Choosing Sub-woofers. Please advise ASAP.

"A full range speaker should sound better with a smaller sub by virtue of its FR and the fact that it’s producing decent bass on its own already. Conversely, a small speaker should benefit from a bigger sub to cover a wider range."

It doesn’t work that way. Here’s the "old school" principles:

Smaller woofers/subs are TYPICALLY more limited in extreme low frequency output than larger woofers/subs. Since the presumption is that the OP has "full range" speakers already and wishes to further enhance the ultra-low bass output of his system, the larger woofer/sub SHOULD go lower, providing more ultra-low frequency enhancement, all things being equal.

Further, if the OPs "full range" speakers already have a strong mid/upper-low frequency output, adding a smaller (higher frequency output) woofer/sub will create boominess in that range (major overlap in the midbass). Worst of all worlds IME.

Conversely, a smaller woofer/sub should TYPICALLY be quicker and more tuneful in the mid/upper-low bass frequencies, thus easier to integrate with a "smaller" speaker, assuming that the latter’s low frequency output rolls off a significantly higher frequency than a "full range" speaker (minor mid/upper-low frequency overlap of the smaller speaker with the smaller sub’s higher output frequency). Ultra-low bass will not be enhanced as with the larger woofer/sub, but that is irrelevant if integration is poor.

Many potential exceptions to this are experienced in the real world as it depends heavily on the cabinet size/design of the sub, crossover adjustment flexibility, design (ported vs sealed), amplifier’s power/characteristics/ability to control the woofer, and placement. Also the newer concept of digital room equalization/correction built into the sub’s digital electronics (a’ la’ JL Audio and a few others) negates the "old school" rules to some extent, allowing a larger woofer/sub to integrate well even with smaller main speakers by tuning/contouring the sub’s output (increasing or reducing the output at certain frequencies based on system characteristics/room acoustics as measured by a microphone and processed by the sub’s digital circuitry).

Subs can also be used for entirely different purposes than "bass enhancement". I use two REL Stadium III sub’s fed via the high level inputs from my amp with the subs’ crossovers set to "out-of-phase" mode to cancel standing waves due to room bass nodes, actually reducing the perceived bass heard at my listening position, and to enhance the soundstage (by loading the room with sound pressure from the subs) as my main speakers need no low-bass enhancement, but actually the opposite in my room. Works quite well.

Dave

  Dave,

     Very interesting how you're utilizing your 2 REL subs set to 'out of phase' to reduce bass standing waves in your room.  I haven't heard of this  before.  

     You state that this has actually reduced the perceived bass at your listening position but, due to the subs loading your room with low frequency sound pressure and your mains ability to go deep, this has resulted in an enhanced soundstage at your listening position.  

     I'm not completely clear on this but, since it's working so well for you, I want to learn more about this method.  A few questions if you don't mind:

1. How did you decide where to position  your subs, through a set procedure or trial and error?

2.  Can you be more specific concerning the sound qualities that result in your perception that the soundstage  being enhanced?

3.. Did you set it up so bass is best at your listening position, or so bass is good throughout the entire room?  

Thanks,
  Tim
 
 

Hi Tim,

Glad to give it a shot.

What I said was that I use the RELs out-of-phase to cancel standing waves due to room bass nodes. The improvement in soundstage happens due to the sub(s) loading the room with sound pressure, either "in-phase" or "out-of-phase". Works both ways if your sub(s) is capable of true ultra-low frequency reproduction and the crossover is set properly (at the lowest crossover frequency setting in my case).

To set up the sub(s) for soundstage enhancement, adjust the crossover frequency and output levels so that the bass enhancement effect of the sub(s) can be felt but not heard. The best way to do it is sit in your preferred listening position and have someone turn the sub on and off (or use the remote if applicable) and adjust crossover and level controls until you don’t notice much difference in the bass level when turning it on, but the soundstage collapses somewhat when you turn it off.

I positioned the RELs by ear. Lots of time and moving the subs to find the best spot by trial and error. One trick for finding the best starting location is to place the sub where you sit and move about the room until you hear the sweet spot, then move the sub to where you were standing (or even better, squatting) when you found that sweet spot. If using two, do it again with the second while the first, already optimally placed, is on.

My experience is that it is impossible to place a sub where it will sound its best "throughout the entire room". You can certainly compromise for a good "all-around" placement but it will only perform optimally in one location in your room for a given listening position.

I hope this helps some. Let me know if not.

Dave

Hi Dave,

     Thanks for the explanation.

     The method you used, playing the sub at your listening position and then walking (squatting) around the room to find the spot where the bass sounds best and then locating the sub to that spot, is the exact same method in the distributed bass array system procedure that I used to place my first sub.

      Doing it again for the 2nd sub placement, while the optimally placed 1st sub is playing, is also the step#2 that I followed.

     However, I disagree with your statement : " You can certainly compromise for a good "all-around" placement but it will only perform optimally in one location in your room for a given listening position."

     I think you're correct if only 2 subs are utilized in the room.  The DBSA (distributed bass array system)'s use of 4 subs in a given room is the key and I found it has the remarkable and empirically proven affect of eliminating all bass standing waves in a given room.  The result is optimal bass response evenly distributed throughout the entire room.  

     The only reason your good bass is limited to a single optimum listening spot is because you stopped halfway through setting up a DBAS in your room.  I am reasonably certain that adding 2 more subs, following the exact same positioning method you used for sub# 1 and 2, will result in the very good bass response, that you're now enjoying only at a single optimal listening position, expanded to every possible listening position in your room. 

     I'm a huge advocate of the DBAS only because I use it and know how amazingly well it works.  It is a system developed by 2 PHDs in Acoustical Engineering, Dr. Gettis and Dr. O'toole, that is based on math and physics and been scientifically and independently proven to be effective numerous times in various rooms.  

     Their published White Papers on their research and experimental results state that as the number of sources of bass wave propagation (subs) in any given room increases,   the number of standing bass waves in the room decreases.  They mention their realization that there is a practical limit to the number of acceptable subs in any residential or commercial space.  

      In a crucial statement about their findings as it relates to home and commercial usage, they also stated that they discovered that a minimum of 4 sources of bass wave propagation (subs) are required to eliminate the vast majority of bass standing waves in any room tested in their research results with any additional subs only resulting in marginal improvements.  This is the reason  most DBAS utilize 4 subs.

     My opinion is that the above is critical information for the original OP, sautan904, to consider when setting up his new system. I'm not sure whether he understands  the info, believes it  or has just chosen to ignore it, however, since he has opted to go with just 2 subs.  My concern is that he doesn't realize the results are completely predictable and inevitable regardless of your room dimensions.  

      When he discovers his 2  sub system results in numerous bass standing waves and resultant uneven bass response in his room, the good news is it'll still be solvable by an extra couple of subs.  

Tim    

Nice to know Tim. Nothing like being set up by someone with an agenda to push posing as a real person with genuine interest in learning. Shoulda known.

I only listen from one position as I am only one person at any given point in time. As for having four subs, I am probably already in the extreme at having two. I am sure there are a few audiophiles that are able to overcome the expense and freedom from real-life constraints (WAF and such) that can or will take advantage of your recommendations. Bet you can count them on your fingers.

You can stop trying to solve the issue for the OP as he went a different direction. One more finger in reserve. Keep counting.

Dave