Can anyone help me understand why someone would wanted a sealed subwoofer over a ported subwoofer for home theater? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 58 Old 02-23-2014, 05:08 PM - Thread Starter
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Can anyone help me understand why someone would wanted a sealed subwoofer over a ported subwoofer for home theater?
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post #2 of 58 Old 02-23-2014, 05:27 PM
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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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post #3 of 58 Old 02-23-2014, 05:33 PM
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Can anyone help me understand why someone would wanted a sealed subwoofer over a ported subwoofer for home theater?
- More compact than a ported sub.
- The possibility of getting deeper, usable extension vs. a ported sub.
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post #4 of 58 Old 02-23-2014, 06:38 PM - Thread Starter
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Originally Posted by Secret Squirrel View Post

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.

Well for instance. It seems SVS ran out of PB12-NSD. But still have some SB12-NSD on closeout. Obviously the SB12-NSD is not as highly regarded as its PB12-NSD cousin.

Why?
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post #5 of 58 Old 02-23-2014, 06:56 PM
 
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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.
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post #6 of 58 Old 02-23-2014, 07:00 PM
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Originally Posted by Acousticality View Post

Well for instance. It seems SVS ran out of PB12-NSD. But still have some SB12-NSD on closeout. Obviously the SB12-NSD is not as highly regarded as its PB12-NSD cousin.

Why?

Well with that specific company a lot of people are upgrading their pb1000 to the pb12 nsd and.more people are looking to fill the bigger size rooms and ported are the cheaper fix as you need around 4 sealed subs to get that deep bass vs 1 big ported sub.
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post #7 of 58 Old 02-23-2014, 07:03 PM
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Originally Posted by eljaycanuck View Post

- More compact than a ported sub.
True, but at the cost of sensitivity and extension.
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- The possibility of getting deeper, usable extension vs. a ported sub.
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:
SealedportedRSS460.jpg


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.
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All THX speakers and subwoofers are sealed designs...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.
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.

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post #8 of 58 Old 02-23-2014, 07:13 PM
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Originally Posted by Acousticality View Post

Well for instance. It seems SVS ran out of PB12-NSD. But still have some SB12-NSD on closeout. Obviously the SB12-NSD is not as highly regarded as its PB12-NSD cousin.

Why?

Strange deduction. How do we know they didn't have a lot more SB12-NSD inventory on hand to start with?

WAF is why I have sealed.

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post #9 of 58 Old 02-23-2014, 07:23 PM - Thread Starter
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Originally Posted by RedLefty View Post

Strange deduction. How do we know they didn't have a lot more SB12-NSD inventory on hand to start with?

WAF is why I have sealed.
I'm talking 1 for 1. it sounds like there are advantages to sealed subs from what all the posters are saying. However, it also sounds like if you are looking to buy just one sub, that ported has a distinct advantage in being able to more effectively fill the room.
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post #10 of 58 Old 02-23-2014, 07:26 PM
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Originally Posted by shadyJ View Post

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.
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post #11 of 58 Old 02-23-2014, 07:28 PM
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Originally Posted by Bill Fitzmaurice View Post

sealed subs are appropriate in small rooms where cabin gain can realize as much as 12dB additional sensitivity and output at 20Hz.
Okay, I hear this a lot but what is small room? 1000ft^3, 1500ft^3, 2000ft^3?
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post #12 of 58 Old 02-23-2014, 07:39 PM
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Originally Posted by tvuong View Post

Okay, I hear this a lot but what is small room? 1000ft^3, 1500ft^3, 2000ft^3?

All three of those are small rooms.

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post #13 of 58 Old 02-23-2014, 07:46 PM
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http://www.svsound.com/sealed-vs-ported

For my situation, I went with dual SVS SB12-NSD's over the PB12 simply because they went into my main living room and small footprint with the gloss black finish met my needs aesthetically vs the larger ported PB12.
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post #14 of 58 Old 02-23-2014, 07:56 PM
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All three of those are small rooms.
Okay, so up to what cubic foot is considered to be small? Thanks.
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post #15 of 58 Old 02-23-2014, 08:19 PM
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Originally Posted by Bill Fitzmaurice View Post

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:
SealedportedRSS460.jpg


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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post #16 of 58 Old 02-24-2014, 05:27 AM
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Originally Posted by tvuong View Post

Okay, I hear this a lot but what is small room?
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.
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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?
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.
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post #17 of 58 Old 02-24-2014, 05:43 AM
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Bill is the expert on this. He has excellent articles that explain why group delay doesn't determine "tightness" in real world cases.
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Originally Posted by Acousticality View Post

Can anyone help me understand why someone would wanted a sealed subwoofer over a ported subwoofer for home theater?

Both sealed and ported have pros and cons, I won't go into them as you'll find enough info on google.

I have just sold a PC Ultra 13 and bought a SB Ultra 13. In my room it works better, takes up less space, and I don't need the headroom of the ported models. I bet the SB Ultra 13 would be plenty in the typical UK sized living room too.

If one type had all advantages and no disadvantages I'd pick that one.
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post #19 of 58 Old 02-24-2014, 05:52 AM
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I've never heard that group delay influenced "tightness". IME it ("tightness" or "speed") is related to cone control and distortion, typically ringing (excess cone movement) before, during, and after signal is applied. Constant group delay will provide better impulse/step response but that is rarely a concern at subwoofer frequencies. Historically sealed has been better at that but a good design with a decent amp should make them equivalent. That leaves the main thing going for sealed sub as slower roll-off, a moot point with the performance of most subs these days since all the better ones play pretty dang low.

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post #20 of 58 Old 02-24-2014, 06:28 AM
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Originally Posted by DonH50 View Post

I've never heard that group delay influenced "tightness". IME it ("tightness" or "speed") is related to cone control and distortion, typically ringing (excess cone movement) before, during, and after signal is applied. Constant group delay will provide better impulse/step response but that is rarely a concern at subwoofer frequencies. Historically sealed has been better at that but a good design with a decent amp should make them equivalent. That leaves the main thing going for sealed sub as slower roll-off, a moot point with the performance of most subs these days since all the better ones play pretty dang low.
Where subs are concerned group delay is moot; if you were to hear it the speaker would be so flawed that it would be unusable. As for 'tightness' and 'speed', those terms don't have any real meaning with respect to subs, and are typically used by those who don't know what technical term does apply to whatever it is that they're trying to describe. As for the slower roll off of sealed, much is made of that, but again, it's only apparent in its effect well below 20Hz, making it a moot point as well in the vast majority of cases. If you're trying to reach the single digits then sealed or IB is the way to do it, but the number of speakers and the amplifier power required to realize it at worthwhile levels is far beyond what the average budget would allow, let alone WAF.

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In my opinion (with one sub)

Smaller room - sealed
Larger room - ported

Small home theatre- sealed
Large home theatre - ported

Now you can buy a couple of sealed boxes ie 2 x SB Ultra 13 in a larger room, home theatre but it would make more economical sense. ie KK 12012 quatto quattro (sealed with passive rad)...insanely expensive and have to wonder that four PB Ultra could match, for much lower price.
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post #22 of 58 Old 02-24-2014, 06:41 AM
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Bill, for the longest dimension, do we use the length of the room or the diagonal (ceiling back left to floor front right)?
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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.
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post #23 of 58 Old 02-24-2014, 06:45 AM
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Originally Posted by Bill Fitzmaurice View Post

Where subs are concerned group delay is moot; if you were to hear it the speaker would be so flawed that it would be unusable. As for 'tightness' and 'speed', those terms don't have any real meaning with respect to subs, and are typically used by those who don't know what technical term does apply to whatever it is that they're trying to describe. As for the slower roll off of sealed, much is made of that, but again, it's only apparent in its effect well below 20Hz, making it a moot point as well in the vast majority of cases. If you're trying to reach the single digits then sealed or IB is the way to do it, but the number of speakers and the amplifier power required to realize it at worthwhile levels is far beyond what the average budget would allow, let alone WAF.

Yes I realize that "tightness" has no "real" meaning but it is used by those promoting the benefits of sealed subs. That's why I used it.
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post #24 of 58 Old 02-24-2014, 06:57 AM
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If you want High Fidelity sound stick with a sealed sub, usually 12inch. IMO, sealed subs hit harder and tighter.

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post #25 of 58 Old 02-24-2014, 06:58 AM
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Originally Posted by Bill Fitzmaurice View Post

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Originally Posted by DonH50 View Post

I've never heard that group delay influenced "tightness". IME it ("tightness" or "speed") is related to cone control and distortion, typically ringing (excess cone movement) before, during, and after signal is applied. Constant group delay will provide better impulse/step response but that is rarely a concern at subwoofer frequencies. Historically sealed has been better at that but a good design with a decent amp should make them equivalent. That leaves the main thing going for sealed sub as slower roll-off, a moot point with the performance of most subs these days since all the better ones play pretty dang low.
Where subs are concerned group delay is moot; if you were to hear it the speaker would be so flawed that it would be unusable. As for 'tightness' and 'speed', those terms don't have any real meaning with respect to subs, and are typically used by those who don't know what technical term does apply to whatever it is that they're trying to describe. As for the slower roll off of sealed, much is made of that, but again, it's only apparent in its effect well below 20Hz, making it a moot point as well in the vast majority of cases. If you're trying to reach the single digits then sealed or IB is the way to do it, but the number of speakers and the amplifier power required to realize it at worthwhile levels is far beyond what the average budget would allow, let alone WAF.

Agree to all, thanks Bill.

Regarding the other post (not yours) about sealed being better for smaller rooms, I am not sure why the room size would matter? Port noise is often cited but a well-designed sub shouldn't really have audible port noise at any reasonable SPL. In a smaller room it seems more desirable to use a smaller ported sub over a larger sealed sub to get the same performance due to space considerations. Not sure room gain matters for this. I must be missing something (not unusual).

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but a well-designed sub shouldn't really have audible port noise at any reasonable SPL.

I didn't get any port noise, even with one port plugged.
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If you want High Fidelity sound stick with a sealed sub, usually 12inch. IMO, sealed subs hit harder and tighter.

I'm using a SVS 12" SB for the hifi and I'm very happy with the results. Whether the extra 1.5" for the SB Ultra means it's worse...who knows. SB Ultra 13 is overkill for a stereo system and not expensive.
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post #27 of 58 Old 02-24-2014, 07:51 AM
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Originally Posted by Bill Fitzmaurice View Post

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I've never heard that group delay influenced "tightness". IME it ("tightness" or "speed") is related to cone control and distortion, typically ringing (excess cone movement) before, during, and after signal is applied. Constant group delay will provide better impulse/step response but that is rarely a concern at subwoofer frequencies. Historically sealed has been better at that but a good design with a decent amp should make them equivalent. That leaves the main thing going for sealed sub as slower roll-off, a moot point with the performance of most subs these days since all the better ones play pretty dang low.
Where subs are concerned group delay is moot; if you were to hear it the speaker would be so flawed that it would be unusable. As for 'tightness' and 'speed', those terms don't have any real meaning with respect to subs, and are typically used by those who don't know what technical term does apply to whatever it is that they're trying to describe. As for the slower roll off of sealed, much is made of that, but again, it's only apparent in its effect well below 20Hz, making it a moot point as well in the vast majority of cases. If you're trying to reach the single digits then sealed or IB is the way to do it, but the number of speakers and the amplifier power required to realize it at worthwhile levels is far beyond what the average budget would allow, let alone WAF.

Agree to all, thanks Bill.

Regarding the other post (not yours) about sealed being better for smaller rooms, I am not sure why the room size would matter? Port noise is often cited but a well-designed sub shouldn't really have audible port noise at any reasonable SPL. In a smaller room it seems more desirable to use a smaller ported sub over a larger sealed sub to get the same performance due to space considerations. Not sure room gain matters for this. I must be missing something (not unusual).

Lots of sweeping generalizations being thrown about...

To quickly address the room gain question: As the low bass gain from a small confined space becomes greater in smaller rooms this quickly helps a sealed sub catch up precisely where a ported sub has it's advantage... near the tuning frequency. Modern auto-EQ systems have helped greatly to even the playing field, where the typically delivered response shape of commercial ported subs tend to be less complimentary to the gain observed in small rooms, where a well designed sealed subwoofer can easily compliment a small room very well.

Something to consider here... If you have a complimentary gain with a sealed subwoofer in a small room (specifically with designs that do not electronically cut the shallow roll off), you can see extension into the 8-14Hz range. With a ported subwoofer, adding more subwoofers means you only get louder at the same frequency range near and above the tuning frequency. With a sealed subwoofer delivering deep, in-room extension, adding more subwoofers from the start or in the future will increase the headroom at those lowest frequencies and make them more and more useful and noticeable. The only VLF limit to a sealed subwoofer is how loud it can get in room. With a ported sub the port tuning sets the hard limit.

Size vs. possible low frequency extension is another huge differentiator. No matter the power or driver available, moving lots of air down below 20Hz with a ported box requires a significant size/area port, and a significant size box to tune it low in. A very compact ported box tuned to 16Hz isn't happening without serious compromises in output capabilities.

As already highlighted in this thread, within some limits of shipping and enclosure/cabinet costs, a large ported box will generally have advantages in bass output capabilities per dollar down to and around it's port tuning frequency. While the port resonance can add significant output, the air-flow through the port can change significantly at high vs low levels. The best designs minimize this to a large degree or within certain limits. By comparison, a sealed design is very consistent dynamically within its excursion and power limits. The key lies in making sure those limits are high enough for your room and uses.

Mark Seaton
Seaton Sound, Inc.
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post #28 of 58 Old 02-24-2014, 08:06 AM
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Quote:
Originally Posted by Mark Seaton View Post

As the low bass gain from a small confined space becomes greater in smaller rooms this quickly helps a sealed sub catch up precisely where a ported sub has it's advantage... near the tuning frequency. .

Thanks Mark for your explanation. Regarding the above statement, would the ported sub benefit as well from the room gain down to its tuning frequency? If it does, wouldn't that mean that it will still maintain its advantage down to the tuning frequency over its sealed counterpart?

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Speakers: 3 JTR 212HTR (LCR), 2 Jtr Single 8LP (S), 2 JTR Triple 12LF (SB)) , 4 Volt 10LX (Atmos)
Subwoofers: 4 Rythmik FV15HP , 5 Crowson Shadow 8 transducers, 3 Buttkicker LFE
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post #29 of 58 Old 02-24-2014, 08:06 AM
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Originally Posted by Secret Squirrel View Post

All THX speakers and subwoofers are sealed designs.

Just to back up Bill, this is not the case. Here are examples of a ported THX speaker and subwoofer respectively:
http://www.klipsch.com/kl-650-thx-bookshelf-speaker
http://www.klipsch.com/kw-120-thx-subwoofer
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post #30 of 58 Old 02-24-2014, 08:50 AM
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Thanks Mark, good to hear from an expert! Room gain is what I was unsure about and you explained nicely.

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