Speaker Cable Buffering?

pt22 · September 2023

Hi folks. Not sure this is a thing, and the question may be academic but I thought I’d put it out there.

There’s a ton of information (and debate) over different types of buffers used before an amps preamp, and even in relation to effects loops send/receive.

What about between an amps power amp section and the speaker itself? I ask because I’m considering placing my CaptorX on my pedal board rather than sitting on top of the amp. That would mean the addition of a few meters of cabling between the power amp output and the speaker.

I’m sure a few meters may not make a difference, but what if it was 10 meters? 20? Does this ever become a problem in the same way cable impedance can be going into an amp?

Thanks.

p90fool · September 2023

Your amp is already a gigantic buffer.

Cirrus · September 2023

No. Long cable runs, the resistance will mean you lose a little power heating up the cable that might have gone to the speakers, but there's no tone change from that.

Sporky · September 2023

Buffers are for instrument/line level signals, not for speaker level.

You can fairly easily do the sums to work out what gauge speaker cable you need for a given power, distance, and speaker impedance. Or even more easily plug the numbers into an online calculator.

goldtop · September 2023

Not needed.

In your planned setup, though, just be aware that there's a much increased risk of accidentally unplugging your amp from the load. If the cable from the amp/speaker gets yanked out or forgotten when setting up.

If it's a setup at home that's unlikely to be altered by you or mischievous kids, then you'll be fine.

ecc83 · September 2023

Cables NEVER have an "impedance" at audio frequencies unless you are trying to send signals to the next town!

All cables have a "characteristic impedance" at RF and video/digital frequencies. TV aerial cable is 75 Ohms as is S/PDIF (but nobody cares!) CAT X network cable is 110R but most peeps just say 100 Ohms. Most other RF cable, remember 'CB'? is 50 Ohms.

But below 20kHz and for even very long audio cables this does not matter a jot*.

*There is cable CAPACITANCE which can be important but not for speakers.

Dave.

pt22 · September 2023

ecc83 said:

*There is cable CAPACITANCE which can be important but not for speakers.

thanks. This certainly is evidence of my depth of knowledge on the subject.

pt22 · September 2023

goldtop said:

Not needed.

In your planned setup, though, just be aware that there's a much increased risk of accidentally unplugging your amp from the load. If the cable from the amp/speaker gets yanked out or forgotten when setting up.

If it's a setup at home that's unlikely to be altered by you or mischievous kids, then you'll be fine.

Thanks for this, and yes I was aware. I do think I'll be ok as the amp actually has a built in load, but I'm not sure if that load is bypassed if the amp end of the speaker cable is plugged in even if it's not terminated at the other end. If not, then your warning stands and I'll have to keep the kiddos away from the board.

Sporky · September 2023

ecc83 said:

Cables NEVER have an "impedance" at audio frequencies unless you are trying to send signals to the next town!

I will clarify - I meant (notional) speaker impedance.

ecc83 · September 2023

Sporky said:

ecc83 said:

Cables NEVER have an "impedance" at audio frequencies unless you are trying to send signals to the next town!

I will clarify - I meant (notional) speaker impedance.

I was referring to the OP's mention of "speaker cable impedance" But yes, speaker impedance has a profound effect on an amplifier's sound, at least with valve OP stages because they have a high source impedance.

Dave.

ICBM · September 2023

For any normal cable length made from decent 6A-rated mains cable (0.75 sq.mm) or 'proper' speaker cable of a similar size, the cable resistance can be safely ignored. Standard copper cable of this size has a resistance of 23 ohms per kilometer for each conductor, so double that for a speaker cable as both halves are in series - ie a 100m cable has a resistance of about 4.6 ohms, and a 10m cable less than half an ohm.

So if you're driving a 4-ohm cab, you would notice a difference at 100m - only half the power would be getting to the cab, and also the amp would be producing less power as it would be seeing an effective 8-9 ohm load. At 50m you might still be able to tell, but at anything much less than that, not likely.

Most 'proper' speaker cable is significantly larger than 0.75 sq.mm too, so the equivalent lengths would become even longer. If the cab impedance is 8 or 16 ohms it would also make proportionately less difference.

https://www.engineeringtoolbox.com/copper-aluminum-conductor-resistance-d_1877.html

Sporky · September 2023

ecc83 said:

Sporky said:

ecc83 said:

Cables NEVER have an "impedance" at audio frequencies unless you are trying to send signals to the next town!

I will clarify - I meant (notional) speaker impedance.

I was referring to the OP's mention of "speaker cable impedance"

Ah! Sorry.

I do a fair few gauge calculations, but when I'm running kilowatts tens of metres. Which is rather different.

ecc83 · September 2023

Yes chaps and when we needed to run multiple speakers over 100s of mtrs we moved to 100V line working* and about 5A cable but that is not the primary reason for the technique.

*70V in the states for some reason I have never fathomed!

Dave.

ICBM · September 2023

ecc83 said:

*70V in the states for some reason I have never fathomed!

Regulations I think. North Americans are scared of proper mains voltage too

.

(Despite the fact that their 117/120V will electrocute you just as easily if you make a decent connection to it, and at least in the past their attitude to earthing made it *more* likely, not less.)

Marshall had to sell their 1970s amps for the Canadian market with the 16-ohm output taps disabled because on the 100W models the output voltage exceeded the regulations.

Sporky · September 2023

As a gross oversimplification, in America they believe that 70.7v can't kill you.

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