I thought I understood cardioids. Spacing between a front driver and a rear driver, delay to rear driver, reverse polarity on rear driver or cabinet and a global 6dB/octave boost from the highest to lowest operating frequency, a simple programme such as EV LAPs readily simulating the response for you.
OK, reverse polarity produces cancellation at all frequencies at a point behind the rear cabinet/driver, up to the maximum spacing dependent working frequency. If you google "cardioid" this is what you get.
It is also the method given by EV, EAW, DAS, etc...looks good!
Then you watch Dave Rats video, part 3! He demonstrates that only like polarity on both drivers/cabinets will produce a fully cohesive summed forward wave, which makes sense as the delay is applied to the front cabinet instead (which matches it in time to the same point as the rear one due to that delay). Simulating it of course you only get cancellation at one frequency/wavelength behind the rear cabinet and this all makes sense also.
He goes on to show that the reverse polarity method has a forward response anomaly and that is you will always hear the sound from the first cabinet before the second one. The wave does sum but not for the first (and last) half wavelength which results in "volume ramping" and compromised impulse response which Mr Rat claims is audible (he should know!)
So I wrote to Meyer, EAW and EV for their take on this..no response, so I have come to this forum!
Perhaps this is just tolerated because complete cancellation at the rear may be more important than optimum sound quality out the front?
Do we understand then that all the mainstream manufacturers avoid discussing this issue? Every single article I have ever read including the original work by Olsen uses reverse polarity rear drivers...are they all "wrong" or perhaps with very short delays it just isn't that audible?
So this really is a question about this anomaly..is it something we tolerate or is Mr Rat right or wrong about this given his working qualifications as a sound engineer of considerable experience? ..
OK, reverse polarity produces cancellation at all frequencies at a point behind the rear cabinet/driver, up to the maximum spacing dependent working frequency. If you google "cardioid" this is what you get.
It is also the method given by EV, EAW, DAS, etc...looks good!
Then you watch Dave Rats video, part 3! He demonstrates that only like polarity on both drivers/cabinets will produce a fully cohesive summed forward wave, which makes sense as the delay is applied to the front cabinet instead (which matches it in time to the same point as the rear one due to that delay). Simulating it of course you only get cancellation at one frequency/wavelength behind the rear cabinet and this all makes sense also.
He goes on to show that the reverse polarity method has a forward response anomaly and that is you will always hear the sound from the first cabinet before the second one. The wave does sum but not for the first (and last) half wavelength which results in "volume ramping" and compromised impulse response which Mr Rat claims is audible (he should know!)
So I wrote to Meyer, EAW and EV for their take on this..no response, so I have come to this forum!
Perhaps this is just tolerated because complete cancellation at the rear may be more important than optimum sound quality out the front?
Do we understand then that all the mainstream manufacturers avoid discussing this issue? Every single article I have ever read including the original work by Olsen uses reverse polarity rear drivers...are they all "wrong" or perhaps with very short delays it just isn't that audible?
So this really is a question about this anomaly..is it something we tolerate or is Mr Rat right or wrong about this given his working qualifications as a sound engineer of considerable experience? ..
1)Complete cancellation never occurs in the real world, but as Dave explained, the cardioid method does achieve more rearward cancellation at the expense of sound quality in front compared to the end fire configuration.He goes on to show that the reverse polarity method has a forward response anomaly and that is you will always hear the sound from the first cabinet before the second one. The wave does sum but not for the first (and last) half wavelength which results in "volume ramping" and compromised impulse response which Mr Rat claims is audible (he should know!)
1)Perhaps this is just tolerated because complete cancellation at the rear may be more important than optimum sound quality out the front?
2)Do we understand then that all the mainstream manufacturers avoid discussing this issue?
3)Every single article I have ever read including the original work by Olsen uses reverse polarity rear drivers...are they all "wrong" or perhaps with very short delays it just isn't that audible?
4)So this really is a question about this anomaly..is it something we tolerate or is Mr Rat right or wrong about this given his working qualifications as a sound engineer of considerable experience? ..
2)Manufacturers accentuate the positive aspects of anything for sale, and minimize the negative. Other than in large arenas, few have the luxury of the distance between cabinets end fire requires.
3) The "compromised impulse response" from a cardioid sub array is the same as the phase inversion experienced already with bass reflex cabinets. No manufacturers that I'm aware of like to refer to their bass reflex cabinets as phase inversion cabinets, as that has a negative connotation, even though technically the reason it works. Since most already accept the "impulse smearing" bass reflex (phase inversion) design as a cost of doing business, no reason to explain that cardioid arrays add another phase inversion to the one already present.
4) Dave is correct, but the audibility of the problem is perhaps overstated, he has not given up use of bass reflex (phase inversion) cabinets. He also ignores a large problem in end fire arrays, the diffraction of the waves from rear cabinet around the front and the front around the rear also causes different frequency dependent arrival times, the response is not as smooth as a stacked array.
Using a "stair step" end fire approach (rear cabinet stacked on a "step" platform the height of the front cabinet) avoids some of the timing and reflection problems of the usual floor mounted end fire approach, but doubles array height and requires lifting the rear cabinets up on to some road case or platform, more than doubling the work for a slight improvement. Hard to sell that plan.
Art
Art,
Concise and totally relevant...also additional relevant input. This has helped me understand the issues and appreciate of course its all about putting the compromises where they may be least audible. Brilliant answer...thanks!
Concise and totally relevant...also additional relevant input. This has helped me understand the issues and appreciate of course its all about putting the compromises where they may be least audible. Brilliant answer...thanks!
All about compromise- when the double bass strings are rattling on the fret boards and the kettle drum drones in sympathetic vibration from certain bass notes, it does not help to explain to the conductor that the end fire array you decided to use "sounds better" out front than a cardioid array that would eliminate those problems on stage :^).
- Status
- Not open for further replies.