Part 5: All About That Bass

songeraudio

Manufacturer Handmade Field Coil Speakers
Aug 3, 2022
57
187
40
54
Portland, OR
www.songeraudio.com
Subjective disappointments aside, it felt good that next morning having managed a public speaking engagement, and successful listening event. Some said that they'd never heard anything better. Others were impressed with the craftsmanship. More than a few had asked the price.

Them: "These speakers are amazing! What's the price?"
Me: "Thanks! I'm trying my best to keep them under twenty thousand."
Them: <long pause> "Dollars..?"

Watches were checked, polite excuses made... that was the end of our conversation.

My wife was the first between us to discover the audio shows. There was so much we didn't know, and it was clear that to get an education, we'd need to attend a few of them. She booked the travel arrangements, and suddenly we were off to the 2018 Capital Audiofest.

CAF was the perfect first show for us to attend. It had an easy, family-friendly vibe, in contrast to the hyper-corporate confection we'd expected. Sure, there were polished marketing machines, but there were plenty of small producers offering hand-crafted work too, often at price points north of anything I had yet considered.

The people were warm and friendly, of which there are too many to mention here. The first exhibitor I ever spoke with at a show was Brian of Charney Audio. He suggested that they design and build cabinets for us, an almost irresistible offer at the time. I met Ze'ev Schlick of Pure Audio Project, who I continued to correspond with about my work long after the show. John Wolff of Classic Audio Loudspeakers played Billie Jean on reel-to-reel for me, so loudly that the opening snare strike made me physically jump out of my chair as his collection of RCA dogs looked on, questioningly.

Months later, we went to the Rocky Mountain Audiofest. There I met Chris Brunhaver of PS Audio, who has answered every email I've ever sent him since, no matter how silly, connecting me to the right resources and giving his thoughtful advice. Steven Norber of Prana Fidelity and his wife showed a speaker he'd thrown together over the prior weekend, and that remains among the best I've ever heard at the shows these past years. Shortly after RMAF, I met David Angress at a small audio event in Portland, Chairman of ADAM Audio in Germany at the time. It was David who urged me to submit a patent on the spider.

Lastly, at those first shows and events, I heard full-range and field coil drivers considered to be among the very best examples in the world. And that, just like the amazing people I'd met, inspired me to push on.

With that in mind, it was time to return to the drawing board. Before Songer Audio was even a twinkle in my eye, I'd made these:

front_1.jpg

They were one of several designs I'd made around the Tang Band W8-1772 driver. It was elegant in its own way, and it solved the problems that had surfaced in my bold but flawed first try. The CAD work went quickly; an internal shelf was added to support the weight of the driver, and a simple access panel in the back for easy swapping and service. A crude prototype in birch ply initially vetted the design - there was to be no guessing or self-delusion, this time around. I learned all that I could from it, and then moved on to a first production prototype, in cherry.

s1_cherry_withbase_driver_fitting.png

s1_cherry_nobase_back.png

They were finished out with polished brass hardware, and a nice lacquer finish over a cherry stain.

final_loudspeaker.png

I hoped that the tonal character of the cherry wood may be pleasing, and only lined about 60% of the interior. There were no other treatments inside the cabinet, and 4dB of baffle step compensation at 1.2kHz. A new version of the driver was developed with higher efficiency, clocking in at about 99dB 1W/1m:
onimaru_v2_dats.png

The Qts was still too low, and the inductance too high. To address the former, I'd learned that Qts can be variably increased with the addition of a series resistor on the positive lead of the driver. I'd give up some efficiency in doing so, but in theory push the Qts high enough for acceptable bass performance.

And it worked. Here's a smoothed response with 15 Ohms of series resistance, a single speaker at a meter, driver height, on axis:

fr-ir-15ohm-1m-6th-octave-nophase.png

This is both speakers, 1/96 octave at 7 feet, toed out about 15 degrees off-axis from the listening position:

fr-ir-15ohm-7ft-sine-both-96oct.png

It wasn't perfect, certainly. I mean, feast your eyes on that strange suckout drifting between 90 - 70Hz. If you were hoping for any treble past 12kHz, you're in for a disappointment. But that said... this result was a giant stride forward. A subwoofer was now unnecessary for satisfying levels of bass performance. While some claim to perceive treble beyond the limits of age-related loss, by way of the eyes or skin, I've never discovered any such gifts in myself. When I check my hearing with a tone generator, I'm deaf as a post at 10kHz and beyond. The last octave is well worth striving for nonetheless, and I was never going to reach it unless I found a way to significantly reduce driver inductance.

At about this time, the makerspace I'd been using as my shop fell on hard times, and shuttered. I suddenly lost access to my studio, fully-outfitted professional wood and metal shops, and a thriving community of similarly afflicted creative individuals, like myself. That might have spelled an end to the dream as well, had it not been for my best friend, Andrew. Even though he had nothing more to offer than his circa-1940's single-car garage, he not only gave me the key and unfettered 24/7 access to it, he bought a basic CNC router for me to use, as well. I am still amazed and humbled by it, to this day.

In the following months, it was in the seasonal freezing cold and boiling heat of that tiny garage, a riot of OSHA violations likely unparalleled anywhere on earth, that the first true S1 was born.
 
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dcathro

Well-Known Member
Sep 16, 2016
563
709
228
Melbourne, Australia
Twenty thousand - how outrageous of you!! :)
 
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DasguteOhr

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Sep 26, 2013
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Germany
Respect,it looks very good optically and metrologically.
Actually, there are only two ways to increase Qts without designing a new speaker.
A series resistors steals damping factor from the amp not uninteresting at tube amps.;)
1.
Increase the membrane mass with paint or soak the membrane.
2.
To weaken the electric drive(Qes), drill an 8mm - 10mm eccentric hole in the magnet. for me it brought 0.25-0.3 higher qts at my 15" woofer.
But I would try it first with a cheap fullrange speaker my tip.

20230730_174453.jpg
 
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songeraudio

Manufacturer Handmade Field Coil Speakers
Aug 3, 2022
57
187
40
54
Portland, OR
www.songeraudio.com
Respect,it looks very good optically and metrologically.
Actually, there are only two ways to increase Qts without designing a new speaker.
A series resistors steals damping factor from the amp not uninteresting at tube amps.;)
1.
Increase the membrane mass with paint or soak the membrane.
2.
To weaken the electric drive(Qes), drill an 8mm - 10mm eccentric hole in the magnet. for me it brought 0.25-0.3 higher qts at my 15" woofer.
But I would try it first with a cheap fullrange speaker my tip.
Thank you, Stephan! Yes, you're absolutely right. The series resistor seemed to work at this stage, but eventually it became clear to me that it wasn't the best way to solve my problem. I didn't want to increase the mass of the cones though, or to alter the motor steel geometry... It turned out that there was yet another way; and that will be much of what the next chapter in the story is about. :) Cheers...
 

the sound of Tao

Well-Known Member
Jul 18, 2014
3,587
4,804
940
Subjective disappointments aside, it felt good that next morning having managed a public speaking engagement, and successful listening event. Some said that they'd never heard anything better. Others were impressed with the craftsmanship. More than a few had asked the price.

Them: "These speakers are amazing! What's the price?"
Me: "Thanks! I'm trying my best to keep them under twenty thousand."
Them: <long pause> "Dollars..?"

Watches were checked, polite excuses made... that was the end of our conversation.

My wife was the first between us to discover the audio shows. There was so much we didn't know, and it was clear that to get an education, we'd need to attend a few of them. She booked the travel arrangements, and suddenly we were off to the 2018 Capital Audiofest.

CAF was the perfect first show for us to attend. It had an easy, family-friendly vibe, in contrast to the hyper-corporate confection we'd expected. Sure, there were polished marketing machines, but there were plenty of small producers offering hand-crafted work too, often at price points north of anything I had yet considered.

The people were warm and friendly, of which there are too many to mention here. The first exhibitor I ever spoke with at a show was Brian of Charney Audio. He suggested that they design and build cabinets for us, an almost irresistible offer at the time. I met Ze'ev Schlick of Pure Audio Project, who I continued to correspond with about my work long after the show. John Wolff of Classic Audio Loudspeakers played Billie Jean on reel-to-reel for me, so loudly that the opening snare strike made me physically jump out of my chair as his collection of RCA dogs looked on, questioningly.

Months later, we went to the Rocky Mountain Audiofest. There I met Chris Brunhaver of PS Audio, who has answered every email I've ever sent him since, no matter how silly, connecting me to the right resources and giving his thoughtful advice. Steven Norber of Prana Fidelity and his wife showed a speaker he'd thrown together over the prior weekend, and that remains among the best I've ever heard at the shows these past years. Shortly after RMAF, I met David Angress at a small audio event in Portland, Chairman of ADAM Audio in Germany at the time. It was David who urged me to submit a patent on the spider.

Lastly, at those first shows and events, I heard full-range and field coil drivers considered to be among the very best examples in the world. And that, just like the amazing people I'd met, inspired me to push on.

With that in mind, it was time to return to the drawing board. Before Songer Audio was even a twinkle in my eye, I'd made these:

View attachment 113651

They were one of several designs I'd made around the Tang Band W8-1772 driver. It was elegant in its own way, and it solved the problems that had surfaced in my bold but flawed first try. The CAD work went quickly; an internal shelf was added to support the weight of the driver, and a simple access panel in the back for easy swapping and service. A crude prototype in birch ply initially vetted the design - there was to be no guessing or self-delusion, this time around. I learned all that I could from it, and then moved on to a first production prototype, in cherry.

View attachment 113652

View attachment 113653

They were finished out with polished brass hardware, and a nice lacquer finish over a cherry stain.

View attachment 113654

I hoped that the tonal character of the cherry wood may be pleasing, and only lined about 60% of the interior. There were no other treatments inside the cabinet, and 4dB of baffle step compensation at 1.2kHz. A new version of the driver was developed with higher efficiency, clocking in at about 99dB 1W/1m:
View attachment 113657

The Qts was still too low, and the inductance too high. To address the former, I'd learned that Qts can be variably increased with the addition of a series resistor on the positive lead of the driver. I'd give up some efficiency in doing so, but in theory push the Qts high enough for acceptable bass performance.

And it worked. Here's a smoothed response with 15 Ohms of series resistance, a single speaker at a meter, driver height, on axis:

View attachment 113660

This is both speakers, 1/96 octave at 7 feet, toed out about 15 degrees off-axis from the listening position:

View attachment 113661

It wasn't perfect, certainly. I mean, feast your eyes on that strange suckout drifting between 90 - 70Hz. If you were hoping for any treble past 12kHz, you're in for a disappointment. But that said... this result was a giant stride forward. A subwoofer was now unnecessary for satisfying levels of bass performance. While some claim to perceive treble beyond the limits of age-related loss, by way of the eyes or skin, I've never discovered any such gifts in myself. When I check my hearing with a tone generator, I'm deaf as a post at 10kHz and beyond. The last octave is well worth striving for nonetheless, and I was never going to reach it unless I found a way to significantly reduce driver inductance.

At about this time, the makerspace I'd been using as my shop fell on hard times, and shuttered. I suddenly lost access to my studio, fully-outfitted professional wood and metal shops, and a thriving community of similarly afflicted creative individuals, like myself. That might have spelled an end to the dream as well, had it not been for my best friend, Andrew. Even though he had nothing more to offer than his circa-1940's single-car garage, he not only gave me the key and unfettered 24/7 access to it, he bought a basic CNC router for me to use, as well. I am still amazed and humbled by it, to this day.

In the following months, it was in the seasonal freezing cold and boiling heat of that tiny garage, a riot of OSHA violations likely unparalleled anywhere on earth, that the first true S1 was born.
Hi Ken,
Very much admire your work, it looks really fabulous and your writings make for great and informative reading and its great to read constantly positive feedback on your speakers.

I am a two way OB guy so especially like the look of your S2 speaker and am intrigued also by your mention of the S3 under development.

A question if poss… I noticed you chose a fixed magnet AE woofer in your S2 to go with your fab field coil and wondering your thoughts on what is best application for field coils ultimately especially in context of open baffle designs.

What is it about the characteristics of the AE 15 inch that made you use it in the S2 and are there any plans to pursue a larger 15 inch field coil or similar as a woofer in the S3… hope that’s not too much of an early reveal for you but trying to get some sense on whether field coils are best suited to any particular frequency range. I get that the QTS needed to get good bass for an OB might mean working typically at a lower voltage than your preference for 12v. Is that an issue at all? Does that mean for bass field coils may be generally suited better to being in cabinets or possibly in front loaded horns.

Many thanks for anything that you can share on this in advance

Graham
 
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songeraudio

Manufacturer Handmade Field Coil Speakers
Aug 3, 2022
57
187
40
54
Portland, OR
www.songeraudio.com
Hi Ken,
Very much admire your work, it looks really fabulous and your writings make for great and informative reading and its great to read constantly positive feedback on your speakers.

I am a two way OB guy so especially like the look of your S2 speaker and am intrigued also by your mention of the S3 under development.

A question if poss… I noticed you chose a fixed magnet AE woofer in your S2 to go with your fab field coil and wondering your thoughts on what is best application for field coils ultimately especially in context of open baffle designs.

What is it about the characteristics of the AE 15 inch that made you use it in the S2 and are there any plans to pursue a larger 15 inch field coil or similar as a woofer in the S3… hope that’s not too much of an early reveal for you but trying to get some sense on whether field coils are best suited to any particular frequency range. I get that the QTS needed to get good bass for an OB might mean working typically at a lower voltage than your preference for 12v. Is that an issue at all? Does that mean for bass field coils may be generally suited better to being in cabinets or possibly in front loaded horns.

Many thanks for anything that you can share on this in advance

Graham
Thanks so much for the kind words about my work Graham, and for reading my posts - I'm glad you're enjoying both. The AE woofer was simply the best performer within the design guidelines, really. As you may have read further along, the sensitivity of the field coil in its complete form is around 94.5dB. While some 15" woofers suitable for open baffle use claim higher sensitivities than that, I've found that when measured it isn't even close to true - the best of them top out at around the same mark, in the neighborhood of 94-95dB. The AE LO15 was right around that when measured on the bench, the Qts of the driver made it a good candidate to try in the folded baffle with a constrained opening, and it wasn't crushingly expensive. The AE Dipole series has lower sensitivity and the Qts was a little higher than I needed - I would have likely redesigned the S2 for two woofers had I chosen them. Supravox and Great Plains Audio were also strongly considered, but both are very costly - it would have made better sense to opt instead for a two-woofer AE design there as well. Two-woofer designs didn't appeal to me creatively however - solutions would have likely been copies of some other well-established loudspeakers that come to mind, and what's more I didn't find the brute force method to be very elegant.

Generally speaking, I feel confident that the governing ideas in the Onimaru expressed in a 15" field coil woofer would result in something equally special. In my modeling, it should be achievable to reach the right Qts and an acceptable sensitivity at 12VDC, as long as the voice coil has been thoughtfully designed and both the suspension compliance and weight of the moving mass are working toward those goals. I'm not sure where that whole project fits in the roadmap, to be honest. I'd love to create the woofer, and it's all but inevitable that I will eventually. I'd certainly offer the possibility within a project proposal to a client with few cost constraints. But for now... it looks to be on the distant horizon, along with the potential to offer drivers for sale. A few years away.

It's a little too soon to reveal any final decisions about the S3, but it is fair to say that it begs the question of whether any woofers are needed to achieve deep open baffle bass at great scale. Considering the more unusual characteristics of the Onimaru, I don't think it is.
 

the sound of Tao

Well-Known Member
Jul 18, 2014
3,587
4,804
940
Thanks so much for the kind words about my work Graham, and for reading my posts - I'm glad you're enjoying both. The AE woofer was simply the best performer within the design guidelines, really. As you may have read further along, the sensitivity of the field coil in its complete form is around 94.5dB. While some 15" woofers suitable for open baffle use claim higher sensitivities than that, I've found that when measured it isn't even close to true - the best of them top out at around the same mark, in the neighborhood of 94-95dB. The AE LO15 was right around that when measured on the bench, the Qts of the driver made it a good candidate to try in the folded baffle with a constrained opening, and it wasn't crushingly expensive. The AE Dipole series has lower sensitivity and the Qts was a little higher than I needed - I would have likely redesigned the S2 for two woofers had I chosen them. Supravox and Great Plains Audio were also strongly considered, but both are very costly - it would have made better sense to opt instead for a two-woofer AE design there as well. Two-woofer designs didn't appeal to me creatively however - solutions would have likely been copies of some other well-established loudspeakers that come to mind, and what's more I didn't find the brute force method to be very elegant.

Generally speaking, I feel confident that the governing ideas in the Onimaru expressed in a 15" field coil woofer would result in something equally special. In my modeling, it should be achievable to reach the right Qts and an acceptable sensitivity at 12VDC, as long as the voice coil has been thoughtfully designed and both the suspension compliance and weight of the moving mass are working toward those goals. I'm not sure where that whole project fits in the roadmap, to be honest. I'd love to create the woofer, and it's all but inevitable that I will eventually. I'd certainly offer the possibility within a project proposal to a client with few cost constraints. But for now... it looks to be on the distant horizon, along with the potential to offer drivers for sale. A few years away.

It's a little too soon to reveal any final decisions about the S3, but it is fair to say that it begs the question of whether any woofers are needed to achieve deep open baffle bass at great scale. Considering the more unusual characteristics of the Onimaru, I don't think it is.
Many thanks Ken, I hope to be able to hear some of your work one day. That you value elegance within design solutions does really come through in the detailing in all of your work.

In options I’d been looking at I’d shortlisted the 16 inch supravox field coils for a multi woofer open baffle configuration but in the specs for optimising for Qts for open baffle it showed I’d maybe running them down at the lower end of their voltage… perhaps even as low as 6 or 7 volts and wondered about the implications of this in terms of if that is really taking full advantage of the field coils.

I had already thought just maybe using the 15 inch AE especially in a multi-woofer design (though I had been looking at the driver in the dipole series). When I saw you were using an AE in your S2 it made me think it’s a good data point on them being a good option at least.

Then since my design precedent is for a two way multiple woofer open baffle would the ultimate gains of going with a field coil might in this application not necessarily be at their best in a multi woofer design… and if I’m thinking multi drivers the crazy cost implications for all the supravox drivers and tungar supplies to power them extraordinarily ramps up in a multi woofer design concept.

What I guess would be great to know if your experiences with field coils led you to think there might be a fundamentally different level of advantage with going with field coil over fixed in this or is it likely to be more subtle… (I should add I’d be crossing them over at about 600hz to a pair of Radian 951 beryllium compression drivers) which is running the woofers good deal higher than you do with the AE in the S2 so the resolution of the field coil would be playing out in a greater fundamental range within the music.

The elegance of field coil is part of what keeps buzzing my thought processes to persist though but I think that could just be the audiophile drive to work at the outer limits of what is realistically viable at times. Would love to get your perspectives given your great experience in this field.
 
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songeraudio

Manufacturer Handmade Field Coil Speakers
Aug 3, 2022
57
187
40
54
Portland, OR
www.songeraudio.com
Many thanks Ken, I hope to be able to hear some of your work one day. That you value elegance within design solutions does really come through in the detailing in all of your work.

In options I’d been looking at I’d shortlisted the 16 inch supravox field coils for a multi woofer open baffle configuration but in the specs for optimising for Qts for open baffle it showed I’d maybe running them down at the lower end of their voltage… perhaps even as low as 6 or 7 volts and wondered about the implications of this in terms of if that is really taking full advantage of the field coils.

I had already thought just maybe using the 15 inch AE especially in a multi-woofer design (though I had been looking at the driver in the dipole series). When I saw you were using an AE in your S2 it made me think it’s a good data point on them being a good option at least.

Then since my design precedent is for a two way multiple woofer open baffle would the ultimate gains of going with a field coil might in this application not necessarily be at their best in a multi woofer design… and if I’m thinking multi drivers the crazy cost implications for all the supravox drivers and tungar supplies to power them extraordinarily ramps up in a multi woofer design concept.

What I guess would be great to know if your experiences with field coils led you to think there might be a fundamentally different level of advantage with going with field coil over fixed in this or is it likely to be more subtle… (I should add I’d be crossing them over at about 600hz to a pair of Radian 951 beryllium compression drivers) which is running the woofers good deal higher than you do with the AE in the S2 so the resolution of the field coil would be playing out in a greater fundamental range within the music.

The elegance of field coil is part of what keeps buzzing my thought processes to persist though but I think that could just be the audiophile drive to work at the outer limits of what is realistically viable at times. Would love to get your perspectives given your great experience in this field.
I hope so too, Graham - what part of the world are you in? The short answer is that a field coil will be the much better performer, even as a woofer running at 6-7 volts if you're still getting acceptable SPL for your application. I'd especially say so because you're crossing as high as 600Hz - the better control of the cone with an electromagnet should be quite apparent.

The Supravox taps out at 50Hz - you won't likely get a lot of deep bass performance from it in an open baffle. You could mechanically increase the driver Qts and lower the Fs, but even then it may feel a little thin in the lowest register, and depending on how you accomplished it the overall effect could be detrimental to content near the crossover point. If you don't need a lot of sub-bass performance, and the price is in your budget, I'd go with the Supravox. If either of those caveats give pause, I think I'd opt for two LO15's per side. You'll be missing out on the field coil magic, but the deep bass will be present, and the LO15 is an excellent performer in it's own right. The world just doesn't yet offer an ideal field coil woofer for open baffle use. Not yet, anyway... ;)
 
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the sound of Tao

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Jul 18, 2014
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I hope so too, Graham - what part of the world are you in? The short answer is that a field coil will be the much better performer, even as a woofer running at 6-7 volts if you're still getting acceptable SPL for your application. I'd especially say so because you're crossing as high as 600Hz - the better control of the cone with an electromagnet should be quite apparent.

The Supravox taps out at 50Hz - you won't likely get a lot of deep bass performance from it in an open baffle. You could mechanically increase the driver Qts and lower the Fs, but even then it may feel a little thin in the lowest register, and depending on how you accomplished it the overall effect could be detrimental to content near the crossover point. If you don't need a lot of sub-bass performance, and the price is in your budget, I'd go with the Supravox. If either of those caveats give pause, I think I'd opt for two LO15's per side. You'll be missing out on the field coil magic, but the deep bass will be present, and the LO15 is an excellent performer in it's own right. The world just doesn't yet offer an ideal field coil woofer for open baffle use. Not yet, anyway... ;)
That’s brilliant Ken… that gives me plenty of perspective to factor in thank you.

It’s harder to sort through a choice like this when there’s no clear answer and not a lot of precedents to be able turn to. I could just be complicating things to draw the field coil option in because it is such an attractive notion and there’s such fundamental design beauty in field coils.

I’m in Australia and I’m sure South East Asia and the Pacific region along with Europe could all be good markets that would value access to your speakers if you decide to go into distribution.

That said a 2 way OB Songer A4 Omnimaru with twin 15 inch field coil Onimarwoofers sounds like a great idea for a very full expression of field coil speakers.
 

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