Extension Speaker

L

Lars Praiseman

Sep 19, 2022
15
10
1,156
#1
I have a Markbass 103 combo that puts out 500 watts @ 4 ohms. The 3 10" speakers are 6 ohms total and they list the amp as having 400 watts at that impedance.
Of course the manual warns not to go below 4 ohms. I have a genz benz 12" cab that is 8 ohms, if I plug that into the ext. speaker outlet it would bring the total impedance down to 3.43 ohms.
Could I get away with this if the gain and master volume knobs never go above 5 (the 12 o'clock position) ?
 
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#2
Lars Praiseman said:
Could I get away with this if the gain and master volume knobs never go above 5 (the 12 o'clock position) ?
Click to expand...

No [maybe for a short while until....]

This is from member 'Agedhorse' Mesa Boogie Design Engineer

"Good question with a more complicated answer than you might expect... (of course)

So talking about class D amps with SMPS (since that seems to be what the question is about), heat is only one factor that needs to be considered. Heat is caused by the average output current, and that will be higher with a lower output impedance.

BUT, there is also limitations on the output current that can be sourced/sinked, and this is often a bigger cause of problems because you do not know what the actual impedance of the speaker is. NOMINAL impedance is the specification that is listed in the specs., and designers of amps need to understand that nominal is some form of average of the impedance versus frequency curve since impedance IS different at different frequencies, sometimes higher, sometimes lower. The problem is that the peak current might occur (actually is LIKELY to occur) at the frequencies where the impedance is the lowest and this can cause big problems."

Most amp designers factor this into the peak current versus thermal load calculations, and each uses different weighting factors in order to come up with a reliable product. When your cabinet combination calculates to below nominal impedance load, this also means that the minimum impedance will be even lower which can endanger the amp. I would NOT recommend doing so, because the damage that is caused becomes quite costly very quickly."
 
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#4
Numbers on gain and volume controls are meaningless. Setting the knobs to 5 does not mean the amp is operating at half power. Unless you actually measure the output at those levels under controlled test conditions, you don't know how much you are applying to the speakers. And that still does not apply during play. The numbers are only relative. They are there so you can recreate some previous setting.

You exceed the minimum impedance rating at your own risk.
 
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#7
Old Garage-Bander said:
Numbers on gain and volume controls are meaningless. Setting the knobs to 5 does not mean the amp is operating at half power. Unless you actually measure the output at those levels under controlled test conditions, you don't know how much you are applying to the speakers. And that still does not apply during play. The numbers are only relative. They are there so you can recreate some previous setting.

You exceed the minimum impedance rating at your own risk.
Click to expand...
 
#9
NEBADON2000 said:
No [maybe for a short while until....]

This is from member 'Agedhorse' Mesa Boogie Design Engineer

"Good question with a more complicated answer than you might expect... (of course)

So talking about class D amps with SMPS (since that seems to be what the question is about), heat is only one factor that needs to be considered. Heat is caused by the average output current, and that will be higher with a lower output impedance.

BUT, there is also limitations on the output current that can be sourced/sinked, and this is often a bigger cause of problems because you do not know what the actual impedance of the speaker is. NOMINAL impedance is the specification that is listed in the specs., and designers of amps need to understand that nominal is some form of average of the impedance versus frequency curve since impedance IS different at different frequencies, sometimes higher, sometimes lower. The problem is that the peak current might occur (actually is LIKELY to occur) at the frequencies where the impedance is the lowest and this can cause big problems."

Most amp designers factor this into the peak current versus thermal load calculations, and each uses different weighting factors in order to come up with a reliable product. When your cabinet combination calculates to below nominal impedance load, this also means that the minimum impedance will be even lower which can endanger the amp. I would NOT recommend doing so, because the damage that is caused becomes quite costly very quickly."
Click to expand...
Great info, thanks..........LP
 
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#13
NEBADON2000 said:
No [maybe for a short while until....]

This is from member 'Agedhorse' Mesa Boogie Design Engineer

"Good question with a more complicated answer than you might expect... (of course)

So talking about class D amps with SMPS (since that seems to be what the question is about), heat is only one factor that needs to be considered. Heat is caused by the average output current, and that will be higher with a lower output impedance.

BUT, there is also limitations on the output current that can be sourced/sinked, and this is often a bigger cause of problems because you do not know what the actual impedance of the speaker is. NOMINAL impedance is the specification that is listed in the specs., and designers of amps need to understand that nominal is some form of average of the impedance versus frequency curve since impedance IS different at different frequencies, sometimes higher, sometimes lower. The problem is that the peak current might occur (actually is LIKELY to occur) at the frequencies where the impedance is the lowest and this can cause big problems."



Most amp designers factor this into the peak current versus thermal load calculations, and each uses different weighting factors in order to come up with a reliable product. When your cabinet combination calculates to below nominal impedance load, this also means that the minimum impedance will be even lower which can endanger the amp. I would NOT recommend doing so, because the damage that is caused becomes quite costly very quickly."
Click to expand...

And the volume knobs have no reliable effect on the the output?
 
#16
crazyBassClown said:
What do you hope to gain by adding a speaker and then not turning up the volume?
Realistically you need a 16ohm cab to add it safely to the amp and they are non existent in the bass world unless you get a custom one built.
Click to expand...
I refuse to believe you can add an extension cab to the existing three 10"s.

The ability to power another cab, sure, that makes sense.
 
#17
Marko 1 said:
I refuse to believe you can add an extension cab to the existing three 10"s.

The ability to power another cab, sure, that makes sense.
Click to expand...
Markbass doesn't have the manual online and I can't find an image of the back but I bet it is just one of their heads in a box so probably has 2 speaker outs on the back, and would work fine powering an additional 16 ohm cab.
 
#19
mike buzzetti said:
get a 2x10 cab with 8 ohm speakers , wire it in series =16 ohms , all good. you will have lower power ( 37.5% of the total )going to the 16 ohm cab but will be moving more air so ?? 4.36 ohms total
Click to expand...
No, the dissimilar loads in series will interact as each load’s impedance varies independently.

This works fine with identical loads though.
 
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#20
agedhorse said:
No, the dissimilar loads in series will interact as each load’s impedance varies independently.

This works fine with identical loads though.
Click to expand...
I knew there was more to it than simple math , thanks ! so is it inductive loads interacting ? Wait a 3x10 cab would be wired series parallel right ? so 2x8 series 1x8 parra. right ?? its still 5.3 ohms so he might be pushing the limits ?? 3.98 total ohms
 
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