Geddes multiple subwoofer method - 3 subs vice 4

@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. 

@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.

@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. 

@rauliruegas wrote:

In general I like the immediacy of the MUSIC reproduced sound that’s a main live MUSIC characteristic.

+1

One " but " on horns ( at least to me ) is that I don’t like its reproduced sound seated at near field position ( say 2m. ) I think we need at least no less than 3m. and obviously that depends of the room too.

It depends on the particular horns (and amps) too. Auditioning the popular JBL 4367 monitors (which are somewhat smaller than my mains + subs system) I’ve found them too "hot" sounding over longer durations in being more forward and incisive in their sonic nature than my own system. To by fair, in many ways the 4367’s are delightful speakers; exhilarating, energetic, honest, clean, extremely informative (I’d say a wee bit too "insisting") and - apart from the low octave shifting towards a warmer imprinting - fairly coherent.

The thing is though, to my ears and sensibilities they simply become too much over time, and moreover I find string instruments like violins to have a slightly "plastic"-like and/or nasal character to them (I prefer the M2’s and 4349’s here with their flatter waveguide), which is a dealbreaker to me. My EV main speakers by comparison with their large format horns + subs are sonically more akin to large panel speakers; more relaxed, less "beamy," fuller and more visceral/physical/dense. Where it becomes apparent they’re a larger package overall, apart from their more natural height of presentation, is at higher SPL’s (not least with movies) where the sheer unadulterated force and power is at full display.

It’s what I’ve been saying quite a few times by now: typically, the larger the horn the less it sounds like a horn. Somehow though it goes contrary to what people expect of smaller vs. larger horns in thinking the latter will be too much for its own good in domestic environments (and they may be in smaller spaces), but often it’s the other way ’round and smaller horns sounding more agitated and "aimed" at the listener. Visitors, upon listening to my setup, have often been surprised at the presentation and that it isn’t intrusive or in-your-face. There’s no way around though that horns are more present and in a way more direct sounding with less reflected sound being part of what hits the ears.

At near field position my ADS are way better than horns or electrostatics.

I would expect that too. I’m sitting about 11ft. from my mains, and here they cohere and sum very well. The TH subs, flanking the mains in the corners, are carefully dialed in delay-wise through the Xilica DSP.

Unfortunatelly I never had the opportunity to listen a true horn subwoofer ( at least that goes to 16hz. ) but I tend to beleive you.

It’s an experience that’s difficult to explain. Those who’ve heard horn subs often find them to sound more convincingly extended than smaller direct radiating subs, even though the latter may extend deeper on paper. For horns to go below 20Hz very large size is required. Mine roll off below 25Hz, and below 20Hz there’s no information whatsoever - both due to the specific design limitations and that they’re high-passed below 20Hz (36dB/octave BW).

@deep_333 wrote:

What horn subwoofers do you use? DIY? or something else? I might be interested in getting one.

They’re the tapped horn principle, DIY and called MicroWrecker (a sibling to the LilWrecker tapped horn, which has a 5Hz lower tune for a 50% addition in volume (30cf.) and ~3-4dB hit in sensitivity). I got the plans over at AVS Forum from a developer there, and had them built by a cabinet maker. The developer also simulated drivers for the specific design in the Akabak (or Hornresp) software, and so had a range of suitable woofer choices to go with. These have to have the proper electromechanical parameters within a fairly narrow window in a given tapped horn design for them to work the best here, which is to say to properly resonate the horn; too weak a motor and the horn isn’t "excited" enough, and too powerful a motor will compress the air too severely at the throat, also leading to insufficient horn resonation. The B&C 15TBX100 (8 ohm) unit I’m using sits right in the middle of the desired performance window here, and so is close to the ideal driver for the purpose. Close, because it lacks the very last bit of excursion range to be fully exploited at its rated power (1000W nominal power handling, 2 hour pink noise test, free air) before hitting Xmax in this design with a ~23Hz tune, but it’ll take 600W up until that point, so perhaps a theoretical 2dB SPL subtraction overall. Fine with me, as a single MW will still do over 120dB’s down to 25Hz with the B&C unit, and I have two of them - corner mounted. The same driver is used in Danley’s TH-115 subs, but being this tapped horn design has a higher tune the driver can be used at full power here.

Size of speakers doesn’t seem to scare you off, but be aware it’s still a 20cf. volume per cab. When you see them "in the flesh" it can a bit unsettling getting a feel for their true size, I know it was for me at first. In the same ballpark there’s also great designs by Josh Ricci over at Databass.com, notably the Skrams, Skhorns and Othorns. The latter is also a tapped horn, though built around the 21" B&C 21SW152 woofer - a beast - and with a ~28Hz tune. Initially I intended to have a pair of the Othorns built, but the woofers were out of stock for months, and so I opted for the MW’s. The Skrams are a great design as well, and more driver "friendly" than the Othorn. Meaning, a range of 21" pro woofers can be used here, whereas the Othorns are only fully pleased with named woofer or its IPAL equivalent.

The inspiration for the MW’s were Danley’s TH-50 tapped horn, and they’re very much alike in vital areas. Josh Ricci opted to develop the Gjallarhorn tapped horns instead (also inspired by the TH-50), which is built around TC Sounds LMS-Ultra 5400 driver (18"), but that driver is no longer built. A beast of a sub, and about the most one can squeeze out of an 18" woofer, I’m told. They’re tuned a bit lower than the MW’s, but I never truly considered them as they are too monstrously sized (plus more than 300 pounds w/driver) and a bit hampered in their upper range due to the slightly lower tune.

In any case any of the above designs are extremely capable in putting out high quality bass at prodigious SPL’s and low distortion levels - certainly compared to most any low eff. "hifi" subs out there.

@deep_333 wrote:

appreciate the info you provided....I have a couple of rooms in my basement for audio (no WAF issues), 1 for multichannel and the other room for stereo. Size of speakers and subs is not an issue (bigger the better).

Interesting, so you could experiment with two different subs approaches (more on that below) with no restrictions in regards to size.

I recently went up to a pair of the 18inch F18 Rythmik subs for my multichannel room, which go infrasonic, usable output down to 10hz, an entire octave below 20hz technically speaking...All you hear from the naysayers is.."There’s no content that hits that low or ya can’t hear that low", whatever. On the contrary, it’s flipping nuts, the impact these monster subs have on many tracks, that i have heard a thousand times. It’s a new phenomenon, lol....

Infrasonics is a big deal with movies (and even music, to an extend), no doubt, and those who haven’t heard the difference the octave below 20Hz can do here (with select movie source material) obviously don’t know any better. A pair of 15"-loaded high power capacity subs (direct radiating, sealed) crawling low enough would begin to give an indication of infrasonics, but the real impact and significance comes with much larger air displacement area - not intended as an effect per se, but rather reflecting the means of what is really necessitated at frequencies that low to attempt and approximate energy linearity and some kind of minimum headroom. Meaning, if one has the intention of trying to investigate on the importance of infrasonics in one’s home setup, be that with movies and/or music, it’s vital that a surplus of effective cone area - in addition to a lot of power (and proper concrete flooring and overall room construction) - is attained for this purpose, and for most audiophiles that’s likely a lot more than they imagine and care to implement in their homes. Which is a shame, because it’ll be a stone unturned (an important one at that) for many on what infrasonics can do to the experience of sound in general.

It is also perhaps a motivation to try out something different in my stereo room....like a pair of large horn subs! My current open baffle GR subs that i have in the same room are good for what they are, but, it’s more for precision (not for the visceral maniac stuff). Have you heard of these Devastator horns? I ran into a couple of AVS threads with guys talking about it....

I’ve heard of the Devestator subs, yes, though technically they’re not really horns but rather a high order bandpass design (basically ported) that utilizes the output from both the front and back wave of the cone, and which mimics suspiciously close the design of Josh Ricci’s Skram subs, just tuned lower and thereby bigger. If I’m not incorrect the front wave of the cone (the 21" driver is situated, and hidden inside the cab) shoots into a short, expanding slot (or horn), while the back wave is loaded via the bigger part of the enclosure into large, square ports. The output is then summed through the short horn/port sections. The important takeaway here is the higher efficiency compared to typical hifi-ish or even cinephile subs, which is also seen by their larger size (i.e.: Hofmann’s Iron Law), but they’re still good to about ~15Hz or so and would make an interesting ground of comparison to the lower eff. subs in the other room for you to embark on. Technically, my tapped horn subs are also a high order bandpass design, but here the front wave of the woofer fires directly into a compression section and then expands into a regular horn path that via its length dictates the tune of the design (which through the Devestator’s is done via the backwave into the ported cab section), which is why the core of the design is really a horn, and the backwave of the cone is situated close to the mouth area that will then sum with the wave of the horn.

If you want to up the efficiency factor further, while maintaining extension down into the 30Hz and (when corner loaded) even 25Hz area, non-truncated front loaded horn subs like the 12Pi horns or similar-ish iteration from John Inlow are the way to go. With this we’re talking a minimum of 105dB sensitivity, and they’re rather massive in size. Imagine the whole front section of the horn being one big mouth area, and it should give you an indication of the power at play here. Really though, it comes down to the sheer quality of bass which is utterly smooth, layered and immersive, and firing these things up to prodigious SPL’s (which requires very little power) the effortless force and presence is something to behold. Hifi subs are mere toys by comparison, sonically and SPL-wise - believe me.

The interesting thing for you will be comparing the importance of infrasonics, not least in music, from the low eff. subs with the more extension restricted higher eff. sub counterparts. Myself I’ve opted for the higher eff. solution (full click @25Hz, and rolling off from here) for both music and movies in a single listening space. The price of infrasonics is lower efficiency and a large sub count to add up on the necessary displacement here, and moreover there’s a sonic implication because lower tuned, direct radiating designs simply sound different compared to higher eff. iterations, not least when they have more or less hidden cones. The latter are inherently more musical to me, and to boot they energize the listening space very differently and more effectively than smaller subs.

It looks like they get down to 19hz, comes with all the flatpacks, i.e. seems to be a more complete easier diy kit. I’d hate to stare at drawings and start cutting wood from scratch, not have it be too much of a time investment.

It’s certainly a much easier process than cutting out the stuff by yourself, which would have also required the proper machinery in a dedicated space and preferably assembly experience.