Matching AMP and Cabinet question.

[devreaux]

100 watt top 8 ohms into 300w at 8 ohms cabinet = good/bad and why?

100 watt top 8 ohms into 100w at 8 ohms cabinet = good/bad and why?

100 watt top 4/8/16 ohms switch into 300w cabinet

how does this work? if the cabinet has 16 ohms and 300w, or 8 ohms and 300 watt

how will it affect the sound if i switch between 4,8 and 16 ohms on the top/head?

is it possible to buy a really really powerful cabinet that would be able to handle most of the tops out there?

alot of questions i know

[Cygnus X1]

My 4x12 is 4x75 watts, 300 watts total.

"Pushing the speakers" lies in the realm of the smaller setups.
If you're playing hard blues or classic rock tones in the realm of
old Joe Walsh then you might want to push everything.

People tend to forget a 100 watt amp will peak far above that.

But if you are pushing a lot of preamp gain then stay with a faithful clean delivery.

I want voicing and some headroom when using the 4x12's.

Switchable is good, more versatility.
I diddle in my garage and the 5150 cab is 4/16 mono, or 8 in stereo (2x12 split in itself).
8 Ohm mode is 150 watts per side.
And I am playing amps that are 50 watts and usually MUCH less.

OTOH my "classic" rig is two 15 watts total 8 ohms, with a 22 watt Deluxe Reverb.
Good for that setup, it "pushes" those speakers to a nice breakup.

Matching 4, 8, or 16 seems to stir up a witches brew of theories.
First of all, just match and don't worry.
Second, I am hard pressed to notice the difference between an amp set to 16/16
and the same amp set to 4/4 or 8/8.
Some will say it is only using "part of the output transformer" but the math
is that one side is always balanced to the other.

[Chief_CrazyTalk]

As long as you're matching the amp's output impedance to the speaker configuration, you're fine. I think most all modern 4x12's can handle any head. I'm partial to greenback cabinets, but really like the 300W JCM800 cabs too.

[devreaux]

okay so the important thing with tube amps is to match the ohms with the speakers, like 8/8?

chief: what kind of heads are you using?

i am planning to buy a 300w cab and 3-4 heads containing ENGL, 5150 or 6505, some marshall and a mesa

[Cygnus X1]

3-4 heads containing ENGL, 5150 or 6505, some marshall and a mesa

What is the master plan?
That's a little much.

[devreaux]

What is the master plan?
That's a little much.

my passion for versatility, and also having cabinets instead of wallpapers in my house

[javert]

lol, sounds like a good plan to me

[Grim]

my passion for versatility, and also having cabinets instead of wallpapers in my house

Get an ENGL Invader 100, you'll knock 3 amps off that list. It can do anything.

My 4x12 is loaded with V30s.

[Grim]

okay so the important thing with tube amps is to match the ohms with the speakers, like 8/8?

chief: what kind of heads are you using?

i am planning to buy a 300w cab and 3-4 heads containing ENGL, 5150 or 6505, some marshall and a mesa

I can give you advice in this department! For what style of music? For Metal, I REALLY like EL34-loaded amps. The ENGL Invader is a fantastic amp - possibly the most versatile amp I've ever owned - the 6534+ is awesome too, and I loved my old EL34 loaded Dual Recto. I was playing a Marshall JVM410H a few weeks back at a music store but it doesn't do anything new for me - Just my 2 cents.

[Spivonious]

100 watt top 8 ohms into 300w at 8 ohms cabinet = good/bad and why?

100 watt top 8 ohms into 100w at 8 ohms cabinet = good/bad and why?

100 watt top 4/8/16 ohms switch into 300w cabinet

how does this work? if the cabinet has 16 ohms and 300w, or 8 ohms and 300 watt

how will it affect the sound if i switch between 4,8 and 16 ohms on the top/head?

is it possible to buy a really really powerful cabinet that would be able to handle most of the tops out there?

alot of questions i know

Cabinet wattage ratings are simply the maximum continuous power the speakers inside can handle. Unless it's a huge mismatch, like a 1W amp into a 300W cabinet or a 100W amp into a 25W cabinet, then the sound won't be affected. In the first case, the sound will be a little weak. In the second case, the sound will be very distorted and then your speakers blow up.

Impedance ratings should be matched between amp and cabinet. If the speakers are lower impedance than the amp, then you end up drawing more current than the amp was designed for and risk blowing things up. If the speakers are higher impedance than the amp, you're usually okay but this does add "backflow" from the speaker to the amp and can cause damage in less-forgiving amps.

The important things are to keep your cabinet wattage rating above the wattage your amp can put out, and to match the impedances.

Switching impedances on the head will change the sound slightly, but the risk of damaging the amp is not worth the very very slight change in sound.

Speakers do not have power, so a "powerful cabinet" is a misnomer. The wattage you see listed with speakers is simply their maximum continuous power handling rating.

An important thing to remember is that the sound comes from the speakers. Different speakers have an incredible effect on sound. In fact, I'd rate speakers as being more important than the amp itself when it comes to finding "your sound".

Finally, remember that wattage in amplifiers is all about headroom, not volume. Even a 4W amplifier can blow your ears off. Headroom gives you a bigger range before the power amplifier clips/distorts. Don't think of it as volume, because it's not.

[devreaux]

Cabinet wattage ratings are simply the maximum continuous power the speakers inside can handle. Unless it's a huge mismatch, like a 1W amp into a 300W cabinet or a 100W amp into a 25W cabinet, then the sound won't be affected. In the first case, the sound will be a little weak. In the second case, the sound will be very distorted and then your speakers blow up.

Impedance ratings should be matched between amp and cabinet. If the speakers are lower impedance than the amp, then you end up drawing more current than the amp was designed for and risk blowing things up. If the speakers are higher impedance than the amp, you're usually okay but this does add "backflow" from the speaker to the amp and can cause damage in less-forgiving amps.

The important things are to keep your cabinet wattage rating above the wattage your amp can put out, and to match the impedances.

Switching impedances on the head will change the sound slightly, but the risk of damaging the amp is not worth the very very slight change in sound.

Speakers do not have power, so a "powerful cabinet" is a misnomer. The wattage you see listed with speakers is simply their maximum continuous power handling rating.

An important thing to remember is that the sound comes from the speakers. Different speakers have an incredible effect on sound. In fact, I'd rate speakers as being more important than the amp itself when it comes to finding "your sound".

Finally, remember that wattage in amplifiers is all about headroom, not volume. Even a 4W amplifier can blow your ears off. Headroom gives you a bigger range before the power amplifier clips/distorts. Don't think of it as volume, because it's not.

thank you very much for your help. that's how an answer should look like.

[Spivonious]

No problem. A couple more random audio theory items:

It takes double the wattage to get an increase of 3 decibels. From experimentation, it's been found that to get double the volume, an increase of 10dB is needed, so the volume doubles as the power triples. To get twice as loud as a 100W amp, you'll need a 333W amp.

Speakers are also rated with "efficiency" or "sensitivity" values. These are usually expressed in dB/W/m. Most guitar speakers are around 100dB/W/m. This means that with 1 Watt of power, the speaker will produce 100 deciBels at 1 meter. Just more evidence that wattage is not important when it comes to volume. My 75W per channel surround sound amp is putting out about 2-3W per channel most of the time, but when that big drum hit comes, or gunshots happen in a movie, that extra headroom is there and the sounds stay clear.

[devreaux]

No problem. A couple more random audio theory items:

It takes double the wattage to get an increase of 3 decibels. From experimentation, it's been found that to get double the volume, an increase of 10dB is needed, so the volume doubles as the power triples. To get twice as loud as a 100W amp, you'll need a 333W amp.

Speakers are also rated with "efficiency" or "sensitivity" values. These are usually expressed in dB/W/m. Most guitar speakers are around 100dB/W/m. This means that with 1 Watt of power, the speaker will produce 100 deciBels at 1 meter. Just more evidence that wattage is not important when it comes to volume. My 75W per channel surround sound amp is putting out about 2-3W per channel most of the time, but when that big drum hit comes, or gunshots happen in a movie, that extra headroom is there and the sounds stay clear.

Interesting!

[Spivonious]

indeed very interesting,

but how does it come that a 4W amp can sound that loud? what is it that makes the volume?

Well, look at the speaker sensitivity. 1W can make 100dB at 3 feet. Doubling wattage adds 3dB, so 4W gives you 106db. To put that into perspective, an jackhammer being operated 3 feet away from you is about 100dB.

Of course, we don't stand 3ft from the speaker, and in a larger room, that volume can dissipate quite quickly by being absorbed by materials/people and reflected back at the speaker, cancelling out some of the sound waves (comb filtering), but it's still "loud".

The reason high wattage amps are desirable is because that initial pick attack is much louder than the sustained guitar sound we hear. The 4W amp will quickly clip and cause the sharp pick attack to soften and be muddled and not much louder than the sustained sound. Let's say this initial attack requires 30W to cleanly amplify. So we get a 30W amplifier. Our volume hasn't changed much, but our initial attack is much much cleaner sounding, which changes our perception of the overall sound.

Now, let's say we're playing in big club with no PA system, or playing outside. 106dB at 3 feet is simply not enough to reach the people in the back row. Let's say we need 115dB (about twice as loud). So we need at least 32W just for the sustained sound. Now to clean up the pick attack we're going to need 100W or more.

Make sense?

And just a note, all of my dB references are actually dB(SPL). dB by itself means nothing without a reference. With dB(SPL), 0dB is defined as "no noise." Digital volume controls are usually dB(FS) where 0dB is the point right before clipping. That's why volume controls are often -infinity to zero, instead of 0-10 or something similar.

All of this is complicated by what manufacturers post as wattage ratings. A lot of times they'll be past the point of distortion. Commonly seen is a listing like "100W @ 0.05%THD". This means that the sound is 0.05% distorted at 100W. Cheaper stereos will often advertise "1000W power" when it's "1000W @ 1%THD" which is audible distortion, not to mention that at 1000W your speakers will have long since blown up. It's all marketing in the home audio world. Guitar amps are usually a bit better about advertising real wattages, although I've had plenty of 100W amps that distort long before 100W.

[devreaux]

Well, look at the speaker sensitivity. 1W can make 100dB at 3 feet. Doubling wattage adds 3dB, so 4W gives you 106db. To put that into perspective, an jackhammer being operated 3 feet away from you is about 100dB.

Of course, we don't stand 3ft from the speaker, and in a larger room, that volume can dissipate quite quickly by being absorbed by materials/people and reflected back at the speaker, cancelling out some of the sound waves (comb filtering), but it's still "loud".

The reason high wattage amps are desirable is because that initial pick attack is much louder than the sustained guitar sound we hear. The 4W amp will quickly clip and cause the sharp pick attack to soften and be muddled and not much louder than the sustained sound. Let's say this initial attack requires 30W to cleanly amplify. So we get a 30W amplifier. Our volume hasn't changed much, but our initial attack is much much cleaner sounding, which changes our perception of the overall sound.

Now, let's say we're playing in big club with no PA system, or playing outside. 106dB at 3 feet is simply not enough to reach the people in the back row. Let's say we need 115dB (about twice as loud). So we need at least 32W just for the sustained sound. Now to clean up the pick attack we're going to need 100W or more.

Make sense?

And just a note, all of my dB references are actually dB(SPL). dB by itself means nothing without a reference. With dB(SPL), 0dB is defined as "no noise." Digital volume controls are usually dB(FS) where 0dB is the point right before clipping. That's why volume controls are often -infinity to zero, instead of 0-10 or something similar.

All of this is complicated by what manufacturers post as wattage ratings. A lot of times they'll be past the point of distortion. Commonly seen is a listing like "100W @ 0.05%THD". This means that the sound is 0.05% distorted at 100W. Cheaper stereos will often advertise "1000W power" when it's "1000W @ 1%THD" which is audible distortion, not to mention that at 1000W your speakers will have long since blown up. It's all marketing in the home audio world. Guitar amps are usually a bit better about advertising real wattages, although I've had plenty of 100W amps that distort long before 100W.

haha you must have been writing the answer at the same time as i was editing my post. i did actually understand what you ment when i read your post the second time, but you made it very more clear to me now, although it's very advanced for me.

but there wont be any risk at all of blowing something up if ohms are matched and running 100W or 120W amp through 300W speakers?