GRS 5PF-8 Bass-midwoofer
Best box: 2.2 L bass reflex tuned to 51.0 Hz · F3 47.4 Hz
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Comparable 8.0" Drivers
Drivers with similar piston area, resonance and Qts — useful alternatives when the GRS 5PF-8 Bass-midwoofer 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 (1.5 L at 85.0 Hz) would need a 50.7 cm port; the recommendation is retuned to 2.2 L at 51.0 Hz so the port can be built.
- Port length (99.3 cm) exceeds a straight internal run; use an elbow bend, slotted vent or 3D folded duct to fit the enclosure.
- Limited linear excursion (Xmax: 2.5 mm); set a high-pass subsonic filter at 25–30 Hz when driven with high power.
Recommended Bass Reflex (Vented)
PORT NEEDS ELBOW / 3D| Net Box Volume (Vb) | 2.2 Liters |
| Tuning Frequency (Fb) | 51.0 Hz |
| F3 (-3 dB Cutoff) | 47.4 Hz |
| F6 / F10 Extension | 45.7 Hz / 43.6 Hz |
| Port Inner Diameter | Ø 5.0 cm |
| Port Physical Length | 99.3 cm |
| First Pipe Resonance | 173.0 Hz |
| Estimated MOL @ F3 | 90.4 dB SPL |
Sealed (Acoustic Suspension) — compromise
SUITS INFINITE / OPEN BAFFLEWith Qts 1.4 a Butterworth (Qtc 0.707) box would be many times Vas. A box equal to Vas reaches Qtc 1.98; for a flat response this driver is better used on an infinite (IB) or open baffle.
| Net Box Volume (Vb) | 0.1 Liters |
| System Q (Qtc) | 1.98 (above Butterworth: Qtc cannot fall below Qts (1.40)) |
| System Resonance (Fc) | 141.4 Hz |
| F3 (-3 dB Cutoff) | 120.6 Hz |
| F6 / F10 Extension | 106.8 Hz / 91.0 Hz |
| Air Spring Linearity | High (Zero port compression) |
Thiele/Small Parameters
| Resonance (Fs) | 100.0 Hz |
| Total Q (Qts) | 1.4 |
| Electrical Q (Qes) | 1.965 |
| Mechanical Q (Qms) | 4.87 |
| Equivalent Volume (Vas) | 0.1 Liters |
| Diaphragm Area (Sd) | 220.0 cm² |
| DC Resistance (Re) | 7.45 Ω |
| Efficiency Bandwidth Product (EBP) | 50.9 |
| Linear Excursion (Xmax) | 2.5 mm |
| Thermal Power (Pe) | 70.0 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 GRS 5PF-8 Bass-midwoofer?
Load Forge's calculated alignment puts GRS 5PF-8 Bass-midwoofer in a 2.2 liter vented enclosure tuned to 51.0 Hz, reaching an F3 cutoff of approximately 47.4 Hz.
Can GRS 5PF-8 Bass-midwoofer be used in a sealed box?
Yes. In a sealed (acoustic suspension) enclosure of 0.1 liters with a Qtc of 1.98 (above Butterworth: Qtc cannot fall below Qts (1.40)), the system exhibits an F3 of 120.6 Hz.
What port dimensions should be used for GRS 5PF-8 Bass-midwoofer to avoid port chuffing?
Sized from cone displacement (Sd × Xmax), a minimum port diameter of 5.0 cm with a length of 99.3 cm is suggested; check the port air velocity at your drive level in the Load Forge Studio.
Shareable Acoustic Card for Forums & Social Media
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