Hello,
I am considering building some PA speakers for my band- I want them to be able to hit 130dB rms @ 1m (really!!) becuase we play outside alot and it is important to have plenty of power to spare-
So- what I am wondeing is how multiple drivers effect max SPL-
I did search and found some articals but I am a bit confused as to how this effects max spl-
So each doubling of speakers that are mounted in the same cabinet = 2 times the effeciency (3dB) due to acoustic coupling right-
So one 90 dB @ 1W driver would be 96dB @ 1W with 4 drivers- No matter how they are wired (is that correct)?
So if I could find speakers that were 90dB sensitive with a 16 ohm VC and 100w power handling. if i had 4 of them in a cabinet then I would get a 6dB gain in sensitivity, a 2 ohm load and a 12dB gain from the parralel wireing? And then each speaker can handle 4 times the wattage so I would need an amp that was stable for 1600W at 2 ohms- OR is the 12dB part the component of going from 400w @ 16 to 1600w @ 2??
So then how do I calculate max spl from here- for each doubling of electric power I get an additional 3dB right? so 1024W = 30dB louder acoustically- so my setup here might be 31.5 (ish)- So is it
A. 90 + 6 + 12 + 31.5 = 139.5dB spl max (this seems unlikly to me, essentially the 12dB is being added twice right??)
or
B. 90 + 6 + 31.5 = 127.5 (This seems like the more likely option)
and to make sure I understand the difference between the wireing options is it- with just two speakers now-
Parrallel = with the same amp I get 2 times the output (6dB) assuming that the amp is stable at half the impedance.
Series = same possible max SPL but requires 4 times the wattage at the same impedance??
So with my (theroretical) drivers above the two different setups would have the potential to produce the same max SPL but- (again just with 2 speakers per cab) the parrallel version would require a amp that would put out 400w at 8 Ohms to reach the max spl-
the series setup would require an amp that was 1600w at 8 ohms (and then 400 at 32 if they were wired in series) to produce the same acoustic level.
Am I on the right track here?? I am trying to find 4 10" drivers that are 16 ohm- designed for ported applications and can handle at least 100w and are about 93dB sensitive to reach my 130dB goal- any ideas- thanks,
Ryan
I am considering building some PA speakers for my band- I want them to be able to hit 130dB rms @ 1m (really!!) becuase we play outside alot and it is important to have plenty of power to spare-
So- what I am wondeing is how multiple drivers effect max SPL-
I did search and found some articals but I am a bit confused as to how this effects max spl-
So each doubling of speakers that are mounted in the same cabinet = 2 times the effeciency (3dB) due to acoustic coupling right-
So one 90 dB @ 1W driver would be 96dB @ 1W with 4 drivers- No matter how they are wired (is that correct)?
So if I could find speakers that were 90dB sensitive with a 16 ohm VC and 100w power handling. if i had 4 of them in a cabinet then I would get a 6dB gain in sensitivity, a 2 ohm load and a 12dB gain from the parralel wireing? And then each speaker can handle 4 times the wattage so I would need an amp that was stable for 1600W at 2 ohms- OR is the 12dB part the component of going from 400w @ 16 to 1600w @ 2??
So then how do I calculate max spl from here- for each doubling of electric power I get an additional 3dB right? so 1024W = 30dB louder acoustically- so my setup here might be 31.5 (ish)- So is it
A. 90 + 6 + 12 + 31.5 = 139.5dB spl max (this seems unlikly to me, essentially the 12dB is being added twice right??)
or
B. 90 + 6 + 31.5 = 127.5 (This seems like the more likely option)
and to make sure I understand the difference between the wireing options is it- with just two speakers now-
Parrallel = with the same amp I get 2 times the output (6dB) assuming that the amp is stable at half the impedance.
Series = same possible max SPL but requires 4 times the wattage at the same impedance??
So with my (theroretical) drivers above the two different setups would have the potential to produce the same max SPL but- (again just with 2 speakers per cab) the parrallel version would require a amp that would put out 400w at 8 Ohms to reach the max spl-
the series setup would require an amp that was 1600w at 8 ohms (and then 400 at 32 if they were wired in series) to produce the same acoustic level.
Am I on the right track here?? I am trying to find 4 10" drivers that are 16 ohm- designed for ported applications and can handle at least 100w and are about 93dB sensitive to reach my 130dB goal- any ideas- thanks,
Ryan
RyanC said:
Yes (with certain limitations).
Yes, if each driver gets 1/4W.
You have, say, one speaker with 96dB and 400W nominal power. This is 96+26=126 dB/1m maximum.
16/4 is 4 not 2; 12dB gain-really?! I don't think so
No. One speaker can handle only 100W, irrespective of what you do with it.
Don't mess with parallel/serial combinations if you want a stable and reliable system. Use an active crossover, 4 amps with 500W/8ohm, three of them for bass boxes with 95 to 97dB/m, fourth for midle-high horns. IMO
10" drivers are too small for this job.
You may find "Sound Reinforcement Handbook" useful (by Gary Davis and Ralph Jones).
Regards
Milan
Put simple:
Each doubling of the number of drivers will give you +6 dB max output level. Period.
So if one driver can give you 120 dB, four drivers could give you 132 dB.
For the electrical connection; each driver should receive the same amount of power (and voltage and current) as in the single driver case. This can be arranged either by separate amplifiers, or by different serial/parallel configurations and a more powerful amplifier.
And, finally, the above only holds for low frequencies (=long wavelengths compared to the driver distance) or straight in front of the speakers.
Each doubling of the number of drivers will give you +6 dB max output level. Period.
So if one driver can give you 120 dB, four drivers could give you 132 dB.
For the electrical connection; each driver should receive the same amount of power (and voltage and current) as in the single driver case. This can be arranged either by separate amplifiers, or by different serial/parallel configurations and a more powerful amplifier.
And, finally, the above only holds for low frequencies (=long wavelengths compared to the driver distance) or straight in front of the speakers.
Some PA designs: www.speakerplans.com
The forum is good too, and there are links to other sites with plans.
The forum is good too, and there are links to other sites with plans.
Use a vertical line array. Eminence Beta 10s with a sensitivity of 98 dB can get to 118dB with 100 watts in; forget about more than that per driver because power compression will eat up most of the additional power input.
Two in parallel will give 124dB with 200 watts in, and the 4 ohm impedance is OK. To get the next 6dB requires two more drivers and 200 more watts, and the impedance at 2 ohms gets dicey, but if your amp is OK for 400 watts at 2 ohms you're OK. If not use the 16 ohm version.
If you can afford them go with 8 drivers in a vertical array; this will allow each driver to loaf with little power input and the overall sound will be much cleaner.
Beta 10s are quite comfortable down to 50Hz; an OEM version of the same driver is used in the Ampeg SVT, so don't let anyone tell you they won't handle bass.
Two in parallel will give 124dB with 200 watts in, and the 4 ohm impedance is OK. To get the next 6dB requires two more drivers and 200 more watts, and the impedance at 2 ohms gets dicey, but if your amp is OK for 400 watts at 2 ohms you're OK. If not use the 16 ohm version.
If you can afford them go with 8 drivers in a vertical array; this will allow each driver to loaf with little power input and the overall sound will be much cleaner.
Beta 10s are quite comfortable down to 50Hz; an OEM version of the same driver is used in the Ampeg SVT, so don't let anyone tell you they won't handle bass.
Thanks guys-
Bill:
That is exactly what I was thinking- What about even the emanence b102 with the wizzer- then a selenium horn on top- I could care less about that 18" horn loaded subwoofer sound myself. All 50hz all day long, no thanks.
The b102 requires a smaller chamber (wich is what I am going for here) and is about at sensitive as the betas with a little more xmax and it would provide redicoulous amount of overlap with a horn- wich is good for experimentablity-
I would not be able to fit more than two cabs with 4 10"s in each and a horn in my car so that is about as big as I could go-
I know the b102 is designed for bass guitar but whenever I have used a bass cab as a makeshift PA (for smaller gigs) it sounded really good. I recently barrowed my friends eden cab powered with a mackie amp and was at a gig where 2 of the gypsy kings showed up and jammed with us- For one little cab running vocals, guitar, and keys (with left hand bass) it really blew me away (in a 3000sf room with 30ft high cielings).
Anyway the one thing that is confusing me is the parrallel wireing beyond two coils- So 4 16ohm speakers in parrallel = 4 ohms or 2? I can get an amp that is stable at 2 but certainly 8 or 4 is safer- if I go series parrallel with 4 drivers then you end up right where you started impedance wise right? And the powerhandling and max spl is the same?
the thing with the 10b is this: http://www.usspeaker.com/BETA10B-1.htm
it is only 98db sensative at 4k- about 92 everywhere else.
the b102 on the other hand hovers right around 100 throughout and I will probably go with a behringer DCX as the XO so I can have all those extras (the multiband peak lims and compressors and the dynamic EQ would be cool for keeping the 2-5k region from getting too painful at high SPL's up close). . .Anyway any thoughts on the b102's?? Thanks again guys-
Ryan
Bill:
That is exactly what I was thinking- What about even the emanence b102 with the wizzer- then a selenium horn on top- I could care less about that 18" horn loaded subwoofer sound myself. All 50hz all day long, no thanks.
The b102 requires a smaller chamber (wich is what I am going for here) and is about at sensitive as the betas with a little more xmax and it would provide redicoulous amount of overlap with a horn- wich is good for experimentablity-
I would not be able to fit more than two cabs with 4 10"s in each and a horn in my car so that is about as big as I could go-
I know the b102 is designed for bass guitar but whenever I have used a bass cab as a makeshift PA (for smaller gigs) it sounded really good. I recently barrowed my friends eden cab powered with a mackie amp and was at a gig where 2 of the gypsy kings showed up and jammed with us- For one little cab running vocals, guitar, and keys (with left hand bass) it really blew me away (in a 3000sf room with 30ft high cielings).
Anyway the one thing that is confusing me is the parrallel wireing beyond two coils- So 4 16ohm speakers in parrallel = 4 ohms or 2? I can get an amp that is stable at 2 but certainly 8 or 4 is safer- if I go series parrallel with 4 drivers then you end up right where you started impedance wise right? And the powerhandling and max spl is the same?
the thing with the 10b is this: http://www.usspeaker.com/BETA10B-1.htm
it is only 98db sensative at 4k- about 92 everywhere else.
the b102 on the other hand hovers right around 100 throughout and I will probably go with a behringer DCX as the XO so I can have all those extras (the multiband peak lims and compressors and the dynamic EQ would be cool for keeping the 2-5k region from getting too painful at high SPL's up close). . .Anyway any thoughts on the b102's?? Thanks again guys-
Ryan
The whizzer cones of the individual drivers would be too far apart for proper integration of the point sources into a single coherent cylindrical wavefront, and that will lead to comb-filtering, so I wouldn't use the B102. There's no point in building a line array that comb-filters; avoiding comb-filtering is one of the reasons you go with a vertical array and never with horizontally arrayed drivers/speakers.
I wouldn't go the single horn on top. Overlap of the ranges, by the way, is a bad thing; avoid it. The Eminence is very good to at least 3.5 kHz, so I'd match them with CTS 1167A bullets. Use two per woofer, vertically arrayed to one side of the woofers, mounted frame to frame and as close to the woofers as you can get them. Have the tweeter array start as close to the top of the box as you can. Wire each pair in parallel, each pair in parallel with one woofer; where the woofers end up going series with each other so will the CTS.
The reason for the tweeter array as opposed to a single unit is you'll get far better horizontal versus vertical dispersion; no need to serenade either ceilings, floors, birds or worms. If you want to you can go with as many tweeters as will fit on the baffle, three per woofer, still wire the same way.
For four woofs the best idea is go with 8 ohm drivers, wired as two sets of parallel pairs in series for an 8 ohm load. Then if you build more boxes later you can stack and parallel two and still be at 4 ohms; when you do that have the tweeter banks meet in the middle if they're not full length. You'll lose some sensitivity over a 2 ohm load but it's a more logical way to go and with a powerful enough amp you'll still get your 130dB output.
I wouldn't go the single horn on top. Overlap of the ranges, by the way, is a bad thing; avoid it. The Eminence is very good to at least 3.5 kHz, so I'd match them with CTS 1167A bullets. Use two per woofer, vertically arrayed to one side of the woofers, mounted frame to frame and as close to the woofers as you can get them. Have the tweeter array start as close to the top of the box as you can. Wire each pair in parallel, each pair in parallel with one woofer; where the woofers end up going series with each other so will the CTS.
The reason for the tweeter array as opposed to a single unit is you'll get far better horizontal versus vertical dispersion; no need to serenade either ceilings, floors, birds or worms. If you want to you can go with as many tweeters as will fit on the baffle, three per woofer, still wire the same way.
For four woofs the best idea is go with 8 ohm drivers, wired as two sets of parallel pairs in series for an 8 ohm load. Then if you build more boxes later you can stack and parallel two and still be at 4 ohms; when you do that have the tweeter banks meet in the middle if they're not full length. You'll lose some sensitivity over a 2 ohm load but it's a more logical way to go and with a powerful enough amp you'll still get your 130dB output.
Svante said:
BillFitzmaurice said:
On SPLs...
"As a general rule, for each doubling of the cluster size, the SPL along the composite main axis of the cluster will increase by between 3dB and the theoretical maximum of 6 dB. The exact level of increase depends on the efficiency of addition among the cabinets and the directivity of the cluster, both of which are functions of specific types of loudspeakers used. We can start making SPL estimations using the worst case figure of 3dB, and take any extra SPL that we may realize as a gift - of headroom." G. Davis, R. Jones "Sound Reinforcement Handbook" (Yamaha) page 351
"Assume that a point source of sound has a level of 94dB SPL at a given distance. Now, let us add another point source with the same 94dB level, again at the same distance. What will be the resulting sum of the two? Since both sounds are individually of the same level, their acoustical powers will be equal, and we will effectively be doubling that power when both are sounded together. This represents an increase of 3dB, making a resultant level of 97 dB."
J. Eargle, C. Foreman "Audio Engineering for Sound Reinforcement" (JBL) page 14
EMINENCE BETA-10 is listed as a bass guitar speaker (and vocal PA!!!). This is very different from main cluster LF transducers. Also, I haven't seen any JBL 10" PA speakers listed as LF. All of them are middle transducers.
Once again, using 10" speaker in PA for LF may be possible (doesn't make any sense, though) by placing drivers in horns, as in your design(?) that was published in aX, but this is just an exception that confirms the general rule. IMO
All serious PA systems (from 1 to 50kW) I have ever seen (or took part in their construction) are built with minimum 12" drivers for low frequency.
Regards
Milan
Cool:
Bill- I am not planning on leaving the overlap- I am thinking about an active system. I like the Behringer DCX alot (I have one for my DIY studio monitors) So I will probably go with that, especially because it also offers EQ's and multiband Comps and Lims-
Are you talking about using those bullets un-crossed over? Or do you at least wire a cap in there for a little protection?
good to know about the wizzer being a problem though-
The problem with the beta 10 is that it is only 98dB sensitive at 4k! the rest is more like 93-95. Not too bad but. . .
MOAmps-
I understand what you are saying here but- I don't need that type of bass- I want bass amp type bass, not 2 horn loaded 18"ers type bass. I don't really like that sound unless it is used just right, typically when I go to local venues I wish they would turn the subs down!! At least for bands, they sound great for electronic kinds of music and experimental subwoofer concerts. But it is just embarrising when you are on stage, trying to rip a solo and all the crowd can hear is the kick drum and bass guitar.
We do our gigs with no sound guy, we just walk around from time to time and make sure things are pretty good. I am just looking for a system that sounds good enough and has the trade off that it will fit in my car.
Also our bass player is way too busy (not necessarrily in a bad way) for boomy type bass sound- It has to be tight and clean, not huge and round.
Right now we do not run the bass through the PA. And his amp with 4 8" drivers provides the type of sound that fits his playing and our group. I only need that, with more clean power, anything more would pretty much require a full time sound guy.
Anyway the short of what I am saying is that I would be perfectly happy with no reproduction below 45hz, and this would make a fine f6 point for my system.
All that said what about the deltalite 10" . In WinISD it models to produce as much bass as the JBL 2206h that you are talking about. Anyone have any experience with these drivers? thanks again,
Ryan
Bill- I am not planning on leaving the overlap- I am thinking about an active system. I like the Behringer DCX alot (I have one for my DIY studio monitors) So I will probably go with that, especially because it also offers EQ's and multiband Comps and Lims-
Are you talking about using those bullets un-crossed over? Or do you at least wire a cap in there for a little protection?
good to know about the wizzer being a problem though-
The problem with the beta 10 is that it is only 98dB sensitive at 4k! the rest is more like 93-95. Not too bad but. . .
MOAmps-
I understand what you are saying here but- I don't need that type of bass- I want bass amp type bass, not 2 horn loaded 18"ers type bass. I don't really like that sound unless it is used just right, typically when I go to local venues I wish they would turn the subs down!! At least for bands, they sound great for electronic kinds of music and experimental subwoofer concerts. But it is just embarrising when you are on stage, trying to rip a solo and all the crowd can hear is the kick drum and bass guitar.
We do our gigs with no sound guy, we just walk around from time to time and make sure things are pretty good. I am just looking for a system that sounds good enough and has the trade off that it will fit in my car.
Also our bass player is way too busy (not necessarrily in a bad way) for boomy type bass sound- It has to be tight and clean, not huge and round.
Right now we do not run the bass through the PA. And his amp with 4 8" drivers provides the type of sound that fits his playing and our group. I only need that, with more clean power, anything more would pretty much require a full time sound guy.
Anyway the short of what I am saying is that I would be perfectly happy with no reproduction below 45hz, and this would make a fine f6 point for my system.
All that said what about the deltalite 10" . In WinISD it models to produce as much bass as the JBL 2206h that you are talking about. Anyone have any experience with these drivers? thanks again,
Ryan
Post #10
Cool:
Bill- I am not planning on leaving the overlap- I am thinking about an active system. I like the Behringer DCX alot (I have one for my DIY studio monitors) So I will probably go with that, especially because it also offers EQ's and multiband Comps and Lims-
Are you talking about using those bullets un-crossed over? Or do you at least wire a cap in there for a little protection?
good to know about the wizzer being a problem though-
The problem with the beta 10 is that it is only 98dB sensitive at 4k! the rest is more like 93-95. Not too bad but. . .
Those CTS drivers don't need a crossover, and being capacitive in nature take practically no power to drive, so I wouldn't bother with biamping. If you use a comparable dynamic tweeter array then biamping is wise, but beyond the cost of the extra amp the tweeters would also cost twice as much. Still use the DCX for it's other features, including running a high-pass at 50 Hz.
You can use other drivers that will run more sensitive but they don't come cheap. This is one case where the extra watts are cheaper to come by with a bigger amp rather than more sensitive drivers. If sensitivity is a real concern then you really need to go horn loaded and get it up to 105dB/watt and better, and that's not something to consider unless you really know your way around a workshop.
Cool:
Bill- I am not planning on leaving the overlap- I am thinking about an active system. I like the Behringer DCX alot (I have one for my DIY studio monitors) So I will probably go with that, especially because it also offers EQ's and multiband Comps and Lims-
Are you talking about using those bullets un-crossed over? Or do you at least wire a cap in there for a little protection?
good to know about the wizzer being a problem though-
The problem with the beta 10 is that it is only 98dB sensitive at 4k! the rest is more like 93-95. Not too bad but. . .
Those CTS drivers don't need a crossover, and being capacitive in nature take practically no power to drive, so I wouldn't bother with biamping. If you use a comparable dynamic tweeter array then biamping is wise, but beyond the cost of the extra amp the tweeters would also cost twice as much. Still use the DCX for it's other features, including running a high-pass at 50 Hz.
You can use other drivers that will run more sensitive but they don't come cheap. This is one case where the extra watts are cheaper to come by with a bigger amp rather than more sensitive drivers. If sensitivity is a real concern then you really need to go horn loaded and get it up to 105dB/watt and better, and that's not something to consider unless you really know your way around a workshop.
moamps said:
This is why I said:
svante said:
PA systems rarely have the drivers mounted close (acoustically) to each other, and special things apply when in the close field of a line array.
moamps said:
Is this text taken out of context? It will hold for the case when the speakers are placed in the reverberant field of a room and the frequency is high. Otherwise (free field or low frequencies), this is simply wrong. He speaks about the theoretical case (point source, same distance), and the result in the theoretical case is + 6 dB (except for the room case).
Svante,
Mutual coupling between drivers, in principle, does not contribute 3dB to the total SPL gain in the entire low-frequency range. This contribution in the case of speakers that are set apart only 0.5 m disappears at a frequency exceeding 200Hz. Besides, this gain is not noticeable by all listeners positioned in front of the speakers Also, mutual coupling between drivers in combination with mutual coupling between an LF system and adjacent surfaces can cause considerable non-linearity in the frequency characteristic of the system, and consequently lead to some heavy-duty equaliser adjustment. So, taking useful gain of 6dB for granted does not seem a particularly advisable line of thinking because this gain is neither uniform across the LF range nor does it always improve the quality of a system.
Electro-voice TL550D Low-Frequency Speaker System
"At relatively low frequencies, below about 150 Hz for typical TL series dimensions, stacking produces additional acoustic output without altering dispersion. When a common signal is applied, a 6-dB increase in maximum acoustic output occurs. The cones “mutually couple” and act as one cone with twice the area (therefore twice the efficiency) and twice the power capacity. The additional cone area provides 3 dB more output and the additional power capacity accounts for the remaining 3 dB.
Specifically, mutual coupling occurs at frequencies whose wavelengths are longer than one-quarter the center-to-center distance between the cones. The highest frequency at which mutual coupling occurs is calculated from the following equation:
f =3000/Dmax
where DMAX (inches) is the distance between the cones, and f (Hz) is the highest frequency at which coupling occurs. When DMAX is greater than one-quarter wavelength, which would occur if two TL550D’s were widely spaced, or at frequencies much above f even when closely spaced, the increase in acoustic output is limited to the 3-dB power-handling increase."
"To calculate the added SPL provided by multiple loudspeakers aimed at one group of listeners, use this equation:
La=10 log N
where:
La is the additional level in dB relative to a single loudspeaker
N is the number of loudspeakers pointed at the same group listeners
(Note: When a listener is precisely the same distance from two identical loudspeakers, the added level can be as high as 6 dB- but this may be true only over a very narrow listening angle)"
J. Eargle, C. Foreman "Audio Engineering for Sound Reinforcement" (JBL) page 261
Signals
f1(t)=Vo sin(w1t) and f2(t)=Vo sin(w1t +fi) are correlated but the gain is not 6dB.
What special things? I'm dying to know.
Milan
Mutual coupling between drivers, in principle, does not contribute 3dB to the total SPL gain in the entire low-frequency range. This contribution in the case of speakers that are set apart only 0.5 m disappears at a frequency exceeding 200Hz. Besides, this gain is not noticeable by all listeners positioned in front of the speakers Also, mutual coupling between drivers in combination with mutual coupling between an LF system and adjacent surfaces can cause considerable non-linearity in the frequency characteristic of the system, and consequently lead to some heavy-duty equaliser adjustment. So, taking useful gain of 6dB for granted does not seem a particularly advisable line of thinking because this gain is neither uniform across the LF range nor does it always improve the quality of a system.
Electro-voice TL550D Low-Frequency Speaker System
"At relatively low frequencies, below about 150 Hz for typical TL series dimensions, stacking produces additional acoustic output without altering dispersion. When a common signal is applied, a 6-dB increase in maximum acoustic output occurs. The cones “mutually couple” and act as one cone with twice the area (therefore twice the efficiency) and twice the power capacity. The additional cone area provides 3 dB more output and the additional power capacity accounts for the remaining 3 dB.
Specifically, mutual coupling occurs at frequencies whose wavelengths are longer than one-quarter the center-to-center distance between the cones. The highest frequency at which mutual coupling occurs is calculated from the following equation:
f =3000/Dmax
where DMAX (inches) is the distance between the cones, and f (Hz) is the highest frequency at which coupling occurs. When DMAX is greater than one-quarter wavelength, which would occur if two TL550D’s were widely spaced, or at frequencies much above f even when closely spaced, the increase in acoustic output is limited to the 3-dB power-handling increase."
"To calculate the added SPL provided by multiple loudspeakers aimed at one group of listeners, use this equation:
La=10 log N
where:
La is the additional level in dB relative to a single loudspeaker
N is the number of loudspeakers pointed at the same group listeners
(Note: When a listener is precisely the same distance from two identical loudspeakers, the added level can be as high as 6 dB- but this may be true only over a very narrow listening angle)"
J. Eargle, C. Foreman "Audio Engineering for Sound Reinforcement" (JBL) page 261
Signals
f1(t)=Vo sin(w1t) and f2(t)=Vo sin(w1t +fi) are correlated but the gain is not 6dB.
What special things? I'm dying to know.
Milan
Moamps: I think we have a problem with terminology. I have the engineers approach when I say "low frequency". If someone asks, what is low, my answer is "sufficiently low, depending on how close to the 6 dB you want to get".
Also, my background is not PA, but hifi, so a spacing of the drivers by 0.5 m is pretty far apart in my world.
Anyway drifting away from the "ideal" case that I describe, in terms of frequency vs wavelength, it is not even sure that there is a 3 dB gain. On average over frequencies or directions, yes, but at some frequencies/directions there will be destructive interference, and again some will coincide to +6 dB.
quote (svante):
That example has two uncorrelated sources, and in that case the gain is +3dB. The loudspeakers produce exactly the same sound, and so the level gain is +6 dB.
quote (moamps):
Signals
f1(t)=Vo sin(w1t) and f2(t)=Vo sin(w1t +fi) are correlated but the gain is not 6dB.
Right, that is why I said "produce exactly the same sound" and not "produce correlated sound". Of course, my reasoning assumes identical distances to the speakers, and this only occurs at low frequencies (as in my definition) or straight in front of the speakers.
quote (svante):
PA systems rarely have the drivers mounted close (acoustically) to each other, and special things apply when in the close field of a line array.
quote (moamps):
What special things? I'm dying to know.
Well, as I said, I'm not the PA expert. But when in the close field of a line source, there is a spectral tilt of -3 dB / octave, if I remember correctly, and this has to be compensated for. Also, the level decreases by -3 dB per doubling of the distance, not -6dB as we are used to from the point source. These are things that the home hifi people like myself don't have to bother about. And of course, since the spacing between PA drivers is usually larger, the + 6 dB gain that we are discussing in this thread only applies for really low frequencies.
Also, my background is not PA, but hifi, so a spacing of the drivers by 0.5 m is pretty far apart in my world.
Anyway drifting away from the "ideal" case that I describe, in terms of frequency vs wavelength, it is not even sure that there is a 3 dB gain. On average over frequencies or directions, yes, but at some frequencies/directions there will be destructive interference, and again some will coincide to +6 dB.
quote (svante):
That example has two uncorrelated sources, and in that case the gain is +3dB. The loudspeakers produce exactly the same sound, and so the level gain is +6 dB.
quote (moamps):
Signals
f1(t)=Vo sin(w1t) and f2(t)=Vo sin(w1t +fi) are correlated but the gain is not 6dB.
Right, that is why I said "produce exactly the same sound" and not "produce correlated sound". Of course, my reasoning assumes identical distances to the speakers, and this only occurs at low frequencies (as in my definition) or straight in front of the speakers.
quote (svante):
PA systems rarely have the drivers mounted close (acoustically) to each other, and special things apply when in the close field of a line array.
quote (moamps):
What special things? I'm dying to know.
Well, as I said, I'm not the PA expert. But when in the close field of a line source, there is a spectral tilt of -3 dB / octave, if I remember correctly, and this has to be compensated for. Also, the level decreases by -3 dB per doubling of the distance, not -6dB as we are used to from the point source. These are things that the home hifi people like myself don't have to bother about. And of course, since the spacing between PA drivers is usually larger, the + 6 dB gain that we are discussing in this thread only applies for really low frequencies.
Svante said:
If LF(1) is a freq. range (within any limits you may wish to specify) of a given LF speaker system, then when two such systems are used, LF(2) is smaller than LF(1), and if four systems are used, LF(4) is smaller than LF(2). In other words, if you want our hypothetical LF system consisting of n individual systems to cover a given LFn range, then the upper frequency limit of each of these individual systems should be LFi>LFn. This is particularly important in any discussion on mutual coupling.
Well, this is a PA thread and you volunteered some advice... FYI, PA is not my background either but I think that anyone with a college/university degree in electrical engineering should know a thing or two about such things.
Two 18" PA drivers placed next to each other are 18" apart which, in the metric system, is almost 0.5m.
Sweet spot is just one spot amidst many others. You realize it's impossible to have the entire audience squeezed into the sweet spot, don't you? The gain in the field in front of a speaker is, depending on the angle, an average +3dB (including the comb filtering effect as well) IMO
This holds true only if you are standing in the near field area in front of the speaker. In the far field region, however, the level decreases by -6dB. The beginning of the far field area, in case of LF, is approximately f=l/pi, which for a 3m high array is only about 1m.
Anyways, as I don't think this discussion is of any particular interest to other DIYers, I do not see much point in pursuing it any further if that's alright with you.
Regards
Milan
I think your both smart inteligent men but are unable to see each other point of view for some reason?
You both make sense but are arguing of peanuts really, i think the orginal thread was just wanting advice on his idea for making his own PA speakers for his band?
Bill gave him simple understandable advice that am sure he has taken and applied by now but i think RyanC is rather humble and knows more about sound than he is letting on.
Shame on you RyanC for cosing a punch up
It was very interesting to read so thank you for such an interesting post with two smart giants of sound but its all debate able and we can agree to disagree but what we believe should not be forced on to anybody else regardless of who is more right or wrong.
There are no lifes at stake! skys wont fall, the world will not stop and the sun will rise tomorrow.
The only problem you 2 men have is communication! thats all.
You both make sense but are arguing of peanuts really, i think the orginal thread was just wanting advice on his idea for making his own PA speakers for his band?
Bill gave him simple understandable advice that am sure he has taken and applied by now but i think RyanC is rather humble and knows more about sound than he is letting on.
Shame on you RyanC for cosing a punch up
It was very interesting to read so thank you for such an interesting post with two smart giants of sound but its all debate able and we can agree to disagree but what we believe should not be forced on to anybody else regardless of who is more right or wrong.
There are no lifes at stake! skys wont fall, the world will not stop and the sun will rise tomorrow.
The only problem you 2 men have is communication! thats all.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.