How many identical microphones do you own? If you can make a half circle of fixed point measurements it could speed up the experiments.
I’m thinking thinking out load again here.
In the thread I posted about what eventually lead up to the D&D 8c we can follow the breadcrumbs. But it’s in the end of the thread that is most important.
The first post show an early version.
To contradict my self somewhat.
It is a combination of the sound taking the shortest length to the side port (not multiple per side) + the result after going thru damping material bounces of the cabinet inner back and everything else then thru damping again and then out the port the makes for the cardioid respons when it combines with the direct sound.
So only changing the back wall position gradually changes to many variables at ones if one does not get lucky. Simulations of the effect of damping material is not something trivial. So no simulation will give as much info as actually testing.
D&D were unintentionally smart when they stacked a closed box behind the midrange chamber so we won’t get a hint on the internals by locking at the externals.
This review 6moons: audioreviews Dutch & Dutch 8c shows a little sneak peak of the internals but does not gives away to much.
I’m thinking thinking out load again here.
In the thread I posted about what eventually lead up to the D&D 8c we can follow the breadcrumbs. But it’s in the end of the thread that is most important.
The first post show an early version.
To contradict my self somewhat.
It is a combination of the sound taking the shortest length to the side port (not multiple per side) + the result after going thru damping material bounces of the cabinet inner back and everything else then thru damping again and then out the port the makes for the cardioid respons when it combines with the direct sound.
So only changing the back wall position gradually changes to many variables at ones if one does not get lucky. Simulations of the effect of damping material is not something trivial. So no simulation will give as much info as actually testing.
D&D were unintentionally smart when they stacked a closed box behind the midrange chamber so we won’t get a hint on the internals by locking at the externals.
This review 6moons: audioreviews Dutch & Dutch 8c shows a little sneak peak of the internals but does not gives away to much.
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Yes Ernie thats a great resource. Which thread was that from?
A few questions pop into my head;
1. could I use a coax and a cheaper mid-bass up to the x-over point for the rear? Or do they need to be identical? I'm not sure about the tweeter arrangement on this build, but I'd be happy enough with what a coax would do. The drivers used in this build add up!
2. How would I calculate the depth of separation needed between the two Mids to get as close to the cancellation effect as possible? I wonder if the two mids have any delay added in the dsp or whether its just a mechanical offset from the depth of the enclosure and the damping. Probably the latter.
3. could this delay offset be done entirely (or tweaked) in dsp? ie. schlep two drivers on front and back and delay the rear one until it works? I'm always looking for the K.I.S.S. route!
Donovad. That Helios speaker is not that well documented, but the pictures I have seen, the waveguide/tweeter reminds me of my Audio Physics in the house.
A few questions pop into my head;
1. could I use a coax and a cheaper mid-bass up to the x-over point for the rear? Or do they need to be identical? I'm not sure about the tweeter arrangement on this build, but I'd be happy enough with what a coax would do. The drivers used in this build add up!
2. How would I calculate the depth of separation needed between the two Mids to get as close to the cancellation effect as possible? I wonder if the two mids have any delay added in the dsp or whether its just a mechanical offset from the depth of the enclosure and the damping. Probably the latter.
3. could this delay offset be done entirely (or tweaked) in dsp? ie. schlep two drivers on front and back and delay the rear one until it works? I'm always looking for the K.I.S.S. route!
Donovad. That Helios speaker is not that well documented, but the pictures I have seen, the waveguide/tweeter reminds me of my Audio Physics in the house.
I'm open to trying an active/passive combo BTW. Never used active, but I get how it could work with two mids per speaker. Active to help achieve the cancellation below the tweeter x-over.
I'm sure I read somewhere that they use a sort of dual slotted chamber before the side vents. Presumably to delay the wave further.
Are you thinking of Fulcrum Acoustic’s ?
https://www.fulcrum-acoustic.com/wp-content/uploads/2019/10/Passive-Cardioid-Speaker-Patent.pdf
I have seen no reference to similar techniques in D&D that I can remember.
Edit:
Their patent: https://patentimages.storage.googleapis.com/15/1a/41/f11b405ff94c5f/EP3018915A1.pdf
https://www.fulcrum-acoustic.com/wp-content/uploads/2019/10/Passive-Cardioid-Speaker-Patent.pdf
I have seen no reference to similar techniques in D&D that I can remember.
Edit:
Their patent: https://patentimages.storage.googleapis.com/15/1a/41/f11b405ff94c5f/EP3018915A1.pdf
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This the D&D 8C controls directivity by an acoustic vent, but you can also use DSP like the KII3 Kii Audio ::: kii_three
Perhaps you could get away with 5" drivers in a room that small.
Perhaps you could get away with 5" drivers in a room that small.
Yes, at the distance I listen, that would be the ideal.
I have been reading this thread by much cleverer people than myself; DSP midrange directivity control aka kinda cardioid
...and whilst a lot goes over my head a few bits stick. In summary, I need to create a time-delayed and low passed rear sound source, with inverted polarity.
"- delay between the sound sources has to resemble effective travel time of sound due to dipole path length
- the levels of both sources have to be matched (also dependent from frequency) at a "cancellation zone" behind the cardioid, which calls for an appropriate lowpass characteristic of the rear source."
So, now I am thinking a sealed test enclosure with a couple of small full rangers I have already. Measure the front and back simultaneously to get an idea of the response and time delay at the rear with just front sound. Minidsp to filter, invert, mimic the time delay and spl on the rear driver....
As if its that simple! But its a good place to start and seems more achievable(?).