Help an idiot with an amp ?

[Sam Hain]

Admittedly im not very good with tech shit...

One of my orange guitar amps has (2) 8 ohm outs and (1) 16. My cab is a Avatar guitar 212 at 8 ohm. It has a daisy chain out.

I have a lead on a nicely priced Ampeg 410 bass cab. It's a 4 ohm cab.

I wanna run the Avatar 212 and the Ampeg Bass cab together.

Help this window licker out....how can I do this?

[dunwichamps]

theres no easy way to run them together.

[Hemisaurus]

Technically speaking, it's impossible

Without buying an extra impedance matching transformer, I think maybe $50 or so from Weber, the closest you could get would be to rig up a cable to run the Ampeg and Avatar in series for 12 ohms, and use the 16 ohm out.

Or, assuming the Avatar uses two 16 ohm speakers, disconnect one of the 12"s for a 16 ohm Avatar cab, rewire the Ampeg (all speakers in series) for a 16 ohm cab there, and you now have two proper 16 ohm loads for 8 ohms total. Be warned in this mode half the amps power goes to a single 12", so make sure it can handle it.

Best would probably be to add a third cab, another 2x12 say, that is the same as your Avatar.

Avatar 1 2x12 (2 x 16 ohm speakers) rewired in series for 32 ohm
Avatar 2 2x12 (2 x 16 ohm speakers) rewired in series for 32 ohm
Ampeg   4x10 (4 x 4 ohm speakers)   rewired in series for 16 ohm

Total impedance of stack 8 ohms.

or get a 4 ohm cab (say a nice 4 ohm 15"  )

Avatar   2x12 8 ohm
Ampeg  4x10 4 ohm
Some    1x15 4 ohm

get a serial cable or box (see Nick's thread) and hook the 3 cabs up in series for 16 ohm

[Sam Hain]

Ah bummer...thanks for the info.

So I can't even daisy chain it off the avatar if I use the 16 ohm amp output right?

I guess tbe easiest thing to do is find another 8ohm cab and use tbe other 8ohm output.

[Sam Hain]

One more...can I use the 4 ohm Ampeg at all with tbe amps 8 & 16 ohm outputs?

[Hemisaurus]

Yes, but you'd have to rewire the cab.

A typical 4x10 4 ohm cab will be made of 4 x 4 ohm speakers, and wired series / parallel for 4 ohms total. You need to wire it straight series for a 16 ohm total load, and then use it with a 16 ohm output.

[Sam Hain]

Yes, but you'd have to rewire the cab.

A typical 4x10 4 ohm cab will be made of 4 x 4 ohm speakers, and wired series / parallel for 4 ohms total. You need to wire it straight series for a 16 ohm total load, and then use it with a 16 ohm output.

Oh ok I see...

This cab would be ok though right?

http://www.samsontech.com/hartke/products/cabinets/xl-cabinets/410xl/

I could just use the other 8 output, or I could daisy chain it off tbe Avatar using tbe 16ohm output. Right? I'm just trying wrap my head around this.

[Mr. Foxen]

Also the result of mixing the two cabs is going to be messy. Even if you get a sound you like with the two dissimilar cabs running the speakers out of phase at various frequencies, the sound will change loads depending on your location, in a much less predictable way that a pair of similar cabs, plus the impedance load might still disagree with your amp because it isn't as simple as a single number of ohms, it varies with frequency, and ported cabs have a big impedance spike around the port tuning.

[Sam Hain]

Never thought about that..thanks.

[dunwichamps]

1: Impedance Conversion

I am building 1 right now, its an autotransformer that converts 4,8,or 16 into 4,8, or 16 up to 100W

2. Buy near speakers.

[Hemisaurus]

Also the result of mixing the two cabs is going to be messy. Even if you get a sound you like with the two dissimilar cabs running the speakers out of phase at various frequencies, the sound will change loads depending on your location, in a much less predictable way that a pair of similar cabs, plus the impedance load might still disagree with your amp because it isn't as simple as a single number of ohms, it varies with frequency, and ported cabs have a big impedance spike around the port tuning.

This seems to be Foxen's pet thing at the moment, and although much of what he says is true, what he says also applies to a stack of two 4x12's as if the top cab is slanted, it has a different volume, is projecting in the wrong direction, etc. etc. Even if you have two identical straight front cabs, if you don't match the centers of the drivers in each cabs perfectly, you will have cancellation, here's what I said about it last time in the Speaker Selection Advice thread.

Have you ever seen the freq response of a regular 4x12?

Patchy and Notchy, I like it, you could do a kids cartoon with that. Teach them sound theory whilst they're young.

You will get destructive and constructive interference with the same type of speaker in the same cab, with different cabs with different types of speaker, and just to bugger you all up, the same speaker in two identical cabs, if you move one cab slightly.

In theory, people shouldn't mix V-30's and Greenbacks or whatever n the same cab, but they do, and they like it, people are weird

Like lots of people do with guitar, play it by ear

Basically, don't ever be afraid to experiment, as long as you get your impedances right

Which btw, if you hang another 8 ohm speaker from the jack of your Avatar, it's going to be 4 ohms, not 16, you will need a special cable or a little serial speaker box to run multiple 8 ohm cabs.

[Mr. Foxen]

Also the result of mixing the two cabs is going to be messy. Even if you get a sound you like with the two dissimilar cabs running the speakers out of phase at various frequencies, the sound will change loads depending on your location, in a much less predictable way that a pair of similar cabs, plus the impedance load might still disagree with your amp because it isn't as simple as a single number of ohms, it varies with frequency, and ported cabs have a big impedance spike around the port tuning.

This seems to be Foxen's pet thing at the moment, and although much of what he says is true, what he says also applies to a stack of two 4x12's as if the top cab is slanted, it has a different volume, is projecting in the wrong direction, etc. etc. Even if you have two identical straight front cabs, if you don't match the centers of the drivers in each cabs perfectly, you will have cancellation, here's what I said about it last time in the Speaker Selection Advice thread.

Have you ever seen the freq response of a regular 4x12?

Patchy and Notchy, I like it, you could do a kids cartoon with that. Teach them sound theory whilst they're young.

You will get destructive and constructive interference with the same type of speaker in the same cab, with different cabs with different types of speaker, and just to bugger you all up, the same speaker in two identical cabs, if you move one cab slightly.

In theory, people shouldn't mix V-30's and Greenbacks or whatever n the same cab, but they do, and they like it, people are weird

Like lots of people do with guitar, play it by ear

Basically, don't ever be afraid to experiment, as long as you get your impedances right

Which btw, if you hang another 8 ohm speaker from the jack of your Avatar, it's going to be 4 ohms, not 16, you will need a special cable or a little serial speaker box to run multiple 8 ohm cabs.

Two amthced 4x12s will have matched impedance curves and phase response, and the issues present themselves in a predictable fashion of poor off axis response. Totally mismatched cabs are not predictable, and present dubious loads to output transformers That means the impedance may well not be right. Polar response is the important part of the tone to consider, unless you have monitoring, and if that is massively inconsistent, you get an inconsistent sound. And if yo do have monitors, you end up with a mic on one of your mismatched speakers and not on the other, so you end up with different sound from your rig and the PA. Not understanding this is why most bands sound totally shit.

[Hemisaurus]

Not understanding this is why most bands sound totally shit.

See, I think this sums up your entire argument. If you want to be Steely Dan, or Pink Floyd worry about all this pseudo-scientific shit, directionalise your cables, mount your supplies on Shakti crystals.

If you want to be any other rock band, make sure you hook it all up so you don't blow your shit up. None of what this chap is wanting to do will damage his equipment if done properly.

This from a guy who can write Sunn, Jucifer and Lightning Bolt off, without seeing them. I assume Om were shite before Al got his matching Ampeg rig? All that mix of 4x15's and 4x12's and multiple amps, Oh No!

When you go up to Lemmy to tell him his sound is shit, make sure you video it, that'll be a big YouTube hit

[grimniggzy]

buy a cheap slave head.

[Mr. Foxen]

Not understanding this is why most bands sound totally shit.

See, I think this sums up your entire argument. If you want to be Steely Dan, or Pink Floyd worry about all this pseudo-scientific shit, directionalise your cables, mount your supplies on Shakti crystals.

If you want to be any other rock band, make sure you hook it all up so you don't blow your shit up. None of what this chap is wanting to do will damage his equipment if done properly.

This from a guy who can write Sunn, Jucifer and Lightning Bolt off, without seeing them. I assume Om were shite before Al got his matching Ampeg rig? All that mix of 4x15's and 4x12's and multiple amps, Oh No!

When you go up to Lemmy to tell him his sound is shit, make sure you video it, that'll be a big YouTube hit

Read and understand what I said. There is plenty of possibility of blowing your shit up right there. Running cabs off different heads negates the impedance problem. Running mismatched cabs from the same head is a whole bunch of potential trouble, both for sound, and amp safety. If you can't actually hear what you sound like, you have no hope of knowing if you sound good, which is why actually being able to hear your output is important, along with being able to hear your equipment protesting.

[Hemisaurus]

I'd understand if it made sense, you used the term polar response, I think you probably meant impedance response, which is the total impedance of a driver at any given frequency. This can also be affected by cab design. Now is your claim that running mismatched cabs is more dangerous because they have different impedance responses? That's ridiculous, you could have the same problem with a single cab. Two separate cabs won't interfere with each others impedances, unless you plan to glue them together, you're pulling technical terms out your ass

The trouble with cab impedances in general is they are an estimate, as you say different cabs will have different responses at different frequencies, using the same cab could aggravate rather than alleviate things though. You have the same problem frequency points in both cabs.

And I'd still go and hear a band first, rather than claiming their shit from their equipment list.

[Mr. Foxen]

Polar response is how well a rig projects sound around it. the pole is the axis where the speaker faces, and you move away from that and it changes to varying degrees. With a matched rig, it means the higher frequencies roll off steadily as you go off axis. With a mismatched rig, it is lobed and unpredictable, changing with frequency in an inconsistent fashion. Nothing to do with impedance in itself. But it is important to playing, since if you stand in a frequency null, you'll eq in that frequency to aim for a sound, and it will be peaking elsewhere, possibly making someone else think they need to be louder and consequently the sound of the whole band goes to shit.

Impedance is a separate issue. A sealed cab will tend towards a single fairly small impedance peak from the driver, while a ported cab generally has two much greater peaks, one from the drivers own properties, and one from the box:



Since the sensitivity of the ported cab is enhanced at the port tuning frequency, the high impedance at that frequency doesn't matter so much as the port reinforcing the sound compensates, because that's all of the point of a ported cab. But introduce the second cab without said impedance peak, and most of the power is shunted to the other cab, since one is a few hundred ohm, and the other is likely around its nominal impedance. Typically a sealed cab is inefficient around the sort of frequency band of a ported cabs peak (again, the point of a port is to reinforce where drivers are getting weaker), so that power is either wasted in not producing sound, and only serves to push that cab closer to its limits, whereupon it  can malfunction and cause trouble. Additionally, the port output from the ported cab could well be out of phase with the sealed cabs output around there, which drops the spl even more, and a player will tend to try and eq the bottom back in, which puts more power into a system ill suited to use it.

The nominal impedance quoted is an estimate sure, but any decent speaker manufacturer published an impedance chart, and they can be derived from Thiele-Small specifications.

Also, do you seriously believe that adding a second cab to an amp doesn't affect the impedance load on the amp?

[bitter]

Guess it's the techs time of the month? Y'all seem to be RMS'ing pretty bad.

Get it? RMS'ing

[Hemisaurus]

Sorry, that's not a polar response, polar response is a type of graph plotted circularly.



So to sum up what you seem to be trying to say is that by using mismatched cabs, you might turn your amp up too loud, and it will blow up. Maybe you should just rub the 10 off your amp, and stick at 6


RMS

[Mr. Foxen]

That's a depiction of polar response limited to two dimensions, only applies to reality if you understand it and have the correct information to go with it. It depicts exactly what I just described. Its missing the frequency labels on the coloured lines but it shows the pattern of radiation. Its a picture of a mic response, but a cab response would be similar, if it were a 4x12: The red one being highs and the broader outlines being high mids and mids, and the db would be -numbers as the sound is attenuated off axis. If you were to add another cab with differing phase response, the mid lines would become lobed kind of  like the red line, but more complex, and would do so in three dimensions, because there would be split sources, and would likely be radiating in half or quarter space (being on the floor or against a wall), which would add a bunch of reflections depending on the properties of the wall and floor.

Edit: here's an simple article: http://barefacedbass.com/technical-information/understanding-sound-dispersion.htm

Edit 2: bigger article: http://barefacedbass.com/uploads/BGM62%20Jan2011.pdf

And here's an equivalent for a sub array:

[Hemisaurus]

Also, do you seriously believe that adding a second cab to an amp doesn't affect the impedance load on the amp?

Missed the last bit of idiocy.

No I was just trying to fathom out how you thought that using two different cabs could blow up an amp, and the only way the impedance of one cab, can affect the impedance of another cab directly, would be by making an air tight seal between the cabs.

So you are basically saying that people that use non-identical cabs have more of a tendency to sound like shit? So people that mix two types of speaker in a cab sound like shit? People that have two different brands of cab sound like shit? Manufacturers that produce an amp, or a cab, like Randall or Gibson, where the same amp drives two different types of speaker at the same time, with no crossover, and it sounds like shit?

Go back to your listening room and play with your Pink Floyd CD's mate, you missed the point

[Hemisaurus]

That's a depiction of polar response limited to two dimensions, only applies to reality if you understand it and have the correct information to go with it. It depicts exactly what I just described. Its missing the frequency labels on the coloured lines but it shows the pattern of radiation. Its a picture of a mic response, but a cab response would be similar, if it were a 4x12: The red one being highs and the broader outlines being high mids and mids, and the db would be -numbers as the sound is attenuated off axis. If you were to add another cab with differing phase response, the mid lines would become lobed kind of  like the red line, but more complex, and would do so in three dimensions, because there would be split sources, and would likely be radiating in half or quarter space (being on the floor or against a wall), which would add a bunch of reflections depending on the properties of the wall and floor.

You still haven't explained the amp blowing up, you can dicker terminology all night if you like.

[Mr. Foxen]

Also, do you seriously believe that adding a second cab to an amp doesn't affect the impedance load on the amp?

Missed the last bit of idiocy.

No I was just trying to fathom out how you thought that using two different cabs could blow up an amp, and the only way the impedance of one cab, can affect the impedance of another cab directly, would be by making an air tight seal between the cabs.

So you are basically saying that people that use non-identical cabs have more of a tendency to sound like shit? So people that mix two types of speaker in a cab sound like shit? People that have two different brands of cab sound like shit? Manufacturers that produce an amp, or a cab, like Randall or Gibson, where the same amp drives two different types of speaker at the same time, with no crossover, and it sounds like shit?

Go back to your listening room and play with your Pink Floyd CD's mate, you missed the point

They won't sound consistent. One place will sound different across a broad frequency band to another place. If one place is where their ears are when they eq, and one place is where the mic is, the mic won't be picking up what the player is hearing. Sometimes people are determined to sound like shit, maybe it benefits them to not be able to hear themselves properly. Bands have a tendency to sound like shit and break their stuff. I see hundreds of bands each year, and am impressed by the sound of very few. And have to fix a lot of their stuff.

The other way mismatching cabs can contribute to equipment damage is through sensitivity mismatch. A very much more sensitive cab will tend to drown out a less sensitive one, should the less sensitive one be making distressed noises of a cab being pushed into damage territory, if you hear it, you know to turn down, cut some bass etc, but if its downed out by a louder cab, you don't hear it, kill the cab, and then present a inappropriate load to your amp. That is the classic 15 from a 15 and 4x10 stack dying scenario. Plus the 15 at the bottom is even less likely to be heard since the generally more sensitive 4x10 will be closer to ear height.

All the Randall amps I've heard did indeed sound shit, and quite a lot broke, Although one cab I've tinkered with was pretty well built, but it got brought to me because someone broke it. Not had much to do with Gibson amps, probably because they are brutally shit and no-one uses them.

Oh yeah, and presenting a load for a few hundred ohms to a valve amp set to 4ohm, and boosting up the frequency where that impedance is in eq because your poor cab choice has attenuated it is a amp blowing up scenario, probably just an arcing around the power valves, but that can short things and kill the OT also, so probably not actual explosions, but damage, sure.

[Hemisaurus]

Oh yeah, and presenting a load for a few hundred ohms to a valve amp set to 4ohm, and boosting up the frequency where that impedance is in eq because your poor cab choice has attenuated it is a amp blowing up scenario, probably just an arcing around the power valves, but that can short things and kill the OT also, so probably not actual explosions, but damage, sure.

Nope, not good enough.

This is FUD (fear, uncertainty, doubt) pure and simple. Telling someone oh don't do that, you'll blow it up then feeding them some random technical bs. to try and back yourself up.

The only difference between running mismatched cabs is the impedance response is different, if you have a frequency where the impedance is rather high, adding another identical cab with the same impedance response, just means the impedance at that frequency is now half. Adding a non-identical cab, which may have a lower impedance at that point means it might be more than half, or it might be less than half, but it's never going to be more than the original impedance of a single cab.

Saying that boosting a certain frequency, ie. turning up the bass/mid/treble is going to cause an amp to blow up is just as ridiculous. That's harking back to the don't turn it up to 10, you'll break it.

Here's a slightly more accurate truism Turning your amp up loud may shorten it's life, I don't think you'll get many converts

[Mr. Foxen]

The important bit being, that the volume output will be significantly cut in the scenario with mismatched cabs at the high impedance frequency, as already described. With the single cab, or pair of cabs, the peak is consistent, so everything is even, with two cabs, most power will be applied to the lower impedance cab, but that could well not be able to actually convert that power into sound effectively. Which means turning up in response to lack of volume. Typically a sealed cab will be 3-6db down compared to a ported cab at the tuning frequency of a ported cab, because that is the benefit of porting. Then you get the port output remaining being subtractive due to being out of phase with the sealed cab (but that's only if the drivers have equivalent phase response, and they probably wont), likely to be out of phase, but probably not by exactly 180 deg.

Edit: 3db is what you get from doubling amp power output, to show how much more strain you are putting on things.