A Stupid Question.

cybermgk

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Here's a really stupid question... is it still necessary to match the impedance at lower volume?
Not sure what you are actually asking.

But, for tube amps. one should match impedance as a rule. It is independent of volume played. You are ALWAYS safe matching impedance amp to cab. To not confuse the issue, we won't go into some amps able to take a 1 step mismatch (i.e. 8 and 16) .
 

ehb

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Here's a really stupid question... is it still necessary to match the impedance at lower volume?


Maximum Power Transfer is when the impedance is matched. No wasted energy.

Maybe simplified incorrectly but consider this: With a mismatch, there is some wasted energy. That energy must be dissipated somewhere and it ain't where it should be nor at the level it should be.... Think of energy reflected back into the source (amp) instead of dissipated within the load.... Something MUST dissipate the energy. In a mismatch situation, them electrons will pick something to heat up... Enough mismatch, TMS, Tuned for Maximum Smoke...

Reneck version: In a five speed car, you CAN drive to work every day in third gear.... Can be done.... For how long?
You are operating out of parameters... Shit be spinning faster than it should, thus working harder than it should for extended periods of time. Just because you've got a redline on the tach, doesn't mean you can run the drive train up there at it all the time.... Something will give....

Why do we plug up speaker cabs to our jugheads before flipping the power switch? No cab plugged in, IMPEDANCE MISMATCH. Load impedance is infinite and infinite Ω doesn't dissipate shit (no path, no flow, so no heat dissipation) ) so them electrons are gonna find something inside to dissipate the energy....and it ain't gonna like it... shit gonna heat the hell up quick, fast, and in a hurry....
 

Big John

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Andy Marshall (THD Amplifiers) always made sure his transformers could handle the heat from mismatched impedances.

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Bobby Mahogany

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There is also a rule that I used to know (!) about being able to plug a higher impedance speaker
into a lower impedance output but not the contrary.
Kind of you "can push" out 8ohms into 16 ohms and the extra resistance is only gonna "resist" more.
If you plug 16 ohms into 8 ohms, not enough resistance will/might cause the amp to blow.

Was it really that?
:fingersx:

Can @ehb confirm, please.
:thumb:
 

efstop

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There is also a rule that I used to know (!) about being able to plug a higher impedance speaker
into a lower impedance output but not the contrary.
Kind of you "can push" out 8ohms into 16 ohms and the extra resistance is only gonna "resist" more.
If you plug 16 ohms into 8 ohms, not enough resistance will/might cause the amp to blow.

Was it really that?
:fingersx:

Can @ehb confirm, please.
:thumb:
Low into high will fly
High into low won't go
 

ehb

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A mismatch is a mismatch first of all and should be avoided for the amp to work at optimum.

That being said, If the amp says 8Ω, then 8Ω is optimum.

Connecting a 4Ω cab will cut the opposition in half which will effectively try to double the current. Not good.

Connecting a 16Ω cab with double the opposition which will try to halve the current, amp not working as hard. There is still an impedance mismatch so much less output power, some wasted internally due to mismatch but if you can't match, this way is preferable until you can.

The docs on the amp should tell you how far off or at least "Don't go below" some Ω value....

The load connected to a source determines current which in turn determines power dissipation. Ω is opposition to current flow. The higher the Ω value, the more opposition, the less current, the less power dissipated. The lower the Ω value, the less opposition to current which means MORE current which will result in MORE power dissipated...

Some amps have switches for matching output Z of amp to Z of cab you have on hand. Some designed (over-engineered) to handle a range. Some pretty much expect you to 'Match Yo Shit".... Depends on the amp...

I'm not gonna say it is OK to run a mismatch because any mismatch is gonna change things somewhere internally. Whether or the magnitude of such being detrimental to the amp rests solely on the designer...
 

ehb

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Low into high will fly
High into low won't go

Confusing: which is which going into what?



Amp Z is Amp Z. Source (Amp) is always reference point

Load (cab) Z higher? More Ω, less current, less power. (preferable)
Load (cab) Z lower? Less Ω, more current, more power. NOT GOOD. Could TMS the amp.

TMS: Tuned for Maximum Smoke

Best is to just match em. You get the best operation and life out of it doing so... Less likelihood of it ever crapping the bed...



Old Peavey stuff must have been designed with Bufords in mind, may have had some there to field test in-house, because some old Peavey stuff would just plain refuse to die.... Lots of old old old Peavey heads/cabs/combos firing up every weekend at VFWs and ALs all over the country.... and PAs powered by CS800s that refuse to die.... They are still out there... Never dis a Peavey around a steel player...they will cut yo ass...
 

efstop

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Confusing: which is which going into what?



Amp Z is Amp Z. Source (Amp) is always reference point

Load (cab) Z higher? More Ω, less current, less power. (preferable)
Load (cab) Z lower? Less Ω, more current, more power. NOT GOOD. Could TMS the amp.

TMS: Tuned for Maximum Smoke

Best is to just match em. You get the best operation and life out of it doing so... Less likelihood of it ever crapping the bed...



Old Peavey stuff must have been designed with Bufords in mind, may have had some there to field test in-house, because some old Peavey stuff would just plain refuse to die.... Lots of old old old Peavey heads/cabs/combos firing up every weekend at VFWs and ALs all over the country.... and PAs powered by CS800s that refuse to die.... They are still out there... Never dis a Peavey around a steel player...they will cut yo ass...
The amp output is going into the cab. I have amps that state 4 (or 8) Ω minimum at the jack. An Orange Micro Terror is a 20W amp only into 4Ω. It easily handles 8 or 16Ω loads and its power drops to roughtly 10 or 5W with more resistance. Mind you, it's an SS power amp. I have three 16Ω Celestion 1x12 cabs, and by gar, I'm gonna use 'em with whatever has an external jack :D

I bet lots of players over the decades have never paid one bit of attention to proper speaker load, or not until they melted the speaker coil or transformer...
 
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ehb

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I bet lots of players over the decades have never paid one bit of attention to proper speaker load, or not until they melted the speaker coil or transformer...

Yep.... Daisy chaining cabs with no conscious thought process...

Amp is an audio power supply.... It operates within parameters.... Just like on a stage, you have to look at the BREAKER on each leg to the stage as a supply and what is can supply to the stage before 'speed of dark' hits.... You have to think a bit... In the old days with a big ass sound system with 18" Sugar Scoops and dbl 18" front loaded, Perkins across the tops of all those, and horn & tweeter banks, lighting truss front & back loaded with big par cans from hell and with all those got damn blinding ass rain lights across front....along with a chest high rack of power amps, we had to do some ciphering and we ain't even got to the Marshals and on stage shit.... We carried our own 'service entrance' trunk so to speak.....

Now, the full range stuff and subs are so damned efficient in speaker design, cab design, and class D power amps, we don't need near the stuff to generate equivalent SPL.... and with LED lights, the current/power requirements went through the floor.... Now JBL has done a PRX freaking stick/sub.... I wanna hear one....I've considered three of those.... Do away with my JBL fronts/subs AND my floors. Two front sticks and one back stick to replace the floors... A blues band I played with, we had Bose sticks with subs... Using them in back for floors was unreal... Hear everydamnthing....
 

efstop

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Yep.... Daisy chaining cabs with no conscious thought process...

Amp is an audio power supply.... It operates within parameters.... Just like on a stage, you have to look at the BREAKER on each leg to the stage as a supply and what is can supply to the stage before 'speed of dark' hits.... You have to think a bit... In the old days with a big ass sound system with 18" Sugar Scoops and dbl 18" front loaded, Perkins across the tops of all those, and horn & tweeter banks, lighting truss front & back loaded with big par cans from hell and with all those got damn blinding ass rain lights across front....along with a chest high rack of power amps, we had to do some ciphering and we ain't even got to the Marshals and on stage shit.... We carried our own 'service entrance' trunk so to speak.....

Now, the full range stuff and subs are so damned efficient in speaker design, cab design, and class D power amps, we don't need near the stuff to generate equivalent SPL.... and with LED lights, the current/power requirements went through the floor.... Now JBL has done a PRX freaking stick/sub.... I wanna hear one....I've considered three of those.... Do away with my JBL fronts/subs AND my floors. Two front sticks and one back stick to replace the floors... A blues band I played with, we had Bose sticks with subs... Using them in back for floors was unreal... Hear everydamnthing....
If I was going to gig as a solo, I'd get a stick system. Small, powerful and fairly wide price ranges. I've seen solo acts use one at the Toucan. Plenty big enough for that room, for sure.

What's remarkable is one could play an acoustic gig and record it with hardly any electric power at all. A plug for the stick, one for for the laptop and maybe one for a few pedals if one wished to go all atmospheric 'n' shit. So, a decent power bar, or a conditioned power system (but them's heavy suckers.)
 
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