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OHM,s, Running Subs parrellel?


PRS MAN

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I have no clue what the OHM's or running subs parrellel means, im confused about all this, I want a bass amp that cuts through the feed of a band and sounds nice. I use a Warwick Rock Bass 5 String Streamer, NO distortion or effects, just high bass, non mids, and medium treble to give a deeper "thud" sound, but when i review on musicians friend i see "OHMs" can someone explain the OHM to me in normal language, I am studying to be a guitar tech, so i know guitar terms but i havent learned amp stuff yet

_____DISCIPLE_ROCKS_____

PAUL REED SMITH GUITARS 4 EVER

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An ohm is a unit of measurement. In the context you are referring to, it is a measure of impedance, the amount of difficulty a signal encounters going through a speaker.

 

Amplifiers are built to so that their output is intended to encounter a certain amount of impedance. It's like an auto engine is designed to encounter back pressure from a muffler. IF you remove that back pressure, the engine will run faster, but it will burn up. Amplifiers need that impedance to keep them from operating at too high a level and burning up.

 

When you run more than one speaker, they can be wired in series or parallel, or sometimes series/parallel. Now this is the part I sometimes get backwards, so guys, please correct me if I'm wrong. What I think I recall is that when you run 2 or more speakers of the same impedance in parallel, the impedance stays the same. So, two or more 8 ohm speakers running parallel still present an 8 ohm load to an amplifier.

 

However, if you run the same speakers in series, the impedance lowers. So if you run two 8 ohm speakers in series, they present a 4 ohm load to the amp.

 

The converse, presenting a higher impedance to the amp, will lower the amount of output from your amp, so it runs quieter. It won't hurt the amp, but it won't work up to it's optimum level.

 

Some amps will take more than one level of load, 16, 8, 4, or even 2 ohms. You want to be sure your amp will handle the load you present to it. You can run your amp into whatever speakers sound good to your ear, as long as you match the impedance to it.

Always remember that you�re unique. Just like everyone else.

 

 

 

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You've got it backwards again Picker!!!! :D

 

Firstly, almost all speaker cab connections from the cab to the amp are in parallel (often, in multi-speaker cabs, 4x10, 8x10, there will be combinations of parallel WITH serial connections - let's not get into that).

 

Let's start with 2 x cabs of 8 Ohms each.

 

Plug 1 in, impedence is 8 Ohms.

 

Plug 2 in, impedence is 4 Ohms.

 

Plug 3 in, impedence is 2.666... Ohms.

 

Plug 4 in, impedence is 2 Ohms.

 

It's like water going out a tank - the more escape routes you provide, the less resistance there is to the water escaping.

 

There's a formula:

 

1/R = 1/r + 1/r + 1/r...........

 

So for 2 cabs,

 

1/R = 1/8 + 1/8

1/R = 2/8

R/1 = 8/2

 

R = 4

 

For 3 Cabs,

 

1/R = 1/r + 1/r + 1/r

1/R = 1/8 + 1/8 + 1/8

1/R = 3/8

R/1 = 8/3

 

R = 2.666...

 

For other values, simply substitute.

 

For Resistances in series, simply add them together.

 

Hope this helps.

 

Geoff

"When the power of love overcomes the love of power the World will know Peace": Jimi Hendrix

http://www.soundclick.com/bands/default.cfm?bandID=738517&content=music

The Geoff - blame Caevan!!!

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It's OK to use a speaker with a higher impedence than the amp would ideally like - i.e. using a 16 Ohm cab with an amp set for 8 Ohms, as the extra resistance will simply cut down the power slightly (maybe not as much as some will tell you),

 

BUT

 

Don't use a speaker rated lower than your amp wants, or can be set to, otherwise there's not enough resistance, the output coil will run too hot, and then the Magic Smoke comes out, and once that's lost, it'll never work again!!! :D

 

Geoff

"When the power of love overcomes the love of power the World will know Peace": Jimi Hendrix

http://www.soundclick.com/bands/default.cfm?bandID=738517&content=music

The Geoff - blame Caevan!!!

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I want a bass amp that cuts through the feed of a band and sounds nice.
Don't we all. ;)
I use a Warwick Rock Bass 5 String Streamer, NO distortion or effects, just high bass, non mids, and medium treble to give a deeper "thud" sound
Sounds more like you want to "sit in the mix" instead of "cutting through". Leave room at the very bottom for the kick drum. Roll off your highs to leave room for the guitars. (If you don't have an EQ on your amp then maybe dial back the treble on your bass a bit; you've already got your mids all the way down.) Tell the guitarists you are playing with to cut their bass and not to use too much distortion. (Like they will ever listen, lol.) Seriously, though, the most likely reason you can't hear the bass is because of the guitars.

 

The attraction of a thuddy bass comes from the fact that it already has lows cut (4 string) and highs rolled off to better sit in the mix. In other words, the sound engineer doesn't need to EQ it. The often quoted formula for thud is a P bass with old flats on it (the older the better). Also, guitarists like a thuddy bass because it opens up more sonic space for them; too bad they rarely return the favor.

 

So shouldn't all bass players play a P with flats?

 

No. Either in the studio or live the engineer should be able to EQ the bass. If you're playing live and don't have FoH you should be able to EQ your amp and/or bass.

 

An even simpler way to create thud is with your fingers. If you pluck over the 12th fret you can reduce a lot of harmonics. (Use a soft pick -- rubber, felt, etc. -- if you don't play fingerstyle.)

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You've got it backwards again Picker!!!! :D

 

Thanx for the correction Geoff. Series keeps the same impedance, parallel lowers it.

 

Now, in series wiring a 4x10, the incoming + and - both got to the + and - lugs of one speaker, and the next speaker is hooked up to the second set of lugs off that lead speaker, and so on. Is that right?

Always remember that you�re unique. Just like everyone else.

 

 

 

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You've got it backwards again Picker!!!! :D

 

Thanx for the correction Geoff. Series keeps the same impedance, parallel lowers it.

 

Series adds the values together.

 

2 x 8 Ohm cabs in series would be 16 Ohms.

 

I've only ever seen one cab (& I'm 63) with a jack socket marked 'Series' and that was in addition to the standard double parallel outs. It was a VOX bass cab.

 

G.

"When the power of love overcomes the love of power the World will know Peace": Jimi Hendrix

http://www.soundclick.com/bands/default.cfm?bandID=738517&content=music

The Geoff - blame Caevan!!!

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...

 

This may help

 

That makes my eyes and brain hurt.

 

I think there is plenty of info on the web on how to wire up speakers in parallel or series and probably some pretty good drawings too.

 

The simple answer is that if you have an 8ohm and add another 8ohm you will go down to 4ohms. BUT If you have a 4ohm and want to add another 4ohm you may not be able to as your amp may not be capable of running at 2ohms.

 

When working with tube amps you have to match the impedance of the speaker to the amp.

When working with solid state amps you need to make sure you do not go below the minimum impedance or the amp will go into "thermal runaway" and as stated above - "release the blue smoke"

 

You are doing several things by adding another speaker.

1. An additional speaker will increase the volume purely because you are adding more cone area and will be able to move more air. This is assuming that your amp can push more power and the speakers can take it.

2. The additional speaker will further increase the volume if you place it next to the first speaker as it will be more efficient and 'help' the first speaker to move more air.

3. Also the additional speaker will present a lower load to the amplifier and allow it to work more efficiently which will also allow you to increase the volume.

 

 

Subs? A bass guitar speaker is NOT a sub. It is a large diameter full range speaker. The thump you hear is reliant on the mid range to define it. Without the midrange you will just get a woolly mess.

Feel the groove internally within your own creativity. - fingertalkin

 

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I think this is right,please correct me if im wrong. From what i understand, if i have a 4 ohm amp or head, and i try to run a single 8 ohm through it, my amp will burn up, if i have 8 ohm speakers running through a amp, it will work out fine?

_____DISCIPLE_ROCKS_____

PAUL REED SMITH GUITARS 4 EVER

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http://www.lennonstudios.com/ampeg4x10.jpg

 

This may help

 

I have an Ashdown 4x10 that I have been trying to figure out how to wire to get an 8 ohm load for a long time. Apparently, it came from the factory with four 16 ohm speakers wired to present a 4 ohm load. But, the guy I got it from had pulled all the OEM speakers out of and put in some 8 ohm speakers, two of which were messed up Bugeras(I got it really cheap). I replaced the Bugeras with two 8 ohm 100 watt speakers, but I'm not getting an 8 ohm load no mater how I hook it up.

 

The wiring harness in the cab has two black leads with two clip connectors on each, and two red leads, also with two clips on each. It also has a red and black lead hooked up to the horn driver, and what looks like a cap & coil filter, I'm assuming to keep the lows out of the horn.

 

I can't get the back panel with the inputs and horn attenuator off to check it out without a lot of yanking and unsoldering, so I haven't pulled it out. I've tried just using just one set of leads, going red into each speaker, then out from the black lead to the red lead on the next, etc and so on to the 4th speaker, which I hooked up to the black lead coming out of the input panel. I've also tried hooking one set of red & black leads each to 2 speakers. But either way, I get meter readings that fluctuate between 0 and 3 ohms. I can't seem to get a steady reading of any sort, and I can't seem to get 8 ohms regardless.

 

On your diagram, BB, I see there is a black lead that goes between a red lug on the lower right speaker and a black lead on the lower left speaker. DO you think the guy who messed up this cabinet left that lead out of the wiring? If I hook a lead that way on my cab, do you think I would get a steady reading on the meter?

Always remember that you�re unique. Just like everyone else.

 

 

 

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Assuming the above diagram has *ALL* 8 Ohm speakers, what you have is 2 seperate sides, wired in parallel - giving 4 Ohms.

 

The two sides are then linked in series - 4+4 = 8 Ohms in total.

 

PRS Man - you'r amp won't burn up if it is 4 Ohms minimum & you use an 8 Ohm cab - the cab just won't get full power, that's all, but it's safe.

 

If your amp is 4 Ohms minimum & were you to use a 2 Ohm cab, then that would be dangerous.

 

G.

"When the power of love overcomes the love of power the World will know Peace": Jimi Hendrix

http://www.soundclick.com/bands/default.cfm?bandID=738517&content=music

The Geoff - blame Caevan!!!

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I think this is right,please correct me if im wrong. From what i understand, if i have a 4 ohm amp or head, and i try to run a single 8 ohm through it, my amp will burn up, if i have 8 ohm speakers running through a amp, it will work out fine?

 

this is not correct.

 

the ohm rating on an amplifier is a description of what it *can do*. the ohm rating on a speaker cabinet is a description of what it *is*.

 

amplifiers source power into speaker cabinets. so you will never have "8 ohm speakers running through a amp." you could have "an amp running through 8 ohm speakers." this probably sounds a little silly as a distinction, but i think it is important for understanding the numbers. the amplifier sources power into the speaker cabinets.

 

the math was covered above. it's easier if you can do algebra. from a practical perspective, you will likely never have to worry about series v. parallel. it's good to know for your edification, but i've only ever seen one amplifier use a series wiring scheme, and that was a combo amp (i.e. an amplifier with a built-in speaker). generally any series wiring is reserved for internal work, like inside a loudspeaker. so all you really have to remember is that when using two speaker cabinets they will be in parallel, and the ohms will be halved (two 8 ohm cabinets will be 4 ohms; two 4 ohm cabinets will be 2 ohms).

 

unless you are using a tube amplifier, you will always be safe using a cabinet that is ohms rated at a larger number than what your amplifier is rated.

 

so in this case, your amp can source power into as little as 4 ohms of loudspeakers. but it can also source power into 8 ohms.

 

you can use one or two 8 ohm speaker cabinets with your amplifier. you cannot use more. you cannot combine 8 ohms with 4 ohms with your amp, either. you could use a single 4 ohm cabinet, but you cannot combine it with any other cabinets.

 

robb.

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It always amazes me the range of comments you get on these questions and how little some people understand this who have to use it day to day, maybe because I'm an electrical engineer. But either way, the last comment was spot on, and the water analogy is the one most people tend to understand - I'll expand on it....

 

Think of a large tank of water. At the bottom is a valve. The level in the tank is the voltage. If it's full, there's a lot of pressure at the bottom - high voltage. If there's an inch of water at the bottom, not much pressure - low voltage. The position of the valve is resistance. If you have it almost turned off, that's high resistance - it's resisting flow (this is Ohms). Open it wide open, that's low resistance (low ohms). The flow of water is current - in the electrical world, measured in amps. Flow (amps) is equal to Pressure (voltage) devided by resistance (ohms). So to get more flow (current, amps), you can increase pressure (voltage) or reduce resistance (ohms). Power is voltage times current.

 

OK, so as others have sort of stated, your amp produces a voltage, but it can only supply a limited amount of current due to it's power rating. Actually, current is generally what creates heat, and that's typically what causes failure of components. So anyway, an amp will have a power rating into a certain "load" - that's the Ohms. Like 100W into 8 ohms. It may still be able to handle 4 Ohms, have to look at the specs - there is a minimum load it can handle (minimum Ohms). That is because that's the limit of how much current it can supply - voltage remains unchanged. As was mentioned, going higher ohms just means you get less power, but is safe for the amp (I'll comment on tube amps in a bit).

 

Calculating impedance (resistance, or Ohms) has been covered. But realistically, unless you know what you are doing and are trying to do something more or less custom, adding speakers will always be parallel. If they are all the same impedance, then just divide it by the number of cabinets and that's what you have. You CAN mix, but you'll have different power distribution to each speaker. Like if you mix a 8 ohm cabinet and a 4 ohm, you would have 2-2/3 Ohms (only safe if your amp can handle a 2 ohm load). The 4 ohm cabinet would get twice the power of the 8 ohm cabinet. Regarding volume, doubling the speaker area adds 3dB boost, plus halving the resistance would theoretically result in a 3dB boost, so overall 2 cabinets would theoretically net you 6dB. In reality, amps aren't linear and do not put double the power into 4 ohms that they do into 8 ohms. And generally the biggest gain you get in adding speaker surface area is at the lowest frequencies, which it sounds like you're looking for.

 

Now tube amps are a slightly different animal. I'm no expert. But basically they have an output transformer that has different taps for different loads, and you should probably always match them - i.e. if you have 8 ohms, hook it up to the 8 ohm tap, etc.

 

Regarding using a sub... I wouldn't do it for bass. But if you want to do it, the proper way to do it would be to get a crossover and only run the lowest frequencies to the sub and the higher frequencies to the other speaker(s). If you use a passive crossover, you don't have to do the calculation. For instance, if you have an 8 ohm sub and an 8 ohm speaker in your main cabinet, as long as the frequencies are split (don't overlap) the overall system impedance is still 8 ohm. Now for a passive crossover you have to have the same impedance for each speaker unless it's designed otherwise. For an active crossover it doesn't matter, but each speaker has to have its own amp, and that layout would be preamp>crossover>2 amps>speakers.

 

Long story short - if you're amp is capable of handling a lower impedance, add an extension cab with the desired response (probably not a sub, just something more bottom heavy), otherwise it would be much more complicated to achieve what you suggest.

Dan

 

Acoustic/Electric stringed instruments ranging from 4 to 230 strings, hammered, picked, fingered, slapped, and plucked. Analog and Digital Electronic instruments, reeds, and throat/mouth.

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One more thing for those who are interested (to the OP: ignore this because your head will probably explode)....the difference between resistance and impedance....

 

Resistance is strictly at DC - no frequency. DC is what you get out of a battery or power supply. No music is DC, DC is 0 Hz. Low E on a 4-string bass is what, 42 Hz or so? Impedance is like resistance, but frequency dependant. Different electrical components respond differently. A capacitor has infinite resistance at DC - it blocks it, but at high frequency it passes it easily (low resistance). An inductor is opposite. But the resistance to frequency correlation is dependant on the resistance that it is going into. Your Tone pot does this. There's a capacitor that is at a fixed value. Your tone pot is a variable resistor, which changes the frequency that the capacitor passes, thus changing the "cutoff frequency" of the lowpass filter... meaing it passes all the frequencies BELOW the "cutoff frequency". So impedance is complex, where resistance is simple. A speaker has a DC resistance, and inductance, and a resonant peak. An "8 Ohm" speaker may have a DC resistance of 5 ohms, a resonant peak (usually close to the low end of it's response) up around 30-50 ohms, and then above that it comes back down to slightly higher than the DC resistance, and increases with frequency after that. 8 Ohms is kind of a standard rating, but really an "8 ohm" speaker is all over the place in resistance depending on content, and very different from speaker to speaker.

 

Furthermore, amp ratings are a whole other can of worms. Manufacturers try to produce specs that look good, but there are no real standards for how they are measured. What's an 8 Ohm Load? Is it a resistor? Based on my statements above, you can see why that would not be accurate. What is the minimum load based on? Failure? Distortion?

Dan

 

Acoustic/Electric stringed instruments ranging from 4 to 230 strings, hammered, picked, fingered, slapped, and plucked. Analog and Digital Electronic instruments, reeds, and throat/mouth.

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The wiring diagram I picked up off a repair site and i see now that the legend was lost! I am thinking that your guy left out that cross connect.

 

80's LZ knows his stuff and I would follow what he says. I used to run a cab set at 2.16 ohms because I modified the power amp to handle it. I needed more volume for little cash at the time. I am (or was ) an IPC610/Mil Spec certified solder assembler so ic ould take plans and put stuff together. As to why it worked, I am not an engineer so did not know the theory behind it. I will try to find the legend, but I think that was for an 8 ohm cab.

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Now tube amps are a slightly different animal. I'm no expert. But basically they have an output transformer that has different taps for different loads, and you should probably always match them - i.e. if you have 8 ohms, hook it up to the 8 ohm tap, etc.

 

time for some real science. this gets really nerdy.

 

tube amps use an output transformer for multiple reasons. the output of a tube is very high voltage (hundreds of Vs) and very low current (tens of mAs). they are also have very high output impedance (tens of kOhms). the primary (no pun intended) purpose of the transformer is to both increase current and decrease voltage, but the wrinkle in the design is to match output impedance to load impedance.

 

tube output transformers will have multiple taps, one for each common load impedance. you will almost always see 4Ohm and 8Ohm taps, but you may also see 2Ohm or 16Ohm taps. 2Ohm is more common on bass-specific amps; guitar amps may have a 16Ohm tap.

 

because of the physics involved in transformers, the rules regarding minimum load impedance are reversed for tube amps. you will damage the amp by connecting too high an impedance to the output. for example, if you have the transformer set to the 4Ohm tap and connect a single 8Ohm speaker it will draw more current from the tubes and risk damage.

 

robb.

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