Speaker question

[sswingle]

Ok, so I have a sound system (cd, radio, tape all in one) with detachable speakers. The speakers say they are 8 ohms. There is an application where I want to use this, but the speakers are too big. I have a couple of smaller speakers that say 4 ohms on the back that would be perfect size wise. Is it ok that they are 4 and the originals are 8?

 

[Linflas]

Depends on whether what you have them plugged into can handle 4 ohm speakers.

 

[DisgruntledVirus]

4 ohm speakers to an 8 ohm output IIRC is okay (if not ideal).

It's been a while since I read up into that stuff lol

 

[OUCaptain]

Most amps I've dealt with will run quite happily with a 4ohm load.

 

[sswingle]

Cool, thanks! This will be a temporary setup, just wanted to make sure I wouldn't hurt the amp.

 

[amdhunter]

Should be fine as long as they aren't overdriven for really long periods of time, and even then, it probably won't do more than heat up the amp a little bit.

Go for it.

 

[Slick5150]

Just be sure to keep an eye on the amp to make sure its not overheating. That's going to be the main problem with driving 4ohm speakers is that it won't be able to handle it (its "harder" for an amplifier to drive 4ohm speakers than it is 8ohm ones). Start with low volumes and work your way up over time.

 

[jemcam]

As long as it is not a tube amp you won't cause any huge problems.

In a tube amplifier, you will overheat the output transformer which will eventually fail and bring other components with it.

 

[Rubycon]

Originally posted by: jemcam
As long as it is not a tube amp you won't cause any huge problems.

In a tube amplifier, you will overheat the output transformer which will eventually fail and bring other components with it.

Unless it has a 4O tap.

With a truly regulated power supply a 4O loudspeaker will draw twice the current from an amplifier producing 3dB gain over an 8O counterpart. This rarely happens outside of the high end realm (Krell, Mark Levinson, etc.). Most receivers can do 4O and produce marginally more power at the expense of higher distortion when driven hard. Their internals will also produce more heat with higher average levels. If the speaker's impedance curve dips too low at a given frequency it can cause the amp's protection circuitry to engage (usually a relay opens with its contacts in series with the speaker terminals) and this would happen when cranking to loud levels. If this happens just lower the volume!

 

[jemcam]

Originally posted by: Rubycon

Originally posted by: jemcam
As long as it is not a tube amp you won't cause any huge problems.

In a tube amplifier, you will overheat the output transformer which will eventually fail and bring other components with it.

Unless it has a 4O tap.

With a truly regulated power supply a 4O loudspeaker will draw twice the current from an amplifier producing 3dB gain over an 8O counterpart. This rarely happens outside of the high end realm (Krell, Mark Levinson, etc.). Most receivers can do 4O and produce marginally more power at the expense of higher distortion when driven hard. Their internals will also produce more heat with higher average levels. If the speaker's impedance curve dips too low at a given frequency it can cause the amp's protection circuitry to engage (usually a relay opens with its contacts in series with the speaker terminals) and this would happen when cranking to loud levels. If this happens just lower the volume!

Yes, of course. My guitar tube amps have 4, 8, and 16 ohm taps on them so I'm good. The problem is tha a lot of speakers and cabinets don't say what ohm rating they are so I break out the good old DVOM to measure them.

 

[Rubycon]

Originally posted by: jemcam

Yes, of course. My guitar tube amps have 4, 8, and 16 ohm taps on them so I'm good. The problem is tha a lot of speakers and cabinets don't say what ohm rating they are so I break out the good old DVOM to measure them.

Sometimes you have to pick a lower tap to prevent saturation though. Our Yorkies (LS1208 cabs) measure 5.2O on the DMM yet are really 8O cabs. Some amps don't like them in parallel (should be 4O via rating) and others don't mind but these are subwoofers (horn loaded 18's) and the current is high when pushing 2kW into each cabinet anyways. It's amazing how much control difference one amp can have compared to another (with subs) anyways. :Q

 

[Modular]

Originally posted by: sswingle
Ok, so I have a sound system (cd, radio, tape all in one) with detachable speakers. The speakers say they are 8 ohms. There is an application where I want to use this, but the speakers are too big. I have a couple of smaller speakers that say 4 ohms on the back that would be perfect size wise. Is it ok that they are 4 and the originals are 8?

Ohms Law: learn it, love it, live it

Basically, you will be forcing the amplifier to output twice the current (and therefore wattage) at any given volume level. While this probably won't cause much trouble at lower volume levels (assuming that the MOSFETS are properly cooled) I can almost guarantee that anything over 1/4 - 1/2 volume is going to ruin the amp.

Given the general quality of those all-in-one setups, the above statement is doubly true. Where car stereos are concerned, it's very common to have amplifiers that are able to go as low as 2 or even sometimes 1 ohm, but those are at the very high end and often are competition-level pieces of hardware. In home theater, most systems are 8 ohms.

 

[jemcam]

Originally posted by: Rubycon

Originally posted by: jemcam

Yes, of course. My guitar tube amps have 4, 8, and 16 ohm taps on them so I'm good. The problem is tha a lot of speakers and cabinets don't say what ohm rating they are so I break out the good old DVOM to measure them.

Sometimes you have to pick a lower tap to prevent saturation though. Our Yorkies (LS1208 cabs) measure 5.2O on the DMM yet are really 8O cabs. Some amps don't like them in parallel (should be 4O via rating) and others don't mind but these are subwoofers (horn loaded 18's) and the current is high when pushing 2kW into each cabinet anyways. It's amazing how much control difference one amp can have compared to another (with subs) anyways. :Q

In a guitar amp, I WANT saturation hence the reason I have tube amps and not solid state!

 

[Rubycon]

Originally posted by: jemcam


In a guitar amp, I WANT saturation hence the reason I have tube amps and not solid state!

No I was talking about inductive (core) saturation in your matching transformer. That would not be good.

 

[Tiamat]

Originally posted by: Rubycon

Originally posted by: jemcam
As long as it is not a tube amp you won't cause any huge problems.

In a tube amplifier, you will overheat the output transformer which will eventually fail and bring other components with it.

Unless it has a 4O tap.

With a truly regulated power supply a 4O loudspeaker will draw twice the current from an amplifier producing 3dB gain over an 8O counterpart. This rarely happens outside of the high end realm (Krell, Mark Levinson, etc.). Most receivers can do 4O and produce marginally more power at the expense of higher distortion when driven hard. Their internals will also produce more heat with higher average levels. If the speaker's impedance curve dips too low at a given frequency it can cause the amp's protection circuitry to engage (usually a relay opens with its contacts in series with the speaker terminals) and this would happen when cranking to loud levels. If this happens just lower the volume!

While I don't want to step on your toes, technically no amplifier can double into half the impedance load due to internal losses. For the higher end amplifiers, they understate the output at the higher impedance to make it look like it doubles into half the impedance.

Also, the phase angle of the impedance in combination with its magnitude can cause the amp's protection circuitry to engage due to thermal overload. The magnitude of the impedance is rarely the sole cause of thermal overload unless it dips significantly below 4 ohms.

I know you already understand these things, but I figured I'd just list these couple of notes for those that do not realize that impedance has a phase angle and a magnitude, otherwise, it would just be resistance.

 

[Rubycon]

Originally posted by: Tiamat

While I don't want to step on your toes, technically no amplifier can double into half the impedance load due to internal losses. For the higher end amplifiers, they understate the output at the higher impedance to make it look like it doubles into half the impedance.

Also, the phase angle of the impedance in combination with its magnitude can cause the amp's protection circuitry to engage due to thermal overload. The magnitude of the impedance is rarely the sole cause of thermal overload unless it dips significantly below 4 ohms.

I know you already understand these things, but I figured I'd just list these couple of notes for those that do not realize that impedance has a phase angle and a magnitude, otherwise, it would just be resistance.

I wanted to keep things simple and just discuss R.

There are designs that do indeed double output or close to it but they are not perfect and the input will increase much more than 100% to make up for said losses. This is done for the purpose of amp bridging which is rather common in pro audio but often frowned upon since it requires stable 2O operation to be of use.