MiniDSP 2x4 HD headroom limitation in active crossover configuration – measurement results

[thcdru2k]

I recently converted my system from standard AVR bass management to a true active crossover topology using a MiniDSP 2x4 HD as the final DAC stage. After calibrating gain structure and performing full REW measurements, I encountered a repeatable limitation that I wanted to document here in case it’s useful for others considering similar topologies.

System chain
WiiM Pro Plus (coax digital out)
→ Denon AVR-X3700H (preamp mode) Front L/R Preout to MiniDSP
→ MiniDSP 2x4 HD (active XO at 70 Hz LR24) outputs to Monolith 2 and each HSU VTF-15H
→ Monolith 2 amplifier (front L/R) - Canton Karat 300 (putty sealed baffle edges and felt applied around tweeters)
→ HSU VTF-15H MK1 + MK2 (stereo subs)



Motivation

The goal was to achieve:

Stereo bass management / independent sub delay alignment

Manual REW-guided integration rather than global room EQ

Consistent time alignment through the crossover region

Measurement observations

Once integration was complete, the system exhibited excellent objective behavior:

Strong alignment of peak energy time through the crossover

Smooth modal behavior and fast decay in the 20–120 Hz range

Low group delay and controlled ringing

Low harmonic distortion across the band

Subjectively - effect was very pronounced with well-mastered tracks like Michael Jackson - Thriller (bass effects become directional) and movies bass pans across the screen

However, during listening tests and when examining gain structure, I discovered that at higher playback levels the signal path was running out of electrical headroom before reaching typical reference listening levels.

Cause analysis

The Denon pre-outs are capable of ~2 Vrms output.
The MiniDSP 2x4 HD analog input stage clips around 0.9–1.0 Vrms.

With active crossover, there is no longer the 10–12 dB efficiency benefit normally provided by bass management inside the AVR. Bringing mains and subs into alignment required applying positive gain inside the DSP, which pushes the MiniDSP into its headroom limits much sooner. Distortion and harshness become audible around -14 dBFS AVR volume, Internal MiniDSP meters confirm approaching digital clipping, Reducing input gain or reducing channel gain re-breaks level matching to the center/surround channels

Discussion

If anyone has measurements comparing the MiniDSP 2x4 HD analog input clipping margins or experiences with active XO headroom behavior, I would appreciate hearing others experiences. Attached is full sweep measurements taken at denon volume -25db with umik1 positioned at MLP (ear level).

 

[thcdru2k]

shit i didnt read the manual i guess you can change input sensitivity to 4v

 

[Waxx]

And this is a very old design (in dsp terms), their former flagship became the cheap series. So it may be outdated to modern standards (the ad and da are at least not at all sota anymore)

 

[thcdru2k]

And this is a very old design (in dsp terms), their former flagship became the cheap series. So it may be outdated to modern standards (the ad and da are at least not at all sota anymore)

Yeah ordering a flex htx . Learned a lot but I need more headroom

 

[Keith_W]

Measurement observations:

- wrong views selected for majority of measurements. For example, no smoothing in the FR graph. Using dBFS instead of % to view the IR graph. Failure to normalize to peak SPL in the spectrogram. Group Delay is unsmoothed and too zoomed out for interpretation.
- Don't look at Clarity - it is useless.
- Distortion is SPL dependent. If you measure at higher SPL, you will get more distortion. Measure at lower SPL, and you will get less. If you want to see bass distortion, you will need to measure from 0Hz up and using a stepped sine wave. Its only use in this context is to check that you're not measuring too loud.
- "Alignment of peak energy through the crossover" has not been demonstrated. You need to look at the first 20ms of the step response.

Please take a look at the REW eBook (you want Book 2) for a guide to how to view and interpret measurements.

 

[Trdat]

Late to the party, but I am really curious with the switch to 4 volts out did it still clip? And did you try reducing the sub volume to minus 12 to reduce voltage....?

I have a Marantz AV which is 12 volts out at maximum volume according to Amir's measurements if I am not mistaken, and not sure if the same voltage is amplified to the sub out. However, if I reduce the volume on the AV for the sub out to minus 12 I am curious what voltage out I will get? This will help me determine if I will clip the minidsp upon purchase for sub woofer integration.