Geddes multiple subwoofer method - 3 subs vice 4

Dear @deep_333 : " " Not true...depends on what you get...I use 8 of the acoustic fields ACDA panels ....clean down to 30hz. ""

Problem with room treatment and especially in the bass range because its main importance is that " clean down to 30hz ". First question could be at which frequency starts to " clean " and if exist in room measurements of frequwency response with and with out those kind of panels. Always is important not only what we are avoiding with but what we are losting with, obviously always exist trade offs and depends of each one of us what kind of trade off we are ready to take. Other alternative is something as the C20 electronic bass trap that operates between 15hz to 150hz :

 

AVAA C20 - Active Bass Trap - PSI Audio

 

I don’t have a dedicated room/system and when I had professional room treatments ( several kind of through the years. ) I really never been totally satisfied with. At random with the stuff in my parlor as wool carpets and the kind of the parlor furniture and treatment diffusors and curtains and mainly to the subs position I’m lucy enough to stay really satisfied as ever with no apparent troubles in all the room/system frequency range quality level reproduction at diffrent S¨PLs and different kind of MUSIC.

In the other side and about the ported loudspeaker still today is what almost all top manufacturers use it and the customers jut buy because there are not to many sealed/acoustic suspension speaker alternatives. Even Wilson uses ported.

For subwoofers I totally agree: must be sealed not ported.

 

R.

 

Dear @deep_333 : " " Not true...depends on what you get...I use 8 of the acoustic fields ACDA panels ....clean down to 30hz. ""

Problem with room treatment and especially in the bass range because its main importance is that " clean down to 30hz ". First question could be at which frequency starts to " clean " and if exist in room measurements of frequwency response with and with out those kind of panels. Always is important not only what we are avoiding with but what we are losting with, obviously always exist trade offs and depends of each one of us what kind of trade off we are ready to take. Other alternative is something as the C20 electronic bass trap that operates between 15hz to 150hz :

I don’t have a dedicated room/system and when I had professional room treatments ( several kind of through the years. ) I really never been totally satisfied with. At random with the stuff in my parlor as wool carpets and the kind of the parlor furniture and treatment diffusors and curtains and mainly to the subs position I’m lucy enough to stay really satisfied as ever with no apparent troubles in all the room/system frequency range quality level reproduction at diffrent S¨PLs and different kind of MUSIC.

There are all kinds of guys making things too confused on different threads...

- Basic physics - standing waves/peaks/nulls occur between 2 parallel walls...Ya "effectively" absorb on those 2 parallel walls just as it pertains to your listening position to mitigate it....and leave the rest of the walls alone for absorption (i.e., don't suck the life out of/kill the room). Get the Harman room mode calc and plot your room modes, for starters. I am not concerned about what happens anywhere else in the room, no corner crap nothing.... I am only concerned about my main listening position. For example, It's a li'l strange to me when i see guys put a bunch of crap in the corners and all over the place as if they are hanging around/dancing around in a corner. I "effectively" absorb down to 30 hz with my  ACDA panels on the front wall, back wall, left wall, right wall for my primary listening position (modes check, sbir check). Yes, they are 16 inches thick and weigh 220lbs each for a reason. I use a couple of different lighter panels on the ceiling for the same purpose and to take care of some floor/ceiling bounce issues.

- That's it...no more absorption...Everything else i use is diffusion (first reflection, ipsilateral, contra, etc, whatever to boost perceived resolution, detail, spaciousness and so on for the listening position)

- I don't usually put subs on the front stage for show...Refer to the harman paper - virtual sub principles, especially If restricted to 2 subs (very few people set up more subs than 2)  Reading the results of a room mode calculator will guide you more on placement for the same purpose. In fact, you can mitigate a certain amount of modal issues with multiple subwoofers, placement and phase adjustment (a bit trickier to do), except only up to the crossover point of the subs...For something higher, you would need absorption.

In short, follow the physics...and when you do, you may rejoice/float around in a uniform warm womb of bass....the core foundation for jawdropping sound.

 

@rauliruegas wrote:

Velodyne ( at least my HGS, not the DD models with Kevlar driver. ) were made for MUSIC sound reproduction systems and not HT where needs are different and especially on SPL.

Velodyne, REL and whatever else don't hold a monopoly on bass reproduction that's especially suitable for music. Subs that are deemed mostly that are usually too small to be an effective Home Theatre equivalent, and so they're really only good in the context of music reproduction at less than elevated SPL's. Home Theatre subs tend to be bigger (sometimes much bigger), for good reason, but the popular crux appears to be that many of them are ported variants. Whether ported or sealed is not the issue for me, but rather overall design execution and adherence to physics; both principles can deliver very good bass performance, but being sealed subs are usually smaller I'd wager they're winning the most hearts.

Therefore, as you can surmise, I don't buy into the music vs. HT subs distinction. Look at the DD18+ review and the section quoted by you. Obviously it's very good at HT duties in addition to music, so the two are not mutually exclusive - it's about having enough effective cone area to cover both bases, and moreover added cone area and higher efficiency equals lower distortion and a cleaner, more effortless bass. Win-win. 

Speaking of which: sealed or ported are only two ways to go about it. Some prefer open baffle iterations, while I myself opt for horn-based subs. Horn subs don't suffer from low efficiency or port noise, and with tapped horns in particular the horn itself does the heavy lifting, not the driver. High efficiency into the lower octaves means a very large air radiation area, and thus very little cone movement (especially from TH's, which have excursion minima at the tune) - even at prodigious SPL's. This is both the most musical, smooth, effortless and naturally full bass I've heard, and as well the most visceral, indeed downright scary powerful bass for movies to boot. The catch: they're large. 

Dear @deep_333  : I agree with you in everything and specially in " I am only concerned about my main listening position. ".

My 2 subs are rigth at the front stage side looking each to other: the drivers sound reproduction  does not goes " direct " to me as the sound from the main speas.kers.

My room is an inverted L with two parlors ( first smaller one ) in the second and main parlor is where the speakers/subs are seated in front of my listening position. Exist a left side wall behid de left sub but the rigth side sub has not a direct wall because there is is the dining room a big one with wood furniu.ture.

Through several months maybe over 1 year I tested every imagined subs positions and was exactly where are seated today what works in that room/system. 

Even that I can be seated at 4m. from the speakers my prefered and day by day listening sessions are at 2.5m ( around ).

 

R.

My room is an inverted L with two parlors ( first smaller one ) in the second and main parlor is where the speakers/subs are seated in front of my listening position.

@rauliruegas , An L shaped room makes things a bit more complicated on the sim domain. Talk to an integrator. It is hard to write technical essays on a thread. Nevertheless, the harman room mode calc will still work between any 2 parallel walls in that room.

Google harman room mode calculator. You would enter your room dimensions to determine where the hell all the strongest nulls/peaks are. The results would look like this....

 

Here’s another way to visualize it....(top view, scratch rough sketch)....Also how you deal with nulls and peaks. Goofy bass is all a guy hears unless he does stuff like this. (Basic Physics - Standing waves/nulls/peaks occur between parallel walls). This again shows you the advantage of larger rooms. The smaller the room, the harder it gets to deal with this.

 

Here’s some expansion on what i was trying to describe with the Harman virtual sub principles. By strategic placement of subs, you can get rid of many of the strongest peaks/nulls upto the sub’s crossover frequency. For nulls/peaks occurring at frequencies higher than the sub’s crossover, you have no other choice but absorption.

In short, you can use subwoofers to REMOVE nulls/peaks. It is not just for giving some oomph on the low end for a flaccid speaker.

 

 

If you had 4 subs, this is how you would place them and phase adjust them to get rid of the maximum number of the strong nulls/peaks in light of the above mentioned principle (up to the sub’s crossover point).

sub 1: 1/4 lengthwise, 1/4 widthwise position

sub 2: 1/4 lengthwise, 3/4 widthwise position

sub 3: 3/4 lengthwise, 1/4 widthwise position

sub 4: 3/4 lengthwise, 3/4 widthwise position.

 

If you only have 2 subs,

sub 1: 1/4 lengthwise, 1/4 widthwise position

sub 2: 3/4 lengthwise, 3/4 widthwise position.

 

Same principle works for the room’s heightwise modes. You ever heard of guys lifting subwoofers off the floor to the heightwise modal points? That is the reason and the physics behind it.

The idea is to tackle the max number of strong nulls/peaks with sub placement...and then use absorption to deal with the rest (modal nulls/peaks/frequencies higher than the sub’s crossover). It is also a very very good idea to get subwoofers with a variable phase knob (not just a 0/180 phase switch). Rythmik is a good example of subwoofer brands that give you a variable phase knob.

 

Everything else should be diffusion so you don’t kill the room with absorption all over the place. Focus only on the main listening position.

Hope that helps you...and some of the other confused guys here...