Does Soundcore Motion+ Sound Different via Aux-in and Bluetooth, and How to Measure Frequency Response at Home

Short answer: no, Soundcore Motion+ sounds the same via bluetooth and aux-in.

Today I noticed that my awesome bluetooth speaker Anker Soundcore Motion+ sounds kind of shitty. There is an Android app by Anker Soundcore with EQ settings and some EQ presets. I connected my phone to the speaker and the app showed that the preset "Bass Off" is turned on:

I tested different EQ presets on "Levitating" by Dua Lipa (Youtube Music, Music video on Youtube). The song is fantastic, and I've been listening to it on repeat these last few days. The music video is fantastic too and so, so beautiful except for the rap part which I don't like. I found some guy recommending these EQ settings:

I tried them and I liked them more than any of the presets. They give Motion+ a high energy dance kind of vibe. I think they might be bad for working or chilling with music in the background because I think I might get tired from the intense sound. "Bass Off" might be better for that use case but we'll see. I would have ended the investigation at that, but I usually listen to music on Motion+ from my laptop, connecting Motion+ through its aux-in port and using an external audio interface iRig HD X because I also use my Motion+ to play on Linnstrument. And I wasn't sure if the EQ in the app affects playback via aux-in.

It was easy to check if the EQ settings affect playback via aux-in - I set the bass frequencies (80, 150, 300 Hz) to the maximum and everything else to the minimum and checked if the music would become very low-heavy when played from my laptop - it did. I reverted the EQ settings to the custom setup shown in the screenshot above and decided to compare the sound via bluetooth from my phone and via aux-in from my laptop. I connected Motion+ to my laptop and also connected it to my phone via bluetooth, at the same time. I would then turn on the same part of the same version of the same song "Levitating" on my phone and on my laptop in order and compare using my ears. I felt like it sounded a little better when played from my phone, but I wasn't sure and suspected that it might be a placebo-like effect - finding signal when in fact there is none. In particular, I felt like some high-pitched drum kit sounds were more pronounced when played from one device than from the other but I wasn't sure about this. I decided that doing some objective measurements is in order.

When a professional reviewer posts a review of a speaker or a headset, they usually produce a frequency response plot like this:

The X axis contains frequency (pitch) in Hertz. The Y axis contains sound power level in decibels. The plot shows how loudly the speaker or the headset plays different frequencies, from about 30 Hz to 20 kHz. I've decided to produce such a plot myself for 2 cases - when Motion+ is connected to my phone via bluetooth, and when it's connected to my laptop via aux-in. I wanted to compare them and see if there is any difference. I had never done anything like this and I don't have any special equipment, but I had a nice Android app called Spectroid. It listens through the phone's microphone and plots sound power level per frequency in real time. For example, here is what Spectroid shows when I play a single note on a harmonica:

The leftmost peak at 374 Hz is the note's fundamental. The peaks to the right are its overtone series. The plot in yellow shows the sound recorded at the current moment. The plot in red shows the maximum power level at a given frequency since the app was started.

So, how did I measure the frequency response? I googled "sine sweep" and found this website: https://www.audiocheck.net/testtones_sinesweep20-20k.php. It offers an audio file download under "The sound files - Logarithmic (20Hz-20kHz, -3dBFS, 20s)" (Direct link, Internet Archive link). This file plays a single sine wave, with frequency going up from 20 Hz to 20 kHz logarithmically. So, I played it from my laptop via aux-in with Spectroid open on my phone and got the following plot:

And this is what I got when playing from my phone via bluetooth:

I eyeballed the two (red) plots and I think they look more or less identical. So I guess there is actually no difference in sound and I just imagined it. I might've thought that the sound from aux-in was worse because in the mornings loud sounds are sometimes unpleasant for me, but this goes away further into the day.

Update from 2024-12-09: mandmandam comments on HN and overlays the two frequency response curves (red and teal):

To his eye, they look "significantly (though not hugely) different". Idk, they look identical plus or minus noise to me, except for maybe the rightmost teal peak. But I don't know for sure. Ideally, I should've done multiple tests for each of the two setups to see if the plots look exactly the same or slightly different on each test, but I didn't do that.

zkd43 says on HN that measuring the frequency response can't help you check if the two setups give different signal to noise ratio and different dynamic range. Yeah, it does not, although I don't know how to check those two things, especially at home without spending money on expensive equipment.

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