Discussion in 'Monitoring' started by philipjent, Mar 23, 2007.

  • AT5047

    The New AT5047 Premier Studio Microphone Purity Transformed

  1. philipjent

    philipjent Guest

    Im looking into getting these speakers but Im a little confused , on the spec sheet it says 250 watts continuous handling and 1'000 watts peak. So does that mean I can put up to a 1'000 watt amp before they explode or do I have to keep my amp around 250 watts ?
  2. dementedchord

    dementedchord Well-Known Member

    May 11, 2006
    there are a myriad of spec possibilities for amps and unfortunately it seems no way to force manuf to adhere to one... the traditional version is called RMS... personally if they dont give an RMS rateing i would runaway!!! as for power it's a good idea to have150-200% of rated RMS power...
  3. philipjent

    philipjent Guest

    Ok check it heres all the specs...

    Passive 2-way design
    15" woofer
    1" exit high-frequency compression driver
    Progressive Transition Waveguide horn
    3/4" acoustically superior MDF cabinet
    Trapezoid cab design for excellent projection
    Dual-socket polemount system
    250W continuous power capacity
    1,000W peak power capacity
    Heavy-duty recessed handles
    Heavy steel grille
    1/4" and Speakon connectors
    SoniGuard protection circuitry
    18-1/4"W x 27-1/2"H x 17"D
    61 lbs.
  4. Massive Mastering

    Massive Mastering Well-Known Member

    Jul 18, 2004
    Chicago area, IL, USA
    Home Page:
    Knowing what sepakers they are might let us know if you can trust the specs at all...
  5. anxious

    anxious Guest

    I've been on the speaker manufacturing side of things for years, so here is an answer from that perspective. It's a >really< complicated question, if you dig deep. Why?

    1- There are very, very few speakers on earth that can stand even 100W of constant input power at a single frequency, (sine wave).

    2- There are very few decent speakers on earth that would be damaged by a very short peak of 2,000W.

    This means that it is tricky to state a speaker spec that gives the customer realistic guidelines for amps. If a manufacturer picks a low number sales will suffer, but also, many customers will not get near the full potential of the speakers. On the other hand, if a manufacturer states a higher number, a certain percentage of customers will be pissed off when they blow out their speakers.

    Here's my advice:

    If you are the kind of person who tends to push the volume limits, and the amp will be running flat out by the end of a long session, stick with a smaller amp. If you are the kind of person who pays attention to volume, playback distortion, etc, you can use a larger amp to get more out of the speakers on peak transients. Just don't run it flat out for hours.



    PS- you may encounter a very ingrained and persistant urban legend in the speaker world that speakers are actually safer with a larger amp, due to clipping. Having worked for the company that helped promote that idea in the 70's, I can tell you that it has since been proven false in 90% of circumstances. No need to get into that argument now, but there are very solid studies about this. Smaller amps are generally safer.
  6. moonbaby

    moonbaby Mmmmmm Well-Known Member

    Feb 23, 2005
    Apparently you are interested in using this box for some sort of live sound application? Are these going to be permanantly mounted somewhere, or carried around from gig to gig?
    NO cabinet made for live sound should be made of MDF (medium-density fiberboard) for several reasons. First off, it is heavier than a comparable plywood box, and is easily damaged by simply banging it into a doorway or loading into a van. MDF can absorb and retain moisture, causing it crumble under the vynl or carpet covering. This can also lead to the failure of the glue joints, resulting in the collapsing of the structure if improperly mounted or God forbid flown. I have seen this happen firsthand. It is the reason that NO professional live sound speaker is made of that crap. It's fine for a hi-fi or studio monitor sitting on a shelf, but otherwise...
    There is no mention in these "specs" about the woofers structure (is it a stamped frame or a cast frame?). Once again, live sound use really needs a cast frame. It can hold a much larger magnet/motor structure together that won't shift when the cab is dropped or knocked around. I have seen stamped frame woofers killed by this because the magnet shifted, putting the voicecoil permanently out of alignment. Not to mention that fact that the speaker manufacturers out there make their best models
    with cast frames.
    There is no mention of the HF driver's composition, either. What material is the diaphragm made from (titanium, aluminum,copper, poly-something, piezo crystal)? A 1" throat horn, is it a cast alloy or plastic? Once again, rough treatment can break the component.
    And as far as this "lower-powered amp" business is concerned, I worked as a sales rep for a company called Cetec-Vega in the 80s. We made the infamous GAUSS line of professional loudspeakers. Massive, castframe components, awesome power handling that was the highest and toughest in the biz at that time. I regularly took a raw frame 15" or 18" woofer and PLUGGED IT INTO THE NEAREST AC POWER OUTLET and let it COOK at 120VAC/60cycles for a good 30 seconds and then played music through it!!!!! I don't know how many sales pitches I did doing that, but it always worked!!! The speakers were inefficient, didn't really sound that great, but you couldn't blow the friggin' things up if you wanted to! The ONLY thing that would blow their HF drivers (I believe they were the 2200 model) was...A CLIPPED POWER AMP!!! Why? Because a voicecoil-in-a-magnet is simply an electric motor. The voicecoil gets real hot, and its' cyclical (actually sinusoidal) movement cools it. When the power amp clips, that sinewave-movement becomes a square wave, and the "keystoning" at the extreme edges of he wave make the voicecoil "hang up" for a nano second, causing it to burn at that spot. Pushing a HF diaphragm with a little Crown D75 or D150 (this was in the 80s) that was driven to clipping
    killed that diaphragm while a non-clipped waveform from a bigger DC300
    Today, I am a partner in a speaker repair business. We see the same thing today. DJ's blowing up diaphragms with ratty under-powered amps.
    If you talk to the design engineers at Eminence and JBL, they'll tell you the same thing: clipped power amps kill speakers more than too much power will.
  7. dementedchord

    dementedchord Well-Known Member

    May 11, 2006
    i'm with you moon dude... been doing this a LONG time and personaly never blown a speaker... but boy i've seen plenty of roached slinky's come through the shop...
  8. anxious

    anxious Guest


    However convinced you are, it doesn't work this way. Really. Some of us have actually studied this question carefully, from both a scientific and an experimental point of view.

    1- The Fourier spectrum of a highly clipped waveform actually contains relatively little RMS energy at potentially dangerous high frequencies.

    2- While air pressure should follow input voltage, cone motion DOES NOT follow input voltage. This is a common misunderstanding. The relationship between input voltage, cone motion and air pressure is much more complex than you suggest, and is described by differential equations, not linear equations. The transfer function is not algebraic, and it is incorrect to visualize cone motion as simply mimicing input voltage.

    3- The cone NEVER stops moving under clipping, not even for a nanosecond. I would bet my life on this, having run many experiments with strobes, lasers and microphones. For the cone to come to a stop for even an instant, working against its momentum, would require an infinite amount of energy input.

    4- The thermal inertia of a voice coil, combined with its inductive reactance makes it impervious to any extremely short electrical events.

    5- The dominant modes of cooling in a voice coil are not related to air flow over the surface of the coil. They just aren't. If they were, it would be easy to improve the power handling of a driver by putting a small fan on the back to blow air over the coil under high output conditions. But, when one tries this, one finds very little advantage.

    There are always counter examples, of course, and some amps that go unstable when clipped, which can certainly cause damage. I'd be curious to know the names of the engineers at Eminence and JBL who are still supporting the clipping damage theory. Both of those companies are well-informed, and probably now know about contemporary research contradicting the idea.






  9. anxious

    anxious Guest

    PS- Here's a question about that *neat* demonstration, plugging the driver into the AC outlet. (I ruined a perfectly good Fender 2x12" cab doing that as an idiot kid. You know, the kind of Fender that today would be worth a small fortune...)

    If the driver's resonance happens to fall right near 60 Hz, you can get away with 120 Vac. Why? Because the driver has a high reactive impedance right near resonance, and so won't dissipate as much heat power.

    Let's say it was an 8 Ohm, 15" driver with an Fs of 58 Hz and a Qes of 0.40. That would typically put Zmax at about 100 Ohms. Plugging it into the wall would dissipate well under 150 Wrms. Enough to get it hot, but not enough to hurt it. Move the frequency to 45 Hz or 75 Hz, and you will toast it in no time.


  10. dcj

    dcj Guest

    Well philipgent, you definately got an earful of comeback for what started out as a seemingly simple question. IMO there's a good answer imbedded in all of the responses. None of them are 100% right, and none are 100% wrong. There's some virtue in everything that's been stated. How it all applies to you is your decision. Speaker specs are ambiguous at best. The RMS rating has always been known to have an inherent flaw. The very equation of root mean square is so outdated and flawed that it is simply used as a "ballpark" calculation. The thing to remember is that a speaker is an electro-mechanical device. It is completely dependent on the laws of physics, and strict electronic specs and guidelines simply do not tell the whole story. However, much can be said for a common sense approach. What moonbaby said about a cast frame versus a stamped frame is great info....check it out. What about the voice coil? The bigger the better....check it out. What about the size, shape, and type of magnet? Check it out. What about the cone? Paper, aluminum....check it out. Compare all of these physical characteristics to comparable products, it's a good starting point. As for the cabinet, I agree, stay away from MDF, you'll live to regret it. As for the trapezoidal shape, I would question that design in regards to projection. It seems to be more acoustically relevant to dispursion. Also, keep in mind that any cabinet up on a pole system is most likely going to have resonance problems. Watch out for descriptions like, "progressive transition waveguide horn". The important element is the high frequency driver. The horn is simply a dispursion lense mounted to the driver. Don't over-exaggerate it's importance as compared to the driver itself. Last, but not least, we get back to your original question about power handling. Remember, there isn't only just one kind of power output. Whatever type of amplifier you plan on using, save your spec digging for it. Your amp is what controls the way the speakers react. The amp says jump, the speakers say, how high. Good clean controlled power will make speaker matching a much easier task with the added benefit of improved sound. Check into damping factors, and other relevant specs. Also, it is always a good idea to use some type of speaker protection circuitry in line.
  11. sheet

    sheet Well-Known Member

    May 28, 2003
    Kansas City, KS
    Home Page:
    Another vote for clipping not blowing speakers directly. Also, another false JBL statement is: "Underpowering a speaker causes failure."

    As for the waveguide issue, I do hear differences in HF horns with the same HF compression drivers. But have never heard any tech or manufacturer blame a horn for causing driver failures. Only inducing a distortion of it's own.
  12. dcj

    dcj Guest

    The waveguide issue is a form of controlled dispursement. The same type of physio-acoustic phenomenon as cupping your hands at various degrees around your ears. A perceived difference in sound using the same driver. Obviously relevant, especially if it induces distortion, but not the cause of driver failures. Another misconception about speaker/pwr-amp matching is the notion that a larger more heavy duty speaker requires far more power to drive it. It can be easy to get caught up in the spec number game. The higher the numbers, the better the component. The real focus should be placed on efficiency when evaluating all components. I hate to date myself, but in the mid-70's I purchased a pair of new EV Eliminator II's. A folded reverse baffle design (projection) using a very highly rated (at the time) EV SRO 15" spkr. and a horn/driver combination. One day out on the road, we fried the small speaker in a cassette recorder that we used for writing purposes. We adapted a "y" connector with a 1/8th inch phono plug to go from the spkr. output of the cassette to the Eliminators. The cassette was rated at 4.5 watts rms. The Eliminators were so efficient that they put out enough db's to prevent normal conversation at a distance of less than 20 feet. Obviously, the quality of the power was sub-standard to say the least, but we all learned an amazing lesson as far as speaker efficiency is concerned.
  • AT5047

    The New AT5047 Premier Studio Microphone Purity Transformed

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