This is a review and detailed measurements of the Raal SR1a "true ribbon earfield" headphone. It is on kind loan from a member. As configured (with Pelican case and cabling) costs US $3,500. But that is not your full cost. You also need a home hifi amplifier that can produce minimum of 100 watts (not a typo!). In other words these are little speakers you wear on your ears:
The drivers are housed in heavy and solid metal enclosures that can rotate to adapt to your preference for sound and to some extent, comfort:
I was disappointed to find the edges of metal and carbon fiber material to be quite sharp. The texture of the metal grid is also quite rough. Don't know about you but I don't want anything like that near my ears let alone touching them. Alas, for best performance I had to rotate them all the way in and that meant the metal grill was touching my ear and became a source of annoyance.
Outside of that, the clever leather belt that holds the headphones suspended on your head is quite soft and comfortable. And easily configurable with more holes.
Just in case one of you is already screaming, no, no leather headband was harmed in above pictures. I did not want to readjust them for the stand and made sure to take pictures quickly and took them off that stand.
As I noted in the intro, you need to feed the SR1a with tons of power. No ordinary headphone amplifier may apply. For my testing, I used the Purifi reference amplifier which you can see in this picture:
That is the red larger box. Company requires 100 watts minimum/channel. The Purifi amplifier produces 130 watts of absolutely clean power. Company says you can go up to hundreds of watts but that you should be mindful of drivers bottoming out. That indeed happened to me a couple of times.
Needless to say, not only do you have zero sound isolation, you are also spitting out good bit of sound to people around you. As such, the SR1a is a solitary headphone. That said, the output level is rather low so the sound is not going to travel far.
Introduction to Headphone Testing
For my testing, I was fortunately enough to have a GRAS 45CA headphone measurement fixture with high resolution pinna on kind loan from the company. It is affectionally called "the hammer:"
While I have tested a number of headphones with the 45CA already, headphone measurement is far less of an exact science than speakers and electronics. So these results are subject to discussion and my interpretation of them which is subject to some error.
Unlike anechoic response for a speaker where we want to see a flat line, headphones are subject to ear resonances which the brain has learned to inversely filter. So the response needs to approximate what we would measure inside our ear. This is called the "target response" and I am using the one from Harman. This curve produces the best preference among listeners (a very long topic outside of the scope here). You will see this as dashed blue line in my measurements.
I play good bit with the headphones to get their timing and levels to match as closely as I can get them around a reference frequency of 420 Hz. This level is calibrated to be at the same point on the target response.
Headphone Measurements
Here is our frequency response per above:
Let's start with the easy part: the bass. Clearly we have a drooping response as we get down to 20 Hz (red and green lines). There is some dispute as to whether bass needs to be as high as Harman target but even if you discount that, we are still quite bass deficient. And this deficiency continues to 100+ Hz. In speaker terms, you have a satellite speaker in dire need of a subwoofer.
The resonance peak arrives early around 2 kHz and exceeds our target by a few dB.
From then on, the graph gets harder to read. The two channels don't quite match. This could be driver differences, positional issues, or both. With two drivers dangling from the fixtures, such things will have to remain vague. Going by the red channel, we do have a few peaks, one around 5.6 kHz and another around 7.2 kHz. Combined with the deficiency in bass, this headphone is bound to sound "light." Notes in these higher frequencies will be louder, accentuating them.
While the rest of the curve is messy, the general curve matches the target so we the headphone is not going be overly bright on the top end.
I did not have time to run a lot of distortion test but here is one on intermodulation distortion and max SPL (loudness) capability:
This matched the subjective listening in the SR1a could get reasonably loud but then some kind of compression would set in where it would not get much louder. If you kept pushing it, you would be hearing increasing distortion especially in highs and eventual driver bottoming out. Whether it was the amplifier clipping at this point is hard to tell but there is certainly enough power to get the driver to clip as well.
Headphone Listening Tests
I built an elaborate chain to get the SR1a starting with RME ADI-2 DAC Version 2 feeding the Purifi amplifier over balanced XLR connections. The output of the Purifi then went into impedance matching box from Raal and the on to the headphones.
The SR1a definitely imparts a sense of "panel speakers" to everything you play. And I mean everything. You get more ambiance with every track -- whether it is part of the recording or not. This is was a very pleasant effect with my audiophile demo tracks. You could take this setup to an audio show and be right at home. Part of this is due to the distance of the drivers from your ears.
There were some issues though. Sound was clean at low to reasonable levels. Turn up the level gradually and the highs would become increasingly grungy as noted before. Max out the volume and you don't get much more volume but plenty of distortion. Fortunately for comfortable long term listening, you would avoid most of this.
The second issue was the lack of bass. Take this track:
This is your standard "audio show demo track." Yet the sound was quite lackluster due to too little bass. I swapped the SR1a with three headphones: the Sennheiser HD-650, Hifiman HE400i and AKG K371 and all three had far more satisfying sound. The bass with these headphones was strong and impactful.
On other tracks such as this Madonna Music track, there was this artificial ambiance that I did not care for:
This is a studio recording and I expect tight and dry sound. What you hear with SR1a is somewhat spacious with high notes grabbing your attention. Mind you, there was something pleasing about this. But proper reproduction it was not.
I read the reviews on this headphone and watched the few videos on it. There was a lot of talk about slam, speed, etc. which I find all to be nonsense frankly. What they think is "speed" is simply lack of bass and increased high frequency energy, combined with drivers being too far from your ears (hence some comb filtering).
For the next phase of testing I created a set of filters in Roon player equalizer:
There is a combo of 3 filters to the left for bass. I had created this for other headphones and it worked very well here. It boosts the lows with two filters and then truncates the deep bass to avoid distortion. Note that the levels are pulled down a bit also to avoid pipeline overflow. The subject impact of this bass boost was very large. It heavily transformed the sound, making the SR1a much more balanced and fuller.
Next I attacked the 2 kHz peak. That was effective as well and took out some of that upper mid-range boost that was giving that "light" sound but which was out of balance.
I was surprised by the next filter at 5.6 kHz. It not only correct the spectrum but also seemed to reduce high frequency distortion! Maybe there is some panel resonance there.
I was not sure if the last filter was necessary as the higher the frequency, the less trust I have in headphone measurements. But it indeed was effective in reducing those upper notes that stood out way too much.
All together the transformation was quite impressive. You still had that "panel open sound" but now with much more balanced frequency response. Could now listen for a long time without saying, "oh wait, was that correct?"
Conclusions
We are way too early in our headphone testing and reviewing for me to give very definitive opinions. That disclaimer aside, the sound of the SR1a out of the box is good and satisfying but can stand to be improved substantially with equalization. If you are a fan of panel speakers in your room, you will definitely appreciate the type of sound the SR1a produces.
The requirement for a hifi amplifier is onerous in my opinion. If you use anything but class D as I did, you will be wasting a ton of power and generating much heat compared to normal headphone listening or even speaker listening. On top of the heat and expense, there is also distortion and limit of playback volume. Brute force was used to solve some technical problems here which shows its ugly edges.
The Raal SR1a takes on you a new journey with headphones which is worth taking, hopefully with proper equalization.
I don't have a recommendation for you one way or the other as I don't want any grief that will come with it.
------------
As always, questions, comments, recommendations, etc. are welcome.
Any fans of Shishido peppers here? If you don't know what they are, they are these Japanese wrinkled green peppers that are mostly sweet. You roast them over high heat, add some lemon juice, soy sauce and salt and you have a wonderful and addicting appetizer (order it next time at a Japanese restaurant). I grew thee Shishido plants this year in the greenhouse and they produced many pounds. Here is the last two pounds cooked and ready to eat:
Yeh, I let some of them ripen to red. The just get sweeter, not hotter. Occasionally you find a hot one which then entices you to eat more of them to cool your tongue! They are only available here in our Japanese grocery stores so it is nice to grow them yourself.
As always, we must finish a review with talk of money. The headphone fixture in this review costs a cool $15,000. I am debating if I am buying it but some motivation in the form of heavy donations could entice me to go there using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
The drivers are housed in heavy and solid metal enclosures that can rotate to adapt to your preference for sound and to some extent, comfort:
I was disappointed to find the edges of metal and carbon fiber material to be quite sharp. The texture of the metal grid is also quite rough. Don't know about you but I don't want anything like that near my ears let alone touching them. Alas, for best performance I had to rotate them all the way in and that meant the metal grill was touching my ear and became a source of annoyance.
Outside of that, the clever leather belt that holds the headphones suspended on your head is quite soft and comfortable. And easily configurable with more holes.
Just in case one of you is already screaming, no, no leather headband was harmed in above pictures. I did not want to readjust them for the stand and made sure to take pictures quickly and took them off that stand.
As I noted in the intro, you need to feed the SR1a with tons of power. No ordinary headphone amplifier may apply. For my testing, I used the Purifi reference amplifier which you can see in this picture:
That is the red larger box. Company requires 100 watts minimum/channel. The Purifi amplifier produces 130 watts of absolutely clean power. Company says you can go up to hundreds of watts but that you should be mindful of drivers bottoming out. That indeed happened to me a couple of times.
Needless to say, not only do you have zero sound isolation, you are also spitting out good bit of sound to people around you. As such, the SR1a is a solitary headphone. That said, the output level is rather low so the sound is not going to travel far.
Introduction to Headphone Testing
For my testing, I was fortunately enough to have a GRAS 45CA headphone measurement fixture with high resolution pinna on kind loan from the company. It is affectionally called "the hammer:"
While I have tested a number of headphones with the 45CA already, headphone measurement is far less of an exact science than speakers and electronics. So these results are subject to discussion and my interpretation of them which is subject to some error.
Unlike anechoic response for a speaker where we want to see a flat line, headphones are subject to ear resonances which the brain has learned to inversely filter. So the response needs to approximate what we would measure inside our ear. This is called the "target response" and I am using the one from Harman. This curve produces the best preference among listeners (a very long topic outside of the scope here). You will see this as dashed blue line in my measurements.
I play good bit with the headphones to get their timing and levels to match as closely as I can get them around a reference frequency of 420 Hz. This level is calibrated to be at the same point on the target response.
Headphone Measurements
Here is our frequency response per above:
Let's start with the easy part: the bass. Clearly we have a drooping response as we get down to 20 Hz (red and green lines). There is some dispute as to whether bass needs to be as high as Harman target but even if you discount that, we are still quite bass deficient. And this deficiency continues to 100+ Hz. In speaker terms, you have a satellite speaker in dire need of a subwoofer.
The resonance peak arrives early around 2 kHz and exceeds our target by a few dB.
From then on, the graph gets harder to read. The two channels don't quite match. This could be driver differences, positional issues, or both. With two drivers dangling from the fixtures, such things will have to remain vague. Going by the red channel, we do have a few peaks, one around 5.6 kHz and another around 7.2 kHz. Combined with the deficiency in bass, this headphone is bound to sound "light." Notes in these higher frequencies will be louder, accentuating them.
While the rest of the curve is messy, the general curve matches the target so we the headphone is not going be overly bright on the top end.
I did not have time to run a lot of distortion test but here is one on intermodulation distortion and max SPL (loudness) capability:
This matched the subjective listening in the SR1a could get reasonably loud but then some kind of compression would set in where it would not get much louder. If you kept pushing it, you would be hearing increasing distortion especially in highs and eventual driver bottoming out. Whether it was the amplifier clipping at this point is hard to tell but there is certainly enough power to get the driver to clip as well.
Headphone Listening Tests
I built an elaborate chain to get the SR1a starting with RME ADI-2 DAC Version 2 feeding the Purifi amplifier over balanced XLR connections. The output of the Purifi then went into impedance matching box from Raal and the on to the headphones.
The SR1a definitely imparts a sense of "panel speakers" to everything you play. And I mean everything. You get more ambiance with every track -- whether it is part of the recording or not. This is was a very pleasant effect with my audiophile demo tracks. You could take this setup to an audio show and be right at home. Part of this is due to the distance of the drivers from your ears.
There were some issues though. Sound was clean at low to reasonable levels. Turn up the level gradually and the highs would become increasingly grungy as noted before. Max out the volume and you don't get much more volume but plenty of distortion. Fortunately for comfortable long term listening, you would avoid most of this.
The second issue was the lack of bass. Take this track:
This is your standard "audio show demo track." Yet the sound was quite lackluster due to too little bass. I swapped the SR1a with three headphones: the Sennheiser HD-650, Hifiman HE400i and AKG K371 and all three had far more satisfying sound. The bass with these headphones was strong and impactful.
On other tracks such as this Madonna Music track, there was this artificial ambiance that I did not care for:
This is a studio recording and I expect tight and dry sound. What you hear with SR1a is somewhat spacious with high notes grabbing your attention. Mind you, there was something pleasing about this. But proper reproduction it was not.
I read the reviews on this headphone and watched the few videos on it. There was a lot of talk about slam, speed, etc. which I find all to be nonsense frankly. What they think is "speed" is simply lack of bass and increased high frequency energy, combined with drivers being too far from your ears (hence some comb filtering).
For the next phase of testing I created a set of filters in Roon player equalizer:
There is a combo of 3 filters to the left for bass. I had created this for other headphones and it worked very well here. It boosts the lows with two filters and then truncates the deep bass to avoid distortion. Note that the levels are pulled down a bit also to avoid pipeline overflow. The subject impact of this bass boost was very large. It heavily transformed the sound, making the SR1a much more balanced and fuller.
Next I attacked the 2 kHz peak. That was effective as well and took out some of that upper mid-range boost that was giving that "light" sound but which was out of balance.
I was surprised by the next filter at 5.6 kHz. It not only correct the spectrum but also seemed to reduce high frequency distortion! Maybe there is some panel resonance there.
I was not sure if the last filter was necessary as the higher the frequency, the less trust I have in headphone measurements. But it indeed was effective in reducing those upper notes that stood out way too much.
All together the transformation was quite impressive. You still had that "panel open sound" but now with much more balanced frequency response. Could now listen for a long time without saying, "oh wait, was that correct?"
Conclusions
We are way too early in our headphone testing and reviewing for me to give very definitive opinions. That disclaimer aside, the sound of the SR1a out of the box is good and satisfying but can stand to be improved substantially with equalization. If you are a fan of panel speakers in your room, you will definitely appreciate the type of sound the SR1a produces.
The requirement for a hifi amplifier is onerous in my opinion. If you use anything but class D as I did, you will be wasting a ton of power and generating much heat compared to normal headphone listening or even speaker listening. On top of the heat and expense, there is also distortion and limit of playback volume. Brute force was used to solve some technical problems here which shows its ugly edges.
The Raal SR1a takes on you a new journey with headphones which is worth taking, hopefully with proper equalization.
I don't have a recommendation for you one way or the other as I don't want any grief that will come with it.
------------
As always, questions, comments, recommendations, etc. are welcome.
Any fans of Shishido peppers here? If you don't know what they are, they are these Japanese wrinkled green peppers that are mostly sweet. You roast them over high heat, add some lemon juice, soy sauce and salt and you have a wonderful and addicting appetizer (order it next time at a Japanese restaurant). I grew thee Shishido plants this year in the greenhouse and they produced many pounds. Here is the last two pounds cooked and ready to eat:
Yeh, I let some of them ripen to red. The just get sweeter, not hotter. Occasionally you find a hot one which then entices you to eat more of them to cool your tongue! They are only available here in our Japanese grocery stores so it is nice to grow them yourself.
As always, we must finish a review with talk of money. The headphone fixture in this review costs a cool $15,000. I am debating if I am buying it but some motivation in the form of heavy donations could entice me to go there using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
