Hertz PRO MPX690 3
Best box: 31.9 L bass reflex tuned to 47.1 Hz · F3 43.7 Hz
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Comparable 8.0" Drivers
Drivers with similar piston area, resonance and Qts — useful alternatives when the Hertz PRO MPX690 3 does not fit your target box volume or tuning. Each entry links to its full enclosure design and Thiele/Small parameters.
⚠️ Engineering Notice for Builders
- The textbook alignment (31.9 L at 44.9 Hz) would need a 48.3 cm port; the recommendation is retuned to 31.9 L at 47.1 Hz so the port can be built.
- Xmax is not published, so the port size is an empirical estimate (area ≥ 12 in² per ft³ of net volume, minimum by driver size), not a displacement calculation. Check air velocity in Load Forge Studio.
Recommended Bass Reflex (Vented)
PORT BUILDABLE| Net Box Volume (Vb) | 31.9 Liters |
| Tuning Frequency (Fb) | 47.1 Hz |
| F3 (-3 dB Cutoff) | 43.7 Hz |
| F6 / F10 Extension | 39.5 Hz / 35.3 Hz |
| Port Inner Diameter ESTIMATED | Ø 12.5 cm |
| Port Physical Length | 43.0 cm |
| First Pipe Resonance | 400.0 Hz |
Recommended Sealed (Acoustic Suspension)
MAX TRANSIENT DAMPING| Net Box Volume (Vb) | 14.1 Liters |
| System Q (Qtc) | 0.707 (Butterworth) |
| System Resonance (Fc) | 80.0 Hz |
| F3 (-3 dB Cutoff) | 80.8 Hz |
| F6 / F10 Extension | 61.0 Hz / 46.0 Hz |
| Air Spring Linearity | High (Zero port compression) |
Thiele/Small Parameters
| Resonance (Fs) | 50.0 Hz |
| Total Q (Qts) | 0.43 |
| Electrical Q (Qes) | 0.548 |
| Mechanical Q (Qms) | 2.0 |
| Equivalent Volume (Vas) | 24.0 Liters |
| Diaphragm Area (Sd) | 224.8 cm² |
| DC Resistance (Re) | 3.0 Ω |
| Efficiency Bandwidth Product (EBP) | 91.3 |
| Linear Excursion (Xmax) | N/A mm |
| Thermal Power (Pe) | N/A W |
| Nominal Diameter | 8.0" |
| Catalog Source | Load Forge catalog (manufacturer datasheets and retailer listings) |
Frequently Asked Questions
What is the recommended ported (bass reflex) box volume for Hertz PRO MPX690 3?
Load Forge's calculated alignment puts Hertz PRO MPX690 3 in a 31.9 liter vented enclosure tuned to 47.1 Hz, reaching an F3 cutoff of approximately 43.7 Hz.
Can Hertz PRO MPX690 3 be used in a sealed box?
Yes. In a sealed (acoustic suspension) enclosure of 14.1 liters with a Qtc of 0.707 (Butterworth), the system exhibits an F3 of 80.8 Hz.
What port dimensions should be used for Hertz PRO MPX690 3 to avoid port chuffing?
Xmax is not published for Hertz PRO MPX690 3, so the port is an empirical estimate: a 12.5 cm diameter with a length of 43.0 cm (area at least 12 in² per ft³ of net volume). Check the air velocity at your power level in Load Forge Studio.
Shareable Acoustic Card for Forums & Social Media
Embed this design card on DIYAudio, AVSForum, Reddit, or Facebook. It shows the calculated F3, MOL (when the power rating is published) and box parameters.
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