Ultra II Subs

[Tobby]

Not exactly a rousing endorsement from Kramskoi and TheEar on the Trinity. I know someone who has some first hand experience with this sub and I will talk to him. If anybody else knows anything about the trinity I would be interested to hear. The 18" footprint would be cool in my room. Back to the ultras. I want to explore something Colterphoto brought up earlier. Can there be a magnetic shielding probem with these subs and tvs. Because of the space the two would take up if I were to use them it would be good if they were placed on the floor side by side under the shelf were the tv would be loacated. Could they, in this close proximity, cause picture problems.

Tom

[TheEAR]

The problem with subs is that publications and respected ones are too lazy to test the top crop of subs and make an easy to follow table(quality of built,quality of sub bass,ease integration,linearity in freq. response across the range they cover and SPL range they can operate with THD that is within reason.,THD figures and so on)

Just take the 25-30 top dogs from the better known and respected companies,and test them in the same room,same spot.I would love to do this,but I hope some realise how much time it would take and effor for one person.Simply not for the working man who wants to have half a life.Give me a paid ONE MONTH and I do the tests and end the BS once and for all,no more opinions,just numbers and facts.

Maybe the Trinity is a fantastic sub,I said I tested an older..former top dog in the Definitive sub range.While it went very deep and has wall moving power it lacked any refinement and had to be cut very deep to integrate well.So Tobby read well,I did not say the Trinity was not up to par.I will look nfor a dealer and maybe get one,..one day too many subs on my list before the Trinity. Damit I have so many subs,I have to pile them up.Aint joking here [:$]

[DrWho]

I just got off the phone with Trey today...it turns out the Ultra2 subs were measured outside in a true 1/8th space environment...which means they're not going to have 'extension issues' in a "large" room. But interpreting the +/- 3dB specs, they're going to be 6dB down at 20Hz. So I'll ask the hard questions - how many people have heard them? And of those people how many have measured their output?

As far as comparing sub performance...all it takes is a trustworthy manufacturer to do some outside testing (since no anechoic chamber would be large enough). I would imagine every serious company is already doing this - it's just a matter of getting the marketing department to let this data become public material. I bet a phone call might go a long way in obtaining this data for the other companies too.

But to be honest, I could care less about the performance of all the expensive commercially available subs on the market. It makes way more sense to go DIY in such applications and due to the nature of low frequency room acoustics you are bound to achieve better results - and spend way less money.

[Raider]

Not exactly a rousing endorsement from Kramskoi and TheEar on the Trinity.  I know someone who has some first hand experience with this sub and I will talk to him. If anybody else knows anything about the trinity I would be interested to hear. The 18" footprint would be cool in my room. Back to the ultras. I want to explore something Colterphoto brought up earlier. Can there be a magnetic shielding probem with these subs and tvs. Because of the space the two would take up if I were to use them it would be good if they were placed on the floor side by side  under the shelf were the tv would be loacated. Could they, in this close proximity, cause picture problems.

Tom

rmlowz over on the "Danley Labs DTS20 on the Way" thread had a Trinity that he let go. He may be able to give some more subjective analysis....

[Raider]

In theory world, the two would be identical.

In practice, cross-firing drivers eliminates a lot of distortions and cabinet vibration (the mechanical motions cancel each other outt. You can even remove a second set by inverting one of the drivers - making the magnet stick out of the box instead of into the box). Anyways, this means you'll have to brace the two smaller cabinets a bit more (making them heavier). You could help alleviate this by going with passive radiators (cross-firing like the RSW series), but then you've got extra costs and it'll be harder to match the room gain to the sub (max SPL for the same distortion should go up though). You'll also have less output way down low (like below 10-15Hz depending on the tuning).

The best thing to do is get yourself WinISD so you can see how the tradeoffs play out.

And for what it's worth, I think a lot of people don't give the Ultra2 subs enough credit for their performance in large spaces. I can think of a couple venues in Indy where they are being used as subwoofers for the PA / dance music type stuff. Heck, plug the drivers into the wall socket and enjoy 60Hz at 130dB. I'm not sure if it was this thread or another thread that I mentioned it, but the Ultra2 subs should be able to do 124dB at 30Hz with an F3 of 25Hz, measured outside. It's only going to get better when you move into a room - even if the room is huge. Those are some pretty impressive numbers...I'm not trying to say theren't aren't better subs, but I don't get the concerns about the output and extension.

DrWho: Reading between the lines here, wwould it be true that a sealed sub seems to have fewer tradeoffs and is easier to tune to the room, generally speaking?

Also, WinSD makes my Mac sneeze. Any similar programs that will run on a Mac? I can run WinSD on my MacMini, but I'd have to buy a copy of XP and run Boot Camp. Alot of money and trouble for one utility.

[DrWho]

You might be able to get UniBox to work on a Mac:

http://home20.inet.tele.dk/kou/ubmodel.html

(It's spreadsheet based - I'm not sure if it's Microsoft Excel specific).

Sealed vs. Ported is an issue I've been mulling over for a long time now without any definitive answer. Thereotically, you can take any sealed system with flat response and add a port to increase the output where the driver naturally rolls off. So from one perspective, a ported system can always trump a good sealed system. But the issue of diminishing returns quickly comes into play.

ALso, thereoetical room gain is 12dB/octave, but in practice it usually comes out to around 6dB/octave. In fact, the Ultra2 subs have "Boundary Gain Compensation" which is a 6dB/octave adjustable frequency high-pass filter to counter these effects and return the system response back to normal.

Ultimately I think it comes down to the particular situation at hand. The room has such a large impact on the low frequency performance of a system.

[mas]

Sealed vs. Ported is an issue I've been mulling over for a long time now without any definitive answer. Theoretically, you can take any sealed system with flat response and add a port to increase the output where the driver naturally rolls off. So from one perspective, a ported system can always trump a good sealed system. But the issue of diminishing returns quickly comes into play.

Ultimately I think it comes down to the particular situation at hand. The room has such a large impact on the low frequency performance of a system.

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! []

[kramskoi]

Sealed vs. Ported is an issue I've been mulling over for a long time now without any definitive answer. Theoretically, you can take any sealed system with flat response and add a port to increase the output where the driver naturally rolls off. So from one perspective, a ported system can always trump a good sealed system. But the issue of diminishing returns quickly comes into play.

Ultimately I think it comes down to the particular situation at hand. The room has such a large impact on the low frequency performance of a system.

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.

[TheEAR]

kramskoi,

"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. "

Amen to that,spot on. In a small room/space a sealed sub will give you this clean tactile feel,and displacement does not need to be in the dozen gallon territory. []

Kramskoi,looking forward to read more of your posts.Keep up the good work.

[DrWho]

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............

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... []

[kramskoi]

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............

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...

[TheEAR]

"acoustic damping being "exactly" the same as a sealed enclosure is questionable"

Exactly,in a sealed cabinet the air will not leave by any perforations,in a cabinet even tuned low air will escape by the port and a good deal when you push the driver with apropriate wattage. No way in blue hell the port will offer the same damping,no matter how low you try to tune(optimise all you want).

Try to tune a box of 1cu ft and under where the woofer occupies most of the space using a port(passive radiator included!).Better build a sealed than waste time with coping with too many variables.

A very smart man once said the best solution is very often the simpler less expensive solution.He was spot on.

[DrWho]

We're talking about "AC" signals, not "DC". The concepts of "leaking"

at DC do not apply to periodic waves. Air doesn't "escape" through the

port unless it's a "high" frequency where the wavelengths are small

enough that it doesn't see a trapped lumped mass of air (and at 12

feet, the wavelength of 90Hz so I don't think we have anything to worry

about).

For what it's worth, I wasn't actually suggesting to use a 1Hz tuning.

Nor would I ever suggest the use of ports below 25Hz in a "small"

enclosure (whatever that means). It was meant to be an exercise at

plugging through the math and looking at the behavior of one

variable (or if you're lazy dropping numbers in a model). All the

factors that attribute to transient response will be "identical" about

1/2 octave above the tuning frequency (gotta get outta the pass band of

the port). Identical is a loosely defined term (as are all the other

words in quotes), but for all practicality it is identical. I would

challenge anyone that feels differently to provide objective reasons.

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".

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...

[kramskoi]

We're talking about "AC" signals, not "DC". The concepts of "leaking" at DC do not apply to periodic waves. Air doesn't "escape" through the port unless it's a "high" frequency where the wavelengths are small enough that it doesn't see a trapped lumped mass of air (and at 12 feet, the wavelength of 90Hz so I don't think we have anything to worry about).

For what it's worth, I wasn't actually suggesting to use a 1Hz tuning. Nor would I ever suggest the use of ports below 25Hz in a "small" enclosure (whatever that means). It was meant to be an exercise at plugging through the math and looking at the behavior of one variable (or if you're lazy dropping numbers in a model). All the factors that attribute to transient response will be "identical" about 1/2 octave above the tuning frequency (gotta get outta the pass band of the port). Identical is a loosely defined term (as are all the other words in quotes), but for all practicality it is identical. I would challenge anyone that feels differently to provide objective reasons.

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".

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.

[Raider]

Wow. Great posts folks. Refreshing to see such a constructive debate.

Thanks for sharing.

[DrWho]

In a small room I'd probably go with a sealed system too []

Btw, what is an LLT alignment?

[Raider]

kramskoi and DrWho;

In both of your posts you make reference to passive radiators that would imply to me that you have to be very careful in their design. Under what conditions would passives be most advantageous over ported, and when would ported be better. When would you choose to use another active driver over a passive, and under what conditions would a passive be most beneficial.

Your discussions would seem to indicate a sealed approach is the most versatile and/or forgiving in many applications, primarily for smaller rooms. More complex designs seem to be best applied to address a specific problem or objective. Would you agree with this -very general - assessment?

I notice that Klipsch engineers have chosen a design with not one, but two passive radiators for their upper end reference subs which are likely to be used in a small to large home environment. A slot ported design has been chosen for the THX line which I think would typically be used in high output applications and larger venues. I 'm just intrigued as to the thought process and analysis they may have gone through, and am trying to filter the route they chose in the context of what you have discussed above.

Perhaps at the Pilgimmage some of you had a chance to talk to designers about this and might share some of the reasoning behind the choices.

[Raider]

In a small room I'd probably go with a sealed system too []

Btw, what is an LLT alignment?

Fairly new acronymn on the DIY forums for "large, low-tuned" which are currently gaining in popularity in that community due to output potential at lower frequencies. In the commercial community however, larger is more difficult to sell.

[Tobby]

I have been following this discussion as best I can. It would really help here to be an elelecrical engineer, I think. At one point I was even considering building my own sub. Then I got an emai today accepting an offer I made on two Ultra II subs and amp several days ago and for better or worse I made a deal. Assuming there is no snafu I should have a complete THX Ultra II 5.1 speaker system before long. I am excited about that. I am really looking forward to hearing them all together. I hate to harp on this but I have this cabinet maker who has a rather small window of oppportunity to build this a/v cabinet I have been talking about for me. I need to get get a final design to him. There are not many places in my room where I can set these ultas side by side except in the middle of the front wall under the tv. You guys could help me out by answering my previous question about placing these subs on the floor under the shelf the tv will be setting on. Would there be a magnetic shielding issue? Now that I think of it, Kramskoi, you had your DIY setting directly behind your tv and just a few inches away. This would seem to indicate it is not an issue for your situation. Speakers are normally shielded but how about subs. I could do some research but this should be an easy one for some of you.

Tom

[RichardP]

One of mine sits directly beside my Mits RPTV, only a couple of inches away, and has caused no problems at all. Can't say anything about underneath any other type of TV, nor about two side by side. I read that the lower part of the cabinet of an RPTV is the most susceptible to magnetic fields, so if mine at 2" away doesn't cause a problem, then maybe yours won't either. You may want to contact Klipsch tech support directly and ask about shielding.