Observation seems to be clashing with my over simplistic (and half forgotten) 'knowledge' (some of that may be flat out wrong) of physics so I'm hoping this simple question can shed light on my confusion. While it makes sense that a bigger speaker needs more power to be moved, the following seems to suggest that in a multi-driver speaker, each driver consumes the same amount of power.
Let's suppose I have a three-way speaker with crossovers at 200 Hz and 2000 Hz, and let's suppose I feed a pure sine wave of 600 Hz with RMS voltage V, and for simplicity, let's suppose the impedance is 8 Ohms at 600 Hz. In this case, the sub and tweeter's contribution to the 8 Ohm impedance is negligible so that about all of the power P = V^2/8 is consumed by the mid driver.
I feel like this says each driver will output the same amount of P for many, if not all, pure sine waves with this same voltage. Since the power's dependence on the frequency is the impedance at that frequency, this is true so long as our frequency is in a region that
1. lies comfortably in one of the three cross-over bands so that the impedance from two of the three drivers is negligible and
2. the total impedance at that frequency is 8 Ohm.
Of course this is overly simplistic, but at least for pure sine waves, is there some reason the power consumed by each of the three isn't about the same, at least for most frequencies?
Let's suppose I have a three-way speaker with crossovers at 200 Hz and 2000 Hz, and let's suppose I feed a pure sine wave of 600 Hz with RMS voltage V, and for simplicity, let's suppose the impedance is 8 Ohms at 600 Hz. In this case, the sub and tweeter's contribution to the 8 Ohm impedance is negligible so that about all of the power P = V^2/8 is consumed by the mid driver.
I feel like this says each driver will output the same amount of P for many, if not all, pure sine waves with this same voltage. Since the power's dependence on the frequency is the impedance at that frequency, this is true so long as our frequency is in a region that
1. lies comfortably in one of the three cross-over bands so that the impedance from two of the three drivers is negligible and
2. the total impedance at that frequency is 8 Ohm.
Of course this is overly simplistic, but at least for pure sine waves, is there some reason the power consumed by each of the three isn't about the same, at least for most frequencies?
Usually, they are less efficient.
The other questions may be better suited for the multi-way subforum.
Yes, there is, and it's simply physics.
Put in it's simplest basic form, a low frequency sound is created by moving a lot of air slowly, while a high frequency sound is created by moving way less air very fast.
This is why a woofer is large and relatively slow moving: you can see it's movements as it produces sound. On the contrary a tweeter is (very) small and moves so fast you can't see the movements.
because of air. air has resistance.
air is moved with a speaker cone. the larger the cone the more resistance is needed to move the air and create the pulse as a lower frequancy has a bigger physical volume than a high one.
for example. lets immagine we have a swimming pool. it is easyer to create and requires less force to create, a small wave with a tea spoon than it does to create a big wave with a sheet of plywood.
luckaly air is not so resistive as water.
one way is to couple the driver to the air to raise the efficency, like horn loading or bass reflex, at the tunning frequancy there is a impedence match between the driver and the air.
bassically the lower the frequancy the larger the cone needed to produce the volume of the node. the larger the cone. the more resistance to move it. therefore a larger voice coil bigger magnet and more power.
Im not explaining well as I am tired and did explain well but my internet decided to disconnect before I sent my origional explanation that was full of great care.
it takes less force to move a peace of paper than a brick.
so as a general rule without nit picking a subwoofer requires more power as it has to exhite pressure waves/move more air. than for say a mid range driver playing at the same volume.
air is moved with a speaker cone. the larger the cone the more resistance is needed to move the air and create the pulse as a lower frequancy has a bigger physical volume than a high one.
for example. lets immagine we have a swimming pool. it is easyer to create and requires less force to create, a small wave with a tea spoon than it does to create a big wave with a sheet of plywood.
luckaly air is not so resistive as water.
one way is to couple the driver to the air to raise the efficency, like horn loading or bass reflex, at the tunning frequancy there is a impedence match between the driver and the air.
bassically the lower the frequancy the larger the cone needed to produce the volume of the node. the larger the cone. the more resistance to move it. therefore a larger voice coil bigger magnet and more power.
Im not explaining well as I am tired and did explain well but my internet decided to disconnect before I sent my origional explanation that was full of great care.
it takes less force to move a peace of paper than a brick.
so as a general rule without nit picking a subwoofer requires more power as it has to exhite pressure waves/move more air. than for say a mid range driver playing at the same volume.
For sure that's the long and the short of it since for all the drivers to 'demand' the same amount of power for a flat response at 'x' acoustic efficiency requires the larger driver to match up to whatever the needs of the [super] tweeter are: TA Speaker Topics: Loudspeaker Design Tradeoffs
GM
GM
typing is hard right now, forgive me, using only my off hand
let's be careful of our wording so as not to confuse
when the term efficient was used, i believe sensitive is more appropriate
when air moving faster was used, that's incorrect. we know what you mean but to clear the confusion, the air moves at the same speed regardless of frequency. the difference lies in the length and amplitude of the wave and henceforth how much air is moved.
let's be careful of our wording so as not to confuse
when the term efficient was used, i believe sensitive is more appropriate
when air moving faster was used, that's incorrect. we know what you mean but to clear the confusion, the air moves at the same speed regardless of frequency. the difference lies in the length and amplitude of the wave and henceforth how much air is moved.
Air has resistance. More air is moved to make bass.
are you saying the Same Volume is moved? just it takes more power to move air slowely that it takes to move it fast?
Im sure that Literally A Larger Body of air is moved to create a 20hz note than would be for say 200hz because it is a larger Wave. it is Bigger. so requires more Force to create.
but I may be needing to fill in some spaces in my own sound knolage of things.. for exmple a organ pipe creates low and high tones equal in volume using just air, of equal pressure? all that alters is the size of the coloum.
that colom or pipe is what. accorning to its size, is making a eqivilent match between air and air
so it is sounding a bigger body from a bigger body. using the same bassic air, AH but im sure it uses More air to power a Big flute than a small one.
Yes it does.
That means im right. It is Literal in as much as a lower note it a bigger size of air being moved and is thus needing more power eather by acousic or electical means.
are you saying the Same Volume is moved? just it takes more power to move air slowely that it takes to move it fast?
Im sure that Literally A Larger Body of air is moved to create a 20hz note than would be for say 200hz because it is a larger Wave. it is Bigger. so requires more Force to create.
but I may be needing to fill in some spaces in my own sound knolage of things.. for exmple a organ pipe creates low and high tones equal in volume using just air, of equal pressure? all that alters is the size of the coloum.
that colom or pipe is what. accorning to its size, is making a eqivilent match between air and air
so it is sounding a bigger body from a bigger body. using the same bassic air, AH but im sure it uses More air to power a Big flute than a small one.
Yes it does.
That means im right. It is Literal in as much as a lower note it a bigger size of air being moved and is thus needing more power eather by acousic or electical means.
Bingo!
When you want to make a moving coil driver with a robust cone and desire the resonance frequency to be below 30Hz and Qts low you end up with something that is not very efficient at converting current to acoustic output.
At one time when amplifier power was not so abundant, you could find large speakers with an 8" or 10" woofer that had rather high sensitivity. Now people want small and unobtrusive speakers, and so the drivers had to change. The result is less efficient drivers!
If you want the "old days" then put the Peerless 12" 830669 in a large box and you are in your happy place.
a high frequancy is moving the same volume of air as a low one. it is just vibrating faster.
but it is also more efficent. as less actual air is being moved in a shorter wavelength than is being moved in a long one.
so while the same volume of 'air' is being 'moved', regardless if it is a high or low frequancy, the air is physically moving more with a low one. more of... Air is moving. the Amount of atual moved air is greater.
but it is also more efficent. as less actual air is being moved in a shorter wavelength than is being moved in a long one.
so while the same volume of 'air' is being 'moved', regardless if it is a high or low frequancy, the air is physically moving more with a low one. more of... Air is moving. the Amount of atual moved air is greater.
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I once ran a mono setup of Karlson K15 (re-tuned per Exemplar with two right angle 3"ID pvc elbow to around 30Hz) with Altec 416Z crossed over @ ~80Hz with a cheap Behringer analog xover to a Karlson K12 with old-weak 1960's Allied Knight 12cx (with cheerful midrange but which by itself had the bass visceral impact of foam ballbat dropped against a fluffy pillow) IIRC I used a parametric for 6dB boost around 30Hz. The amplifier was a old/cheap solid state JVC Penney receiver with about 15 watts per channel so the sub ran off one channel and the coax, the other. My theater organ CD's sounded great. The room was about 14x23x8 and low bass much better and more solid than my pair of Klipschorns (in an 18x27x8 room). A small cone excursion was all needed for pipe organ. 15 watts per sub would have been adequate for theater organ - which can be demanding
in the lower regions.
Those old Altec speakers had relatively low mass, a lack of "cardboardy" coloration, and seemingly good linearity within their specified xmax limit. Perhaps a regular 6th order bass
reflex the size of the Karlson's rear chamber would have done as well - but fwiw, Exemplar used the modified K15 as they felt it was the only reasonably sized way
to keep up with the subjective speed of their reflex/horn system.
Exemplar's system a few years back
http://www.6moons.com/industryfeatures/vsac20082/exemplar2.jpg
tuning of K15 with 2 3"ID right angle ducts
http://i.imgur.com/GDJegwz.jpg
in the lower regions.
Those old Altec speakers had relatively low mass, a lack of "cardboardy" coloration, and seemingly good linearity within their specified xmax limit. Perhaps a regular 6th order bass
reflex the size of the Karlson's rear chamber would have done as well - but fwiw, Exemplar used the modified K15 as they felt it was the only reasonably sized way
to keep up with the subjective speed of their reflex/horn system.
Exemplar's system a few years back
http://www.6moons.com/industryfeatures/vsac20082/exemplar2.jpg
tuning of K15 with 2 3"ID right angle ducts
http://i.imgur.com/GDJegwz.jpg
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So we learned that same sensitivity same spl. And that a lot of energy is in the bass region.
I put the crest factor down on the table.
A standard HiFi amplifier, with a certain voltage swing, can be oversized for high frequencies, where the crest factor is high, and bend to the bass, where continuous power is required. And a few decibels correspond to several watts.
I would like also to put a sort of quality factor down on the table but I do not do how.
30 w from an IC seem to me good watts for medium but weak for bass. It is something related to the movement of high mass, air and cone, coupled in the modal region of sound reproduction. Good engineers have played around dumping factor for decades, but IMO something is missing, servo control helps but does not solve: I hope to learn something about digital signal processing. In doubt, oversized power for bass helps.
I put the crest factor down on the table.
A standard HiFi amplifier, with a certain voltage swing, can be oversized for high frequencies, where the crest factor is high, and bend to the bass, where continuous power is required. And a few decibels correspond to several watts.
I would like also to put a sort of quality factor down on the table but I do not do how.
30 w from an IC seem to me good watts for medium but weak for bass. It is something related to the movement of high mass, air and cone, coupled in the modal region of sound reproduction. Good engineers have played around dumping factor for decades, but IMO something is missing, servo control helps but does not solve: I hope to learn something about digital signal processing. In doubt, oversized power for bass helps.
This is incorrect.
Look at the size of a tweeter diaphragm, and the tweeter's Xmax, and then compare to an 18" subwoofer. No way are they moving the same amount of air.
A 1" tweeter moving 0.07mm (one way) at 4kHz will produce 100dB at 1m.
An 18" subwoofer moving 2.13mm (one way) at 40Hz will produce 100dB at 1m.
Piston Excursion calculator
To answer the original question, it's a function of the following:
- Speaker efficiency
- Program material
Chris
a high frequancy is moving the same Volume of air as a low one.
(say you have both a tweeter and a woofer, one is outputting 100db at 4000hz, the other 100db at 40hz. They are the Same volume. the higher tone is mearly vibrating the air faster)
*While the same Volume of 'air' is being 'moved', regardless if it is a high or low frequancy, the air is physically moving more with a low one. more of... Air is moving. the Amount of atual moved air is greater. more air is being moved.
So yes the 18 inch subwoofer and the 1inch tweeter are 'moving' the same amount/volume/mass of air. sound is vibration and high frequancys are quicker vibrations.so at a given spl the same Volume of air is being moved.
whats lacking here is the terminology or distintion of words.
as the 18 inch subwoofer is moving the air, 'to a greater extent' yet still the same 'volume of thing Air'
so more air is being moved within the same volume of it
lord of strength.
a more acurate way to word it would be that both the tweeter and woofer are vibrating the same volume of air at a given volume level.
there is a void of no words in my brain of how to put into words that what I mean.
the best I can do right now is say a sub moves more air but is also moving the same amount of air? to move it slower takes more force? some one needs to add to this.
lets look at a ultrasonic dog wistle for example.. or a wolf howl
(say you have both a tweeter and a woofer, one is outputting 100db at 4000hz, the other 100db at 40hz. They are the Same volume. the higher tone is mearly vibrating the air faster)
*While the same Volume of 'air' is being 'moved', regardless if it is a high or low frequancy, the air is physically moving more with a low one. more of... Air is moving. the Amount of atual moved air is greater. more air is being moved.
So yes the 18 inch subwoofer and the 1inch tweeter are 'moving' the same amount/volume/mass of air. sound is vibration and high frequancys are quicker vibrations.so at a given spl the same Volume of air is being moved.
whats lacking here is the terminology or distintion of words.
as the 18 inch subwoofer is moving the air, 'to a greater extent' yet still the same 'volume of thing Air'
so more air is being moved within the same volume of it
lord of strength.
a more acurate way to word it would be that both the tweeter and woofer are vibrating the same volume of air at a given volume level.
there is a void of no words in my brain of how to put into words that what I mean.
the best I can do right now is say a sub moves more air but is also moving the same amount of air? to move it slower takes more force? some one needs to add to this.
lets look at a ultrasonic dog wistle for example.. or a wolf howl
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hmmm maybe air is more resistive as the freqancy lowers prehaps it itstelf has a impedence curve
it is logical that Volume is Volume. so 300hz or 100hz at the same Volume are the Same Volume. This is to say the same Volume of air is being vibrated/moved.
so how could a lower longer slower waveform (sub) and a higher shorter faster waveform (tweety) being played at the same volume mean the lower longer slower one is vibrating/moving more air than the higher shorter faster one? its just a broader slower wave from a slower moving cone that moves more. so prehaps it is because air is more resistive to lower frequancys or more acuratly production there of as the cones are heavyer thanks to gravity, so maybe thats to blame for our subs needing to work harder to create the same volume, the box plays a role.. If it where entirely infinate baffle would the woofer still be needing more Power to move? to create the same volume or sound pressure level?
Facinating stuff.
it is logical that Volume is Volume. so 300hz or 100hz at the same Volume are the Same Volume. This is to say the same Volume of air is being vibrated/moved.
so how could a lower longer slower waveform (sub) and a higher shorter faster waveform (tweety) being played at the same volume mean the lower longer slower one is vibrating/moving more air than the higher shorter faster one? its just a broader slower wave from a slower moving cone that moves more. so prehaps it is because air is more resistive to lower frequancys or more acuratly production there of as the cones are heavyer thanks to gravity, so maybe thats to blame for our subs needing to work harder to create the same volume, the box plays a role.. If it where entirely infinate baffle would the woofer still be needing more Power to move? to create the same volume or sound pressure level?
Facinating stuff.
Well, just my two cents.
I have read statements here that make me doubt if 2 + 2 add up to four .....
This is what is currently called "post-truth"?
I have read statements here that make me doubt if 2 + 2 add up to four .....
This is what is currently called "post-truth"?
As I said before, this is simply not the case.
The two examples produce the same SPL by moving different amounts of air.
The reason is this:
SPL is proportional to the peak acceleration of the diaphragm.
ie, constant acceleration vs frequency = flat frequency response.
Constant acceleration means displacement gets large towards low frequencies in order to maintain the flat frequency response we're looking for.
That's why we need big drivers with lots of excursion (to displace large volumes of air) for bass, and little tweeters work just fine for the upper kHz range.
It's all Physics, and that's something I happen to have a degree in.
Chris
PS - the speed of sound is about 344m/s. Sound is neither "fast" nor "slow", unless you're passing it through a medium other than air.
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