20 foot long speaker cable: is it ok?

What impedance speakers, what sensitivity and what amplifier?

Generally, use no less than 14 gauge wire and you will be fine. Have you seen the low profile/super flat cable? Great for running under rugs and carpets. 

Best,

E

Here are the important factors in choosing a speaker (or any electrical cable):

1) The dc ohmic IN PHASE resistance.  This causes voltage drop & heat.  It negatively affects the amplifier output impedance, hence the slew rate of the output.  Solution:  Use a THICKER cable or one with VERY GOOD QUALITY copper and/or silver.  Silver is the BEST but it expensive and oxidizes very quickly so connections must be very well made.

2) The skin effect.  This is the tendency of HIGH FREQUENCY ac current to travel on the outer extremities of a wire, which may therefore experience elevated resistance at hi frequencies.  Solution:  Use a cable which is covered in silver towards the outside (this is really not very practical or cheap and does it even exist).

3) The cable is SOOO LONG that your ear almost starts detecting the electrical signal delay reaching from the amp to your speaker.  Electricity travels approximately 1 meter in 3 nanoseconds.  By this calculation, a 100 mile speaker cable will delay the sound by about 5 microseconds.  Noone can hear this so pretty much you can ignore this effect.  However this also exasperates bullet item number 1.

4) Capacitance & inductance of the wire.  Now these are probably the most important factors that negatively affect the sound quality.  Mostly, these  will increase with length but ingenious geometries may minimize these.  So, when u pick a cable look at its inductance & capacitance per meter.  The lower they are the better the cable is for audio purposes.

If you change your mind about gear placement and want to put it in the middle thus needing a longer power cord contact Patrick at Cullen Cable and he will make one to whatever length you need.

I am far from being an expert so I pick up on odd comments. Did I hear correctly that in theory a longer power cable is better than  a shorter one?
It was explained to me at the time but I didn't retain the reasons

I used a 20ft pair of Mogami 2477 Blue Neglex OFC coaxial with my KLH Nines for 23 years! Excellent sound, never felt the need or urge to change! The cost: $1 a foot (dealer accommodation)!