Sealed vs. IB and output

[cobra93 47]

This was posted on a different forum and I'd like some input from some of brainiacs on this forum.

It seemed to be a simple answer at first, but became more complicated the more I thought about it.

I don't know if more information is needed to answer this or not.

Here's the proposed question as well as a link to the thread. http://www.diymobileaudio.com/forum/general-car-audio-discussion-no-question-dumb/110780-noobish-question-but-ive-never-heard-answered-fully-sealed-vs-ib-output.html

Default Noobish question but I've never heard it answered fully. Sealed vs IB and output....

I'm still not understanding why a sealed box would have more output than an IB in any frequency range. Ported is obvious so I'll leave that out.

If the same sub in both configurations can hit xmax over it's intended frequency range, how can the sealed setup offer more output? I've heard acceleration as an answer but at a given excursion at a given frequency how can acceleration be any different?

I hear the fact that IB setups can take less power than sealed thrown around as a con but if it takes less power to hit full excursion, isn't this a very good thing?

What's the big piece to the puzzle that I'm missing or is this one of those myths like a small sub is quicker and large is slower? If two identical subs are moving the same distance, how can one be louder than the other?

[cobra93 47]

Nobody?

[///M5 2,833]

At any range? You run out of excursion capabilities without the box there to help control the woofer when running IB. Conveniently this box "control" is where excursion can get out of hand if it's IB allowing you to use more power across the board on the sealed driver. The question is worded rather poorly and is somewhat self evident when you state it differently. The question should be why can you run more power at sub-bass frequencies on a sealed enclosure than an IB considering they have basically the same output at the same excursion. This of course is the nice air spring that you have built as an enclosure Hopefully that addresses what you were asking, if not please reword it since I am not interested in visiting DIYMA. I find it amusing that the OP there thinks that it is "obvious" for ported, but not for sealed, my guess is that he doesn't understand much about enclosures at all.

[cobra93 47]

I'll try to restate what I believe he's after.

I assume he means at a given frequency, say 45 hz.

If both systems are pushed to the same excursion at the same freq. and the woofers are identical. This could be a stretch, but maybe not.

If we could assume the only difference is the amount of power sent to the woofer to achieve this criteria.

Would they measure the same output on a meter?

My original thought was that you could send quite a bit more power to the sealed system and the acceleration of the cone would be faster/quicker. I would think this would make a difference leaning in favor to the sealed system.

This leads me to my next issue. Both woofers would have to receive the same clean or partially clipped signal in order to compare them.

I would have to believe that all woofers can play a 45hz freq., let's say just below clipping (an identical wave form) and the faster accelerating cone would achieve a higher (to some extent) output.

I don't have the background/knowledge to prove this one way or the other. Which is why I was hoping for a select few , like yourself, to give an answer/ explanation as to "is there a difference and why"

I have read the sticky by Neil and believe that Force = Mass x Acceleration has to be a factor.

I don't know that this could be achieved over a freq. range and therefore wouldn't matter to me in in any of my systems, but it got me thinking.

[Tirefryr 1,742]

You can never compare because they are all different applications and all behave differently.

[shizzzon 461]

if i'm understanding this right-

This guy assumes the more a speaker moves, the louder it is and hitting xmax or xmech, whatever is it's loudest point possible...

If that's true, hahahahahahahaha.

The end.

No but really, in spl competitions, subs do not move no where near as much as they do when playing music but "burps" are louder than music...

Maybe he should figure out why that is.

[An-i-no 86]

if i'm understanding this right-

This guy assumes the more a speaker moves, the louder it is and hitting xmax or xmech, whatever is it's loudest point possible...

If that's true, hahahahahahahaha.

The end.

No but really, in spl competitions, subs do not move no where near as much as they do when playing music but "burps" are louder than music...

Maybe he should figure out why that is.

If a sub hit full excursion at the power levels that it sees during a burp it would go kablammo?

...I mean unless of course you burp at the same power you play music at.

[Tirefryr 1,742]

SPL comps push drivers at and beyond their limits. Competitors are constantly repairing or replacing equipment. When you push it, things break.

[cobra93 47]

I'm unsure if the restated question is not clear.

If two subs are paying the same tone and seeing the same excursion, it could be half of rated xmax or close to xmax, and are placed in identical environments (in front of the woofer).

Assuming the only difference is the amount of power required to achieve identical excursion from the woofers cone.

Would there be a difference in output?

I'm not asking about a sub on the edge of destruction, but would more power result in a faster accelerating cone and therefore more measurable output?

Tirefrye> Are you trying to tell me something with your response but no explanation or is this something obvious to you but not to me?

Shizzzon> No, that's not his or now my question

I'm attempting to make these two different situations as comparable as possible. Look at this as snapshot or moment in time. A broad range of frequencies doesn't matter to me as far as an answer goes.

The question I guess would be does power matter if all else is equal as it can be?

Will each in its own perfect environment deliver the same result as the other for a single tone if the only difference is power to achieve the same excursion?

I posted this here because I value the math/facts shown here to back up the statements made by some of the more knowledgeable members.

[Impious 1,476]

if i'm understanding this right-

This guy assumes the more a speaker moves, the louder it is and hitting xmax or xmech, whatever is it's loudest point possible...

If that's true, hahahahahahahaha.

The end.

There's not much to debate. It's a simple fact of physics that in a 2nd order alignment output is directly determined by displacement. The more displacement, the more output. In fact you can figure out the (anechoic) potential output for a given displacement at a given frequency for a subwoofer (or any driver) by the formula

SPL = 102.4dB + 20log(xmax) + 20log(Sd) + 40log(freq)

*Sd in square meters; xmax in meters, one-way

Certainly Xmax isn't the loudest possible point, as frequency needs considered also and there's no reason a driver couldn't exceed Xmax........but it's (ideally) the point of the maximum displacement the subwoofer can achieve while maintaining sufficiently low distortion.

This ofcourse excludes environmental affects such as the transfer function of the vehicle. But assuming transfer function is identical in both instances, we can ignore it and focus strictly on the drivers and alignments themselves.

No but really, in spl competitions, subs do not move no where near as much as they do when playing music but "burps" are louder than music...

Maybe he should figure out why that is.

Nobody cares about SPL competitions and competive "burping" in this scenario. It's irrelevant. We are discussing 2nd order alignments, not 4th order (or higher) alignments that the majority of SPL competitors utilize. Behavior and peak output potential is different between the two. In 2nd order alignments, peak output is limited to peak displacement potentials. We could discuss 4th order (or higher) alignment behavior, excursion isn't irrelevant there either, but that's neither here nor there concerning the topic at hand. In our case, if driver A has 2x the displacement potential of driver B, and they are placed in the same environment, driver A has 6db more output potential.

[cobra93 47]

if i'm understanding this right-

This guy assumes the more a speaker moves, the louder it is and hitting xmax or xmech, whatever is it's loudest point possible...

If that's true, hahahahahahahaha.

The end.

No but really, in spl competitions, subs do not move no where near as much as they do when playing music but "burps" are louder than music...

Maybe he should figure out why that is.

If a sub hit full excursion at the power levels that it sees during a burp it would go kablammo?

...I mean unless of course you burp at the same power you play music at.

No offense intended, however this is exactly where I didn't want this thread to go. I am not asking about being on the ragged edge and blowing woofers up.

[cobra93 47]

if i'm understanding this right-

This guy assumes the more a speaker moves, the louder it is and hitting xmax or xmech, whatever is it's loudest point possible...

If that's true, hahahahahahahaha.

The end.

You are right, there's not much to debate. It's a simple fact of physics that in a 2nd order alignment output is directly determined by displacement. The more displacement, the more output. In fact you can figure out the (anechoic) potential output for a given displacement at a given frequency for a subwoofer (or any driver) by the formula

SPL = 102.4dB + 20log(xmax) + 20log(Sd) + 40log(freq)

*Sd in square meters; xmax in meters, one-way

Certainly Xmax isn't the loudest possible point, as frequency needs considered also and there's no reason a driver couldn't exceed Xmax........but it's (ideally) the point of the maximum displacement the subwoofer can achieve while maintaining sufficiently low distortion.

This ofcourse excludes environmental affects such as the transfer function of the vehicle. But assuming transfer function is identical in both instances, we can ignore it and focus strictly on the drivers and alignments themselves.

No but really, in spl competitions, subs do not move no where near as much as they do when playing music but "burps" are louder than music...

Maybe he should figure out why that is.

Nobody cares about SPL competitions and competive "burping" in this scenario. It's irrelevant. We are discussing 2nd order alignments, not 4th order (or higher) alignments that the majority of SPL competitors utilize. Behavior and peak output potential is different between the two. In 2nd order alignments, peak output is limited to peak displacement potentials. We could discuss 4th order (or higher) alignment behavior, excursion isn't irrelevant there either, but that's neither here nor there concerning the topic at hand. In our case, if driver A has 2x the displacement potential of driver B, and they are placed in the same environment, driver A has 6db more output potential.

If I'm reading into what you're stating correctly, then both ideal systems would produce the same output or at least a minimal difference regardless of the power applied.

[cobra93 47]

I'm out for tonight, I'll be back tomorrow.

[Impious 1,476]

Fair warning, I've not read the link on DIYMA. I clicked it, saw it was 4 pages and closed it.

I'll try to restate what I believe he's after.

I assume he means at a given frequency, say 45 hz.

If both systems are pushed to the same excursion at the same freq. and the woofers are identical. This could be a stretch, but maybe not.

If we could assume the only difference is the amount of power sent to the woofer to achieve this criteria.

Would they measure the same output on a meter?

Same excursion (and assuming same cone area, meaning same total displacement) at the same frequency in the same environment?

Yes, they would measure the same output.

See formula previously mentioned in my response to shizzon.

My original thought was that you could send quite a bit more power to the sealed system and the acceleration of the cone would be faster/quicker. I would think this would make a difference leaning in favor to the sealed system.

This leads me to my next issue. Both woofers would have to receive the same clean or partially clipped signal in order to compare them.

I would have to believe that all woofers can play a 45hz freq., let's say just below clipping (an identical wave form) and the faster accelerating cone would achieve a higher (to some extent) output.

No, acceleration would be the same. It would be required to be the same by the fact they were playing the same frequency at the same level of excursion. One can't accelerate "quicker" than the other and both play the same frequency at the same excursion level. If the acceleration were different, one driver would necessarily need to either be moving faster in time (different frequency) or moving farther with each stroke (different excursion level). But acceleration would be identical for two different subs moving at the same frequency at the same excursion level.

The only difference would be the amount of power input required to achieve this condition. One subwoofer might require more power input than the other, which would mean one subwoofer had a higher sensitivity/efficiency than the other at that given frequency.....but that's it.

[Tirefryr 1,742]

Output would be the same in a perfect world; this is not possible to duplicate in the auto environment though. Perhaps a large anechoic chamber with precision testing instruments and meticulous measurements. Everything equal aside from the alignment, which is what we are debating, will lead to a different response, different peaks, and different bandwidths. Granted the sealed enclosure and IB should be similar, but far from it given the application. We have to think about aiming , reflection, cancellation, etc. . . You may consider this semantics, but it's most relevant due to the nature of the environment.

[///M5 2,833]

All answered in my first post.

The question should be why can you run more power at sub-bass frequencies on a sealed enclosure than an IB considering they have basically the same output at the same excursion.

I included other details indicating that was a ridiculous parameter to use considering it will only pertain at that one point. I left out the assumptions to "make it equal" but those don't take any creativity to figure out.

[///M5 2,833]

Depressing that diyma has gotten to a state that they aren't answering that simple of a question. Went downhill like hell a few years ago and I haven't really visited since, didn't realize it was caraudio.useless.

[Impious 1,476]

Output would be the same in a perfect world; this is not possible to duplicate in the auto environment though. Perhaps a large anechoic chamber with precision testing instruments and meticulous measurements. Everything equal aside from the alignment, which is what we are debating, will lead to a different response, different peaks, and different bandwidths. Granted the sealed enclosure and IB should be similar, but far from it given the application. We have to think about aiming , reflection, cancellation, etc. . . You may consider this semantics, but it's most relevant due to the nature of the environment.

I think if you break it down to the basics of his question, he's not concerned about environmental affects and more concerned about the basis of the physics involved at the driver level. Which tells us that output would be identical as it's determined by the displacement of the driver for a 2nd order system.

[Tirefryr 1,742]

True, but then you get someone repeating this in terms of the automotive environment in which case they would be incorrect. There's always something someone misses.

[///M5 2,833]

True, but then you get someone repeating this in terms of the automotive environment in which case they would be incorrect. There's always something someone misses.

Which I am sure is what started it in the first place.

One other thing to point out. That truth will only hold for one location on the curve for each sealed alignment without SERIOUS filters to tame/amp the excursion to match elsewhere. I know you and Brad realize this but obviously there is some confusion.

[Impious 1,476]

True. The overall shape of the response will be different for the differing alignments without a lot of work involved to match the overall response. I was presuming this was more of a theoretical question about whether same displacement = same output for sealed and IB, which is true (for any 2nd order system). They have the same displacement potential which means the same output potential, even though that potential will rarely be realized simultaneously in the different alignments over their bandwidth without intentionally trying to do so.

[cobra93 47]

Fair warning, I've not read the link on DIYMA. I clicked it, saw it was 4 pages and closed it.

I'll try to restate what I believe he's after.

I assume he means at a given frequency, say 45 hz.

If both systems are pushed to the same excursion at the same freq. and the woofers are identical. This could be a stretch, but maybe not.

If we could assume the only difference is the amount of power sent to the woofer to achieve this criteria.

Would they measure the same output on a meter?

Same excursion (and assuming same cone area, meaning same total displacement) at the same frequency in the same environment?

Yes, they would measure the same output.

See formula previously mentioned in my response to shizzon.

My original thought was that you could send quite a bit more power to the sealed system and the acceleration of the cone would be faster/quicker. I would think this would make a difference leaning in favor to the sealed system.

This leads me to my next issue. Both woofers would have to receive the same clean or partially clipped signal in order to compare them.

I would have to believe that all woofers can play a 45hz freq., let's say just below clipping (an identical wave form) and the faster accelerating cone would achieve a higher (to some extent) output.

No, acceleration would be the same. It would be required to be the same by the fact they were playing the same frequency at the same level of excursion. One can't accelerate "quicker" than the other and both play the same frequency at the same excursion level. If the acceleration were different, one driver would necessarily need to either be moving faster in time (different frequency) or moving farther with each stroke (different excursion level). But acceleration would be identical for two different subs moving at the same frequency at the same excursion level.

The only difference would be the amount of power input required to achieve this condition. One subwoofer might require more power input than the other, which would mean one subwoofer had a higher sensitivity/efficiency than the other at that given frequency.....but that's it.

This was exactly the answer and explanation I was looking for.

Thanks for taking the time to break it down.

I tend to over think things sometimes and whether the acceleration of the cone would change the freq. was my hang up.

[cobra93 47]

Output would be the same in a perfect world; this is not possible to duplicate in the auto environment though. Perhaps a large anechoic chamber with precision testing instruments and meticulous measurements. Everything equal aside from the alignment, which is what we are debating, will lead to a different response, different peaks, and different bandwidths. Granted the sealed enclosure and IB should be similar, but far from it given the application. We have to think about aiming , reflection, cancellation, etc. . . You may consider this semantics, but it's most relevant due to the nature of the environment.

Thanks for you input and for pointing out that in the real world it may be far form what is expected.

I've come to realize that most of the time "It's not that simple" applies to most everything in (especially) in the harsh/reflective environment of our cars since I joined this forum.

[cobra93 47]

Depressing that diyma has gotten to a state that they aren't answering that simple of a question. Went downhill like hell a few years ago and I haven't really visited since, didn't realize it was caraudio.useless.

I agree that the OP's question may not have been specific enough to give an accurate answer to, but I believe I restated it well enough to allow you(the members of this forum) to help me to understand.

I've seen you state this same opinion of DIYMA before, which is why I brought it here to get an accurate answer.

Thanks.

[cobra93 47]

True. The overall shape of the response will be different for the differing alignments without a lot of work involved to match the overall response. I was presuming this was more of a theoretical question about whether same displacement = same output for sealed and IB, which is true (for any 2nd order system). They have the same displacement potential which means the same output potential, even though that potential will rarely be realized simultaneously in the different alignments over their bandwidth without intentionally trying to do so.

You would be correct in assuming this Sir.

This forum and its members are awesome!

Edited August 5, 2011 by cobra93