Short answer: the Optimal Audio Cuboid 15 for better sound quality, the Optimal Audio Cuboid 3 for the lower price. The Optimal Audio Cuboid 15 ranks #16 of 32 surface-mount and background music speakers, rated 3.0/5, at $1,035. The Optimal Audio Cuboid 3 ranks #30, rated 2.3/5, at $85, $950 cheaper.
The Optimal Audio Cuboid 15 is the more accurate, deeper-bass choice. 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 measured preference score, a predictor of how neutral it sounds, is 1.94 against -0.18 for the Optimal Audio Cuboid 3. Its bass reaches about 45Hz before falling 3dB, against 115Hz for the Optimal Audio Cuboid 3. 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.
The case for the Optimal Audio Cuboid 3: A tiny installation speaker from Optimal Audio with a 3” driver. The tradeoff: Bass is very limited, so it needs a subwoofer, and the on-axis response is very uneven (2.07 average deviation).
Buy the Optimal Audio Cuboid 15 when sound quality outweighs the price for you, and the Optimal Audio Cuboid 3 when the price outweighs sound quality instead.
Looking for alternatives? See the complete PA & Live Sound rankings.
Specifications Side By Side
| Optimal Audio Cuboid 15 | Optimal Audio Cuboid 3 | |
|---|---|---|
| Price | $1,035 each Passive | $85 each Passive |
| Ranked | #16 of 32 in Surface-Mount and Background Music Speakers | #30 of 32 in Surface-Mount and Background Music Speakers |
| Passive | Yes | Yes |
| Bluetooth | No | No |
| Drivers | 15” woofer, 2-way | 3” driver |
| Bass Extension (-3dB) | 45.0Hz (measured, manufacturer data via spinorama.org) | 115.0Hz (measured, manufacturer data via spinorama.org) |
| Bass Extension (-10dB) | about 30.9Hz (derived, log-interpolated between spinorama.org -9dB/-12dB points) | about 82.4Hz (measured, manufacturer data via spinorama.org) |
| Spinorama Preference Score | 1.94 (spinorama.org) | -0.18 |
| Spinorama Preference Score with Perfect Sub | 3.71 (spinorama.org) | 3.43 |
| DIY Kit | No | No |
| Maximum SPL | - | 104dB peak (manufacturer specified) |
| Weight | - | 2.8 lbs (1.26 kg) |
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 15 (measured by the manufacturer) and Optimal Audio Cuboid 3 (measured by the manufacturer), via spinorama.org.
Related Speaker Comparisons
How Optimal Audio Cuboid 15 compares with other leading options:
- Optimal Audio Cuboid 10 vs Optimal Audio Cuboid 15
- Optimal Audio Cuboid 8 vs Optimal Audio Cuboid 15
- Optimal Audio Cuboid 12 vs Optimal Audio Cuboid 15
- Optimal Audio Cuboid 15 vs Optimal Audio Cuboid 5
- Optimal Audio Cuboid 12 vs Optimal Audio Cuboid 3
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 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
Optimal Audio Cuboid 3: $85 each Passive eBay
Same family: the Optimal Audio Cuboid 5 (larger model, ranked higher, rated 2.5/5).
Pros: A tiny installation speaker from Optimal Audio with a 3” driver. Optimal Audio’s measurements show a preference score of -0.18 that reaches 3.43 with an ideal subwoofer, with 0.82 listening window deviation.
Cons: Bass is very limited, so it needs a subwoofer, and the on-axis response is very uneven (2.07 average deviation). That data is low quality and comes from Optimal Audio. Bass reaches 115.0Hz (-3dB) and about 82Hz (-10dB). That data is low quality.
Full Optimal Audio Cuboid 3 review and specifications →
| Released | Nov 2022 (3 years ago) |
|---|---|
| Bass Extension (-10dB) | about 82.4Hz (measured, manufacturer data via spinorama.org) |
| Bass Extension (-3dB) | 115.0Hz (measured, manufacturer data via spinorama.org) |
| Bluetooth | No |
| DIY Kit | No |
| Drivers | 3” driver |
| Maximum SPL | 104dB peak (manufacturer specified) |
| Passive | Yes |
| Spinorama Preference Score | -0.18 |
| Spinorama Preference Score with Perfect Sub | 3.43 |
| Weight | 2.8 lbs (1.26 kg) |
- Reviews, Comparisons and Sound Samples
- Head-to-Head Comparisons