Does flipping a sub around also flip its polarity?
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- Опубліковано 14 жов 2024
- This question made my brain hurt so I had to make a video to explain it to myself. The answer is NO for the common subwoofers we encounter in the field that are closed in the back and have ports in the front. The answer would be YES if the sub were open in the back, but then the coverage pattern would be a figure-8, not omni.
Why do you polarity invert the rear sub in a cardioid array? • Why do you polarity in...
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FIGURE 4.12 Summation zones from Sound Systems: Design and Optimization by Bob McCarthy amzn.to/2Y02sLE
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I love to geek out about the physics of sound. This channel focuses on the growing opportunity for live sound engineers to improve their confidence and consistency through the understanding of the principles of sound system design and optimization. My goal is to make this channel upfront and honest about my success and failure, so you can learn from both.
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Phase should first be understood for signals, and it is introduced in signal processing with time-to-frequency transformations such a Fourier or Laplace. In signal processing we work with complex scalars. What seems to confuse a lot of people is that they try to understand phase via waves instead, but for waves we have complex vectors, so there are vector directions to take into account, and also directivity.
changing the orientation just adds a slight delay but the subs still fires positive air pressure at a time.
I nailed it. thank you teacher
I have a pair of old LEM 18" (horn design) subs. The actual sub driver is situated in the bottom of the subs facing upwards. I feed them signal below 100hz through a stereo behringer Graphic eq that has a dedicated mono subwoofer (low pass) output. The subs are paired with two 15" full range EV speakers on the top fed with full range signal, obviously not an ideal scenario due to conflicting low frequencies... Since the subs are not of generic direct front facing driver design. Is there excess phase cancelation between subs and tops? Its really confusing :P
Hard to say. Do you have an audio analyzer. Can you share the measurement data?
Alternatively, put them on the ground together play a test signal (eg. band limited pink noise, red pulse, black pulse) while inverting the polarity of one of them. Do you hear a big change?
What about a flipped subwoofer in a sealed box? Would the dispersion be figure 8 due to the basket and magnet intrusions?
Oh, wow, I have no idea.
A sealed sub is practically omnidirectional, so it does not matter which way it points. It is only if you somehow have a directional sub that it matters.
Excellent explanation... Cleared all my doubt
Glad it helped!
Orgasmic explanation...thanks Nathan .
😂
How much delay is applied to the top phase inverted and rear facing sub on a 2 stack L&R sub array?
The amount of delay required to reach matching phase slopes and maximum cancellation in the rear.
@@nathanlively So help me understand how to accomplish the delay between cabinets. It makes sense to me how to setup a gradient array with one speaker physically located behind another. The driver is physically delayed in space 1/4 wave length to get summation and polarity inverted plus delay is set to phase align so we get cancellation in back correct? When setting up an inline gradient array how do you calculate the delay for the reversed speaker? Would you double the delay amount needed in the end fire style gradient array? Or do you calculate what the physical delay would be and add that to the delay amount needed for phase alignment?
Great explanation!
Glad it was helpful!
You said, the sound of the bottom of the snare is polarity inverted compared to the sound of the top of the snare...
So, the polar diagram of a snare is a figure of 8 ?!?
Did I? Hmmm, what I meant is that as there is compression on one side of the snare head then there is rarefaction on the other side.
@@nathanlively i think is not as simple as we see at the exact moment of the shot of the stick on the snare. What we hear is not just the impact of the stick but the resonance of the snare.
I think the resonance of the snare is not polarity inverted between the top and the bottom of the snare, what we see between the waveforms of the top and the bottom is just a delay because the sound start from the top of the snare and the bottom mic is further from the top of the snare than the top mic.
Historically we use a polarity reverse between the two mics because on the analog desks we dont have acces to a delay. Today, with the digital desks, the good way is not the polarity reverse but just a few delay on the top mic.
Much better explanation here of what's happening the sound from the back of the driver - ua-cam.com/video/fvi6YsnRG8A/v-deo.html