ISC Speaker Processing

Interactive System Control - What is it?
I.S.C stands for Interactive System Control, ARX's innovative speaker and electronics Interface.
There is a lot of myth, magic and hype attached to the Electronic Processing, Treatment or Control (call it what you will) of speaker systems.
Some manufacturers would rather not use words like Processed, Controlled etc, but if we look at what's happening in a purely audio electronics context, and leave the marketing to the guys with ponytails and Porsches, we find that irrespective of what people call this style of speaker system, they all basically perform the same functions.
In these Application Notes and FAQs we'll try to clarify what these functions are, the way ARX's ISC system works and reacts to audio signals in everyday use, and clear up some of the common misconceptions surrounding all systems that marry Electronics and speakers together as an integrated package.

How Does It Work?
The Basic Principles of Feedback style Gain Control

I.S.C monitors the output of the power amplifier driving each set of speaker components and compares this signal with an internal model of the SOA (safe operating area) of the speaker. When the signal applied to the speaker tries to exceed that SOA, the signal is limited or held at a level which is safe for the speaker to reproduce. Since the speaker signal forms part of a feedback loop this SOA can never be exceeded.

Why Monitor the Outputs of the Amplifiers?
Let's put it this way: can you tell how fast your car's going by looking at the Rev counter? No, you have to measure the rotation of the tyres!
For the same reason, what we really need to know is the actual power being applied to speaker components, not the signal being applied to the input of the Power Amplifier. To measure this accurately and allow the user their personal choice in Power Amplifiers we have to go where the action is - the outputs of the amplifier. This is used as the reference.

What size amplifier do I need?
You'll notice that on all ARX speaker system Spec sheets we quote a recommended minimum amplifier size - we don't quote power handling. The ISC processor determines the amount of power supplied to each speaker, ensuring this remains within the Safe Operating Area of the driver. By recommending the minimum amplifier size, we are saying that this is the least amount of amplifier power required for ISC to operate in the way ARX engineers designed it.
For example: If you operated a system from, say, a 100 watt per channel amplifier, and the ISC processor was designed to begin operation at around the 200 watt level, you would find the 100 watt amplifier completely squared off into clipping (gross overload distortion) before the ISC processor was aware that any action was required, thus for all intents and purposes rendering the system protection totally ineffective.

Do Processor Controlled Systems cost me more?
No way! In fact they will most likely save you money with their built-in protection against speaker over-powering and burnout. Processed Systems may appear initially to be more expensive than conventional home built systems, because each component is carefully selected to operate as a system. Drivers are specially manufactured to conform to precise specifications, since off-the-shelf, 'one spec fits all' drivers frequently don't deliver the performance needed.
And we don't mean to denigrate the efforts of the thousands of Do-It- Yourself speaker enthusiasts. After all, that's where we all started, and some amazing industry breakthroughs have been made in this environment.
But, when guaranteed performance, long term reliability and resale value are taken into consideration, a processor controlled speaker system from a reputable manufacturer like ARX is really the only way to go.

Isn't processing cheating?
No, of course not. What the processing is really doing is making sure that each speaker component works at its highest efficiency. You can't get a quart out of a pint pot, but at least we can make sure that you get a pint! (Sorry - there's no metric equivalent!)

Doesn't the system change it's sound at high SPL's?
Not ours. Some other processing systems change the frequency response of the system at high SPL's, usually in the low frequencies.
However, ARX's ISC does not have this variable high pass filter arrangement. We start our system design with drivers capable of reproducing low frequencies at very high SPLs, and leave them alone to do just that.
The last characteristic anybody wants in a Sound Reinforcement system is for it to lose low frequency output at high SPLs, since this is when you need all the low frequency output you can get.

Processing Myths - Fact and Fiction

A few common fictions surround our ISC system, and most other manufacturer's systems. Here are some of them:

Fiction
When the indicator LEDS come on the volume goes down

Fact
No it doesn't. It's a basic misconception that limiting and compression turns the sound down! At best, a good limiter can hold the sound at a level determined by the threshold setting: more commonly the limiter reduces the level increase once the level passes the threshold. This holds true with all ratio settings, until you get to infinity: 1 (hard limiting).

Fiction
I need a processor for every pair of speakers!

Fact
No. Sure, with some companies you do, but not with an ARX ISC processor. One processor will run multiples of the same speaker system without any change in wiring or calibration.

Fiction
Do I have to use the processor? Won't the speakers go louder without it?

Fact
No they won't. In fact, they'll sound much better with the processor because it is designed to work as a system with the speakers.
Every speaker has a point at which it won't deliver any more output no matter how much more power you try to stick into it; a point at which it curls up its toes and says "That's it - No More! I'm outta here!"

The ISC Processor already knows exactly the correct amount of power that can be applied to each speaker, and stops it from getting any more than it can handle, like an electronic safety valve. Normal compressors and limiters can only provide protection against electronic headroom overload (Clipping) protection and also need to be accurately calibrated to the sensitivity of each power amp.
Think of it this way - would you take the brakes off your car to make it go faster?

Alignment and EQ
Modern Low Frequency designs call for the correct alignment to match speakers and enclosures together correctly. CD (Constant Directivity) High Frequency horns call for a fixed amount of High Frequency EQ for smooth frequency response over their quoted dispersion range.
The ISC processor provides these to the speaker system at the correct settings. No more leaving these important details to chance.

Let's sum it all up
At ARX we believe that ISC provides a simple, user friendly way of ensuring that a speaker system delivers reliable peak performance day after day, night after night. Since 1983, when we first introduced the concept, our pioneering work is finally being acknowledged by the vast majority of speaker manufacturers, who now offer systems based on similar principles.

We hope you've found these ISC Frequently Asked Questions useful. Remember, if you need any more information on ARX products and you can't find it in these Application Notes, send us an email with your questions, and we'll be more than happy to help you.