A question of watts...

[Damonjames]

Hey chatters,

I feel ashamed to have to ask this as I am an electrician with Industrial electronic experience so I SHOULD know the answer, but hey it's Saturday night, I've had a few beers and can't be bothered with the math so here goes.

I am looking for a new stage amp, in between pecking my head as to which brand/head to go with I have this question for my learned brethren out there. Take for example an orange terror bass 1000 (rated 1000 watts) in a perfect world I could run an orange 8x10 (rated at 1200 watts) flat out without blowing the cab into its next life. Now here's the question if I was to run the same head through a orange 4x10 and 1x15 (rated 600 watts each) given perfect world scenario could you run said amp flat out or only to an output of 600 watts.

Hope this makes sense and someone can explain it to me. Cheers.

D

[xgsjx]

If amps & cabs was rated on watts alone, then your maths would be correct. However, they're not & your TB1000 could blow the 1200 watt 8x10 fairly easily.

Scenario: Amp is 1000 w at 4Ω & 650 w at 8Ω. At full tilt, that's what it's gonna put out regardless of the cabs attached. So 2 600w 8Ω cabs are gonna get 500w each at full waldy.
What the cabs then do with that wattage is down to loads of different factors such as the excursion of the driver, how well the cab has been designed to get the most from the driver & so on.

2 4x10s or 2 1x15s will normally sound better than one of each.

Hope that helps slightly?

[Bill Fitzmaurice]

[quote name='Damonjames' timestamp='1348347375' post='1812710']
if I was to run the same head through a orange 4x10 and 1x15 (rated 600 watts each) given perfect world scenario could you run said amp flat out or only to an output of 600 watts.
[/quote]The Orange 410 is displacement limited (http://barefacedbass.com/technical-information.htm) to only 150 watts, the 115 to 100 watts, so a 1kW amp is massive overkill. This points out why you have to consider much more than just power ratings of both amps and cabs, and for that matter why this particular 419/115 combination is a poor one, as are most.

[Mr. Foxen]

Watts tell you nothing about a cab, and very little about an amp, so best ignoring them, and anyone who stresses the importance of the relationship between the two.

[ThomBassmonkey]

To sum up an answer, the wattage of th head is theoretically split evenly between cabs.

Real world though, a 1000w head could blow a 1200w cab or a 1000w head could be run happily for years into a 600w cab, it all depends on the user.

Just buy what you like then make sure you're using it properly.

[RandomBass]

With that lot running at full tilt on stage, I'd be more concerned for my hearing and innards than the cabs.

[Count Bassie]

Buy for sound and most useful features, not for wattage. Depends, but 200-400 is probably enough for anything if you pair with well-designed cabs, and if you learn how to get the most out of your amp. The trend for high-power is mostly due to buying into the bogus marketing feed.

My Eden head runs "400w at 4 ohms" and does just fine wherever I go with it. Punch, nice tones, and good solid presence in the mix. Ta-da.

[Phil Starr]

As you are an electrician I'll assume you know about watts,volts amps and ohms law.

the trouble is that speakers and amps aren't rated in the same way because they don't work the same way and the processes by which they fail are different..

Excluding old age speakers fail in two ways. They can be driven so hard that the coil leaves the magnetic field and suffers mechanical damage when it returns, in any case it will sound crap when it reaches this stage. this is the excursion limit Bill talks about and is a real problem with bass speakers. It isn't usually mentioned in any of the cab makers specs.

The second and probably most common cause of failure is burning out. With 300W going through a tiny copper wire it gets hot (200C isn't unusual) and eventually the materials in the construction of the voice coil break down. This is the thermal rating, the 600W that Orange rate their cab. The problem is in measurement and interpretation. You can't just feed DC current through the speaker because in real life the movement of the cone creates a cooling effect. For a long time a 1000Hz signal was used as a test signal but this doesn't work for all speakers, like horn drivers which only operate at very high frequencies. Now the most common method is to use some sort of filtered mix of a wide range of frequencies (often called pink noise) as the source. Pump this continuously through the speaker for several hours and, if it survives, that is its rating. There are a number of international and national standards for doing this sort of test but basically this is how they work.

The problem is that speakers don't run continuously like electric motors so this isn't a very fair test. Music has loud and quiet bits and in the gaps the speaker cools down. So long as you don't distort the sound speakers will handle short bursts many times their thermal rating. Hence the 'normal music programme' and 'peak' ratings many manufacturers give. So you can use a 1000W amp with a 250W speaker so long as you don't distort and so long as you don't push it beyond its excursion limits, which you probably will as a bassist.

Amps are rated differently. By and large it is very hard to break a well designed solid state amp as they have protection circuits built in which limit the power when you push them hard. However they will only swing a certain voltage, just below the power supply voltage and then they run out of volts and distort. Their ratings are then given at the voltage where distortion cuts in. As an electrician you will realise that applying a voltage across a lower resistance will give more current and power, so adding an extra speaker in parallel draws double the power from the amp. In practice the power supply in the amp will be limited to a certain current and so the full doubling won't happen so it is a rare amp that will actually double its power into 4ohms from 8ohms. Just to complicate things a little as the amp warms up the resistances (especially in the power supply) increase so the current available is less in a hot amp than a cold one. Valve amps run at very high voltages and have transformers to match the speakers so provide the same power to any speaker they have a tap in the output transformer for.

So, don't get too hung up about wattage ratings, most of the time you will only be operating at a few tens of watts or less anyway, The extra power is only to keep the loud bits clean. It's unlikely you will ever really need more than 200W for bass so any amp that gives at least 200W into 8ohms will do nicely. Most speakers will handle several times their rating of undistorted music but as a bassist you need to be aware of the possibility of over excursion. If you hear your speakers distorting at high levels on the low notes you need to turn down or roll off the bass and fairly promptly. I'd roughly match the ratings of my amps and speakers but I wouldn't worry too much if I had 1000w of amp going through 800W of speaker, frankly at that volume I'd be more worried about my hearing than my speakers.

Choose something that sounds good, try it out before you buy.

[0175westwood29]

as long as you listen and make sure your not distorting or the speakers are farting, you'll be fine.

saw a guy last week using a db750 with 2x112 cabs sounded wicked and was loud as hell! and that amp puts out 750w at 4 ohms.

as above play as much as you can then get what you like the most.

andy

[Mr. Foxen]

Important thing to remember about ohms law in this context is that the nominal impedance of the speaker (the 8ohm rating) isn't even close to its actual impedance for the most part, which varies across the range of frequencies it is expected to handle, and some of that variation is dependent on the cab, like having a big peak dependent on the port tuning and such.

[alexclaber]

I've been spending a lot of time on power handling recently and it's incredibly complicated. Something Phil didn't mention is that as a voice coil warms up, its resistance increases. This increases the impedance the amplifier sees, thus reducing the power delivered. And speakers are thermally rated based on the nominal load rather than the actual load, a cab that's rated at 1200W may only be actually capable of coping with 600W thermally. But an amp that's rated at 1200W into that nominal load may only be delivering 600W into that actual load, so one thing cancels the other (apart from the SPL being halved!)

[bremen]

[bremen]

^^^ that's four Eminence Beta 10 inch drivers, common enough, in a reasonable sixed sealed box. The thermal rating (the one in the advert) is 600W (assuming 150W per driver). Note how much power they can actually handle in the lowest octave of a bass guitar...

[Mr. Foxen]

[quote name='alexclaber' timestamp='1348755438' post='1817782']
(apart from the SPL being halved!)
[/quote]

SPL halved sounds like a massive deal, but it isn't perceived volume that is halved, it is just a bit quieter. I'm sure Alex knows this, but I can totally see people reading that in disbelief thinking its half volume.