Trying to understand how designers " match " directivity of the mid-HF unit to the low/mid section .
Having difficulty to find info about that although it seems to be partially in every thread around here ( i might not be using the correct terms, please let me know what i should be looking for in the search/google )
I stumble upon Altec paper on directivity/driver circumference and their " ka " value ..that helped somewhat to understand what is happening.
But then i'm still back at the following point :
If this is approximately what would be considered near " optimal " ( Dutch 8c i think ..sorry took it on google image )
Why is it that all i see around is stuff like this :
or the NS15 of much respected dr Gedes :
where we can see that the directivity starts falling from 1K down .. ( i know this is a super good design i'm simply using it as " best case " here )
So shouldn't the 400~1Khz or something like that fall in line with the directivity of the mid/HF like the 8c does ?
I'm trying to understand how can the directivity be "matched " it it just starts going when it crosses over to the woofer . 🤔
I haven't been able to find many examples, but i've seen a few " mid/low " woofer WAVEGUIDES in pictures .. doesn't work good cause of size ??
Surely a woofer could achieve better matched directivity to some lower extent using a similar waveguide than the HF unit is ? at least i'd assume so lol
I'd like to read more on directivity between the low and mid/high crossover point , if you guys have some pointers or papers or just good threads about it i could read in the coming week , would be mucho appreciated 🙂
Thanks again for your patience, time and sharing !!
Having difficulty to find info about that although it seems to be partially in every thread around here ( i might not be using the correct terms, please let me know what i should be looking for in the search/google )
I stumble upon Altec paper on directivity/driver circumference and their " ka " value ..that helped somewhat to understand what is happening.
But then i'm still back at the following point :
If this is approximately what would be considered near " optimal " ( Dutch 8c i think ..sorry took it on google image )
Why is it that all i see around is stuff like this :
or the NS15 of much respected dr Gedes :
where we can see that the directivity starts falling from 1K down .. ( i know this is a super good design i'm simply using it as " best case " here )
So shouldn't the 400~1Khz or something like that fall in line with the directivity of the mid/HF like the 8c does ?
I'm trying to understand how can the directivity be "matched " it it just starts going when it crosses over to the woofer . 🤔
I haven't been able to find many examples, but i've seen a few " mid/low " woofer WAVEGUIDES in pictures .. doesn't work good cause of size ??
Surely a woofer could achieve better matched directivity to some lower extent using a similar waveguide than the HF unit is ? at least i'd assume so lol
I'd like to read more on directivity between the low and mid/high crossover point , if you guys have some pointers or papers or just good threads about it i could read in the coming week , would be mucho appreciated 🙂
Thanks again for your patience, time and sharing !!
How did you come to that sentence?
Have you listened to your favorite music with those? For being Super Good (well, not absolutely the best but near..) It should have been placed in a SG room with SG elettronics & SG source and SG interconnets, then a judgement of the valute of the whole (usually you judge the ability of the musicians /record) and the imprint of the single piece.
Sorry for being pedantic...
Here are a few papers to get you started
http://www.gedlee.com/Papers/directivity.pdf
https://www.pispeakers.com/Pi_Speakers_Info.pdf
https://aaltodoc.aalto.fi/bitstream...Kantamaa_Olli_2020.pdf?sequence=2&isAllowed=y
The 8c is different than many speakers that aim for directivity control as it uses a passive cardioid enclosure, this leaks sound out of the side in a carefully designed way to create higher directivity at lower frequencies. It does this through destructive interference. The price to pay for this is lower maximum output and higher distortion. Genelec's W371A does a similar thing but actively.
The 8c plot is not all that easy to read as it includes the full 360 spread. If you trace the bottom of the orange line you can see that the waveguide is nominally 120 degrees transitioning closer to 160 degrees when the radiation pattern is cardioid.
In a speaker like Earl's the 15" woofer becomes more directive as frequency rises and the waveguide becomes less directive as frequency falls. The match is where the patterns of the two are the same or substantially the same. In that case 90 degrees somewhere around 700 or 800Hz.
http://www.gedlee.com/Papers/directivity.pdf
https://www.pispeakers.com/Pi_Speakers_Info.pdf
https://aaltodoc.aalto.fi/bitstream...Kantamaa_Olli_2020.pdf?sequence=2&isAllowed=y
The 8c is different than many speakers that aim for directivity control as it uses a passive cardioid enclosure, this leaks sound out of the side in a carefully designed way to create higher directivity at lower frequencies. It does this through destructive interference. The price to pay for this is lower maximum output and higher distortion. Genelec's W371A does a similar thing but actively.
The 8c plot is not all that easy to read as it includes the full 360 spread. If you trace the bottom of the orange line you can see that the waveguide is nominally 120 degrees transitioning closer to 160 degrees when the radiation pattern is cardioid.
In a speaker like Earl's the 15" woofer becomes more directive as frequency rises and the waveguide becomes less directive as frequency falls. The match is where the patterns of the two are the same or substantially the same. In that case 90 degrees somewhere around 700 or 800Hz.
Due to physics, directivity get harder to control as frequency gets lower. Thats why you see the pyramids so often. To master this you either have to build a very big structure (> 1 meter) or use signal processing (DSP) combined with for the purpose dedicated drivers as in the 8c.
It's physics.
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It's physics.
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You are right - I missed the passive variant for achieving directivity as well as was wrong on how 8c does it - my bad.
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Besides this price, it is out of reach for many designers - especially if you want to do it well (passive enclosure) or implement tricks to limit how much output is lost (DSP / multi driver approach).
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I think you're seeing it as like matching a 90 tweeter to a 90 woofer, or a 70 tweeter to a 70 woofer.
No. It's only meant to match at the crossover point so it is smooth. Sure, the whole thing changes from low to high but it matches at the crossover point so there is no sudden jump.
And how steep you X-overs are, the bandwidth where blending (and it's curses) occurs will differ. Say that you use 2nd order (12 dB/oct) and lets assume that sound 20+ dB below starts to get irrelevant, and you have a 2k crossover - you have a band that is effected that is between 500Hz - 8k
8-o
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8-o
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Hi,
I get your point TnT but i think it is only one variable upon a set of design choice and expected results.
I mean i tried something like 100db/octave xover to transition from a 15" to a 5" at 750hz with very mixed results ( obviously! But at that time i wasn't aware of directivity match importance as i am now... for my own preferences).
And with careful selection of drivers you can implement 6db/octave filters on multiway ( Dunlavy loudspeakers) while still maintening a smooth polar behavior in horizontal plan ( smooth because wide over a wide region!).
I think the main point about directivity is the smoothness in transition ( if there is).
I get your point TnT but i think it is only one variable upon a set of design choice and expected results.
I mean i tried something like 100db/octave xover to transition from a 15" to a 5" at 750hz with very mixed results ( obviously! But at that time i wasn't aware of directivity match importance as i am now... for my own preferences).
And with careful selection of drivers you can implement 6db/octave filters on multiway ( Dunlavy loudspeakers) while still maintening a smooth polar behavior in horizontal plan ( smooth because wide over a wide region!).
I think the main point about directivity is the smoothness in transition ( if there is).
Not an active crossover, but an active cardioid. A passive cardioid uses the back wave and the natural physical delay to set the directivity. However it can also be done with multiple monopoles to achieve the same thing.
Ok, there is misunderstanding: Fluid stated ' the price to pay is lower output level and increase in distortion'.
As i understand it it is true for both passive and active cardioid approach.
I get from where it could come from in active cardioid but i don't for a passive cardioid approach:
Afterall it is not this different than an aperiodic or a bass reflex ( there is differences but the filter/delay induced by absorbing material should not make distortion higher? ).
As i understand it it is true for both passive and active cardioid approach.
I get from where it could come from in active cardioid but i don't for a passive cardioid approach:
Afterall it is not this different than an aperiodic or a bass reflex ( there is differences but the filter/delay induced by absorbing material should not make distortion higher? ).
A passively achieved cardioid bass response is extremely rare in commercially available speakers.
For a long time there was only ME Geithain but 30 years later Dutch&Dutch came along so there are now 2.
As far as I know ME Geithain builds everything ie amps and drivers in house.
Doesn't seem to increase distortion. Looks pretty good to me: musikelectronic geithain gmbh - RL 901K
(click on Acoustic Diagrams)
For a long time there was only ME Geithain but 30 years later Dutch&Dutch came along so there are now 2.
As far as I know ME Geithain builds everything ie amps and drivers in house.
Doesn't seem to increase distortion. Looks pretty good to me: musikelectronic geithain gmbh - RL 901K
(click on Acoustic Diagrams)
It is different. Aperiodic works as a closed box. Vented uses resonance to load the driver (very low frequencies are not relevant in this discussion, their effect is obvious)
However in the passive cardioid, loading is somewhat more like with a dipole.
Yep, 6db octave drop like with dipole, if there is full leak, alias good cardioid(ish) response. I think it is possible to tweak the passive cardioid system so that leak is much less, less cancellation, less lost bass. There seems to be bit more than two octaves good response from good passive cardioid, perhaps someone can tweak it for a system so that full 3 octaves of rather smooth pattern control happens, almost constant DI without much drawbacks. If its a bass box use big drivers, multiples, like with open baffle. If its a mid, use monopole bass. DSP would certainly help tweaking the response.
Matching waveguide to another or to a direct radiating driver about happens when the two are similar in size, their response would behave somewhat similarly around diameter size wavelength, where abouts the crossover could be. There are some small variations to this depending on waveguide asymmetry and coverage angle and what not, usually the crossover can be adjusted quite well, perhaps within an octave or so, when directivities of the two match nicely.
Example, i got two different waveguides about 20cm wide and 8 inch woofer. The other one makes nice crossover around 1.2khz and the other smaller and narrower directivity one around 2khz. 8" driver is roughly 1.8kHz in diameter.
Matching waveguide to another or to a direct radiating driver about happens when the two are similar in size, their response would behave somewhat similarly around diameter size wavelength, where abouts the crossover could be. There are some small variations to this depending on waveguide asymmetry and coverage angle and what not, usually the crossover can be adjusted quite well, perhaps within an octave or so, when directivities of the two match nicely.
Example, i got two different waveguides about 20cm wide and 8 inch woofer. The other one makes nice crossover around 1.2khz and the other smaller and narrower directivity one around 2khz. 8" driver is roughly 1.8kHz in diameter.
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fluid: thanks for the links, i'll go through each a few times ( already read gedlee once )
So you guys are saying that achieving a directivity similar to the 8c does in the lower part of the spectrum, isn't necessarily the goal ?
I understand it can't be done with regular loudspeakers setup without complex design/electronics etc,
but the reason why i asked the questions on the first post is that i haven't seen much ..let's use the word " efforts " , to have a similar directivity as low as possible , as the HF unit does.
I understand better what " matching " is about now, thank you all . Getting it right in the transition zone .
Would it even be possible to get something in the ~90deg @ -6db in regions such as 300-500hz with waveguides ?
So you guys are saying that achieving a directivity similar to the 8c does in the lower part of the spectrum, isn't necessarily the goal ?
I understand it can't be done with regular loudspeakers setup without complex design/electronics etc,
but the reason why i asked the questions on the first post is that i haven't seen much ..let's use the word " efforts " , to have a similar directivity as low as possible , as the HF unit does.
I understand better what " matching " is about now, thank you all . Getting it right in the transition zone .
Would it even be possible to get something in the ~90deg @ -6db in regions such as 300-500hz with waveguides ?
It could be but its a big physical object and thus not very common to see.
Yes, the device needs to be huge though, closing one meter in dimeter, perhaps someone has more exact dimensions.
edit. Cardioidish could about do it in smaller package, almost like a cheat, thats nominal 180degree dispersion. Or just a big baffle >20" wide. 90deg nominal dispersion like many waveguides are is -6db point at 45 degrees, and this would need a waveguide and big one. Not possible with cardioid. Open baffle would be close I think, but has back radiation.
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Sure
They are not small and not cheap though but there might be others who make similar things.
Sure. Limmer Horns make a few waveguides for 6 and 8 inch drivers:Limmerhorns - Home
They are not small and not cheap though but there might be others who make similar things.