#1

i have read a lot of threads about amp/speaker resistance but i just cant grasp it exactly so i wanted to ask and be sure.

Im looking to buy a head and cab, the head is rated 575w(RMS) and minimum 4ohms, the 2x10 cab is rated 350w(RMS) at 8ohms

As i understand it your amps power is not suppose to exceed the the cab's but seeing as the cab is 8ohms this should bring the power down to a level suitable for the cab.

is this right or have i got it completely wrong?

Im looking to buy a head and cab, the head is rated 575w(RMS) and minimum 4ohms, the 2x10 cab is rated 350w(RMS) at 8ohms

As i understand it your amps power is not suppose to exceed the the cab's but seeing as the cab is 8ohms this should bring the power down to a level suitable for the cab.

is this right or have i got it completely wrong?

*Last edited by seanms at Feb 16, 2012,*

#2

Correct. Next time read the FAQ or use the search bar. Or read the amps specs even, it should say what wattage it puts out at 8ohms.

The only time it would be an issue would be if the head was designed to run at 4 ohms ONLY. But I can't think of any modern amp that's wired like that.

The only time it would be an issue would be if the head was designed to run at 4 ohms ONLY. But I can't think of any modern amp that's wired like that.

#3

Thanks for the helpful, if slightly condecending reply. As i said i'v searched and read a lot of threads about it which is how i found this information in the first place. Just asking to be on the safe side.

thanks again.

thanks again.

#4

Thanks for the helpful, if slightly condecending reply. As i said i'v searched and read a lot of threads about it which is how i found this information in the first place. Just asking to be on the safe side.

thanks again.

He says that to everyone, but so do most people, your questions easily found on the FAQ, searched, google etc. If anything now it's in the back of your mind to look at next time, so it's actually extra help.

#5

As i understand it your amps power is not suppose to exceed the the cab's but seeing as the cab is 8ohms this should bring the power down to a level suitable for the cab.

1 - this is wrong. the head must have equal or LESS power (watts) than the CAB, ASSUMING they're both working with matching ohms. IF the amp pulls 350 watts at 8 ohms, and the cab pushes 350 watts at 8 ohms, they're even, so there's no problem. BUT if the head pushes something like 400 watts at 8 ohms, that cab would be underpowered, and there's a chance that you could damage the speakers, particularly at high volumes.

2 - It's supposed to be better that the cab has more power tolerance than what the head can produce.

3 - if you get two 8 ohms cabs, and wire them in parallel, you will make them work at 4 ohms, therefore, using the full power of the head. then, you should sum the power of both cabs and it must be equal or higher than the head's power, so there is no chance of the speakers getting damaged.

hope this helps..

I have edited part 1, so that it makes sense. it was a tipping mistake

*Last edited by Sudaka at Feb 17, 2012,*

#6

Honestly, this wattage matching stuff is bullshit really. You can match up pretty much any head and cab combo as long as the impedance is greater than or equal to the minimum level of the amp. You just have to make sure you don't turn up your speakers so ridiculously loud that you get a load of farty sounding distortion from them, that is the speakers way of saying that you're going to **** them up if you don't turn it down.

Don't just take my word for it though:

http://barefacedbass.com/technical-information/mythbusters1.htm

Don't just take my word for it though:

http://barefacedbass.com/technical-information/mythbusters1.htm

*Last edited by eddiehimself at Feb 17, 2012,*

#7

cheers for that info eddie, and thats an awsome link, gonna favorite that.

And Suduka... you kinda didnt make sense, you compared a head to a head. That and the amp im after is 4ohms and the cab is 8ohms so according to eddiehimself im as safe as houses, long as i don't hear any distorting.

And Suduka... you kinda didnt make sense, you compared a head to a head. That and the amp im after is 4ohms and the cab is 8ohms so according to eddiehimself im as safe as houses, long as i don't hear any distorting.

#8

1 - this is wrong. the head must have equal or LESS power (watts) than the head, ASSUMING they're both working with matching ohms. IF the amp pulls 350 watts at 8 ohms, and the cab pushes 350 watts at 8 ohms, they're even, so there's no problem. BUT if the head pushes something like 400 watts at 8 ohms, that cab would be underpowered, and there's a chance that you could damage the speakers, particularly at high volumes.

lulwut?

The head should have equal or less power than the head?

I think what you are trying to say is that if the cabinet is underpowered, it could damage the speaker cones, but this is wrong.

#9

edited my reply. i had a mistake. now it makes sense

#10

lulwut?

The head should have equal or less power than the head?

I think what you are trying to say is that if the cabinet is underpowered, it could damage the speaker cones, but this is wrong.

Avatar has a FAQ where they do mention if you have your amp that's say 100 watts turned way up for maximum volume, then plugged it into a 700 watt cab you'd work the speakers but cause a lot of heat buildup and melt the speaker coils effectively destroying the speaker, cones can be replaced (expensive) but dead coils = paper weight.

Now I had a very difficult time understanding avatar, and I really what to know exactly how under powering works, and how close do the watts really need to be?

Overall if your amps 200 watts at 4 ohms get two 8 ohm 300ish cabs or one 4 ohm cab same wattage.

#11

Avatar has a FAQ where they do mention if you have your amp that's say 100 watts turned way up for maximum volume, then plugged it into a 700 watt cab you'd work the speakers but cause a lot of heat buildup and melt the speaker coils effectively destroying the speaker, cones can be replaced (expensive) but dead coils = paper weight.

Now I had a very difficult time understanding avatar, and I really what to know exactly how under powering works, and how close do the watts really need to be?

Overall if your amps 200 watts at 4 ohms get two 8 ohm 300ish cabs or one 4 ohm cab same wattage.

And they, as far as my understanding of it are, completely wrong. I know I've posted this article about a hundred times, but I am going to post it again

There are only two ways that a speaker can be damaged, both of which occur from too much input power. 1. Mechanically 2. Thermally

http://billfitzmaurice.info/forum/viewtopic.php?t=1886

#12

One more thing to keep in mind is that if you had, for example, one 150w 8ohm cab and another 200w 8ohm cab, you should think of them combined as a 300w stack. The amp will tend to send power to both cabs equally if the impedances are the same so a safe rule is 2 x the lowest value.

EDIT: I've noticed a lot of amps only give the maximum rms output, usually at 4 ohms. Is there a rule to work out how much power, roughly, the amp would put out at 8 ohms? Ive seen some amps list it as just over half of the maximum and some as just under so is 50% a good guideline?

EDIT: I've noticed a lot of amps only give the maximum rms output, usually at 4 ohms. Is there a rule to work out how much power, roughly, the amp would put out at 8 ohms? Ive seen some amps list it as just over half of the maximum and some as just under so is 50% a good guideline?

*Last edited by sic6505+ at Feb 17, 2012,*

#13

Usually about two thirds.

#14

One more thing to keep in mind is that if you had, for example, one 150w 8ohm cab and another 200w 8ohm cab, you should think of them combined as a 300w stack. The amp will tend to send power to both cabs equally if the impedances are the same so a safe rule is 2 x the lowest value.

EDIT: I've noticed a lot of amps only give the maximum rms output, usually at 4 ohms. Is there a rule to work out how much power, roughly, the amp would put out at 8 ohms? Ive seen some amps list it as just over half of the maximum and some as just under so is 50% a good guideline?

sure? i thought that you should sum the power handling... i didn't know that you should multiply the lowest rating cab...

#15

If its two fairly similar numbers it should be fine but imagine a 200w 1x15 and a 500w 4x10 connected to a powerful head. If the impedances match and the same power is sent to each cab, the 200w speaker would be damaged far quicker than the speakers in the 500w cabinet.

#16

And they, as far as my understanding of it are, completely wrong. I know I've posted this article about a hundred times, but I am going to post it again

http://billfitzmaurice.info/forum/viewtopic.php?t=1886

what exactly is thermally? I thought it was what they said, a under powering melting (heating) the coil.

I am not trying to correct or challenge you I legit don't know, and asked before but no one answered me. I just need a clear answer as to how a speaker can be destroyed. I know the impedance and over power, but the thermal and mechanically?

#17

If its two fairly similar numbers it should be fine but imagine a 200w 1x15 and a 500w 4x10 connected to a powerful head. If the impedances match and the same power is sent to each cab, the 200w speaker would be damaged far quicker than the speakers in the 500w cabinet.

Depends on the head. If your putting out say 400 watts at 4ohms in to the two cabs you spec'd each cab would get 200 watts so it wouldn't matter. Obviously if you go over that 400 watts your 200 watt cab could be in some trouble if the amps turned up too loud.

That's assuming of course that the amp is indeed outputting the wattage the manufacturer claims it is

*Last edited by consecutive e at Feb 18, 2012,*

#18

Everyone needs to read this.

barefacedbass.com/technical-information/mythbusters1.htm

I'm thinking of buying one of his cabinets. He really knows his stuff.

barefacedbass.com/technical-information/mythbusters1.htm

I'm thinking of buying one of his cabinets. He really knows his stuff.

#19

what exactly is thermally? I thought it was what they said, a under powering melting (heating) the coil.

I am not trying to correct or challenge you I legit don't know, and asked before but no one answered me. I just need a clear answer as to how a speaker can be destroyed. I know the impedance and over power, but the thermal and mechanically?

No problem.

Mechanical damage is where too much power is applied, and the speaker cone moves too far, causing ripping, or bottoming out the back plate.

Thermal damage occurs when you drive a speaker cone too hard over a longer period of time, causing the voice coil to melt.

Neither occurs when you apply too little power.

*Last edited by Killerfridge at Feb 18, 2012,*