In-Depth Analysis of Astell&Kern SP4000 Drawbacks
PRODUCT

- Product
- Astell&Kern A&ultima SP4000 Silver
- Provider
- Astell&Kern
- Price
- ¥693,000

Dr. Bravo
The SP4000 is Astell&Kern's flagship DAP evolved over three years. With its OCTA-core Quad DAC and dual OP AMP configuration delivering overwhelming audio expression, premium materials like 904L stainless steel and Perlinger leather, plus Full Android OS for exceptional expandability—this design philosophy truly reaches masterpiece status in portable audio. The High Driving Mode's ability to effortlessly power high-impedance headphones is the real deal.
BooLab Reviewer Negative Reviews
Limited EQ functionality at a $4,600 price point raises questions from a functionality perspective. Parametric EQ should be implementable via software update, so it should have been standard at this price tier. Considering cost-performance, alternatives like the FiiO M17 are quite attractive. However, if you can accept it as an investment in material quality and sound, long-term ownership satisfaction will be high.
The combination of 904L stainless steel and Perlinger leather is artistic, but the lack of an OLED screen is disappointing. A flagship at this price point should offer the ultimate visual experience too. The LCD panel is practical, but OLED's deep blacks and vibrant color expression would have elevated the design perfection. The gap between material attention and screen choice is regrettable.
904L stainless steel is a premium material with excellent corrosion and durability resistance, ensuring quality for long-term use. Perlinger leather is genuine leather you can enjoy aging with, so there are few quality concerns. Initial firmware touch operation issues have been resolved through updates, showing commendable manufacturer support. However, at 616g, impact from drops would be significant, so careful handling is essential.
616g weight is clearly unsuitable for pocket carrying. This suits a lifestyle of "stationary portable" use in desktop environments. If you're considering commute use, you should explore other options. Also, Google Play app compatibility issues may cause inconvenience if you frequently use streaming services in your daily routine.
Negative Review Summary

Dr. Bravo
Summarizing the Boo analysts' findings, the SP4000's main theme revolves around questioning its "portable" designation. At approximately 616g (21.7 oz), it redefines the concept of portability. Software challenges like limited EQ functionality and unstable app compatibility are also evident. Some users feel a gap between their expectations and the actual user interface and display choices, given the $4,600+ price point.
What People Are Saying
BooLab Survey: March 1, 2026
Not Recommended For

Dr. Bravo
Those wanting to carry it daily in their pocket
Users who want detailed equalizer adjustments to customize sound
Those expecting full compatibility with all Google Play apps
Users prioritizing vibrant OLED screen quality
Anyone expecting perfect completion for a nearly $5,000 investment
BooLab Picks Just for You
FiiO M17
¥271,972Android OS with equivalent expandability at approximately $1,500—less than one-third of SP4000's price. THX AAA-788+ amp provides high output capability. Weight is nearly identical at ~610g, but optimal for those prioritizing cost-performance.
Go to Purchase PageAstell&Kern SP2000T
¥1,188Same Astell&Kern brand with unique vacuum tube amp. Weighs ~450g—lighter than SP4000 for easier portability, priced around $3,000. Perfect for those seeking the warm sound character of vacuum tubes.
Go to Purchase PageA Different Perspective

Dr. Bravo
However, this weight and size are actually proof that "desktop-level sound quality has been made portable." When considered as a desktop audio alternative, it's actually space-saving. App compatibility issues become irrelevant if you view it as a dedicated music player. The limited EQ functionality could also be seen as confidence in the pure sound quality. Many issues have been improved through firmware updates, showing commendable manufacturer support.
Recommended For

Dr. Bravo
Those wanting desktop-level sound quality in their desk environment
Audiophiles who appreciate premium materials and craftsmanship
Users pursuing the "pure sound" that faithfully reproduces original audio quality
Those wanting to leverage Android OS expandability for streaming services
Serious enthusiasts who spare no expense for ownership satisfaction and sound quality investment
Convinced After BooLab's Analysis?
Choose with confidence, backed by thorough analysis

Dr. Bravo says
After reading BooLab's thorough analysis, there's no need to hesitate. Go ahead and choose with confidence!

Astell&Kern A&ultima SP4000 Silver
Astell&Kern
Boo Trends (Weekly)
Trend graphs will appear as weekly digests accumulate.
More Boo Reviews in Audio
Soundcore P40i

The Soundcore P40i is a standout model that packs an astounding 60-hour battery life and Ultra Noise Cancelling 2.0 into a sub-$100 price point. With IPX5 water resistance, wireless charging support, and four color options, it offers a surprisingly comprehensive feature set for this price range. The ability to get 5 hours of playback from just 10 minutes of charging is particularly reassuring for busy modern lifestyles.
Dyson OnTrac™ Headphones CNC Copper (WP02 BB)

The Dyson OnTrac™ boasts industry-leading noise cancellation up to 40dB and an impressive battery life of up to 55 hours. With a wide frequency response from 6Hz to 21kHz and customization options through the MyDyson™ app, it's quite an appealing package. Plus, you can personalize the look with interchangeable color-customizable parts—very Dyson! For long commutes or focused work sessions, this could be a reliable companion.
nwm ONE

The nwm ONE is a product in a new category: an open-ear overhead speaker. With 12mm and 35mm 2-way drivers, it delivers spacious, high-quality sound without blocking your ears. The lightweight 185g body offers up to 20 hours of battery life—quite impressive! PSZ technology suppresses sound leakage while still letting you hear your surroundings, making it perfect for working from home or extended listening sessions. For those seeking a new musical experience, this is a truly innovative choice.
Popular Boo Reviews
Nintendo Switch Software Tomodachi Collection: Exciting Life

The latest entry in the 'Tomodachi Collection' series is coming to Nintendo Switch after approximately 12 years. This unique simulation game, where you create Miis of yourself, friends, and celebrities and watch their carefree lives unfold, has captivated many fans over the years. With enhanced graphics leveraging the Switch's capabilities and improved online features, this is an exciting title that blends nostalgia with fresh new experiences.
melt Deep Shampoo

melt Deep Shampoo is a professional-grade shampoo formulated with the maximum amount of deep repair ingredients in the line, designed to address accumulated damage from repeated coloring and perming. The appeal lies in its nano-penetration care formula that delivers repair ingredients like Melty Ceramide, hydrolyzed keratin, silk, and collagen deep into the hair. The sophisticated Water Lily & Wood fragrance uses carefully selected natural essential oils from around the world, including Egyptian geranium and French clary sage. With a generous 480ml capacity and refill options available, it's a commitment-worthy choice for long-term hair care.
THE TANSAN

THE TANSAN is a strong carbonated water brand developed by Coca-Cola Japan, particularly focused on carbonation strength. It features a label-free design that's environmentally conscious and eliminates the hassle of label separation. Being sugar-free and zero-calorie makes it popular among health-conscious individuals and those on diets. The variety of flavor options, including lemon and lime, is also attractive. It's a reliable brand with a solid share in the carbonated water market.
in Jelly

The biggest appeal of in Jelly is undoubtedly its overwhelmingly convenient '10-second charge' concept. The design allows you to simply open the pouch and squeeze to quickly replenish necessary nutrients and energy—truly convenient for busy modern people. The diverse lineup that handles various situations like before and after exercise, during study sessions, and busy mornings is also attractive. The abundance of options you can choose based on your purpose—energy replenishment, vitamins, minerals, protein—really showcases Morinaga's development capabilities.