|   Vented vs. ported | WH
Jul 27, 2002 12:49 AM | | What are the differences in the sound characteristics of ported cabinets versus those of sealed cabinets. It seems to me that I have seen a lot of older speakers that are sealed but most newer speakers are ported. Why?
What about ported vs. sealed subwoofers. There seem to be quite a few of each style. What does one have or lack that the other doesn't? |
| re: Vented vs. ported | Tomn8r
Jul 27, 2002 2:47 AM | | Ported cabinets almost always produce more bass & are usually more efficient needing less watts to drive them. On the other hand sealed enclosures are usually faster. I have two sets of speakers with 12" woofers, one ported & one sealed. The sealed seam to produce almost as much usable bass as the ported however i dont think they are as efficient. Tom |
| re: Vented vs. ported | raindance
Jul 27, 2002 4:24 AM | | Sealed cabinets strive to simulate the "ideal" infinite baffle - a speaker mounted in an infinitely large panel so the rear radiation is never heard or used. This usually provides an extremely flat bass response. With actual sealed cabinets, the physical size is a constraint on the lowest bass, but this can be compensated for electronically - which is why there are servo-controlled subs. When the box is too small, for example, a bass hump occurs similar to a ported box! The difference is that the bass rolls off very fast below this "hump".
Vented cabinets, if there is only one vent, have one "tuned" frequency that they resonate at, and, if improperly designed, can reproduce tons of one note bass - not musical. Some manufacturers, such as Hsu, have managed to produce quite musical ported sub-woofer cabinets, but they use a variation on the bass reflex principle requiring some electronic compensation.
Ported boxes can be more efficient (theoretically***), but with subs it is the quality of the built-in amplifier that determines how efficient it really seems. And efficiency is a specification of the drive unit, not the box.
(*** sealed boxes are better damped and can usually be driven harder without excessive excursion)
If you are a home theater buff, consider where the port is - front ported speakers can often be successfully integrated into furniture/walls, etc. So can sealed speakers. Rear ported speakers can NEVER be successfully intgrated in this way.
Of course, if you are an audio buff, you wouldn't put any speakers into a wall or furniture... |
| re: Vented vs. ported | CHRIS8
Jul 27, 2002 1:17 PM | | "Sealed cabinets strive to simulate the "ideal" infinite baffle - a speaker mounted in an infinitely large panel so the rear radiation is never heard or used"
This is only true for Qtc alignments approaching 0.5. Normally, sealed cabinents in fact utilize a 2nd order resonant principle to enhance output levels. In general, they do not strive for an infinite baffle. Very few sealed designs every attempt this, as it results in poorer bass impact, lower SPL, and massive/expensive enclosures.
"such as Hsu, have managed to produce quite musical ported sub-woofer cabinets, but they use a variation on the bass reflex principle requiring some electronic compensation."
Electronic compensation is certainly not required to achieve high fidelity bass. The end result is a product of the chosen alignment. If you are referring to servo subs, these are really more of a marketing ploy than anything else. The servo feedback system is only effective at increasing fidelity considerably with steady state signals. ANy corrections made to increase linearity of the speaker, also, only are feasbiel at high excursion rates, to correct for motor non linearity. Music is not improved at playing levels within the linear range of the woofer, and even then the improvement is marginal at high excursion as complex waveforms can not be predicted as the steady state signals can. THe servo feeback system operates by mounting an acclerometer or other motion sensor to the woofer, and sending the signal to a feedback circtuit that changes the next cycle's output accordingly. Good for steady state, but unless time travel has been invented, it can not predict the next signal if it is not the same as the preceding one. The greatest effect would be noticed in music with long, constant bass signals such as in some pop and a lot of R&B, rap, etc. Again, and only at high excursion rates. More effective, is clamshell isobarik subooofer mounting, or push-pull normal configurations since the motors working in opposite directions of teh magnetic field tend to help equalize each other non linearities. This is much more effective than servo subwoofers, also this is effective with all music and steady state signals equally well. OF course, significant improvements are only made to non linear woofers just like with servo feedback. Some woofers have such exceptional linearity that using either techinique rarely has any worthile improvements. Examples being TC Sounds and Lambda woofers, that have extraordinary linear motors even at considerable excursions.
"And efficiency is a specification of the drive unit, not the box. "
Since efficiency is determined for a bass alignment by resonance of the system....indeed efficiency is a specificiation of the system alignment. Not the dirve unit by itself. Effiency of the drive unit by itself is only a factor when the driver is operating in a range that is outside the band of an external resonant system, relative to the driver.
"(*** sealed boxes are better damped and can usually be driven harder without excessive excursion)"
Sealed boxes have lower power handling. Sealed boxes induce signifcanlty higher levels of distortion. These are resulsts of the high excursion levels required, as compared to a ported alignment. If your intent is a very small volume compared to the driver's compliance(VAS), then you will achieve very low efficiency and poor bass extension in order to achieve higher power handling.
-Chris |
| re: Vented vs. ported | CHRIS8
Jul 27, 2002 12:39 PM | | "What are the differences in the sound characteristics of ported cabinets versus those of sealed cabinets"
The defining characteristics, mostly, are a product of the final alignments. The biggest difference is the ported box having much higher output levels and efficiecny in the lowest octave as compared to it's sealed counterpart. Misconceptions of 'looseness' are generally impressions resulted from a room with room modes occuring aroung the vented box's lower octaves, and/or the generally poor aligned vented designs that are usually produced and distributed on the market.
"I have seen a lot of older speakers that are sealed but most newer speakers are ported. Why? "
4th order alignments are very sensitive to variation of speaker paramters. Not until the last decade has it been cheap to produce speakers with close enough tolerances to get predicatble results that are nesecarry for mass production units. Additionally, it is easier to get very poor quality, 'louder' bass from a vented box to impress the general consumer.
-Chris |
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