I bought Ethan a wireless speaker to let him enjoy other people's performance (because he is learning the piano himself, see our experience in buying a piano), and did a lot of homework and comparison during the process. Here are some good wireless Bluetooth speakers, including very cheap, entry-level, and mid-range price points.

Audioengine

Audioengine A5+ Shelf Case

$499.00
The Audioengine A5+ wireless speaker is a complete home music system featuring a 5" custom aramid fiber woofer, 0.75" silk dome tweeter, high fidelity Premium Bluetooth aptX-HD, built-in power amplifier, wrapped in precision tuning inside the handmade speakers. The volume can be controlled with the aluminum remote or the front knob, and the auto-sensing sleep mode conserves power when not in use. It's only 10.75 x 7 x 9″, but it sounds big, with 150 watts of peak output and stereo sound capable of filling any room. Easily connect an Audioengine S8 or other subwoofer via the RCA variable outputs, or via HD Bluetooth to connect with apps or devices.

Ultimate Ears

Ultimate Ears Hyperboom Bluetooth

$390.57
Weighing in at a whopping 13 pounds, the Ultimate Ears Hyperboom Bluetooth speaker packs crowd-pleasing sound, is splash-proof and has a helpful companion app, perfect for parties. It comes with an adaptive equalizer that can customize the sound to the environment, and it can stream music from four different devices. 24 hours of battery life, and the ability to connect with other Boom or Megaboom speakers for even more party-heavy effects (beware of neighbor complaints if you live in an apartment).

JBL

Xtreme 3 Waterproof Speaker

$299.95
The JBL Xtreme 3 Portable Bluetooth Speaker has powerful sound and deep bass. Four drivers and two JBL bass radiators effortlessly deliver dynamic, immersive sound with deep bass and rich detail. It's fully P67 rated waterproof and dustproof, and the included carrying strap makes it easy to take it anywhere, plus its durable design makes it easy to take to the pool and park (it even has a built-in bottle opener ). Bluetooth 5.1 connectivity for 15 hours of music playback.

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Bang & Olufsen

Beosound A1 Portable Speaker

$248.60
Bang & Olufsen's 2nd generation Beosound A1 speaker combines style and sound quality; IP67-rated water and dust resistance, battery-operated battery life of up to 18 hours (up to 43 hours at low volume), indoor and outdoor use; Only 1.23lbs, very portable. Although the volume is small, the peak power is as high as 2 x 140W, which is enough for use in a small area. Built-in Alexa voice assistant for voice calls; 3 microphone arrays for clear calls.

Bose

Revolve+ II Portable Speaker

$229.00
The Bose SoundLink Revolve+ II is Bose's best Bluetooth speaker yet. Its body is small and exquisite, but it accommodates a lot of acoustic components, including high-efficiency sound units that can produce full-range sound effects, passive resonant double membranes, and omnidirectional sound reflectors, so that it can create realistic sound effects, as if you are on the scene. This is a 360-degree surround sound omnidirectional speaker that delivers deep and powerful sound from every direction, giving everyone around the speaker the same listening experience. You can also put it close to the wall, and the sound will spread and reflect around the room through the wall. It has a built-in microphone, supports Siri/Google Assistant, can take calls and access other devices, and can also connect to Amazon Alexa-enabled devices (such as Echo Dot) for flexible wireless control.

Echo

Amazon Echo Studio Smart Speaker

$199.99
Amazon Echo Studio supports powerful Dolby Atmos directional sound technology, and its functionality is not inferior to other similar smart speakers, but the price is only about half of the latter. Contains three 3-inch midrange speakers, a 1-inch tweeter, and a 5.25-inch woofer; five speakers produce powerful bass, dynamic mids, and clear highs.

Sonos One SL

Multiroom WiFi Speaker
$194.00
Sonos One SL has great sound that fills a room, and can be controlled via the Sonos app or Apple Airplay 2 to stream music from your iPhone or iPad. Its compact, versatile design fits in any room, including kitchen countertops, office bookshelves, and even bathrooms (it's moisture-resistant). Its biggest feature is its support for multi-room audio, which can easily connect Sonos speakers in different rooms via Wi-Fi to create a whole-house audio system. It's also the #1 seller in the "Multi-room Music System" category on Amazon.

Marshall 

Marshall Emberton U.K.

$116.49
Compared with similarly priced products, the Marshall Emberto delivers big sound in a small package. It supports Bluetooth 5.0 and USB connectivity, is IPX7 waterproof (not dustproof), has a battery life of up to 20 hours (20 minutes of fast charging for 5 hours), weighs only 1.5lbs, and is extremely portable.