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Post by John on Jun 25, 2007 5:23:26 GMT -7
Does anyone have any knowledge about comparing the following:
All things being equal (if possible), what's the volume difference between one 100db 12 inch speaker, and two 96db 12 inch speakers.
I figure the 2x12 at 96db is still going to be louder, simply because there's two of them. But does anyone know for sure?
I'm sure there's a mathematical formula out there, but I can't find it. (Not that I even want to)
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Post by benttop (Steve) on Jun 25, 2007 12:29:36 GMT -7
The thing you have to realize is this. If your amp is putting out 50 watts, if you have one speaker, the whole 50 watts dissipates there, but if you have two speakers, you dissipate 25 watts on each speaker. So even if the speakers have the exact same sensitivity, I don't think it's any louder. In fact, each speaker is 3db quieter, although the dispersion of sound is twice as wide. I remember noticing this exact effect when I switched from a 2x12 to a 4x12 with the same amp. It seemed I could hear it better, but getting right up close to the cab, I could tell that each speaker had far less energy than with the 2x12 setup. At least that's my experience with this scenario...
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Post by Hohn on Jun 25, 2007 20:18:11 GMT -7
True, but does half the power to each speaker mean half the volume? Are we talking mathematical volume or perceived volume? Don't we consider a 3db change to be doubling or halving the volume?
I mean, don't we always talk about how a 100w amp is NOT twice as loud as a 50W amp?
Does doubling the number of speakers double the volume, if the amount of power fed to each speaker is constant?
Maybe we should "ask Ted Weber"?
Justin
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Post by benttop (Steve) on Jun 25, 2007 22:12:13 GMT -7
Splitting the same power between two speakers lowers each speaker's volume by 3db. That's not a huge amount, but you can definitely hear it. I've never felt that adding a speaker and keeping the same power gave me any more volume, but I think I'm in the minority on that because I see people talk about it all the time.
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Post by John on Jun 26, 2007 4:39:52 GMT -7
I copied this into the "Ask Ted Weber" section.
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Post by dixiechicken on Jun 26, 2007 9:21:36 GMT -7
Well this issue is a bit more complex than simply adding numbers I suspect..
It's true that the same speaker driven at 25w instead of 50w will sound 3dB lower. That is NOT a percieved halving of volume - 9dB difference is however.
Driving two speakers side by side with each with a 3dB lower volume will make up some of that loss. But lets assume that som frequencies from each speaker ends up out of phase - that's almost bound to happen - I would think. These frequences will get a volume loss instead of a boost..
The total end-result is dependent on most of all the cabinett construction in such a case. Open back, ported, hornloaded - whatever there's lots of parameters to consider.
Cheers: Dixiechicken
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Post by benttop (Steve) on Jun 26, 2007 9:35:01 GMT -7
Well this issuse id a bit more complex than simply adding numbers I suspect.. It's true that the same speaker driven at 25w instead of 50w will sound 3dB lower. That is NOT a percieved halving of volume - 9dB difference is however. Driving two speakers side by side with each with a 3dB lower volume will make up some of that loss. But lets assume that som frequencies from each speaker ends up out of phase - that's almost bound to happen - I would think. These frequences will get a volume loss instead of a boost.. The total end-result is dependent on most of all the cabinett construction in such a case. Open back, ported, hornloaded - whatever there's lots of parameters to consider. Cheers: Dixiechicken Indeed, the number of variables is almost limitless. That's why in this case, more than most others, YMMV!
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Post by Shannon on Jun 26, 2007 13:08:47 GMT -7
Whether it's louder with 2 or 4 speakers, I'm not sure. I do know that 4 speakers moves more air than 2 speakers. So is more sound at a lower volume "louder" than less sound at a higher volume? And where do babies come from?
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Post by dixiechicken on Jun 26, 2007 16:08:22 GMT -7
For us techie-nerds heres a little math experiment. V=FxL, V= speed of sound ≈340m/s (given certain circumstances)F = frequence in Hz L = the wavelength of a soundwave at a specific frequency. example: 340 = 1000 x L -- after some algebraic tricks -- L = 34 cm Lets consider 2 12" speakers mounted together on the same baffle in a cab. Assume they are mounted as closely together as possible i.e.touching each other. Then the center of the dustcaps are in fact 12" separated from each other. ( well lets forget about the metal cone-baskets, the fact you never mount speakers this way etc etc )12" translates to roughly 30.48 cm. Lets calculate: 34000 cm = F x 30.48 cm F ≈ 1115 Hz. This frequency then is critical. Even assuming this is the only note generated - a fundamental sinewave - never true for music of course. If the speaker cones move in phase - pushes in the same direction - this frequncy will get a volume-boost at the center of the dustcaps. ( I think but I dont know for sure)However this frequency gets generated all over the speakercones - lots of different distances. This will in itself result in a rather complex radiation pattern of sound. Then there's the influence of the baffle and cab construction, the inter action with room accoustics. The fact that music contains lots frequences and harmonics. Phew - at this time I start to sweat profusely . I'll call it quits and do what most of us probably do - just connect the damn cab, turn on the amp, crank the volume up and play - oh holy crap these weber blues sound good ;D Cheers: Dixiechicken
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Post by benttop (Steve) on Jun 26, 2007 16:30:39 GMT -7
...I do know that 4 speakers moves more air than 2 speakers... Are you sure? Let's pretend we know what we're doing and say a single speaker running at 50 watts has excursions of 1/2" (after all the speaker cone moving is what moves the air), and let's pretend we know that halving the power halves the excursion. Is more air moving? I don't think so. Now lets pretend we have no flipping idea - no I don't have to pretend! But I'll bet I could do a demonstration that can illustrate it. Yeah, that's the ticket. Resolve it experimentally!
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Post by eliot1025 on Jun 26, 2007 23:27:28 GMT -7
...I do know that 4 speakers moves more air than 2 speakers...[/quote] Are you sure? Let's pretend we know what we're doing and say a single speaker running at 50 watts has excursions of 1/2" (after all the speaker cone moving is what moves the air), and let's pretend we know that halving the power halves the excursion. Is more air moving? I don't think so.
Hi Benttop, i just want to add my 2 cents here. (2 cents being the right value as I'm no expert.) Halving the power is a different parameter than the one sbrantley was referring to - i.e. doubling speakers moves more air. IF ALL OTHER FACTORS ARE EQUAL, doubling the number of speakers will definitely move more air. It has to. (Even 2 tens will move more air than 1 twelve - 2x10=20 inches of speaker surface as compared with twelve inches.) Moving more air does not mean louder (dbs). It gives the impression of more sound because moving more air means a greater dispersion of sound. Greater dispersion is not necessarily the same as higher number of dbs (loudness). Maybe moving more air is different than higher air pressure. I'd say that moving more air gives one a BIGGER sound, not necessarily a LOUDER sound. Eliot
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Post by dixiechicken on Jun 27, 2007 4:12:13 GMT -7
Let me just add... if you do a couple of searches on the net - on line arrays used in sound amplification, you'll get an idea of the complexity on these matters of sound reinforcement, sound projection, phase alignment etc etc etc. ( granted that is an even more complex problem ) Maybe I had better follow F.Zappa:s advice: "Shut up and play yer guitar". ;D Cheers: Dixiechicken
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Post by kruzty on Jun 27, 2007 6:04:40 GMT -7
Hi Benttop, i just want to add my 2 cents here. (2 cents being the right value as I'm no expert.) Halving the power is a different parameter than the one sbrantley was referring to - i.e. doubling speakers moves more air. IF ALL OTHER FACTORS ARE EQUAL, doubling the number of speakers will definitely move more air. It has to. (Even 2 tens will move more air than 1 twelve - 2x10=20 inches of speaker surface as compared with twelve inches.) Moving more air does not mean louder (dbs). It gives the impression of more sound because moving more air means a greater dispersion of sound. Greater dispersion is not necessarily the same as higher number of dbs (loudness). Maybe moving more air is different than higher air pressure. I'd say that moving more air gives one a BIGGER sound, not necessarily a LOUDER sound. Eliot But would they move more air? The way a speaker works has to do with size, but it also has to do with excursion (how much the speaker moves in and out). Halving the power will reduce the excursion of the speakers. So, maybe 2 speakers don't move more air, they just move it in a wider area.
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Post by dixiechicken on Jun 27, 2007 7:09:37 GMT -7
Speakercone excursion is corralated to volume. Small movments quiet volume., large movments loud volume.
Also the cone excursion is frequency correlated.
Small speaker 8" and low frequency == large excursion Big speaker 18" and low frequency == lesser excursion.
Thats why tweeters are usually small and basspeakers are usually large.
Cheers: Dixiechicken
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Post by benttop (Steve) on Jun 27, 2007 11:38:02 GMT -7
I think our ability to understand the physics of these matters is somewhat limited. At least my ability to understand is limited. And terms are not defined nearly tightly enough - does "moves more air" mean air moves at twice the velocity, or does it mean more air molecules are moving, but perhaps at a slower velocity? I think it's getting pretty deep in here - where's my shovel? Think about this for a moment. If you are running your 50 watt amp wide open into one 12" speaker, and you switch that out for two 12" speakers instead (assuming all other variables are held constant), will a person across the room hear the difference? Or is the difference only on the stage where there is a proximity effect? I think I've been saying that the person across the room won't notice a difference, but the person on stage will.
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Post by rcrecelius on Jun 27, 2007 11:42:46 GMT -7
Ok, Ive been sucked in Think about this for a moment. If you are running your 50 watt amp wide open into one 12" speaker, and you switch that out for two 12" speakers instead (assuming all other variables are held constant), will a person across the room hear the difference? Or is the difference only on the stage where there is a proximity effect? I think I've been saying that the person across the room won't notice a difference, but the person on stage will. They will hear the difference but only if he/she is a guitar player
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Post by kruzty on Jun 27, 2007 11:58:04 GMT -7
As mentioned earlier, when you get into line arrays, you will hear a difference from across the room. It isn't a tone thing, but volume doesn't drop off as fast the farther away you get. However, you'll need more than 2 speakers (especially 12"!) to get that effect.
I have a Bose PS1 and it is pretty amazing that you can stick your ear up to it and there isn't that much volume difference 20 feet away. I have 1 bass module with it, too. It has 2 6.5" drivers that put out some impressive bass. The Bose engineers say that magic is in the excursion of those speakers (apperently it is abnormally large).
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Post by benttop (Steve) on Jun 27, 2007 13:25:10 GMT -7
Ok, Ive been sucked in Think about this for a moment. If you are running your 50 watt amp wide open into one 12" speaker, and you switch that out for two 12" speakers instead (assuming all other variables are held constant), will a person across the room hear the difference? Or is the difference only on the stage where there is a proximity effect? I think I've been saying that the person across the room won't notice a difference, but the person on stage will. They will hear the difference but only if he/she is a guitar player Ah yes, the little known physics variable known as "The Guitarist Constant." That would account for nearly all of these observations...
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dave
New Member
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Post by dave on Jun 27, 2007 14:09:42 GMT -7
...I do know that 4 speakers moves more air than 2 speakers... Now lets pretend we have no flipping idea - no I don't have to pretend! But I'll bet I could do a demonstration that can illustrate it. Yeah, that's the ticket. Resolve it experimentally! Done the experiment. Only last week in fact. 1) Procure 1 thiele ported Mesa 1x12 cab and 1 Z best thiele ported 2x12 cab. (NB All three drivers by good fortune give 100db spl at 1 meter) 2) Place said cabs side by side. 3) Procure 1 Carmen Ghia and plug unto cab 1 4) Dime all the knobs and shred away 5) plug CG into cab 2. 6) Dime all the knobs and shred away 7) repeat steps 3-5 until ears bleed Conclusion. The 2x12 is louder, absolutely no question, than the 1 x12. I'd say twice as loud. ;D ps anyone want to sell an airbrake? I thought using an airbrake with a CG was for wusses. I've changed my mind.
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Post by rcrecelius on Jun 27, 2007 14:43:00 GMT -7
ps anyone want to sell an airbrake? I thought using an airbrake with a CG was for wusses. I've changed my mind. hehe...Ive used the airbrake with mine a few times...the CG can flat put out some sound for a lowly 18 watter
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Post by Hohn on Jun 27, 2007 15:19:31 GMT -7
Sorry if this gets REALLY long..
Sound is just wave energy travelling through the air. That wave is produced by a speaker that causes a momentary change in air pressure, and this difference propagates as a wave. When the cone moves out, it attempts to compress the air in front of it, and when it moves in, it will create a region of low pressure. So if we have 14.7psi of atmospheric pressure, the "compressed" hi pressure part of the wave formed when the cone goes out might hit up to 18psi. Assuming linear speaker action, then the "expanded" low pressure part formed when the speaker moves back in might cause a pressure drop to 11.4psi. Thus, we have a total "amplitude" of 6.6psi.
Volume, as we perceive it, is just the magnitude of these pressure changes. The greater the difference, the louder it is.
Now, what happens when you add a second identical speaker to the mix? Assuming they are perfectly in phase relative to the listening position, you have two identical waves propagating from two difference sources. When waves meet, they will interfere with each other. Now, if they are out of phase, you get destructive interference, and the perceived amplitude will go down as each wave "fills in the gaps" of the other, just like negative voltage reduces a positive voltage.
But if those waves are perfectly in phase, you get CONstructive interference, and they perceived magnitude of the waves will increase-- just like adding negative voltage to an already negative voltage makes it "more negative."
But the pivotal question here is one of cone excursion relative to input power. I'm under the impression that the relationship between excursion and power is not linear. In other words, if 1W causes a movement of 1mm, then 2W is not equal to 2mm, though it may be close. Hence, 10W would not cause 10mm excursion.
So if it's not linear, on which side does it err? Assuming inefficiency, we can say that if 1W=1mm, then 10W<10mm excursion. Certainly 50W won't give you 50mm!
Because it's not linear, then it becomes more efficient to use multiple drivers at lower power dissipation than to have one driver dissipating it all. We'd agree that mathematically, the same air is displaced by one driver moving 4mm as by 4 drivers moving 1mm each. Do the math for the shape of the theoretical cylinder of air displacement and you'll see they're functionally equivalent.
So, what this leads us to is the idea that the first watt of power is the "loudest watt" to a given speaker. I can double the power to 2W, but it's something less than twice the wave energy of the first watt. Eventually you get to the point that no matter how much more energy (power) you send to a given speaker, you won't get any more wave energy transmitted to the air.
If you agree with me that the "first watt is the loudest watt", then you can see why multiple drivers are more efficient at converting input power to output wave energy, and hence why a 2x12 cab with 50W should be louder than a 1x12 with 50W, assuming all drivers are identical. The identical drivers in phase will produce constructive wave interference which very efficiently creates one larger wave by summing two smaller, in-phase waves.
The earlier post about the spacing between the speakers within the cab and the relationship to wavelength and frequency is interesting, but irrelevant to our discussion here as far as I can see. The spacing of the drivers within the cab is only relevant when you are talking about listening off-axis. I am assuming here that we are talking on-axis, i.e. you are standing in front of the cab such the the distance from the left speaker to your left ear is identical to the distance from the right speaker to your right ear. When you are no longer perfectly on axis, then the distance between the speakers matters because the two separate waves emitted by the speakers are no longer perfectly complimentary. They will have a mixed phase relationship that's frequency-dependent-- iow, some frequencies will appear louder, and others will appear quieter based on the time/phase/wavelength relationship.
All that to say that I think the a multiple driver cab is louder than a single driver cab when all the drivers are identical and in phase.
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dave
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Post by dave on Jun 27, 2007 15:39:30 GMT -7
Yes, good explanation. The key is the diminishing cone excursion with increasing power, so two drivers displace more air than one with the same power input. It is certainly borne out by experiment!
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Post by benttop (Steve) on Jun 27, 2007 19:39:30 GMT -7
I simply MUST test this.
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Post by Hohn on Jun 27, 2007 20:50:30 GMT -7
Please do! I'd love to know the real answer, instead of just my own theoretical conjectures.
jh
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Post by benttop (Steve) on Jun 27, 2007 21:07:54 GMT -7
I will actually, but I've had a major computer crash here (lost the boot drive on my main machine, and ALL of everything on it) so I'm here courtesy of my ancient old studio computer. Once I get my main machine back up (probably several more days of installs) I plan to do several test recordings. One is to see if I can understand this thread. Another is to see if I can document the differences between non-attenated and attenuated (I have an idea how to go about that one) and make a comparison between the Airbrake and Hot Plate. I really don't know what to expect with those - should be interesting all round. Now if I can just get all my software back on my main machine, I can get started....
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dave
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Post by dave on Jun 28, 2007 1:13:11 GMT -7
Phil Jones might have something to say on this. You dont put 32 drivers in a bass stack without a good reason.... Those cabs are spectacular - anyone heard one? postscript - he does have something to say...see www.philjonesbass.com/TECH%20INFO/piranha.htm
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Post by dixiechicken on Jun 28, 2007 2:31:34 GMT -7
Hohn in priciple your reasoning is quite correct, as an answer to the first asked question in this thread. In real life situations our listening position is more off axis tha on axis I'll wager. This basically have resulted in two schools of speaker design. 1) As examplified by typical studiomonitors - where you try eliminate every external factor that can influence what you hear. (I.E romm accoustics, placement of peakers etc etc.)This is NOT really possible even if you can come pretty close - most studio monitors have switches mechanical or electrical to change the treble and bass curves, to adjust for different rooms and placements. 2) This school is perhaps best exemplified by the Stig Carlsson speakers: A swedish electro accoustics engineer - spent his whole life in the quest for perfect sound reproduction. He specifically designed all his speakers to interact with the room they were placed in. Since he very well knew peoples livingrooms could look any ol' way - he had very detailed instructions on HOW to place his speakers. ( cornerplacement or not, distance from the walls, proximity to textile materials etc etc ) Correctly placed many of his constructions made the listening room disappear completely, in a classical orchestra not only did you hear the steroimage, close your eyes and you could identify each an every instrument, depth and height placement relative to other instruments. It was a revelation. As you can easily see there's just one huge drawback to this design philosophy. Tell your missus - Hey honey I've just bought the best damned speakers ever, but we must tear the house down, rebuild it around my new stereo. ;D Cheers: Dixiechicken
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Post by Hohn on Jun 28, 2007 10:02:11 GMT -7
DC, you're exactly right.
The other point is missed was how to QUANTIFY the difference in loudness. So what if a 2x12 is louder than a 1x12 given the same power and identical speakers: what if the speakers are different, as in the lead post? In other works, HOW MUCH louder is the 2x12?
Are two 96db speakers louder than a 100db speaker? This is where it get's really complicated, to me. Since the speakers are different now, the perceived volume will be different because of each speaker's different frequency response. Even if a Blue and a Greenback had identical sensitivities, the Blue might seem louder because it's a little brighter.
If I had to guess at quantifying the volume difference (ignoring perception issues), I'd suspect that a 2x12 is generally 3db louder than a 1x12.
So in this case, I'd guess that a 2x12 with 96db speakers would be only AS loud, perhaps a little quieter than a 1x12 with a 100db speaker.
Again, like all the rest of this, that's just conjecture on my part.
Justin
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Post by dixiechicken on Jun 28, 2007 10:14:38 GMT -7
Amen to that Hohn!
The Fletcher-Munson curves will defintely kom into play here. I forget exactly which frequencies our ears are most sensitive to, but if two speakers with the same effiency have different spectral components - one will almost certainly sound louder than the other.
Cheers: Dixiechicken
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Post by Shannon on Jun 29, 2007 17:02:22 GMT -7
Wow. Great posts guys.
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