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Sehlin Helium DIY Speaker Review

BYRTT

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I wouldn't find that surprising at all considering we're talking about a "woofer" that's smaller than many midrange drivers employed in 3-way designs.
Right but a XO region above 5kHz is very high and nearly impossible for a 3 incher piston to match tweeter directivity up there and what makes some of the chaos in spinorama plot for this review where if that bump in directivity index curve had not been there 3,3kHz-8kHz then all the curves 3kHz and up had looked alot smoother..
 

Mudjock

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maybe Mudjock can confirm if XO region is that high..
Yes, the crossover point is a little above 5 kHz. The tweeter, in theory could support a crossover point down to around 3.5 kHz and it would be interesting to try that.

Wondering how Helium would fare for cinema use, especially for L, R, height and surround, where room correction is applied by the receiver? And how they'd compare to other very small speakers such as Cambridge Minx, Klipsch Chorus, B&W M-1 and so on.
That is one of the use cases I thought about when these were designed, particularly in a smaller room. These still have reasonable output in the 80-100 Hz range, where many other speakers this size don't.

So very very small, it's interesting but they are not really portable, I think that the use cases are a bit limited for something like this no?
People have found quite a few use cases for these. I designed them when Parts Express introduced the flat pack enclosure and I started to think about what could be built at that size. In addition to desktop applications, there have been portable bluetooth boom boxes and table radios made using this design. I also published a soundbar design based on the Helium in 2016. Some have wall mounted or ceiling mounted them and used them in small HT setups. From my perspective, spousal approval factor was a major consideration. Once some people have seen something like the Bose lifestyle systems, almost anything else seems big. I had NHT Super Zeros in the family room at one point and received that comment. No one calls the Heliums big.

How did you place the microphone for 0°? Was it tweeter axis offset to the center of the tweeter, or center of the cabinet?
I wonder this as well as I had my mic at tweeter height and the on-axis measurement here shows the tweeter SPL a couple dBs low relative to the woofer. I can try to measure the other speaker from the center of the baffle to see if I can duplicate that.
 

Soniclife

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And it's truly a user friendly "computer speaker" as it has a some interesting I/O including USB, Toslink and RCA input and a subwoofer output; probably very nice with their TS107 sub.
They are. The usb input, and single volume control on the front make them drop in replacements for PC speakers. They don't go loud, as if that needs saying with 3" driver. They have almost zero hiss, max volume and ear to the tweeter there is a tiny amount of noise, by 6" away nothing that I can hear. They are not usable at max volume, with digital input, so in reality zero hiss.
 

PeteL

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People have found quite a few use cases for these. I designed them when Parts Express introduced the flat pack enclosure and I started to think about what could be built at that size. In addition to desktop applications, there have been portable bluetooth boom boxes and table radios made using this design. I also published a soundbar design based on the Helium in 2016. Some have wall mounted or ceiling mounted them and used them in small HT setups. From my perspective, spousal approval factor was a major consideration. Once some people have seen something like the Bose lifestyle systems, almost anything else seems big. I had NHT Super Zeros in the family room at one point and received that comment. No one calls the Heliums big.
Yes fair enough, I realised afterward that my post could be read as a touch pompous. My use case doesn't have to be everybody's use case of course. Congrats on this nice little guy. I also thought that the headless wass a little tough, to me doesn't look all that bad for what it is.
 

Mudjock

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Yes fair enough, I realised afterward that my post could be read as a touch pompous. My use case doesn't have to be everybody's use case of course. Congrats on this nice little guy. I also thought that the headless wass a little tough, to me doesn't look all that bad for what it is.
No worries. I think it is ok to question the use case. Since I introduced these in 2014, many more compact micro speakers, soundbars and bluetooth speakers have become available at a variety of price and performance points. The playing field is ever changing.

I also think the headless panther is reasonable as Amir indicated that it sounded "gritty". What I don't know is whether the speaker he listened to represents a fully functional Helium or one that is somehow compromised and I will continue to investigate that. Amir can only review what is in front of him.
 

ttimer

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Desk space can be a luxury in some rooms. If I get bigger than 27" screen I will have to downsize my current speakers.

We need some sort of innovation in this area. Under-monitor, behind monitor, speaker array of 1-inch drivers etc.

Wall-mount speakers, assuming there is a wall behind the desk? Something like Dali Oberon/Opticon/Rubicon On-Wall or Elac DOW42/WS1645.
 

ace_xp2

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I've never achieved satisfactory subwoofer integration with tiny speakers that have such high bass rolloff frequencies.

Keep in mind that with a typical 12dB/octave crossover slope, a subwoofer crossover of 100hz means your subwoofer will be reproducing audible output up at 200hz. That is localizable and right smack dab in the middle of the human vocal range. Steeper crossover slopes cure some issues and cause others.

Many feel otherwise, so I suppose I'm doing it wrong or imagining things. :)

As he's referring to them, are there avrs that cross a sub at 12db? I've only seen 24, though a shocking number of them still cross the speakers at 12db, which they do with intent that the speakers will be sealed with a 12db rolloff at the correct hz for a cumulative 24db.
 

Mudjock

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I have had a chance to investigate the returned speaker, so here is the post mortem report...

One discrepancy I noted between the ASR spinorama measurements and my gated measurements was the lower SPL level seen in the ASR measurements above 5.5 kHz (the approximate crossover point between woofer and tweeter). Having the reviewed speaker back, we have a pretty clear answer to that discrepancy. The yellow line is the reviewed speaker, while the red line is the speaker that stayed behind.

1602347911363.png


Response is about 5 dB lower in the reviewed speaker between 6 and 8 kHz and explains why the ASR measurements are what they are in that region.

The remaining question is whether the discrepancy is due to tweeter variation or high pass crossover component variation. Without disassembly, about all we can do is measure impedance, which should change if there is a significant difference in crossover components or a wiring error.
1602348605715.png


The low frequency differences are likely due to slight differences in cabinet leakage and port length, which were pretty quickly-cut PVC sections on a chop saw. At high frequencies, there is a 1-2 ohm difference between 2.5 kHz and 6.5 kHz, which could be impacted by the high pass filter. I'm not sure if that would be enough to produce the 5 dB difference. Probably the easiest way to isolate the contribution will be to bypass the crossover and measure the tweeters directly.

The other thing that showed up in the ASR measurements were discontinuities at 800 Hz, and two between 1 and 2 kHz. At the time I speculated that the likely causes were either port contributions that my gated measurements weren't catching or damage to the woofer. We have a gated frequency response comparison above that shows good agreement between the two speakers in the woofer's frequency range, so the next thing to do is take a closer look at the port. To do that, I placed the microphone about a quarter inch inside the port and took ungated frequency response measurements.
1602349402848.png


We clearly have our answer. The 3 primary peaks are at very similar frequencies as the ASR measurement discontinuities were and they show up in both speakers, which indicates that they weren't a result of damage to the review sample.

From this, I can conclude that the ASR spinorama measurements do agree with things I can measure with the Liberty Instruments Praxis measurement suite, an older tool, that was used by a number of commercial speaker manufacturers "back in the day". I have to keep a Windows XP PC in order to run it. The fact that I can't pick up the port contributions well in my gated measurements is something I need to think about. I also need to isolate the cause of the variation in the high frequency response, and ultimately determine how these issues could be avoided and/or improved upon for the next mini speaker project (or even if there is something "quick and dirty" that can help this design perform at a higher level).
 

BYRTT

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I have had a chance to investigate the returned speaker, so here is the post mortem report.....
Thanks a very fine feedback :)..
.....We clearly have our answer. The 3 primary peaks are at very similar frequencies as the ASR measurement discontinuities were and they show up in both speakers, which indicates that they weren't a result of damage to the review sample.
.....
Good answers we get there how imperfect a simple port can pollute things, could imagine the blib up at 5400Hz area also can add a bit error to the impedance difference you measured there conflict close to in middle of the crossover region, in below animation have overlaid your port interference of the returned speaker to Amir's spindata where it makes its real sense, looks if port feature could be improved low cut anything 500Hz up it would be a big improvement, the vertical tilt of Amir's spindata relative to microphone at 2 meter (-20º/+40º) is a feature in the free CAD software used and if you like to get Amir's review spindata presented to spinorama graphs there's a guide here to do that, link https://www.audiosciencereview.com/...-vituixcad-using-amirs-shared-spindata.13136/..

Mudjock_port_overlay_x1x1x1x1_1000mS.gif
 
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Ron Texas

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A headless panther, but it has helium in the name. The horror. Thank you @amirm for adding to the database. Every review is important, even the bad ones.
 
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