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Isophon P30/37A

Best box: 9.6 L bass reflex tuned to 46.8 Hz · F3 66.0 Hz

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Comparable 6.5" Drivers

Drivers with similar piston area, resonance and Qts — useful alternatives when the Isophon P30/37A does not fit your target box volume or tuning. Each entry links to its full enclosure design and Thiele/Small parameters.

JL Audio

C7-650cw

6.5" · Fs 54.5 Hz · Qts 0.605 · Vas 13.1 L

Goldwood

GW-6024 6-1/2" Butyl Surround Woofer 4 Ohm

6.5" · Fs 53.7 Hz · Qts 0.57 · Vas 11.9 L

Dayton Audio

PCS175-4 6-1/2" Poly Cone Woofer 4 Ohm

6.5" · Fs 56.0 Hz · Qts 0.73 · Vas 13.7 L

Goldwood

GW-S650/4 6-1/2" Poly Cone Woofer 4 Ohm

6.5" · Fs 55.0 Hz · Qts 0.71 · Vas 15.6 L

B2 Audio

35691

6.5" · Fs 52.0 Hz · Qts 0.59 · Vas 11.4 L

Dynaudio

Esotec MW 162

6.5" · Fs 55.0 Hz · Qts 0.55 · Vas 15.0 L

Compare them in the same box → Browse all 6.5" drivers →

⚠️ Engineering Notice for Builders

Limited linear excursion (Xmax: 1.5 mm); set a high-pass subsonic filter at 25–30 Hz when driven with high power.

Recommended Bass Reflex (Vented)

PORT BUILDABLE

Net Box Volume (Vb)	9.6 Liters
Tuning Frequency (Fb)	46.8 Hz
F3 (-3 dB Cutoff)	66.0 Hz
F6 / F10 Extension	54.0 Hz / 41.3 Hz
Port Inner Diameter	Ø 5.0 cm
Port Physical Length	24.4 cm
First Pipe Resonance	704.0 Hz
Estimated MOL @ F3	96.0 dB SPL

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Sealed (Acoustic Suspension) — compromise

SUITS INFINITE / OPEN BAFFLE

With Qts 0.65 a Butterworth (Qtc 0.707) box would be many times Vas. A box equal to Vas reaches Qtc 0.919; for a flat response this driver is better used on an infinite (IB) or open baffle.

Net Box Volume (Vb)	12.0 Liters
System Q (Qtc)	0.919 (above Butterworth)
System Resonance (Fc)	77.8 Hz
F3 (-3 dB Cutoff)	66.9 Hz
F6 / F10 Extension	54.2 Hz / 42.9 Hz
Air Spring Linearity	High (Zero port compression)

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Thiele/Small Parameters

Resonance (Fs)	55.0 Hz
Total Q (Qts)	0.65
Electrical Q (Qes)	0.798
Mechanical Q (Qms)	3.5

Equivalent Volume (Vas)	12.0 Liters
Diaphragm Area (Sd)	132.0 cm²
DC Resistance (Re)	4.0 Ω
Efficiency Bandwidth Product (EBP)	68.9

Linear Excursion (Xmax)	1.5 mm
Thermal Power (Pe)	15.0 W
Nominal Diameter	6.5"
Catalog Source	Load Forge catalog (manufacturer datasheets and retailer listings)

Frequently Asked Questions

What is the recommended ported (bass reflex) box volume for Isophon P30/37A?

Load Forge's calculated alignment puts Isophon P30/37A in a 9.6 liter vented enclosure tuned to 46.8 Hz, reaching an F3 cutoff of approximately 66.0 Hz.

Can Isophon P30/37A be used in a sealed box?

Yes. In a sealed (acoustic suspension) enclosure of 12.0 liters with a Qtc of 0.919 (above Butterworth), the system exhibits an F3 of 66.9 Hz.

What port dimensions should be used for Isophon P30/37A to avoid port chuffing?

Sized from cone displacement (Sd × Xmax), a minimum port diameter of 5.0 cm with a length of 24.4 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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