Fosi Audio i5 Open-Back vs HD 660S2 Headphones

Every tracked fact about the two, side by side - prices, history lows, ratings and measured tuning. No verdict: which one to buy is the visitor's decision, always.

Fosi Audio i5 Open-Back Planar Magnetic Headphones fosi Now ₹52,194 at Bloom Audio Lowest on record ₹52,024 on Thursday, 22nd Oct, 2026 ★★★★★ 4.9 4.9 · 74 reviews Full prices & history

HD 660S2 Headphones Sennheiser Now ₹45,547 at Moon Audio Lowest on record ₹31,120 on Thursday, 22nd Oct, 2026 ★★★★★ 4.7 4.7 · 3 reviews Full prices & history

What is being compared

Both sides are headphones. The rows below are the facts each store publishes for this shelf - driver setup, impedance, sensitivity, back design and connectivity. A dash means the listing does not state that spec.

Spec fosi Sennheiser

Driver configuration Planar magnetic —

Connectivity Wired Wired

Back design Open-back —

Measured tuning, side by side

Both curves are real community measurements (gold: fosi · ink: Sennheiser). Each is level-aligned to its own 200 Hz–1 kHz mean, so rig offsets don't skew the comparison.

fosi Sennheiser

Tuning distance ±3.16 dB RMS 81% match - Close. Computed on a shared 40-point log grid, 20 Hz–10 kHz. A measurement-space fact, not a promise two ears agree.

Bass · 20–250 Hz Level Average level difference in this band, both curves aligned to their own 200 Hz–1 kHz mean. Plus means fosi plays louder there on the measured files; minus means Sennheiser does.

Mids · 250–2,000 Hz fosi −0.3 dB Average level difference in this band, both curves aligned to their own 200 Hz–1 kHz mean. Plus means fosi plays louder there on the measured files; minus means Sennheiser does.

Treble · 2,000–10,000 Hz Level Average level difference in this band, both curves aligned to their own 200 Hz–1 kHz mean. Plus means fosi plays louder there on the measured files; minus means Sennheiser does.

What a curve cannot seeBuild, driver QC unit-to-unit, comfort, isolation, accessories, warranty and resale value sit outside the graph - usually what the pricier one is charging for.

Price over the last 30 days

Daily lowest price across every tracked store, from the site's own price history. The line is one product's own range - the two cards are not drawn to a shared scale.

Fosi Audio i5 Open-Back Planar Magnetic Headphones Now ₹52,194 1% below its 30-day median Lowest on record ₹52,024 on Thursday, 22nd Oct, 2026 In stock at 3 tracked stores

HD 660S2 Headphones Now ₹45,547 44% above its 30-day median Lowest on record ₹31,120 on Thursday, 22nd Oct, 2026 In stock at 1 tracked store

Price gap right now ₹6,647 13% of the dearer one's price.

Stores with it in stock 3 vs 1 Active stores carrying each one right now - more stores usually means easier replacement and a steadier price.

The decision, factually

Cheaper right now HD 660S2 Headphones Lowest current price across all tracked stores - ₹45,547 vs ₹52,194.

Deepest discount ever seen HD 660S2 Headphones From each product's own recorded price history.

This page reports facts and expresses no opinion on which to purchase.

Keep going

EQ preset: fosi EQ preset: Sennheiser All Headphones More comparisons