1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  

Help. I am ignorant regarding impedance matching.

Discussion in 'Amps and Cabs [BG]' started by olddave, Oct 8, 2019.

  1. olddave

    olddave Supporting Member

    May 26, 2011
    Please do not waste your time explaining impedance to me. I have read all kinds of explanations and still do not understand it. But my question is a simple one: I have a Sunn 200s amp but getting too old to lug the 215 cab around and am not good enough to merit a roadie. Can I plug my 2 lightweight GK cabs (115 and 210) into the 200s without doing harm? My taps are not marked so I do not know what impedance they are. Have read that they could be an 8 ohm and a 4 ohm, but have also read that they could be an 8 ohm and a 16 ohm. Thanks in advance for a hopefully simple answer.
  2. bholder

    bholder Affable Sociopath Supporting Member

    Sep 2, 2001
    Vestal, NY
    Received a gift from Sire* (see sig)
    There's no simple answer without knowing the actual impedance of the cabs.
    Aqualung60, MattZilla and Wisebass like this.
  3. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    The wires on the secondary of the output transformer are color coded, they identify the 4, 8, and 16 ohm taps. There is a main speaker out and jack that switches the impedance when you connect a second cabinet.

    You don’t know if your amp has been rewired. The only way to know for sure is to have a tech look at it. They will be able to see how it’s set up and can explain what the jacks do. They can also rewire the speaker out to suit your needs.
  4. olddave

    olddave Supporting Member

    May 26, 2011
    . both cabs are 8 ohms. sorry i forgot to mention that important info.
    MCF likes this.
  5. jlepre

    jlepre Supporting Member

    Nov 12, 2007
    Cedar Knolls, NJ
    I have no hands on experience with this head, but I would have to say that it should be safe down to 4 ohms. So adding (2) 8 ohm cabs shouldn't be an issue. I'm sure others more experienced will chime in concerning this particular head.
    olddave likes this.
  6. BogeyBass


    Sep 14, 2010
    Think he figured it out.

    4 ohm tap is automatically switched with the Ext Speaker jack.
    200s has a switching jack which automatically switches over to the 4 ohm tap when 2x 8 ohm cabs are plugged in

    impedance can be confusing at first.
    I wouldnt say its a waste of time to explain. Once your head wraps around it, its rather simple and youll feel better knowing how it works.

    if running parallel and 2 equal cabs the impedance will half=

    16 + 16= 8 ohms
    8 + 8 = 4 ohms
    4 + 4 = 2 ohms

    in your circumstance 2x 8 ohm cabinets is 4 ohms. And the load will be on a 4 ohm tap.
    as mentioned as long as the amp has not been modified.

    Still misssing my 200s :( sold when times got tough. have fun man great amp.
    looks really beautiful on the best looking 2 x15 cab ever. The matching Sunn 200s cabinet
    Last edited: Oct 8, 2019
    MCF, P_Robyn and olddave like this.
  7. olddave

    olddave Supporting Member

    May 26, 2011
    thanks again, Bogeybass. You have been more than helpful. Can I bother you with a few more dumb questions? Impedance is resistance, right? so adding a cab reduces resistance? and increases volume, for instance? but reduces power output (wattage?) all very confusing to me.
  8. bholder

    bholder Affable Sociopath Supporting Member

    Sep 2, 2001
    Vestal, NY
    Received a gift from Sire* (see sig)
    Impedence is partially resistance, but also includes the effects of capacitance and inductance (since the audio signal is effectively AC, electronically).
    HolmeBass likes this.
  9. tadawson


    Aug 24, 2005
    Lewisville, TX
    More or less (and yes for this discussion) - resistance is a component of impedance. The proper definition of impedance includes both resistance and reactance . . . .
    HolmeBass likes this.
  10. BogeyBass


    Sep 14, 2010
    Getting more volume or SPL (sound pressure leve)l. Is more related to getting more air pressure.
    In a nutshell using more speakers or moving more air is the easier way to do it.

    Then again if your expecting a minimal amount of speakers to get louder. That cone has to move back and fourth more... and move more air.
    so yes technically it requires more voltage/current or watts to get the speaker to move more air.
    of course as we know, the actually limit of how much extra power eventually is limited, cause the speaker will reach high distortion.
    at that point throwing more power at it is pointless.

    Increasing sensitivity of the system or sensitivity of the speaker helps to move more air with less power. A system rated at say 96dB will put out less sound pressure than a system rated at 99dB. likewise the 99dB system needs less power to reach the same SPL

    every time you double the effective speaker area you gain 3dB. example would be a 96dB 2x10 becomes a 99dB 4x10
    as with wattage in general 10x power is needed to gain 3 dB. meaning 100 watts opposed to 1000 watts.
    as you can see eventually its much easier to add more speakers.

    As far as getting more power from a amplifier its related to Ohms law. So yes a 4ohm load will draw more Current/ wattage than a 8ohm load.
    Following basic ohms law a lower impedance uses more current. So yes wattage will be higher with a lower impedance. impedance or resistance refereed to as Ohms.
    or 4 ohms is a lower impedance than 8 ohms

    ohms law is little different for AC voltage ( sound) then DC but its all the same formula. You just have to use RMS values for amplifiers or AC waveforms

    say a amplifier made a AC voltage at 80 volts Vpp or voltage peak to peak. RMS value would be 28 volts

    28 volts into 8 ohms would be 98 watts or 3.5 amps of current
    28 volts into 4 ohms would be 196 watts or 7 amps of current

    as you can see if voltage remains the same the 4 ohm load requires more current than the 8 ohm load.
    So yes technically we are getting more " watts " that is assuming the amplifier has a power supply that will provide that extra current. which is the heart of any amp and the watts it can provide. how big or how much current it can provide. how far a speaker moves forward or back is related to voltage. more voltage, more it moves

    With tube amps its a little different. The tubes also have a max voltage swing. but they cannot be directly coupled to a speaker. that is done with the output transformer.
    A tube amp say rated at 100 watts will make 100 watts into 4 ohms or 8 ohms, and however many taps that are provided.

    It works that way cause tubes need to drive a certain load to work proper. Lets say 4k ohms or 4000 ohms. little bit higher than 8 ohms LOL
    so you use a transformer. one side of the transformer is wound to provide a 4k load for the tubes. the other side is wound to provide a 8 ohm load for the speaker.

    Transformer works in ratios, so if you change one side, the other side changes. So if you put a 8 ohm speaker on a 4 ohm tap. the ratio would change and the tubes would also operate at the wrong impedance.

    this is why they have several taps on a transformer so the tubes and cabinet remain at the correct ratio. But power and overall voltage swing remains the same.
    Getting more power from a tube or solid state is basically the same. eventually you need more voltage, and likewise enough current to maintain that voltage.

    Benefit with solid state devices is they can drive 8 or 4 ohms directly. They dont need a transformer. As with tubes, they need high voltage and can only drive 3000 to 8000 ohms.
    so you need a transformer to couple them to a low impedance

    Last edited: Oct 8, 2019
    Jim Carr, olddave and DeathSlanger like this.
  11. Wasnex


    Dec 25, 2011

    Short answer. Your amp will make the same power as long as it sees the expected impedance. I believe the 200S is considered about a 60W amp.

    Since you have two 8 ohm speakers, you need to have a technician make sure the amp is set up for 4 and 8 ohms and label the back panel. Then you can use either one or two of your speakers and the amp will automatically ensure it's configured properly.

    Normally the Speaker out is labeled 8 ohms and the EXT out is labeled 4 ohms.

    This is the part that can be confusing so consider saving this where you can find it:

    --If you use just the Speaker Out, the amp expects 8 ohms. Use one 8 ohm speaker.
    --If you use both the Speaker Out and the EXT Out, the amp expects 4 ohms total. Use two 8 ohm speakers.
    --If you use just the EXT Out, the amp expects 4 ohms. Use one 4 ohm speaker.
    Haroldo, olddave, Rip Van Dan and 2 others like this.
  12. Alice peered over edge, and fell down the hole! Oops.

    The tube amp adds a big wrinkle to the more usual solid state impedance maths. Tube amps supply the same rated power through each of the taps when you match what you plug in to the tap rating.

    Adding cabs on a tube amp increases your sensitivity to the available power but not the available power itself.
    olddave and HolmeBass like this.
  13. You do not need 10x the power to get a 3dB increase, only twice the power (wattage). The 10x power is for “double” the perceived loudness.
    Jim Carr, olddave and Rip Van Dan like this.
  14. BogeyBass


    Sep 14, 2010
    yes correct
    i reverse the 2 sometimes.
    usually I also fail, when i attempt to write quick answers as well lol

    then proceed with the shortest long answer as possible
    Jim Carr and olddave like this.
  15. Rip Van Dan

    Rip Van Dan DNA Endorsing Artist Supporting Member

    Feb 2, 2009
    Duvall, WA
    Won't go into the specific ohms because that has been covered well. With tube amps, there is often a toggle switch that you have to physically move to match the impedance load you are putting on it. Sounds like your amp automatically changes it according to what you plug into the power outputs. Usually, with an all-tube amp, the power stays the same regardless of whether you use 4 ohm or 8 ohm load on it.

    In a Solid State (SS) amp or a hybrid amp, there usually is no toggle switch (Mesa has a 4/8-ohm to 2-ohm toggle on some of their amps) and as the ohms load drops, the power output goes up. Drop the ohms too much though and amp components can start to melt and release the "magic smoke". Once the magic smoke is gone you are left with an expensive paperweight.

    So two 8 ohm cabs would put a 4 ohm load on a SS amp and typically almost double the power going to the output jack. For instance, I have a dual powerblock amp (2 separate power channels) and it will deliver 240-watts RMS at 8 ohms or 400-watts RMS at 4 ohms. If I plugged a single 8 ohm cab in one side, that cab would get 240-watts. If I plug in two 8 ohm cabs, that drops the ohms load to 4 ohms in that channel and the amp puts out 400 watts. However, that 400-watts is then split evenly between the cabs. So it would send 200-watts to each cab.

    Instead of that, I used to hook one 8 ohm cab on one side and the other 8 ohm cab on the other. Since my amp has two discrete power channels, each channel will put out 240-watts to 8 ohm the cab that is plugged into it. That's more power than splitting 400-watts between them when plugged into the same side, so that's how I used to run that stack. Now, I use a single cab and run my amp bridged so it puts out 800-watts into my single 8 ohm cab.

    Two things will make your amp louder - either getting a more powerful amp, or adding more speakers. Double your amp's power to get a 3db increase in SPL or double your speaker area to get that same 3db increase. Either way will move more air, but it's usually much cheaper to get more speakers.
    olddave likes this.
  16. okcrum

    okcrum in your chest

    Oct 5, 2009
    Verde Valley, AZ
    RIP Dark Horse strings
    If the OP is the original owner, or if the 215 is 8 ohms (the Fender/Sunn was), the amp is wired correctly, and they can plug in their 8 ohm cabs and go.
  17. Wasnex


    Dec 25, 2011
    The amp has a problem...see this link: Sunn 200s matched to GK CX210 cab?
    olddave likes this.
  18. Ampslut


    May 15, 2017
    I ran my 200s at 4 ohms for years. Mine has 2 speaker jacks on the right hand side of the back of the amp. The furthest one to the right is labeled 4 ohms and that is the only one I ever used.
    olddave likes this.
  19. micguy


    May 17, 2011
    Impedance in parallel is much simpler if you look at it as conductance. Impedance is measure in ohms, conductance in...mhos. Yes, as silly as that sounds, just spell ohms backwards. Conductance is the reciprocal of impedance, so...assuming we're going to talk purely resistive impedance for the time being, an 8 ohm speaker has 1/8 mhos conductance. A 4 ohm speaker has 1/4 mhos conductance, etc.

    Conductance flips Ohm's law on it head - rather than doing division, you multiply. So, if you have a one volt source, a 1 mho load will draw 1 Ampere of current. A 1/8th mho load will draw 1/8th of an Ampere for the same 1 volt source, etc.
    When you wire stuff in parallel, you add the mhos - 2 1/8th mho speakers in parallel have 1/8th plus 1/8th mhos, or....1/'4th mhos conductance. So, to flip it back to resistance, that load is now the reciprocal of 1/4th, or....4 ohms. 3 8 ohms loads in parallel are 1/8th plus 1/8th plus 1/8th mhos of conductance - 3/8ths total. Flip that back to ohms, you get 8/3rds, or 2.67 ohms.
    olddave likes this.
  20. olddave

    olddave Supporting Member

    May 26, 2011
    Thanks! I even understood some of it!

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.