Geddes multiple subwoofer method - 3 subs vice 4

@rauliruegas wrote:

That’s why THD in the bass range is just so critical due that high THD levels as the JTR ( that are for HT not MUSIC: ) subs afects all the whole MUSIC frequency range system due that the different bass frequency ranges develops harmonics that has direct influence in the midrange and from here to the HF range.

True, but..

You are fine with that 5%-10% on THD and no problem with me, it’s only that’s way to high in frony/against the 0.5% at 120 db in the Velodyne.

Let’s get real - there’s no magic bullet here. According to the Audioholic’s review a single Velodyne DD18+ won’t even reach 120dB’s; it runs out of steam just above 115dB’s - at 50Hz and ~7% distortion. At 20Hz it’ll do some 103dB’s with a distortion level going well beyond 20% at this output. By all accounts these are very respectable numbers for a sub this size, but after all - it’s just physics and their limitations. What you’re referencing (i.e.: 120dB’s with no more than 0.5% distortion) is close to impossible with anything other than a truly gigantic subs system that wouldn’t fit anywhere practically.

You want low distortion in the lower octaves at higher levels you need much more displacement, and in effect efficiency and size. No technological trickery with small, low eff. cube subs will do that, unless multiplied in significant numbers at a very hefty price tag (unless it’s a DIY approach). Go high efficiency with 2-4 large boxes (likely also DIY) on the other hand is another matter.

So, lower distortion in the bass area is very important indeed, but to get there there’s no way around what I just specified above. Few however are willing to do what it takes, if they even realize it. Instead they resort to finger pointing and calling the likes of stacked sub towers flanking main speakers for being "overkill" and what not, thinking their puny and expensive cubes are all what it takes. If only they knew..

Excerpt from named review. 

Velodyne specifies that distortion is held below 0.5%THD during normal operation by the servo system. Perhaps it is but what is “normal” operation? Probably rather modest playback levels without much deep bass accounted for. Any subwoofer system I have ever measured the distortion for or seen test results for has had distortion that rises dramatically in the deep bass frequencies when the system is pushed towards its upper output limits. This is due to the increased demands for air displacement from the driver, passive radiator, ports or all of the above as the frequencies get lower.

@audioquest4life wrote:

I feel like the Geddes approach for sub integration closely resembles what I have been doing for years without even knowing this method. So, my 18” deep bass and 15” mid bass drivers on the field coil speakers become part of the solution instead of being taken out of the equation. That’s what I have been doing and that’s what I thought sounded best to me. Multiple ways to do sub integration but this method is the one that pretty mirrors how I have been doing it for years.

For your 15" and 18" woofers to have the "Geddes effect" they'd have needed to be properly spaced apart, and not placed in the same pair of speakers. What you can do however is using your no doubt great Classic Audio Loudspeakers in their intended full-range mode as two bass sources, and then add two subs placed along the opposing wall or side walls for a 4 bass source DBA. 

Good video on it. 
 

My subwoofers offer high pass connectivity and filtering. The manufactures instructions suggests:  

If your main amplifier has difficulty driving your main speakers bass to your satisfaction then give the subs high pass circuit a try.

If your main speakers are small and lack bass then give the subs high pass a try.

I love the way my amps drive my speakers low bass. A few of my older LP's simply sound better with the subs off.

Since these subs multi parameter, frequency band auto optimization does so well matching the speakers low frequency presentation, high pass filtering is noticeably wasted. Surprisingly, this decade old twenty minute optimization software quickly and easily solves much of todays hifi subwoofer setup and integration issues.     

Dear @phusis : 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.

The Velodyne aceleromete/servo ( patented. ) avoid that THD can goes over 0.5% and when it’s approaching that figure power gone lower but not the bass frequency.

I never had a problem with my HGS and maybe because my main speakers has 95db efficiency but I measured at my seat position ( near field. ) 97db SPL with peacks at around 105db and the bass range is fabolous.

I readed other reviews on the DD models where what you read it did not happens but at the ned the critical subject is to mantain ( for listen MUSIC not HT. ) the THD at minimum in the bass frequency range. This is the why of my post more than about thisor that sub.

In your link review we can read this ( HT ):

" 

Batman Begins followed by the Dark Knight, both of which offer not only a very powerful and engaging audio track but also are enjoyable movies to watch. The master volume was set to -15 for the entirety of both films.

Throughout the various action and dramatic sequences of the films the DD18+ provided a stellar performance. Subtle background bass undertones were just that and when demanded the DD18+ provided a lot of power and room shake. On sections that contained deeply extended bass the DD18+ had generous extension that provided an extra feel or size to the sound that lesser subwoofers simply do not. As previously discussed the performance of the DD18+ as far as definition and ability to track notes is excellent. If there was any small caveat to the DD18+ performance it might be that it was not quite as sharply dynamic on a few parts as I recall they can be, the tumbler chase scene being one example, the gatling gun test, bankers shotgun blasts and the hospital explosion being others. My large listening room acoustics are such that it is very difficult for a single subwoofer, even a very capable and powerful one such as the DD18+, to handle alone so perhaps the DD18+ was being limited a little on a few extremely loud sections. Audio memory is a hazy thing at best so I can’t be sure and to be quite honest I’m stretching to find even that small caveat with the DD18+’s audible signature. It is that good. What I can be sure of is that the DD18+ always sounded composed throughout and easily produced one of the top performances that I have experienced from a single subwoofer in my room. Very deep bass was presented with apparent ease and fundamental tones or pitches of bass transients were spot on.  "

Not so bad as those measurements and the reviewer seats one DD-18 at 4 meters from his seat position, not near field.

R.