🔧 INSTALLER LEVEL: Design and Tuning

Bandpass Enclosure Design — Chamber Ratios

Frequency-response chart comparing narrow, balanced, and wider-bandwidth fourth-order bandpass chamber ratios to show the tradeoff between peak output and usable bandwidth — The chart shows the central bandpass tradeoff: tighter chamber ratios create a higher, narrower peak, while larger ported chambers spread output across more notes at the cost of peak efficiency.

For a 4th-order bandpass (one sealed, one ported chamber):

Step 1: Sealed chamber volume

Vs = 0.7 × Vas

The sealed chamber controls the upper -3 dB point. Smaller Vs = higher upper cutoff. Larger Vs = lower upper cutoff, more output.

Step 2: Ported chamber volume

Vp = 1.5 to 3.0 × Vs

Larger Vp / Vs ratio = wider bandwidth but less peak efficiency.

Step 3: Port tuning

Tune port to the desired center frequency of the passband:

Fb = target_frequency ± 5 Hz

Calculate port length using the Helmholtz formula with Vp and target Fb.

Step 4: Verify bandwidth

Approximate passband (−3 dB points):

f_lower ≈ Fb × 0.7
f_upper ≈ Fc_sealed × 1.4

Where Fc_sealed is the sealed chamber resonance.

Adjust chamber ratio iteratively (or use WinISD's bandpass design mode) until bandwidth covers desired range.

Isobaric Design

The isobaric pair behaves as a single driver with:

Fs_iso = Fs × √2
Vas_iso = Vas / 2
Qts_iso = Qts (unchanged)

Wiring:

For push-push (both cones moving in same direction simultaneously): - Both drivers receive the same signal - Both voice coils must be wired in same polarity (both positive to same terminal) - Outer driver: positive terminal to amp positive - Inner driver: positive terminal to amp positive (reversed physical orientation means same acoustic polarity)

Physical arrangement:

Face-to-face: Magnet-out on both. Inner faces of cones touching or near-touching. Sealed air pocket between them = isobaric volume. Mount outer driver in enclosure baffle.

Magnet-to-magnet: Cones both facing outward. Sealed pocket at back. Less popular (larger depth required).

Enclosure calculation:

Use Vs_iso = 0.5 × Vas for sealed alignment. Calculate as normal sealed box using modified parameters.