Presonus Eris Sub 8BT pass-through and HPF measurements

[roladyzator]

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)

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.

IMD

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.

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.

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?

 

[komhst]

What do you guys think? Is this deal-breaking performance, or something to expect at this price range?

I think, considering its price, is an OK product.

 

[Berwhale]

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.

 

[roladyzator]

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.

 

[lonelyboyll]

I’ve got this one to accompany Kali LP6 v2 and I think they’re so good. The sub really relief the stress on the Kali which makes the mid more clearer and less distortion.

 

[Berwhale]

@taloyd - I noticed you liked my post above, so I thought I should add that I did make the Y-cables to drive the MTMs and Sub8 separately. The cable routing is much better for my height adjustable desk and the thinner cable also makes routing easier. The details of the cable I used and a picture of the finished cables are here: https://www.audiosciencereview.com/...commendation-please.56860/page-3#post-2223304

 

[roladyzator]

@taloyd - I noticed you liked my post above, so I thought I should add that I did make the Y-cables to drive the MTMs and Sub8 separately. The cable routing is much better for my height adjustable desk and the thinner cable also makes routing easier. The details of the cable I used and a picture of the finished cables are here: https://www.audiosciencereview.com/...commendation-please.56860/page-3#post-2223304

Impressive work with the cable. Does everything work from noise / buzz / ground loops perspective?
I'm thinking from the perspective of upgrading my subwoofer in future and not having to be limited to one with balanced pass-through.

 

[FireEmblem]

I’ve got this one to accompany Kali LP6 v2 and I think they’re so good. The sub really relief the stress on the Kali which makes the mid more clearer and less distortion.

I'm currently thinking about the same thing, coupling something like Adam Audio T5V or the Kali LP6 or JBL 305p with the Eris Sub 8 since it's the only sub available at such a nice price.

But isn't it difficult to mix two brands? How do you know there isn't a gap where crossfade happens?

 

[Berwhale]

As noted above, the cross-over in the Sub8 works as expected, but it is fairly noisy. This noise was never an issue for me (and if you are worried about noise do not get the 305p Mk II, the hiss from the tweeters is horrible!)

There is no issue with mixing brands.

The best way to find out if you have the cross-over frequencies set correctly is to measure the frequency response. However, you can probably just set the Low Pass Filter (LPF) to 80Hz, enable the High Pass Filter (HPF) and forget about it.

 

[FireEmblem]

The best way to find out if you have the cross-over frequencies set correctly is to measure the frequency response. However, you can probably just set the Low Pass Filter (LPF) to 80Hz, enable the High Pass Filter (HPF) and forget about it.

There's no way without a measurement microphone to check? No casual DAW tricks, sine sweeps or something?

 

[Berwhale]

There's no way without a measurement microphone to check? No casual DAW tricks, sine sweeps or something?

I'm sure there are simple iPhone and Android apps out there that will give you some idea. However, Presonus did a pretty good job with the HPF filter at 80Hz, so there's no reason to believe that LPF does not perform as expected. Setting the LPF to 80Hz should be sufficient. You would then expect the LPF to mirror the HPF response, something like the green line i've added to the HPF response (in blue) below...

 

[FireEmblem]

I'm sure there are simple iPhone and Android apps out there that will give you some idea. However, Presonus did a pretty good job with the HPF filter at 80Hz, so there's no reason to believe that LPF does not perform as expected. Setting the LPF to 80Hz should be sufficient. You would then expect the LPF to mirror the HPF response, something like the green line i've added to the HPF response (in blue) below...

View attachment 495727

And how do you do that, with software EQ? Because on the back of the monitors is usually only the little switches with presets, without any precise crossover knob.

 

[Berwhale]

The Sub8 has a knob to adjust LPF, with 80Hz clearly marked on the dial. There is a switch to enable HPF, with the frequency fixed at 80Hz.

The LPF sits between the input of the sub8 and the internal amplifier for the subwoofer. The HPF sits between the input of the Sub8 and the output of the Sub8.

With the following setup: Source --> Sub8 --> Monitors

The Sub8 will play the source signal filtered by the LPF as per the green line. The monitors will play the source signal filtered by the HPF as per the blue line.

The affect of the HPF on the source signal can be measured easily on the output of the Sub8 (no microphone required), hence the filter frequency response graph above. However the affect of the LPF on the source signal (going to the Sub8 amplifier) cannot be measured directly without taking taking the Sub8 apart.