#1
What would happen if i put a 8 ohm speaker into a 4 ohm amp? Will it still be usable but just with lower volume? Or will it just ruin the amp?

Its a solid state amp, by the way
#4
my question is what if i plugged an 8 ohm into a 4 omh....what would that do?
UG's HIPPIE
#5
^depends on the amp. a mismatch can blow the amp.
Jenneh

Quote by TNfootballfan62
Jenny needs to sow her wild oats with random Gibsons and Taylors she picks up in bars before she settles down with a PRS.


Set up Questions? ...Q & A Thread

Recognised by the Official EG/GG&A/GB&C WTLT Lists 2011
#6
lol dumb question...but would it hurt (the amp, i know what'll happen to the speaker lol) if i hooked up a 1.5 watt speaker to a 120 watt amp?
UG's HIPPIE
#7
Quote by ~G{}{}BER~
my question is what if i plugged an 8 ohm into a 4 omh....what would that do?


If you're talking about plugging an 8 ohm amp, into a 4 ohm speaker, bad things could happen.

Quote by jj1565
^depends on the amp. a mismatch can blow the amp.

Here we go again...

He said it's solid state, that's not going to happen.
#8
Quote by ljplum12
If you're talking about plugging an 8 ohm amp, into a 4 ohm speaker, bad things could happen.


Here we go again...

He said it's solid state, that's not going to happen.


Putting too high of a load will just lower the volume, but putting too low of a load can fry the transformer, even in a SS amp. Most amps have protection systems in place to prevent this from happening though.
"Everybody, one day will die and be forgotten. Act and behave in a way that will make life interesting and fun. Find a passion, form relationships, don't be afraid to get out there and fuck what everyone else thinks."
#9
Quote by ~G{}{}BER~
lol dumb question...but would it hurt (the amp, i know what'll happen to the speaker lol) if i hooked up a 1.5 watt speaker to a 120 watt amp?

Your little speaker wouldn't stand a chance.

To random_hero, yeah, sorry, I thought she was talking to the TS.
#10
Quote by ljplum12
Your little speaker wouldn't stand a chance.

To random_hero, yeah, sorry, I thought she was talking to the TS.


That's cool buddy, I've seen you give a lot of great advice around these forums and figured it might have just been a mistake.
With the little speaker, provided you didn't push it too hard, it might last for a little while
"Everybody, one day will die and be forgotten. Act and behave in a way that will make life interesting and fun. Find a passion, form relationships, don't be afraid to get out there and fuck what everyone else thinks."
#11
volume will go down... but we're talking about 93%+ output (so you're only losing around 7% or so). It's fairly insignificant. Generally, tube amps will take a mismatch of 1:2, regardless of whether it's lower or higher. Though, generally, you'd still want to match the amp and cab.
#12
I spoke to an engineer the other day, he told me that tubes are generally more forgiving when it comes to mismatches, but transistors aren't.

I'd rather just match the ohms rating, I'd rather spend a few more bucks on the appropriate cab configuration than to save by getting a cab that didn't match.
#13
If you plug a lower impedance source (amp) into a higher impedance load (speaker) you'll incur a loss of signal.

If it's the other way around, the current might be too high for the source to handle (especially if it's transistors, and if it's finer integrated circuitry, kiss it goodbye).
Dear God, do you actually answer prayers?

Yes, but only in a way indistinguishable from random luck or the result of your own efforts.
#14
Quote by greenbox
volume will go down... but we're talking about 93%+ output (so you're only losing around 7% or so). It's fairly insignificant. Generally, tube amps will take a mismatch of 1:2, regardless of whether it's lower or higher. Though, generally, you'd still want to match the amp and cab.



its good man, im not doing this with my tube amp
#15
Quote by ljplum12

Here we go again...

He said it's solid state, that's not going to happen.



here we go again. i put the arrow "^" cause i was talking to the other guy above me that also asked. didnt say specifics.
Jenneh

Quote by TNfootballfan62
Jenny needs to sow her wild oats with random Gibsons and Taylors she picks up in bars before she settles down with a PRS.


Set up Questions? ...Q & A Thread

Recognised by the Official EG/GG&A/GB&C WTLT Lists 2011
#16
OH! and plus, since its only 1 of the original 2 speakers, its a 60 watt speaker into a 120 watt amp. So i just have to make sure my volume doesn't go past the 5 right?
#17
You should be all right at any volume. You're technically cutting the power in half by doubling the load.
#18
ljplum12: are you really an electrical engineering major about to graduate?

by doubling the load, you're cutting the power by only APPROX 10%

It's all part of the maximum power transfer theory (you know, matching impedances, rho - the reflection coefficient, SWR, etc)
#19
Can I see your source please?

EDIT: BTW Yes, I am about to graduate, but that doesn't mean I know everything and am never incorrect.

matching impedances, rho - the reflection coefficient, SWR, these things are all dealing with transmission lines. You may be right, but I didn't know the connection between an amp and a cab was long enough to be considered a transmission line.
Last edited by ljplum12 at Mar 2, 2007,
#20
I thought it was a bell shaped curve?

Just quickly, I think I have 6 ohm cab for a 4 ohm head, If i added resistors and rethought the wiring etc would i get better power output or would this severly affect tone and therefore be a waste of time for that extra 5% transfer of power
#21
I'm not sure how resistors affect the tone. You'd have to get some pretty high power ones, and I'm not sure if that'd be recommended or not. As far as rethinking the wires, what are the impedances of the individual speakers?
#22
This is the problem I really don't know! I know two of them are 6 Ohms each and the other two I am unsure about. to be safe I wired the two 6 ohm ones in parallell and the two unknown ones in parallel and then connected the whole lot in series.

I really should buy a multimeter!
#24
Quote by ljplum12
Can I see your source please?

EDIT: BTW Yes, I am about to graduate, but that doesn't mean I know everything and am never incorrect.

matching impedances, rho - the reflection coefficient, SWR, these things are all dealing with transmission lines. You may be right, but I didn't know the connection between an amp and a cab was long enough to be considered a transmission line.

Reflection and SWR deal with transmission lines directly, but they're derived from power transfer (I mentioned them as they're theoretically relevant). As far as my source goes, it's me:

P is power
i is current
Zl is load impedance
Zt is amp impedance
v is voltage

P = i^2 * Zl
i = v / (Zl + Zt)
therefore: P = ( vs / (Zl + Zt) )^2 * Zl
take the derivative of the function, equate it to zero to find the peak value, or maximum power, you and you get Zl = Zt for maximum power transfer.

So:
Pmax = v^2 * Zt / (2*Zt)^2
Simplify and you get Pmax = v^2 / (4*Zt)

Representing the ratio of power, you get:
P/Pmax = i^2 * Zl / (v^2/(4*Zt))
Perform a change of variables using an equivalent norton representation and you get
P/Pmax = 4 * Zt * Zl / (Zt+Zl)^2
Now just divide by Zt^2 and expand the polynomial at the bottom:
P/Pmax = 4 * R / (R^2 + 2*R +1)
Where R is the ratio between the load impedance and the output impedance.
Graph that within the realistic ranges (ie, 0-N since you can't have a negative ratio), and you'll get the graph that I posted up.

QED.

(I'm REALLY sorry for the over dramatization , but it's VERY FAR OFF that the power will drop by half. A 120w amp to a 60w cab, even with a mismatch will very likely blow the cab if you crank it, you'd need a mismatch on the factor of 6 to get half power, which is more likely to damage the amp anyways. If the amp was 8ohms, you'd want a 1.3 or 48ohm cab to get half the power output. This brings up fairly obvious problems.)
Last edited by greenbox at Mar 2, 2007,
#25
Quote by jcwear
I thought it was a bell shaped curve?

Just quickly, I think I have 6 ohm cab for a 4 ohm head, If i added resistors and rethought the wiring etc would i get better power output or would this severly affect tone and therefore be a waste of time for that extra 5% transfer of power

It will be hard to find resistors that will cope with such high wattages for continuous use. If you do you will need to use a great big heatsink, and possibly a water cooling system. With a resistor I would also want to use at least double the expected wattage for the amp because amps are rated for a certain percentage THD. When a tube amp is cranked and fully distorted the THD is significantly higher than this rating at the wattage can be MUCH higher, I seem to remember someone telling me a "50 watt" plexi at full volume will actually be sending closer to 80watts to your speaker.

Tbh though I wouldn't bother with resistors, the change in tone/output is negligible and (although not likely) something could go wrong and cost you an output transformer.

For sale: Early 1985 Ibanez AH10 (Allan Holdsworth signature model) PM for details
#26
Quote by greenbox
Reflection and SWR deal with transmission lines directly, but A 120w amp to a 60w cab, even with a mismatch will very likely blow the cab if you crank it,

Even set at half the max volume, a 120w amp can blow up a 60 watt cab:
- because the impedence of the cab changes with the frequencies of the signal that goes through it,
- because of power spikes of certain frequencies that may occur even at half of the max volume of the amp, that are significantly higher than the max power rating of the speaker(s).
#28
Quote by ljplum12
The speakers don't say on them anywhere?


I know!! Ridiculous! I'm quite sure that the overall resistance of the cab is over 4 Ohms purely because half of the series circuit is 3Ohms so unless both of the other speakers are less than 2 Ohms (highly unlikely) I'm safe

This is a home built cab BTW with speakers scavanged from EX PA system cab and a a HiFI cab. Works pretty well actually, especially clean. Only drawback to it being it's slightly bassier than I'd like, but then again I am using closed-back Cabs!

To PowerFreak: Yeah I'll pass on the resistors... I don't think It's worth it tbh. I'll buy a multimeter at some point this month and check things out for a possible best wiring solution.

Can someone confirm wether this external resistance against power graph is a Bell shape rather than that weird shape posted earlier?
#29
Quote by ljplum12
Once again, I'd like to see your source.

Once again, I mathematically proved it to you using rudimentary equations, if that's not enough for you, I don't know what is.

But, if you REALLY need external sources:
http://en.wikipedia.org/wiki/Maximum_power_theorem
fficial&client=firefox-a">fficial&client=firefox-a">http://www.google.com/search?q=maximum+power+transfer&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-USfficial&client=firefox-a
Last edited by greenbox at Mar 3, 2007,