The driver produces heat but that has nothing to do with why polyfill or wool works.
Both ported enclosures and PR enclosures don't want or need "stuffing". Wall absorption of higher freqs, sure.
The port and the PR are very similar - they are both "transformers", impedance transformers in fact.
The air in the port is not "light" at all, in fact it is pretty darn stiff at resonance, which is why it works.
The "backwave" of the speaker isn't what drives the port or the PR at least not the way you'd think. It's a "phase inverter" set up. That means that when the driver moves in, the PR or Port also moves IN!
Within the linear range of the PR, neither the PR nor the Port is particularly able to "move" more air. In fact in some cases the PR is more effective since it starts with a larger surface area, meaning the velocity of the air being moved can be lower - closer to a 1:1 ratio (perfect match).
(ie. better radiation impedance)
Also the PR has no problem with "chuffing" or port noise - it has other problems.
At resonance both the Port case and the PR case have the strong short motion of the driver being converted to weaker long motion... the driver cone "stands still." It's a phase inverting "lever" in concept...
Both ported enclosures and PR enclosures don't want or need "stuffing". Wall absorption of higher freqs, sure.
The port and the PR are very similar - they are both "transformers", impedance transformers in fact.
The air in the port is not "light" at all, in fact it is pretty darn stiff at resonance, which is why it works.
The "backwave" of the speaker isn't what drives the port or the PR at least not the way you'd think. It's a "phase inverter" set up. That means that when the driver moves in, the PR or Port also moves IN!
Within the linear range of the PR, neither the PR nor the Port is particularly able to "move" more air. In fact in some cases the PR is more effective since it starts with a larger surface area, meaning the velocity of the air being moved can be lower - closer to a 1:1 ratio (perfect match).
(ie. better radiation impedance)
Also the PR has no problem with "chuffing" or port noise - it has other problems.
At resonance both the Port case and the PR case have the strong short motion of the driver being converted to weaker long motion... the driver cone "stands still." It's a phase inverting "lever" in concept...
more questions about passives
Hi ! does anybody know if there is something to gain whith two instead of one passive radiator ,if the size is relative to the driver. say you have a 10" peerless xls and a 12" passive or a 10"perless and two 10"passives? most bang for the buck but sound quality is the most importent.
Hi ! does anybody know if there is something to gain whith two instead of one passive radiator ,if the size is relative to the driver. say you have a 10" peerless xls and a 12" passive or a 10"perless and two 10"passives? most bang for the buck but sound quality is the most importent.
OK, guys, here is a plot of a typical PR system.
The black curve is the response. It is very similar to a bass-reflex system down to some 30 Hz in this case.
The red curves are the amplitude of the driver (solid) and the PR (dashed).
-The resonance between the mass of the PR and the compliance of the air in the box occurs at about 37 Hz. This resonance is equivalent to the helmholtz resonance of a BR box. At this frequency, the cone is almost at standstill.
-At ~13 Hz, the free air resonance ot the PR can be seen (ie the resonance between the mass and the suspension of the PR). At this frequency, the radiation from the PR and the driver is equal, but of opposite phase. This causes a dip in the response. This dip is not present in a BR system.
-It be seen that the PR moves considerably more than the driver at the PR resonance.
-It can aslo be seen that the driver moves more than the PR at higher frequencies.
-Finally, it can also be seen that the PR moves about the same as the driver at low frequencies, but in opposite phase. This last one is the only that we have any intuition for (unfortunately, since this is different from the others, and not very important).
HTH
The black curve is the response. It is very similar to a bass-reflex system down to some 30 Hz in this case.
The red curves are the amplitude of the driver (solid) and the PR (dashed).
-The resonance between the mass of the PR and the compliance of the air in the box occurs at about 37 Hz. This resonance is equivalent to the helmholtz resonance of a BR box. At this frequency, the cone is almost at standstill.
-At ~13 Hz, the free air resonance ot the PR can be seen (ie the resonance between the mass and the suspension of the PR). At this frequency, the radiation from the PR and the driver is equal, but of opposite phase. This causes a dip in the response. This dip is not present in a BR system.
-It be seen that the PR moves considerably more than the driver at the PR resonance.
-It can aslo be seen that the driver moves more than the PR at higher frequencies.
-Finally, it can also be seen that the PR moves about the same as the driver at low frequencies, but in opposite phase. This last one is the only that we have any intuition for (unfortunately, since this is different from the others, and not very important).
An externally hosted image should be here but it was not working when we last tested it.
HTH
ume said:Do the grafs explain my question ? maybe i´m stupid ,but please try again...10" activ whith one 12" passive or 10" active whith two 10" ?do you really need two passivs?for better sound qualaty?
I think that post was unrelated to your question...
Generally speaking, rule of thumb, if you use a 10" active driver, you want to go TWO "driver sizes" up for the PR. That means a 15" PR.
If you want to use two PRs (and the mounting relationship between them does matter) then you can figure out Sd for the 15" case and see how the pair of 10" drivers compare since you need at least the same surface area.
As far as sound quality, it's difficult to predict that. But generally speaking, the larger the PR, the less it has to move for the same output which usually equates to greater linearity, or "lower distortion". In practice, that may not be meaningful unless you're pushing your system up toward its max power handling & max SPL.
If ur choice is between one 12" PR and two 10" PRs the pair wins given similar Xmax ratings.
_-_-bear
ume said:Do the grafs explain my question ? maybe i´m stupid ,but please try again...10" activ whith one 12" passive or 10" active whith two 10" ?do you really need two passivs?for better sound qualaty?
No, it was in response to the original question.
Fazorcat said:
It can clearly be seen in the graph that the PR moves more than the driver at certain frequencies.
Svante said:
(not sure what is what on the top graph... and I'm not sure where the Xmax graph is for the PR... you might get a more classical looking curve if you "tuned" the PR up at least an octave from where it appears to be at 13 Hz... I'm not seeing the PR's Xmax peak at its resonant frequency? )
Again, the *displacement* is greater at maximum, but the Xmax depends on the Sd of the PR. Given a large enough PR or enough PR surface area spread across multiple PRs, the Xmax may or may not be greater than the active driver...
Thus, the rule of thumb to use a PR two speaker sizes up from the active driver...
_-_-bear
The graph shows displacement (red curves) and response. The frequency that corresponds to the "tuning frequency" (let's call it fh) of a BR box is about 37 Hz, which is pretty normal, I think.
The displacement of the PR does not, typically, have a maximum at fh, even though the sound from the PR has. If you tilt the displacement curves by + 12 dB/octave, you will get the more commonly shown sound pressure curves, and the knee in the PR curve at ~37 Hz will become a peak.
Note: the displacement should be read on the "mm" axis, the "dB" scale is out of sync with that.
The displacement of the PR does not, typically, have a maximum at fh, even though the sound from the PR has. If you tilt the displacement curves by + 12 dB/octave, you will get the more commonly shown sound pressure curves, and the knee in the PR curve at ~37 Hz will become a peak.
Note: the displacement should be read on the "mm" axis, the "dB" scale is out of sync with that.
Rule of Thumb
Thus, the rule of thumb to use a PR two speaker sizes up from the active driver...
I thought the rule of thumb was that the air displacement of the PR should be at least 2 times the displacement of the active. Where displacement = Sd*Xmax. I think the reference is in the LSCB in the PR chapter.
Rajiv
Thus, the rule of thumb to use a PR two speaker sizes up from the active driver...
I thought the rule of thumb was that the air displacement of the PR should be at least 2 times the displacement of the active. Where displacement = Sd*Xmax. I think the reference is in the LSCB in the PR chapter.
Rajiv
Vikash said:I don't see the rule of thumb significance here anyway. Just load Unibox etc. and model it properly.
Agree, but if one looks at the graph in my previous post, one can see that the maximum displacement of the PR is about 4 mm, and for the driver it is a bit more than 1 mm (above fh). So, in this example, the factor is slightly less than 4.
Ron E said:
Bear, you'd best not answer any more questions about box theory until you study a bit.
And what are you famous for?
Guess I don't know who you are or what your agenda might be.
And thank you very much for the concise and considerate answer to the question - apparently you are unable to type that part? Ok... nice meeting you.
And no, the inclusion of
does not make your posting humorous._-_-bear
- a wink is as good as a nod to a double blind horse -
Svante said:
Ok... I now see what ur displaying...
displacement in the red makes sense... I thought you were showing response entirely in the lower graph with the two red curves showing response of the woofer and the PR respectively - in which case it looks puzzling.
As far as the 4mm xmax, that might be fine for this given SPL and this given driver, but it seems likely that for a very high Xmax/high BL, high performance woofer that the required Sd* x Xmax for the PR will be quite a bit higher than 4mm from a same size basket PR.
Having built PRs for a long, long time, it's been my experience that while the "book" picks a minimum requirement, and the earlier papers were even *tighter* in that respect, that you get better (closer to ideal) results when the PR is actually a goodly amount larger Sd than the driver. This permits *less* excursion by the PR, which in turn also effectively improves the result.
Of course, you decide what you want to do or not do...
_-_-bear
Vikash said:I don't see the rule of thumb significance here anyway. Just load Unibox etc. and model it properly.
Vikash... very nice and professional looking website!
Looking at your Peerless/PR subwoofer, I see you mounted the PR downward firing...
- what sort of effect (if any) did you find with different distances between the PR and the floor?
- what effect (if any) did you find with different floors? (wood, concrete, etc?
- what mass is on the PR, (stock or added?)
- and what do you do about the offset due to the mass and gravity?
_-_-bear
The sub is yet unfinished. Getting round to spray finishing is the hold up. At present I've only tested it with both drivers on the vertical plane. And boy does that PR move at resonance (It will hit the MDF brace if volume is high enough: >22mm)
Despite this, in my brief realistic tests I couldn't see a requirement for another or larger PR. But then again the PR does already have almost twice the linear excursion of the active driver.
The PR is 265g with no additional weight added.
Despite this, in my brief realistic tests I couldn't see a requirement for another or larger PR. But then again the PR does already have almost twice the linear excursion of the active driver.
The PR is 265g with no additional weight added.
No need to worry about rules of thumb with the software available.
The PR's volume displacement is the key requirement, not size. So, same as with a driver, look at its Sd and xmax to decide how many of what size you need.
Hopefully your software tells you PR excursion; if its greater than xmax of your PR for the power and tuning, you need one with more xmax, a bigger one, or more of them.
BTW it makes more sense to compare the PR with what the port air is doing, not the driver, since that's what its replacing, so If the PR was the same diameter as the port, it would need the same displacement capability - lots.
Whoever used the mass spring analogy was on the right track. The driver is driving the PR through the spring stiffness of the enclosure air.
Svante,
What software are those nice plots from?
Thanks
The PR's volume displacement is the key requirement, not size. So, same as with a driver, look at its Sd and xmax to decide how many of what size you need.
Hopefully your software tells you PR excursion; if its greater than xmax of your PR for the power and tuning, you need one with more xmax, a bigger one, or more of them.
BTW it makes more sense to compare the PR with what the port air is doing, not the driver, since that's what its replacing, so If the PR was the same diameter as the port, it would need the same displacement capability - lots.
Whoever used the mass spring analogy was on the right track. The driver is driving the PR through the spring stiffness of the enclosure air.
Svante,
What software are those nice plots from?
Thanks
Could you help me with this one.
I'm searching for this and can't find good answer. How can I calculate/measure Vap of passive radiator if it's made of loudspeaker, and tuned to a lower resonance frequency?
And can I use 2 equal passive radiators and input them in speakershop as one item with 2 times greater Vap?
I'm searching for this and can't find good answer. How can I calculate/measure Vap of passive radiator if it's made of loudspeaker, and tuned to a lower resonance frequency?
And can I use 2 equal passive radiators and input them in speakershop as one item with 2 times greater Vap?
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