You might not "like" the formula, it´s nevertheless correct and post #98 is wrong.
But ok, I wish you all a happy discussion about things that are solved since 40 years.
But ok, I wish you all a happy discussion about things that are solved since 40 years.
I was just playing with Basta!, and the first thing I noticed was the easiest way to change the compliance value was to alter the Vas. The next thing was, of course, when you change Vas the overall output goes up and down. Fs (Fc for us geezers) didn't change, however!
Selecting different parameters so the force and mass didn't change and the compliance could be inputted directly did get the resonance to shift, but the program still insisted that the sensitivity was changing.
Just what sort of mass to compliance ratio is needed for things to be asymptotic?
Selecting different parameters so the force and mass didn't change and the compliance could be inputted directly did get the resonance to shift, but the program still insisted that the sensitivity was changing.
Just what sort of mass to compliance ratio is needed for things to be asymptotic?
Analogy time...
If I were oblivious to the concept of engine power, and just believed that RPM-gain/time was a constant characteristic of the engine in my car, then I could convince myself that doubling the tire size on the vehicle would double my acceleration rate. I would be very wrong of course, because I would be ignoring physics.
Yes, I can change the tire size, but I will change the relationship of available engine power for a given speed in doing so... Lets try not to concern ourselves with the other complications for the analogy, the important part is that the the tire is not an effect, it is a cause of effects.
The misunderstanding that I believe is taking place here, is the idea that Vas is like the tire on the car, and RPM-gain/time is a constant. Neither is true. The engine has fixed power [BL, Re], and Vas is a way of summarizing a characteristic EFFECT of changing the tire size. Vas is NOT the tire.
Regards,,
Eric
If I were oblivious to the concept of engine power, and just believed that RPM-gain/time was a constant characteristic of the engine in my car, then I could convince myself that doubling the tire size on the vehicle would double my acceleration rate. I would be very wrong of course, because I would be ignoring physics.
Yes, I can change the tire size, but I will change the relationship of available engine power for a given speed in doing so... Lets try not to concern ourselves with the other complications for the analogy, the important part is that the the tire is not an effect, it is a cause of effects.
The misunderstanding that I believe is taking place here, is the idea that Vas is like the tire on the car, and RPM-gain/time is a constant. Neither is true. The engine has fixed power [BL, Re], and Vas is a way of summarizing a characteristic EFFECT of changing the tire size. Vas is NOT the tire.
Regards,,
Eric
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Most of the programs make particular choices about what variables are independent and which are dependent. You have to watch the different number fields to see what changes when you change the others (which it sounds like you did)
I'm not sure what you mean by mass to compliance ratio, but I would look at it as distance from resonance. Depending on system Q I would think that you would be within a dB or so of the flat mass controlled region when you are an Octave above resonance
David S
Post #98 and the formula of reference efficiency using VAS and Fs are both correct :
Post#98 points that it is paradoxical to use Fs and Vas while they are strongly correlated to Cms and while Cms does not enter in the formula based on physics :
As said in the Wikipedia entry "Thiele/Small" from which I copied these images, the above first formula eases the calculation from published parameters, but it tends to induce the fallacy that the reference efficiency has a kind of proportionality to Fs and Vas which it has not.
Even more than not liking this formula, I do not consider efficiency as being a pertinent criterion for drivers quality.
Thank you!
As I explained in post 90, Fs and Qes are both dependent on Vas.
"Plug in any numbers, then double Vas, at the same time Understand that Fs sqrd will half. This leaves the term Fs over Qes. Understand that Fs/Qes is constant with changes of resonance and, a change in Vas results in no change in efficiency!"
This is where the confusion comes from, the first equation is full of derived parameters. The second is based on fundamental parameters and gives a clearer idea of what the relationships are.
David
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Hi
It might be more useful to look at the why of the 6dB increase in power a different way.
The radiators velocity drives the acoustic radiation resistance of the air but for a woofer, it’s radiator is small compared to the wavelength. If one examines a plot of radiation resistance vs radiator size, one sees part of the curve is flat and part is a slope.
Acoustic radiation resistance curve;
http://www.vxm.com/nxtimage1.GIF
This slope implies two things for the woofer, first, that to have flat response, one needs to adjust the excursion so that it accounts for the slope (decreasing radiation efficiency with falling frequency).
This is why a direct radiator woofer has to have 4 times the excursion to have flat response an octave lower.
More to this issue, it also means that if one doubled the radiator size, it would push you up the curve resulting in a 3dB greater electro acoustic efficiency at any frequency on the slope. Having twice the power handling means the total is 6dB greater (4X). Fwiw, an ideal horn is a way to connect a driver far down on this curve to the radiation resistance of the flat region (large mouth).
Doubling the radiator area is easy all you need to do is place two of the woofers less than ¼ wavelength apart and they sum into a new source coherently.
Spacing larger than about 1/3 wavelength and one has the two radiators starting to radiate independently and producing an interference pattern where what you measure depends on the vector addition of the path / time / phase difference between the two sources at the measurement point.
An interference pattern can be recognized by a pattern of lobes and nulls caused by the periodic addition and cancellation of the two separate sources.
Conversely, if the two sources were a quarter wavelength or less apart, then they radiate as a single source in an omnidirectional pattern, that is an omni directional point source.
With two separate sources but positioned such that they add where your measuring, the sum appears to be identical to the coherent addition case but that is not the case.
The coherently adding case, radiates twice the acoustic power of the non-coherent case, the difference is made up by the energy not radiated in the interference patterns nulls.
As a result if one placed the two cases in a huge reverberant room, one finds the reverberant level (which is the sum of the sound energy radiated in all directions) indicates the total radiated power in each case.
As was already obvious, when one has something other than a simple omni source, you cannot take one measurement and get a grip on acoustic power. A radiation pattern can alter what you measure at any given point while the issue of efficiency sets the total conversion rate.
Hope that helps a bit,
Tom Danley
Danley Sound Labs
It might be more useful to look at the why of the 6dB increase in power a different way.
The radiators velocity drives the acoustic radiation resistance of the air but for a woofer, it’s radiator is small compared to the wavelength. If one examines a plot of radiation resistance vs radiator size, one sees part of the curve is flat and part is a slope.
Acoustic radiation resistance curve;
http://www.vxm.com/nxtimage1.GIF
This slope implies two things for the woofer, first, that to have flat response, one needs to adjust the excursion so that it accounts for the slope (decreasing radiation efficiency with falling frequency).
This is why a direct radiator woofer has to have 4 times the excursion to have flat response an octave lower.
More to this issue, it also means that if one doubled the radiator size, it would push you up the curve resulting in a 3dB greater electro acoustic efficiency at any frequency on the slope. Having twice the power handling means the total is 6dB greater (4X). Fwiw, an ideal horn is a way to connect a driver far down on this curve to the radiation resistance of the flat region (large mouth).
Doubling the radiator area is easy all you need to do is place two of the woofers less than ¼ wavelength apart and they sum into a new source coherently.
Spacing larger than about 1/3 wavelength and one has the two radiators starting to radiate independently and producing an interference pattern where what you measure depends on the vector addition of the path / time / phase difference between the two sources at the measurement point.
An interference pattern can be recognized by a pattern of lobes and nulls caused by the periodic addition and cancellation of the two separate sources.
Conversely, if the two sources were a quarter wavelength or less apart, then they radiate as a single source in an omnidirectional pattern, that is an omni directional point source.
With two separate sources but positioned such that they add where your measuring, the sum appears to be identical to the coherent addition case but that is not the case.
The coherently adding case, radiates twice the acoustic power of the non-coherent case, the difference is made up by the energy not radiated in the interference patterns nulls.
As a result if one placed the two cases in a huge reverberant room, one finds the reverberant level (which is the sum of the sound energy radiated in all directions) indicates the total radiated power in each case.
As was already obvious, when one has something other than a simple omni source, you cannot take one measurement and get a grip on acoustic power. A radiation pattern can alter what you measure at any given point while the issue of efficiency sets the total conversion rate.
Hope that helps a bit,
Tom Danley
Danley Sound Labs
Tom, and others,
I agree with what you are basically saying, but adding another woofer to double the area is not the answer. The acoustic power radiated by any two sources of equal strength will increase by 6dB over either source by itself. Cone area has nothing to do with it. Cone area affects the individual efficiency of each driver but is totally irrelevant with regards to how two sources sum.
Also, the 1/4 wave length this is not technically accurate. It's just an approximate cut off point. The power radiated by two ideal sources vs. frequency is shown here for a spacing which is 1/4 wave length at 1k Hz.
An externally hosted image should be here but it was not working when we last tested it.
"Acoustically close" is better approximated at 0.1 wave length which occurs at 400 Hz. As you can see from the plot, the 6dB increase starts to drop off at just about 400 Hz.
Additionally, as stated, source size has nothing to do with it. The arguments typically say add another (similar) driver and then everyone starts on the reason being the doubling of area and they start bringing these efficiency equations into the argument, which simply don't apply.
Go back to the definition of efficiency:
Power radiated / Power input.
The equations presented above are simply expressing of this FOR A SINGLE DRIVER and do not apply to a multi-driver system. When we use two of the same drivers things are simple because each driver has the same efficiency to start with. So we know that when connected in parallel we supply twice the power and from observation, if acoustically close, the resulting acoustic power increases by a factor of 4, thus a 3dB increase in efficiency. But trying to relate this to the efficiency equation for a single driver is bogus. For example, if you double the cone area of a single driver, all other things equal, efficiency does not double, it quadruples.
The way correct way to look at this is to start with the efficiency of each source and work forward. Say we have a 5" woofer with efficiency of 0.5% and a 10" woofer with efficiency of 0.9%. The small woofer will radiate 1W with an input power of 200W. The 10" woofer will radiate 1W with an input of 111 watts. When acoustically close they will radiate 4W with a total of 311 W input for an efficiency of 1.26% = Radiated power / Input power = 4/311.
Size doesn’t matter.
Interesting. What would cause a DC offset in one woofer that wouldn't also be the same in the other (hopefully identical) woofer ? It does sound like a rare edge case though, the vast majority of speakers with multiple woofers tend to put them in the same enclosure unless the enclosure is very tall, where it might be beneficial to segregate them to avoid standing waves in the tall enclosure encroaching down into the operating frequency range of the woofer...
Doesn't it also depend on whether the series connected woofers are sharing the same enclosure ? If they're in separately partitioned enclosures their resonant frequency may well be significantly different, and cause odd effects due to the series impedance of each driver peaking at a different frequency altering the drive to the opposing woofer.
But if they are in the same enclosure their mechanical resonances will be forced to align with each other - they form a composite driver with a single resonant frequency.
One such program is WinISD Pro, which will let you choose multiple woofers, either in parallel or isobaric configurations...
This is stated confusingly.
I first read it and thought, "he's wrong".
I read a second time and changed my view, "It's OK, he's right".
I read it a third time to confirm that "he's right".
I have read it a fourth and fifth time to be sure, before writing this post.
is your 0.1WL or 0.25WL based on centre to centre of the two radiating cones or is it based on the overall width of the radiating areas?
I think you will find that the frequency for 1/4WL of the overall width (longest dimension) of the radiating areas is very likely to be close to the 0.1WL centre to centre frequency of the two radiating areas.
BTW,
I have now read that phrase from the previous post about 10times because I am still not that sure I am interpreting it correctly. Yes, you are allowed to conclude I am slow in the uptake.
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Hi John
I elected to explain this from the “change in loading” point of view because THAT is the acoustic mechanism that causes the efficiency to double when one has two identical closely coupled woofers, not the formula’s used to describe it.
That same mechanism IS how a horn can increase the efficiency of the driver connected to it, it couples a tiny radiator to the part of the curve which is a plateau (un-changing load).
That is also why horn drivers are velocity profile devices as opposed to the tiny direct radiator which is an acceleration profile (and why the motor strength is typically much larger for the horn driver).
I chose to say ¼ wavelength because that is an obvious transition point, your graph shows the effect I talked about if one were measuring acoustic power in a large reverberant room (integrating the acoustic power radiating in all directions).
What that shows in while they are about a quarter wl or less, the acoustic power is +6dB and when larger, the power is +3dB which only reflects the increase in electrical input power with two sources. AS it shows, by the time you’re at 2K, you are not coupled, not benefiting from the mutual coupling effect and producing an interference pattern.
In commercial sound this effect is seen fairly often but not as often recognized, it is common to place subwoofers one either side of the stage for convenience. This causes a “power alley” in the center where the bass is very powerful but also weak or non-existent to the sides. Placing them in the center closely coupled allows the same on axis pressure AND much more even pressure off axis.
All that is complicated when you put either system in a room.
In the last 20 years or so, the use of super position theory has become popular and while that math works to predict local pressure, local pressure is not acoustic power and it does not explain the acoustic radiation resistance needed for a more complete picture or to see how horns work.
The acoustic pressure does increase +6dB when two identical sources add in phase but the acoustic power is not the local pressure but that integrated over all angles.
Also, if one takes a single driver and doubles the area, one has to also change the other parameters to retain the same T&S alignment (same frequency response).
One can arrive at a given set of T&S parameters with any size driver (within the range of physical possibilities) and these all have the same efficiency regardless of size..
About 3min into this video is an old subwoofer Tapped Horn I designed with multiple drivers, all of which act as a single unit. This can be modeled as a single giant driver or many small ones, the answer is the same.
Discovery Channel Video Player
Best,
Tom
I elected to explain this from the “change in loading” point of view because THAT is the acoustic mechanism that causes the efficiency to double when one has two identical closely coupled woofers, not the formula’s used to describe it.
That same mechanism IS how a horn can increase the efficiency of the driver connected to it, it couples a tiny radiator to the part of the curve which is a plateau (un-changing load).
That is also why horn drivers are velocity profile devices as opposed to the tiny direct radiator which is an acceleration profile (and why the motor strength is typically much larger for the horn driver).
I chose to say ¼ wavelength because that is an obvious transition point, your graph shows the effect I talked about if one were measuring acoustic power in a large reverberant room (integrating the acoustic power radiating in all directions).
What that shows in while they are about a quarter wl or less, the acoustic power is +6dB and when larger, the power is +3dB which only reflects the increase in electrical input power with two sources. AS it shows, by the time you’re at 2K, you are not coupled, not benefiting from the mutual coupling effect and producing an interference pattern.
In commercial sound this effect is seen fairly often but not as often recognized, it is common to place subwoofers one either side of the stage for convenience. This causes a “power alley” in the center where the bass is very powerful but also weak or non-existent to the sides. Placing them in the center closely coupled allows the same on axis pressure AND much more even pressure off axis.
All that is complicated when you put either system in a room.
In the last 20 years or so, the use of super position theory has become popular and while that math works to predict local pressure, local pressure is not acoustic power and it does not explain the acoustic radiation resistance needed for a more complete picture or to see how horns work.
The acoustic pressure does increase +6dB when two identical sources add in phase but the acoustic power is not the local pressure but that integrated over all angles.
Also, if one takes a single driver and doubles the area, one has to also change the other parameters to retain the same T&S alignment (same frequency response).
One can arrive at a given set of T&S parameters with any size driver (within the range of physical possibilities) and these all have the same efficiency regardless of size..
About 3min into this video is an old subwoofer Tapped Horn I designed with multiple drivers, all of which act as a single unit. This can be modeled as a single giant driver or many small ones, the answer is the same.
Discovery Channel Video Player
Best,
Tom
DC offset is an obscure but interesting topic. A lot of woofers are succeptable to at frequencies just above resonance. It comes from the DC term associated with a lot of nonlinearities, and from the phase shift between force direction and cone location. Just above resonance the vc force is trying to push the cone back into the gap (rather than away from the center position) and since BL drops when the coil is well out of the gap the cone might not make it back in! Read T.H. Wiik of SEAS on the subject.
Woofers tend to offset inwards because there is a solenoidal force trying to draw the corepole into the coil (related to the l vs. x term), but many woofers are a bit bistable and will just as happily offset out as in. Put a pair like that together in the same volume and one will offset in its preferred direction and the other will flop in the opposite direction. The cabinet stiffness doesn't resist opposing displacement.
I see these phenomena every once in a while. You have to abuse the system a bit to get them to come out. The general cure is better woofer design and usually a progressively nonlinear spider is very helpful.
The combined impedance curve is the complex parallel sum (real/imaginary) of the two impedance curves. Yes, sharing the same volume would tend to force some mutual allignment, although if they were way off you could still get a double peak. I haven't seen it in practice. Voltage sharing will also swing around a little.
Rather than the two woofers being lumped parameters where you can add all parameters (double mass, half compliance, etc.) you have a higher order system with box stiffness coupling the seperate woofers together.
I just don't run into this as a significant problem, although assuring that shared volume woofers were reasonably well matched sounds like a safe precaution.
David
Well, it's just superposition of the pressure fields radiated by each source. The radiation impedance of the two driver system is a different animal. It is not like a horn; there is not a transformer in the loop. What matters here is that the two sources have the same volume velocity. They will each radiate a pressure field that is the same as if they were isolated. When brought close together (less that 1/4 wave length or 1/10th, which ever you choose is only a matter of convince) they act correlated and the 3d integral of the superimposed pressure fields yields twice the pressure at all points, (6dB). At higher frequency where they become uncorrelated we see only a 3dB increase. That the result goes form 6 to 3 dB is itself an indication that it is just superposition of the two independent pressure fields. The dips and peaks shown in my plot also indicate how these vector sums vary with frequency. They are correlated a very long wave length and uncorrelated at very high frequency with a mis mash in between. The acoustic loading of the two source system is different than the acoustic loading of each driver individually, even when operating in close proximity. However, if the acoustic loading of driver 1 changed due to the proximity to driver two, then pressure field radiated by driver one would necessarily be different than when isolated, and conversely for driver 2. The result would be that the total pressure field in the correlated region would have to be either less than or greater than 6dB.
Anyway, this topic has been beaten to death so many time I fail to see why it keeps coming up.
Anyway, this topic has been beaten to death so many time I fail to see why it keeps coming up.
It is just superposition of the pressure fields, at least until the system efficiency becomes significant and radiation impedance starts to rival motor impedances. At that point we need to put radiation resistance into the equivalent circuit.
When you say "becomes uncorrelated and we see only 3dB" I assume you mean in the spherically integrated field. The axial gain seems to be an exact +6 for all frequencies. Since axial gain is +6 but power gain starts at +6 for long wavelengths and drops to +3 for shorter waves, the directivity index curve must be revealed as the difference between the two (it makes up the difference to achieve the +6).
It has been beaten to death but we all enjoy jumping in each time it comes up. It is a subject of confusion for many, especially the novices. Perhaps we should have a sticky section for "fundamentals explained" (if we could ever agree on an explanation!).
I'll ask: "3rd integral of the superimposed pressure fields"?
David S.
When you say "becomes uncorrelated and we see only 3dB" I assume you mean in the spherically integrated field. The axial gain seems to be an exact +6 for all frequencies. Since axial gain is +6 but power gain starts at +6 for long wavelengths and drops to +3 for shorter waves, the directivity index curve must be revealed as the difference between the two (it makes up the difference to achieve the +6).
It has been beaten to death but we all enjoy jumping in each time it comes up. It is a subject of confusion for many, especially the novices. Perhaps we should have a sticky section for "fundamentals explained" (if we could ever agree on an explanation!).
I'll ask: "3rd integral of the superimposed pressure fields"?
David S.
Well thank you Speaker Doctor!
I'm at work testing a big pair of Christie 35k Lumen video projectors before we ship to China, but I hope to sneak away early and meet my wife for a nice dinner.
David S.
Hi John
I believe we are speaking of the same things but from a different vantage point.
While a typical ‘hifi” sized driver is so far down the radiation slope it is possible to ignore with a mathematical expedient, it is still present.
In a larger system one can see a change in the resistive part of the impedance when one goes from one to say four radiators / enclosures.
That change caused by the change in the acoustic load, same as a horn. Mutual coupling causes one driver to “feel” another if they are acoustically close.
From my perspective, this is identical to how a horn works to raise efficiency too, they are not a transformer btw, although they can appear to be one (the most common simplification) IF they are close to optimal at the driver and mouth ends.
If one considers what the theoretically optimum mouth size is and then examines the radiation resistance curve, one finds a related connection.
In the case of the direct radiators, the shape / packing factor limits the maximum actual efficiency to around 25% while with a horn, it is possible to have 50% or a bit more efficiency (over a narrower bandwidth).
In the case of the 50% efficient horn, that resistive acoustic load appears in series with and has an equal value of the resistive Rdc and the sum of all the mechanical losses, thus half the power radiated into space, half into electrical and mechanical heating.
Perhaps the reason so many get confused is that they forget acoustic power is like electrical power, it exists as the result of pressure AND velocity, like the electrical Voltage and Current or shaft power, the product of torque and RPM. Acoustic impedance being the relationship between the two components.
Not having a routine way of measuring both and accounting for phase angle(as Heyser wished to do), we only use the easier to measure pressure part of it with an assumption but pressure is not actually power no more than Voltage is..
Also too, there is more than one way to get an answer.
For example in a very large very reverberant room we place an acoustically small woofer playing a signal. After a time, the reverberant sound level in the room becomes asymptotic and we record the value.
We add a second identical woofer, driven identically but in a distant location. We now have twice the radiated power with two sources and the SPL raises 3dB.
Move the two close together (sources less than ¼ wl apart) and now the reverberant SPL raises 6dB over a single unit.
The same woofer set up outdoors also produces an SPL but now the inverse square law governs the SPL vs distance (while in the room it only did up close) .
Adding the second woofer at a distance from the other but the same distance to the microphone and you see the SPL rise 6dB. Move the two close together and the SPL doesn’t change appreciably at the same point but now one has an omni directional source radiating twice the acoustic power instead of an interference pattern of lobes and nulls.
The simpler approach gives the right number as an answer, but it doesn’t include how it works acoustically and i don't believe regular wave Superposition would predict the visibility of the acoustic resistive load in the drivers impedance resulting from mutual coupling.
Best,
Tom Danley
I believe we are speaking of the same things but from a different vantage point.
While a typical ‘hifi” sized driver is so far down the radiation slope it is possible to ignore with a mathematical expedient, it is still present.
In a larger system one can see a change in the resistive part of the impedance when one goes from one to say four radiators / enclosures.
That change caused by the change in the acoustic load, same as a horn. Mutual coupling causes one driver to “feel” another if they are acoustically close.
From my perspective, this is identical to how a horn works to raise efficiency too, they are not a transformer btw, although they can appear to be one (the most common simplification) IF they are close to optimal at the driver and mouth ends.
If one considers what the theoretically optimum mouth size is and then examines the radiation resistance curve, one finds a related connection.
In the case of the direct radiators, the shape / packing factor limits the maximum actual efficiency to around 25% while with a horn, it is possible to have 50% or a bit more efficiency (over a narrower bandwidth).
In the case of the 50% efficient horn, that resistive acoustic load appears in series with and has an equal value of the resistive Rdc and the sum of all the mechanical losses, thus half the power radiated into space, half into electrical and mechanical heating.
Perhaps the reason so many get confused is that they forget acoustic power is like electrical power, it exists as the result of pressure AND velocity, like the electrical Voltage and Current or shaft power, the product of torque and RPM. Acoustic impedance being the relationship between the two components.
Not having a routine way of measuring both and accounting for phase angle(as Heyser wished to do), we only use the easier to measure pressure part of it with an assumption but pressure is not actually power no more than Voltage is..
Also too, there is more than one way to get an answer.
For example in a very large very reverberant room we place an acoustically small woofer playing a signal. After a time, the reverberant sound level in the room becomes asymptotic and we record the value.
We add a second identical woofer, driven identically but in a distant location. We now have twice the radiated power with two sources and the SPL raises 3dB.
Move the two close together (sources less than ¼ wl apart) and now the reverberant SPL raises 6dB over a single unit.
The same woofer set up outdoors also produces an SPL but now the inverse square law governs the SPL vs distance (while in the room it only did up close) .
Adding the second woofer at a distance from the other but the same distance to the microphone and you see the SPL rise 6dB. Move the two close together and the SPL doesn’t change appreciably at the same point but now one has an omni directional source radiating twice the acoustic power instead of an interference pattern of lobes and nulls.
The simpler approach gives the right number as an answer, but it doesn’t include how it works acoustically and i don't believe regular wave Superposition would predict the visibility of the acoustic resistive load in the drivers impedance resulting from mutual coupling.
Best,
Tom Danley
huh... So as long as the sources are within 1/4 wavelength of a tone the wavefront couples efficiently and you get +6db. Once the frequency moves above the 1/4 spacing of the drivers the radiating wavefront is no longer coupled and forms comb patterns coupling 1/2 the energy of the lower frequencies thus +3db.
Say, drivers spaced 2.825' apart (1/4 WL of 100Hz) below 100Hz you get +6db gain above 100Hz you get 3db (averaged). Out doors of course, the wall interactions in a room make this much more complex.
Yes?
Say, drivers spaced 2.825' apart (1/4 WL of 100Hz) below 100Hz you get +6db gain above 100Hz you get 3db (averaged). Out doors of course, the wall interactions in a room make this much more complex.
Yes?
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