Small powered mixers - why no insert?

[Taller]

In addition to my band gig, I'm starting an acoustic side project with a lovely female friend of mine. :)
I've never really paid attention to small powered mixers until now and I'm wondering why they typically do not have an insert to allow the use of a compressor on the mic inputs?
Am I missing something or not interpretting the inputs on these things correctly?
Specifically, I've been looking at a Carvin product:
http://www.carvinguitars.com/products/XP1000L

Thanks -

[Reincaster]

Because it's an overall effects loop unfortunately, basically, like an insert point, but for everything That "EFF" knob regulates the signal sent to the effects unit.

[GCDEF]

I would assume because most people buying a small powered mixer want cheap and simple, so there's no point adding a feature almost none of its purchasers would use.

[rokpunk]

forget about the carvin mixer...they are junk.
you'd be better off with an A&H MixWizard if you want/need inserts on all the input channels.

[RustyAxe]

forget about the carvin mixer...they are junk.
you'd be better off with an A&H MixWizard if you want/need inserts on all the input channels.Junk? Evidently you know something that thousands of us very satisfied Carvin PA owners do not. My passive RX1200R does everything I need it to do ... and does it well. Recommending something at 2X the cost of the OP's target, and is unpowered, when the OP clearly is interested in a powered mixer, isn't helpful.

To the OP, check out the Carvin RX1200L ... the 1/4" jacks on channels 1-6 are switchable between line input or insert functions. Costs a bit more, but you won't outgrow it soon.

[loudboy]

They're built to a pricepoint. Plus, the target market would have no idea how to use a feature like that.

[rokpunk]

Junk? Evidently you know something that thousands of us very satisfied Carvin PA owners do not. My passive RX1200R does everything I need it to do ... and does it well. Recommending something at 2X the cost of the OP's target, and is unpowered, when the OP clearly is interested in a powered mixer, isn't helpful.

To the OP, check out the Carvin RX1200L ... the 1/4" jacks on channels 1-6 are switchable between line input or insert functions. Costs a bit more, but you won't outgrow it soon.


Carvin PA's are what musicians buy when they need a sound system. They are cheap in every aspect. They are most certainly NOT what sound companies use, because, in general, we know better. To answer the powered mixing board question, I would steer far away from a powered mixer. First of all, they rarely offer enough power, second, if the amp section of the console blows (and it will with time), you are not only down an amp, but now you are down an amp AND a board. Bad move. But why listen to me....I know nothing at all about live sound :sarcasm. Taking advice from guitar players who spend more time on stage than behind the board makes much more sense. Not that it should matter, but know that professionals put Carvin in the same group as Behringer and Mackie. In fact, most pros would rather use a Mackie. If you want cheap and unreliable, Carvin is for you! Good luck with that.

[frank4001]

My Yamaha has a built in compressor...probably not great but its there in 4 channels.. EMX512c.

[RustyAxe]

But why listen to me....I know nothing at all about live sound :sarcasm. Taking advice from guitar players who spend more time on stage than behind the board makes much more sense. Not that it should matter, but know that professionals put Carvin in the same group as Behringer and Mackie. In fact, most pros would rather use a Mackie. If you want cheap and unreliable, Carvin is for you! Good luck with that.Bull----. If the OP was a pro sound engineer he wouldn't have asked the question. If the OP had a pro engineer, he wouldn't need a PA, would he? The OP is in a duo, and WILL be running his own sound from the stage ... just like the vast majority of us weekend warriors do. You make your money running sound, and have the gear to do it your way. We make money playing the music ... that is, creating the sounds you are paid to reinforce.

My objection to your post isn't your opinion of Carvin (or the other "junk" brands you name), but rather, the complete worthlessness of your reply to someone with a $500 budget and no pro-sound experience.

[Taller]

Glad to see TGP is still populated by those with some strong opinions!:D (Like I expected otherwise.)

Thanks for the responses. For the record, I've had positive experiences in the past with Carvin gear, from guitars and amps, to pickups, speakers and parts, and I know someone personally who runs open mic nights regularly with an older Carvin powered mixer and speakers...without a hint of trouble.

My question was just out of curiosity. I realize thousands of small acoustic combos perform every weekend without the ability to run a compressor inserted into the input. Was just wondering if I was missing something, or that's just the way it is.

Thanks -

[speakerjones]

I have a couple of Soundcraft Spirit Powerstation 600 powered mixers in my rental department (large regional AV company). They're pretty robust for powered mixers, and have channel inserts, as well as some routing options that most powered mixers don't have. They have actual faders which is nice. They also have some built in Lexicon effects that sound way better than the crap on an A&H. Not sure if they're still built, but I'd even take a used one over the Carvin you linked.

Under normal band circumstances, I would agree with rokpunk's advice to stay away from powered mixers, as they are extremely limiting, but if the OP already has some passive speakers that work well, in the context of a duo, I see no problems with going with a powered mixer. There are multiple acceptable tools for every job. Just do your research and go for the quality stuff when it counts.

PS - those one-knob compressors on the Yamaha mixers usually do more harm than good to a mix.

[billyguitar]

Count me as one of the very satisfied Carvin owner/users! I've had 4 different ones over the last 14 years or so and still use 3 of them regularly. I'm currently selling the previous generation 12 channel because I bought the new lightweight (18 pounds) 12 channel powered head. I fully realize it's not full blown concert equipment but that's what sound companies are for! I mic up my 7 piece band with it and run 4 main speakers and 2 or 4 monitors and it sounds quite nice at moderate volumes.
It does have 4 "Amp Insert" jacks on the back of the head above the speaker jacks, for each amp in it. I know these aren't channel inserts but I see the 10 channel head doesn't even have these. I don't know if this would help the OP or not, I never use them!

[FlyingVBlues]

My band has a Mackie 808M powered mixer that we use for small gigs. Each of the eight channel strips has an insert for connecting external processors into the channel’s signal path. We use a pair of DBX 166XL compressor’s for vocals with the 808M without any issues. There is also a loop that can apply effects globally. Each channel has a EFX send control that can be used to set the level of global effects in a given channel and a bypass switch to remove the effect from the signal path of that channel.

Mackie has replaced the 408/608/808 mixers with the 608/1008/1012 mixers, which have individual channel inserts on most of the channels and dedicated in-line compressors on channels 1-4 (channels 1-6 on the 1012). I haven't tried the new models, but the older 808's are very reliable and sound good for a small mixer. We also have a much larger PA rig for larger gigs, but it would be overkill for a small bar or restaurant. I think a 808M or a PPM608 with good quality speakers would be more than sufficient for a duo in small venues.


FVB

[GCDEF]

forget about the carvin mixer...they are junk.
you'd be better off with an A&H MixWizard if you want/need inserts on all the input channels.

I've had better luck with Carvin mixers than the MixWizard, but that's just me. Regardless, OP is asking about small, powered mixers for an acoustic duo, not a 16 channel passive mixer.

For the OP's intended use, a powered mixer is an acceptable solution.

[rokpunk]

here is the OP's question and my final answer

question:
"I've never really paid attention to small powered mixers until now and I'm wondering why they typically do not have an insert to allow the use of a compressor on the mic inputs?"

answer: Because space is limited and it's too cost prohibitive to put more connectors on the mixer. In addition people using this type of box-head mixer generally don't have a clue how to, or a reason why they would need to, insert a compressor on a channel. this type of mixer is what is known in the industry as a "plug and pray" mixer. As a side note, typically these box-head systems will have a line out, which can be run into a "real" power amp, and from the amp to the speakers, so that you are not using the very limited amplifier in the mixer. This will preserve the life of your speakers and your mixer, due to the fact that under powering speakers is one of the main reasons that speakers blow, and the less you have to tax your mixer/amp, the longer it is likely to last.

[GCDEF]

here is the OP's question and my final answer

question:
"I've never really paid attention to small powered mixers until now and I'm wondering why they typically do not have an insert to allow the use of a compressor on the mic inputs?"

answer: Because space is limited and it's too cost prohibitive to put more connectors on the mixer. In addition people using this type of box-head mixer generally don't have a clue how to, or a reason why they would need to, insert a compressor on a channel. this type of mixer is what is known in the industry as a "plug and pray" mixer. As a side note, typically these box-head systems will have a line out, which can be run into a "real" power amp, and from the amp to the speakers, so that you are not using the very limited amplifier in the mixer. This will preserve the life of your speakers and your mixer, due to the fact that under powering speakers is one of the main reasons that speakers blow, and the less you have to tax your mixer/amp, the longer it is likely to last.

You should have stopped at the first sentence. The middle section is condescending, and the underpowering thing is just nonsense.

Why are you so angry?

[rokpunk]

Underpowering a speaker most certainly IS a major reason that speakers blow. I work on PA systems day in and day out....I'm not making this shit up. Underpowering a speaker can damage the voice coil due to the excess heat created by distortion. This distortion is created when the amp is not able to supply the power demand when the volume is turned up. If you turn the volume up very high without the power to back it up, you'll end up clipping the signal coming out of the amp. The speaker will try to reproduce this clipped signal, and if played under these circumstances for any length of time, the speaker will not last very long.

The middle section may be condescending, but it's also not made up, it's the truth. Call a sound company that does rentals and tell them that you want a "plug and pray system" and I'm willing to bet that 9 out of 10 will rent you a box-head mixer/amp and a pair of speakers.

You wouldn't want to see me when I'm "angry" :)

[GCDEF]

Underpowering a speaker most certainly IS a major reason that speakers blow. I work on PA systems day in and day out....I'm not making this shit up. Underpowering a speaker can damage the voice coil due to the excess heat created by distortion. This distortion is created when the amp is not able to supply the power demand when the volume is turned up. If you turn the volume up very high without the power to back it up, you'll end up clipping the signal coming out of the amp. The speaker will try to reproduce this clipped signal, and if played under these circumstances for any length of time, the speaker will not last very long.

The middle section may be condescending, but it's also not made up, it's the truth. Call a sound company that does rentals and tell them that you want a "plug and pray system" and I'm willing to bet that 9 out of 10 will rent you a box-head mixer/amp and a pair of speakers.

You wouldn't want to see me when I'm "angry" :)

You're not making it up, but you're not understanding it correctly. What you're describing is overdriving an amp, not underpowering a speaker.

Here's a pretty good read from Peavey's Live Sound Product Manager
http://www.peavey.com/support/technotes/poweramps/HOW_MUCH_POWER.pdf

"First … let’s stop the spread of a big myth. You cannot burn out a speaker by using too little power"

"The mistake people make is they don’t realize how much power their amplifier is actually creating when it clips. An amp under hard clipping conditions has the potential to almost double the amount of power that it puts out at its full continuous (RMS) rating. That is to say that an amp with a 200W continuous rating can put out (the duty cycle equivalent of) 400W during hard clipping. So if you burned up your 300W speaker with a 200W amp, it was not because you were underpowered … it’s because the 400W generated by your amp when you weren’t looking exceeded your speaker’s rating."

[rokpunk]

the info you provided is from peavey, the undisputed kings of misleading power ratings. i understand the fact that underpowering a speaker can cause damage just fine. i see it happen quite often. it's cool that you can cut and paste from peavey's .pdf file, but it's ME who doesn't understand? really?

[GCDEF]

the info you provided is from peavey, the undisputed kings of misleading power ratings. i understand the fact that underpowering a speaker can cause damage just fine. i see it happen quite often. it's cool that you can cut and paste from peavey's .pdf file, but it's ME who doesn't understand? really?

I'm afraid it is. I cut and paste because I didn't feel like typing it all in myself.

I understand and agree that overdriving an amp will cause it to clip which sends spikes to the speakers that can damage them. That's pushing an amp beyond it's capabilities. Perhaps you're just using the term that confuses a lot of people, but it's not underpowering that damages speakers, it's overpowering by pushing an amp too hard.

[rokpunk]

<forehead slap>
you win. you are right. underpowering a speaker can cause no damage whatsoever.
obviously i just don't understand.

[Reincaster]

I'm afraid it is. I cut and paste because I didn't feel like typing it all in myself.

I understand and agree that overdriving an amp will cause it to clip which sends spikes to the speakers that can damage them. That's pushing an amp beyond it's capabilities. Perhaps you're just using the term that confuses a lot of people, but it's not underpowering that damages speakers, it's overpowering by pushing an amp too hard.

It's kind of the same thing? You would only overdrive the amp into clipping if the amp wasn't providing enough clean power? It's no secret that an amp overdriven produces more power than it was rated for, but that power is now rapidly intermittent, in other words it is clipping.

400 watts of distorted, hard clipping is different than 400 watts of unclipped signal? You're both intelligent guys, but the terms get mixed up for what I feel is the same thing.

[MrBanjo]

the info you provided is from peavey, the undisputed kings of misleading power ratings. i understand the fact that underpowering a speaker can cause damage just fine. i see it happen quite often. it's cool that you can cut and paste from peavey's .pdf file, but it's ME who doesn't understand? really?

You could learn a few things from that Peavey article, and GCDEF has been right on.

If underpowering a speaker causes damage, why doesn't every speaker blow up when the volume is turned down (ie, less power)? Do you really think the speaker knows how many watts the amp is capable of producing? You're just wrong.

The truth that gets confused is that using an amp that is underpowered leads to user error (turning it up so that it is constantly clipping). Over time, this is what burns up a speaker. You can "underpower" a speaker all week long, and as long as you are not clipping the amp, the speaker will be fine. Are you trying to say otherwise?

It is possible that you understand this and are just not explaining it very well, but I don't want the poor chap to be misled.

[GCDEF]

<forehead slap>
you win. you are right. underpowering a speaker can cause no damage whatsoever.
obviously i just don't understand.

You don't. Instead of shutting down, perhaps you could try to change that.

[GCDEF]

It's kind of the same thing? You would only overdrive the amp into clipping if the amp wasn't providing enough clean power? It's no secret that an amp overdriven produces more power than it was rated for, but that power is now rapidly intermittent, in other words it is clipping.

400 watts of distorted, hard clipping is different than 400 watts of unclipped signal? You're both intelligent guys, but the terms get mixed up for what I feel is the same thing.

No, it's not the same thing. The problem with calling it "Underpowering speakers" is that then people come up with silly "rules of thumb" such as you need twice the amp wattage as you do speaker wattage, which if you think about it really makes no kind of sense. Here's why.

Let's say you have 400 watt speakers. The rule of thumb guys would tell you that you need and 800 watt amp so you don't "underpower". Now let's say you hook that same amp up to 1600 watt speakers. The rule of thumb guys would then tell you since your amp only puts out half the power the speakers are rated for, you're underpowering and putting your speakers in jeopardy.

Following that logic, the conclusion has to be that the lower powered speakers are somehow more robust than the 1600, as with the same amp, they are regarded as the safer match. Ask yourself though, if you push the amp into clipping, which speakers you think would be more likely to survive.

You're only going to push your amp into clipping if you don't have enough amp. The power handling ability of your speakers really has nothing to do with that, but if you do accidentally overdrive your amp, higher powered speakers are going to have a better chance of survival.

Somehow using an amp that's too small and pushing it too hard has become known as "underpowering your speakers', which just isn't what's happening. You can run a 10 watt amp int 1,000 watt speakers all day and not hurt anything.

The bottom line is, don't run your equipment at its limits and expect it to survive long.

[modulusman]

GCDEF is corect in his posts in this thread. I suggest Rokpunk should do some research on other forums like http://acapella.harmony-central.com/forumdisplay.php?33-Live-Sound-amp-Production. Don Boomer posts over there as well as agedhorse who not only designs musical gear for a living but also owns a recone shop.

[rokpunk]

Well, if we are going to listen to Peavey and their take on underpowering speakers, why don't we have a look at what Yorkville has to say about the matter, shall we?

Why do speakers "blow"?

There are many reasons speakers "blow". The most common ones include over powering, under powering, transients, feedback, dropping and bad cables.

Under Powering:
Yes, you read it right - under powering can blow speakers. In fact, it is a very common cause for speakers failing. This is a little bit difficult for people to understand, however, we will attempt to present a brief explanation here. Speaker science is very complicated (very few people in the world understand it fully), so we cannot hope to give a very thorough explanation in just a few lines in this booklet.
When a speaker receives power from your amplifier it converts most of the power into sound by moving back and forth and causing the air to vibrate. However, it is not 100% efficient and some of the energy is converted into heat. The higher the power, the higher the heat. When a speaker is given a signal that is clipped, it actually receives far more continuous power than it would when it is given a clean (not distorted) signal. This is converted into more heat than the speaker was designed to handle and the coil literally burns. It can, in extreme situations, actually catch on fire (remember, the cone is made of paper)!
So, you can use a power amplifier that puts out considerably less power than the speaker is rated for, and yet, because it is being run into clipping, the speaker will blow. The harder the amplifier is clipped (the louder the distortion), the greater the chance of this happening. Tweeters are particularly sensitive to clipping because a clipped signal generally has lots of extra high harmonics (high frequencies) and tweeters are normally able to handle only small amounts of power. However, woofers can be blown due to clipping as well.


You can tell me I am wrong until you are blue in the face. I've worked in the AV industry for just about 25 years now, from being house engineer at clubs to being tour manager/FOH mixer for several touring bands, to system engineer for million dollar + sound systems, to owning my own sound company, and I can tell you from REAL LIFE experiences that underpowering a speaker can, and will, blow a speaker. I'm not going to argue with you about this any further. You've done a fine job interpreting what you have read on the internet from Peavey. I'm telling you what I have seen in my 2 decades of working behind the scenes, on PA systems from sound on a stick, to plug and pray systems, to amphitheater systems comprised of 50+ speakers. I've seen speakers catch on fire. It happens. Feel free to believe what you want. Nobody is going to try to stop you.

[GCDEF]

Well, if we are going to listen to Peavey and their take on underpowering speakers, why don't we have a look at what Yorkville has to say about the matter, shall we?

Why do speakers "blow"?

There are many reasons speakers "blow". The most common ones include over powering, under powering, transients, feedback, dropping and bad cables.

Under Powering:
Yes, you read it right - under powering can blow speakers. In fact, it is a very common cause for speakers failing. This is a little bit difficult for people to understand, however, we will attempt to present a brief explanation here. Speaker science is very complicated (very few people in the world understand it fully), so we cannot hope to give a very thorough explanation in just a few lines in this booklet.
When a speaker receives power from your amplifier it converts most of the power into sound by moving back and forth and causing the air to vibrate. However, it is not 100% efficient and some of the energy is converted into heat. The higher the power, the higher the heat. When a speaker is given a signal that is clipped, it actually receives far more continuous power than it would when it is given a clean (not distorted) signal. This is converted into more heat than the speaker was designed to handle and the coil literally burns. It can, in extreme situations, actually catch on fire (remember, the cone is made of paper)!
So, you can use a power amplifier that puts out considerably less power than the speaker is rated for, and yet, because it is being run into clipping, the speaker will blow. The harder the amplifier is clipped (the louder the distortion), the greater the chance of this happening. Tweeters are particularly sensitive to clipping because a clipped signal generally has lots of extra high harmonics (high frequencies) and tweeters are normally able to handle only small amounts of power. However, woofers can be blown due to clipping as well. It's not the under powering that causes the problem, it's the distortion that often occurs as a result of under powering that is the culprit.


You can tell me I am wrong until you are blue in the face. I've worked in the AV industry for just about 25 years now, from being house engineer at clubs to being tour manager/FOH mixer for several touring bands, to system engineer for million dollar + sound systems, to owning my own sound company, and I can tell you from REAL LIFE experiences that underpowering a speaker can, and will, blow a speaker. I'm not going to argue with you about this any further. You've done a fine job interpreting what you have read on the internet from Peavey. I'm telling you what I have seen in my 2 decades of working behind the scenes, on PA systems from sound on a stick, to plug and pray systems, to amphitheater systems comprised of 50+ speakers. I've seen speakers catch on fire. It happens. Feel free to believe what you want. Nobody is going to try to stop you.

They're saying the same thing Peavey did. When you clip your amp it generates way more power and that's what blows the speakers. Don't clip and you're fine. That goes right back to using an amp beyond its limits, and has nothing to do with underpowering your speaker. The power handling ability of your speaker has nothing to do with whether you clip your amp or not, but if you do, higher powered speakers have a better chance of survival. The bottom line is don't use too small an amp for the job, which is NOT the same thing as saying don't underpower your speakers.

You didn't even address any of the points I made and you're misinterpreting what the speaker companies are saying. It really doesn't matter if you've been in the field for 25 years or not, you're still wrong.

[rokpunk]

OK, since you obviously need to be right and have the final word, it's all you. You are the winner! Good job!

[3dognate]

They're saying the same thing Peavey did. When you clip your amp it generates way more power and that's what blows the speakers. Don't clip and you're fine.

I'd wager that >90% of non-professional people run their amps with the inputs cranked... Chances of clipping the amps and causing spikes is quite high.

Properly setting gains and Maximizing headroom is very important if you are going to tax a system.

[GCDEF]

OK, since you obviously need to be right and have the final word, it's all you. You are the winner! Good job!

I still don't know why you're so angry.

[modulusman]

Well, if we are going to listen to Peavey and their take on underpowering speakers, why don't we have a look at what Yorkville has to say about the matter, shall we?

Why do speakers "blow"?

There are many reasons speakers "blow". The most common ones include over powering, under powering, transients, feedback, dropping and bad cables.

Under Powering:
Yes, you read it right - under powering can blow speakers. In fact, it is a very common cause for speakers failing. This is a little bit difficult for people to understand, however, we will attempt to present a brief explanation here. Speaker science is very complicated (very few people in the world understand it fully), so we cannot hope to give a very thorough explanation in just a few lines in this booklet.
When a speaker receives power from your amplifier it converts most of the power into sound by moving back and forth and causing the air to vibrate. However, it is not 100% efficient and some of the energy is converted into heat. The higher the power, the higher the heat. When a speaker is given a signal that is clipped, it actually receives far more continuous power than it would when it is given a clean (not distorted) signal. This is converted into more heat than the speaker was designed to handle and the coil literally burns. It can, in extreme situations, actually catch on fire (remember, the cone is made of paper)!
So, you can use a power amplifier that puts out considerably less power than the speaker is rated for, and yet, because it is being run into clipping, the speaker will blow. The harder the amplifier is clipped (the louder the distortion), the greater the chance of this happening. Tweeters are particularly sensitive to clipping because a clipped signal generally has lots of extra high harmonics (high frequencies) and tweeters are normally able to handle only small amounts of power. However, woofers can be blown due to clipping as well.


You can tell me I am wrong until you are blue in the face. I've worked in the AV industry for just about 25 years now, from being house engineer at clubs to being tour manager/FOH mixer for several touring bands, to system engineer for million dollar + sound systems, to owning my own sound company, and I can tell you from REAL LIFE experiences that underpowering a speaker can, and will, blow a speaker. I'm not going to argue with you about this any further. You've done a fine job interpreting what you have read on the internet from Peavey. I'm telling you what I have seen in my 2 decades of working behind the scenes, on PA systems from sound on a stick, to plug and pray systems, to amphitheater systems comprised of 50+ speakers. I've seen speakers catch on fire. It happens. Feel free to believe what you want. Nobody is going to try to stop you. Probably from overpowering.
Well as I posted earlier go educate yourself on other forums. If agedhorse who is currently the design engineer for Genz Benz says you can't underpower I believe him.

[rokpunk]

Probably from overpowering.
Well as I posted earlier go educate yourself on other forums. If agedhorse who is currently the design engineer for Genz Benz says you can't underpower I believe him.

Well, if you want to take a wild guess that speakers catch on fire "probably from overpowering" them, that's your prerogative. I'm not going to stop you from believing that. I don't believe everything I read on forums, but I do believe what I've experienced in real life. YMMV.

[orogeny]

have to agree that the mackie powered amps are what you are looking for. you can even get a 406m for like 200 used these days! and they have channel inserts on every channel. i would recommend the extra power in the 808 series though.

. . . . and why NOT have twice as much power as a speaker is rated for?

if i have a speaker that can run 225w program . . . . how many watts do i want my amp to have?

[GCDEF]

. . . . and why NOT have twice as much power as a speaker is rated for?



Because the rating means something and you can blow speakers by overpowering them. :horse

[orogeny]

Because the rating means something and you can blow speakers by overpowering them. :horse
well, can you answer the second part of the question?

legitmate question. . . qsc actually is one of those companies that recommends twice your needed wattage

[GCDEF]

well, can you answer the second part of the question?

legitmate question. . . qsc actually is one of those companies that recommends twice your needed wattage

QSC sells amplifiers too. Bigger ones cost more.

For 225 watt speakers, I'd probably look at 250 to 275 for an amp. That'll let you get the most sound out of your speakers while minimizing the risk of overpowering either by clipping or just too much power.

Again though, the key to safety is don't run anything really close to its limits for extended periods and expect it to survive.

[3dognate]

QSC sells amplifiers too. Bigger ones cost more.

For 225 watt speakers, I'd probably look at 250 to 275 for an amp. That'll let you get the most sound out of your speakers while minimizing the risk of overpowering either by clipping or just too much power.

Again though, the key to safety is don't run anything really close to its limits for extended periods and expect it to survive.

Power amps generally sound like ass when pushed close to thier power limit... 2X power ensures that you get clean power to your speakers... Do not expect more than 175-200 clean watts out of a 250 watt amp. Definitely size the amp bigger than the speaker for this reason if nothing else.