MAB
Major Contributor
I just bought a pair of used Yamaha NS-18 speakers from a local sale. They are from the early '70s, about 50 years old. Here is a 1973 print ad with the NS-18 and siblings:
I used an online translator on the the text that describes the driver technology.
They feature an ear-shaped woofer made from coated Styrofoam in an open-back cabinet with a horn tweeter. According to the add, these are the most revolutionary speaker advancement since the early 1920's.
There were a few print adds featuring ears in the early '70s:
Yes of course, design by analogy.
If the ear's shape is what we use to hear sound, why not also use that same shape to reproduce sound?!?
This ear-shaped Styrofoam woofer concept was originally featured on the NS-30:
In the NS-30 marketing material it said:
Regarding 'the split vibration produced by the bending of the board'... These ear-shaped drivers have no surround as found on a typical woofer, the Styrofoam membrane is attached to a neoprene rubber surround. All of the driver's excursion is the distributed flex of the entire foam membrane, with the boundary of the membrane held stationary.
Here are the pair I just bought. I removed the JA-5004 woofer and JA-0506 Tweeter (on top) from one of the speakers.
The speakers are open back design. The driver looks more like a potato chip than an ear to me.
Here is the back side of the woofer:
It's really quite impressive, with an incredible magnet and chassis. It has similar surface area to a 50cm (20 inch) round driver.
The Styrofoam is adhered to the stiff rubberized surround, which is then adhered to the aluminum frame.
The Styrofoam has a coating that appears to have been applied by hand with a brush. Everything is in great shape, especially for the age.
Getting a bit ahead with the disassembly... Before I did anything, I measured each speaker's impedance:
I bought them without testing, and was relieved to see both speakers had reasonable impedance and were matched, or were identically broken! Those are some wild impedance traces!
I listened for a few hours. I had to get used to speakers so low to the floor. I don't care for what they do to some voices. Sounds like lots of my favorite singers got nose work done. They don't have deep bass. They are inoffensive, even pleasant, but uneven. I hear no rattling, no odd sounds, nothing to indicate they are 50 years old. I pushed the bass hard enough to distort, they sound very bad very quickly when pushed too hard. They are fairly sensitive. TBH, there are way worse speakers, even with the odd and enigmatic midrange.
I measured the on-axis response of the speaker at 1 meter with each of the different tweeter contours, Soft, Flat, and Clear.
I wonder what all of the artifacts are. If we look at the FR and distortion, each of the cancelations have large spikes in all HD components.
Not all of the impedance resonances map to far field response artifacts.
Not quite 35-20kHz as claimed. I wonder if they are worn out. Both speakers have nearly identical frequency response, and impedance traces. Even the distortion plots and impedance resonances are matched. I found Yamaha's datasheet on the JA-0506 tweeter. I used an online translator to read it in English:
I hope this isn't too inaccurate translation.
That's a great datasheet. It's nice that they have a frequency response at the bottom, although highly smoothed.
I digitized Yamaha's graph and compared their data to the measurements of the tweeters in my pair:
I used similar smoothing to Yamaha. I measured with the 12dB/oct passive crossover. Looks like the same response, assuming Yamaha's trace is without crossover. The tweeter appears to have aged really well. Both tweeters are dramatically well matched. The lenses and magnets look and feel like finely crafted high quality pieces, and have survived 50 years with no defect.
I decided to check the tweeter's electrolytic filter capacitor, it's so popular to cast shade on these components.
I'm embarrassed I doubted it, it's also perfectly fine after all these years.
Not much different than a Hovland 2.2 uF fancy-film-cap except for the cap value:
I am confident the tweeter and crossover are working as new. I did hear a few instances of static on the tweeter tone control. It was easy to clean and now works perfectly. I soldered the electrolytic cap back in place.
I measured the woofers. First the impedance and resonant parameters:
I am not confident on V(as) and M(ms). I used added mass, and am not convinced that the change in resonance is going to lead to the correct values with this method due to the woofer not working like an ideal piston. In any case, these are odd parameters for sure, much like those Fostex 31" super woofers.
I did some nearfield frequency sweeps of the woofer in the cabinet.
More resonances show up at different frequencies than the far-field measurements of the full speaker. Many of the resonances measured nearfield correspond to resonances in the woofer's impedance trace. I have to wonder if the Styrofoam membrane is driven into a large sea of standing waves. Add to that the peaks and valleys caused by cancellations from the front and back of the speaker. Resulting in me recording different modes as I measure from different locations.
I thought I would do some 3D measurements of the JA-5004 woofer alone in the cabinet.
It's rough. But fun. I've never measured an open back speaker and am not sure how illuminating this is.
What is a bit lost is the woofer's response is smoother off axis. I love these funky woofers.
The woofers appear to have aged as well as the tweeter. Both are matched to each other's unique performance. No rubs or buzzes, just extremely uneven frequency response and moderately large doses distortion.
The whole speaker exudes quality and attention to detail, plus quirkiness. All of the fasteners are were secured with fine hardware and thread-clocking compound. The solder joints are all immaculate. The wires are all harnessed. The cabinet work is solid. They sound pretty good until the woofer is pushed too hard. I am really satisfied with these and am going to try to get the cabinets cleaned up as much as possible. I'll clean the other tweeter trim pot, but no need to change any capacitors.
Regarding the quirky idea to make this look like and ear, or a piano, or whatever... I have to wonder if at least one engineer on the team was face-palming at the nonsense about the woofer shape. Yamaha abandoned this unique woofer technology after just a few years, moving to more traditional drivers, including focusing on more practical applications of driver design in models like the NS-1000.
I'll stop here and follow up later with some in-room measurements. Comments and suggestions are welcome.
I used an online translator on the the text that describes the driver technology.
They feature an ear-shaped woofer made from coated Styrofoam in an open-back cabinet with a horn tweeter. According to the add, these are the most revolutionary speaker advancement since the early 1920's.
There were a few print adds featuring ears in the early '70s:
Yes of course, design by analogy.
If the ear's shape is what we use to hear sound, why not also use that same shape to reproduce sound?!? This ear-shaped Styrofoam woofer concept was originally featured on the NS-30:
In the NS-30 marketing material it said:
Wait, is it based on the shape of the ear or the shape of a piano's soundboard?!?
Regarding 'the split vibration produced by the bending of the board'... These ear-shaped drivers have no surround as found on a typical woofer, the Styrofoam membrane is attached to a neoprene rubber surround. All of the driver's excursion is the distributed flex of the entire foam membrane, with the boundary of the membrane held stationary.
Here are the pair I just bought. I removed the JA-5004 woofer and JA-0506 Tweeter (on top) from one of the speakers.
The speakers are open back design. The driver looks more like a potato chip than an ear to me.
Here is the back side of the woofer:
It's really quite impressive, with an incredible magnet and chassis. It has similar surface area to a 50cm (20 inch) round driver.
The Styrofoam is adhered to the stiff rubberized surround, which is then adhered to the aluminum frame.
The Styrofoam has a coating that appears to have been applied by hand with a brush. Everything is in great shape, especially for the age.
Getting a bit ahead with the disassembly... Before I did anything, I measured each speaker's impedance:
I bought them without testing, and was relieved to see both speakers had reasonable impedance and were matched, or were identically broken!
Those are some wild impedance traces!I listened for a few hours. I had to get used to speakers so low to the floor. I don't care for what they do to some voices. Sounds like lots of my favorite singers got nose work done. They don't have deep bass. They are inoffensive, even pleasant, but uneven. I hear no rattling, no odd sounds, nothing to indicate they are 50 years old. I pushed the bass hard enough to distort, they sound very bad very quickly when pushed too hard. They are fairly sensitive. TBH, there are way worse speakers, even with the odd and enigmatic midrange.
I measured the on-axis response of the speaker at 1 meter with each of the different tweeter contours, Soft, Flat, and Clear.
I wonder what all of the artifacts are. If we look at the FR and distortion, each of the cancelations have large spikes in all HD components.
Not all of the impedance resonances map to far field response artifacts.
Not quite 35-20kHz as claimed. I wonder if they are worn out. Both speakers have nearly identical frequency response, and impedance traces. Even the distortion plots and impedance resonances are matched. I found Yamaha's datasheet on the JA-0506 tweeter. I used an online translator to read it in English:
I hope this isn't too inaccurate translation.
That's a great datasheet. It's nice that they have a frequency response at the bottom, although highly smoothed.
I digitized Yamaha's graph and compared their data to the measurements of the tweeters in my pair:
I used similar smoothing to Yamaha. I measured with the 12dB/oct passive crossover. Looks like the same response, assuming Yamaha's trace is without crossover. The tweeter appears to have aged really well. Both tweeters are dramatically well matched. The lenses and magnets look and feel like finely crafted high quality pieces, and have survived 50 years with no defect.
I decided to check the tweeter's electrolytic filter capacitor, it's so popular to cast shade on these components.
I'm embarrassed I doubted it, it's also perfectly fine after all these years.
Not much different than a Hovland 2.2 uF fancy-film-cap except for the cap value:
I am confident the tweeter and crossover are working as new. I did hear a few instances of static on the tweeter tone control. It was easy to clean and now works perfectly. I soldered the electrolytic cap back in place.
I measured the woofers. First the impedance and resonant parameters:
I am not confident on V(as) and M(ms). I used added mass, and am not convinced that the change in resonance is going to lead to the correct values with this method due to the woofer not working like an ideal piston. In any case, these are odd parameters for sure, much like those Fostex 31" super woofers.
I did some nearfield frequency sweeps of the woofer in the cabinet.
More resonances show up at different frequencies than the far-field measurements of the full speaker. Many of the resonances measured nearfield correspond to resonances in the woofer's impedance trace. I have to wonder if the Styrofoam membrane is driven into a large sea of standing waves. Add to that the peaks and valleys caused by cancellations from the front and back of the speaker. Resulting in me recording different modes as I measure from different locations.
I thought I would do some 3D measurements of the JA-5004 woofer alone in the cabinet.
It's rough. But fun. I've never measured an open back speaker and am not sure how illuminating this is.
What is a bit lost is the woofer's response is smoother off axis. I love these funky woofers.
The woofers appear to have aged as well as the tweeter. Both are matched to each other's unique performance. No rubs or buzzes, just extremely uneven frequency response and moderately large doses distortion.
The whole speaker exudes quality and attention to detail, plus quirkiness. All of the fasteners are were secured with fine hardware and thread-clocking compound. The solder joints are all immaculate. The wires are all harnessed. The cabinet work is solid. They sound pretty good until the woofer is pushed too hard. I am really satisfied with these and am going to try to get the cabinets cleaned up as much as possible. I'll clean the other tweeter trim pot, but no need to change any capacitors.
Regarding the quirky idea to make this look like and ear, or a piano, or whatever... I have to wonder if at least one engineer on the team was face-palming at the nonsense about the woofer shape. Yamaha abandoned this unique woofer technology after just a few years, moving to more traditional drivers, including focusing on more practical applications of driver design in models like the NS-1000.
I'll stop here and follow up later with some in-room measurements. Comments and suggestions are welcome.
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