Rel Acoustics No.25 Subwoofer Listening Demo Results

Long-time subwoofer manufacturer Rel Acoustics has decided to bring something special to the market in 2017. To commemorate their 25th year as a subwoofer manufacturer they’ve launched a new flagship in their ‘No.25.’ subwoofer. The No.25 is the new top dog in their Reference line, which is their highest-end product series. The No.25 is a sealed subwoofer using a 15” woofer, but to describe it as plainly as that is like saying the Bugatti Veyron is a car that uses four wheels. There is quite a bit more to the No.25 than base specs. Yes, it is a sealed 15”, but what a sealed 15”!

Design Overview

Let’s begin with the cabinet. This is a massive sealed 15” sub with an enclosure volume larger than some 18” subs on the market. It uses width and curvature to its advantage to not seem like a behemoth. It is a large sub, but it doesn’t look as large as it really is. However, this is not to say that it will go unnoticed in a living room, which given its size, would be impossible. In order to make such a large subwoofer aesthetically palatable, Rel has given it an exquisite shape and finish, a trait that Rel is known for. The No.25 uses a backward curving cabinet for a sleek and elegant appearance, and it does remind one of a high-end sports car. The paneling is a substantial 1.2” thick with bracing that Rel claims is like the spars in a ship’s hull. This likely comprises most of the No.25’s titanic 168 lb weight, but over-building is all a part of making the highest-end subwoofer that a high-end subwoofer manufacturer can make.

Another part of the equation of making a high-end subwoofer is the driver. The cone is made from a high-grade carbon fiber, which has a great combination of being both stiff and light-weight. The 15” cone is a healthy diameter size, but a large diameter woofer doesn’t necessarily guarantee that a lot of displacement is available. However, with a 4” peak-to-peak stroke, the No.25 can move a tremendous amount of air.

Having a lot of air displacement is nice, but the mark of a good subwoofer is how precisely it can move that air. Towards this end, John Hunter, owner of Rel, told me that their design team worked very hard at getting the internal geometry balanced. Rel subs use ultra tight gaps and precision aluminum formers so they have very little room for error. The attention to detail that Rel has for the No.25 is very exacting. One example is the lead-in wire and how to route it.  Hunter says,

“There is exactly one company that can do lead in wire for a project of this caliber and it takes tremendous work to keep the wires attached because the acceleration forces on large transients can literally leave the wire behind.”

As with displacement vs precision of air movement, a good driver is essential, but it is nothing without power. On this Front, Rel has supplied the No.25 with a beefy 1,000 kW advanced class D amplifier that they have called a NextGen3 design. This amp is loaded with connectivity and control. For connectivity, the No.25 can accept high-level Neutrik Speakon, line-level stereo RCA inputs, LFE input of both RCA and XLR, and it also has a wireless adapter. Daisy-chaining subwoofers is made easy with the Speakon and LFE outputs. The No.25 has two parametric EQs that can be set at any frequency from 20 Hz to 90 Hz that can boost or cut the signal by 6 dB. A digital display in the front of the sub allows you to see the changes being made all with the use of  Rel’s remote control. The remote control is a luxury statement unto itself, with a carbon fiber face-plate and a stainless-steel body.

Demo Results

The No.25 are made to be easily stacked for a ‘line-array’ of subwoofers, in case just one does not suffice the user’s craving for bass. I took an opportunity to hear a “six-pack” of No.25 subwoofers at Joseph Audio Video Solutions, Inc in Midlothian, IL recently (not to mistaken for the loudspeaker manufacturer Joseph Audio, by the way). The overall sound was stellar, which is what one might expect from high-end Dynaudio speakers run from top-of-the-line Mark Levinson electronics. But the subs stole the show. The bass was refined and precise yet almost physiologically-damaging in output capability. Joseph Hesse, the proprietor, walked me through some demo music including the popular demo piece for audiophile bass, Chris Jones’ “No Sanctuary” with its deep bass guitar and baritone chorus, and Yello’s “Planet Dada” with its pinpoint-sharp electronic bass line. Bass was felt as much as it was heard, and the physical sensation of each note was as distinct as its sound. Joseph also demo’d some movie content, and we viewed the bombastic finale of Cher’s 2010 musical “Burlesque”, that, on a system like that, proved to be sensory overload. The whole experience was a lot of fun.

The Rel No.25’s are pricey subwoofers at $7,500 each, but if you want something that packs as much build quality and technology in a gleaming package like the No.25’s, it cannot be done inexpensively. Although, the high price of entry affords one the pride of ownership of such a finely-crafted device. Have you heard these subwoofers yet? If so, share your experiences in the related forum thread below.

Unless otherwise indicated, this is a preview article for the featured product. A formal review may or may not follow in the future.