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Who knows about audio equipment?

ghaleon

TRIBE Member
I need your help setting up some bass cabinets.

My power amp is putting out 300-400 watts at 8 ohms, 575-480 watts at 4 ohms (in stereo mode)

One channel is hooked up to a 4x10 cab that will handle up to 550 watts at 8 ohms (this is fine)

Now comes the tricky part: for the other channel, I have one 18' woofer that will handle 250 watts at 8ohms, and one 2x15' cabinet, each 15' handles 125 watts at 8 ohms.

How do I setup the other channel with the 2 latter cabinets? They are cheap speakers, and honestly I just want to be able to hear sound coming through them. Any suggestions? Connect them in SERIES or PARALLEL? The 2x15 cab has an input, and an output....so maybe I could run cable from the 2x15, then out to the 18'? Will this then add the wattage handling together? But will it also add the impdence together as well?

Thanks for your help in advance,

-Ryan
 

Syntax Error

Well-Known TRIBEr
when you connect impedances in series you add them, this will give you less power than you would get by connecting in parallel. however if you connect them all in parallel, the impedance will be too low and your amp will catch on fire. i think series is the only option if you're only using one channel for the 3 speakers.
 

labRat

TRIBE Member
buy another amp. or just rent a Sanyo boombox with AM/FM radio and cassette.

otherwise, running it in series would work. parallel will most likely blow the amp as the impedance may be too low.
 

SENSEi

TRIBE Promoter
Can someone explain impedance?

If you have 2 outs on your amp, L & R and you run wires out of that, 2 per side into 4 speakers, is that in series or parallel?

Does this make sense?
Basically running 4 speaker off of 2 outputs.

The speakers are not wired to each other, just the amp.

I've always assumed that's the way to do it.
What's the alternative and what would be the point?
 
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Syntax Error

Well-Known TRIBEr
Originally posted by SENSEi
Can someone explain impedance?

If you have 2 outs on your amp, L & R and you run wires out of that, 2 per side into 4 speakers, is that in series or parallel?

Does this make sense?
Basically running 4 speaker off of 2 outputs.

The speakers are not wired to each other, just the amp.

I've always assumed that's the way to do it.
What's the alternative and what would be the point?
what your talking about would be in parallel. the amp probably wouldn't be able to handle all four 8 Ohm speakers that way since the output connections on the amp are probably in parallel and that would make the total impedance 2 Ohms.

most cabinets have two inputs/outputs on them, if you run one cable from the amp to one input and then another cable from that speaker to another cabinet that would be in series. if two cabinets are connected to each channel this way the total impedance would be 8 Ohms which is totally acceptable. keep ion mind that i'm assuming that the two outputs on the amp are in parallel, i have no idea if that's really the case.
 

SENSEi

TRIBE Promoter
Originally posted by Syntax Error
what your talking about would be in parallel. the amp probably wouldn't be able to handle all four 8 Ohm speakers that way since the output connections on the amp are probably in parallel and that would make the total impedance 2 Ohms.

most cabinets have two inputs/outputs on them, if you run one cable from the amp to one input and then another cable from that speaker to another cabinet that would be in series. if two cabinets are connected to each channel this way the total impedance would be 8 Ohms which is totally acceptable. keep ion mind that i'm assuming that the two outputs on the amp are in parallel, i have no idea if that's really the case.
I have a QSC amp.
450 watts @ 8 ohms.
900 @ 4 ohms think.
Rack style.

I have:
2 Cervin Vega 12 inch 3 ways - I think they are 250 watts each, maybe more 2 Circle 5 studio monitors which are 8 inch I believe.

Lately my amp fan has been coming on a fair bit.
Are you saying that I'm running the risk of blowing the amp?

I can't see any other way of wiring up my speakers.
Are you saying run L R to one set of speakers, then run wires from the speakers to the other set of speakers?

That makes a big difference?

I understand series, as far as electrical wiring.
I guess I just need to understand the whole ohms resitance thing.
 

Humanjava

TRIBE Member
Before you get into anything you should say if you are running a passive crossover network between the two cabinets?
You can not just run two separate speaker systems off each other with out a proper crossover for the reason of impedances, polarity,etc.
For example If they are different speakers and they say they have a written impedance of four ohms (just for argument sake) then you will still have deviations from that. When ever a speaker or driver/transducer is given a rating it is an average. Combine two four ohm speakers in one manner you now have an average of 2 ohms that can fluctuate down to .5ohms even or as low as 16 ohms. With the other cabinet say its two speakers with 8 ohm loads combined to run at four ohms….With out a proper crossover there is a gross mismatch between the two systems. If they are not crossed over then you will have one set of speakers pulling the other… This can get really complicated easily but I am trying to make it simple.
To often ppl don’t understand the science of what is happening.

If you need more info just ask.
 

Humanjava

TRIBE Member
Originally posted by Syntax Error
what your talking about would be in parallel. the amp probably wouldn't be able to handle all four 8 Ohm speakers that way since the output connections on the amp are probably in parallel and that would make the total impedance 2 Ohms.

most cabinets have two inputs/outputs on them, if you run one cable from the amp to one input and then another cable from that speaker to another cabinet that would be in series. if two cabinets are connected to each channel this way the total impedance would be 8 Ohms which is totally acceptable. keep ion mind that i'm assuming that the two outputs on the amp are in parallel, i have no idea if that's really the case.
Just for the record most integrated amps run stuff in series...
Very few amps can run a continous load at 2 0hms as an average because you still have to take into account reactive loads caused from the speakers pushing current back at the amplifier and the cross over phase fluctuations..
 

Mike Richards

TRIBE Member
Originally posted by SENSEi
I have a QSC amp.
450 watts @ 8 ohms.
900 @ 4 ohms think.
Rack style.

You should be fine running it all in parallel just cross down your signal to the subs and if possible give your amp it's own Electrical circuit. What model is the amp? Just curious. An impedance is resistance measured in ohms. Everything that runs of any kind of electrical signal has impedance.
 
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SENSEi

TRIBE Promoter
Originally posted by Mike Richards
You should be fine running it all in parallel just cross down your signal to the subs and if possible give your amp it's own Electrical circuit. What model is the amp? Just curious. An impedance is resistance measured in ohms. Everything that runs of any kind of electrical signal has impedance.
Parallel meaning 4 wires out of the amp to the 2 sets of speakers?

So is the heat issue just a matter of load?
My amp is about 8 or 9 years old.

It's a 2 U, 450 watts @ 8 ohms I believe.

Would it matter if 1 set of speakers was 8 ohms and 1 set was 4?
I don't believe they are, I'm just wondering.

Arn't home speakers 8, while car are usually 4?

What kind of problems can you have if the ohms are not right?
 

Humanjava

TRIBE Member
Originally posted by SENSEi
Parallel meaning 4 wires out of the amp to the 2 sets of speakers?

So is the heat issue just a matter of load?
My amp is about 8 or 9 years old.

It's a 2 U, 450 watts @ 8 ohms I believe.

Would it matter if 1 set of speakers was 8 ohms and 1 set was 4?
I don't believe they are, I'm just wondering.

Arn't home speakers 8, while car are usually 4?

What kind of problems can you have if the ohms are not right?
What kind of problems can you have you ask. Well how is a fire or a fried amp for starts on the more severe side or lack of bass and volume on the less severe side.

As I think I mentioned before the way you hook it up also matters. Saying that you are running 4 wires out of the amp with both positives going to positive ends on the speakers is a parallel connection. In this scenario you would if both speakers are four ohms would have a 2 ohm circuit for (average impedance). This is only the average and depending on various factors such as load (Cabinet Pressure) or just the natural deviation of impedance at various SPL ( Sound Pressure Levels) this could change. This usually is most evident in Bass Speakers.

Again I will stress that two four ohm speakers if they are not identical can have vary different impedances.
 

ghaleon

TRIBE Member
my 2x15 cabinet has speakers that are both 8 ohms, and I have discovered they are connected in parallel. so this means that the cabinet in total has a 4 ohms impedence?

If I connect the other 8ohm 18' cab (in series), then that makes a total of 12 ohms? correct?

Is my amp going to have trouble driving that? It's not rated for 12 ohms, it only has power ratings for 8 ohms.

Also, what would the total wattage handling be here? For my 2x15 cab, each speaker handles 125 watts.... so whats the total handling of that cabinet? When I add the other speaker rated for 250 watts, do I add that to the total or what?
 

Humanjava

TRIBE Member
Originally posted by ghaleon
my 2x15 cabinet has speakers that are both 8 ohms, and I have discovered they are connected in parallel. so this means that the cabinet in total has a 4 ohms impedence?

If I connect the other 8ohm 18' cab (in series), then that makes a total of 12 ohms? correct?

Is my amp going to have trouble driving that? It's not rated for 12 ohms, it only has power ratings for 8 ohms.

Also, what would the total wattage handling be here? For my 2x15 cab, each speaker handles 125 watts.... so whats the total handling of that cabinet? When I add the other speaker rated for 250 watts, do I add that to the total or what?

Yes it does make a total of 12 ohms, but you have a problem now. First you are not running a crossover so the speakers will work at different speeds and as i mentioned before one set will end up pushing or pulling the other. Think of it like a tandem bike with two riders. If you have two riders one being substancialy stronger then the one rider may actually find the other to be more of a bother than a help as he or she is pulling extra weight. Also if both speakers cabs are 8 just for the sake of argument unless they are identical and matched pairs you would still be facing a similar problem because this is just an average rating. Its like saying each person is 120lbs. As we know there are many different body strength and shapes.


I would not get hung up on watts vs speakers. I have had a Carver power amp that was 750 watts per channel that could not even come close to my 60 watts a channel Audio Research tube amps I am now using.

You really need a crossover to do this correctly. I also stress that you need the crossover to be designed correctly.

Just for the record though if you are running one cabinet off one channel of the amp and the other on the next channel it will have less of a factor than having two per channel. But why run big speakers if they are not crossedover in the first place? They won't produce bass.
 

RhesusMonkey

TRIBE Member
I like Science!!!

Just a nerdy interlude:
Impedance is the term applied to a 'complex' resistance (link).
Z = R + iX where Z is the impedance, R is the resistance and X is the reactance. If you have a DC source, then all you measure is resistance (eg: like in a resistor), for any device however that stores energy (like a capacitor or inductor) you have to take into account the change in inductance due to changing phase and frequency of your AC source.

Series inductance follows the rules of Z = (R1+R2)+i(X1+X2), which means that inductive loads wired in series produce an equivalent inductive load greater than either of the individual loads.

Parallel inductance follows the rules of Z = 1/{(1/R1+1/R2)+i(1/X1+1/X2)}, which means that inductive loads wired in parallel produce an equivalent inductive load less than either of the individual loads.

Since sound waves are produced by your driver moving forwards and backwards in its cage, you require an AC source to produce the changing magnetic fields that move the driver forwards and backwards. This means that the drivers have an inductive load, and that it changes based on the frequency and phase of the source (eg: your music).

The purpose of a crossover circuit is to break up the frequency range of the source into discrete intervals that drive specific loads, as well as to balance the phase of the drivers. EG: so you don't send a 16kHz tone through your 15" subs, or worse send a 200Hz tone through your 1" tweets. Other scenarios would be say sending the same 200Hz signal to two 15" subs in the same cabinet, but have one driver be out of phase with the other by about 10 degrees... Mmmm... warbly...

Now, your power load is P = (V**2)/Z, so if your impedance (Z) drops down really low, your voltage (V) stays more or less the same, and your power consumption jumps up. This power is dissipated by your driver into sound energy, heat energy and motion, based on your driver's efficiency. Usually speakers in cabinets have a pretty low efficiency (heat to motion), and a pretty high power rating. If you run them in excess of their power rating you run the risks of: a) melting the voice coil, b) tearing the surround or spider cone(s), both of which more or less turn your driver into a fancy magnetized paper weight.
 
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Humanjava

TRIBE Member
That stuff is correct but not absolute. Crossovers play huge factors in impedances. Also The cab itself does. Cable can to a certain degree but not usually as much. But if you have ever set up hug sound rigs in say the 400K plus range you learn not to have any cable coil up or overlap to much because they act like a resistor and can heat up and cause a fire.

If you look at say an electrostatic speaker not a dynamic which are often known to have impedance curves in the .5 to 1 ohm load you will see why good solid state amps are preffered over tube amps. Simple reason and this ties into what you just kinda went over is they may dip down to these loads within certain freq ranges. What does this mean to the normal person you ask?
Well it means that you may loose or grossly have dips in sound in these areas of sound. So say it dips to 2 ohms through 1.5 Khz to 5Khz but has a nomanal impedance of 8-16 ohms through out the rest of its playing range. If you ran your standard tube or solid state amp that has say 400 watts of power but can not go down to these loads you would have a loss of sound energy in this area or a similar effect to using and eq and turning it down in this range. On the other hand you could run a 60 watt calss A amp that can do a .5 ohm load it would seem to have more accurate and extended freq through the same speakers.

Go listen to a pair of mini monitors like the size of little dyna audio or something similar with one amp of the same power out put then go listen to it with an amp that can do the dip so to speak and it will be two different speakers sounds all together.
 
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