On September 21, 2017 at 06:56, ILO said...
The proper remedy is the same in both instances, you need to turn the connected amplifiers volume down.
This is exactly why I wrote the procedure in my previous post. It gets the quietest room as loud as you'll ever want it with the POWER AMP volume only as far up as is needed to do that.
The autoformers in the individual volume controls are what are make the thumping sound and it is as Buzz states, you are hearing the louder bass frequencies overload the laminated coils in the autoformer.
This is especially prevalent in systems where it's easy to change the power amp's volume.
The first time I ran across this, the client's Marantz remote (it was the late 90s) had Zone 2 volume. One day we heard a thumping and went to investigate. Someone had turned the wall volume control down to about 1, then turned up the power amp output to get sound of of that speaker. The cure was to take power amp volume control off the programmable remote, then turn up the wall control and adjust the power amp only as high as was needed.
I've overcome people's tendency to try to increase power amp volume by pointing out that speaker systems like this bear a resemblance to watering systems. The power amp is the city's water supply and each volume control is a faucet. If your faucet is turned on to 1 on a scale of 10, you don't call the city and tell them to increase the system pressure. You open the faucet more. ONLY when the volume controls/faucets are all the way up do you even consider turning up the power amp/asking the city for more water pressure. This seems to get it across.
Also, in most cases, if a volume controls autoformer is thumping, the speakers will play too loudly when that individual volume control is turned all the way up.
This gets a loud thumping AMEN.
So lowering the amplifier volume not only solves the thumping problem, it also provides more resolution in the volume settings (e.g. the lowest setting can now play at a lower level and the highest setting plays no louder than ever needed).
The issue of resolution is a great one but it takes understanding the rest of this to even think of it! Furthermore, individual room volume controls can do better than a switch like this Niles switch, because you can set an outdoor speaker volume control to be, say, X4, while the powder room volume control is set to X16. That way, more power goes to the outdoor speaker, which needs it, than to the powder room, which is a small enclosed space. Without being able to make this adjustment in the setup, the powder room volume might be overbearing at just 3 or 4 out of 10.
