Subwoofer recommendation for Dynaudio Confidence C4

     I'm thinking of adding 2 subwoofers to my Dynaudio Confidence C4. Leaning towards REL S/5 pair. Is this the right choice for Dynaudio?  Do I need 2 sub's? Does anyone see any issues with this setup? My AMP is Bel Canto e600 Mono block.
I own a set of C4 signatures and use a REL R-528.  It’s quite sufficient.  If you do end up using 2 subs, you may face some challenges with getting them phased and integrated properly, key word being “may.”  I use a DEQX to get the alignment for the sub and C4’s.
2 subwoofers offer better room and system integration. You get better seat-to-seat consistency, less peaks and dips, less localizability, deeper extension or louder output, etc.  
REL sub’s are a bit over-rated.  
If you don’t have bass mangement (dedicated subwoofer out), and this either need to use REL’s Speakon method or XLR passthru, look at something like a pair of Neumann KH 805’s or a pair of Rythmik E15’s with the H600XLR2 amp option (if you want a nice looking subwoofer, Salk will build you the kit version of the E15 in whatever finish you want, plus they make the cabinet thicker and improve the internal bracing, so it also performs better, just specify you want the H600XLR2 amp, this will of course have a wait time as they have to make it).

We agree with you totally about having dual subs. Disagree with your comments about Rel.

Rel makes some of the best woofers on the market known for speed, accuracy and integration. The exact model mentioned received a rave review from TAS.

Salk makes decent speakers using other peoples drivers. Rel or JL Audio
design from scratch everything, this generally means a better performing product.

The Salk product is very impresive in terms of weight, however a well constructed box doesnt need to be that heavy and for music servo woofers can often times be considered slow.

The only issue with Rel is that there is competition from JL and Paradigm is coming on strong with some unbelievable models. Paradigms better woofers come with the Perfect Bass Kit a version of Anthems Room correction system tailored for bass. The Perfect bass kit allows for sophisticated room tuning for flat, tight bass in room.

Dave and Troy
Audio Doctor NJ
JL Audio makes outstanding subs. Are you going to use the high pass filter option ? If not the Dominion model will work just fine with those speakers!

     It sounds to me like your system is for music only, no ht duties.

     If so, you're probably only concerned with good bass response at your listening position and don't require good bass response throughout your entire room.

     The Audio Kinesis Swarm 4-sub system, that I linked an Absolute Sound review of, is what is called a distributed bass array that provides sota bass response throughout the entire room in virtually any room provided the progressive locating procedure for each of the 4 subs is followed. 
     This system utilizes a 10" long-throw woofer in each of its rather compact cabinets(2 x2 x 1 foot).  It's ideal for music, since each sub is providing only a portion of the total bass, it's capable of both taut and tight bass and deep and powerful bass that is felt as well as heard.  This also allows the system  to possess large reserves of power for impressive bass dynamics. 
     It is true that 2 subs will provide better bass response than 1 sub and 3 will perform better than 2.  However, 4 subs properly positioned has been scientifically proven to provide the best in-room bass response.  This results because 4 sub distributed bass arrays reduce or eliminate the vast majority of bass standing waves in virtually any room which, in turn, reduces or eliminates the vast majority of bass room modes (spots in the room of bass exaggeration,  attenuation or cancellation) throughout the entire room.
     So, it's basically your choice; is very good bass response at your listening position sufficient or do you prefer very good bass response throughout your entire room?  Cost is really not an issue since the 4 sub AK Swarm system (including 1,000 watt sub amp) is priced about the same or less than 2 very high quality subs ($3K).


Rel makes some of the best woofers on the market known for speed, accuracy and integration.
I don’t disagree that they make well performing subs, just that there are equally performing subs for cheaper
Salk makes decent speakers using other peoples drivers. Rel or JL Audio design from scratch everything, this generally means a better performing product.

Disagree. It may mean their costs are lower as they don’t need a middle-man, but that doesn’t mean they make better sounding drivers than RAAL, SEAS, Scanspeak, etc. if the drivers are well performing, the crossover is well designed, the cabinet is inert, etc. who cares if the drivers are a third party, as long as the end result is good. There have been some “showdowns” between different equally priced speakers that included a Salk speaker, and everyone I found ended up saying the Salk sounded the best, including ones that were blind testing. I’m not saying they make the absolute best for the price hands down, but the certainly are up there.  

for music servo woofers can often times be considered slow. 

Untrue, at least for Rythmik (who Salk uses). Look up measurements, their subs usually have impulse response that is fast and clean, group delay is below 1 cycle, well controlled decay, etc. They are very tight and fast subs, even their ported models.
Look at a pair of 18.0 or 21.0 from Funk Audio. Nathan can match the finish of your C4. 

If you don’t care about finish that much, may want to look at JTR S1. 
I took over a year to decide on my last speaker upgrade, the Dynaudio's were "finalists" in my search, eventually bought a then brand new model, a pair of Focal Sopra No2's.  IMO both these speakers' bass response is good, for as low as they go, but IMO there's no speaker in that price range that can truly compete with a great sub woofer in the low bass region.
I compared the JL Audio F112V2's with the F113V2's and chose the latter.  IMO, the F112V2's might have been a better match for a pair of stand mounts, as they go higher up in the bass range than their larger brother.  But with the bass that both the Dynaudio's and the Focal's produce, either model would contribute a lot to the final sound.
As for going with a pair of subs (that's what I did), there is something "visceral" in the musical experience when a low bass sound is coming predominantly from one channel or another.