4ohm, 8ohm or 16 ohm

[bent]

hi everyone,

i just have a question on the ohm of amp.....

many amp have the choice between 4 ohm , 8 ohm or 16 ohm.... i know that the speakers have to match the ohm....

but is there a difference in sound or tone in witch ohm we selected..?

exemple: 16 ohm - sound is more clear than 4 ohm.... or something like that...

thank's
bent

[soulsonic]

Oh, that kinda depends I guess.... Different impedances will involve different voltage and current values at a given power level, so who's to say that there won't be some kind of difference in the sound. I've never bothered to listen for it myself. Sometimes you can hear a difference between an 8 ohm 4x12 versus a 16 ohm 4x12, but that might be more due to the differences in how the speakers are wired. There's alot of potential variables there, but I've never done any sort of head to head comparison to see if there's a big difference.

I think it's something that could vary a great deal from amp to amp. So maybe one amp might sound better at 16 ohms, but another one might sound better at 4.

[R.G.]

i just have a question on the ohm of amp.....

That's a common confusion. Amplifiers don't have ohms. They have preferred speaker loads.  The reason that's
an important distinction is that all amplifiers will drive a range of speaker loads, as you're alluding to. And tube
amplifiers are different from solid state.

many amp have the choice between 4 ohm , 8 ohm or 16 ohm.... i know that the speakers have to match the ohm....

The speakers don't have to match the ohm (sic). They just have to be within the allowable range.

On solid state amps, the amp largely doesn't care what the speaker impedance is as long as it's above some minimum
value, often 2 ohms or 4 ohms. Below that, the amp's protection circuits kick in to keep it from self destructing. Any load
up to an open circuit is fine with a SS amp.

On tube amps, the amp doesn't care what load you attach as long as it's a LOW enough impedance. A short circuit is fine,
and they work OK up to some value X which differs on each one as to where they start oscillating and self destructing.

On tube amps, matching is important to get the most power out, which is why there is a selector switch for speaker
impedance. If the tubes don't see the right load, they might produce half or even less of the amp's rated power. That
is probably OK, and is a good trick if you ever need to go quieter.

but is there a difference in sound or tone in witch ohm we selected..?
exemple: 16 ohm - sound is more clear than 4 ohm.... or something like that...

Yes, but it's not as simple as "16 is more clear than 4".

First, the SPEAKER has a different tone at different drive levels. The most notable is cone breakup , which only happens
at higher powers, and if your amp is set up for lower powers, you'll never get to cone breakup. That's a noticeable
tone change that has nothing to do with the amp except that it makes less power. Other things about speakers happen
differently with different drive powers as well.

Second, damping will be changed. Think of damping as the amount of grip the amp has on the speaker. A high damping
factor is a tight grip on the speaker. Moving the impedance selector off the nominal value lessens that grip, so the
speaker can wiggle around more on its own. This generally translates into a more poorly controlled bass.

Third, there are some tonal differences in the amp's frequency response if it's mismatched. What are they?

Who knows? It's a factor of the amp's internal design - how much gain, how much feedback, what the internal rolloffs
are.

So the right answer is - yep, there are differences, but no, you can't make blanket statements. No, it's not harmful to
try them, so tinker with it and find the ones you like. On another amp, other speakers, you'll have to repeat the
tinkering.

[bent]

well.....

that's more technical that i thought   

i was hopping for a answer like- this is better than this....

but like RG said, i will have to make some try....

So thank's to both of you for the very well explain answer 

bent

[Electric_Death]

Bent even in hi fi audio, there is often a different frequency reproduction curve when you toy with impedances, not simply a cut in volume. I may not be familiar with the math but I am familiar with what teaches you the most, actually taking some speakers, experimenting with an amp and utilizing my soundcard as a spectrum analyzer.

In general though, I didn't need the analyzer to hear the mass difference in frequency reproduction that occurred with some speakers. Usually it's as simple as this however, there's a huge spike or dip in the midrange frequency. The inductance of the coil for a 16 ohm speaker run on an amp designed under the intentions it will power 4 ohm loads can dramatically change the sound.
In short, you can put two identical model speakers on that amp but one being a 4 ohm version and the other a 16, crank the volume on the amp then use the balance control to get the 16 ohm version up to the same perceived volume level as the 4 ohm and in most cases you're going to hear a big spike or dip in the midrange.
Even if you eliminate any variables and just use the left speaker out and disconnect and reconnect each speaker, you'll generally experience what I'm talking about. It's simply due to the difference in inductance of the coils.

[MikeH]

Bent even in hi fi audio, there is often a different frequency reproduction curve when you toy with impedances, not simply a cut in volume. I may not be familiar with the math but I am familiar with what teaches you the most, actually taking some speakers, experimenting with an amp and utilizing my soundcard as a spectrum analyzer.

In general though, I didn't need the analyzer to hear the mass difference in frequency reproduction that occurred with some speakers. Usually it's as simple as this however, there's a huge spike or dip in the midrange frequency. The inductance of the coil for a 16 ohm speaker run on an amp designed under the intentions it will power 4 ohm loads can dramatically change the sound.
In short, you can put two identical model speakers on that amp but one being a 4 ohm version and the other a 16, crank the volume on the amp then use the balance control to get the 16 ohm version up to the same perceived volume level as the 4 ohm and in most cases you're going to hear a big spike or dip in the midrange.
Even if you eliminate any variables and just use the left speaker out and disconnect and reconnect each speaker, you'll generally experience what I'm talking about. It's simply due to the difference in inductance of the coils.

I've noticed this too.  In most amps I've owned that could be run with different loads (not all, but most) there was a differce in how the mids sounded.  I like my mids to be punchy and more pronounced than most people, and I found that in most cases lower impedances were more to my tastes.

[Electric_Death]

MikeH that's what I always noticed in my tests as well, the mids really "honked" out at you the lower I went in impedance. In some cases, they were PA speakers and the mids were so overbearing it rendered the speakers useless with any other pairs slapped on my P.A. because you had to suck the mids out with the EQ.

[bent]

i am looking to build a dg103 hiwatt amp, with the schem of mhuss, and i want to put 4 x fane speakers ax12, but i have to choose between 8 ohm or 16 ohm , the amp have the choice of impedance but not the speakers ... 

so before buying i have to choose ... 8 or 16.... 

i read somewhere (can't find it anymore), that 16 ohm produce better high or low ( ) end...think is low

BTW i love Gilmour sound and tone....that's why i want to build the dg103...

decision...decision...

bent

[soulsonic]

If that's the case, why not just figure out whatever it is Gilmour uses? I've seen that they have an entire discussion forum centered around his gear, so I'm sure there's someone out there who can put you in the right direction. I don't personally think it's enough of a difference to be worth getting stressed over.

[Electric_Death]

I'll always be one to insist that it's not all that difficult to nail someone's tone with completely different gear if you've got enough EQ bands to fuss with, gain stages that can be molded to behave a certain way and most of all, the fingers to deliver those tones and feel.

[Shepherd]

No, it's not harmful to
try them, so tinker with it and find the ones you like. On another amp, other speakers, you'll have to repeat the
tinkering.

Is this license to disregard ohm matching from a head to a cab?

[soulsonic]

No, it's not harmful to
try them, so tinker with it and find the ones you like. On another amp, other speakers, you'll have to repeat the
tinkering.

Is this license to disregard ohm matching from a head to a cab?

I hope not - that can be an unwise practice with some amplifiers. Any time you mismatch, the circuit is driven out of spec and it may behave in a way it's not designed to. When the amp was designed, it was intended for the tubes to drive a certain impedance which is determined by the primary of the output transformer, which in turn, is a reflection of what's connected to the secondary, ie; the speaker cab. In some cases, a deliberate changing of this impedance might improve the sound or give a cool tone. In other cases, it may damage the amplifier. This is a path one must tread down very carefully; it wouldn't be smart to plug a 4 ohm cab into a 16 ohm amp and turn it up to 11.

[dirk]

Soulsonic is right. The output tube circuitry will be changed.
Is like changing the anode resistor by a factor 2 or 4. This can damage your amp!

[Electric_Death]

Don't forget that solid states aren't so temperamental.
Stick a 16 ohm load on a s.s. intended for 8 ohms and your only real worry should be when you're driving it at extremely higher levels.
I've been prone to design some pretty eccentric cabinets both inside and out, most knowledgeable players would take one look at the circuits in my cabs and likely not see the point...until they hear them anyway.