kramskoi

very nice Mr. Hurd...always nice to see fellow TC Sounders...happy rendering to you...mb

wow! and i thought i had it bad !...nice...and definitely check out the offerings from Mark Seaton...the man really knows his business...

the 20 Hz performance will be affected by any highpass filtering be used...i would expect the RT12 to roll off much faster, given it's a 4-6th order system...if it's truly -6 dB @ 19 Hz, then i'd say that with the excursion envelope of the f113 and a Linkwitz transform coupled with PEQ, it's very possible to match the transfer function "and" SPL output at 20 Hz... Judging by the Sound & Vision article, Tom N. found in-room spl to be 105 dB> 25 Hz and 110 Hz @ 32 Hz...no 20 Hz output numbers are given... The f113 tested outside at 2m GP (craigsub): Distortion is ~13% at 20 Hz but this would likely fall in-room as the fundamental gets pushed up and the spl would rise 6-10 dB, depending on the size, layout and construction of the room...hardly a cut and dried vented vs. sealed argument...

well given the scarcity of Klipsch subwoofer reviews with subjective opinion or "objective" numbers...i would'nt hold my breath...that said, the RSW 15 has been said to be very musical for a PR design...how the RT12 will deal with a SOTA sealed subwoofer is another matter...the JL w7 has the displacement of a Tumult 15" driver...even then, these commercial designs, JL included, are limited in what they can do with a single driver...this affects ultimate extension the most and just looking at posted data from Craigsub's evaluations, it looks as though some sort of highpass filtering is being used at the bottom...the rolloff would seem to be even steeper with 12TD using passive radiators which would attenuate VLF much faster...i remember the "Under the Xmas tree shootout in 2001", which noted the lack of impact below 30 Hz compared to other offerings...knowing what i did'nt know a year ago, there is no way i would leave VLF duties to a single driver subwoofer...especially not Home Theater...not for an uncompressed, low distortion presentation... Bl product does'nt always tell the whole story...for instance the tc3000's i use have more motor force (29 teslameters) than the LMS offerings from TC sounds...the downside to huge amounts of BL is usually a rise of inductance, which inhibits the upper bass and introduces higher amounts of flux modulation distortion...the FR also becomes less linear so more equalization is needed to flatten it...this begins to negate the advantages of the high motor force used...shorting rings can be used to combat, to a degree, this inductance rise, but they are'nt always totally effective...this is one of the reasons why the LMS series weigh so much...the gap must be made wider to accomodate the linear coil, losing force...the HUGE linearized coil adds back the motor force, but lots of copper must be used to attenuate the inductance and keep it low... Its a very good chance that the RT12 will surpass the f113 at 20 Hz but i would'nt bet on it...the HTW7 has a huge excursion envelope (3.6 to 4" iirc) and indeed it would seem that the modified drivers would have greater thermal capacity, given the amplification which is being used...my guess is that the f113 would provide a better "sound signature"...which is the current rave of this subwoofer at the moment...JL, it seems, definitely did their homework with these subs...i'm personally waiting on the Gotham, which is more in line with the sort of implementation i currently use...even so, i plan to upgrade to LMS drivers once they are released...

TheEar, "Outclass,then let anyone here buld a sealed sub using the most capable 12" in the TC SOunds catalog and pit it against the f113,lets see who comes on top. Will be very close in the worst case for the W7.I have no doubt." Arthur i would'nt think that you'd outclass the f113, but there are some peculiarities to note... Tc Sounds incorporates a high-roll surround with a smaller footprint which allows more of the cone area to be used (more sensitivity)...i'm not sure if JL, with their wider surround, has increased the sensitivity for the HTW7 implementations of the Fathom and Gotham...the 13w7 comes in around 86 dB, iirc...the question becomes how much does the wider surround eat into the effective Sd of the driver... The LMS 5400 will have the advantage in both linear excursion and max output before compression (4" VC)...and it will boast good sensitivity to boot... While there is no BL profile given for the HTW7, i would imagine that the 32-34mm Xmax figure does'nt represent lossless BL. If we use the typical 70% BL formula, then the LMS will xmax at ~45 mm one way...with maybe 10-12mm more to xmech...no BL loss out to 38-40 mm...we must remember that, with traditional motor topologies, BL begins it's decline as soon as the driver starts moving... I think the w7 driver uses a SGLC motor design (overhung), and though this has probably undergone rigorus FEA to maximize linearity, i'm sure it still exhibits the normal parabolic BL roll off, characteristic of the architecture... We also don't have an inductance value for the 13w7, so flux modulation distortion is a question mark, along with frequency response linearity... That said, i think the LMS 12 would offer some "similar" performance to the f113, provided it is implemented correctly...with a 4" VC and no BL loss at 38 mm, it should definitely set a new standard for extension and output from a 12" driver.

the fathom and gotham series, iirc, are using enhanced versions of the 13w7, called the HTW7...looks like a beefier magnet/coil/surround implementation...i think it's excursion capability has been enhanced also...the envelope is supposedly 3.6 - 4" peak to peak...how much of that is "linear" is another matter (normal 13w7's are 32mm xmax)...perhaps they've raised the sensitivity of the driver also (from 86 dB)...also, the driver used in the fathom is different from the one used in the gotham...or so it is stated...

JL in miramar, ran a test of the f112 in a 3200 cubic feet room, in response to the test by T.N. in his 7500...10 % THD (@ 2m) (1/8 th space) as follows: B&K mic 3" from cone center for distortion measurements/ELF trim off, ARO off, LP off, sub level to maximum 83 dB----------16 Hz 92.8 dB--------20 Hz 100.3 dB------25 Hz maximum SPL @ 2 meters-1/8th space B&K mic at listening height 32 Hz-------112.4 dB 40 Hz-------116.2 50 Hz-------113.3 62 Hz-------117.6 average 32-62 Hz----114.9 dB ----------------------------------------------- Keep in mind that this is stated by the mfg. and will be confirmed later by a subwoofer shootout which will take place on AVS...both the f112 and dual f113's...Now i give JL props...and having heard a few high Xmax 15" designs (in 3-3.5" peak to peak range), these should deliver the goods, however, that said, single sealed drivers are usually limited in more ways than one and usually extension takes a hit... The Gotham should present some interesting data points once it is released commercially next year...if it is allowed to run unlimited, then i'd say "keep the cats in the cradle" and look out! We'll have to wait on the testing to tell exactly what type of limiting is being used with these subs and also what their respective roll off rates are. This will determine if they can offer the 99th percentile extension of non-commercial designs (100th being the $25K TRW rotary sub)...While the 99th percentile won't appeal to most, once you've felt VLF infrasound (< 10 Hz) at levels which are palpable (100 dB+), DVD viewing becomes a "listening event", as the full emotional impact of the scenes are delivered with bone crushing precision and frightening dynamics...

thanks MAS...enjoyed the posts...and point taken!...*wink

okay MAS..."uncle"...i have'nt much to add here... I'm still in the infant phase with most of these advanced sound concepts...the driving force behind most of my curiosity is subwoofers...the what, when, why and wherefore of any and everything pertaining to them...there's a slow focus with all the hazy generalizations/myths that persist in the audio community...i guess the learning curve depends on your desire to uncover the ultimate truths. These concepts become important from a design and integration standpoint, with the room weighing in as a "major factor" in total system synthesis...as such, one needs to be wary of all mitigating factors which inhibit said integration. I guess that "gross signal alignment between transducers" would be a DSP issue? Or could we manage it manually with the appropriate software and a laptop? How many HT enthusiasts actually undertake what "seems" a painstaking process of precise time alignment between all channels? This delay compensation would give us something close to the unity you stated, no? In any event, i look forward to an increasing knowledge of the "deviled" details of sound reproduction...Thanks for the great posts...

good layman's term description, i'm of the same opinion as Doc on the time delay issue...these are time-domain issues, and to say that they are'nt interrelated would be a bit premature IMO...a constant delay through the signal envelope "is" desirable but here we are talking about delay in the 2-4 msec range in the higher frequencies and anywhere from 10 to 100msec in the lower bass range down to 10 Hz... it is my thinking that the "room" is the great equalizer in all this. If we agree that the basic loudspeaker is a highpass circuit, passing the highs and rolling off the lows, would this "temporal shift" be more noticeable in an anaechoic chamber? How much is the "room" masking the issue? especially larger rooms, with their reverberant sound fields. Or perhaps our ear/brain learning has compensated for this phase shift between high and low frequencies...over many years of less than perfect acoustic reproduction. Keeping the phase shift as minimal as possible seems to contradict the practice (by some) of crossing over mains to the subwoofer at frequencies appreciably lower than 80-100 Hz...for example, 40 Hz, which would add twice the group delay of an 80 Hz crossover...cross lower and it becomes even worse... Of course, the biggest question is always "when does it become audible"?

first of all...i apologize if i come off a little confrontational...not my intention...i'm still a baby with all this stuff...while i do think that sealed is a potent performer in small rooms, it would'nt necessarily be the best way to go in larger rooms...here the LLT is perhaps the best option, although it will also require multiple drivers and substantially larger cabinetry...this becomes more feasible with the larger space involved...if you can get your wife or s.o. to accept these monster sized enclosures, you can give sealed enclosures a real run for their money... That said, this design will naturally fall outside the mainstream for output and extension. LLT subs are usually tuned between 12-16 Hz, with enclosure sizes of about 250-300 liters per driver...so you can see that using multiple drivers really chews up real estate. The design is run without highpass filtering so this requires amp limiting the driver(s) for infrasonic protection...this is one of the drawbacks to the system, but if you use enough drivers it becomes less of a problem. Care must still be taken with infrasonic material though. Over the audible range, it supposedly mimics the characteristics of a sealed enclosure but, because of the abnormally low tuning, it allows you to extend lower than a comparable sealed unit. Group delay is quite high at the lowered tuning point, but falls to inaudibility in the muscial range so it is nothing to worry about...in theory of course. In summary, it is supposed to mimic the sealed box in the audible range and extend the Fb of the system to a lower level than normal vented or sealed designs...and you keep massive midbass output with the multiple drivers. A best of both worlds solution for all. This design is not without drawbacks though, as i mentioned in previous posts...markedly reduced midbass output, distortion limited output below Fb, size, port velocity (audibility), elevated 20-30 Hz distortion and possible bottoming above Fb, cabinet colorations and port resonance issues...although if carefully designed, a lot of these concerns can be marginalized...it is a sound theory and has been put into practice by various DIY'ers like me...and with good results. Granted we have'nt seen one tested head to head, those who've built them swear by the output and musicality.

This is a very good,simple description. When a cone/piston has to travel say 4" to produce a given note a say X dB the group delay will be much higher than say the same note produced with a 4mm travel and Y dB. In a perfect world there would be no group delay and full range,point source would be the summum of perfection.In the real world the engineers have to work to minimize group delay or at least keep it in check,if I may say. Also more travel means recuperation time,the woofer's cone/piston does not reach its central position as fast when under full excursion as it does at moderate levels where the cone has little travel. basically, a driver in an enclosure is a high pass filter...allowing the highs to pass and rolling off the lows...with any highpass filter, decreasing frequency brings increasing time delay/group delay (the delay between two differing frequencies, i.e. 10 and 100 Hz)...past a certain point it becomes audible...it is "generally" accepted that group delay becomes noticeable between 1 and 2 cycles of the frequency being reproduced...the allowed limit gets higher as frequency decreases...for example, 20 Hz = 20 cycles per second, or one cycle every .05 second, or 50 ms...so the onset of audible delay @ 20 Hz would be between 50 and 100 ms, or 1 - 2 cycles...at 10 Hz it would increase to 100 and 200 ms... If we use the phase adjustment on subwoofer plate amps as an example...why do two frequencies canel each other? It is because they are both arriving at different times (out of phase) to the listening position, cancelling rather than reinforcing one another...by adding or reducing delay, one can cause the frequencies to sum together...with this example we can see that reducing the amount of time delay between frequencies allows a closer approximation of the intended sound signature...the different frequencies arrive virtually simultaneously, reducing the "time smearing" effect. The shallower the rolloff (highpass filter), the least amount of phase shift over the passband...and if this also represents time delay the way i think it does, then we should strive to keep this delay as small as possible, in the interest of the most cohesive reproduction of sound. That said, all this becomes moot, however, once you factor in room acoustics...this is what lots of mfgs. conveniently forget when pushing for sales...a ruler flat frequency response means nothing once placed in a particular room...the loudspeaker is then at the mercy of a myriad of reflections cancelling and reinforcing various frequencies throughout its range... I'm no EE, but group delay, phase shift, and impulse response are all related to a degree, and all will affect the final presentation in the time domain. I don't pretend to have this all figured out...this is a "very" tricky and confounding subject...one in which i feel uncomfortable responding to...so take the above with a grain of salt and do your own independent research...the axiom, "rely but verify", definitely applies here...

When using passive radiators none of this is an issue, but that's not the point I want to make. The reason I bring this up is because you rejected the original premise because you didn't feel it feasible to accomplish with ports. The practicality of a concept is a mute issue when discussing the behavior of single variables. All audio is a system of compromises, but it is up to the designer to decide when things aren't practical. I agree that it's important to be practical, but it just adds to the confusion when that is used as grounds for an argument. Allow me to present an example to illustrate the point. I have seen a lot of IB / Sealed systems that rely on room gain that start pooping out at around 15Hz with some output down to 10Hz. EQ is often used to flatten out this response, which doesn't increase the maxSPL capabilities of the system...it just effectively reduces the output at higher frequencies to match the peak at the lower frequencies. To get 6dB more output down low, one would need to double up on drivers and amplifier power. This also requires the cabinet to double in size as well. If you're already running 4 drivers in two cabinets and pulling 8000W, then doubling up is extremely expensive. An alternative would be to use about 8 PR's, which would also free you up from the EQ. The cone unloads below the tuning frequency, but this can be easily controlled with EQ. It's important to note that ports/PRs introduce about the same level of group-delay as EQ on a sealed system - basically affecting the transient response in the same way. The only downside I see to this kind of approach is that the cost of 8 PR's is rather expensive and the cabinets often need to be a touch bigger to account for the lower efficiency of PR's. And usually the extra costs could have been spent on better drivers in the first place (and then you could just add PR's to the better drivers) [] I wonder how many people have had the chance to directly compare Sealed and Ported systems with similar frequency responses. Another trippy concept to throw out there is that the transient response of a system is also contained in its frequency response - I still don't believe it, but that's what the profs tell us in our signal processing classes... first of all...8000 watts is hardly needed, just add more drivers...if i add a second 2x15 unit and amplifier, using my current driver choice...i'm looking at 130 dB (30 Hz) at 3.5 meters and output around 110 dB at 10 Hz (10 % 3rd HD limited)...it would be unbearable to listen for an extended period of time...2- 24" cubes would stay well hidden in my theater space...this (PR) design presents a steeper rolloff (below the notched Fs of the drone) and therefore worse transient response than a ported system...using two overlapping shelving filters or a Linkwitz Transform circuit (actually improves group delay a bit) would allow group delay to remain below the levels of vented and pr systems... In the end, unless you are using an EBS/LLT type alignment, it just makes since, once headroom is taken care of, to use a sealed alignment...fewer drawbacks...the F6 bandwidth will be much wider with a 6 dB/octave or less roll off (with less system ringing)...with drivers sporting up to 4" peak to peak excursion capability, these sealed systems can run unhindered by high pass filtering, with no fear of destroying the driver with infrasonic material...a first order system should'nt sound the same as a 5th or 6th. Most sealed subs without highpass filtering will couple perfectly with smaller rooms, negating the need to add boost below 20 Hz, unless one wanted to implement a house curve...my on room exhibits this characteristic...room gain negates roll off down to 10 Hz and this is measured, not theoretical...personally, i see vented and pr systems as more output than extension oriented...ultimate extension anyways...and then there's the sound signature...i guess we'll just have to "agree to disagree" here...i''ll defer that i'm a little biased, with my current implementation of a sealed subwoofer in a smaller room...in "some" cases, the simplest solution is often the best.

I'm in the middle of a lab at the moment, but wanted to playfully rebutal that you can avoid all those issues by using a better driver [] Or on a more serious note, you can still maintain the exact same acoustic damping as a sealed system above the tuning point. As a crazy example, take a normal sealed enclosure and thow in a 1Hz tuned port (I'd say 0Hz, but the model falls apart at DC). The port really only affects the system right at the tuning frequency and below. This should make sense when you consider that there are losses in any cabinet that could essentially be considered as very low tuned ports. Also, the acoustical damping is greatest in the region immediately surrounding the port - and the driver barely moves at all. In the analogy I was going to make, but stopped cuz it was 2am and I figured it was time to go to bed, was that you can slide the tuning up from 1Hz until you're boosting the failing output of the sealed system - essentially using the the port as an EQ at the bottom corner of the extension. Throw in a peaking 2nd order high-pass filter and now you don't sacrifice anything from the sealed system - you just end up spending more money for marginal gains. Btw, the effects of the room to which I was referring wasn't the modal structure, but rather the behavior below the last mode where the reflections are always in phase and result in constructive interference. I've been wanting to do some experiments comparing flat extension down to 10Hz in a small room to flat extension down to 10Hz outside. So many people refer to "pressurizing the room" which is really a pet peave because SPL = pressure. It is my hypothesis that the room will have some issues that only show up in the time-domain, based on the fact that the output boosting reflections take time to arrive at the listening position. Speaking of science crap, I better get back to this CPU I'm building... [] yes, theoretically, like i said with the LLT, you can lower this tuning point (with enough drivers and enclosure space) to 1 Hz but what are the implications as far as size of enclosure, port resonance in the passband, wall flex, standing waves, port velocity, etc....this enclosure would have to be "much larger and heavier"...to each his own here...personally i think there are too many "potential" drawbacks in both audible artifacts and enclosure size/construction to realize this system in a typical setting...and i do think that acoustic suspension is a more stable system, as far as driver protection is concerned... acoustic damping being "exactly" the same as a sealed enclosure is questionable, given enclosure size, electrical and mechanical damping of the drivers themselves...the summed acoustical damping should be a factor of all of these combined no?...and if the sealed enclosure has losses, then it would seem that the vented enclosure would have as much or more losses...even the amount of polyfill will vary this acoustic damping, with heated air from compression presenting the driver(s) with a stiffer air spring. Lots of variables to the equation...

Doc, I will take issue with one aspect of the carte blanche claim above, not with the intent to rebut your information, but simply to try to present a bit of balance to it with regards to a few variables . Given the example where all things are kept constant, by properly porting a sealed box, you can extend the low frequency extension and efficiency of the speaker just as Mike has accurately mentioned. But if the focus is on a subwoofer, one must address the desired LF cutoff frequency of the sub. As one goes lower in frequency you approach the free air resonance of the driver and the free lunch of increased efficiency and low frequency extension offered by a reflex/ported enclosure is in danger of 'being eaten'. In a sealed box you maintain significant mechanical damping - a significant factor in tight defined LF transient response, whereas in a reflex loading the speaker is totally undamped at its free air resonance! It is literally flapping in the breeze with only the negligible electromotive damping is provided by the amplifier (not to mention the speaker's mechanical excursion limit! []) which is MANY orders of magnitude less than the mechanical damping afforded by the air in a sealed enclosure. Very Generally speaking, and with all other variables being equal, given that you are employing an optimally designed cabinet of either topology providing for tuning to the desired LF cutoff frequency, you can get away with using a reflex configuration in a sub where the LF cutoff is in the >30 Hz arena. And this is quite common in SR applications where the LF extension is not that extreme. But if you are expecting response much below this region as you approach the free air resonance of the driver, I personally would opt for the less efficient but much improved transient response offered by the acoustic suspension (sealed) enclosure loading. In this region, the increase in efficiency of the reflex loading is not as important as the accuracy afforded by the increased transient response. After all, the issue of effciency and the availability of low cost amplifier power, just like the change in availability in low cost memory capacity over the past 15 years, is no longer an issue. And I am politely ignoring the issues involved in the brick wall filtering required to prevent the LF extension from approaching the free air resonance region of a reflex enclosure used for subwoofer applications. Naturally these limits are factors in properly designing a complete LF speaker 'system', regardless of the topology utilized, so a combination of various interactive factors are involved. So it is not really possible to say which is by definition 'better'. Rather you must evaluate the total system design. But all things being equal - the same driver, and an enclosure with the only difference being whether it is optimally ported or sealed - for the best accurate LF extension regardless of efficiency, my money will head for the sealed enclosure. It is hard to have tight defined bass response with an undamped speaker [] But as regards which speaker topology will have the greater effect on room modes?... Again, generally speaking, as both speaker topologies are low Q (directivity) transducers, neither speaker topology matters as much as the room geometry and the total amount of LF acoustic energy being generated within the room (and to a lesser degree speaker placement). So I would not worry about the cabinet topology when evaluating the subwoofer with respect to room modes. You will get to worry about the room modes after you select your sub regardless of the speaker topology! [] ah the old sealed vs. ported battle...the vented subwoofer really comes into its own in large rooms, where soundwave propagation/diffusion is the chief characteristic of the space...with these large rooms come long dimensions. Because of this, as the room dimensions get larger, the frequency at which room gain begins, falls lower and lower. This limits the amount of help from the room and puts the onus on the driver system for ultimate low frequency output...combine this with the 5th to 6th order roll off in the response (depending on the high pass filter rate), and the sub is too far down before room gain can pick it up... Now their are ways to combat this with EBS or LLT alignments tuned to very low frequencies, however, these require much larger enclosures (~300 liters (12 cu. ft.)for a single 15" driver), larger ports, heavier construction and bracing... With these extremely low tuning points (12 Hz in some instances) you move group delay down to frequencies where it won't be noticeable. This "supposedly" more closely mimics the sound signature of sealed subs...this is debatable of course...There is a price to pay with this approach though... First, you reduce midbass output and increase the possibility of bottoming the driver "above" the tuning point...there's also added distortion in the 20-30 Hz range because you've moved the contribution of the port to a lower frequency, thus the driver has to make up for this decrease in port output... Second, depending on the size of the enclosure and porting, you are adding the risk of port resonance falling into the audible band of the subwoofer Third, port velocity above 17 m/s becomes a serious concern, adding audible artifacts to the sound signature at higher levels of output. Fourth, the cabinet must be extremely well built to combat enclosure colorations, wall flex, vibrations, and standing waves... Finally, the subwoofer usually would need to be amp limited to protect the driver from the rapid unloading of such a low frequency tune...otherwise you are back to the extreme roll off mentioned above... Normal vented subs tuned in the 20-25 Hz range, exhibit good midbass output and low frequency extension, a compromise of sorts. That said, EBS/LLT alignments are probably the best bet for VLF in large, high ceiling, multiple entry rooms. If the sacrifice in midbass output is acceptable, you can achieve lower extension and better transient response, albeit at the cost of a huge enclosure... In larger rooms, because of the early roll off of sealed designs, it takes multiples to achieve the VLF of EBS "and" Butterworth alignments, for that matter. Again, we are talking < 20 Hz here, not midbass output, at which sealed subs excell. The compensation (highpass) circuit of the Ultra2, i would guess, is a trimming of the VLF to reduce peaking in that region, thereby flattening the response...it is also causing earlier and steeper rolloff in the response. In summary, it is difficult to effectively couple the subwoofer to a large room and it takes a considerable amount of displacement to pressurize it, which, in turn, increases the cost of the subwoofer system. The sealed subwoofer reaches the zenith of its power in the small "pressure mode" rooms, where inadequate diffusion of soundwaves causes the room to become overloaded. Because of the smaller dimensions, room gain starts earlier and is much more pronounced than larger rooms. Here it is possible to negate the earlier rolloff with the earlier onset of room gain, producing a coupling of the subwoofer to the room, culminating in flat frequency response to very low frequencies, depending on how well the room seals. The low frequencies tend to be well below what is possible in larger rooms...down to 10 Hz in most cases...one need only add additional subs for the desired output and the system is set for some "very" impressive performance. With dual driver, single cabinet units, one can improve on this and allow the sub to roll off at 5-6 dB per octave, really improving the amount of infrasonic impact delivered. This would be the closest one could come to an Infinite Baffle sound signature, assuming one does'nt see fit to punch holes in living room walls. Here you have the best of all possible worlds...lowest group delay, flat frequency response to infrasonic regions, minimal phase shifting and excellent VLF "and" midbass theatrics...a lethal combination. In summary, IMO, it is doubtful that a comparable vented system in a larger room, can deliver the impact of the smaller room with its pressure mode characteristics.