Coast Buyouts 1208P-138A 3" x 5" 5W Paper Cone Speaker 8 Ohm
Best box: 1.2 L sealed · Fc 217.5 Hz · F3 186.7 Hz
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Comparable 3.0" Drivers
Drivers with similar piston area, resonance and Qts — useful alternatives when the Coast Buyouts 1208P-138A 3" x 5" 5W Paper Cone Speaker 8 Ohm 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
- 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.
Textbook Bass Reflex — not recommended (9.2 dB bass hump)
PORT BUILDABLE| Net Box Volume (Vb) | 1.5 Liters |
| Tuning Frequency (Fb) | 130.7 Hz |
| F3 (-3 dB Cutoff) | 195.4 Hz |
| F6 / F10 Extension | 177.9 Hz / 152.6 Hz |
| Port Inner Diameter ESTIMATED | Ø 5.0 cm |
| Port Physical Length | 19.4 cm |
| First Pipe Resonance | 887.0 Hz |
| Estimated MOL @ F3 | 95.7 dB SPL |
Sealed (Acoustic Suspension) — compromise
SUITS INFINITE / OPEN BAFFLEWith Qts 2.296 a Butterworth (Qtc 0.707) box would be many times Vas. A box equal to Vas reaches Qtc 3.247; for a flat response this driver is better used on an infinite (IB) or open baffle.
| Net Box Volume (Vb) | 1.2 Liters |
| System Q (Qtc) | 3.247 (above Butterworth: Qtc cannot fall below Qts (2.30)) |
| System Resonance (Fc) | 217.5 Hz |
| F3 (-3 dB Cutoff) | 186.7 Hz |
| F6 / F10 Extension | 171.0 Hz / 151.1 Hz |
| Air Spring Linearity | High (Zero port compression) |
Thiele/Small Parameters
| Resonance (Fs) | 153.8 Hz |
| Total Q (Qts) | 2.296 |
| Electrical Q (Qes) | 4.936 |
| Mechanical Q (Qms) | 4.29 |
| Equivalent Volume (Vas) | 1.2 Liters |
| Diaphragm Area (Sd) | 40.7 cm² |
| DC Resistance (Re) | 6.58 Ω |
| Efficiency Bandwidth Product (EBP) | 31.2 |
| Linear Excursion (Xmax) | N/A mm |
| Thermal Power (Pe) | 4.0 W |
| Nominal Diameter | 3.0" |
| Catalog Source | Load Forge catalog (manufacturer datasheets and retailer listings) |
Frequently Asked Questions
What is the recommended ported (bass reflex) box volume for Coast Buyouts 1208P-138A 3" x 5" 5W Paper Cone Speaker 8 Ohm?
A simple ported box is not recommended for Coast Buyouts 1208P-138A 3" x 5" 5W Paper Cone Speaker 8 Ohm: the textbook alignment (1.5 liters tuned to 130.7 Hz) needs a 19.4 cm port, and no nearby retune stays buildable without a bass hump. A sealed box, a passive radiator or a folded duct is the practical choice.
Can Coast Buyouts 1208P-138A 3" x 5" 5W Paper Cone Speaker 8 Ohm be used in a sealed box?
Yes. In a sealed (acoustic suspension) enclosure of 1.2 liters with a Qtc of 3.247 (above Butterworth: Qtc cannot fall below Qts (2.30)), the system exhibits an F3 of 186.7 Hz.
What port dimensions should be used for Coast Buyouts 1208P-138A 3" x 5" 5W Paper Cone Speaker 8 Ohm to avoid port chuffing?
A straight 5.0 cm port would need 19.4 cm of length, which does not fit a practical cabinet. Use a passive radiator or a folded/3D duct instead of a straight tube.
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