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Radically upgrade your sound and music experience with this 100dB HiFi Bluetooth speaker/portable audio monitor. 50 hours playtime!
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Max SPL level and first impressions: listening to wireless stereo FS-X

Posted by Frankenspiel Ltd. (Creator)

Hi guys,

Here's some stuff you might like to read.

Max SPL level
We have now finished our max SPL measurements for the production version of the FS-X.

We will be pubblishing the official re-calculation of the max SPL values for the pubblished technical specification, but what we can now tell you in advance of that is that compared to the measurements shown in the Kickstarter document, the maximum SPL level for the mono FS-X has been increased by roughly 3 dB (flat from 93.3 dB to 96.5 dB @ 0.5m). 

On top of this there is about a further 3 dB for stereo operation.  

The measurements were carried out in a similar sized listening room as the original @ 0.5 m from the loudspeaker and as before the track used was Adele's "Rolling in the Deep". Please see "Sound tests & measurements" on our main project page for the previous numbers/measurements.

Note the (by now) usual caveat: this value is without distortion. So, your FS-X will sound louder than ever, without distortion even at high volume.  

Basically, to cut a long story short, the way we have been able to achieve this is by putting more power through the system, partly through circuit re-design, partly through specifying improved component values.  

More important than the fact that the SPL numbers have improved, is the fact that we believe sound and music experience with the FS-X has also been improved. 

A first listen: wireless stereo FS-X
In hotel room testing FS-X wireless stereo. Taking time from rushing around to get an idea of how FS-X wireless stereo does the job and to listen to some good music. 

In all the work that had be done, you can sometimes lose track of the fact that ultimately this is all about the sound and the music... 

In the last few days it happens that I've been listening to higher power speakers with bass but FS-X wireless stereo is still surprising me. 

Playing James Blake's “Retrograde”, there’s a really deep bass. You can position left and right anywhere you want in the room, but what I noticed is by putting them close together, about 1 meter away from each other, it seems to increase the resonance effect of the bass. Audioslaves’ “Doesn't Remind Me” is at 50% volume (this room is 5 x 7 m) and it’s just about comfortable. It’s not that higher volume distorts, but for me personally I’m comfortable with this volume.

The voicing on "Someone like you" by Adele is great to test with. Again, in this room I can only play this comfortably at 60% volume. Up to about one minute into "Lovesong" it's quiet but then there's a moment when they all come in, it sounds really strong and there’s real resonance.

In stereo the FS-X can really drive Ellie Goulding's "Lights", the intro bass is very impressive. FS-X really comes into it’s own, you can really pick out all the hidden details. Wonderful!

Full volume now on "Amsterdam" by Imagine Dragons. Wow!!! 

Now playing some jazz, Charlie Haden and Pat Metheny’s CD Beyond the Missouri Sky. Very sad, Charlie Haden passed away just about a week ago. We've been using "First Song" to test the FS-X for as long as I can remember. It’s lovely music, but the reason why we use that track to test? For any speaker the bass in this is a real challenge, but for this tiny 9cm cube it’s no problem! In mono it really can handle it, in stereo it sounds very strong.
By the way anybody who's into jazz, who hasn't got Beyond the Missouri Sky, get it because you’d love it.

I've been listening to the FS-X in mono for a long, long time. For me, actually just listening in stereo is a novelty. Thing about the FS-X is after a while you forget all about how small it is, you just get into the music. Stereo FS-X is a revelation. It has real punch in the bass. All the detail I'm used to is still there, but something great happens with stereo.  

Technically I think the bass is resonating together to produce an even richer, deeper sound. And of course, FS-X is great on sound stage, but with stereo you just get that much more.

FS-X Wireless Stereo. The biggest compliment I can pay to it is that you're totally unaware of it. It just plays. Hats off to the guys at ISSC (the guys who did the Bluetooth chipset), they have done us proud here, great job. Stereo left and right channel separation and synchronisation are amazingly good. No jitter, apparently left/right channel difference is held at less than 1 millisecond. For somebody who has been in the wireless audio business for a while, that is really impressive!

Stereo is adding loudness, (the famous 3dB). In terms of listening levels, of course it's all individual, but for me, somewhere around just over 50% volume in this room sounds perfect.
I don't think I could play it louder for long, but it's nice to know that when you need the horsepower it's there. 

 - David


All the best, 

The Frankenspiel Team 

Sven Hanl, Andrew Whittle, and 16 more people like this update.


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    1. Missing avatar

      bsl100 on

      Great work Craig..

      All this makes it difficult to wait for the speaker. Am really keen to hear how these songs sound on the FS-X. From the reviews, its clear that these will have beautiful and smooth midrange higher frequencies. Acoustic material is really going to shine on these. Its the bass department which will be the real test.

      Its going to be the first true-wireless stereo set up that I will own. Cant wait to see this tech in action.

    2. Missing avatar

      Craig Trickett on

      Ok guys, I thought I'd take 5 minutes out to link up some youtube videos to the tracks that David has given as good testing tracks. Please see below

      James Blake - Retrograde…

      Audioslaves - Doesn't remind me…

      Adele - Someone like you…

      Ellie Goulding - Lights…

      Imagine Dragons - Amsterdam…

      Charlie Haden and Pat Metheny’s - First Song…

    3. Missing avatar

      bsl100 on


      Some speaker manufacturers are now using SPL readings instead of RMS data. The SPL readings of normal bookshelf or floorstanding speakers are usually done at 1m or 2m. As small wireless speakers are not able to reach the levels of the above, there is a trend to show SPL readings at 0.5m.

      SPL readings are 6 dB higher at 0.5m as compared to 1m. The issue with all this is how this sound is delivered. Around 90 - 100 dB can be achieved at 0.5m with smaller speakers. But, the sound quality delivered at that volume or sound pressure levels is not necessarily full-range. Its pretty subjective. For eg. if you cut down bass levels, a speaker is able to go louder and deliver higher SPL levels. It does not have to struggle to deliver the bass frequencies and hence all its power is used to push out the midrange and higher frequencies.

      Lets say you sit across a large room and place a small speaker at the same distance as a regular bookshelf or floorstanding speaker, you will hear the voice of the singer and instruments from across the room from the smaller speakers. But, its the larger speakers which will be able to deliver more of the lower frequencies out to you and sound full-range.

      Having said this, I would really be keen to see and hear the FS-X in action. As long as it can deliver quality sound, the higher SPL will only act as an added bonus.

    4. Missing avatar

      Craig Trickett on

      Being a complete novice is have no idea on the difference between these spl's could someone clarify it for me?

    5. Missing avatar

      Andreas Hamm

      @Craig: Take a look at the original sheet and the info given here. David was talking about the flat SPL, which was 93 dB, yet the ITU-R 468 SPL was 100 dB. Maybe they'll show us the sheet with the new SPLs soon.

    6. Missing avatar

      Craig Trickett on

      Well done guys, I'm so excited. One question though, I thought the original advertised spl was 100db? It's only a minor thing but just thought I'd check to clear up any confusion.


    7. Missing avatar

      Andreas Hamm

      I recently had the first real failure (means no delivery of a product) in one of the KS projects I've backed. The creator had a deal with a company called bluegiga, which just released a new BT chip. The KS project was about bluetooth in-ear headphones and as far as I remember, the chip has a very long range. Is that too late for considerations in your circuit design? Here's the link to the websige and this chip is still on the frontpage.