Under Powering My Cab?

kennyisnotdead · #1 03-07-2011, 12:21 PM

I have an Orange OBC 410 with a Ampeg B2RE (US) and a Sansamp RBI preamp.

To give alittle background. The sansamp I bought off a friend, which I am so happy with. The cab was purchased from an orange dealer. I wanted to get the orange head but could not afford it. The head was bought from Daddys Junkie Music used. Every head they recommended was $1500+. Then about a month later im talking to someone and they explained if it is under powered it can be ruined just as if you over powered it...

of course the used gear shop wanted the sale, so they just sold it to me.

I am very concerned with the head under powering it. I'm 120% sure you guys on this board will know whats the best thing I could get on a budget for this cab if it is indeed in danger of being ruined by an under powered head.

I'm still learning the the science behind the ohms/watts. My cab runs on 8ohms at 400 watts. The head is only 250 at 8ohms. Will this damage my cab?

If so could I get a recommendation for a good fit for a budget under $1000, if its possible

Thanks for your time!

steamthief · #2 03-07-2011, 12:26 PM

No such thing as underpowering a cab. Do be aware that pushing the amp too hard may result in clipping, which can damage the drivers.

rockstarbassist · #3 03-07-2011, 12:27 PM

I recommend not using the cab or head at all to avoid any potential issues.

rockstarbassist · #4 03-07-2011, 12:28 PM

I recommend not using the cab or head at all to avoid any potential issues.

JimmyM · #5 03-07-2011, 12:28 PM

Quote:

Originally Posted by rockstarbassist

I recommend not using the cab or head at all to avoid any potential issues.

lol!

look, your rig is fine. underpowering is such a myth that it's not funny. if it were true, amps wouldn't have volume knobs.

kennyisnotdead · #6 03-07-2011, 12:43 PM

Thanks for the info that is the best news ever

Corey Y · #7 03-07-2011, 12:51 PM

"Underpowering" needs to be a sticky. There's no such thing as too little power blowing up a cab, it's an issue of running an amp to it's meltdown point and the resulting power spikes overpowering the cab. Putting a v6 engine in a truck meant to have v8 won't make the truck catch on fire. Overworking the v6 until it blows up might catch the truck on fire. If you can't play a gig loud enough without blowing up your amp get a louder amp, if not you're fine. That's the heart of the headroom issue, just having a power rating lower than your cab does nothing bad.

hdracer · #8 03-07-2011, 12:55 PM

^^^^ It is in the "AMPS FAQ!! Info on OHMS, Allsize RIGS-OverUnderPowerCabs DIY TechTalk-Links "

fretster · #9 03-07-2011, 12:58 PM

Just remember your amp is rated at 250 watts at a certain amount of distortion. That doesn't mean it can't put out more watts. It can, but with higher distortion. Crank it up, crank up your preamp, crank up the bass boost, and sure that amp will put out more than 400 watts, and fry your speakers. At that point, and well before that point, you will hear some serious distortion. Your ears will tell you! Ignore your ears and melt the voice coils. Pay attention to them, back off when it sounds distorted, and everything is going to be fine!

Note: this topic has been discussed almost as much as "are tube watts louder than solid state watts".

kennyisnotdead · #10 03-07-2011, 01:18 PM

I think the problem is places like Guitar Center, who are very customer facing. Hiring people to work in areas they don't fully understand or using wrong information to make sales. I was told in both Guitar center and daddys junkie music about the underpowering "myth".

I didn't mean for this to be a talk on ohms and watts I just wanted to double check my gear is safe and not going to burnout on me.

Corey Y · #11 03-07-2011, 01:19 PM

Quote:

Originally Posted by hdracer

^^^^ It is in the "AMPS FAQ!! Info on OHMS, Allsize RIGS-OverUnderPowerCabs DIY TechTalk-Links "

Well, there ya go.

BigOldHarry · #12 03-07-2011, 01:22 PM

Quote:

Originally Posted by steamthief

No such thing as underpowering a cab. Do be aware that pushing the amp too hard may result in clipping, which can damage the drivers.

+1

This has been discuessed AD NAUSEUM on this forum - it's always better to have more cab than amp.

spaz21387 · #13 03-07-2011, 01:23 PM

but guitar center uses those myths to sell you more expensive amps. thats the only reason they will say that.

Electricblue · #14 03-07-2011, 01:26 PM

I underpower every single one of my amps on a daily basis. Even all of my combo's. By turning it down to listening level.

If you could underpower a cab, nothing would have a volume knob.

I kind of think of it as overpowering an amp, rather than underpowering a cab. If anything.

kennyisnotdead · #15 03-07-2011, 01:26 PM

Quote:

Originally Posted by fretster

Note: this topic has been discussed almost as much as "are tube watts louder than solid state watts".

This is the information people are being fed at large stores like guitar center to make sales on expensive equipment. Its sales and marketing. Why try and sell someone a $500 head when we can sell them a $2000 head that they don't need when starting out.

BigOldHarry · #16 03-07-2011, 01:26 PM

Quote:

Originally Posted by spaz21387

but guitar center uses those myths to sell you more expensive amps. thats the only reason they will say that.

Not the only reason - - it's popular mythology that you can fry your amp/damage your drivers with too much of a mismatch. I have read folks argue fiercely over this subject here on TB, but the guys who we know and respect (Amp/speaker guys with real cred) all say the same thing: It's a myth. I'll bet that some of those GC guys really think that it could damage your amp/speakers. Keep in mind the usual hiring criteria at GC...

will33 · #17 03-07-2011, 01:29 PM

For the last time....speakers are tested using 1 (that's one) watt of power, I don't think they'd do that if it would damage them.

billfitzmaurice · #18 03-07-2011, 01:39 PM

Quote:

Originally Posted by kennyisnotdead

My cab runs on 8ohms at 400 watts. The head is only 250 at 8ohms. Will this damage my cab?

Yes, if you drop the amp onto it from a height of 20 feet or so.

Quote:

"Underpowering" needs to be a sticky.

It is. Perhaps if it was labeled "DO NOT READ THIS" someone on occasion actually would.

Quote:

Keep in mind the usual hiring criteria at GC...

That your Mom has a car to drive you to work?

Meyatch · #19 03-07-2011, 01:40 PM

for the record, I'm a firm disbeliever in the under-powering a cab myth, but the volume knob analogy you guys are all using is exactly the opposite of the actual under-powering "problem"

James Judson · #20 03-07-2011, 02:04 PM

Here is the rule of thumb.

Match watts to save speakers. To many watts into to little speakers can cause speaker failures.

Match impedance (measured in ohms) to save amplifiers. Impedance mismatches cause the amp to dissipate watts causing the amp to work to hard over heat and die.

There is a lot of grey area here. Think for a moment, 1000 watts into a 10 watt speaker will run just fine (that is until you turn up the amp past 10 watts). If you switch that around a 10 watt amp will run a 1000 watt speaker just fine until you try to get 1000 watts out of it. In theory your amp will start clipping around 10 watts. Past this point your signal starts looking like a square wave. A square wave is essentially DC. Heres the potential for under powered speakers getting blown. Will it happen on your 10 watt amp, your 100 watt amp, your 1000 watt amp, your 10,000 watt amp. Under powering speakers may be a worry for the sound engineer but probably never for the average musician.

Impedance??? To get maximum power transfer you need to match output impedance to input impedance. Your amp sucks up the same amount of watts as it delivers to your speakers (you don't have to believe me just touch the heat sink (fins) on the back of your amp. If you have a mismatch (high or low), now the amp has to dissipate more watts (heat) and at some point, melt down.

We could get into ohm's law that proves all this stuff but I haven't the time. Lots of good books on it though (pretty boring reading).

We should get Mythbusters in on this. They will need one big ass amplifier. I say "no myth" but not very likely.