Jim, they will be in phase and at equal levels if the mic is half way between them.
10x is for power, 20x is for pressure.
I think we are talking past each other... or there are several discussions going on at the same time.
Planet 10 asked if 3 woofers in parallel gives a 9.77 dB increase in sensitivity. I was answering that: 3 drivers is 3x the radiated power and 3 times the surface area, 20Log(3) = 9.542 ... I should have left "watts" out of it.
DonVK explained it well in posts 3 and 6.
Planet 10 asked if 3 woofers in parallel gives a 9.77 dB increase in sensitivity. I was answering that: 3 drivers is 3x the radiated power and 3 times the surface area, 20Log(3) = 9.542 ... I should have left "watts" out of it.
DonVK explained it well in posts 3 and 6.
They will be in phase and at equal levels if the mic is half way between them.
From this earlier
..and yes, there is more going on in the bigger picture, however I was talking pressure. I was hoping to get your take on the importance of 1/4 wavelength, as I think it's a broad consideration that really requires qualifying.AllenB said:
Allen -
For the situation of multiple woofers in a single box, I am confident the normal rules apply. The multiple woofers at bass frequencies will act in concert as a single point source.
Spread apart in a room, with a mic located halfway between? In theory it makes sense that the sound waves will add constructively at the mic location. It makes sense we would see a + 6 dB gain (after accounting for loss due to distance). But room modes can be complicated, so I am not really sure what happens. Will we normally get the full 6 dB of gain in most rooms? Are the room modes so complicated that the reality will rarely match theory? I am just not sure...
j.
For the situation of multiple woofers in a single box, I am confident the normal rules apply. The multiple woofers at bass frequencies will act in concert as a single point source.
Spread apart in a room, with a mic located halfway between? In theory it makes sense that the sound waves will add constructively at the mic location. It makes sense we would see a + 6 dB gain (after accounting for loss due to distance). But room modes can be complicated, so I am not really sure what happens. Will we normally get the full 6 dB of gain in most rooms? Are the room modes so complicated that the reality will rarely match theory? I am just not sure...
j.
i have a feeling mutual coupling does not really exist. It is the term for 2 drivers within a quarter wavelength acting as if they are a single driver. Move them far enuff apart and they start to un-mutual.
Boundary reinforcement is very heavily dependent on th eroom and room construction.
dave
I'm inclined to see where you're coming from. Some have described it in spatial terms as you just have. However in the strictest sense, while a suggests b, b is not necessarily a.
At a distance you also see +6dB, and at this point you're out of the drivers' near-field. This is unlike mutual coupling with antennas, or with inductors.
Normal circuit analysis rules apply, so two woofers in series have twice the resistance and twice the inductance. For parallel it is half the resistance and half the inductance.
4 drivers in series will have no change in sensitivity (+ 0 dB/V). The impedance will be 4X a single driver, and the efficiency will be +6 dB/W.
4 drivers in parallel will have +12 dB/V increase in sensitivity, +6 dB/W increase in efficiency, and the impedance will be 1/4x that of a single driver.
Now imagine putting 4 of these 4-driver-series arrays in parallel... A 16 driver series-parallel system. The impedance will be the same as a single driver. Sensitivity will be 12 dB higher than a single driver. Efficiency will be 12 dB higher than a single driver. Max SPL capability will be 24 dB higher than a single driver.
You are right that energy can not magically appear, but a loudspeaker transducer is a very low efficiency device, about 0.5% to 1.5% efficiency. By increasing the number of drivers we are increasing surface area, and this leads to an increase in efficiency. Double the surface area leads to double the efficiency... This can make is seem like energy is magically appearing.
j.
As long as the drivers centre-to-centre is a quarter wavelength of less the 2 woofers will act as a single woofer.
dave
thanks I seem to continue to mix sensitivity per voltage and efficiency per watt.
so by using 16 (or 2^4) drivers with assumed 1% efficiency each i can theoretically achieve a 10log(2^4) sensitivity (4% or 4/1 ratio) = +12dB or (efficiency?) with the same amp load and 1/16 of the movement on each driver hence 16x power handling and therefore 12dB sensitivity + 12dB additional power handling = +24dB max SPL.
Wow, it makes sense now thanks I just realized what to do for my next subwoofer. also great to revisit old calculus.
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Thanks for answering. I do realize that it is nearing off-topic territory for the OP, but I am still just starting out in understanding speaker technicalities and have been reading in sub woofer threads references to the positives of low Le.
Seeing the OP was investigating possibilities for series connection, I wondered where inductance sits on the list of pros and cons.
Radiation impedance per area of a piston in a baffle is (linearly) related to the diameter of the piston (big wavelengths compared to piston size). As radiation impedance is directly related to efficiency of such a piston, you may derive from this that any bigger cone area will be more efficient than smaller ones. So: more acoustic Watts per electric Watt. Now this changes when cone dimensions come close to wavelengths. The radiation impedance changes to proportional to the cone area. And so does the efficiency.
So much for acoustic theory in a nutshell...
So much for acoustic theory in a nutshell...
op here.
2 in series, basically as loud as 1 driver but double impedance, ty.
Maybe a mtm, 15' listening distance I think I can get away with 10" mtm crossing at 2khz.
But a tmm would help with floor bounce, while getting away from a point source.
I've had luck with b102 (10" with whizzer) run wide open and a morel cat378 slid back a couple of inchs.
I have a b102 and 4 morels sitting.
Maybe next project in 3-6 months...…………………...
2 in series, basically as loud as 1 driver but double impedance, ty.
Maybe a mtm, 15' listening distance I think I can get away with 10" mtm crossing at 2khz.
But a tmm would help with floor bounce, while getting away from a point source.
I've had luck with b102 (10" with whizzer) run wide open and a morel cat378 slid back a couple of inchs.
I have a b102 and 4 morels sitting.
Maybe next project in 3-6 months...…………………...
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I think you need to take a step back when deciding between these two approaches (mtm/tmm). Define your directivity needs first by considering your own reflection problems, then see if you can get either design to work for you.
The potential trends that you've indicated tend to happen over a small band, meaning that they can't just be considered on the basis of how they perform in isolation. Instead you also may have to consider how much of an interruption, or compromise they represent to the whole performance, as well as where in frequency you best want any effects to happen.
The potential trends that you've indicated tend to happen over a small band, meaning that they can't just be considered on the basis of how they perform in isolation. Instead you also may have to consider how much of an interruption, or compromise they represent to the whole performance, as well as where in frequency you best want any effects to happen.
I think....Sensitivity is irrelevant to the whole scenario unless power is of concern.
The only thing worth talking about is efficiency and induction...
Both parallel and series will have the same efficiency (excursion) from the woofers...
Parallel- "Low Le leads to a flatter impedance at higher frequencies."
Series- Amplifiers operate cleaner at higher impedance, looking at thd.
TMM you can't do this nearfield unless you crossover the bottom woofer lower like me in my design. bottom woofer interaction with the crossover further causes beaming on the vertical axis....
MTM is pretty cool I think...theoretically, in my brain...one midrange is better than two when excursion isn't an issue, I'd like to hear other comment on that...obviously no one hates mtm midrange.
From my studies IIRC MTM actually beams more on the vertical axis than TMW....MTM vs TMW, I think TMW wins....TMW then MTM then TMM.... in regards to vertical polar performance.
The only thing worth talking about is efficiency and induction...
Both parallel and series will have the same efficiency (excursion) from the woofers...
Parallel- "Low Le leads to a flatter impedance at higher frequencies."
Series- Amplifiers operate cleaner at higher impedance, looking at thd.
TMM you can't do this nearfield unless you crossover the bottom woofer lower like me in my design. bottom woofer interaction with the crossover further causes beaming on the vertical axis....
MTM is pretty cool I think...theoretically, in my brain...one midrange is better than two when excursion isn't an issue, I'd like to hear other comment on that...obviously no one hates mtm midrange.
From my studies IIRC MTM actually beams more on the vertical axis than TMW....MTM vs TMW, I think TMW wins....TMW then MTM then TMM.... in regards to vertical polar performance.
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You'd be surprised on a tmm.
I had the morel solstice tmm kit, crossing 1,750hz.
double 6" crossing to dome tweet (with a bit of flange also).
Technically with frames, I'd call the double 6" as a 13" driver (vert dispersion), certainly a no no for 1750hz crossover.
Sounded lovely at 7', sit and stand.
But yes, a 10" 2 way is a weird beast, crossing higher than the 10" would like, let alone this tmm vs mtm idea (6db time/phase aligned with offset tweeter), they would sound different, let alone 7' away versus 15' away I bet.
I had the morel solstice tmm kit, crossing 1,750hz.
double 6" crossing to dome tweet (with a bit of flange also).
Technically with frames, I'd call the double 6" as a 13" driver (vert dispersion), certainly a no no for 1750hz crossover.
Sounded lovely at 7', sit and stand.
But yes, a 10" 2 way is a weird beast, crossing higher than the 10" would like, let alone this tmm vs mtm idea (6db time/phase aligned with offset tweeter), they would sound different, let alone 7' away versus 15' away I bet.
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This is a lovely mess.
Have you considered the change in loudspeaker parameters when going from having the terminals shorted to having another loudspeaker hooked to it in series. The resonant frequency and Q will change, and then your box will be wrong. If you are designing your enclosure with series speakers in mind, then I guess you will be all right, but I can't help but think your bass will be a little undamped.
Putting speakers in parallel puts a heavier load on the amp, but that is the amplifier's job.
Have you considered the change in loudspeaker parameters when going from having the terminals shorted to having another loudspeaker hooked to it in series. The resonant frequency and Q will change, and then your box will be wrong. If you are designing your enclosure with series speakers in mind, then I guess you will be all right, but I can't help but think your bass will be a little undamped.
Putting speakers in parallel puts a heavier load on the amp, but that is the amplifier's job.
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