Seeking advice on integrating two subwoofers with full-range stereo speakers with passive radiators

[Smoey22]

Hi,

I'm in the process of building two sealed subwoofers to add to my full-range stereo setup and plan to use the miniDSP SHD Studio I currently own. I know this can be trial and error, but I'd appreciate any starting points or tips you can offer.

This post covers two main topics: finding a good crossover strategy (Topic 1) and exploring options to DSP and amplify the subwoofers (Topic 2). The first topic can be visualized in the attached picture, while the second topic might require a deep dive into my setup. Any feedback is welcome and much appreciated. For those willing to take the journey, thank you. TL;DR at the end.

Topic 1:
The mains are full-range with two passive radiators each, currently tuned with 50 g / PR (see the attached picture, green curve). What would be the best strategy for integrating with the subwoofer (blue curve)? Should I remove the weights (red curve), or could that complicate integration by introducing four additional sub-points to consider (phase, delay, distortion, etc.), even after high-passing?" Should I opt for a typical crossover point at 80 Hz for both subwoofers and mains?

Topic 2:
The miniDSP Studio has a 2x4 DSP configuration. If I opt for a 2-channel DAC and a 2-channel amplifier, I would have the option to use all four miniDSP channels, and Dirac the subs individually (if integrated with the mains as Dirac is only 2-channel), see link below, "First Option".

Alternatively, I could choose a Hypex Fusion amplifier with a built-in DAC and 1x2 DSP to drive both subs, see link below, "Second Option". This may limit or exclude Dirac since both subs will be mono (L/R/L+R). Is there any benefit of using Fusion DSP (HFD) on top of a mono signal from the miniDSP versus a stereo signal in the "First Option"? Perhaps I could bypass the DSP in the Fusion amp and use it purely as an "nc502mp" amp with a separate 2-channel DAC (similar to the "First Option")?

How is the MSO compatibility between the "First Option" and "Second Option"?

Please see this Miro board for a complete detailed flowchart of my setup (viewing and adding comments are possible without registering):
https://miro.com/app/board/uXjVLfZQj8w=/?share_link_id=410648611747

<Digression> I don't understand the decision to not include a 2-channel DAC in the multichannel Fusion DSP. It may not suit the product's intended purpose, but it seems like a neat, relatively low-cost feature to include, especially since stereo through S/PDIF and AES/EBU is already present </digression>.

TL;DR:

1. What's the recommended tuning weight/frequency for the passive radiators in this scenario?
2. What's the ideal crossover frequency between the main speakers and subwoofers?
3. Should I purchase a stereo amplifier and a separate 2-channel DAC, or opt for the Fusion amplifier?

I hope you are having a great Sunday, thanks for your attention!

BR,
Smoey22

 

[Smoey22]

Out of curiosity I ran it through chatGPT (o1-preview), nothing revolutionary, but it's a great sparring partner:

Spoiler: ChatGPT's answer

Topic 1: Crossover Strategy and Passive Radiator Tuning​

1. Should You Remove the Weights from the Passive Radiators (PRs)?

• Impact of Removing Weights:
  • Tuning Frequency Change: Removing the weights will raise the tuning frequency of the passive radiators. This can reduce the low-frequency extension of your mains but may improve transient response and integration with the subwoofers.
  • Integration Complexity: Altering the PRs introduces additional variables like phase response and potential overlaps in frequency ranges, which could complicate the crossover setup.
• Recommendation:
  • Keep the Weights On: To maintain the designed low-frequency performance of your mains and simplify integration, it's advisable to leave the weights as they are.
  • Simplify Integration: Keeping the PRs unchanged reduces the number of variables, making it easier to achieve a seamless blend with the subwoofers.

2. Ideal Crossover Frequency Between Mains and Subwoofers

• Starting Point:
  • 80 Hz Crossover: An 80 Hz crossover is a common standard that effectively balances the load between mains and subs. It keeps low frequencies non-directional and relieves your mains from handling deep bass.
• Factors to Consider:
  • Main Speakers' Capabilities: If your mains have strong performance down to, say, 60 Hz, you might consider a slightly lower crossover frequency.
  • Subwoofer Performance: Ensure your subs can cleanly handle frequencies up to the chosen crossover point.
  • Room Acoustics: Room modes and placement can affect the ideal crossover frequency.
• Recommendation:
  • Start with 80 Hz: Begin with an 80 Hz crossover using a 24 dB/octave Linkwitz-Riley filter for both high-pass and low-pass to ensure phase coherence.
  • Fine-Tune with Measurements: Use room measurement tools like REW (Room EQ Wizard) to adjust the crossover frequency and slopes for the smoothest response.

---

Topic 2: DSP and Amplification Options for Subwoofers​

First Option: MiniDSP Studio with Separate DAC and Amplifier

• Advantages:
  • Individual Sub Control: Allows for independent DSP adjustments on each subwoofer channel, which is beneficial for room correction and dealing with room modes.
  • Dirac Integration: Since Dirac Live is limited to two channels on the miniDSP Studio, integrating subs with mains allows Dirac to optimize the entire system cohesively.
  • Flexibility: Full use of all four DSP channels gives you granular control over crossover settings, delays, and EQ.
• Considerations:
  • Additional Components: Requires purchasing a separate 2-channel DAC and amplifier, which may increase complexity and cost.

Second Option: Hypex Fusion Amplifier with Built-in DAC and DSP

• Advantages:
  • Integrated Solution: Combines amplification, DAC, and DSP in one unit, simplifying the system.
  • Powerful DSP: Hypex Fusion's DSP (HFD) is robust and can handle complex processing.
• Considerations:
  • Mono Signal Limitation: Feeding a mono signal to both subs may limit stereo imaging in low frequencies.
  • Dirac Compatibility: Using the Fusion's DSP separately may complicate or preclude integration with Dirac Live corrections from the miniDSP.
  • Bypassing DSP: If you bypass the Fusion's DSP to use it purely as an amplifier, you're essentially reverting to a setup similar to the First Option but with potentially redundant features.

MSO (Multi-Sub Optimizer) Compatibility

• First Option: Better suited for MSO as it allows independent control of each subwoofer channel, enabling more precise optimization.
• Second Option: Limited MSO compatibility due to the subs receiving a summed mono signal, reducing the ability to correct individual subwoofer interactions with the room.

Recommendation:

• Opt for the First Option: Using a separate DAC and amplifier gives you maximum flexibility, better integration with Dirac Live, and full compatibility with tools like MSO.
• Consider System Complexity: While the First Option is more complex, the benefits in sound quality and system control are significant.
• Using Fusion Amp as Pure Amplifier: If you prefer the Fusion amp's qualities, you can bypass its DSP and use it as a straight amplifier, but this may not be cost-effective given its integrated features.

---

TL;DR Answers​

1. Recommended Tuning Weight/Frequency for Passive Radiators:

• Keep the Current Tuning: Maintain the 50 g weights on your passive radiators to preserve your mains' designed low-frequency performance and simplify integration with the subwoofers.

2. Ideal Crossover Frequency Between Mains and Subwoofers:

• Start at 80 Hz: Use an 80 Hz crossover frequency with appropriate filter slopes (e.g., 24 dB/octave Linkwitz-Riley) and adjust as needed based on measurements and listening tests.

3. Equipment Recommendation:

• Choose Separate DAC and Amplifier (First Option): This setup offers greater flexibility, better integration with your miniDSP and Dirac Live, and full compatibility with optimization tools like MSO.

---

Additional Considerations​

• Phase and Time Alignment:
  • Use your DSP to adjust delay and phase settings to ensure the mains and subs are in sync at the crossover frequency.
  • Inverse polarity or adjust phase if you notice cancellations around the crossover point.
• Room Acoustics:
  • Placement Matters: Experiment with subwoofer placement to minimize room mode issues.
  • Acoustic Treatment: Consider adding bass traps and absorptive materials to improve room response.
• Measurement Tools:
  • Utilize software like REW to take in-room measurements, helping you fine-tune crossover points, EQ settings, and identify any acoustic issues.
• Dirac Live Calibration:
  • Run Dirac calibration after setting initial crossover and placement to allow it to correct frequency and phase response effectively.
  • Remember that Dirac on miniDSP Studio is limited to two channels; integrating subs with mains ensures they are included in the correction.

 

[dualazmak]

Hello @Smoey22,

We have so many critical factors for crossover (XO) between subwoofer(s) (SWs) and main woofer(s) (WOs) in our audio system for better/best low frequency (Fq) sound reproduction in our own/individual listening environments including room acoustics. Of course, the final goal would be greatly dependent on your music listening personal preferences, and hence there would be no general/standard procedures and approaches, I assume.

The major factors would be;
A1. Room acoustic mode(s) including reflection, dispersion, absorption, standing waves, resonances, etc.
A2. Precision (1 ms precision) time-alignment (a kind/side of phase tuning) between SWs and WOs, at your listening position,
A3. Optimization of relative gains for SWs and WOs, should be flexibly controlled on-the-fly while listening to music,
A4. Optimal selection of XO filter type(s) (i.e. BW, LR, Bessel, etc.), XO Fq, slopes at both side, phase inverse or not, further specific EQs or not, etc.

Before starting your optimization/tuning exploration journey in this regard, you need to know/understand several features/aspects; the major points would be;
B1. "Major" low Fq sound reflective plane/wall in your acoustic environment (not always needed to be fully eliminated),
B2. Be aware of that we always have overlapped Fq zone where SWs and WOs sing together, whatever XO Fq and slopes we would use,
B3. Basic understandings on the physical configuration(s) of SWs and WOs, especially ported or sealed, difference in mass of moving parts, etc.,
B4. Difference in transient behavior (step response?) of SWs and WOs, both kick-up responses and fade-out patterns;
____Damping factor/performance of the amplifier(s) driving SWs and WOs more-or-less do "matter" for transient behaviors.

As you may well aware, many audiophile people use REW and/or similar advanced audio measurement/tuning software tools together with suitable measurement microphone(s) for the optimization. I too used wonderful REW during my early stage in my multichannel project as you can find my posts #17, #18, #20, #21, #22 on my project thread.

Because of various reasons, however, nowadays, I use REW mainly as validation and confirmation tool for my rather primitive but reliable reproducible understandable (to me) validated simpler measurement and tuning methods as shared below; If you would be interested, please read carefully these posts on my project thread;
- Precision measurement and adjustment of time alignment for speaker (SP) units: Part-1_ Precision (time-shifted) pulse wave matching method: #493
- Precision measurement and adjustment of time alignment for speaker (SP) units: Part-2_ Energy peak matching method: #494
- Precision measurement and adjustment of time alignment for speaker (SP) units: Part-3_ Precision single sine wave matching method in 0.1 msec accuracy: #504, #507
- Measurement of transient characteristics of Yamaha 30 cm woofer JA-3058 in sealed cabinet and Yamaha active sub-woofer YST-SW1000: #495, #497, #503, #507
- Identification of sound reflecting plane/wall by strong excitation of SP unit and room acoustics: #498

I believe the above linked my posts well cover almost all the aspects and tunings relating to above A1 through A4 and B1 through B4.

Let me emphasize that the use of rectangular-sine-tone-bust signals (8-wave, 3-wave, and even 1-wave) of various Fq and the analysis of the recorded air sound (by second independent PC) of these tone-burst signals using Adobe Audition (or Audacity) would give you really useful information on optimization of SWs and WOs. Especially the 3D (gain-Fq-time) color spectrum of Adobe Audition showing "3D sound energy distribution" is much useful (at least to me!) for observing and tuning the XO configuration for SWs and WOs (and other SP drivers). You can find typical example case in my posts #503 and #507.

If you would be seriously interested in using the test tone signal tracks I prepared and applied in these my measurements and tunings, please simply PM me writing your wish.

These posts would be also of your interest and reference;
- Perfect (0.1 msec precision) time alignment of all the SP drivers greatly contributes to amazing disappearance of SPs, tightness and cleanliness of the sound, and superior 3D sound stage: #520

- Not only the precision (0.1 msec level) time alignment over all the SP drivers but also SP facing directions and sound-deadening space behind the SPs plus behind our listening position would be critically important for effective (perfect?) disappearance of speakers: #687

- Reproduction and listening/hearing/feeling sensations to 16 Hz (organ) sound with my DSP-based multichannel multi-SP-driver multi-amplifier fully active stereo audio system having big-heavy active L&R sub-woofers: #782

- A nice smooth-jazz album for bass (low Fq) and higher Fq tonality check and tuning: #910, #63(remote thread)


Furthermore, I highly recommend you to establish your own consistent "reference/sampler music playlist" consists of tracks of various genres hopefully fitting well for your/our music preferences.

At least in my case, I have been using my own consistent "reference/sampler music playlist" consists of 60 tracks as I shared here #670 on my project thread, and also I have dedicated thread;
- An Attempt Sharing Reference Quality Music Playlist: at least a portion and/or whole track being analyzed by 3D color spectrum of Adobe Audition

You would please find details of my latest audio setup, well covering all of the above mentioned topics, in my post here #931 on my project thread.
- The latest system setup of my DSP-based multichannel multi-SP-driver multi-amplifier fully active audio rig, including updated startup/ignition sequences and shutdown sequences: as of June 26, 2024: #931


I do hope much pleasure and success in optimization efforts in your audio system.