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Mesa Boogie 800 Watt Amp with 600 Watt Cabinet...Risky?

Discussion in 'Amps and Cabs [BG]' started by violenteer, Mar 4, 2021.

  1. violenteer

    violenteer Supporting Member

    May 23, 2014
    Hey there,

    This topic of higher watt amp used with lower watt cabinet has surely been covered before at some point...but for those that know more about the science and physics involved here: I have acquired a Mesa 600 watt 2x12 combo cabinet, I am assuming from an M6 or M9 Carbine combo, but it is amp-less at this point. Instead of tracking down a Carbine head, I'd rather get one of the newer amp heads (Mesa WD-800 or TT-800), and then get a rackmount kit and throw it in this combo cabinet. Does anyone foresee any problems, here, if I am not cranking the amp beyond the halfway point? Thanks for the insight...and any sarcasm that may follow...
  2. Wild Rice Chris

    Wild Rice Chris Commercial User

    May 7, 2005
    Palatine, IL
    Rice Custom Guitars, Inc
    If you set the WD to 2 ohms while using the (presumably) 4 ohm cab, it will limit the amp's output to about 600 watts.
  3. Wasnex


    Dec 25, 2011
    Obviously you have more than enough power the blow the cab if you push the amp to its max power. So the answer depends somewhat on how loud you need to play.

    Another concern is that you could have an accident that would send a large burst of power to the speaker. Same issue here, the danger increases as you turn the amp up.

    I don't know exactly how the cab is rated, but typically drivers are given a RMS power rating and a Program power rating. RMS is basically the average power the speaker can handle on a long term basis without melting the voice coil Some people call this the continuous power handling, but music is not continuous.

    Program Power is double the RMS rating. The idea is the cab can handle short transients of 1,200W as long as the long term average power remains under 600W. Realistically if you want your cab to last a long time, you probably don't want to hit it with double the RMS power rating, but 1.5 x the RMS should be fairly safe; 1.5 x 600 = 900W. Keep in mind this is an occasional burst at 900W, and long term average of 600W or less.

    The 900W may be overly optimistic though. A third type of power handling is the Mechanical Power rating, which is often unpublished. The relates to how much power it takes to push the driver to Xmax. Xmax refers to the driver's linear excursion limit. Driver excursion is dependent on how the driver performs in the specific cab it is loaded in. Often the Mechanical Power rating is less than the RMS Power rating for certain frequencies below 100hz, and especially below the cab's port tuning frequency. This is one reason why an HPF can be useful. The HPF prevents the amp from sending power to the cab that is below its intended pass band.

    So you have a better idea of what I am talking about, here is the cone excursion plot from a small ported cab design for the Eminence 2512. The notes for the plan say: Displacement Limited to 250 Watts; F3 of 82 Hz. Use a steep high pass filter set to 50 Hz to protect your woofer.
    Xmax for this driver is 4.9mm. Note the excursion trace turns from black to grey as it crosses 4.9mm at about 45hz. As you see, driver excursion begins to increase as the frequency drops from about 1K. Then just above 100hz the excursion starts to decrease. The decrease in excursion is due to the port is becoming active. Excursion continues to decrease towards 65hz, which is Fb or the tuning frequency of the box/port. At Fb the port is making almost all of the sound. Below FB the response of the cab drops of quickly, and cone excursion increases quickly towards Xmax. The HPF is required to keep the driver from hitting Xmax at about 45hz.

    I have attached the cab design document if you want to check out other charts for this design, or other tunings for this driver.

    Attached Files:

  4. violenteer

    violenteer Supporting Member

    May 23, 2014

    Thank you for this! I did think about the high pass filter thing protecting from some of the sub-frequencies...and incidentally, both the Mesa WD-800 and TT-800 amps have a high pass filter. So I assume that could be a partial line of defense built in to the amp itself...?
    macmanlou, Element Zero and Wasnex like this.
  5. violenteer

    violenteer Supporting Member

    May 23, 2014
    That's crazy. Had not heard that. The only time I ever went with 2 ohms was running 2 road-ready 2x15 cabs with my 400+ back in the day. Good to know...but I wonder...does that put any stress on the amp? Sorry, I dunno, because I've never used an impedance that didn't match the cab. Appreciate your input.
  6. If you're concerned about it, you're probably playing too loud.
    Fumble Fingers likes this.
  7. Wasnex


    Dec 25, 2011

    I think you may have misunderstood. When operating the amp under 4 ohms there is a switch that you need to set to the 2 ohm position.

    The amp actually makes 800W at either 4 ohms or 2 ohms, but if you set the switch to 2 ohms and run the amp at 4 ohms, you get 600W.


    Impedance matching relates to tube amps because they have output transformers. The transformer matches the high impedance of the tubes to the low impedance of the speakers.

    With solid state amps it's not a matter of matching the impedance, it's only a matter of making sure you don't connect a load that is lower than the amp can handle. Essentially the amp tries to make the same voltage regardless of impedance. So as the speaker impedance is reduced, more current flows through the amp's the output devices. More current equals more heat. If you keep reducing the impedance, eventually you reach a point where the current becomes so high that the output devices are damaged.

    AFAIK the impedance switch on the back of the Subway amps reconfigures the power supply to limit the current to a safe level so the amp can be run 2 ohms. So if you run 4 ohms with the switch in the 4/8 ohm position, the amp makes 800W, but if you run 4 ohms and set the switch to the 2 ohm position the amp only makes 600W.

    If you run the amp at 2 ohms with the switch in the 4 ohm position, I am not sure what would happen but I don't recommend it.
    Jazzdogg, MAXSPINRUN, DrMole and 2 others like this.
  8. Wasnex


    Dec 25, 2011
    If you try hard enough, you could probably blow the cab with a 600W amp as well.
    mikewalker likes this.
  9. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Do not run the amp into a 2 ohm load with the switch set to 4-8 ohm position. It’s not good for the amp.
    Jazzdogg, macmanlou, ELG60 and 5 others like this.
  10. baxter_x


    Nov 27, 2013
    Does the switch limits the power like on the Mesa Titan or is it totally different ?
    If different, how does it allow 2 ohms load?
  11. NeonVomit


    Jan 29, 2013
    You're gonna have a bad time, that's what's gonna happen lol
  12. jeff62

    jeff62 Supporting Member

    Oct 24, 2005
    Central FL
    Fire! Run away! :smug:

    Seriously, having an amp that produces more power than your cabinet is NOT an issue if you use your noggin' (and your ears) and adjust the dials correctly to ensure you're not overdriving the cab. I've always owned amps that have a higher value and have *never* had a problem.

    Further, you could just as easily have a lower powered amp and a higher rated cab and still have an issue with cab longevity if you are not properly eq'ing your sound. Bottom line, use your ears and you'll be fine.
  13. jeff62

    jeff62 Supporting Member

    Oct 24, 2005
    Central FL
    Yup. But can you set the amp for 2 ohm (to limit the wattage it produces), and then connect it to a 4 or 8 ohm load without damaging the amp?
    violenteer and Element Zero like this.
  14. Element Zero

    Element Zero Supporting Member

    Dec 14, 2016
    Yup. Nifty feature of the Subway line. It’s how I run mine.
    violenteer likes this.
  15. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    The switch operates differently than the Titan, but will limit the power as a byproduct of its function.

    Yes, this is a (useful) byproduct of its operation.
    Toddbass65, Engle, violenteer and 4 others like this.
  16. Ric5

    Ric5 Supporting Member

    Jan 29, 2008
    I disclose nothing
    Mesa Boogie 800 Watt Amp with 600 Watt Cabinet...Risky?

    If you play loud enough to blow 600 watt speakers then you are totally risking long term hearing loss!
    swarfrat and agedhorse like this.
  17. Kael


    Dec 26, 2004
    Oklahoma City
    Just turn the damned thing down and you'll be fine. Amps that are more powerful than the cabs they are driving won't blow them unless you drive the amps to the upper limit. I've used amps more powerful than the cabs they are driving for years with no issues beyond one brain fart moment with a pre/power amp rig that was totally my fault (for some idiotic reason I left the amp and pre dimed and slapped a low E as soon as I powered up the amp the next day to make sure it was hooked up).
    macmanlou likes this.
  18. Kael


    Dec 26, 2004
    Oklahoma City
    Huh? I can't hear you, speak up. Will someone shut off that ringing sound coming from their phone!
  19. violenteer

    violenteer Supporting Member

    May 23, 2014
    Hey, thanks for the responses. I understand impedance in a basic, old school sense. I have for the most part use vintage tube amps that didn't provide many impedance options, with the exception of the Mesa 400+ and my Hiwatt 100. But in those situations, I never used differing wattages from amp to cab, it was only about how speakers were wired. I just don't have a lot of experience with some of these amp features that have been mentioned, so I really appreciate that. As far as playing too loud, those days have come and gone...I mean, you saw my mention of a 400+ with 2 2x15s at my bigger gigs back then, right? LOL. but I have always use prescription musicians earplugs, which to an extent is probably what saved me. I'm just into different and/or evolved projects now, with guitar players that don't have a full stack to contend with. Again thanks for the insight into the new Mesas!
    Last edited: Mar 5, 2021
    Element Zero likes this.
  20. Killing Floor

    Killing Floor Supporting Member

    Feb 7, 2020
    Austin, TX
    Not risky. First of all you can blow a 600W driver with a 250W amp if you want to. Next, headroom is a good thing. My normal single cab rig is a Mesa 800 with a 600W program cab, 1,200 peak. If you happen to have all your ins and outs dimed A) that’s rockin! And B) you need a bigger rig and ear plugs.
    Element Zero likes this.
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    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

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