Short answer: the Optimal Audio Cuboid 8. It ranks #8 of 32 surface-mount and background music speakers by sound quality, rated 3.2/5, at $490; the Optimal Audio Cuboid 15 ranks #16, rated 3.0/5, and costs $1,035, which makes this an easy call rather than a real tradeoff.
The case for the Optimal Audio Cuboid 8: A larger member of Optimal Audio’s Cuboid installation range, with a 8-inch woofer that reaches 51.5Hz at -3dB in vendor measurements, deep for an installation box, and a cabinet matching the smaller Optimal Audio Cuboid 5. Watch for: Directivity is uneven (3.97dB variation) and the on-axis response is uneven (0.64 band deviation), so it scores 2.28 on its own and 4.45 with an ideal subwoofer.
The Optimal Audio Cuboid 15 is the deeper-bass option. A larger member of Optimal Audio’s Cuboid installation range, with a 15-inch woofer that reaches 45.0Hz at -3dB in vendor measurements, deep for an installation box, and a cabinet matching the smaller Optimal Audio Cuboid 5. Its bass reaches about 45Hz before falling 3dB, against 51.5Hz for the Optimal Audio Cuboid 8. The catch: Directivity is uneven (4.54dB variation) and the on-axis response is uneven (0.84 band deviation), so it scores 1.94 on its own and 3.71 with an ideal subwoofer.
Buy the Optimal Audio Cuboid 8. It is rated higher for sound quality than the Optimal Audio Cuboid 15 and costs less, so only choose the other one for a particular feature it does better.
Still deciding? The full PA & Live Sound rankings cover every ranked option.
Specifications Side By Side
| Optimal Audio Cuboid 8 | Optimal Audio Cuboid 15 | |
|---|---|---|
| Price | $490 each Passive | $1,035 each Passive |
| Ranked | #8 of 32 in Surface-Mount and Background Music Speakers | #16 of 32 in Surface-Mount and Background Music Speakers |
| Passive | Yes | Yes |
| Bluetooth | No | No |
| Drivers | 8” woofer, 2-way | 15” woofer, 2-way |
| Bass Extension (-3dB) | 51.5Hz (measured, manufacturer data via spinorama.org) | 45.0Hz (measured, manufacturer data via spinorama.org) |
| Bass Extension (-10dB) | about 38.1Hz (derived, log-interpolated between spinorama.org -9dB/-12dB points) | about 30.9Hz (derived, log-interpolated between spinorama.org -9dB/-12dB points) |
| Spinorama Preference Score | 2.28 (spinorama.org) | 1.94 (spinorama.org) |
| Spinorama Preference Score with Perfect Sub | 4.45 (spinorama.org) | 3.71 (spinorama.org) |
| DIY Kit | No | No |
Frequency Response Compared
Both speakers’ spinorama measurements, overlaid. A flatter line is more neutral: peaks sound forward or harsh, dips sound recessed. Each curve is shifted so its average from 300 Hz to 3 kHz sits at 0 dB, so loudness differences between the two are removed and only the shape is compared.
Measurement data: Optimal Audio Cuboid 8 (measured by the manufacturer) and Optimal Audio Cuboid 15 (measured by the manufacturer), via spinorama.org.
Related Speaker Comparisons
How Optimal Audio Cuboid 8 compares with other leading options:
- Optimal Audio Cuboid 10 vs Optimal Audio Cuboid 8
- Optimal Audio Cuboid 8 vs Optimal Audio Cuboid 12
- Optimal Audio Cuboid 8 vs Optimal Audio Cuboid 5
- Optimal Audio Cuboid 8 vs Optimal Audio Cuboid 3
- Optimal Audio Cuboid 10 vs Optimal Audio Cuboid 15
Prices on this page were last checked October 14, 2026 at 2:38 PM UTC. Product prices and availability are accurate as of that date/time and are subject to change; the price and availability shown on Amazon at the time of purchase will apply to the purchase of this product.
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The Two Speakers In Full
Optimal Audio Cuboid 8: $490 each Passive eBay
Pros: A larger member of Optimal Audio’s Cuboid installation range, with a 8-inch woofer that reaches 51.5Hz at -3dB in vendor measurements, deep for an installation box, and a cabinet matching the smaller Optimal Audio Cuboid 5. Measured bass extension of 38.1Hz (-10dB).
Cons: Directivity is uneven (3.97dB variation) and the on-axis response is uneven (0.64 band deviation), so it scores 2.28 on its own and 4.45 with an ideal subwoofer. It is sold through Allen & Heath and Optimal Audio installers with no US retail listing.
Full Optimal Audio Cuboid 8 review and specifications →
| Bass Extension (-10dB) | about 38.1Hz (derived, log-interpolated between spinorama.org -9dB/-12dB points) |
|---|---|
| Bass Extension (-3dB) | 51.5Hz (measured, manufacturer data via spinorama.org) |
| Bluetooth | No |
| DIY Kit | No |
| Drivers | 8” woofer, 2-way |
| Passive | Yes |
| Spinorama Preference Score | 2.28 (spinorama.org) |
| Spinorama Preference Score with Perfect Sub | 4.45 (spinorama.org) |
- Reviews, Comparisons and Sound Samples
- Head-to-Head Comparisons
Optimal Audio Cuboid 15: $1,035 each Passive eBay
Pros: A larger member of Optimal Audio’s Cuboid installation range, with a 15-inch woofer that reaches 45.0Hz at -3dB in vendor measurements, deep for an installation box, and a cabinet matching the smaller Optimal Audio Cuboid 5. Measured bass extension of 30.9Hz (-10dB).
Cons: Directivity is uneven (4.54dB variation) and the on-axis response is uneven (0.84 band deviation), so it scores 1.94 on its own and 3.71 with an ideal subwoofer. It is sold through Allen & Heath and Optimal Audio installers with no US retail listing.
Full Optimal Audio Cuboid 15 review and specifications →
| Bass Extension (-10dB) | about 30.9Hz (derived, log-interpolated between spinorama.org -9dB/-12dB points) |
|---|---|
| Bass Extension (-3dB) | 45.0Hz (measured, manufacturer data via spinorama.org) |
| Bluetooth | No |
| DIY Kit | No |
| Drivers | 15” woofer, 2-way |
| Passive | Yes |
| Spinorama Preference Score | 1.94 (spinorama.org) |
| Spinorama Preference Score with Perfect Sub | 3.71 (spinorama.org) |
- Reviews, Comparisons and Sound Samples
- Head-to-Head Comparisons