Help with amps/volts/watts/sepakers. (Leland's Article)

Is this amp OK?
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byacey
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Re: Help with amps/volts/watts/sepakers. (Leland's Article)

#16 Post by byacey »

Is that a mosfet amp? I don't see as many emitter resistors as output devices. I like that they used full size components rather than surface mount; which makes it repairable vs a throw away device.

The conventional power supply is heavy to be sure, but also simple and reliable.
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Re: Help with amps/volts/watts/sepakers. (Leland's Article)

#17 Post by Grant Bunter »

Bas Gooiker wrote:I would advise noone to run all their cabs of one amp or amp channel. If one of your drivers dies in a series parralel configuration you will screw up the whole line.
That's a great point Bas, and not one I ever considered :)
Bas Gooiker wrote:My advise would be to get 2 smaller amps and run 2 cabs parallel per channel. With Lab 12's this would already give you a nominal 3ohm load.
Umm isn't a pair/channel 4 ohms? Lab 12 is nominally 6ohms, + 2 ohms for the cab = 8 for one cab, halved is 4.

Charles,
Technically speaking, you should be able to run 4 x 8ohm cabs in parallel per channel if the amp is rated to 2ohms, as that would be a 2 ohm load overall.
Running an amp to 2 ohms when it's 2 ohms capable though is taking the amp to the bleeding edge, and while it may be designed to do that, eventually something will give.
Ideally then, the thing to do is use 2 amps with 2 cabs/channel (4ohms/channel), with an amp
that is 2 ohms capable.

The only reason to get overly powered amps is because they are unbelievably priced in comparison to anything else in the market.
Since we brick wall limit, that eliminates head room, or the residual power capability above the voltage limit.
The Crown XLS 2500 is about bang on the money output wise for running lab12/3012lf loaded cabs. That should give you an idea of the output required...
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Bas Gooiker
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Re: Help with amps/volts/watts/sepakers. (Leland's Article)

#18 Post by Bas Gooiker »

Grant Bunter wrote:
Bas Gooiker wrote:I would advise noone to run all their cabs of one amp or amp channel. If one of your drivers dies in a series parralel configuration you will screw up the whole line.
That's a great point Bas, and not one I ever considered :)
Bas Gooiker wrote:My advise would be to get 2 smaller amps and run 2 cabs parallel per channel. With Lab 12's this would already give you a nominal 3ohm load.
Umm isn't a pair/channel 4 ohms? Lab 12 is nominally 6ohms, + 2 ohms for the cab = 8 for one cab, halved is 4.
I know this is very popular point of view on this forum which i feel no need to challenge today, but... If you stick a multimeter to a lab12 loaded cab you will measure a ~ 4.5 ohm load. And the amplifier might not be a member here so won't know about this +2 ohm rule. :wink:
Grant Bunter wrote:Charles,
Technically speaking, you should be able to run 4 x 8ohm cabs in parallel per channel if the amp is rated to 2ohms, as that would be a 2 ohm load overall.
Running an amp to 2 ohms when it's 2 ohms capable though is taking the amp to the bleeding edge, and while it may be designed to do that, eventually something will give.
Ideally then, the thing to do is use 2 amps with 2 cabs/channel (4ohms/channel), with an amp
that is 2 ohms capable..
+1
The damping factor of the amplifier, thus control over the motor of the driver, goes down with low impedance loads.
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Re: Help with amps/volts/watts/sepakers. (Leland's Article)

#19 Post by Grant Bunter »

Bas Gooiker wrote:I know this is very popular point of view on this forum which i feel no need to challenge today, but... If you stick a multimeter to a lab12 loaded cab you will measure a ~ 4.5 ohm load. And the amplifier might not be a member here so won't know about this +2 ohm rule. :wink:
Fair enough...
Built:
DR 250: x 2 melded array, 2x CD horn, March 2012 plans.
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Re: Help with amps/volts/watts/sepakers. (Leland's Article)

#20 Post by MissileCrisis »

The technical difference that he is missing is that the DC resistance of the lab 12 may be 4.5 but the AC impedance of the sub is 6 ohms (they use the same units for impedance and resistance). I wont mention the horn part because we all know about that. Regardless you'll notice that a 4 ohm nominal speaker wire measure about 3 ohms with a multimeter and a 6 ohm impedance speaker will measure approx 4.5 ohms as you've noticed. If you want to measure the impedance of a load you have to connect it to an impedance bridge (a different piece of equipment).
Reference : undergrad electrical engineer. Hope I was able to contribute something :).
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Re: Help with amps/volts/watts/sepakers. (Leland's Article)

#21 Post by Bill Fitzmaurice »

Bas Gooiker wrote: If you stick a multimeter to a lab12 loaded cab you will measure a ~ 4.5 ohm load.
If you stick a multimeter on a cab you will measure DC resistance, not impedance.
The damping factor of the amplifier, thus control over the motor of the driver, goes down with low impedance loads.
Damping factor is moot.
http://www.diyspeakers.net/Articles/Ric ... FACTOR.pdf

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Re: Help with amps/volts/watts/sepakers. (Leland's Article)

#22 Post by byacey »

The impedance of an inductor (voice coil) is the DC resistance of the coil plus the inductive reactance added together.

If you want to figure out the actual impedance of the driver in the cabinet, simply apply a known voltage, like a 1V RMS sine wave at 60 Hz to the cabinet, and measure the AC current with your handy digital multimeter. Use the formula Z=E/I
A 1 volt RMS signal across an 8 ohm load will yield 125ma. A 6 ohm load will have a current draw of .166ma, and a 4 ohm load will be 250ma.

Note: This is to find the nominal impedance of a sub. For a mid/hi box, you must use frequencies within the operating range of the box. If you take measurements at various different frequencies, it will be found the impedance varies considerably with frequency. Generally the cited impedance is an averaged value.

If you measure and document the impedance of the driver unloaded and tested free-air, and then make the same measurement loaded in the cabinet, you will prove or disprove the idea of cabinet loading increasing the overall impedance.
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Re: Help with amps/volts/watts/sepakers. (Leland's Article)

#23 Post by TheCesar »

Thank you for all the responses on this one.

I have another question:

I have 2 speakers, 8Ohms, 350 Watts each, according to the calculation if connected in series 16Ohms they should handle up to 100Volts (I'm rounding out) :oops:

If I follow the steps, get the 1k tone into my PA adjust the amp sensitivity to lets say 80 volts, wont the volts change at the time I plug both of the speakers to that amps Channel? or will it remain close to that?

Is it safe to use the voltmeter while the speakers are plugged in running music to the PA system?

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Re: Help with amps/volts/watts/sepakers. (Leland's Article)

#24 Post by byacey »

Voltage will drop a little; just ignore the difference and consider it an extra safety margin.
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Charles Jenkinson
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Re: Help with amps/volts/watts/sepakers. (Leland's Article)

#25 Post by Charles Jenkinson »

TheCesar wrote:Thank you for all the responses on this one.

I have another question:

(1) I have 2 speakers, 8Ohms, 350 Watts each, according to the calculation if connected in series 16Ohms they should handle up to 100Volts (I'm rounding out) :oops:

(2) If I follow the steps, get the 1k tone into my PA adjust the amp sensitivity to lets say 80 volts, wont the volts change at the time I plug both of the speakers to that amps Channel? or will it remain close to that?

(3) Is it safe to use the voltmeter while the speakers are plugged in running music to the PA system?
I've numbered your questions:
(1) What I'm hearing through this discussion is that is better to wire speakers in parallel, since it keeps max voltage down, then should one driver inadvertently fail, the other won't go pop too. If your speakers are properly limited (on voltage) subs and they have twin speakers wired in series then you will be at the higher voltage, yes. But I only see the sense in doing this if you have another 16 ohm cab and wire them in parallel to bring the total load back down to 8 ohms. There's been other discussions in other places on this forum about 'voltage swing' - can an amp actually produce the higher voltages required for the higher impedance load - something to consider. (A 16 ohm load is surely 'harder' to drive , i.e. the power needs to be there...? I've put this in brackets because I don't know for sure. If you look at amp ratings you see it all going the other way, from 8 ohm down to minimum 2 ohm loads, and different power ratings associated with each different impedance rating)

(2) I think byacey answered this, but overall, I haven't picked up whether you are talking about subs or tops...? Apol's.

(3) I would say yes, but if you're setting a sub limiter there is no need to do so, and overall people would advise you to set the limiter before running ANYTHING programme-material-wise to the speakers. The voltage is there without having anything connected up.

I haven't finished what I wanted to say to Grant. I appreciate this is your thread. May I continue here? I'm happy to go somewhere else and reference this thread.
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Re: Help with amps/volts/watts/sepakers. (Leland's Article)

#26 Post by TheCesar »

I haven't finished what I wanted to say to Grant. I appreciate this is your thread. May I continue here? I'm happy to go somewhere else and reference this thread.
Go for it, gives me an opportunity to keep learning. :D

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Re: Help with amps/volts/watts/sepakers. (Leland's Article)

#27 Post by Charles Jenkinson »

Thank you. Very kind. I referred elsewhere anyway, just to be safe, and because I'm back home now. My day job is major toss it off time at the moment, but when I get home there's worthy things to do. Something is going to have to change or I'll go mad. Too much forum is not good for me.
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Re: Help with amps/volts/watts/sepakers. (Leland's Article)

#28 Post by Radian »

TheCesar wrote:why is it that most websites and stores such as guitar center do not use this method. :conf:
Because at the end of the day it will get the average joe in the ball park. Close enough. :fingers:
TheCesar wrote:it does not see to hard to get a grasp of. :shock:
Well think about it this way, you are here asking about it. :idea:

The general misconception is that the electricity that powers our gear is a natural phenomenon that we gleefully model in math for the sheer heck of it, in order to confuse the piss out of everyone. It is not. We conceive it in the power plant, "distribute" it, and then put it into "use".

We craft and fine tune this "fuel" so that all the other gizmos tapping into it downstream will function usefully, as advertised, and without blowing up.

That being said, math is entirely what makes that possible. 120/240V is not simply sitting there awaiting at the socket by happenstance. Lemme repeat it again, Wall power is born entirely from math, not the other way around. It is an abomination of linear algebra.

So.....Know the math = know the electricity. :horse:

That'll keep you from being a slave to your own gear. :wink:
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Re: Help with amps/volts/watts/sepakers. (Leland's Article)

#29 Post by TheCesar »

So let me tell you what I have and tell me how you would power it up:
Behringer EP2500Stero
•1 kHz
•8ohm -500W per/Chan
•4ohm- 750W per/Chan
•2ohm-1200w per/Chan

Bridge mode
•1 kHz
•8ohm-1300w
•4ohm-2400w

2 Sub cabs
1 Black widow peavey 1801 on each cab
•8 Ohms
•1400 W Peak, 700 W Program, 350 W Continuous

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Re: Help with amps/volts/watts/sepakers. (Leland's Article)

#30 Post by Radian »

TheCesar wrote: and tell me how you would power it up:
I've learned what I've learned by spending an inordinate amount of time studying books, paying people a lot of money to teach me, and by 1st-hand experience putting it all to work in the real world.

Time for you to step up to the plate. No more freebies from me.

I'll give you the first clue: Figuring out your amp loading, is only a tiny fraction of the pie.

Learn exponents, so that logarithms, exponential functions, and hence the decibel will make sense to you. Otherwise they will own you...for the rest of your life. :evil:

If you need help, start with Kahnacademy on youtube.

Math seems like :bull: until you figure out that it's the only thing standing between you and pretty much the entire man-made world.
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