AIYIMA A20 Stereo 2.1 Amplifier Review

[Ropeburn]

Regardless of how you and @Mark185 feel, I stand by my assessment that the HPF filter in the unit Amir tested was first order. The cutoff frequency was set to 80 Hz.

The HPF response was textbook first order response. Yes, you can adjust the Q of a second order analog filter to get close to this response, but the cutoff frequency (as defined by the filter poles) will not be 80 Hz. Only a first order filter or a second order Butterworth ( Q = √(1/2) ) will give -3 dB attenuation at the cutoff frequency, and I am possitive that this response is not second order Butterworth.

There's way not enough slope visible to make any reliable assessment.

 

[NTK]

There's way not enough slope visible to make any reliable assessment.

The overall shape of the curve is more than sufficient for me to make my assessment. See my post #151. It was a perfect match.

 

[Mark185]

Amir's measurement shown is not conclusive. The Y axis scale is in 0.5 dB increments and you cannot see the final slope of the filter in the plot he shows. We also do not know if the filter is Butterworth or some other alignment which will affect slope in the area near crossover. I will test this again setting the crossover frequency higher than 80 Hz so we can see the slope 2 octaves down.

Another point to make. This amp is not the solution to drive larger bookshelf or floor standing speakers and high pass them around 60-80 Hz. It is most appropriate driving smaller speakers with high pass set around 150-200 Hz depending on the -3 dB frequency of the speaker in question. Cascading 2 Butterworth 12 dB per octave responses with same frequency gives 24 dB per octave Linkwitz Riley response. This assumes you are using a small sealed enclosure speaker with a natural 12 dB per octave Butterworth low end rolloff due to the physics of the speaker in that enclosure. Using a ported speaker is not recommended in the scenario I like.

I think that is the sweet spot for this A20 amplifier if you want to use the high pass and low pass filters without any external signal processing. This recommendation assumes that a subwoofer is being used.

I will add that I am currently using mine with a Dayton Audio DSP-408 instead of the built in filters and it sounds very good. I know this is getting out of the realm of cheap equipment because the DSP unit is $199 by itself but it is a nice combination.

 

[Ropeburn]

This here (emphasis mine):

This is Amir's measurement. The - 3dB point is ~80 Hz. At 1 octave higher (~160 Hz), the attenuation is about -1 dB.

If you look at the graph from Aiyima, the -3 dB point is ~200 Hz. At 1 octave higher (~400 Hz), the attenuation is close to 0 dB. It is not the same filter as the one Amir measured (after considering the change in the filter cutoff frequencies).

...is exactly the looking the wrong way around I was talking about. That is not how you determine the slope from a measurement. Too many variables: unknown filter type, unknown exact cutoff frequency, unknown Q, exactly the "knee" area. For highpasses, you have to look at the response below, not above the -3dB point. That graph simply doesn't show enough of that.

Aiyima's data shows a textbook 12dB response.

We need more data, as already suggested: higher cutoff setting, then measurement. Then, and only then, we can confirm or debunk Aiyima's data.

 

[fwwwk]

Another point to make. This amp is not the solution to drive larger bookshelf or floor standing speakers and high pass them around 60-80 Hz. It is most appropriate driving smaller speakers with high pass set around 150-200 Hz depending on the -3 dB frequency of the speaker in question. Cascading 2 Butterworth 12 dB per octave responses with same frequency gives 24 dB per octave Linkwitz Riley response. This assumes you are using a small sealed enclosure speaker with a natural 12 dB per octave Butterworth low end rolloff due to the physics of the speaker in that enclosure. Using a ported speaker is not recommended in the scenario I like.

Plugging bass-reflex might be a solution? Are we getting more 12dB/oct or 18dB/oct while plugging, I mean, empirically? 150-200Hz is questionable scenario with single, not-centered sub

 

[Mark185]

Plugging will only work if the interior volume is correct for the specific woofer's Thiele-Small parameters. It is related to the volume of air displaced by the woofer and the volume of air in the enclosure. 150-200 Hz works in a small room even if sub is not centered. You are never going to get perfectly matched crossover characteristics with equipment like this. That requires more expensive equipment such as the DSP unit I am using.

The biggest benefit of the high pass filter in the A20 is reducing the distortion of the bass driver in small speakers. That is very audible even if the crossover between speakers and sub is not the greatest. I just wanted to point out the sweet spot for using the A20 and that is matching it to the roll off of a small sealed speaker.

 

[Ropeburn]

Plugging will only work if the interior volume is correct for the specific woofer's Thiele-Small parameters. It is related to the volume of air displaced by the woofer and the volume of air in the enclosure. 150-200 Hz works in a small room even if sub is not centered. You are never going to get perfectly matched crossover characteristics with equipment like this. That requires more expensive equipment such as the DSP unit I am using.

The biggest benefit of the high pass filter in the A20 is reducing the distortion of the bass driver in small speakers. That is very audible even if the crossover between speakers and sub is not the greatest. I just wanted to point out the sweet spot for using the A20 and that is matching it to the roll off of a small sealed speaker.

I really think subwoofers should have highpass passthrough by standard. It exists but is rare, and often not adjustable. Such an easy method, you can use any speakers and amplifier as long as the source is separate.

 

[Mark185]

I measured frequency response with and without high pass filter set at 200 Hz. I also measured THD+Noise with and without high pass filter. I then tested with the volume control bypassed running this as a straight amplifier. Interesting thing about that, the high frequency rise above 20 kHz is reduced when bypassing the volume control. Frequency response at the low end was not changed by bypassing the volume control.

It is 12 dB/octave roll off. 200 Hz is the -3dB corner frequency. In other words, the roll off starts before 200 Hz and that is correct. This looks like it is Butterworth.

Here is the same data zoomed out a bit.

Now here is something interesting and not surprising. THD+Noise is worse with the high pass filter on. This makes sense because the phase is changing through the crossover region and that will cause distortion. At -77.88 dB it is still not audible. What is surprising is the 3rd Harmonic distortion at 3000 Hz is much higher when the 200 Hz filter is on. I did not expect that to happen several octaves above the filter frequency. I still do not believe that is audible to 90% of the population but is an interesting artifact.

Here is THD+Noise without the high pass filter.

 

[Ropeburn]

Nice! That settles it then.

 

[NTK]

I measured frequency response with and without high pass filter set at 200 Hz. I also measured THD+Noise with and without high pass filter. I then tested with the volume control bypassed running this as a straight amplifier. Interesting thing about that, the high frequency rise above 20 kHz is reduced when bypassing the volume control. Frequency response at the low end was not changed by bypassing the volume control.

It is 12 dB/octave roll off. 200 Hz is the -3dB corner frequency. In other words, the roll off starts before 200 Hz and that is correct. This looks like it is Butterworth.

View attachment 496690

Here is the same data zoomed out a bit.
View attachment 496687

Now here is something interesting and not surprising. THD+Noise is worse with the high pass filter on. This makes sense because the phase is changing through the crossover region and that will cause distortion. At -77.88 dB it is still not audible. What is surprising is the 3rd Harmonic distortion at 3000 Hz is much higher when the 200 Hz filter is on. I did not expect that to happen several octaves above the filter frequency. I still do not believe that is audible to 90% of the population but is an interesting artifact.
View attachment 496688
Here is THD+Noise without the high pass filter.

View attachment 496689

Have you tried lower frequencies? Implementing a 2nd order adjustable frequency filter can be tricky. For 2 channels it needs a 4 gang potentiometer, which the A20 seems to have (the top one, next to the speaker output connectors). So I may have to eat crow for my Christmas dinner.

Project 155

Variable High And Low Pass Filters For Use In Mixing Desks Or Recording Intergaces

www.sound-au.com

 

[JSmith]

Project 155​

Variable High And Low Pass Filters For Use In Mixing Desks Or Recording Intergaces www.sound-au.com

Always a great reference.


JSmith

 

[Mark185]

@NTK that link to Elliott Sound Products is a blast from the past. I spent way too much time going down 'rabbit' holes on that site many years ago. Enjoyed every minute but my wife did not appreciate it.

After my post above, I tested the subwoofer output on the A20. It is a 200 Hz 24 dB/octave filter. It does track the input signal level as Aiyima has indicated but on my A20, the maximum voltage output at 20 Hz is ~950 mV RMS with a 2 Volt RMS input signal and output voltage decreases with frequency. That means the subwoofer amp needs to have a decent preamp section to handle this signal. I thought about buying circuit board(s) from ESP to build my own preamp but he no longer sells to USA customers due to tariffs.

 

[Fxfighter]

I use Aiyima A20 HPF to Monitor audio bronze 50, sub out to monitor audio bronze w10. Any suggestions for frequency settings for both? Thanks.

 

[Mark185]

I use Aiyima A20 HPF to Monitor audio bronze 50, sub out to monitor audio bronze w10. Any suggestions for frequency settings for both? Thanks.

Without frequency response measurements in your listening room it is difficult to make a suggestion guaranteed to work well. A solid recommendation will also require knowledge of where you sit in relation to the speakers and subwoofer. If this is a desktop system, that is very different than if you use this system to watch TV and listen to music while sitting further away.

1. Port tuning frequency of the Bronze 50 is 47 Hz and output will drop rapidly below that frequency. Because it is ported, you cannot set A20 high pass filter to same -3 dB frequency as the Bronze 50 and get a 24 dB/octave Linkwitz Riley acoustic response.
2. I don't know what the low pass filter type on the Bronze subwoofer is but I definitely do not recommend using the A20 subwoofer output. Use only the filter on the Bronze subwoofer if at all possible.
3. This will require running an RCA cable from the T20 to the Bronze 10 subwoofer inputs and running XLR cables from the T20 to the A20 amplifier. I am assuming that both the RCA outputs and XLR outputs on the T20 are active all the time.
4. If you can't use both outputs, you are stuck using the A20 subwoofer output. You will not get good subwoofer performance if you are using both the Aiyima A20 subwoofer output and the Bronze 10 subwoofer low pass filter.
5. The A20 should be set to bypass the volume control. It is cleaner that way. With volume control bypassed and XLR inputs being used, the A20 will sound great with your speakers.
6. If you are able to drive the A20 and the Bronze 10 with separate cables, then I suggest setting both to 100 Hz and adjust from there according to how it sounds to you or if you have a microphone and software like Room EQ Wizard, measure the system response and adjust based on what you measure. The software is free. USB microphones are available from many outlets including Amazon.
7. Low pass on the Bronze W10 does not have to be at the same frequency as the A20 high pass filter for best sound in your environment. You are never going to get a perfect response in the crossover region with the equipment you have but you can very likely get it to sound pleasing to you.
8. A digital signal processor (DSP) is the only way to approach perfect blending of the subwoofer and bookshelf speakers in the crossover region. How to do that is way beyond what I can tell you here and it is also way off the original topic.

 

[fwwwk]

I still dont’t understand why abandoning HPF sub out on A20, which is most useful part of this amp. Plug monitor audio main speakers bass-reflex and measure steepness of bass rolloff. “New” sealed response should have higher system resonance frequency than previous port tuning (probably around 60hz) with roll-off below this systemic resonance closer to 12dB/oct. Cascaded with 12 dB/oct butterworth on output should give roughly LR4 360-0 deg phase shift. Your subwoofer is probably 24dB/oct LPF and should therefore sum well to 0dB crossover. Minimum impedance of monitor audio mains should increase and thus making them easier to drive, omitting port resonance with its own phase imparity and reducing woofer distortions. Please correct me if I am getting this wrong. 200hz LPF on A20 sub out is irrelevant as way over crossover region, acting as safety measure

 

[Mark185]

The sub out is a low pass filter. 200 Hz low pass filter on the A20 is less than 2 octaves away from the likely subwoofer filter setting on the Bronze W10. That is too close and the two filters will interact. My guess is the bass will be 'muddy' with a one note boom and not much clarity. There is also a strong possibility that the 900 mV max output from the A20 sub out will not be enough to drive the Bronze W10 to the desired volume because the two filters interacting will attenuate the signal more than if only the subwoofer's built in filter was used.

Optimum would be to use either the A20 subwoofer out to drive an active sub with no filter on the sub or do it the way I described above and use both the XLR and RCA outputs from the T20 to drive the high pass amplifier and the subwoofer separately. The advantage of my recommendation is the low pass filter on the sub and high pass filter on the Aiyima A20 can be adjusted separately.

There is no way to predict the effect of plugging the port on the bookshelf speakers. (Actually, if I knew the Thiele-Small parameters of the Monitor 6" driver and the cabinet volume, I could predict it.). Woofers designed for a ported alignment are not usually also equally suited to a sealed enclosure. I base this on 40 years of designing and building my own speakers. My guess is plugging the port on the Bronze bookshelf speakers will result in a mild acoustic roll off below 120 Hz with a Q in the range of 0.4 - 0.5. That may sound good but no way to know without actually trying it and measuring.

 

[Snix]

This would be great for my upgrade and I would buy it in a heartbeat if they offer a barebone unit option (without their way overpriced power supply)

 

[fwwwk]

@Mark185 i know of some speakers manufacturers equip packages with fitted plugging foams of certain volume. Dynaudio I know of for sure.

 

[obsessive9119]

@Mark185 i know of some speakers manufacturers equip packages with fitted plugging foams of certain volmue. Dynaudio I know of for sure.

KEF does this too (at least for the LS50 - not sure about other models)

 

[Fxfighter]

I tried 120hz for both speaker and subwoofer. But I find this, so I set both at 120hz. Then adjust volume. Try to maximize speaker characters.