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why no sEALed fEARfuls???

#42
DukeLeJeune said:
The key thing is the reduction in cone excursion at and near the port tuning frequency; that's what saves the vented box's bacon.
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And below it? My novice simulations show the vented box with much higher excursions below the tuned frequency than the closed box for a given power input. I suppose that such frequencies might be excited with any number of the usual transient plucking events. Is this not a concern with respect to a given driver's xlim?
 
#44
rpsands said:
What was the frequency range of the human voice?
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My memory has grown foggy about whose voices we used. Margot Timmons (Cowboy Junkies), Eva Cassidy and Stephen Stills were among them, but that's all I remember at this time.

My characterization of the difference would be that the ported box sounded more open/less wooly or boxy.
 
#46
Codger said:
And below it [the tuning frequency]? My novice simulations show the vented box with much higher excursions below the tuned frequency than the closed box for a given power input. I suppose that such frequencies might be excited with any number of the usual transient plucking events. Is this not a concern with respect to a given driver's xlim?
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Well yes, a vented box's excursion goes through the roof well below the tuning frequency. That's why choosing the tuning frequency is always a juggling of tradeoffs. Sealed or vented cab, there will be a limiting factor somewhere. I believe that a well-designed vented cab can usually go considerably louder than a comparable sealed cab before fartout, but that may be somewhat dependent on the technique of the bassist.
 
#47
As always, Duke, your answers are always very concise and make sense to a layman like me. No offense to you, rp, but I still can't figure out your reply ;)

Codger, in fairness to Duke, he did say this starting the next paragraph in the post you quoted:

"If a vented box isn't driven by high-level signals well below the tuning frequency, it is actually less demanding of x-max than a comparable sealed box."
 
#48
seamonkey said:
What did the measurements of the cabinets say?
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Beyond the crossover design work, I didn't make any measurements, sorry. I probably should have, but that would have added a lot of time to the procedure, especially if I'd run measurements every time I stuffed in or took out a handful or two of polyfil.

Both boxes were actually ported with a round port that I could seal with a plumber's test plug. I alternated between boxes as to which was the vented box and which was the sealed one, as I wanted to see if the difference was attributable to the different internal damping techniques used. So if one set of drivers + crossover sounded better for some reason, or if internal damping material was the decisive factor, listener preference should not have followed the port.

I wasn't trying to do a documented set of tests and had zero expectation that I'd one day be talking about 'em on an internet forum. The only person I was trying to educate was myself, and I certainly don't expect anyone else to be convinced by my alleged tests and their alleged results.
 
#49
Well this is far from scientific, but I did my own little test, too. When I got my 64 B-15N, I didn't know this because I was woefully ignorant about them for the first few years I had it, but all the port slots in the inner baffle were blocked with foam. Jess Oliver told me to throw those out and don't ever use them because Everett Hull would keep screwing with his cab's tuning because he had bad hearing and wouldn't admit it. Honestly, it didn't sound bad with the ports stuffed. But it was a whole new ballgame with them unstuffed. I gained some low end response, and I honestly think the midrange improved as well.

You'll still have to pry my vintage (and sealed) Ampeg 810 out of my cold, dead hands, though ;)
 
#52
Duke, I'm not sure but I'd lay my wager that if you used a high pass to make the ported cab have less bass content you'd find people not being able to tell the difference again. A lot of vocal content down under 200hz would make the ported box sound a lot nicer (and acoustic guitar, say, as well, despite instruction:)

Only other guess I'd have is the "character" imparted by a ported box having less stuffing (and therefore a little bit more in the wall reflections. I'm really not an expert though obviously. I wouldn't expect that to be consistent across a group.

Cool stuff for sure, regardless.
 
#53
rpsands said:
Duke, I'm not sure but I'd lay my wager that if you used a high pass to make the ported cab have less bass content you'd find people not being able to tell the difference again. A lot of vocal content down under 200hz would make the ported box sound a lot nicer (and acoustic guitar, say, as well, despite instruction:)

Only other guess I'd have is the "character" imparted by a ported box having less stuffing (and therefore a little bit more in the wall reflections. I'm really not an expert though obviously. I wouldn't expect that to be consistent across a group.

Cool stuff for sure, regardless.
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Thanks!

I do think there was enough difference above 200 Hz that it would still be audible with a high-pass filter, but I could be wrong.

Transmission line guru Irving Fried argued that backpressure on the cone of a sealed box woofer caused midrange coloration, with a vented box being an improvement in that regard, and a transmission line better still. His was definitely a minority position in his day.

Anyway I came away from my investigations with some opinions about how to port a box and how to use damping material inside a box. Damping material inside a box is sort of like capacitance in a crossover: More isn't necessarily better; rather, the right amount in the right place is what we want. But that's another tall tale for another late night.
 
#54
DukeLeJeune said:
I used two speakers which were identical except for the port and internal damping material (which was optimized for each type, and adjusted several times over the course of the test).

The music used had no bass instruments, and the test subjects were instructed to focus only on the human voice in the recordings, and judge how natural or realistic it sounded. Recordings of spoken voice were also used.

I expected the sealed box to be preferred, and was quite surprised by the outcome.
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Ahh.... but Duke, have you ever ever grabbed a P-Bass and a pick and cranked up an SVT through a sealed 810 cab? I don't care what the specs say, it's sheer bass bliss and there really is nothing quite like it.
 
#55
True. So true. Again, when someone puts out a ported cab that has the same midrange character as a sealed one, I'll own it. My sealed cab just sits in a mix so well and the it's never muddy. Just too damn big and heavy. Im not looking for a response, just say'n.
 
#56
:D You can always count on a fEarful thread to spark some kind of controversy! :D

eyeballkid said:
for the record, I wasnt bitching that he doesnt make those designs, just wondering why, thats all, cos it seems that most GOOD cab designers have some of both in their arsenal.
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Why?
'Cause GB didn't start designing a fEarful for the masses. He designed it for himself, then shared it with us.



Kinda reminds me of the old joke where the hooker asks the john "Who do ya think you're gonna satisfy with that thing?"


"ME", says the john......:smug:
(yeah, it's corny, I know)
 
#57
DukeLeJeune said:
The key thing is the reduction in cone excursion at and near the port tuning frequency; that's what saves the vented box's bacon.
.
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The only 'advantage', if you want to call it that, to the sealed cab is higher harmonic distortion. THD is directly proportional to excursion. Sealed cabs have higher excursion for equal output, so they have higher harmonic distortion, which is often equated with 'warmth'. When you push drivers past xmax THD literally skyrockets, and since sealed cabs are pushed past xmax at far lower power levels than vented that further raises the 'warmth' factor of sealed. But all that warmth is obtained at the expense of low end output, so consider well if it's a worthwhile goal.
 
#58
R Baer said:
Ahh.... but Duke, have you ever ever grabbed a P-Bass and a pick and cranked up an SVT through a sealed 810 cab? I don't care what the specs say, it's sheer bass bliss and there really is nothing quite like it.
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Its refreshing to hear this from a guy who works with specs on a daily basis, specially in a forum where many people seem to forget to use their ears when judging equipment...
 
#60
allexcosta said:
Its refreshing to hear this from a guy who works with specs on a daily basis, specially in a forum where many people seem to forget to use their ears when judging equipment...
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You might be assuming that engineers don't use their ears as much as non-engineers when judging gear. That's not only untrue, the opposite is the case. Engineers know what causes what they hear, and how to make changes in the gear so that it will sound the way they want. They may do so using data, but the data is only a means to an end, good sound, and not the end in itself. Those who do not understand data can only use their ears. Those who do use both their ears and their eyes, and most importantly, their brains, unfettered by misconception.
 

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