thats a lot of bass from this little box!), but when you get it home you realize the sound is hyped and anything but accurate. the ubiquitous smiley-faced curve--- but i digress.
anyway, sorry for the long post. my suggestion is to try and procure the specs of the drivers in your cabs, calculate the current tuning, and go from there.
this can lower the resonant frequency of the cab, and may sound better. My old Trace cabs had tunable ports, that came with 'bungs' to plug one or both; I got the deepest bass by plugging one of the ports.
Just IMHO, from what I heard in real world testing.
Just a thought. I'm sure Bill Fitzmaurice will chime in here shortly and attempt to belittle and humilitate us with his slide rule...tell us we're all idiots.
He already did (post 9). I don't think he met your expectations though
i may be wrong, but isnt there an issue about pressure???
Yak yak yak - the paralysis of analysis.
Try it and see how it sounds.
If no good, put it back.
A port extends into the cabinet much like a pier extends into the water. The port allows extraction of bass frequencies much like a pier allows extraction of boats, people, etc. So in essence, it's all about pier pressure.
There are two. The first is what happens when you seal a cab. The increased internal pressure resists the movement of the cone, and that reduces bass response. This can be compensated for with a larger cabinet, or by using a driver that has specs that work better with a sealed cab, but in either case unless the cab is huge the bass response will never approach that of the vented box.
The second concern with pressure is when port sizes are reduced to lower the tuning frequency. The air in the port moves faster when the port is made smaller, and if too small will create chuffing noise. The preferred method to lower tuning is to make the duct longer.
Did you write that yourself?
Hopefully, the OP will check back with this thread to see the real answers.
probably screw it up
All this talk of "Pier Pressure" & "Port size" leaves one feeling their about to take a shower at the YMCA.