Basic ohmage question.
- Thread starter RFR
- Start date
Sizzle and then burn! LOL!
Geez jimmy you're a lot of help too......
Not!
I can't believe in three pages no one has answered the question posed in the very first post.
Miro came close with links to impedence matching boxes, a lot of extra theory was thrown around, but the actual question was never answered.
Oh, and I have people trying to help me out with language.
Btw, I noticed Dave is MIA. Normally in a thread like this, he'd be trying to give instructions on how to build a Mars Rover or something.
I wonder if he's ok.
rob aylestone
Moderator
You mean the question about is there a resistor network? We did that. The problem is that to bring the impedance down, this network would pad the speakers. A 6 Ohm resistor in parallel with the speaker would do the trick electrically, bringing the impedance down to just over 4 Ohms - BUT - nearly ¾ the power output would be converted into heat - so the resistor would need to be big enough to dissipate this - and power capable resistors are not very small! you also are wasting three quarters of the amps power too, so it's a pretty poor solution.
witzendoz
Senior Member
No, you cant put a resistor inline with the speaker, it does not correct the ohm's and I suspect that the amp would see it as some short circuit and load the amp up either setting fire to the resistor or blowing up the amp. Maybe one the electronic bods here have the technical answer.
Alan.
Alan.
Thank you. Best answer yet.
So you're saying you'd need something on the order of a dummy load.One thing I don't get. How would the amp lose one third of it's power???
If is 4 ohms @ output and sees 4 ohms @ destination wouldn't it be in it's happy place power-wise?
Why does it care if that 4 ohms is a speaker or speakers or a resistor?
I just don't understand enough of this stuff
What makes a speaker 4 ohms, 8 ohms, 16 ohms.?? Windings on the coil like a guitar pickup? If i want to decrease the ohms on a pup, i just take some of the winds off.
Painstaking, time consuming, but it drops the resistance.
rob aylestone
Moderator
The amp won't get hot because it sees the load in the same way as it would see a speaker.
I'll try to explain how the loss of volume works.
We need to simplify the explanation a bit - but it's the old question of multiple speakers. Two 15 Ohm speaker cabinets daisy chained together in parallel have an impedance of 7.5 Ohms - handy for the 8 Ohm output amp - good matching, full amp output divided between the two cabs. Add two more of these cabs and the impedance drops to 3.75 Ohms, close to the 4 Ohm amp's requirement (a tiny bit low - but of course all that cable probably amounts to maybe another half an Ohm.)
All the amp power goes to the 4 speakers. If we remove one cabinet and replace it with a nice big chunky resistor that is 15 Ohms then we've removed a 15 Ohm speaker and swapped it for a 15 Ohm resistor - the amp sees no change at all - BUT - resistors make no sound, so the missing cabinet's output sound is gone. Do the same with two more cabs, replacing these with 15 Ohm resistors, and it leaves just one cabinet producing sound, but four things dissipating the energy from the amp. remember that this energy MUST go somewhere - 25% turns into sound from the working cabinet, but 75% of the energy turns into heat. Hence the volume drop. The amp is perfectly happy. It can object of the volume is too low, so you turn up to 11 of course.
In practice these figures are slightly different, because some energy is converted into heat in the speaker coil and some is even turned into heat in the cable - but the physics is essentially correct. Purists will also want to point out the other differences in sound compared to simple DC resistance - but these components are small and confuse the understanding.
On the what makes speakers a certain value - you got it. The number of turns, and the diameter of the wire used set the impedance value. As power levels go up, the windings get chunkier because the current requirements go up. Current is the key - not so much voltage. A welder uses quite thick cable at a low voltage, those power cables across fields might well be 11 thousand volts, but are thinner than the welding cable. If they distributed power at a lower voltage, higher current, then more would be wasted as heat, and would be heavier and far more expensive. Speaker manufacturers design their products to suit the need. Those old speakers in the much loved twin cabs - the Vox and Fenders, for example - they sounded nice, but weren't mega loud. The drivers in Marshall guitar amps were louder but sounded different - different cone sizes, power handling and wire sizes all combine.
I'll try to explain how the loss of volume works.
We need to simplify the explanation a bit - but it's the old question of multiple speakers. Two 15 Ohm speaker cabinets daisy chained together in parallel have an impedance of 7.5 Ohms - handy for the 8 Ohm output amp - good matching, full amp output divided between the two cabs. Add two more of these cabs and the impedance drops to 3.75 Ohms, close to the 4 Ohm amp's requirement (a tiny bit low - but of course all that cable probably amounts to maybe another half an Ohm.)
All the amp power goes to the 4 speakers. If we remove one cabinet and replace it with a nice big chunky resistor that is 15 Ohms then we've removed a 15 Ohm speaker and swapped it for a 15 Ohm resistor - the amp sees no change at all - BUT - resistors make no sound, so the missing cabinet's output sound is gone. Do the same with two more cabs, replacing these with 15 Ohm resistors, and it leaves just one cabinet producing sound, but four things dissipating the energy from the amp. remember that this energy MUST go somewhere - 25% turns into sound from the working cabinet, but 75% of the energy turns into heat. Hence the volume drop. The amp is perfectly happy. It can object of the volume is too low, so you turn up to 11 of course.
In practice these figures are slightly different, because some energy is converted into heat in the speaker coil and some is even turned into heat in the cable - but the physics is essentially correct. Purists will also want to point out the other differences in sound compared to simple DC resistance - but these components are small and confuse the understanding.
On the what makes speakers a certain value - you got it. The number of turns, and the diameter of the wire used set the impedance value. As power levels go up, the windings get chunkier because the current requirements go up. Current is the key - not so much voltage. A welder uses quite thick cable at a low voltage, those power cables across fields might well be 11 thousand volts, but are thinner than the welding cable. If they distributed power at a lower voltage, higher current, then more would be wasted as heat, and would be heavier and far more expensive. Speaker manufacturers design their products to suit the need. Those old speakers in the much loved twin cabs - the Vox and Fenders, for example - they sounded nice, but weren't mega loud. The drivers in Marshall guitar amps were louder but sounded different - different cone sizes, power handling and wire sizes all combine.
witzendoz
Senior Member
Is this a valve amp?
If so there may be a multi impedance output transformer that you can select output ohms on my using a different transformer tap?
I seem to remember we did this back in the 1970's when we added 2 extra speakers to a valve PA head. The electrical guy in the band figured this out.
Alan.
If so there may be a multi impedance output transformer that you can select output ohms on my using a different transformer tap?
I seem to remember we did this back in the 1970's when we added 2 extra speakers to a valve PA head. The electrical guy in the band figured this out.
Alan.
Thanks. That was a good explanation. I read every word and picked up a bit more wisdom.
Thanks for taking the time to write out such an in depth answer..
No it's solid state.. i haven't opened it up to see if I can get different output ohms.
From everything I've read, it seems like I'll be hunting for a 15 inch four ohm speaker if I want portability.
rob aylestone
Moderator
If it's solid state - to be honest, I'd just try the 15 Ohm speaker and see if you get enough volume without having to turn up the output too much. I've got quite a few POA amp racks - and the amps are all capable of driving into a ridiculous 2 Ohm load, and as a result, I can hang anything on them - the only unpredictable thing is the actual volume. Sometimes you might see the peak light come on at a pretty low level - that's the limit. If you play at modest levels, you will probably be perfectly happy with the result. keep in mind that solid state amps nowadays are built to survive accidental short circuits - or 3 year warranties wouldn't exist, plus of course there are few of us who have never accidentally run into no load when a plug comes adrift. Clearly - lots of people don't understand electronics which is perfectly normal. If amps died this easily, returns would be sky high - and they aren't.
If it's a solid state amp, there won't be any different taps - these only happen when there is an output transformer - solid state amps don't need them. Give it a blast and see what the results are.
If it's a solid state amp, there won't be any different taps - these only happen when there is an output transformer - solid state amps don't need them. Give it a blast and see what the results are.
"Btw, I noticed Dave is MIA. Normally in a thread like this, he'd be trying to give instructions on how to build a Mars Rover or something.
I wonder if he's ok."
Do you mean me ^ RFR because I have indeed dropped my pearls (aka "waffled on a lot").
But the whole "speaker/impedance/vave/Silicon/safe working debacle IS complicated.
Back in the day it was a lot more simple. No transistors to speak of (I remember the first Perdio transistor radios, expensive, useless effing things). So you had chunky valve amps driving "proper" 12" and bigger 15 Ohm speakers. This was for PA and "quality" hi fi. The domestic market used low power, sub 5watts, single ended OP stages in radios, record players and such and these universally used 3 Ohm speakers. "He" was in his heaven, amplifiers got the load they wanted, all was right with the world.... THEN came the transistorized power amplifier!
Fragile bloody things. Not only could they not deliver enough voltage for decent power into 15R but a momentary slip of the screwdriver and ZAPPO! 12 transistors and 6 resistors were smoke. Eeeeeventually they fixed the fragility, a bit, but the drive capability remained so the 8Ohm speaker was born (bit of a cockup really since the optimum is actually 6 Ohms but much depends upon the actual amp design) .
"We" always knew that you must never drive a valve amp into an open circuit and that higher than optimum Z loads were fraught, especially with overdriven guitar amps. The transistor just muddied the waters!
I could go on (and on!) but I won't.
Dave.
I wonder if he's ok."
Do you mean me ^ RFR because I have indeed dropped my pearls (aka "waffled on a lot").
But the whole "speaker/impedance/vave/Silicon/safe working debacle IS complicated.
Back in the day it was a lot more simple. No transistors to speak of (I remember the first Perdio transistor radios, expensive, useless effing things). So you had chunky valve amps driving "proper" 12" and bigger 15 Ohm speakers. This was for PA and "quality" hi fi. The domestic market used low power, sub 5watts, single ended OP stages in radios, record players and such and these universally used 3 Ohm speakers. "He" was in his heaven, amplifiers got the load they wanted, all was right with the world.... THEN came the transistorized power amplifier!
Fragile bloody things. Not only could they not deliver enough voltage for decent power into 15R but a momentary slip of the screwdriver and ZAPPO! 12 transistors and 6 resistors were smoke. Eeeeeventually they fixed the fragility, a bit, but the drive capability remained so the 8Ohm speaker was born (bit of a cockup really since the optimum is actually 6 Ohms but much depends upon the actual amp design) .
"We" always knew that you must never drive a valve amp into an open circuit and that higher than optimum Z loads were fraught, especially with overdriven guitar amps. The transistor just muddied the waters!
I could go on (and on!) but I won't.
Dave.
witzendoz
Senior Member
Can I make a suggestion,
Keep the speakers you have and go out and buy a compact 4 ohm bass cab for the smaller gigs.
I am a bass player and I own several amps and cabs of various sizes and I take the amp that suits the gig. However as I am not getting any younger I tend to take the compact lightest amp with me these days
Alan.
Keep the speakers you have and go out and buy a compact 4 ohm bass cab for the smaller gigs.
I am a bass player and I own several amps and cabs of various sizes and I take the amp that suits the gig. However as I am not getting any younger I tend to take the compact lightest amp with me these days
Alan.
Can I make a suggestion,
Keep the speakers you have and go out and buy a compact 4 ohm bass cab for the smaller gigs.
I am a bass player and I own several amps and cabs of various sizes and I take the amp that suits the gig. However as I am not getting any younger I tend to take the compact lightest amp with me these days
Alan.
Yeah, thanks Allen, that's most likely what I'll do. The monster cab actually sounds very good, it just lacks in portability. It's almost SVT size.
In my studio it'll be great. Also, it sounds very good with my 4 ohm Showman head.
Most likely I'll just build a 1x15 cab for the bass head. I just have to find an appropriate speaker.
As to the Showman, did mention, also 4 ohm? I have a 2×12 matching cab. Again, I need speakers. But in that case, 2 8 ohm speakers are easy to wire up for 4 ohms.
I have no issue with building and tolexing cabs, it's the buying of speakers I was trying to avoid.
Last edited:
Yeah, thanks Allen, that's most likely what I'll do. The monster cab actually sounds very good, it just lacks in portability. It's almost SVT size.
In my studio it'll be great. Also, it sounds very good with my 4 ohm Showman head.
Most likely I'll just build a 1x15 cab for the bass head. I just have to find an appropriate speaker.
As to the Showman, did mention, also 4 ohm? I have a 2×12 matching cab. Again, I need speakers. But in that case, 2 8 ohm speakers are easy to wire up for 4 ohms.
I have no issue with building and tolexing cabs, it's the buying of speakers I was trying to avoid.
http://www.lean-business.co.uk/esho...MIm6KzvpOC3AIVaL7tCh1M0QzFEAYYASABEgL84PD_BwE
^ Or, you might pickup a decent 4 Ohm car woofer from a ICE fitter or scrapyard for less?
Dave.
Looks like a nice speaker. Dave.
I'm thinking about building a closed back ported cab.Ps. What in the hell is an ICE fitter?
Looks like a nice speaker. Dave.
Ps. What in the hell is an ICE fitter?
In Car Entertainment. IF you are going with a reflex design I strongly urge you to go "Celestion". Get their box design and do it EXACTLY as per! And, small constructional point, instead of the ubiquitous jack use a Speakon, one of the airtight ones, leaky jacks can 'chuff' even whistle!
Have to say, many people do not like reflex boxes for bass G. Look up the spec for the amp. You want the "damping factor" or it might be specced as 'output impedance' You want a factor of over 40 or a Zout of 0.1 Ohms or lower. If worse than that, go sealed box. (JUST MY HO)
Dave.
Car speaker? No way! Were you talking to Dave?