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Presonus Eris Sub 8BT pass-through and HPF measurements

roladyzator

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Feb 4, 2023
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The Sub 8BT's standout feature amongst cheap subwoofers is a build-in high-pass filter, so it's very easy to off-load smaller monitors and reduce the interaction between the sub the and the small woofers.

I've decided to measure how the pass-through affects the line level audio signal, out of curiosity.
In case this is important to someone as a part of their purchasing decision, I'm sharing the results here.

Setup:
  • Source: Shanling M0 portable DAP. It has a 2V RMS output and is based off of an ESS DAC. Amir has measured its successor - M0 Pro.
  • ADC: The built-in ADC in a Creative Sound Blaster GC7's Line-In
  • Source is connected to RCA inputs on the Sub 8, then Sub 8's RCA outputs are connected to the sound card's Line-In.
  • Test is using RMAA test signal, played back using the M0 and recorded using the GC7.
  • The reference setup is when M0's headphone output is connected directly to GC7's line-in.
Frequency response:
There is a slight treble roll-off (-0.5 dB at 20 kHz) and even slighter bass roll-off (0.2 dB at 20 Hz)

bt8-passthrough-fr.png


THD + noise:
I've measured a significant increase in the noise floor.
I'm surprised to see some peaks at 60 Hz, given that I live in Poland where the power grid is 50 Hz.
bt8-passthrough-thd.png


IMD
bt8-passthrough-imd.png


High-pass filter
Company states it's a 12dB / octave high pass filter with cutoff frequency at 80 Hz.
I've measured this one using REW's RTA, so some the jaggedness there wouldn't show up in a typical sweep measurements.
I'm too lazy to re-do this one, though.

It looks like it delivers on the promise and doesn't affect anything above 200 Hz or so.
bt8-hpf.png

My thoughts:
The HPF works as expected, but the pass-through itself is quite noisy, so perhaps not the best idea for using with monitors with high gain.
With my Edifier MR4's, I did not find the noise disturbing.
I've recently upgraded to Kali IN-8 V2 and on my desk they still benefit from the sub.
I've done some MMM measurements using a dayton iMMM-6 microphone.
I don't trust the treble measurements too much with this one, but it's good enough to evaluate bass in my opinion.
in-8-sub.png


I'm not hearing any hiss from them at my listening position (85 cm and more), but I'm tempted to use a 3.5mm jack splitter from my source and feed the sub and IN-8 V2 separately, so that I have a cleaner signal to the IN-8. However, before spending any more money, I think it's worth experimenting with placement and sub low pass frequency and improve the things a bit.

What do you guys think? Is this deal-breaking performance, or something to expect at this price range?
 
I use the older, non-BT, version of the Sub8 with my iLoud MTMs (also older version). I can't say I noticed any increase in noise from the MTMs when I added the Sub8 in-line, although that was several years ago. The MTMs have their own high-pass filter which is implemented in DSP, so I could drive the Sub8 and MTMs separately - I might consider this as it would reduce the cabling under my standing desk.
 
I also don't think I'm hearing any noise or hiss from the sub line outputs. I suppose it's just buried within the ambient noise.
 
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