D1sco,
There is ways to identify if there is peaks of directivity (and nulls): go outside, lay the loudspeaker down on the floor and pointing to the sky.
Play something musical and move around the box. If you can spot an issue then try again with pink noise for confirmation.
You should be able to identify most directivity issues this way.
And yes i'm aware of coloration that this can imply. I even gave hints on how to mitigate the effects by room's acoustic strategy. 😉
It's not a 'large' coax but the 6,5" of tannoy system 600 does have a polar map at ASR. I would not expect a larger one to be this much different.
There is ways to identify if there is peaks of directivity (and nulls): go outside, lay the loudspeaker down on the floor and pointing to the sky.
Play something musical and move around the box. If you can spot an issue then try again with pink noise for confirmation.
You should be able to identify most directivity issues this way.
And yes i'm aware of coloration that this can imply. I even gave hints on how to mitigate the effects by room's acoustic strategy. 😉
It's not a 'large' coax but the 6,5" of tannoy system 600 does have a polar map at ASR. I would not expect a larger one to be this much different.
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This sounds like a clever trick, to point the speake up. I will remember that one!
I have plenty of outdoor space to take measurements, and I have a decent measurement microphone. I am sure I won't go far enough with measurements to satisfy everyone on the forum, but I intend to do measurements to confirm that the speaker is working as intended.
I thought I should remind you that your first few comments on this thread had the theme of, "Coaxials are a proven technology". And you shared pictures of designs. And GM has stated the same by sharing information about older coaxials. So is it fair to call them "unproven"? I'll let you decide.
Except if you clone the design one to one yes there is incertitude.
That said i'm confident enough to know they can be used for inspiration. 😉
Nice you have access to space and mic! It is mandatory. 🙂
That said i'm confident enough to know they can be used for inspiration. 😉
Nice you have access to space and mic! It is mandatory. 🙂
This makes a ton of sense. Ironically I’ve never seen it demonstrated. No one pulls the tweeter out and says “here’s the difference in and out of the woofer”. Not even EAC, with his tremendous work on the q100 driver measurements. It’s definitely the one aspect of coaxes that is still somewhat mysterious and, in other cases such as high excursion, up for debate.
I tend to think about coaxials like this: they’re a two way point source instead of a single full range driver. Whether they help or hurt each other is up to the driver designer and the speaker designer.
Thanks for putting in the effort on these answers, it’s been good my dude.
Adason is a smart dude and we are absolutely trying to help. We all want to see success here. It’s why we’re talking about this idea for five straight pages. Being successful at designs like this directly involve critical thinking and criticism. If you want this project to work, that attitude isn’t the way. Everybody here wants you to end up with a super rad speaker and induct more people into the hobby. The worst way to do that? Encouraging someone to spend a lot of money and time and fail. I’ve always wanted your project to turn out well. However it’s done in the end.
Yes we willing to help for sure! But i remember being multiple time discouraged to start designing without understanding why when i engaged in it.
It is as frustrating as a failure! 🙂
Now it's been said let our ego on the side and keep discussing the ideas... 😉
D1sco, yes Erin displayed a lot of the inward about these Kef drivers. But you can find other measurements: in Mr Sticha's thread, Zvu's one here and at ASR, Fluid probably have measurements of Sica's coax too.
I could probably gives you more from the Tannoy's i have ( or have access too) but not in a close future ( i have kids ( 3 and 7), an house to renovate and my business is not in good shape thanks to Covid and M.Putin ocd's ...).
That said i don't get what you want to see exactly? The behavior of the woofer by itself? The tweeter by itself? It seems to me they are available in the threads i talked about.
And i kind of agree with your view of coax as 2way fullrange ( and why GM should be listened too imo).
I'm cautious about 'point source': a pulsating sphere of zero physical size is a nice basis for reasonning but in practice... at best you have coincident drivers and even if it is closer to the ideal, it is still not a point source. Blame AllenB if it doesn't fit your own definition ( but i think Allen is right about being picky with it!).
It is as frustrating as a failure! 🙂
Now it's been said let our ego on the side and keep discussing the ideas... 😉
D1sco, yes Erin displayed a lot of the inward about these Kef drivers. But you can find other measurements: in Mr Sticha's thread, Zvu's one here and at ASR, Fluid probably have measurements of Sica's coax too.
I could probably gives you more from the Tannoy's i have ( or have access too) but not in a close future ( i have kids ( 3 and 7), an house to renovate and my business is not in good shape thanks to Covid and M.Putin ocd's ...).
That said i don't get what you want to see exactly? The behavior of the woofer by itself? The tweeter by itself? It seems to me they are available in the threads i talked about.
And i kind of agree with your view of coax as 2way fullrange ( and why GM should be listened too imo).
I'm cautious about 'point source': a pulsating sphere of zero physical size is a nice basis for reasonning but in practice... at best you have coincident drivers and even if it is closer to the ideal, it is still not a point source. Blame AllenB if it doesn't fit your own definition ( but i think Allen is right about being picky with it!).
I am happy that you guys are willing participants, and the reason I continue discussing and asking questions is because that is all I am able to do at this moment! (Still waiting for the replacement DSP unit!) And I don't think it is completely unproductive?
Krivium planted an idea in my head that takes the project well beyond what I was originally prepared to do. I haven't committed to doing it yet, but I'm trying to learn as much as I can as quickly as I can so I can do it justice, if I choose to pursue it. Or atleast so I know what I am choosing!
I mean, I was just building a fancy DSP subwoofer. Adding a custom main speaker was not something I planned to do right away. But then I had an idea that I could integrate a coax into the cabinet; I asked the question, and here we are.
Krivium is right that it is expensive to add the coax driver, amplifiers, etc. I could buy a nice pair of speakers for the same money. Or I could keep my existing speakers, which was the original plan. Then there is the fact I haven't been able to test anything about my prototype, so I don't know if I like it in practice. If I don't like it, I still have the possibility of 4 individual subwoofers controlled with DSP. (Dr. Floyd Toole is a proponent of this, and rightly or wrongly I assumed Genelec was doing a version of this...)
The point is, please, if you think there is something better or different that should be done, be more specific! That's what I meant for Adason too. What part shouldn't I do? Why? What other thing are you suggesting instead? Atleast then I know what you mean.
Back to your initial W371A inspired sub and concerns.
I've read the link you provided. It all makes sense: using acoustic phenomemon for an outcome requires to keep an eye on acoustic conditions for sure.
The issue with stage was obvious to me. Putting a large ( acoustic) screen between drivers is not wise.
It is the acoustic interaction of both drivers (in an active application of principle) which define the overall directivity.
It's the same principle which apply with unidirectional dynamic mic and feedback: if you ever done a bit of live, under some location/condition the mic ( let's say a sm58) induce feedback. The first reaction most musicians have when it happen is to cover the hadbasket with their hands in order to 'cut' the feedback... which always end in the opposite effect ( aggravating the feedback)!
This happen because most dynamic unidirectional mic achieve their directivity through a passive approach, using what is known as an 'acoustic labyrinth' with openings which are located at the lower end of the capsule ( lower part of the protective 'ball' grill of the mic headbasket).
By closing the openings you change the conditions under which the capsule is working: from a pressure gradient to a pure pressure regime :
_pressure gradient 'sense' difference between both side of diaphragm and with the help of the acoustic labyrinth 'shape' the native figure of 8 pattern into an unidirectional one,
_ pure pressure are what they are: a diaphragm 'closing' a box hence omnidirectional behavior.
The same things happen with our loudspeakers ( there is a lot of similarity between this two kind of transducers): if you disturb acoustic conditions the directivity cannot be achieved.
For low it isn't dramatical as this is the 'natural' behavior we are used too, but it dismiss all the work/technology put into it...
This is the first point the author displayed, second being more 'sneaky' in my view: low end reflection.
Here the issue is an acoustical one: move the sub location and it can vanish /solve the issue! Or make another one appears: it happened to me in the past when we tryied to improve on a problematic modal behavior in a control room: we 'solved' the issue ( checked by measurements) to discover... it was worst than when we started: the mode we treated masked another oblique one which appeared in it's full glory once the first one was taken care of...
So from there what to expect: first the room conditions will be differents: no stage. One issue solved.
Second issue close to a wall. Well the w371 design should have been a warning by itself: it use a bass reflex port on the rear side. By itself this ask for a bit of space to the rear wall not to disturb the port.
That won't tell you if you'll face a low end reflection issue but it impose the loudspeaker location by itself. For this only real world will tell you what to expect.
If you face an issue you'll have to investigate if this is a port issue, an acoustical one or other things. This might be frustrating. Really frustrating as it is not easy to recognise cause when there is acoustic at play.
A good thing to do is to have a reference about the sound of the loudspeaker: listen to it outdoor, far away from any walls/obstacle: except for the ( theorical in practice it'll more be 3db ime) 6db lost of efficiency it should give you a reference of how it should sound.
Now the 'crude/philth' rearward sound from active cardioid: Fulcrum sound loudspeaker are aimed at live/PA applications. In this case if the loudspeakers are located on front of stage then it can potentialy be an issue as this have the potential to interact with what happen on stage.
In your room there is low chance you'll ever locate your listening point between the backside of your sub and the wall. 😉
It could induce some artefact but this is not what i would focus on at first...
Anyway, if it fail for whatever reason it fail you already have a B plan with a multisub approach a la 'Geddes' ( or Waltier or ...).
You could try D&D approach too if you miust be close to the wall...
I hope i didn't lost you in this explanations.
I've read the link you provided. It all makes sense: using acoustic phenomemon for an outcome requires to keep an eye on acoustic conditions for sure.
The issue with stage was obvious to me. Putting a large ( acoustic) screen between drivers is not wise.
It is the acoustic interaction of both drivers (in an active application of principle) which define the overall directivity.
It's the same principle which apply with unidirectional dynamic mic and feedback: if you ever done a bit of live, under some location/condition the mic ( let's say a sm58) induce feedback. The first reaction most musicians have when it happen is to cover the hadbasket with their hands in order to 'cut' the feedback... which always end in the opposite effect ( aggravating the feedback)!
This happen because most dynamic unidirectional mic achieve their directivity through a passive approach, using what is known as an 'acoustic labyrinth' with openings which are located at the lower end of the capsule ( lower part of the protective 'ball' grill of the mic headbasket).
By closing the openings you change the conditions under which the capsule is working: from a pressure gradient to a pure pressure regime :
_pressure gradient 'sense' difference between both side of diaphragm and with the help of the acoustic labyrinth 'shape' the native figure of 8 pattern into an unidirectional one,
_ pure pressure are what they are: a diaphragm 'closing' a box hence omnidirectional behavior.
The same things happen with our loudspeakers ( there is a lot of similarity between this two kind of transducers): if you disturb acoustic conditions the directivity cannot be achieved.
For low it isn't dramatical as this is the 'natural' behavior we are used too, but it dismiss all the work/technology put into it...
This is the first point the author displayed, second being more 'sneaky' in my view: low end reflection.
Here the issue is an acoustical one: move the sub location and it can vanish /solve the issue! Or make another one appears: it happened to me in the past when we tryied to improve on a problematic modal behavior in a control room: we 'solved' the issue ( checked by measurements) to discover... it was worst than when we started: the mode we treated masked another oblique one which appeared in it's full glory once the first one was taken care of...
So from there what to expect: first the room conditions will be differents: no stage. One issue solved.
Second issue close to a wall. Well the w371 design should have been a warning by itself: it use a bass reflex port on the rear side. By itself this ask for a bit of space to the rear wall not to disturb the port.
That won't tell you if you'll face a low end reflection issue but it impose the loudspeaker location by itself. For this only real world will tell you what to expect.
If you face an issue you'll have to investigate if this is a port issue, an acoustical one or other things. This might be frustrating. Really frustrating as it is not easy to recognise cause when there is acoustic at play.
A good thing to do is to have a reference about the sound of the loudspeaker: listen to it outdoor, far away from any walls/obstacle: except for the ( theorical in practice it'll more be 3db ime) 6db lost of efficiency it should give you a reference of how it should sound.
Now the 'crude/philth' rearward sound from active cardioid: Fulcrum sound loudspeaker are aimed at live/PA applications. In this case if the loudspeakers are located on front of stage then it can potentialy be an issue as this have the potential to interact with what happen on stage.
In your room there is low chance you'll ever locate your listening point between the backside of your sub and the wall. 😉
It could induce some artefact but this is not what i would focus on at first...
Anyway, if it fail for whatever reason it fail you already have a B plan with a multisub approach a la 'Geddes' ( or Waltier or ...).
You could try D&D approach too if you miust be close to the wall...
I hope i didn't lost you in this explanations.
My project has moved on quite a bit since my last post here. I now have speakers that use B&C 12FHX76 coaxials.
Before I got them I purchased a pair of Beyma 12CXA400ND drivers on Ebay for seemingly a killer price. They ended up being New Old Stock. By the date markings they were 10 years old, and they were damaged when I received them. It might have been shipping damage since they were shipped in beat up old boxes with no padding...or maybe they fell off a truck years ago? I returned them, and then bought new B&Cs for the price I paid for the Beymas. I would have loved to keep the Beymas, because they seemed like excellent quality.
But the B&Cs are nice too. They are a bit cheaper, and the difference seems to be that the wave guide is plastic, and the cone is pretty thin. The B&Cs "can" play down to 100hz, but they develop a steep spike in distortion starting at 120hz. I avoid that by using a steep filter at 120hz.
By comparison, I think the Beymas would do better for lower frequencies due to the stiffer cone. But it isn't make or break in my case, since I am able to use a slightly higher crossover frequency. Maybe the B&Cs are better for midrange because of the lighter cone? I don't know.
What I liked about the Beyma and the B&C is the visible horn wave guide. I think it is better aesthetically, because it would feel strange to hear high frequencies coming from a 12" cone.
I was not able to compare the two coaxial drivers in an A/B test, so I can't say if one is better sounding. But I can say that the B&Cs do sound quite accurate and direct/ detailed. I am enjoying the fact that I do not have to be in the exact right spot to hear all the details.
I have not seen any benefit to setting up the speakers to have directivity, so I have them configured as a multiple subwoofer scheme. I have achieved roughly flat response throughout my room just by manipulating delays, even in spots that should be terrible!
I also abandoned the woofer + PR arrangement. This speaker design starts out being quite large, so I'm trying to make the cabinet as small as possible. And getting rid of the woofer + PR arrangement let me save some space. (And the woofers seemed cheaply constructed compared to the coax and subwoofer.)
Instead I landed on the Eminence Lab 12 for the front woofer. It plays down to 45hz in a 30 liter cabinet. I did a lot of searching, but I was not able to find anything else that could play low in a small sealed enclosure. The Lab 12 barely extends above 100hz, but I am able to cross it over at 120hz to meet the coaxials. (I could have used any subwoofer driver, but I don't like the bulbous surrounds that most subwoofer drivers have. So the Lab 12 works aesthetically for my design, since the surround is not as large as others.)
Currently I have been experimenting with subwoofer port designs. I have tried a few already, experimenting with port cross sectional area and port type. More detail on that will be posted in the subwoofer forum.
Before I got them I purchased a pair of Beyma 12CXA400ND drivers on Ebay for seemingly a killer price. They ended up being New Old Stock. By the date markings they were 10 years old, and they were damaged when I received them. It might have been shipping damage since they were shipped in beat up old boxes with no padding...or maybe they fell off a truck years ago? I returned them, and then bought new B&Cs for the price I paid for the Beymas. I would have loved to keep the Beymas, because they seemed like excellent quality.
But the B&Cs are nice too. They are a bit cheaper, and the difference seems to be that the wave guide is plastic, and the cone is pretty thin. The B&Cs "can" play down to 100hz, but they develop a steep spike in distortion starting at 120hz. I avoid that by using a steep filter at 120hz.
By comparison, I think the Beymas would do better for lower frequencies due to the stiffer cone. But it isn't make or break in my case, since I am able to use a slightly higher crossover frequency. Maybe the B&Cs are better for midrange because of the lighter cone? I don't know.
What I liked about the Beyma and the B&C is the visible horn wave guide. I think it is better aesthetically, because it would feel strange to hear high frequencies coming from a 12" cone.
I was not able to compare the two coaxial drivers in an A/B test, so I can't say if one is better sounding. But I can say that the B&Cs do sound quite accurate and direct/ detailed. I am enjoying the fact that I do not have to be in the exact right spot to hear all the details.
I have not seen any benefit to setting up the speakers to have directivity, so I have them configured as a multiple subwoofer scheme. I have achieved roughly flat response throughout my room just by manipulating delays, even in spots that should be terrible!
I also abandoned the woofer + PR arrangement. This speaker design starts out being quite large, so I'm trying to make the cabinet as small as possible. And getting rid of the woofer + PR arrangement let me save some space. (And the woofers seemed cheaply constructed compared to the coax and subwoofer.)
Instead I landed on the Eminence Lab 12 for the front woofer. It plays down to 45hz in a 30 liter cabinet. I did a lot of searching, but I was not able to find anything else that could play low in a small sealed enclosure. The Lab 12 barely extends above 100hz, but I am able to cross it over at 120hz to meet the coaxials. (I could have used any subwoofer driver, but I don't like the bulbous surrounds that most subwoofer drivers have. So the Lab 12 works aesthetically for my design, since the surround is not as large as others.)
Currently I have been experimenting with subwoofer port designs. I have tried a few already, experimenting with port cross sectional area and port type. More detail on that will be posted in the subwoofer forum.
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Photo is the most recent cabinet featuring the B&C coaxial. This cabinet has 2 ports running vertically and exiting out the back. Ports are about 30"x 4". Cabinet is tuned to ~20hz.
This cabinet is 18"x18"x48" tall, and I intend for the final design to be 16"x16"x 54"(?). I think this optimizing of the design is the tricky part of speaker design!
This cabinet is 18"x18"x48" tall, and I intend for the final design to be 16"x16"x 54"(?). I think this optimizing of the design is the tricky part of speaker design!
I just started a new thread for the speaker build:
https://www.diyaudio.com/community/...ting-multiple-subwoofers.401343/#post-7403576
https://www.diyaudio.com/community/...ting-multiple-subwoofers.401343/#post-7403576