Short answer: the Definitive Technology ProMonitor 1000 for better sound quality, the Sehlin Helium for the lower price. The Definitive Technology ProMonitor 1000 ranks #55 of 63 bookshelf speakers at $249. The Sehlin Helium ranks #56 at $140, $109 cheaper.
On the Sehlin Helium side: An entire pair of drivers and crossover parts costs about $140, with a Parts Express flat-pack enclosure keeping the build simple - genuinely small enough to fit in the palm of a hand. Set against that: CEA2034 spinorama shows an uneven response that the designer’s own re-measurements confirmed rather than explained away as error.
What the Definitive Technology ProMonitor 1000 offers: Bass distortion is well controlled per the measurements, and the slow bass rolloff means it can be pushed fairly hard for its size. The tradeoff: CEA2034 spinorama shows severely reduced bass energy between 40-120Hz, a directivity mismatch between the tweeter and woofer, and a severe resonance/interference issue around 14kHz.
Buy the Sehlin Helium if the price matters more than sound quality. Buy the Definitive Technology ProMonitor 1000 if sound quality matters more than the price.
If sound quality matters at all to you, skip both of these and look higher up the 63 bookshelf speakers instead.
Specifications Side By Side
| Sehlin Helium | Definitive Technology ProMonitor 1000 | |
|---|---|---|
| Price | $140 | $249.00 |
| Ranked | #56 of 63 in Medium Size Bookshelf Speakers | #55 of 63 in Medium Size Bookshelf Speakers |
| Bass Extension (-3dB) | approx. 170Hz (measured, Audio Science Review) - low confidence - this tiny single-driver design has a highly irregular response with a deep notch around 30Hz, not a simple monotonic rolloff | 95Hz (measured, Audio Science Review) |
| Bass Extension (-10dB) | approx. 70Hz (measured, Audio Science Review) - low confidence - this tiny single-driver design has a highly irregular response with a deep notch around 30Hz, not a simple monotonic rolloff | 80Hz (measured, Audio Science Review) |
| Drivers | Dayton Audio ND91-4 3.5" full-range driver (single-driver design) | 1" aluminum dome tweeter, 5.25" BDSS mid/woofer, 5.25" planar bass radiator |
| Dimensions | 6.5W x 4.5H x 5D in (0.04 cu. ft. enclosure) | 10.88H x 6.25W x 6.5D in |
| Weight | not published (DIY kit) | 7.3 lbs / 3.29 kg each |
| Woofer Cabinet | sealed | passive radiator |
| Sensitivity | approx. 82dB (2.83V/1m, measured, Audio Science Review - low confidence, irregular response with no clear flat region) | 86dB (2.83V/1m, measured, Audio Science Review - reviewer noted this vs. a manufacturer spec of 91dB) |
| Frequency Response | - | 47Hz - 30kHz (Manufacturer specified) |
| Impedance | - | 8 ohms nominal |
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- Fluance Signature HFS vs Polk T15
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- Q Acoustics 3020i vs Polk T15
- Polk T15 vs Definitive Technology ProMonitor 1000
- Definitive Technology ProMonitor 1000 vs Klipsch R-41M
The Two Speakers In Full
Sehlin Helium: $140
Pros: An entire pair of drivers and crossover parts costs about $140, with a Parts Express flat-pack enclosure keeping the build simple - genuinely small enough to fit in the palm of a hand.
Cons: CEA2034 spinorama shows an uneven response that the designer’s own re-measurements confirmed rather than explained away as error. The reviewer described the sound as muffled, boomy, and gritty even up close, concluding “this is a failing attempt” relative to larger designs. Maximum output is limited to about 80dB SPL, well below normal listening levels for most rooms.
Full Sehlin Helium review and specifications →
| Bass Extension (-10dB) | approx. 70Hz (measured, Audio Science Review) - low confidence - this tiny single-driver design has a highly irregular response with a deep notch around 30Hz, not a simple monotonic rolloff |
|---|---|
| Bass Extension (-3dB) | approx. 170Hz (measured, Audio Science Review) - low confidence - this tiny single-driver design has a highly irregular response with a deep notch around 30Hz, not a simple monotonic rolloff |
| Dimensions | 6.5W x 4.5H x 5D in (0.04 cu. ft. enclosure) |
| Drivers | Dayton Audio ND91-4 3.5" full-range driver (single-driver design) |
| Sensitivity | approx. 82dB (2.83V/1m, measured, Audio Science Review - low confidence, irregular response with no clear flat region) |
| Weight | not published (DIY kit) |
| Woofer Cabinet | sealed |
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- Reviews, Comparisons and Sound Samples
Definitive Technology ProMonitor 1000: $249.00 Amazon
Pros: Bass distortion is well controlled per the measurements, and the slow bass rolloff means it can be pushed fairly hard for its size. Ships with a footer that keeps the small cabinet planted despite its light weight.
Cons: CEA2034 spinorama shows severely reduced bass energy between 40-120Hz, a directivity mismatch between the tweeter and woofer, and a severe resonance/interference issue around 14kHz. Distortion at 96dB SPL was so bad the reviewer limited testing to 86dB. Direct comparison to a $118/pair Pioneer SP-BS22-LR left the reviewer calling the $500/pair ProMonitor 1000 “a bad experiment that should be forgotten” and concluding “there is nothing Pro about it.”
Full Definitive Technology ProMonitor 1000 review and specifications →
| Bass Extension (-10dB) | 80Hz (measured, Audio Science Review) |
|---|---|
| Bass Extension (-3dB) | 95Hz (measured, Audio Science Review) |
| Dimensions | 10.88H x 6.25W x 6.5D in |
| Drivers | 1" aluminum dome tweeter, 5.25" BDSS mid/woofer, 5.25" planar bass radiator |
| Frequency Response | 47Hz - 30kHz (Manufacturer specified) |
| Impedance | 8 ohms nominal |
| Sensitivity | 86dB (2.83V/1m, measured, Audio Science Review - reviewer noted this vs. a manufacturer spec of 91dB) |
| Weight | 7.3 lbs / 3.29 kg each |
| Woofer Cabinet | passive radiator |
As an eBay Partner, we may be compensated if you make a purchase.
- Links
- Reviews, Comparisons and Sound Samples
- Head-to-Head Comparisons
- Definitive Technology ProMonitor 1000 vs Polk T15
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- Definitive Technology ProMonitor 1000 vs Fluance Signature HFS
- Definitive Technology ProMonitor 1000 vs Pioneer Elite SP-EBS73-LR
- Definitive Technology ProMonitor 1000 vs JBL Stage A130
- Definitive Technology ProMonitor 1000 vs Klipsch R-41M
- Definitive Technology ProMonitor 1000 vs Q Acoustics 5020
- Definitive Technology ProMonitor 1000 vs Micca RB42
- See all 14 comparisons