D-Fend

[Tom Smit]

It's most likely a switching circuit, operating at 100+ kHz. If the voltage produced by the amp is too high - as determined by the in-circuit DSP - it will simply start switching on and off rapidly, with a pulse width that averages to the limit. Capacitors and inductors will smooth that, although close enough to the driver that isn't very important. Pretty much the same as a Class D amplifier.

+1

Duh, an open circuit is high impedance! Oh well, I was kind of close.

[SirNickity]

So you're thinking the "resistance" is actually an intermittent (at kHz speeds) open circuit? Interesting concept.

[Tom Smit]

Not really resistance (unless you call it an open circuit), but rather impedance.
It's also a way to get LEDs to go dimmer....by limiting the power through on/off switching. (LED would be "off" more than it is "on" which results in less light output in the same time frame, and therefore appears dimmer.

[nastyford77]

Sounds like pulse width modulation.

[SirNickity]

That's exactly what it is.

[JerryAllen]

Did this product go by the wayside?

Jerry

[Dan30]

Did this product go by the wayside?

Jerry

I hope not.

[LelandCrooks]

No. Bringing something like this to market is hard. Really hard. Considering the market it's aimed at, it has to be right the first time. Pro sound is unforgiving.

[Bill Fitzmaurice]

FWIW, I have one of the early evaluation units. The good news is that it works, the bad news is that it seems the instructions were written by the same person who wrote those for my DEQ 2496, as they're just as worthless. If you aren't an engineer you can't figure out what the hell they're talking about. I am an engineer and barely deciphered them.

[JerryAllen]

I got a response from Eminence..... the units are in FCC testing right now.... possibly mid October 2012.

Used with permission from the author.

Jerry,

Yes, it will be available in the US. The unit is off at FCC testing right now. As soon as we get the official "all clear" from them, we will start production. It will take about a month to get the boards built and into production here at our plant in Eminence. Assuming we get the board back from FCC in the next couple of weeks, we should be in production by mid-October. This unit I'm describing is our D-fend Stand Alone unit that will come in a little enclosure that can be mounted to the back of any speaker cabinet to retrofit the existing systems. If you have any other questions, please let us know. Thanks! Take care!

Regards,

Josh Martin

Jerry

[dheafey]

FWIW, I have one of the early evaluation units. The good news is that it works, the bad news is that it seems the instructions were written by the same person who wrote those for my DEQ 2496, as they're just as worthless. If you aren't an engineer you can't figure out what they hell they're talking about. I am an engineer and barely deciphered them.

That can't be good. Bad documentation leads to incorrect settings which leads to believing your speakers are protected. The first guy who jams 100 volts into something and sees/smells smoke out of his cab is gonna be pretty PO'd. Or maybe it's his own damn fault for not limiting properly in the first place.

[Bill Fitzmaurice]

FWIW, I have one of the early evaluation units. The good news is that it works, the bad news is that it seems the instructions were written by the same person who wrote those for my DEQ 2496, as they're just as worthless. If you aren't an engineer you can't figure out what they hell they're talking about. I am an engineer and barely deciphered them.

That can't be good. Bad documentation leads to incorrect settings which leads to believing your speakers are protected. The first guy who jams 100 volts into something and sees/smells smoke out of his cab is gonna be pretty PO'd. Or maybe it's his own damn fault for not limiting properly in the first place.

IMO these should not be released until they've written instructions that make sense to the average user, and I told them so. It remains to be seen if they do so.

[osse]

FWIW, I have one of the early evaluation units. The good news is that it works, the bad news is that it seems the instructions were written by the same person who wrote those for my DEQ 2496, as they're just as worthless. If you aren't an engineer you can't figure out what they hell they're talking about. I am an engineer and barely deciphered them.

That can't be good. Bad documentation leads to incorrect settings which leads to believing your speakers are protected. The first guy who jams 100 volts into something and sees/smells smoke out of his cab is gonna be pretty PO'd. Or maybe it's his own damn fault for not limiting properly in the first place.

IMO these should not be released until they've written instructions that make sense to the average user, and I told them so. It remains to be seen if they do so.

Would you recommend this kind of processing over the usage of drpa or the such for the small scale enthusiast? Did you get any picture on how the processing sounded, compared to digital/line level processing?
I wonder if the stand-alone and rack-mount units will have some kind of digital remote for setting the filters to make it more user friendly...

[byacey]

From what I can gather, I think they have a serial port connection for setup parameters. Once you set it up for a particular driver, there's no need to change it in the field.

My biggest thought is: I wonder how much limiting it will do before it becomes audibly objective? The duty cycle of signal off time vs on time would have to remain fairly low to be inaudible. I wonder how much back EMF there is across the voice coil when the defend opens the circuit?

Most likely this would still be used in conjunction with DSP limiting, the Dfend being the last line of defense against driver failure.

If Bill had the opportunity to evaluate one, I'm sure he can fill in some of the gaps.

[Bill Fitzmaurice]

If Bill had the opportunity to evaluate one, I'm sure he can fill in some of the gaps.

The unit I have is an evaluation unit, not the finished product, so I can't say how that will work.