Ohms and Watts

[thefatone]

New to the formus. WOuld like to start by saying "HI".

 

My question is about seting up heads and cabs correctly. I did some searchin, but couldnt find what i was looking for.

 

Ill start with my gear

 

Ampeg SVT400T (I do have the owners manual if needed)Two seperate channels 200 watts 4 ohms each

 

SWR 4x10 cab 500 Watts 8 ohms

 

hartke 15 cab 200 Watts 8ohms

 

The way I had them setup was one cab into each channel.

Now, my understanding was that the cab ohm should never be below the head ohm. having it setup like this would give each Cab 100 watts of power, right?

an 8 ohm cab into a 4 ohm head would give the cab half (approx) power from the head. Am i wrong on this? I ask because my harkte 15 has recently blowen (it sounds like a big fart). Did I have it setup wrong?

If any more info is need, please let me know.

Thank you.

[Bassplayerjoe]

Welcome to the forum!!!

[LLroomtempJ]

I'll respond to bump your thread up, so that the uber knowledgeable will feel more inclined to respond.

 

Your speaker probably blew from either fatigue (speakers do blow from time to time), or clipping issues with your amplifier.

 

My guess would be fatigue, but you should try hooking your 15 to the channel that your 410 is currently in to see if the speaker is actually blown or if it is the other channel is having issues. Are there any cracks in the 15?

 

It doesn't sound like your set up is incorrect.

 

In theory, you could hook both spekaers up to one channel because the combined load of both speakers is only 4 ohms...which is equal to the minimum load allowed on your two channel amplifier.

 

 

jason

[thefatone]

Thank you for the welcome and the reply.

How about the Watts? am I correct on that?Hopefuly u guys can still help me out with some more info.

[alexclaber]

Good evening and welcome!

 

It would normally take some serious abuse to get a 200W power output @ 4 ohm amp to blow a 200W thermal power handling 8 ohm speaker. But those Hartke 15" speakers have a terrible reputation for blowing far too easily. And beneath an SWR 4x10" it'll be really struggling to be heard so you might push it beyond its limits without hearing it complaining.

 

If you can measure the internal cab volume and the port dimensions we can probably recommend a better replacement speaker - but whatever you do, don't stick any old 15" in there, it's more complicated than that!

 

But I wouldn't take much notice of cab wattage ratings - they're based on the thermal power handling of the woofers (i.e. how much heat they can dissipate before the insulation melts) which is pretty much irrelevant for dynamic low frequency signals (if you use a lot of compression or distortion you might manage thermal damage though...)

 

Woofers tend to get blown because they're pushed further than they can handle, creasing the cone / damaging the suspension / leaping out of the magnetic gap. You'll hear this as farty/growly distortion when you hit a low note or crank your bass knob.

 

Alex

[thefatone]

so ... would having the gain and stage volume close to max be pushing it too much? I have to have my setup up really loud cause (you'll never guess) the lead guitar MUST be loud.

 

also, how about some more info on the watts. I always thought that if the ohms on the cab were higher than the head,t hen the cab was going to get get less power than the head can fully deliver.

i.g. a 8 ohm cab into a 4 ohm 200 watt head would get about 100 watts from the head.

[LLroomtempJ]

Your cab can handle a certain amount of watts. But in this case, the wattage rating is one that describes on average how much heat can be dissipated by the cab before things begin to melt, not necessarily what amp you should buy to match the cab.

 

C alex is trying to say that when you play bass, you aren't delivering a consistent wattage, ever. The only way to deliver something like that would be to just play sustained, relatively low frequency whole notes. Notes that have a more aggressive attack to them...like slap, for example result in power output peaks...so when you hit a hard note with your amp setting really high, you could possibly be delivering 200w from one channel.

 

Even though your head can deliver x amount of watts, if you push the gain stages (pre amp and/or power amp) as you are currently doing, it wouldn't surprise me if your amp began to clip. When you clip, the amp both loses control of the speaker and puts out a lot more wattage than it is rated for. This is a dangerous situation for both your amplifier and your speaker. Your amplifer because the circuitry is not build to withstand that kind of wattage, and your cab b/c heat cannot dissipate as quickly enough for damage to not occur.

 

To sum it up, wattage matching doesn't matter. C. alex has something like 2000w going into a speaker that is rated at less than 1000w. His 2000w setup is CAPABLE of delivering that much power but it is not doing so continuously.

 

I would reccomend a higher power amp if you find that you have to turn your volume up that loudly in order to hear yourself. Or you can make the wiser decision to lower your overall volume as a band.

 

jason