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I am seeking recommendations for powered speakers with a flat frequency response.

For example, I work with

  • animals who produce low-frequency (<125 Hz) vocalizations (e.g., blue and fin whales)
  • animals who produce low-frequency (< 200 Hz) non-song vocalizations but also vocalizations that span higher frequency ranges (1000s of Hz) when singing (e.g., humpback and bowhead whales)
  • animals whose vocal range is 100s of kHz (e.g., odontocetes)

While most of our analyses involve looking at visual representation of sound (i.e., spectrograms), it helps sometimes to discriminate among species by listening to the vocalizations.

Are there any powered speakers that can handle that range? Would it make more sense to invest in speakers that specialize in one or the other (low vs high)?

Alternatively, if asking for direct recommendations is frowned upon here, are there any specifications I should look for when making a decision about which powered speakers to get?

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I prefer headphones to speakers for identifying animals sounds since I can often hear things in headphones that are not audible when played through speakers. See What's more accurate: Speakers or headphones?

Don't neglect other parts of your audio system. Computer sound cards are subject to picking up electronic artifact noise from other components of your computer, an effect especially noticeable when playing back faint signals. I prefer using a USB DAC (see video discussion), which effectively moves the analog audio circuit out of the computer case. Many USB DACs have amplifiers with adjustable gain, which can be a lifesaver when playing back faint signals.

Noil makes a good point about modifying playback rate for animals sounds with very low or very high frequencies to a frequency where you can perceive a greater dynamic range. See Human auditory field: frequency-intensity curves.

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Most bookshelf speakers, even budget ones will reproduce the range of 150 Hz to the limits of normal hearing 20 kHz, you would usually expect them to be able to handle much lower frequencies 45 Hz would be a standard cut-off. Better; 35 Hz to 25 kHz is not uncommon among medium/high-end speakers available from high-street stores. A flat response (no more than 3 db deviation across the whole range is optimal for faithful reproduction without the speaker adding colour to the sound. See this blog for more details on response and range.

As to powered speakers, a brand new pair from a reputable manufacturer such as Sony (the cheaper end of the better ones) shouldn't break the bank. Alternatively a pair of compact powered speakers (one is slaved to the other's power supply) such as these (commercial link, no affiliation) can be found on E-Bay for approximately £85 (~$100). Their response is down to 80 Hz, within the spec you asked for and they can be driven by a low-level signal such as a tablet or laptop.

Since Humpbacks can produce frequencies of 20 Hz (right a the limit of human hearing), you would likely need either to add a sub-woofer or to disregard the potential sound they might produce, and use visualisations from an oscilloscope or frequency-analyser software.

The second-hand market provided myself with a powered sub-woofer, (Paradigm - commercial link, no affiliation) for less than £100 ($130), well worth exploring your local papers and bazaars as the new product is upward of £800 ($1000). Worth noting that the frequency response is on a little plaque on the back of the unit - handy to check when buying.

An alternative offering greater flexibility regarding speaker choice would be to invest modestly in a compact amplifier unit such as this that can be powered by a single or duel 12v battery, ideal for boat or other vehicle.

Worth bearing in mind that outdoors - say on-deck, the sound will be attenuated considerably and need to be boosted in order to appreciate particularly the low frequencies. Also, check the response of your amplifier covers the range you need, most will. The hydrophone should already be of a specialist design to be used for whale song and cover the range.

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As human hearing is limited to < 20 kHz, you won't be able to hear "animals whose vocal range is 100s of kHz (e.g., odontocetes)" on a speaker whatever its quality.

However, you can decrease the speed of your recording with software to be able to hear those frequencies on a normal speaker (e.g. multiply it by 0.01). Same for very low frequency sounds: just increase the playback speed.

With this technique, you can hear any animal sounds, with any speakers (even cheap).

For instance, the multi-platform open-source software

  • Audacity supports a playback speed from 0.01 to 3 times the original speed (doc).
  • VLC supports a playback speed from 0.25 to 4 times the original speed (doc); but this option seems to be available on MacOS only.
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    $\begingroup$ Good point! I would add that Raven Lite has a greater range of playback speeds than Audacity and VLC, better spectrograms, and a convenient spectrogram annotation feature. $\endgroup$ Jul 1, 2022 at 2:50

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