Basically none or very little. Directivity in low frequencies are more or less lost in a small room, the room modes will dominate.
There was one study, however, that showed that cardioid pattern were the least sensitive to placement. But the benefit were minimal compared to monopole. Dipole came out worse of the three, but probably of no real consequences.
No; here's what we want. Assuming a 32" cube, as illustrated in post 28:
WITHOUT FIR Filters:
1) a delay of 3.33 milliseconds, which will line up the wavefronts to create a narrowband cardioid at a critical frequency of 75Hz.
3.33 milliseconds corresponds to the 90 degree phase shift that we require to create a cardioid at a single frequency : 75Hz.
WITH FIR Filters:
1) a delay of 3.33ms at 75Hz (same as above)
3.33 milliseconds corresponds to the 90 degree phase shift that we require to create a cardioid at a single frequency : 75Hz.
2) a delay of 1.66ms at 150Hz (half as above)
1.66 milliseconds corresponds to the 45 degree phase shift that we require to create a cardioid at a single frequency : 150Hz.
3) a delay of 6.66ms at 37.5Hz (twice as above)
This is the one I'm iffy on. To figure this one out, I really need to create a sim.
The easiest way to understand what the goal is, is to understand that we're trying to keep the radiation from the BACK of the loudspeaker in-phase with the FRONT of the speaker. To do this at a single frequency is trivially easy; we just delay the front loudspeaker by a distance equal to the separation between the two drivers.
But doing the same trick at MANY frequencies means that we have to vary the amount of delay of the front speaker.
So we'll have a 'critical' frequency, and the we'll have LESS delay ABOVE that critical frequency, and MORE delay BELOW that critical frequency.
As noted in another post, this is certainly what B&O is doing with the Beolab 90, what Kiii is doing with their flagship, and what Lexicon is doing with Soundsteer.
Lexicon is possibly the most interesting, because it works in the vertical AND the horizontal axis.
Kii is undoubtedly the simplest, as it appears to only function in the bass and midbass.
IMHO, the Kii solution is the best match for DIY, because few of us really care about the variable beamwidth that the Lexicon and B&O solutions can do.
Did you find a way to make a variable phase filter that will keep the sub cardioid the entire bandwidth?
Yes, the methods described in this thread will yield a cardioid for 2-3 octaves, which is plenty for a sub.
You'll need a miniDSP HD to do the fir filters, or a mini DSP to do the all-pass filters.
The trick is to vary the phase vs frequency.
Does anyone know if Geoff Martin from B&O or Horbach from Harman post here?
They could confirm if this is the same processing used in their speakers.
You'll need a miniDSP HD to do the fir filters, or a mini DSP to do the all-pass filters.
The trick is to vary the phase vs frequency.
Does anyone know if Geoff Martin from B&O or Horbach from Harman post here?
They could confirm if this is the same processing used in their speakers.
If it were me, I'd shrink the dimensions and make a cardioid similar to the Kii Audio speaker. It would use a waveguide for directivity above 1200hz and cardioid array for the three octaves from 150hz to 1200hz.
Picture something like the gedlee Abbey. But the woofers are on the side, not below the waveguide.
A Geddes style sub array would be below that.
So... I have a pair of speakers, amp , REW and a miniDSP and also a semianechoic chamber to try to see how the cardioid directivity can be used over multiple octaves.
I would have to keep the distance between the 2 speakers under 75 cm because of room dimensions .
The problem is I don't know how to create allpass filters with miniDSP 2-4 so I would need your help. Those Byquad equations are giving me headaches
I would have to keep the distance between the 2 speakers under 75 cm because of room dimensions .
The problem is I don't know how to create allpass filters with miniDSP 2-4 so I would need your help. Those Byquad equations are giving me headaches
Charlie Laub's Active Crossover Designer (ACD) has an allpass filter block, you can put the parameters in that you need and then copy and paste the minidsp biquad parameters. Just make sure you set the sampling frequency to what you will use otherwise the biquads will be wrong.
You can visually see in ACD what the effect of the filters is. If you need a second order allpass you just cascade two first order sections at the same frequencies. You will probably need some trial and error to see what effect the allpass has and if you have the right frequencies.
Some information on all pass filters here from linkwitz Active Filters
What's the difference between your FIR method vs delay + polarity switch method of going cardioid? Wouldn't the delay + polarity switch method get you cardioid from a certain frequency down to DC without any FIR?
Interesting article. The idea seems to be the same, but I'd have to do some sims to see if there's a difference.
The idea proposed in this thread is that the rear speaker reinforced the output of the FRONT speaker, to make a FORWARD lobe that's louder than the rear lobe.
The idea proposed in your link is that the rear speaker negates the output of the FRONT speaker, to make a REAR lobe that's quieter than the front lobe.
But both solutions have a differential of ninety degrees, so I'm not sure if there would be any difference at all. But I could be wrong, the trick would be to do some sims.
One (fairly) major difference discussed in this thread is the idea of varying the phase to address the comb filtering that's mentioned in the link you posted.
I need to dig into that spreadsheet for Paul, but the only copy of Excel that I own is on my work PC. It had some issues for a few weeks there and then I got laid off last week
(Nothing to worry about though, the field that I work in has plenty of jobs available.)
The idea proposed in this thread is that the rear speaker reinforced the output of the FRONT speaker, to make a FORWARD lobe that's louder than the rear lobe.
The idea proposed in your link is that the rear speaker negates the output of the FRONT speaker, to make a REAR lobe that's quieter than the front lobe.
But both solutions have a differential of ninety degrees, so I'm not sure if there would be any difference at all. But I could be wrong, the trick would be to do some sims.
One (fairly) major difference discussed in this thread is the idea of varying the phase to address the comb filtering that's mentioned in the link you posted.
I need to dig into that spreadsheet for Paul, but the only copy of Excel that I own is on my work PC. It had some issues for a few weeks there and then I got laid off last week
(Nothing to worry about though, the field that I work in has plenty of jobs available.)
Interesting article. The idea seems to be the same, but I'd have to do some sims to see if there's a difference.
The idea proposed in this thread is that the rear speaker reinforced the output of the FRONT speaker, to make a FORWARD lobe that's louder than the rear lobe.
The idea proposed in your link is that the rear speaker negates the output of the FRONT speaker, to make a REAR lobe that's quieter than the front lobe.
But both solutions have a differential of ninety degrees, so I'm not sure if there would be any difference at all. But I could be wrong, the trick would be to do some sims.
One (fairly) major difference discussed in this thread is the idea of varying the phase to address the comb filtering that's mentioned in the link you posted.
I need to dig into that spreadsheet for Paul, but the only copy of Excel that I own is on my work PC. It had some issues for a few weeks there and then I got laid off last week
(Nothing to worry about though, the field that I work in has plenty of jobs available.)
AFAIK this is the standard way of creating a cardioid response. Linkwitz and many others also mentioned this as the way to create a cardioid response out of 2 monopole sources. That article I linked just had by far the clearest explanation of the analysis of what's going on.
I'm trying to find a way to extend this above the target frequency to get a midrange cardioid response like the Kii Audio Three.
Sorry to hear about your job loss, but in this market, you'll probably find an even better and higher paying job.
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It would all boil down to baffle width vs freq; as long as the baffle step freq is higher than the freq you are targetting, the same principle applies
As I understand it, an all-pass filter is a 2nd order high pass filter AND a 2nd order low pass filter, tuned to the same frequency, then combined.
IE, the output of the low pass filter will be the lows
the output of the high pass filter will be the highs
Combine the two outputs and you get a full range signal, but with a delay, and that delay is 'tuned' to a single frequency. The 'Q' of the filter will determine the amount and the bandwidth of the delay.
Easiest way to visualize this is to tinker with the spreadsheet here:
Car Audio | DiyMobileAudio.com | Car Stereo Forum - View Single Post - Advanced filters (Allpass/LT etc) with MiniDSP
B&O's speaker looks like this
An externally hosted image should be here but it was not working when we last tested it.
Lexicon's speaker looks like this
An externally hosted image should be here but it was not working when we last tested it.
Amazon Alexa looks like this
It turns out Amazon appears to be using the same technology as B&O and Lexicon, but in reverse in their Amazon Alexa:
"Amazon Alexa 7-Mic Far-Field Dev Kit
Designed to help commercial device manufacturers easily create far-field voice experiences, this development kit features the same 7-mic circular array and technology for “Alexa” wake word recognition, beam forming, noise reduction, acoustic echo cancellation, and barge-in capabilities found in the Amazon Echo. This solution is supported by leading chipset providers, enabling device manufacturers to quickly integrate Alexa voice capabilities into their products.
• Far-Field Voice Recognition
• Alexa wake word technology
• Compatible with leading chipset solutions, including NXP"
I love a good conspiracy, and it sure seems a little suspect that Amazon is packing absolutely state-of-the-art beamforming technology into a $49 device :O Big Brother is listening...
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