ohms and impedance (speakers)

8/10/2019 Ohms and Impedance (Speakers)

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OHMS & IMPEDANCE from the OUTPUT (speaker) perspective

...and additional speaker related topics in the FAQ

below.

We've broken the explanations down into two FAQ

articles: Ip!t "evicessuch as instruments andpreamps, and o!tp!t "evices, usually speakercabinets or headphones. This article is about the

!T"!T side, what you plu# into the $"%A&%

!T"!T o( an amp. There is another FAQ that talks about ohms and impedance (rom theinstrument, or input perspective.

#hat the heck are impe"ace a" ohms$When you plu# speakers into the output )ack o( your amp, those speakers become part o( the

circuit. When your amp was built, it was desi#ned (or a speci(ic minimum impedance load*expressed in ohms+, and what you plu# into it a((ects the outcome. And i( it isn't compatible

with what is expected, stran#e andor very dama#in# thin#s can happen. This article is a brie(overview to help you understand what works with what, what doesn't, and why.

#h% sho!" I care$-ecause you can blow up your ampli(ier, or it could mean that you mi#ht buy speaker cabinets

you won't be able to use with #ear you already own.

Impe"ace is measured in ohms, typically a measure o( resistance, but impedance involvesmore than a simple resistance measurement. ou'll see the value expressed as /ohms/ orrepresented by this symbol: . $peakers *drivers, the actual device in the cabinet+ and $peaker

cabinets are typically 0 or 1 .

Drivers*a term used to describe the various speakers inside a cabinet+ usually have coils thatare wound to be (our, ei#ht, or sixteen ohms2 there are other, less common values, but they arerelatively rare. The drivers are then wired in di((erent con(i#urations inside the cabinet, and that

desi#n usually results in a total impedance /load/ o( (our or ei#ht ohms. We are not #oin# to

address the #uts o( the speaker cabinet ri#ht now *see below in the FAQ section+, all we'rediscussin# here is the use o( one or more cabinets with an ampli(ier.

The importace of Ampifier Specificatios' the miim!m oa" i ohms$olid $tate *non3tube, and we're includin# those amps with tubes in the preampli(ier sta#e+

ampli(iers will have a minimum impedance speci(ication, (or example /minimum 0 load. *Truetube ampli(iers are di((erent, see the para#raph to the ri#ht.+ This value is usually printed or

stamped next to the speaker output )ack on the amp.


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4ere's why it's important: you'll (ind that the load

*impedance+ plu##ed into the unit a((ects the amount o(power delivered to the speaker cabinet*s+. For example,

you may see a power ratin# o( 567 watts into 1 , 677

watts into 0 (or a #iven amp. 8( you want andor need the maximum available power the ampcan potentially produce, you want to match the lowest impedance (or which the amp is rated. -ut

don't obsess about it, the di((erence in actual volume is typically not that #reat. 9ost solid3state

amps will handle a 0 load, thou#h those that will handle as low as a load are becomin# morecommon.

Cac!ati speaker caiet impe"ace oa"s'8( two cabinets are the same impedance, it's very simple:

8( it is a mix, the math makes it more complicated. To arrive at the numbers one must use /hms;aw/, which is a mathematical (ormula. Want to know more< =oo#le /hms ;aw/ (or more

in(ormation and some on3line calculators, thou#h you'll also run into more complex volta#e,

current, etc., calculations that are not pertinent to this discussion. There's a #ood discussion o(impedance calculations here, and an impedance calculatoron o#er $adowsky's site.

For your convenience, here's the ohm load (or another common con(i#uration:

ou'll have to be care(ul to interpret the speci(ication (or combo amps *those with a built3in

speaker+ as they may express them in di((erent ways. $ome indicate total minimum impedance,

so the internal speaker's impedance has to be (actored in. thers will indicate the minimumimpedance o( the extension speaker that can be added.

The key thin# to remember:

The impe"ace oa" of the comiatio of the coecte" speaker caiets m!st

ever e eo* the miim!m impe"ace oa" specifie" % the amp ma!fact!rer+

#hat happes if there is a mismatch$

If the speaker caiet impe"ace oa" is hiher tha the ampifier rati, e++, a eiht ohmcaiet p!e" ito a ampifier *ith a miim!m impe"ace oa" of fo!r ohms, %o!-re

coo+ou're not #ettin# the amp's maximum output, but don't panic over it. *A#ain, this appliesonly to solid3state amps 3 i( you have a tube power amp, the impedance needsto match>+

If the speaker caiet impe"ace oa" is o*er tha the ampifier it is o* time to paic.
http://www.prestonelectronics.com/audio/Impedance.htmhttp://www.prestonelectronics.com/audio/Impedance.htmhttp://www.sadowsky.com/audio/impedance.htmlhttp://www.prestonelectronics.com/audio/Impedance.htmhttp://www.prestonelectronics.com/audio/Impedance.htmhttp://www.sadowsky.com/audio/impedance.html


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Do-t tr% it.

Ampli(iers can react in di((erent ways, most contemporary #ood ?uality amps have circuitry that

detects the current (low, and i( it is hi#her than speci(ied *the result o( a speaker load belowspeci(ications+ the amp will temporarily shut itsel( down. 4owever, not all amps have this

protection circuitry, so you may be playin# with (ire... literally>> Another distinct possibility is

that you'll see curls o( smoke escapin# (rom the amp as you (ry the output devices.

Ho* ca I avoi" a mismatch$@hoose your speaker cabinets care(ully and know their impedance loads, know your amp's

minimum impedance speci(ications, and think o( the conse?uences be(ore )ust plu##in# in

cabinets.

Series a" Parae, *hat the he$.$When you discuss multiple drivers or cabinets, you'll invariably #et into the sub)ect o( series and

parallel connections. 8( you care to know, here's the lowdown:

Parae speaker coectios are the most commo+

When you plu# two speaker cabinets into the two speaker )acks on the back o( a typical

ampli(ier, the overwhelmin# odds are that the cabinets are connected in parallel. 8( thereis a commonly available amp out there wired with output )acks that results in series

connections, 8've never seen or heard o( it.

When you plu# one speaker

cabinet into an ampli(ier,and then run a second cable

(rom the (irst speaker

cabinet's second speaker

)ack to the second speaker,the cabinets are connected in

parallel. A#ain, i( there are

popularly available cabs out there wired with dual )acks that results in series connections,8'm not aware o( any.

When you plu# a speaker cabinet into a combo amp's *amp with internal speaker+

extension speaker )ack, the internal speaker and external cabinet are connected in parallel.

A#ain... you know what 8'm #oin# to say.

Paraeis when speakers or speaker cabinets are all connected postive *+ to positive *+ and


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to $peaker *cabinet+ BC positive *+, (rom $peaker *cabinet+ BC ne#ative *3+ to $peaker *cabinet+

B positive *+, (rom $peaker *cabinet+ B ne#ative *3+ to Ampli(ier ne#ative *3+. ou could make

custom cables or a box to connect two speakers or more in series to an ampli(ier.

The dia#ram to the ri#ht demonstrates wirin# two drivers in parallel and series con(i#urations.

Common Questions regarding amplifier outputs and speakers:

Can I change a cabinet's impedance from eight to four ohms, or four to eight

ohms?"robably not, but it will depend on what is inside. 9ost two driver *we're speakin# o( two main

bass drivers, like a xC7, etc.+ cabinets don't have that (lexibility. For example, i( you have a (ourohm xC7, it is likely that the two drivers are ei#ht ohms each, and they are wired in parallel,

which results in (our ohms at the output )ack. The only other choice would be to wire them in

series, which would result in a sixteen ohm load. The other drivers *tweeters, horns, midran#e

drivers, etc.+, i( applicable, are wired to a crossover circuit that (ilters out lower (re?uencies#oin# to a midran#e, tweeter, etc., that would otherwise dama#e the device. They can also (actor

into impedance loads, which, by the way, vary over the (re?uency band.

My speaker cabinet/full range driver/bass driver is not marked !o" can I find out

its impedance?While impedance is not exactly the same as resistance, you can use a D9 *Dolt hm 9illiampmeter+ to measure the resistance o( the device to #et a (airly accurate measurement. $et your

meter to the lowest resistance scale and measure across the hot and #round *(or accurate

measurement the driver or cabinet should not be wired or plu##ed into any circuitry+. 8t will

likely settle around (our or ei#ht ohms, which will #ive you the answer.

My amp can go do"n to # , but my speaker cabinet is $ %hould I try to get it

lo"er, like buy a different cabinet or try to modify mine?Eon't #et your panties in a twist. The audible di((erence in volume between, say 567w1 and

677w0 , i( usin# otherwise identical speaker cabinets, is not really that #reat.

&he back of my amp says #() "atts* is that the po"er?"ossibly, but only i( it is near the speaker output )acks or has lan#ua#eindicatin# so. 8( it is near the power cable and alon# with /CC73C7DA@/ or

similar lan#ua#e, it re(ers to the A@ power consumption o( the ampli(er, notthe

amp's output watta#e, as shown in the #raphic on the ri#ht.

&he +ine rint:The in(ormation contained herein is based on what's in my

brain andor my opinions as o( today and is sub)ect to chan#e. ;ike any

topic, a #reat deal more in(ormation could be addedbut the intent o( these

writin#s is to present easy to understand, ?uick FAQs, to address common


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?uestions and improve the reader's #eneral knowled#e. What's written here

is by no means the authoritative absolute answer, 8 am not the world's

#reatest authority on bass *not even close+, or on anythin# else (or thatmatter. 8 hope the in(ormation and opinions here are help(ul to you, that's

the point>

8 welcome email with dissentin# and additional viewpoints that help

improve my personal awareness and the content pa#es. 8( you have a

?uestion that you think belon#s here, please let me know.

Bob
http://www.gollihurmusic.com/contact.cfmhttp://www.gollihurmusic.com/contact.cfmhttp://www.gollihurmusic.com/contact.cfm

ohms and impedance (speakers)

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