There is more then one reason. All THX speakers and subwoofers are sealed designs. As far as I know all movie theaters use sealed speakers and subwoofers. Acoustic suspension speakers and subwoofers can usually take more abuse at high SPL levels then a ported cabinet without blowing the speaker or bottoming out the driver. You need to be more careful and listen to a ported subwoofer the harder you play it compared to a sealed subwoofer.
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Everything else being equal, a sealed sub is smaller and lighter. It's also a simpler design to build than a ported, for those who go with DIY. Ported subs tend to have longer decay times and more group delay, so sealed can have a tighter sound. For those who listen to music, many of these ported subs offer no advantage since many of them are tuned to 20 Hz. Porting doesn't offer much mid or upper bass advantage to subs tuned that deeply, and since music doesn't dip below 40 Hz very often, porting just doesn't help in those circumstances. Also, as was mentioned above, sealed offers better protection for the driver, everything else being equal. Those are a few advantages that sealed have over ported. Another advantage of sealed is for those who chase after super deep bass, the lower teens and even single digit frequencies. Ported rolloff is usually pretty sharp, and doesn't cough up much output below its tuning point. Everything else being equal, a sealed sub will offer more output below a ported sub's tuning point. This diagram explains the difference, sealed being the blue line:
To get any real output at those deep frequencies, you need a bunch of very serious sealed subs, but at least it is achievable with sealed, whereas it can not be done at all with ported.
To get any real output at those deep frequencies, you need a bunch of very serious sealed subs, but at least it is achievable with sealed, whereas it can not be done at all with ported.
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OP, sealed subs are appropriate in small rooms where cabin gain can realize as much as 12dB additional sensitivity and output at 20Hz. In larger rooms they're not, unless you use so many of them that you can compensate for their shortcomings with sheer power.
True, but at the cost of sensitivity and extension.
Also true, but on average the sealed only works better below 15Hz. These charts are typical of the difference between sealed and ported eighteens. The upper chart is sensitivity, the lower maximum SPL. Sealed is the blue trace, ported is the green:
OP, sealed subs are appropriate in small rooms where cabin gain can realize as much as 12dB additional sensitivity and output at 20Hz. In larger rooms they're not, unless you use so many of them that you can compensate for their shortcomings with sheer power.
None of that is true. As for acoustic suspension, which is a specific type of sealed alignment, it ceased to be widely used in the 1980s. Very few examples still exist today.
Had 2 Sealed ultra 5400's... They're now ported to 15hz and I can say that they absolutely destroy the sealed setup as far as output for music. Now in this particular box my first port resonance came in a little low but with a little EQing they sound just as good as my sealed boxes but a whole lot more output.
Bill pretty much covered it.
Quote:
Originally Posted by shadyJ /t/1519488/can-anyone-help-me-under...rted-subwoofer-for-home-theater#post_24399812
Everything else being equal, a sealed sub is smaller and lighter. It's also a simpler design to build than a ported, for those who go with DIY. Ported subs tend to have longer decay times and more group delay, so sealed can have a tighter sound. For those who listen to music, many of these ported subs offer no advantage since many of them are tuned to 20 Hz. Porting doesn't offer much mid or upper bass advantage to subs tuned that deeply, and since music doesn't dip below 40 Hz very often, porting just doesn't help in those circumstances. Also, as was mentioned above, sealed offers better protection for the driver, everything else being equal. Those are a few advantages that sealed have over ported. Another advantage of sealed is for those who chase after super deep bass, the lower teens and even single digit frequencies. Ported rolloff is usually pretty sharp, and doesn't cough up much output below its tuning point. Everything else being equal, a sealed sub will offer more output below a ported sub's tuning point. This diagram explains the difference, sealed being the blue line:
Had 2 Sealed ultra 5400's... They're now ported to 15hz and I can say that they absolutely destroy the sealed setup as far as output for music. Now in this particular box my first port resonance came in a little low but with a little EQing they sound just as good as my sealed boxes but a whole lot more output.
Bill pretty much covered it.
This says it's true for THX satellites and I think it's true for the mains since THX often uses the same speakers through out the room. Possibly subwoofers as well?
I pulled the following from a Secrets of sound article.
To correctly achieve this, THX satellite speakers are sealed systems with an 80 Hz –3 dB low frequency cutoff (preferably with a Qtc of 0.71). The electronic high-pass filter applied to them is an 80 Hz, 2nd order (12dB/octave) Butterworth alignment. The speaker and the filter sum to a 4th order Linkwitz/Riley roll-off which matches the electronic filter applied to the subwoofer, and an excellent crossover is achieved.
Quote:
Originally Posted by Bill Fitzmaurice /t/1519488/can-anyone-help-me-under...rted-subwoofer-for-home-theater#post_24399842
True, but at the cost of sensitivity and extension.
Also true, but on average the sealed only works better below 15Hz. These charts are typical of the difference between sealed and ported eighteens. The upper chart is sensitivity, the lower maximum SPL. Sealed is the blue trace, ported is the green:
![]()
OP, sealed subs are appropriate in small rooms where cabin gain can realize as much as 12dB additional sensitivity and output at 20Hz. In larger rooms they're not, unless you use so many of them that you can compensate for their shortcomings with sheer power.
None of that is true. As for acoustic suspension, which is a specific type of sealed alignment, it ceased to be widely used in the 1980s. Very few examples still exist today.
This says it's true for THX satellites and I think it's true for the mains since THX often uses the same speakers through out the room. Possibly subwoofers as well?
I pulled the following from a Secrets of sound article.
To correctly achieve this, THX satellite speakers are sealed systems with an 80 Hz –3 dB low frequency cutoff (preferably with a Qtc of 0.71). The electronic high-pass filter applied to them is an 80 Hz, 2nd order (12dB/octave) Butterworth alignment. The speaker and the filter sum to a 4th order Linkwitz/Riley roll-off which matches the electronic filter applied to the subwoofer, and an excellent crossover is achieved.
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Longest room dimension approximately 20 feet. That will have cabin gain starting at 28Hz; lower than that and it's not going to add enough to make up for the lower sensitivity of a sealed sub. Even 20 feet is a bit large. Look at the SPL chart I posted above, showing the f3 of the sealed sub at 38Hz. Ideally you'd want cabin gain to begin no lower than 38Hz as well. That requires a maximum room dimension of 15 feet.
THX is a standard for frequency response and output capability. It has nothing to do with cabinet types. The Secrets of sound article is way off base.
At least you admit it.
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