The BK201 is a 30-ish year old horn that is from an era when we were guessing at how to design a BLH. You will find many variations, including from Coral, these, and lot sof lets just iscale this for my driver.
You may get lucky & it will sound OK or even good, but you are unlikely to get anywhere near optimum.
Do note that the current BK12 is a modern design using modern modeling tools, so the nature of the folding works — the Dallas 2 is another example of a similarily folded modern horn.
I would not approach building anything without having it modeled.
You may get lucky & it will sound OK or even good, but you are unlikely to get anywhere near optimum.
Do note that the current BK12 is a modern design using modern modeling tools, so the nature of the folding works — the Dallas 2 is another example of a similarily folded modern horn.
I would not approach building anything without having it modeled.
No doubt about it, pre T/S consumer BLHs, especially DIY, were based on the JBL Harkness, which is nowadays known as 'scoop bins' [AKA big vent reflex/BVR] designed to pump up the mid bass, lower mids, which back then with rare exception was as low as recordings, radio went at any useful amplitude.
Regardless, when I read the article my question was why didn't they do the time honored/proven mod of cutting out the baffle and add a new one, using spacers to fine tune it, so it's what I recommend.
Less low pass filter chamber [driver 'box'] interior volume rolls off the upper bass/lower mids, ergo more 'pumps it up', i.e. more baffle step compensation [BSC], so if the 201 has similar 'horn' specs as the 301, then if driven with a high output impedance you want little space like it already has and low output impedance more as required.
GM
Regardless, when I read the article my question was why didn't they do the time honored/proven mod of cutting out the baffle and add a new one, using spacers to fine tune it, so it's what I recommend.
Less low pass filter chamber [driver 'box'] interior volume rolls off the upper bass/lower mids, ergo more 'pumps it up', i.e. more baffle step compensation [BSC], so if the 201 has similar 'horn' specs as the 301, then if driven with a high output impedance you want little space like it already has and low output impedance more as required.
GM
@planet10 @GM
Dallas boxes are very beautiful, I have searched for some pictures and discussions and I must say that I really like ...
Unfortunately I do not have the technical competence to size one in relation to the Goodmans Axiom 201, I would not even know where to start, I imagine there are softwre able to do this but it was not my intention to request IT assistance from anyone but I could start studying a little more the theory "before" giving something ...
basically, I hoped that the realization of the box was empirical enough to allow my enjoyment, obviously if empiricism leads to a modest result I have serious doubts that it might be worth it, perhaps it would be more appropriate to request a suggestion on where to learn the necessary theory for doing a correct box-sizing...
Dallas boxes are very beautiful, I have searched for some pictures and discussions and I must say that I really like ...
Unfortunately I do not have the technical competence to size one in relation to the Goodmans Axiom 201, I would not even know where to start, I imagine there are softwre able to do this but it was not my intention to request IT assistance from anyone but I could start studying a little more the theory "before" giving something ...
basically, I hoped that the realization of the box was empirical enough to allow my enjoyment, obviously if empiricism leads to a modest result I have serious doubts that it might be worth it, perhaps it would be more appropriate to request a suggestion on where to learn the necessary theory for doing a correct box-sizing...
I apologize Dave, but this passage of the text I struggle to understand: can you write it in a more simpler form? Perhaps, with other words, I will be able to better understand your thinking.
Thanks so much
.
I guess you're referring to the Thiele/Small Parameters ... is that correct?
I am not aware of any BLH theory, it is just horn theory and you have to figure out how to adapt it to your needs. Fortunately, there are two papers adapting it to T/S theory, so of course it is best to know it first.
Thiele's, Small's AES papers: Read Research - Articles
Keele's 1977 AES paper: http://www.xlrtechs.com/dbkeele.com...Preprint) - LF Horn Design Using TS Paras.pdf
Prof. Leach's 1979 AES paper: https://leachlegacy.ece.gatech.edu/papers/HornPaper/HornPaper.pdf
GM
Buongiorno landrupp
I‘ve made the enclosures for my Triaxioms according (+/-) to the original plans published in the web. The Triaxioms came with ARU 172. The Bass response in a room of about 50 m3 is limited. It will be much better in a larger room! I‘ve read, that only enclosures with a tunnel (BR/Helmholtz) or with a damped vent will work good with these drivers. I think that a TL will also work good. Furthermore Ted Jordan has written once, that absorbing completely the rear soundpressure of the drivers is useful.
Cheers
Eric
I‘ve made the enclosures for my Triaxioms according (+/-) to the original plans published in the web. The Triaxioms came with ARU 172. The Bass response in a room of about 50 m3 is limited. It will be much better in a larger room! I‘ve read, that only enclosures with a tunnel (BR/Helmholtz) or with a damped vent will work good with these drivers. I think that a TL will also work good. Furthermore Ted Jordan has written once, that absorbing completely the rear soundpressure of the drivers is useful.
Cheers
Eric
Hello landrupp
I had the same problem years ago: how to use Goodmans 201.
I started with Open Panels because it was the fastest way to listen to these drivers. The major problem of this configuration is it is visually very cumbersome and has constraints for the placement in the room.
Then I studied the ARU concept and designed a box similar to that proposed by Goodmans with an ARU. I made my own ARU and checked that they worked correctly. To this end, make impedance measurements of the driver in the box. The ARU is a way to lower the impedance peak at resonance. Acoustically the bass sounded muddy.
I made a very simple test blocking the ARU with a piece of Board and made closed enclosures. The result is more than acceptable. The bass extension is down 50 Hz the top end culminates et 14 KHz and what is in between is very pleasant.
Conclusion, make closed boxes of about 130 litres. Stiffen and damp properly the panels. I used cheap cushions from IKEA to damp the acoustic modes, (they are very fluffy and can be easily attached to the panels).
The impedance peak at resonance rockets up to about 100 ohms which most amplifiers accept without problem.
Post scriptum, my experience confirms that cancelling completely the rear soundpressure works.
Would you need more details, (measurements, drawings), give me a mail address and I'll this to you.
Bon courage with this Coronavirus and good listenings, Jacques
I had the same problem years ago: how to use Goodmans 201.
I started with Open Panels because it was the fastest way to listen to these drivers. The major problem of this configuration is it is visually very cumbersome and has constraints for the placement in the room.
Then I studied the ARU concept and designed a box similar to that proposed by Goodmans with an ARU. I made my own ARU and checked that they worked correctly. To this end, make impedance measurements of the driver in the box. The ARU is a way to lower the impedance peak at resonance. Acoustically the bass sounded muddy.
I made a very simple test blocking the ARU with a piece of Board and made closed enclosures. The result is more than acceptable. The bass extension is down 50 Hz the top end culminates et 14 KHz and what is in between is very pleasant.
Conclusion, make closed boxes of about 130 litres. Stiffen and damp properly the panels. I used cheap cushions from IKEA to damp the acoustic modes, (they are very fluffy and can be easily attached to the panels).
The impedance peak at resonance rockets up to about 100 ohms which most amplifiers accept without problem.
Post scriptum, my experience confirms that cancelling completely the rear soundpressure works.
Would you need more details, (measurements, drawings), give me a mail address and I'll this to you.
Bon courage with this Coronavirus and good listenings, Jacques
I couldn't resist an inexpensive set of 201s so am joining this thread. I'm fortunate enough to be able to work from home so may not get to measure the T/S parameters (but may get to keep the house!) while waiting for the covid all-clear.
@planet10, how sensitive to T/S drift would the maxi-mini-onken be? (Translation: tell me I need to send you $10USD for the plans Or whatever today's price is )
@planet10, how sensitive to T/S drift would the maxi-mini-onken be? (Translation: tell me I need to send you $10USD for the plans
Or whatever today's price is )
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joining the bandwagon
Hopefully this topic is not dead yet
I too have been under the influence of the article in TNT-audio and have since purchased the drivers. Jumped on the occasion for two reasons:
- first, the pair of Axiom 201 I got are in mint condition, almost NOS.
- second, I already own an enclosure based on the very same Coral plans, that has been *already* enlarged and is now housing a pair of vintage RFT drivers.
So now I am stuck with many of the problems that @landrupp is quoting in his posts.
I wrote to the author of the articles in tnt-audio (Chris Templar) in february and he has been very friendly by responding to my e-mail. I am a bit hesitant to continue nagging him so now am on my own with my project. It seems he had a difficult time sculpting a place for the hefty 201 magnet. His initial build has been for Tannoy coaxials, that have a lot smaller magnets (in diameter), plus the housing for the magnets is slightly rounded in the Tannoys and quite squarish in the Goodmans (even more so in the Axiom 301).
An alternative would be to try and push the driver slightly forward by adding a baffle/ring/distancer. But am not sure what would be the sonic consequences, as this would effectively enlarge the volume of the first chamber/horn fold just behind the driver.
landrupp - where are you with your project? I am kind of stubborn and feel like pursuing the horn version. Anyway, good seeing that I am not the only one that got interested in this coral/axiom mix.
Hopefully this topic is not dead yet
I too have been under the influence of the article in TNT-audio and have since purchased the drivers. Jumped on the occasion for two reasons:
- first, the pair of Axiom 201 I got are in mint condition, almost NOS.
- second, I already own an enclosure based on the very same Coral plans, that has been *already* enlarged and is now housing a pair of vintage RFT drivers.
So now I am stuck with many of the problems that @landrupp is quoting in his posts.
I wrote to the author of the articles in tnt-audio (Chris Templar) in february and he has been very friendly by responding to my e-mail. I am a bit hesitant to continue nagging him so now am on my own with my project. It seems he had a difficult time sculpting a place for the hefty 201 magnet. His initial build has been for Tannoy coaxials, that have a lot smaller magnets (in diameter), plus the housing for the magnets is slightly rounded in the Tannoys and quite squarish in the Goodmans (even more so in the Axiom 301).
An alternative would be to try and push the driver slightly forward by adding a baffle/ring/distancer. But am not sure what would be the sonic consequences, as this would effectively enlarge the volume of the first chamber/horn fold just behind the driver.
landrupp - where are you with your project? I am kind of stubborn and feel like pursuing the horn version. Anyway, good seeing that I am not the only one that got interested in this coral/axiom mix.
Sorry for the post flooding but I thought there is something I should add. There is a reason why I am so hell-bend on copying Chris Templar's success story and applying the old Coral cabinet design to the Goodmans driver. I have listened extensively to the Coral cabinet fitted with the Beta 10 it was intended for. I also listened a bit to the Coral Beta 8 version, also with the original driver. Driven by an Audionote Quest clone. All I can say is these are stunningly good drivers in cabinets that do them justice. I have no intention to discuss the pluses and minuses of single-driver reproduction: am simply not qualified enough to do so.
Back to my experience:
Since one year I am listening to my pair of modified Coral enclosures, resized for 12-inch by adding size to the bottom. They have their quirks. The driver is from a very much lower price league and is anything but bass-efficient and not exactly linear but hugely efficient - perhaps 98dbm RFT 3402). It has weird resonances from time to time (perhaps due to the lack of dampening) but - boy! is it a pleasant change from my old Tannoys. So much detail and - when paired with a decent 300B - the imaging made me rethink what stereo is. They totally changed my modest system.
So - you see - I sort of want the best I can get in this very enclosure, because I believe in it. This is why I want to experiment with the Goodmans Axiom 201 in them.
Here are my pupies, the left one ornated with my son's impression of a horror-themed Christmas tree:
Back to my experience:
Since one year I am listening to my pair of modified Coral enclosures, resized for 12-inch by adding size to the bottom. They have their quirks. The driver is from a very much lower price league and is anything but bass-efficient and not exactly linear but hugely efficient - perhaps 98dbm RFT 3402). It has weird resonances from time to time (perhaps due to the lack of dampening) but - boy! is it a pleasant change from my old Tannoys. So much detail and - when paired with a decent 300B - the imaging made me rethink what stereo is. They totally changed my modest system.
So - you see - I sort of want the best I can get in this very enclosure, because I believe in it. This is why I want to experiment with the Goodmans Axiom 201 in them.
Here are my pupies, the left one ornated with my son's impression of a horror-themed Christmas tree:
Attachments
hi Rikiki
thank you for your interest and for the passion you have.
Unfortunately I didn't carry out my projects with axiom, due to covid I had to change my life priorities and currently hifi no longer occupies the place it had when I opened this thread.
However, I hope for better and more profitable times to dedicate myself again to this project which I hope to bring back to life sooner or later, currently the axioms are at a standstill along with a pair of Goodmans Dimension 8 and a dual 1229 turntable ... all to be restored .
I am interested in what you do with enthusiasm, the photo you published is very fascinating [including your son's "horror tree" ...], I hope to be able to disturb you in the coming times to find out what you have managed to do with the your axiom 201: at the point where I stopped I had come to find a laboratory that measured the TS parameters of my axioms and a technician ready to calculate the development of the horn on the Coral model, unfortunately I did not have the same luck to receive a answer from Chris Templer and I would be grateful if you post what he recommended here, if in your opinion it was interesting for the forum.
Thanks for everything, you made me remember good times that I hope will be back soon.
Greetings and best wishes from Italy, to you and your family.
Obviously, Best wishes and greetings to the whole forum, soon it's Christmas, I hope it's peaceful enough for everyone.
Landrupp
thank you for your interest and for the passion you have.
Unfortunately I didn't carry out my projects with axiom, due to covid I had to change my life priorities and currently hifi no longer occupies the place it had when I opened this thread.
However, I hope for better and more profitable times to dedicate myself again to this project which I hope to bring back to life sooner or later, currently the axioms are at a standstill along with a pair of Goodmans Dimension 8 and a dual 1229 turntable ... all to be restored .
I am interested in what you do with enthusiasm, the photo you published is very fascinating [including your son's "horror tree" ...
], I hope to be able to disturb you in the coming times to find out what you have managed to do with the your axiom 201: at the point where I stopped I had come to find a laboratory that measured the TS parameters of my axioms and a technician ready to calculate the development of the horn on the Coral model, unfortunately I did not have the same luck to receive a answer from Chris Templer and I would be grateful if you post what he recommended here, if in your opinion it was interesting for the forum.Thanks for everything, you made me remember good times that I hope will be back soon.
Greetings and best wishes from Italy, to you and your family.
Obviously, Best wishes and greetings to the whole forum, soon it's Christmas, I hope it's peaceful enough for everyone.
Landrupp