Phlatman and Bobbin: Episode One - Why Speaker Wires Sound Different

In this episode, our hero Phlatman tries to explain to his trusted sidekick Bobbin why he hears differences in speaker wires. Phlatman , being a facts and figures guy, looks at the numbers and tries to correlate what he hears to what is measurable striving to find the most linear frequency response possible. Bobbin, a bumbling off-the-wall pimple-faced juvenile who thinks that iPods and ear buds are the bomb, explicitly trusts Phlatman to share sonic truths with him so that one day audio crime will not pay! Donning capes and masks so as to not reveal their true identities while risking getting laughed out of vinyl record stores, our masked marauders are on a continuing crusade to demystify audio subjectivity with supporting scientific data in the never-ending quest for the flat line.

Phlatman was truly shocked the first time he swapped out a variable L-pad with a fixed-resistor attenuator on his speakers. Up until then, he had used these L-pads for convenience in matching sensitivity levels between drivers and thought nothing about the effect they may have on the sound. After all, only with REAL transmission lines encountered only with radio, television, CB, or HAM transmitters would one ever encounter issues with standing waves, return losses, and the like, right?

BZZZT! WRONG ANSWER! Thank you for playing.

 

Common L-Pad Variable Attenuator

Any time electricity flows down a pair of wires (and that pretty much is how this works folks regardless if you are running tubes or transistors), there is ALWAYS the influence of impedance mismatch and the resulting loss of power between a source and a destination.

HOLY MOUTHFUL, PHLATMAN. THIS IS TOO TESTOSTERONELY TECHNICAL. WHAT DOES THIS MEAN TO YOUR EARS?

Good point, Bobbin, I’ll take it down a notch. When you connect your speakers to your amplifier, inserting ANYTHING in between the terminals of the speaker driver and the terminals of the amplifier's output devices will electrically alter the signal. This is called by engineers an "insertion loss" (the loss encountered by inserting something in between). More often than not, this alteration (aka insertion loss) is measurable in the form of what radio engineers call a Standing Wave Ratio (SWR).

The SWR is by definition anything other than exact impedance match between the source and the destination. A SWR=1 means that the output impedance and the input impedance are exactly the same (1:1). A SWR not equal to "1" shows the losses encountered by this mismatch and hints at the resulting effects it places on the circuit.  So if you have an 8-ohm speaker connected to your tube amplifier's 8-ohm tap, maximum power is transferred between the amp and speaker ONLY at one point: exactly 8 ohms (SWR=1@8.00 ohms). So when the amplifier tries to drive a load that is not the same as its impedance, the output power changes up or down and the speaker will sound different.

HOLY SNAKE OIL, PHLATMAN! DO YOU MEAN THAT THOSE LUNATIC FRINGE AUDIOPHILES WHO CLAIM TO HEAR DIFFERENCES IN SPEAKER WIRES ARE RIGHT?

In a word, Bobbin, yes. Some naysayers dismiss what is measurable against what is audible, but that's another story we can discuss later (BTW, these are typically the same skeptics who focus on lowering total harmonic and inter-modulation distortions to miniscule amounts). What I am confining this discussion to (for the moment) is only what is measurable. BTW, here is an excellent link for your enjoyment to show you the effect of mismatched values (Note: set the value of J=0 to monitor the effects of resistance-only changes).



First, here a few definitions to help you understand what the values in the analysis are telling you. Know that these are complicated issues and I am trying to explain them in general terms. The Reflection Coefficient is the ratio of the reflected wave to that of the original wave (what portion of the outgoing signal bounces from the speaker back to the amplifier). The VSWR is the ratio of the maximum voltage to that of the minimal voltage of the next node. The Return Loss is the reciprocal of the Reflection Coefficient in dB.


This is what’s going on regarding a tube amplifier's 8-ohm tap output terminals and an 8-ohm speaker’s input terminals. Below is a graph showing the effects adding speaker wire whose DC Resistance increases between 0.1 and 1.0 ohms (thereby mismatching the input and output impedances).

Load	Reflection Coefficient	VSWR	Return Loss	Mismatch Attenuation
8.0	0	1	infinite	0
8.1	0.0062	1.013	44.14	0
8.2	0.0123	1.025	38.17	0.001
8.3	0.0184	1.038	34.7	0.001
8.4	0.0244	1.05	32.26	0.003
8.5	0.0303	1.063	30.37	0.004
8.6	0.0361	1.075	28.84	0.006
8.7	0.0419	1.088	27.55	0.008
8.8	0.0476	1.1	26.44	0.01
8.9	0.0533	1.113	25.47	0.012
9	0.0588	1.125	24.61	0.015

Remember that the total DC resistance of a speaker wire is the sum of both the positive and negative wires, not just one wire. So if the DC resistance of your speaker wire is given “per foot,” you must double that value to know what the total DC resistance is for that length of speaker wire. Below is a total DC wire resistance (DCR) chart for two-cord style wires (two conductors, not four or more) for various sizes of stranded copper wire.

Speaker Wire Length	#14 DCR	#16 DCR	#18 DCR
10 feet	0.0514	0.082	0.1302
15 feet	0.0771	0.123	0.1953
20 feet	0.1028	0.164	0.2604
25 feet	0.1285	0.205	0.3255
30 feet	0.1542	0.246	0.3906

Total DC Resistance for Both Plus and Minus Wires

For example, if you use 15 feet of #18 speaker wire, the total DC resistance of your speaker wire is about 0.2 ohms.  Changing this wire to #14 lowers the total DC resistance of the wire to less than 0.1 ohm.

Now, let's look at what is going on regarding a solid state amplifier's output terminals (assumed output impedance of 2 ohms) using this same 8-ohm speaker.

Load	Reflection Coefficient	VSWR	Return Loss	Mismatch Attenuation
8.0	0.6	4	4.44	1.938
8.1	0.604	4.05	4.38	1.971
8.2	0.6078	4.1	4.32	2.003
8.3	0.6117	4.15	4.27	2.035
8.4	0.6154	4.2	4.22	2.067
8.5	0.619	4.25	4.17	2.099
8.6	0.6226	4.3	4.12	2.13
8.7	0.6262	4.35	4.07	2.162
8.8	0.6296	4.4	4.02	2.193
8.9	0.633	4.45	3.97	2.224
9	0.6364	4.5	3.93	2.255

HOLY SNOBS, PHLATMAN! WHAT THE HECK IS GOING ON? IT LOOKS LIKE TUBE AMPS HAVE MEASURABLY-LOWER LOSSES THAN TRANSISTORS?

Well, sort of, Bobbin. The reason for this apparent dilemma is that the tube amplifier’s output impedance more closely matches the speakers impedance to start (input = output). This may be why audiophiles prefer the sound of tube amps (it may be that, saying it another way, they do not prefer the sound of high-level impedance mismatches).

So the problem starts with an amplifier’s output impedance and is compounded by adding anything in between the amp and the terminals on the speaker drivers not equal to this output impedance.  Such things that add the total DC Resistance to the amplifier are things like speaker wire, passive crossover components, or L-pads.  But there’s more that complicates this issue to a new level: speaker impedance is not constant.

HOLY LOSSES, PHLATMAN! YOU MEAN THAT THERE ARE OTHER THINGS TO INCREASE TOTAL DC RESISTANCE?

You bet, Bobbin. One thing speaker manufacturers routinely publish is the impedance plot for their speakers. Below is a sample impedance plot for a typical 3-way loudspeaker. This common characteristic is a woofer resonance at the low end and gradually-rising tweeter impedance at the high end.

Typical Dynamic Speaker Impedance Plot

So what IS the actual impedance of this speaker? Good question since it ranges from 3 ohms to over 17 ohms. The manufacture states 8 ohms, but the speaker is only 8 ohms at three places: about 47Hz, 97Hz, and 3,500Hz. Add to this the 0.2 ohms total DCR of speaker wire and the 8-ohm points shifts to about 45Hz, 95Hz, and 3,300Hz.  At all other points, the total DC resistance the amplifier “sees” is NOT 8 ohms.
When an amplifier does not “see” the same impedance as its output impedance, everything changes: Reflection Coefficient, VSWR, and Return Loss. All of this results in the “mismatch attenuation” meaning that the amplifier does not always deliver the same amount of power to the speaker and therefore makes things slightly louder or quieter as a result (i.e., the power delivered to the speaker is not linear).

And this resulting mismatch also causes internal reflections in the speaker wire between the amplifier and the speaker drivers.  These reflections cause other things like phase (i.e., time) distortions even when speaker drivers themselves are “time aligned.” And these reflections themselves are non-linear meaning that as the impedance changes, so does the amount of phase shift.

HOLY COMPROMISES, PHLATMAN! WHAT IS ONE TO DO?

Good question, Bobbin.  That’s what swapping speaker wires can do to improve the sound.  Some wires are more inductive and some more capacitive meaning that the wires themselves can help to correct this non-linear problem. Finding the right combination of wire design between your amplifier and your speaker can help in adjusting these mismatches. You never get anything for nothing and when it comes to recommending a solution for your specific problem, no “vanilla” solution exists. What works for speaker with one impedance plot will not work or not work as well for a speaker with another impedance plot.

What you must do is to swap speaker wires and then L-I-S-T-E-N closely and thoroughly to the differences you hear. Become familiar with how your system sounds and then change only one thing at a time. Speaker wires are a really good place to start, especially if you are presently using #18 zip cord. Moving to #14 zip cord will demonstrate to you at a budget what the world of matching equipment is all about and can be done so very inexpensively.

Join us next time as Phlatman and Bobbin continue their never-ending pursuit of the straight line audio graph. You may find them in your local audio salon, arms crossed and frown faced, encouraging you to be very serious about the things you allow into your home theater. Until next time boys and girls, remember what Phlatman always says, "On the Eight Day, God created vacuum tubes..."

DISCLAIMER: Phlatman and Bobbin are purely fictitious characters. Any resemblance to any or all real people, politicians, lawyers, or super heroes living, dead, or otherwise is purely coincidental. The USDA does not certify this as 100% organic. These are professional drivers on a closed course: do not attempt to do these things by yourself. Seriously, cars cannot fly. No speakers, capacitors, inductors, wires, tubes, transistors, circuit boards, knobs, gauges, meters, test probes, graph paper, instruments, or electricity were harmed in the production of this thing-a-ma-bob whatchyamacallit. Your mother was right.

SERIOUS NOTE:
My eBook Extreme Audio 5: Speaker Wires discusses this issue and others that help you make informed decisions about which speaker wires to try and what you can possibly expect. Knowing the “sonic signature” of a type of wire connected to a type of amplifier can help you narrow-down your search but the final choice should be made with your ears. What sounds right to you is what you should get.

Yours for higher fidelity,
Philip Rastocny 

I do not use ads in this blog to help support my efforts. If you like what you are reading, please remeber to reciprocate, My newest title is called Where, oh Where did the Star of Bethlehem Go? It’s an astronomer’s look at what this celestial object may have been, who the "Wise Men" were, and where they came from. Written in an investigative journalism style, it targets one star that has never been considered before and builds a solid case for its candidacy.

My other titles include:

·  Extreme Audio 1: House Wiring	·  Build an Extreme Green Hot Water Solar Collector
·  Extreme Audio 2: Line Filtering	·  The Extreme Green Guide to Wind Turbines
·  Extreme Audio 3: Chassis Leakage	·  The Extreme Green Guide to Solar Electricity
·  Extreme Audio 4: Interconnect Cables	·  Meditation for Geeks (and other left-brained people)
·  Extreme Audio 5: Speaker Wires	·  Althea: A Story of Love
·  Extreme Green Guide to Improving Mileage	·  Build an Extreme Green Raised Bed Garden
·  Extreme Green Organic Gardening	·  Build an Extreme Green Rain Barrel
·  Extreme Green Organic Gardening 2012	·  Build an Extreme Green Squirrel-Proof Bird Feeder
·  Build an Extreme Green Composter	·  Extreme Green Appliance Buying Guide

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