CurtPalme.com Home Theater Forum

[stefuel]

I'm curious. Some swear by sealed cabinets and others swear by ported. How do you feel and why? Why do I ask, because I just don't know but I'm thinking of perhaps building one for a fun project.

[lostmandan]

If you are looking to build one then the specifications of the driver/speaker that you design with will typically determine if the cabinet is ported or sealed.

I build this massive subwoofer quite a number of years ago using two 12" woofers in a ported isobaric configuration. It has a roll-off point of 18Hz (calculated) and I think it does it. Unfortunately the excursion is pretty extreme and I am concerned about damaging the drivers when they move that much.

Let me see if I can dig up some information for you. I know there are a fair number of programs that allow calculations. I spent a fair bit of time working out the information using an older book from Radio Shack Also, make sure that you know the Theile-Small (TS) parameters of the driver(s) being used. The book I used described an "Added Mass" technique for determining the TS parameters of drivers using a frequency generator, multimeter, and a resistor. I used this for the sub I mentioned above and I think it was fairly accurate.

The best part of speaker building is the woodwork IMO

[greg_mitch]

I think as a general rule of thumb you can get more dB with less power in a ported enclosure.

Hypothetical example is something like a sealed 18" 1000 watt sub may have same dB as 15" 500 watt sub in ported enclosure.

I have only had ported before and I like them so I don't see why go to sealed. Also, I read that sealed are supposed to be better for music. Haven't experienced it myself.

[-Pjackso]

Excellent speaker building software is WinISD.
It's a free download, just google for it.

It'll accept all TS parameters, and you can change box size, driver configurations, ports/sealed.
It'll show you the resultant charts for frequency vs. db, power requirements, excursion, etc...

[lostmandan]

I second WinISD. Good and free

Although some may laugh, I used a soft called Perfectbox for quite a while. This is actually so old that is runs on MS-DOS (or in a Windows DOS Prompt). It definitely did the trick though.

I've always wanted to build a dual 18" folded horn design. I have the urge to do structural damage .. or do stage productions

[jask]

I keep thinking it would be fun to build a rear seating plinth into a HUGE sub box, but worry I would end up with a null in one of the viewing positions.... Hmmmm a 1000L sub box!!!!

[perisoft]

I swear by large, large numbers of hacked-together subwoofers. But my budget is essentially zero, so I take what I can get.

[ecrabb]

[perisoft]

[greg_mitch]

[ecrabb]

[ecrabb]

[greg_mitch]

[zGman]

The trade-off for ported vs sealed sub cabinets goes beyond efficiency and cabinet size.
In fact for some drivers the sealed cabinet can be substantially smaller - however the
low-end response drops off rapidly and must be EQ'd substantially. The advantage with
sealed boxes is accurate phase response = no phase error. A ported enclosure tuned for max
output at the lowest frequencies will have substantial (up to 135 degrees or more) phase error.
This makes for "muddy" bass. Another drawback to tuning for max output is that you
can end up with "one-note" bass - there is no articulation or musicality, whatever the input
signal, you just hear one big boom - which some people think is just great! ... However,
with good tuning and a little EQ you can have the best of both. This can take a lot of
modeling and experimenting with port/box sizes looking for a reasonable response curve
with the lowest phase error. You need to start with a driver that has a low resonance freq.
preferably under 20Hz, and a Qts around .35, and Xmax +/- 15mm linear one way (30mm p-p)
Pics of a dual 12" project I did a while ago might be found at the link below. The room was long
and narrow - so we didn't want to have the sub in the front, which would overdrive the room modes.

http://www.theaterdimensions.com/galleries/subwoofer/index.html

Other speaker projects and theater projects also at

http://www.theaterdimensions.com

G

[Mark_A_W]

The best is an Infinite Baffle sub - a sealed box so big it is in effect, infinite. Two to four 15" woofers (cheap ones will do) and a roof cavity/spare room/floorspace/basement.

With a suitable driver, you get both deep extension (mine will literally shake the roof, projector and all, at 14hz), output (huge cone area), and good phase response (due to flat response - they are entwined) - giving you "tight" bass. And use bugger all power (huge cone area again).




With conventional boxes, well, you can make a ported box with and effective "Q" of about 0.6 giving you a "sealed box sound". It's not so simple as sealed = "tight" and vented = "boomy". That all depends on the frequency response, and associated group delay, and associated phase response - they are all basically sides of the same thing.


But as a rule of thumb, NEVER, EVER, NEVER make an EBS alignment ported box (tuned for maximum extension). They sound like crap and this is why ported boxes are regarded as "one notey". The EBS alignment is "one-notey", but not all vented alignments are.


Oh, and there is no spoon...nor fast bass. Fast bass is treble, if anyone mentions fast bass they deserve a smack in the back of the head I'm glad no one has dropped that clanger in this thread so far.

[Heywood Jablome]

[greg_mitch]

Talking about one note bass...I have a coworker with a Klipsch 10" sub and he has the thing cranked up so high on gain it is sooo muddy but he loves it. It does shake the couch but it gets to a point that you can't hear anything else but this humming of bass constantly. He doesn't understand what I mean when I talk about accurate bass and he actually thinks my 15" sub isn't as good as his because it doesn't constantly rumble.

That might be the "audiophile" snob in me.

[ecrabb]

[Rdean]

Don't want to hi-jack the thread but I think this is in the spirit of the OP. I am putting in component speakers in my Suzuki Vitara. The rear driver locations have much to be desired. There is literally no baffle/enclosure, the speaker was just flapping in the wind so to speak. Obviously not much bass output.

I realize car manufacturers in many instances take little if any consideration in sound quality, but to just bolt a driver to some sheet metal with practically nothing surrounding it is really lame.

Regardless I can see where there are places I can install wood/epoxy etc to form an enclosure behind it. It will end up being a roughly 12" by 12" by 10" enclosure with a 6.5 " driver. My question has been do I completely seal it or allow some port.

After reading this thread I am leaning towards completely sealing it as the last thing I want is to sound like the "Kid in the Civic", one note booming muddily. I doubt I would take the time and effort to do all the calculations involved with trying to make a port sound good.

I realize I will give up some efficiency. They are driven by 50W RMS per side so I may not get as much output as I would like.

I guess if after this I still want more bass there is more "cavity" space to the rear where I can install more drivers and another higher watt amp to drive them. Another project down the road to keep me busy.

Am I making the right choice?

[bbfarmht]