bodia
Authorities said.....best leave it.....unsolved
Good! Just wanted to make sure. Some folks get them confused, or just don't know the difference.
Confusion on ohms and cabinets for amps.
- Thread starter PRSfanboy46
- Start date
PRSfanboy46
Don't lick doorknobs and stay in school
Well my concern is that if I do get an 8 ohm cabinet, I wouldn't be able to exactly run say a 16 ohm head through it, wouldn't I? I found a Mesa mini rec 1x12 thats 60 watts and it has an 8 ohm impedance, but I've seen pictures of people running the head in question (Orange micro dark terror) through a 4x12 with no issue. I think personally, it would be better for me to get a higher impedance cabinet, say a 16 ohm cabinet such as the orange 1x12 60 watt at 16 ohms than say a 1x12 with a matching impedance, since I couldn't have much versatility with amps because they're not the same matching impedance. I think it's decided for me, an orange micro dark tiny terror that is 8 ohms minimum and 20 watts into a 60 watt 16 ohm cabinet. Yes I'm not getting as much sound as I would like, but tone wouldn't be diminished, but on the bright side, I could use 16 ohm amps with the 1x12 in the future since I have one
garrett
...
I'm still pretty new to this stuff, too, since I've always played combo amps. When I looked into it last year, the impression I got was that running low from amp to high in speaker cab doesn't have significant impact on sound or output.
You can also wire the speakers in a cab in parallel or in series to get the match you're looking for.
You can also wire the speakers in a cab in parallel or in series to get the match you're looking for.
Straight_six
Always originate, never duplicate
- Joined
- Aug 5, 2020
- Messages
- 96
Afaik most (but not all) tube amps have switchable impedance, such as the Egnater that I mentioned I had. I can select 4, 8, or 16 ohms output as needed.
Roy
Still warming up
- Joined
- Jun 14, 2020
- Messages
- 123
And just for background, here’s a primer on Ohms Law: https://en.wikipedia.org/wiki/Ohm's_law
The main takeaway is lower load increases current. V=IR
The main takeaway is lower load increases current. V=IR
I am also of the opinion that running the 8 ohm amp into the 16 ohm cabinet will produce half the volume the amp is capable of. Your results may vary.
Back when I was trying to make the jump from solid state amps to tube amps, I too considered the small Orange brand offerings. I actually bought one new and it was bad right out of the box.Exchanged it for a Vox AC15c.
It seems to me that 16 ohm cabinets are very common for those big rig stage players who for example play through Marshall stacks. Today, my big amp is a PRS Blistertone and my lunchbox amps are both from Mesa.
RickP
Established 1960, Still Not Dead
Agree. Sixteen ohm wired cabinets are a great way to double up speaker cabs without going below the 8 ohm minimum many amps require. My 2x12 cabs are 16 ohm speakers in parallel for 8 ohm load as well.
shinksma
What? I get a title?
- Joined
- Mar 20, 2014
- Messages
- 5,320
As part of one of the courses I took in college (seems like a million years ago), we did the math for a power source (amplifier) going into a resistive/inductive load (speaker cab).
Power transfer is maximized when the impedance of the power source matches that of the connected load. So an amp marked "8 ohms" transfers the most power to a load that is also 8 ohms. Or 16 into 16.
Now, a speaker cabinet is not exactly the same inductance across all frequencies. It can drop a fair bit, and rise a fair bit, from the published "nominal impedance". Pretend we have an amp rated at 8 ohms. A cab rated at 8 ohms, that has a drop to 4 ohms at 1000Hz (for example), will respond differently than a "16 ohm rating" cab that drops to 8 ohms at 1000Hz. In the first case, the power transfer is lower than optimal at 1000Hz (so tones around 1000Hz seem suppressed compared to the rest of the signal), in the second case the power transfer at 1000 Hz is exactly optimal, so other frequencies will seem suppressed. So changing the impedance of the cab will alter not just the overall amount of power, but also how it sounds. In this hypothetical case, the 16 ohm cab would have brighter high-mids than the 8 ohm cab. But on average, the 16 ohm cab would not be as loud.
Which is why some folks prefer the sound of 8 ohm amps into 16 ohm cabs, while others prefer to match the (rated) impedance of each (8 into 8, or 16 into 16).
On top of all that, a 16 ohm speaker fed by a 16 ohm amp can sound different from a 8 ohm speaker of the same nominal design fed by an 8 ohm amp of the same nominal design. The speakers will be physically different due to number of windings in the coil, which is what "causes" the impedance, and the coil will be heavier, changing the mass equation slightly.
Power transfer is maximized when the impedance of the power source matches that of the connected load. So an amp marked "8 ohms" transfers the most power to a load that is also 8 ohms. Or 16 into 16.
Now, a speaker cabinet is not exactly the same inductance across all frequencies. It can drop a fair bit, and rise a fair bit, from the published "nominal impedance". Pretend we have an amp rated at 8 ohms. A cab rated at 8 ohms, that has a drop to 4 ohms at 1000Hz (for example), will respond differently than a "16 ohm rating" cab that drops to 8 ohms at 1000Hz. In the first case, the power transfer is lower than optimal at 1000Hz (so tones around 1000Hz seem suppressed compared to the rest of the signal), in the second case the power transfer at 1000 Hz is exactly optimal, so other frequencies will seem suppressed. So changing the impedance of the cab will alter not just the overall amount of power, but also how it sounds. In this hypothetical case, the 16 ohm cab would have brighter high-mids than the 8 ohm cab. But on average, the 16 ohm cab would not be as loud.
Which is why some folks prefer the sound of 8 ohm amps into 16 ohm cabs, while others prefer to match the (rated) impedance of each (8 into 8, or 16 into 16).
On top of all that, a 16 ohm speaker fed by a 16 ohm amp can sound different from a 8 ohm speaker of the same nominal design fed by an 8 ohm amp of the same nominal design. The speakers will be physically different due to number of windings in the coil, which is what "causes" the impedance, and the coil will be heavier, changing the mass equation slightly.
PRSfanboy46
Don't lick doorknobs and stay in school
Well you may have had a dud, but I am still standing by my future choice
Nice F Holes
New Member
Matching speaker impedance to minimum output impedance of the amplifier maximizes available power, at the sacrifice of control or 'amplifier headroom'. If you increase the speaker impedance, you lose a little bit of max power, but you create 'headroom' over the range of available power. Basically the amplifier has better control of the speaker when the bottleneck is at the speaker end. It's like throttling the amplifier. Imagine a garden hose 100% open with no restriction on the end. That's like 1:1 impedance match. Then imagine putting your thumb over the end. You gain control of the flow, but technically there's a little loss due to the restriction and associated pressure drop. The total flow coming out is reduced by your thumb, but you can do so much more with what's available.
The ratio of volume loss to impedance is not 1:1. If you go from 8 ohm to 16 ohm speaker you won't lose half the power. It's important to note that, while we're discussing 'Ohms' (a measure of resistance), we're actually talking about AC impedance. The two are not the same, so Ohm's law doesn't apply 100%. It's the same with pickups - people talk about the DC resistance as a measure of their output, but its really the impedance that determines the output. The assumption is that impedance/resistance remains constant, but that's not really the case.
The ratio of volume loss to impedance is not 1:1. If you go from 8 ohm to 16 ohm speaker you won't lose half the power. It's important to note that, while we're discussing 'Ohms' (a measure of resistance), we're actually talking about AC impedance. The two are not the same, so Ohm's law doesn't apply 100%. It's the same with pickups - people talk about the DC resistance as a measure of their output, but its really the impedance that determines the output. The assumption is that impedance/resistance remains constant, but that's not really the case.
Roy
Still warming up
- Joined
- Jun 14, 2020
- Messages
- 123
Another way to look at balanced loads.
The load sets the current:
I = V / R
power is:
P = V I
so it’s obvious that doubling the resistance halves the current which halves the power.
The confusion is that halving the power is lowering the sound by only 3dB. Not a lot to the ear...
The load sets the current:
I = V / R
power is:
P = V I
so it’s obvious that doubling the resistance halves the current which halves the power.
The confusion is that halving the power is lowering the sound by only 3dB. Not a lot to the ear...
Roy
Still warming up
- Joined
- Jun 14, 2020
- Messages
- 123
Ok, understanding ohms law is the simple steady state case. When you switch to AC the load gets modeled as a resistor, capacitor, and inductor in parallel and is referred to as impedance, Z.
And ohms law becomes:
V = I Z
But then the math starts to use imaginary numbers and gets fun...
We can go there if you want...
And ohms law becomes:
V = I Z
But then the math starts to use imaginary numbers and gets fun...
We can go there if you want...
Nice F Holes
New Member
Don’t forget the speaker isn’t the only resistor in the circuit. Changing circuit resistance from 100,008 ohms to 100,016 ohms doesn’t half the power. Using 100k ohm volume pot value as an example. Idk what the circuit resistance actually is.
PRSfanboy46
Don't lick doorknobs and stay in school
So in general I am losing head room at that point.
Nice F Holes
New Member
Yes, assuming everything sounds good at max volume. If the speaker starts to fart out when it gets loud, it could be worth trading a little power for better sound and using a higher impedance speaker. If you have more power than you really need, using a higher impedance speaker is a good idea. If you need to milk every last watt, then you want to impedance match. You can look up 'damping factor' for a better explanation. Some people go overboard with damping factor, but most people agree it's good to have at least some, so the amp has better control of the speaker.
I'm in the middle of building my 3rd tube amp and am learning about this as I have to decide how to wire this transformer. My supplier says wire for 4 ohms if I plan on using 8 ohm speaker, unless I need to milk the power then wire for 8 ohms. It's a low power tube amp, 4 watts max power (impedance matched). He said if I wire for 4 ohms and use 8 ohm speaker, my max available power will be around 3.8 watts. It's not a huge loss because there's other restrictions (resistance) in the circuit.
I'm in the middle of building my 3rd tube amp and am learning about this as I have to decide how to wire this transformer. My supplier says wire for 4 ohms if I plan on using 8 ohm speaker, unless I need to milk the power then wire for 8 ohms. It's a low power tube amp, 4 watts max power (impedance matched). He said if I wire for 4 ohms and use 8 ohm speaker, my max available power will be around 3.8 watts. It's not a huge loss because there's other restrictions (resistance) in the circuit.
PRSfanboy46
Don't lick doorknobs and stay in school
I'm not exactly wanting to milk this thing, because my orange crush 20 is already VERY loud, and this head, having a 12ax7 I think and being 20 watts, and pairing that with a 1x12, It will DEFINITELY move some air.
