Originally Posted by mthomas47
Thanks, Adam! I appreciate the kind words. I honestly don't know whether I am onto anything here or not. In theory, a ported sub should be able to sound just as good for music as a sealed sub. But, sounding good is a very subjective quality, and not everyone will hear exactly the same things in the same way. There are people who rightly or wrongly, do draw distinctions between the sounds of a sealed sub and a ported sub.
I was simply speculating whether there might be some difference in the sound, for some kinds of music, if a ported sub emphasized low bass (< 40Hz) frequencies more than a sealed sub did? Would someone either consciously or subconsciously register more low fundamentals with some acoustical instruments and consequently hear a difference between the two subs? The differences might be pretty subtle even if my hypothesis were correct, and I'm not sure that it is. But, it's interesting to speculate about it.
FWIW, I think that the LF Adjust could be a factor in creating some difference in sound even with a ported sub. For instance, if someone listened to music with the LFA set at 1/4, would that sound different than the same music played with the LFA set at 3/4? I can't be sure that it would, but I think so, because the second setting would make the very low bass (low fundamentals of notes which would not normally be emphasized) more prominent. And, if there were a significant sub boost added, I think that the low bass would sound proportionately even more prominent.
You would definitely want that for movies, or at least I would, but you might not want it set high for certain types of music. I find that LF adjustment very interesting. If there were anything to my theory about potentially hearing more low fundamentals with a ported sub, it's possible that the LFA could be used to attenuate some of that low bass for certain types of music, and then cranked for movies. The same approach could also be used for sealed JTR subs. Again, though, I think that the benefit of that would primarily be for music involving natural acoustical instruments, such as most classical and some jazz music.
One of the more common debates on AVSforum is the matter of which is superior: sealed or ported subwoofers. Some say that ported subwoofers are no good for music, and are only useful for delivering big sound effects, or conversely that sealed subwoofers are “musical”, but lack the depth to deliver the ULF frequencies in movie blockbusters. While some subwoofers may certainly fit these stereotypes, the truth is considerably more complex. Ultimately, sound quality is far more a function of good engineering and choosing the right tool for the job rather than a question of sealed vs ported. While both alignments come with specific strengths and weaknesses, JTR subs are well designed and manage to avoid most of the drawbacks. This makes them equally beneficial for both music and movies with choice of configuration more dependent upon the room size and SPL/extension priorities than the content.
Music frequencies span the audible range of human hearing. While we are most sensitive to sounds in the midrange between 250 Hz - 2 Khz, the majority of musical instruments operate in the mid-bass region of 60 to 250 Hz, and some even reach the sub-bass region of 20 Hz to 60 Hz. More importantly, each musical sound will also induce harmonics at octaves below it's center frequency at 1/2 (first harmonic), 1/4 (second harmonic) or 1/8 (third harmonic). So a note at 160 Hz will produce harmonics at 80 Hz, 40 Hz and 20 Hz in the sub-bass region. A kick drum may center around 500 Hz, but it's harmonics and impact will be audible down to 50Hz well within the prevue of the subwoofer. On the other hand, most vocals and acoustic instruments get no where near the SPL volume or PVL particle velocity of special effects in a movie soundtrack.
So while output is a factor in selecting a sub for music, it's impulse response, phase coherence, group delay and ability to integrate with the main speakers will determine the system's optimum performance for music.
Movie Frequencies (LFE)
Movie soundtracks with large special effects will have tremendous output in the bass and sub-bass frequencies. Older movies tend not to go below 30 Hz which was the typical limitation of commercial theaters. With the advent of Dolby sound and THX, movies added content under 90 Hz for the LFE channel. Most films have a particular emphasis on the range between 30 Hz - 100 Hz which is where the human body is most sensitive to sympathetic vibration. Recently sound mixers have been venturing more often into the sub 20 Hz region for extreme ULF. This increases sympathetic vibrations, tactile immersion and he enhances the realism of large special effects.
The New Master List of BASS in Movies with Frequency Charts
So while impulse response, phase coherence, group delay are factors in selecting a sub for movies, SPL output to reference levels without compression and extension into the ULF frequencies down to 10 Hz (and below with room gain) will determine the system's optimum performance. Integration with the main speakers is still important, however usually the challenge is about selecting main speakers with the dynamics and SPL output to match the capability of the JTR subs.
In a sealed subwoofer, the driver is responsible for 100% of the system’s output. Overall system performance is a function of the driver’s Thiele/Small parameters and enclosure volume, which together will determine system Q and the system’s resonant frequency. Below the resonant frequency, sealed subwoofers typically feature a shallow roll-off of 12dB/octave, which also corresponds with relatively low levels of group delay and ringing in the deep bass. It’s possible to get a wide variety of response profiles from sealed subwoofers by simply varying box volume, with a Qtc of 1.0 being achieved in a small 54L box, 0.707 in a medium sized 136L box, and 0.5 in a very large 525L enclosure. While a Qtc of 0.5 corresponds with a relatively extended response, there is a price to pay as this requires tremendous amounts of amplifier power and cone excursion at low frequencies. Subjectively speaking, lower Q boxes (0.707 and lower) tend to be characterized as relatively tight, while high Q enclosures can be a bit boomy without equalization due to their response hump in the mid-bass range. On the other hand, one benefit of higher Q enclosures is that they offer a greater degree of protection for the driver against high-energy, low-frequency transients.
While not all sealed subwoofers are created equal, properly done the alignment has a lot to offer. Size is typically manageable, giving it a lot of flexibility in placement as well as a high WAF (wife acceptance factor). While small size tends to come at the expense of extension, sealed subwoofers generally have a shallow low-end roll-off profile, which corresponds with good performance in the time domain (i.e. group delay / ringing). What sealed subs lack in SPL output compared to a ported subs can be compensated by using multiple sealed subs to provide the extension of a sealed sub with the output of a ported design. Last but not least, sealed subwoofers offer some degree of protection against bottoming out the driver, though it is still possible with sufficient power and the right content.
In a ported subwoofer, both the driver and the port contribute to the system’s output. Porting augments the driver's output at the vent’s resonant frequency, which extends the subwoofer’s response and allows for substantially more output capability at the tuning point relative to a comparable sealed subwoofer. However, below the tuning frequency, the driver is no longer loaded by the enclosure, and acts as if it is in free air. This results in a much steeper roll off rate of 24dB/octave relative to the 12dB/octave slope typical of sealed subwoofers; as a consequence, group delay is typically higher in ported models. In addition, below the tuning frequency, the woofer is in danger of over-excursion without appropriate filters for protection, which can further exacerbate problems related to group delay. Of course, like sealed subwoofers, many different response profiles are possible by varying enclosure size as well as port length vs diameter (larger enclosures and longer ports result in lower tuning points). It should also be noted that ported enclosures are typically much larger than sealed enclosures.
At their tuning point, ported subs typically offer better low-end extension and greater output than sealed subs. However, there is no free lunch; deeply-tuned ported subwoofers tend to be quite large, making them less décor friendly as well as reducing placement options. Further, while ported subwoofers have a big output advantage down to their tuning point, below tune, frequency response drops off steeply while driver excursion goes off the charts. Subwoofer amplifiers usually employ DSP filters to protect the driver from over-excursion, which can result in an even steeper low end roll off, and consequently problems with group delay and ringing.
Because the design parameters are so different between sealed and ported subs, it might be hard to make a quantifiable direct comparison between the two for music and movies. However we are lucky enough that JTR uses the exact same drivers, amplifiers, cabinet construction materials and sophistication of DSP control in both the Captivator S2
sealed sub and the Captivator 4000ULF
ported sub. The only difference being the ported versus sealed alignment and applicable DSP optimization to adjust the driver's parameters to the specific enclosure. Below is a comparison between the systems with information from data-bass.com.
JTR 18" Driver (Same)
• Hand built in the USA to JTR's specifications
• Ti frame originally introduced by TC Sounds
• Large half roll foam surrounds
• Carbon fiber dust caps
• 10" spiders for linearity even at high voice coil displacements
• Large ferrite based motors with a shorting ring
• Powerful BL^2/Re rating of 256
• Xmax of 66mm (linear), peak to peak (33mm each way)
• Xmech of 101mm, peak to peak (2" each way, 4" peak to peak)
• Weight around 60lbs (each)
SpeakerPower SP1-4000HT Amplifier (Same)
• Hand built in the USA to JTR specifications
• 4000 watts @ 2 ohms 40 Hz (1% THD)
• 2800 watts @ 4 ohms 40 Hz
• 1250 watts @ 8 ohms
• Custom DSP preconfigured (limiters, equalization, high pass filter) to match JTR driver/enclosure
• User DSP rotary controls for Volume, Low Frequency equalization, Crossover, Delay
• Post-filter feedback class-D topology, achieves ruler-flat frequency response, low distortion and very high damping
• Latest generation power MOSFET transistors and highly optimized output stage for up to 95% efficiency
• Full featured protection: DC, overload, low impedances, shorts, under/over-voltage, overheating.
JTR Cabinet Build (Same)
• Built for JTR by a custom woodworking shop that normally builds fine furniture
• Construction 18mm, 13ply, void free, Baltic Birch (several times stronger and more expensive than MDF)
• Heavy internal bracing, recessed front baffle
• Thick cotton and Polyester sound dampening
• Oversized bonding posts for heavy gauge speaker wire
• Heavy duty isolation feet
• Finish matt black paint (Cherry, Maple, Walnut, Zebra Wood and other veneers can be custom matched to existing cabinetry)
Captivator S2 (Sealed)
• Dimensions 40″x21″x18″ (HxWxD)
• Volume 8.76 cu ft (exterior)
• Weight 220 lbs
• Frequency 16 Hz - 157hz +/- 3db (under 10hz in room performance)
Captivator 4000ULF (Ported)
• Dimensions 41x40x20.5" (HxWxD)
• Volume 19.45 cu ft (exterior)
• Weight 265 lbs
• Frequency 10.5 Hz - 125hz +/- 3db
CEA Max Burst
The Cap 4000ULF definitely has the advantage over the S2 for greater maximum output at reference levels and deeper extension for high SPL movie special effects and very low ULF frequencies.
CEA Max Passing SPL
The Cap 4000ULF definitely has the advantage over the S2 for deeper extension less limited by distortion at reference SPL levels movie special effects and very low ULF frequencies.
Sealed subwoofer's shallow roll off profile can make them quite suitable for smaller spaces thanks to room gain. Below a certain frequency (nominally denoted as F=(speed of sound / (2 x Longest Room Dimension)), the room naturally boosts the low end at a theoretical rate of 12dB/octave (less in the real world, as real walls are lossy barriers). This means that in spite of the fact that they may roll off earlier relative to ported subs, sealed subwoofers have the potential to offer extension down to 10Hz and below in the right room. In addition, their small size (excluding huge overdamped enclosures) makes them much more at home in smaller spaces. Conversely, big, deeply-tuned ported subwoofers are right at home in larger spaces where room gain is minimal (though they can work well in smaller spaces with a bit of EQ).
The S2 exhibits a flatter frequency response (+/- 1dB between 110-112 dB SPL) than the 4000ULF that could be better for music. It has a slower roll off which could be usable with room gain in smaller rooms or with the use of multiple S2's for reaching single digit extension for ULF on some movies.
The 4000ULF exhibits more variance in frequency response (+/- 2 dB between 104-106 dB SPL) that might be audible for music. However differences between the +/- 1 dB variation in the S2 and the +/- 2 dB variation in the 4000ULF would be hard to detect with varied program material (as opposed to static tone) and would be more than offset by the fluctuations caused by the acoustics of in-room response at various frequencies. The faster roll of on the 4000ULF is more than compensated by it's prodigious output to 10 Hz. It should reach single digits with room gain in all but the largest rooms.
Low frequency Adjust
The S2 LF adjust control at maximum the S2 exhibits at relatively flat FR down to about 15Hz and with the control set to minimum the response rolls off a bit quicker below 20Hz. The effect is largest at 10Hz and below where the response is cut about 4dB with the control at minimum. In either case the S2 is still employing significant low frequency boost in order to extend and flatten the response down to below 20Hz. The S2 was tested with the LF adjust at minimum for all of the high output testing. In that configuration the basic overall response fits within a 6dB total window from 15-170Hz. Increasing the LF adjust to maximum extends the low end response even further.
With the Cap 4000 LF adjust knob at maximum the response fits within a tight 2dB window from 10-120Hz outdoors. With the LF adjust at minimum the response below 25Hz gradually slopes down towards 10Hz. The maximum effect is at 10Hz where there is an 8dB range of adjustment. Even with the LF adjust at minimum the 4000-ULF may exhibit a rising "house curve" towards the deep bass in most rooms.
The 4000ULF definitely has a greater LF adjustment range, allowing you to dial it in for a wider range of room sizes. However since most musical soundtracks don't reach to the deepest frequencies that are boosted by room gain, this flexibility will mostly come into play for optimizing the system for home theater use.
There is no significant compression in the S2 through the first 4 output levels corresponding to 90-105dB nominal referenced to 50Hz. The 105dB sweep causes an insignificant compression of about 0.5dB in the upper octave of the measurement. The next 5dB increase for the 110dB measurement again produces little compression in the output with a negligible amount in the deep bass and just about 1dB in the upper bass octave. Another 5dB increase for the 115dB sweep produced a bit of driver excursion flutter or warmth at the bottom and finally a significant increase in output compression indicating that the system is now being driven towards the edge of its performance envelope. Compression of the output has now reached about 4dB below 20Hz and about 1.5-2dB in the upper bass octave. Another full 5dB increase in output demand from the S2 results in even greater levels of output compression and audible harmonic distortion in the deepest bass. It can be seen that the 120dB sweep produced virtually no more output below 22Hz indicating that the S2 was already out of headroom during the prior sweep.
It appears that there is significant low end boost to the 4000-ULF's response even with the LF adjust at minimum. During the 125dB sweep the 4000-ULF reaches 106dB at 10Hz, which is one of the strongest readings that's been recorded by Data-Bass at this frequency, during this test type. Output rises smoothly from there to just under 118dB at 20Hz and finally reaches 125dB up at 36Hz, before dropping a bit to about 122-123dB over the rest of the measurement bandwidth. The output below 35Hz is strong indeed and places this as one of the most powerful low frequency systems that has been Data-Bass tested. During these slow sine wave measurements there was some vent chuffing and wind noise noticed around the vent tuning, especially during the loudest couple of measurements. Also a hint of driver distortion below 20Hz on the loudest measurement. The cabinet itself was remarkably inert and dead throughout. Overall the 4000-ULF was quite clean even driven to the limits with the exception of a bit of vent air noise at the 10-15Hz frequencies.
Most acoustic instruments in music would not reach SPL levels of 115 d, so the compression in the S2 would be relatively inaudible. However the greater output at lower compression of the 4000ULF definitely makes it better for movies at reference levels.
Total harmonic Distortion
As SPL increases, the S2 exhibits higher THD below 30 Hz, while the 4000ULF shows higher THD above 30 Hz. This indicates that the THD increase in the S2 is primarily due to the electronics and amplifier rather than the drivers. It is likely related to the amplifier clipping or a limiter circuit. The SpeakerPower amplifier is quite powerful but in this case it appears to limit comfortably before the pair of 18" drivers. That is a good thing as this means it is unlikely that the drivers will be damaged by the amp.
The S2 has slightly lower THD above 30 Hz which could be beneficial for music. In addition, the S2's THD distortion below 30 Hz would probably be unnoticeable for music because most acoustic instruments never reach that low. However movie soundtracks are much more heavily processed and often bear small resemblance to live acoustical recordings. The THD difference above 30 Hz for the 4000ULF for cinema presentations would be barely noticeable, meaning either one would probably be suitable for music or movies.
The response of the S2 in the time domain shows no issues and a clean controlled decay. There is a very slight bump in the group delay way down at 18Hz likely due to a bit of signal shaping of the response but it is well below even 1 cycle of delay.
One concern with ported subs is weather the group delay might affect music performance. However, that’s where the limitations of human hearing come into play. Because of the relatively deep tuning points involved, the frequencies where group delay becomes a problem are areas where human hearing isn’t terribly sensitive to the issue; moreover, they’re frequencies that just aren’t particularly relevant to the vast majority of music. As such, when put in appropriate rooms and/or EQed to scrub off a rising low end resulting from room gain to achieve relatively flat in room response, it’s possible for ported subwoofers to be very capable performers, both for music and movies.
The group delay graph shows that the 4000-ULF is slightly higher than the S2 but remains well below 1 cycle of delay until way down near 13Hz where it starts to exceed 1 cycle slightly. At 13 Hz, this will be completely inaudible in music and unnoticeable in a LFE movie soundtrack.
The S2 has slightly better impulse response for music with a shorter oscillation in the driver after the input signal. This could be audible in quiet musical passages with sharp transients like a kick drum, However the differences would be minimal in a complex movie soundtrack. Integration with the rest of the system could be effected if the impulse response of the main speakers was much faster (i.e.: full range electrostats or ribbons). However for most cone based speakers this would not be a problem.
The Spectrogram shows a slight ringing in the 4000ULF that might effect it's performance on music. However in complex movie soundtracks this ringing would not be readily audible.
The waterfall decay also shows a slight ringing in the 4000ULF that might effect it's performance on music. However in complex movie soundtracks this ringing would again not be readily audible.
The Captivator S2
is an excellent sub for music, tight, responsive with flat frequency response and more than adequate output for acoustical instruments. For music, it has a number of advantages like flat frequency response, fast impulse response, low THD above 30 Hz with minimal group delay and ringing that makes it cleaner for than the 4000ULF. For movies, with a little room gain in a moderately sized space, it could probably hold it's own compared to the mighty 4000ULF in output (which would might need to have it's LF adjust turned down to not overload the room). However in a larger room or in an open floor plan with access to other areas, the S2 would not keep up with the 4000ULF on movie soundtracks at high references SPLs between 120 dB and 130 dB. If you were in a normal sized room chasing after single digit response for movies, then multiple S2's might just be just the ticket with their slow roll off and deep extension. However the 4000ULF would be more cost economical with one sub achieving almost the same performance under 10 Hz as multiple S2's.
The Captivator 4000ULF
is an extraordinary sub. It has the higher SPL output of a ported design with the deep extension to 10 Hz of a sealed alignment. That makes it unbeatable for movie soundtracks and special effects. This is especially true for larger rooms or open floor plans that would require multiple 18" subs by other manufacturers to achieve the same level of performance. For music, many ported subs exhibit much sloppier impulse response and greater ringing in the time domain with greater THD distortion. However Jeff did such a great job ofd engineering this sub that these potential drawbacks to ported a sub are seriously minimized. The S2 might be ever so slightly more articulate and faster to integrate into a high resolution music based system. But most people use their set up for both music and movies so the relative tradeoff is immaterial. The differences for music between the S2 and the 4000ULF are so small, the vast majority of people would hardly notice the difference. But the difference between the systems for movies is substantial in terms of raw output at reference SPLs.
If your priorities are a music and movie based system, it mostly comes down to room size and how large a sub your wife will accept. Smaller room or more music based, get the S2 and never look back. Larger room or movie based, get the 4000ULF (WAF permitting) and enjoy the satisfaction that comes from landing the biggest fish in the pond. If your priorities are mixed music and movies, or your room is mid-sized and can be enclosed from adjacent areas, then you can't go wrong with either sub, they are both excellent contenders.