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matching amp&drivers, 4vs8 ohm

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jngggggggg View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jngggggggg Quote  Post ReplyReply Direct Link To This Post Posted: 12 February 2022 at 7:04pm
Originally posted by Elliot Thompson Elliot Thompson wrote:


This is why many have smaller systems (B, C, D Rig) to accommodate venues that offer such access limitations.  

Best Regards,

interestingly enough, i know people that are deploying this exact set up on 120v 15a service in my city. 3 sw152s in the same cabinet on the same amp specs i quoted without running into much issues for power interuptions. utilizing 4ohm version though - i'm the type of person who needs to understand a concept myself before committing, so i cant simply do what others are doing, hence me trying to understand 4 vs 8ohm (all else being equal)


Edited by jngggggggg - 12 February 2022 at 10:50pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jngggggggg Quote  Post ReplyReply Direct Link To This Post Posted: 12 February 2022 at 7:08pm
Originally posted by JonB67 JonB67 wrote:

Im surprised we dont see more guys on your side of the pond building for more efficient output? Everyone seems to be racing for bigger amps and drivers that suck up the most power. Cant be the best plan on limited supplies of electricity.

yeah, there definitely is a shortage of horn systems in Canada. hopefully trying to change that! 
that being said, festivals are a big part of the scene here in western canada and when you can rent generators, power doesn't become a limitation compared to small clubs
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 12 February 2022 at 9:00pm
Originally posted by jngggggggg jngggggggg wrote:

i think that we may be saying the same thing here, but just different? (you assume constant output voltage from the amp). in the example i had quoted below, if choosing 4ohm instead of 8ohm (less resistance and therefore more current demand) wouldn't one just lower the voltage output of the amp from 63v in this example to 45v rms to keep the total power dissipated the same at 500w average? 

That would make the 4ohm setup quieter than the 8ohm though. Loudspeaker drivers are also fundamentally a voltage responsive device, and if you dig into the specs you will see that 4ohm versions are in fact 3dB less sensitive than 8ohm versions. The power dissipated in a driver is secondary to it's functionality and this focus we have with big power numbers is misguided, in designing a system one should really aim for an amplifier with a very high output voltage swing and pair that with high impedance drivers to minimize the power dissipated. With this amp I'd actually suggest you buy 8ohm drivers and connect a pair to each channel wired in series at 16ohms, this means they would only disipate 1000w each but they would generate the same SPL as 4ohm drivers getting 2000w each.. and the AC current supply requirement is 1/2 as much. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jngggggggg Quote  Post ReplyReply Direct Link To This Post Posted: 12 February 2022 at 10:43pm
i see your argument here but the numbers tell me otherwise? 

4ohm spec sheet says 2.00Vrms produces 96dB
if fed 45Vrms, this equates to 96+27=123dB

8ohm spec sheet says 2.83Vrms produces 96dB
if fed 63Vrms, this equates to 96+27=123dB


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Elliot Thompson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 13 February 2022 at 9:15am
Originally posted by jngggggggg jngggggggg wrote:

Originally posted by Elliot Thompson Elliot Thompson wrote:


This is why many have smaller systems (B, C, D Rig) to accommodate venues that offer such access limitations.  

Best Regards,

interestingly enough, i know people that are deploying this exact set up on 120v 15a service in my city. 3 sw152s in the same cabinet on the same amp specs i quoted without running into much issues for power interuptions. utilizing 4ohm version though - i'm the type of person who needs to understand a concept myself before committing, so i cant simply do what others are doing, hence me trying to understand 4 vs 8ohm (all else being equal)

Not knowing how much voltage loss is occurring due to not having any means of metering monitoring the AC voltage is the reason you will find some individuals doing such things. They may think the amplifier is offering optimum performance on a 15 A 120-volt circuit but it is not.



https://ohmslawcalculator.com/ohms-law-calculator


Best Regards,


Edited by Elliot Thompson - 13 February 2022 at 9:32am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 13 February 2022 at 4:37pm
Originally posted by jngggggggg jngggggggg wrote:

i see your argument here but the numbers tell me otherwise? 

4ohm spec sheet says 2.00Vrms produces 96dB
if fed 45Vrms, this equates to 96+27=123dB

8ohm spec sheet says 2.83Vrms produces 96dB
if fed 63Vrms, this equates to 96+27=123dB

OK that is quite interesting but then this is a high end speaker manufacturer so stands to reason they are on the ball regarding specs.

This doesn't help your dilemma as to how to operate this amp most effectively on an badly undersized AC source, if it has effective self protection built-in it will throttle output when it encounters a situation where it can't produce any more output but it would be better to plan ahead rather than just wing it. 

The standard way to connect speakers to an amp is in parallel but that drives up current demand and you don't have much to play with. If you chose 4ohm drivers then you will never be able to connect more than 2 per channel in parallel, where as if you chose 8ohm you could potentially connect up to 4 per channel. In parallel all drivers see the full voltage swing available and therefore the maximum power available. You could use a combination of series/parallel wiring but that requires an even number of drivers to get equal power and therefore equal output from each one, the only way to get equal output with an odd number of drivers is with them all in parallel. 
If you series connect drivers then the voltage swing and therefore power is divided between them, but every time the number of drivers is doubled you get 3dB gain in SPL due to increases in acoustic efficiency that come from a doubling of cone area. So for example if there is only 2000w available because of AC source current limiting, then 2 drivers sharing that power will be 3dB louder than a single that consumes it all.
I have to assume you want to be able to fully utilize the output potential of this amplifier at some point when the conditions allow it, there is no point buying it if it has to be limited to something well below it's full output all the time. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jngggggggg Quote  Post ReplyReply Direct Link To This Post Posted: 20 February 2022 at 10:56pm
Originally posted by Conanski Conanski wrote:

This doesn't help your dilemma as to how to operate this amp most effectively on an badly undersized AC source, if it has effective self protection built-in it will throttle output when it encounters a situation where it can't produce any more output but it would be better to plan ahead rather than just wing it. 

when this throttling occurs, how does one know if the internal power supply of the amplifier will hit its voltage limit first, or current limit first? i suppose reaching voltage limitations (usually caused by increasing level sensitivity on the amp itself) results in clipping while reaching the amplifiers's current limitations (from too many loads in parallel) results in overheating?


Originally posted by Conanski Conanski wrote:

If you chose 4ohm drivers then you will never be able to connect more than 2 per channel in parallel, where as if you chose 8ohm you could potentially connect up to 4 per channel. 

i dont think there would ever be a situation where i would connect anymore than 2 drivers in parallel per channel (4 drivers total per amp) given that in my unique situation:
1. 120v 15a rail limitations in majority of venues
2. even if i found a venue with 240v 20a service, the power specs of the amp at 2,4,8ohm don't seem to support anymore than 2 subs per channel if i wanted to provide sufficient headroom on the amp (~2x driver's continuous power rating or 4000w per driver); irregardless of whether i choose 4 or 8ohm speakers.


Originally posted by Conanski Conanski wrote:


If you series connect drivers then the voltage swing and therefore power is divided between them, but every time the number of drivers is doubled you get 3dB gain in SPL due to increases in acoustic efficiency that come from a doubling of cone area. So for example if there is only 2000w available because of AC source current limiting, then 2 drivers sharing that power will be 3dB louder than a single that consumes it all.
I have to assume you want to be able to fully utilize the output potential of this amplifier at some point when the conditions allow it, there is no point buying it if it has to be limited to something well below it's full output all the time. 

when i initially chose this amp, the plan was to either load it with 2 or 3 subs depending on rail limitations and # of independent receptacles available which was why i made this thread.

isn't it incorrect to now use this 15a x 120v =1800w continuous power rating of the rails in this argument? i thought that power at rails doesn't equate to power driving the loads?
or should i assume that if the total combined *continuous* power demand of the loads together are greater than 1800w, then i will most definitely exceed the rail limits and blow the breaker? this intuitively makes sense as i presume the amplifier's power capacitance bank supports peak demand and not this continuous power demand.

i ran some quick numbers and if i was feeding 1000w to one 4ohm speaker, the load would require 63vrms, 16a and result in 126db sensitivity. if i fed 1000w to two 4ohm speakers in series (500 + 500w), the current goes down to 11a, but voltage increases to 90vrms. the sensitivity per driver is 123db in comparison; but are we saying that there is an additional 6db of gain or 129db total (3db from the second driver, and 3db from coupling assuming that the cabinets are deployed side by side). am i understanding this correctly?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 21 February 2022 at 3:00am
Originally posted by jngggggggg jngggggggg wrote:

when this throttling occurs, how does one know if the internal power supply of the amplifier will hit its voltage limit first, or current limit first?
You won't know but it's likely going to be current limiting first. If the amp has some smart DSP it will protect itself before a breaker trips or something blows up, of not it's anybodys guess what will happen. 

Originally posted by jngggggggg jngggggggg wrote:

i dont think there would ever be a situation where i would connect anymore than 2 drivers in parallel per channel (4 drivers total per amp) given that in my unique situation:
1. 120v 15a rail limitations in majority of venues
2. even if i found a venue with 240v 20a service, the power specs of the amp at 2,4,8ohm don't seem to support anymore than 2 subs per channel if i wanted to provide sufficient headroom on the amp (~2x driver's continuous power rating or 4000w per driver); irregardless of whether i choose 4 or 8ohm speakers.
If you never have anything better than single 120v circuits to use then this amp and these big drivers are not a good choice, because a single circuit won't even fully power a single driver.  So how do the other guys make it work? Whether they realize it or not they are not fully powering the drivers. 

Originally posted by jngggggggg jngggggggg wrote:

when i initially chose this amp, the plan was to either load it with 2 or 3 subs depending on rail limitations and # of independent receptacles available which was why i made this thread.
Your terminology is confusing, when you say "Rail" are you referring to the AC supply voltage or the amplifiers internal voltage rails?

Originally posted by jngggggggg jngggggggg wrote:

isn't it incorrect to now use this 15a x 120v =1800w continuous power rating of the rails in this argument? i thought that power at rails doesn't equate to power driving the loads?
It doesn't because music isn't a continuous never ending sine wave so power doesn't translate 1:1 between sides.

Originally posted by jngggggggg jngggggggg wrote:

i ran some quick numbers and if i was feeding 1000w to one 4ohm speaker, the load would require 63vrms, 16a and result in 126db sensitivity.
Wrong term again here, speaker sensitivity does not change, but the SPL generated does with voltage applied. The 16A part would be a peak as well, the actual continuous current would be much lower... it depends entirely on the music being amplified. 

Originally posted by jngggggggg jngggggggg wrote:

if i fed 1000w to two 4ohm speakers in series (500 + 500w), the current goes down to 11a, but voltage increases to 90vrms. the sensitivity per driver is 123db in comparison; but are we saying that there is an additional 6db of gain or 129db total (3db from the second driver, and 3db from coupling assuming that the cabinets are deployed side by side). am i understanding this correctly?
Nope.Wink You only gain 3dB from adding the second driver if the total power dissipated doesn't change. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jngggggggg Quote  Post ReplyReply Direct Link To This Post Posted: 22 February 2022 at 4:31am
Originally posted by Conanski Conanski wrote:

If you never have anything better than single 120v circuits to use then this amp and these big drivers are not a good choice, because a single circuit won't even fully power a single driver.  So how do the other guys make it work? Whether they realize it or not they are not fully powering the drivers.
 
perhaps the true nominal impedence of the cabinet+driver combination is quite a bit more than the driver's nominal 4ohms; so the amp is seeing a much higher impedence?  

Originally posted by Conanski Conanski wrote:

Your terminology is confusing, when you say "Rail" are you referring to the AC supply voltage or the amplifiers internal voltage rails?
 
Yes, as in 120v 15a AC supply

Originally posted by Conanski Conanski wrote:

Originally posted by jngggggggg jngggggggg wrote:

isn't it incorrect to now use this 15a x 120v =1800w continuous power rating of the rails in this argument? i thought that power at rails doesn't equate to power driving the loads?
It doesn't because music isn't a continuous never ending sine wave so power doesn't translate 1:1 between sides.
hmm ok but if i am discussing in 'continuous or average power terms' - if the speaker load's continuous power demand was >2000w, that would certainly trip the breaker? it seemed like that was implied by your comment "for example if there is only 2000w available because of AC source current limiting"

Originally posted by Conanski Conanski wrote:

Originally posted by jngggggggg jngggggggg wrote:

if i fed 1000w to two 4ohm speakers in series (500 + 500w), the current goes down to 11a, but voltage increases to 90vrms. the sensitivity per driver is 123db in comparison; but are we saying that there is an additional 6db of gain or 129db total (3db from the second driver, and 3db from coupling assuming that the cabinets are deployed side by side). am i understanding this correctly?
Nope.Wink You only gain 3dB from adding the second driver if the total power dissipated doesn't change. 
if thats the case, i don't see the benefit of two 4ohm drivers in series (500+500w) over one 4ohm driver (1000w) as the total SPL generated appear to be the same here.
unless there is a specific benefit of the dual series drivers consuming less current in exchange for more  voltage when thinking about ac power limitations


Edited by jngggggggg - 22 February 2022 at 4:34am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 22 February 2022 at 10:37am
Originally posted by jngggggggg jngggggggg wrote:

hmm ok but if i am discussing in 'continuous or average power terms' - if the speaker load's continuous power demand was >2000w, that would certainly trip the breaker? it seemed like that was implied by your comment "for example if there is only 2000w available because of AC source current limiting"


A K30 operating @ 4 ohms per channel, both channels driven, from a continuous average standpoint, will consume 56.6 amperes from a 120-volt line source. You need to come to the realization that 15 A, 120-volt circuit is aimed for the home consumer market. Either you step up and get a distro in order feed the amplifier 208 – 240 volts or, step down and buy an amplifier that will operate with no issues on a 15 amp, 120 – volt line source.


There is no “What if” in this scenario. The breaker is designed to protect the wire enclosed in the wall from overheating. You have no control under the given circumstances and will encounter tripping the breaker if you try to operate the K30, K35 and/or, AD 42 on a 120-volt 15 Amp circuit.


There is a reason Canadian & US amplifier manufactures do not offer amplifiers offering the output power that the K30, K35 and/or AD42 delivers.


Best Regards,




Elliot Thompson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 23 February 2022 at 12:10am
Originally posted by jngggggggg jngggggggg wrote:

perhaps the true nominal impedence of the cabinet+driver combination is quite a bit more than the driver's nominal 4ohms; so the amp is seeing a much higher impedence? 
That is a possibility.

Originally posted by jngggggggg jngggggggg wrote:

but if i am discussing in 'continuous or average power terms' - if the speaker load's continuous power demand was >2000w, that would certainly trip the breaker?
Yes likely but it's because 2000w of continuous audio implies 6000w peaks or more. There is some unofficial peak current supply capacity available from that 15A circuit but I doubt you could get that much. You could likely get 3000w peak though. 

Originally posted by jngggggggg jngggggggg wrote:

it seemed like that was implied by your comment "for example if there is only 2000w available because of AC source current limiting"
I just picked the 2000w number to make the numbers easy.

Originally posted by jngggggggg jngggggggg wrote:

  i don't see the benefit of two 4ohm drivers in series (500+500w) over one 4ohm driver (1000w) as the total SPL generated appear to be the same here.
No... the pair is 3dB louder.




Edited by Conanski - 23 February 2022 at 12:12am
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