Synergistic ResearchFEQ X4 - Frequency EqualizerusedSynergistic Research FEQ X4 - Frequency Equalizer - trade-in unitThis unit is a trade-in. It has a few light marks on one side. Can only see it close in a bright light (I tried to take a photo, but it doesn't show much). It is for 120V and comes with original bo...495.00

Synergistic Research FEQ X4 - Frequency Equalizer - trade-in unit [Expired]

no longer for sale

This unit is a trade-in. It has a few light marks on one side. Can only see it close in a bright light (I tried to take a photo, but it doesn't show much). It is for 120V and comes with original box, grounding plug and power supply with US-Plug. 

The FEQ X4 dramatically improves upon the original single antenna FEQ with 4-large broadcast antennas for a full 360-degree immersive experience. 4 times the antenna and 8 times the power of the older FEQ generation. 

This is SR’s ultimate set it and forget it acoustic field generator and is perfect for people who want increased performance from their audio systems and SR products with UEF Technology but without the complexity of the iPad controlled Atmosphere. Moreover, while the FEQ X4 is larger than the original single antenna FEQ it’s still small enough to hide in furniture, behind drapes and sofas, or in bookcases for the ultimate in invisible acoustic control.

FEQ X4 is a single channel ULF (Ultra Low Frequency) RF pulse generator that acts as a low-frequency dither to overpower the ambient RFI and EMI fields in your listening room broadcasting over (4) separate channels for a more immersive experience than was possible from the original single and smaller antenna FEQ. In addition to acoustic benefits, it also improves the performance of all SR products with UEF Technology. UEF Tech responds to specific ultra-low frequencies so your Core UEF, Atmosphere X, and Galileo SX cables perform better, along with your HFT’s and UEF Acoustic Panels. Even Tranquility Base UEF component platforms and Black Box low-frequency resonator arrays perform with noticeably increased levels of performance when excited by the strategic ULF signal generated in a 360-degree wave pattern from the new FEQ XL4. Dimensionally the chassis and antennas were extended from 7″ to 14″ giving the FEQ X4 approximately 8x the broadcast strength of the previous generation FEQ with a 360-degree radiation pattern to the original’s 180-degree pattern so placement is less critical while overall performance is increased.

To use, plug the FEQ X4 and its internal Ground-Plane into two separate wall sockets in your listening room and place behind and between your two main speakers or where ever you find space. Then turn it on for an immediate and unmistakable improvement in sound. One FEQ X4 will improve an average size listening room with a greater sense of clarity, a lower noise floor, and more natural harmonics.

Dimensions - 14" tall (Base 4.1" wide x 4.1" deep)

Atmosphere Tuning Module (ATM) sold separately

Global MSRP - $995.00

Order today:

Reviews and Award for the first generation FEQ:





Michael Fremer, Stereophile, Feb. 2015:

"...after listening, I pulled the FEQ’s plug and listened again. Damned if the stage didn’t narrow somewhat, and lose a bit of the vivacious depth and retrieval of ambiance I’d heard with the FEQ plugged in. It just sounded more spacious, and especially more transparent, with the FEQ plugged in. So I plugged it in again..."


Michael Girardi, The StereoTimes, Dec. 2014:"...the largest component in one’s system is the listening room yet it the one component that is commonly overlooked and misunderstood. The HFTs are tiny high frequency transducers that clean up high frequency harmonics in your listening room by cancelling the harmonic noise generated by room resonances. The FEQ is an ultra low frequency RF pulse generator that acts as a low frequency dither to overpower the ambient RFI and EMI fields. The combination of the FEQ and HFTs has made the biggest improvement in my system’s performance since I been reviewing high end audio components over the last 11 years. Considering the physical size of the HFTs and FEQ as compared to all other room acoustic enhancement devices and their comparative performance, the FEQ and HFT resides in the best in class category for room acoustic treatment. From an ergonomic and aesthetic standpoint alone they are revolutionary in the application of room acoustic enhancement. Happy was the day I removed my previous reference room acoustic treatments and replaced them with the FEQ and HFT’s (and it wasn’t a secret that my family felt the same way). The combination of the FEQ and HFT is a paradigm shift in room treatment device design and delivers on its promised performance..."



Steve Plaskin, Stereophile’s, Oct. 2013:

"...I have never heard anything that was as effective in elevating the performance of a high end system as the combination of the Synergistic Research HFT and the FEQ... soundstage, noise floor, bass detail and dynamic power, midrange and high end clarity all improve with the use of these products... the Synergistic Research High Frequency Transducer and Frequency Equalizer will become a permanent part of my audio system. Removing these components is simply unthinkable given the quality of the sonic enhancement achieved with their use..." Check out the entire review


Customer Feedback:

"...I had no idea how imbalanced my listening room was until I plugged this bad boy in! Words cannot describe how linear my system now is. Bass definition is unreal, instrument separation is very life live, and voices are scary real, with amazing focus and sound staging! Very very happy with these and the HFTS!!!"

" FEQ and 3 packs of HFTs completely transformed my room creating the listening experience I’ve been looking for a very long time. While a lot of upgrading of components and wire over the years improved the quality of sound, the HFTs and FEQ have created a realistic 3 dimensional soundstage, with more inner detailed revealed and a profound overall improvement in listening enjoyment..."

"...picked up 3 HFT 5 pacs (15 HFTs) and an FEQ at Rocky Mountain and just wanted to let you know how wonderful my system now sounds... there’s a Betsy Larkin track playing and it’s as if she’s singing in my living room. The clarity now rivals my headphone rig, no shit. Anyway an amazing product that has whetted my appetite for more..."

"...they [FEQ & HFT] really souped up my system dramatically there was no accessory that I bought ever made this level of improvement..."

Big improvement for your system and your listening room!

- Actively enhances system performance and room acoustics

- Lends weight and definition to low frequencies

- Dramatically improves high frequency air and refinement

- Improves mid-range palpability

- Significantly expands soundstage layering

- Multiplies the benefits of HFTs in system and room

- Like a Tranquility Base for your listening room

- Unconditional no-risk 30-day money back guarantee

- Available for 120V and 240V

- $995 international retail price

As a business we have to collect 8% TAX from buyers in California.


member since December 2004

HighEnd Electronics  Verified Dealer

Last 12 months
Items from this seller