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Poweramp question - please help

Discussion in 'Amps and Cabs [BG]' started by Direct Box Rox, Aug 28, 2016.


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  1. Direct Box Rox

    Direct Box Rox Silence = Deaf

    Feb 12, 2012
    USA
    I have one 8 ohm 15" Bag End cabinet. I'm looking for a power amp (as I plan I just using a power amp + a Sansamp unit). I noticed in the specs it gives output wattage in stereo and in bridged mono mode. I noticed a lot of times it will say something like; 1000 watts bridged mono @ 4 ohms.

    Well what if the cabinet is 8 ohms? Can you not run the amp then in "bridged mono"? To me, I understand it that if you are going to use bridged mono mode then the cabinet or total cabinet load has to be 4 ohms.

    Can anybody clear this up? Here's just one of the spec sheets I'm referring to;

    http://www.oregrundsbio.se/rmxspc.pdf
     
  2. You only want to bridge mono if the amp is short on power for one channel to drive one 8 ohm cab.

    If amp is ok bridged into 4 ohm it is doubly ok for the amp into 8 ohms but generally you are risking toasting a old school 15 like yours. Caution!!!
     
    Sartori and Direct Box Rox like this.
  3. DigitalMan

    DigitalMan Bring Back Edit/Delete Supporting Member

    Nov 30, 2011
    Bay Area, CA
    Page 2 shows bridged mono into 8ohms, so yes, it is possible.
     
    Direct Box Rox likes this.
  4. Direct Box Rox

    Direct Box Rox Silence = Deaf

    Feb 12, 2012
    USA
    Ok, thank you for the quick reply. Not to complicate matters, but I've got my eye on this amp (Crown XLS 1000) Crown XLS 1000

    I think it's pretty cut and dry where it states 8 ohm bridged mode is 700 watts (which would be the amp into my 8 ohm 15" speaker cab). But what if I added a second 8 ohm cabinet? I know that my speaker load will now be at 4 ohms.....but; can I run two 8 ohm cabinets with this particular amp in 4 ohm bridged mode? Or would I have to use the two channels at 8 ohm each and have 215 watts going to one cab and another 215 watts going to the other cab?

    I apologize that I am less than savvy when it comes to this as I've never had to deal with it the last 25 years.

    Thanks guys :)
     
  5. DigitalMan

    DigitalMan Bring Back Edit/Delete Supporting Member

    Nov 30, 2011
    Bay Area, CA
    You can run two 8ohm cabs in bridged mode. They will present a 4ohm load to the amp.
     
  6. Arthur U. Poon

    Arthur U. Poon

    Jan 30, 2004
    SLC, Utah -USA-
    Endorsing Artist: Mike Lull Custom Basses
    I use a pair of 8 ohm speaker cabinets with my power amp, but I run mine in stereo. I think my amp puts out 600 watts per side into 8 ohms, which seems to match the power handling specs of my speaker cabinets.

    I tried bridge-mono with my amp once into 2 cabinets, but it seemed to be more wattage than I felt safe running.
     
    Sartori, Al Kraft and Direct Box Rox like this.
  7. Arthur U. Poon

    Arthur U. Poon

    Jan 30, 2004
    SLC, Utah -USA-
    Endorsing Artist: Mike Lull Custom Basses
    Yes, you'd be a-ok running your amp bridge-mono as your two 8 Ohm cabinets equal a 4 ohm load. I'd listen closely to the 1-15" just to make sure you're not stressing it, but it should be fine. Do you know how many watts your 1-15" handles?
     
  8. Jazz Ad

    Jazz Ad Mi la ré sol

    For some reason, people get obsessed with the idea of bridging their power amp as soon as possible.
    It is an option but often not the best one. It if perfectly fine to only use one channel.
    Just do what makes the most sense.
     
    Snowglo, Sartori, Al Kraft and 4 others like this.
  9. Direct Box Rox

    Direct Box Rox Silence = Deaf

    Feb 12, 2012
    USA
    Thank you. I don't but I'll take a look and see if it says anything on the actual magnet. I also plan to call Bag End tomorrow to see if they can give me any info on this particular cab of theirs when I provide them the serial number.
     
    Arthur U. Poon likes this.
  10. Direct Box Rox

    Direct Box Rox Silence = Deaf

    Feb 12, 2012
    USA
    It's not obsession. It's trying to get the most bang for your buck. If I (or anyone) can save money by getting an amp where if you run it bridged mono you get more power - that's what I'm going to do. If money was not a factor then of course I was just get the 1.21 gigawatt model.
     
  11. As mentioned, single channel should be plenty. You might get a little extra clean headroom in bridge mode but the potential to give it death with 700W on tap would put me off.
     
    Arthur U. Poon, Sartori and Al Kraft like this.
  12. DWBass

    DWBass The Funkfather

    Today's power amps have quite enough wattage where you do not need to bridge. Just find one that matches your cabs rating. And the term 'headroom' is grossly overused!
     
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  13. DWBass

    DWBass The Funkfather

    More power is NOT going to make you louder. Common misconception. Most cabs max out with way less wattage. You want to be louder? Use more cabs! Those Bag End 15's are designed to handle 300w with peaks of 600w. You're looking to throw 1000w into it? Why?
     
    Last edited: Aug 28, 2016
  14. Nev375

    Nev375

    Nov 2, 2010
    Missouri
    I looked up a Bag End 15 and the one I looked at was only rated for 300 watts. I don't know if its the exact same model as yours. But that sounds typical for a many higher end 1x15s

    If so, I'd be looking for something that puts out around 280 - 350 watts or so into one channel of an 8 ohm load so you can use the other channed to power 2 - 8 ohm cabs in the future.

    Any of the amps on that page have the potential to fry that cab in bridged mode if the volume gets set wrong.
     
  15. InhumanResource

    InhumanResource

    Dec 28, 2012
    Beat me to it! OP is on the fast track to frying that poor 15 with the amp he is talking about.
     
  16. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    You are likely to get more "bang" than your buck can afford... All it takes is a momentary lapse of good judgement, or an accident to send that poor speaker to the place speakers go when they have been executed.
     
    Last edited: Aug 29, 2016
  17. Zooberwerx

    Zooberwerx Gold Supporting Member

    Dec 21, 2002
    Virginia Beach, VA
    Bridged mono better accommodates the wider voltage swings of an 8 ohm load...but not in your case. You would be better off with an XLS 1500 given the enclosure and desire to expand in the future. Just run the Bag End off one side.

    Riis
     
  18. Coolhandjjl

    Coolhandjjl Supporting Member

    Oct 13, 2010
    Appleton
    Any disadvantages to bridging such as running hotter, increased distortion, drop in damping factor?
     
  19. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    All of the above, but none of these are significant compared with the greater potential for damage.
     
  20. Rip Van Dan

    Rip Van Dan DNA Endorsing Artist Supporting Member

    Feb 2, 2009
    Duvall, WA
    That amp is a dual power-block amp. My WT500/800 is also has a dual power-block power section. That means that it has two discrete power channels that you can hook speakers up to and what you put in one side has no effect on what you put on the other side. My Eden is an older amp that will run a 4 ohm load off each side at the same time. I can hook up two 8 ohm cabs on one side and two 8 ohm on the other; two 8 ohm cabs on one side and one 4 ohm on the other; or one 4 ohm cab on each side. Running an amp like this is often called operating in "dual-mono" mode. My amp also has a balance knob that lets me adjust the mix of the two channels and I used to run a 115 off one side and a 410 off the other without the need to make drastic EQ changes on your preamp. That balance or mix-adjustment is a huge advantage when running different speaker configurations in each channel.

    My particular 115 was really boomy, so I used the balance knob to adjust the mix so the 410 got more power than the 115 and I wasn't overwhelmed with a boomy sound and drastic EQ choices that were good for the 115 but not for the 410. So operating in dual-mono mode was the right choice for those cabs. I have since replaced those two cabs with a single 410 (DNS410) that kicks that combo across the lot and down the street. My new cab has a power handling of 1400 watts, but at 8 ohms, if I ran it from just one of the channels, I'd only be putting out about 285 watts into it. So that's where this "bridged" stuff comes in.

    Instead of just plugging my one cab into one side of my dual power-block amp, I put the amp in "bridged" mode and hook my cab up to the bridged output. What this does is take the power output from one side of my amp (right side in my case) and combines it with the power output of the other side resulting in a doubling of the power. So in bridged mode, my amp puts out 800-watts rms into an 8 ohm load. My cab is an 8 ohm cab and it works perfectly. So now I can put out up to 800 watts into that one speaker cab and have huge amounts of power available.

    The one thing that bridged mode does though is require a different minimum ohms load to run it safely. My amp goes down to 4 ohms on each side but requires 8 ohms bridged. Basically running the bridged output at 8 ohms requires the two channels to run at 4 ohms each. Later Eden WT800B and C models (with backlit logo) could run at 4 ohms bridged (at 1100 watts) because their individual channels could operate down to 2 ohms each. So you do have to pay attention the minimum ohms load rating of the bridged output because it will be different than the two individual channels.

    The other thing you have to be careful of in bridged mode is putting too much power to your speakers. This really isn't a big problem unless you run a lot of distortion in your sound. If you hear the speakers making a farting sound, you're either running too much bass EQ into them (exceeds Xmax) or too much power. Easiest thing is to just dial back the master when you hear that. If you need more volume then dial back the bass EQ and try boosting the master back up but don't run the cab making that farting sound or you WILL damage your speakers. It's pretty easy to have a little more power available in your amp than your cab can handle - say 800-watts of power into a 700-watt power-handling cabinet as long as you listen to your speakers for stress. It's much harder when you have a drastic mis-match such as 800-watts into a cab that can only handle 200-watts. It's very easy to overdrive and damage speakers with that much difference. Usually it just makes more sense to plug such a cab into one of the channels instead of bridging the amp into it.

    Hope that helps.
     
  21. Primary

    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.

     
    Mar 4, 2021

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