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Old 17th September 2009, 08:06 PM   #6011
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OB bass don't need to be big. Just look at orion or Phoenix. Mine uses 2x10" /ch, just cheap $14 woofers and I equalise them to 20Hz Q=0.5.

Don't know how loud you guys listen to your system, but mine is loud enough for the other half to complain.

The thing here is: active line-level eq. Passive system can forget OBs as they won't have the ability to eq the bass.

Anyway I hope the Ariel replacement will be a great system (and not expensive!) to build.
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Old 17th September 2009, 08:24 PM   #6012
cuibono is offline cuibono  United States
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This is an interesting discussion, I appreciate hearing peoples opinions! OB v. Horn, etc. Size seems to be an issue for both of these - and it seems like horns have it worse, on average. It is possible to build sensitive (>90dBspl) OB's that have modest size and don't need 20dB EQ - it just takes a careful design, and probably has to be a 4 way (and it would have an exceptionally regular off axis response).

While horns can have very smooth off-axis responses, their directivity is rising - so radiation at right angles to the design axis are bass and mid heavy. OB, if done well, can have an off axis response that is the almost the same as on axis, just lower in level. I'd guess this might have a big impact on their perceived presentation. Similarly, I would presume horns wouldn't step up as strong a 'reverberant' field, as OBs have symmetrical front and rear radiation (again, design specific). I'd guess this is why horns are perceived as rendering more detail, while OBs are known for the 'spaciousness' of their sound. Just guesses though, I have no experience with domestic horns.

Quote:
Originally Posted by TrueSound View Post
...I think two per side is adequate down to around 140 Hz. Four to 100 Hz, eight to 60 Hz...
Quote:
Originally Posted by CLS View Post

... 2 or 4 15" pro sound woofers per side are more than enough in domestic use...
I've had a different experience with 15" OB bass drivers. I use MJK's Alpha15a design in a 16" by 16" by 17" H frame, one per side. I measured outdoor (again) two days ago, with 2.83Vrms in, at 1 meter, mic 8" off the ground, a single H frame is 94.5dBSPL sensitive at 50Hz. Add 6dB for the other side, for a total of 100.5dBspl. Due to the drivers Qes/Qms, there is no need for eq, being flat from 40-100Hz. Clearly, in this bandwidth, it is easy to hit +105dB in room. Who here is listening at an average of 110dBspl? And below 40-50Hz, IMO, is sealed/bandpass sub territory.

I have two issues with MJK's h-frame - its footprint, and its distortion spectrum mid-bass. But I'm finishing a design that has a 11" by 13" footprint, need no EQ, is almost as sensitive, has more output, and lower distortion, for almost the same cost.

So in summary, unless your in a large room, and listening at very high levels for long periods, OB bass is easy to pull off, particularly if you have the space. In domestic situations (less spl needs, more WAF needed), OB is a cinch.
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Old 17th September 2009, 08:42 PM   #6013
Paul W is offline Paul W  United States
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Since we are all checking in with suggestions...

I thought the concept with a horn top end, cardioid mid, dipole bass, and monopole sub could have worked well.
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Old 17th September 2009, 08:45 PM   #6014
BudP is offline BudP  United States
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The thoughts behind the system are:

To use the Lowther from 20 kHz to 300 Hz.
Use the Delta 8 from 300 to wherever it quits.
Use the Tang Band Cardioid bass up to perhaps 70 Hz.

As all will be EnABL'd, they will have somewhat better performance in low frequency, without baffle support, than is typical. We shall see how much better.

I wanted the Delta 8 in there because it can handle large amounts of power and should be able to portray the all important upper bass better than the Lowther ever could.

The Tang Bands are 10 dB less sensitive, but they have 12mm of xmax and will be driven by a separate bass amp and should be able to reach 103 db at 20 Hz very clean. This will be rather more than enough for my circumstances.

I also have plans laid for a Berringer 2496, with replaced DAC's (the designer of the Alpha Dac wants to help here) to get rid of the embedded op amp buffer stage in their DAC and replacement of the output op amps with transformer volume controls, with 24 steps and isolation, to match voltage out to the various amps, without using the Berringer's digital volume control, which looses bits. This will allow the Dacs to run without buffering the DC, just gap the primary. I also intend to provide an isolation transformer volume control on the input, as a main volume control. So, the Berringer is really only needed because it has a great set of DSP driven crossover circuits, is quiet, and already sorted.

The final insult will come from using Gary Pimm's front end from the push pull SS Tabor rev 2, into a PP to SE nickle core interstage, to... a 300 B, to drive the Lowther. SS amps, running at tube voltages, appear to be much more linear than when used as current devices only. So, SS driver stages driving a 300 B should be a very pretty sound.

The Audio Prisim has our OPT's in it and is a superb amplifier, sort of an insult to only use it to 300 Hz. And finally Sure tri-path 100 watt amps for the Tang Bands.

I realize that this is anathema in a general sense. However, I have heard all of the components, in various stages of completeness and am confident I will have what I am looking for.

And, all of this is just weird enough to suit my nature.

Bud

Last edited by BudP; 17th September 2009 at 09:07 PM.
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Old 17th September 2009, 09:27 PM   #6015
SunRa is offline SunRa  Romania
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Quote:
Originally Posted by BudP View Post
And, all of this is just weird enough to suit my nature.

Bud
Mr. Purvine, you would need a web-site! Or at least a blog. There are to many of your ideas scattered in these forums.

Quote:
I use MJK's Alpha15a design in a 16" by 16" by 17" H frame, one per side. I measured outdoor (again) two days ago, with 2.83Vrms in, at 1 meter, mic 8" off the ground, a single H frame is 94.5dBSPL sensitive at 50Hz. Add 6dB for the other side, for a total of 100.5dBspl.
cuibono, this is pretty significant... I guess that it would definitely match a waveguide/horn.

Quote:
Since we are all checking in with suggestions...

I thought the concept with a horn top end, cardioid mid, dipole bass, and monopole sub could have worked well.
Remember Magnetar's system? 5 10'' woofers per side? And it was quite compact also..
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Old 17th September 2009, 10:52 PM   #6016
BudP is offline BudP  United States
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Gary's "V-bass" (or whatever you would call it) is a darn good compromise. Not huge, good extension with modest EQ. Super clean. Not an easy build, tho.
Pano is suckering you guys here. I was there, during a typical Portland thunderstorm trapped in the Columbia river basin. Gary put on a record, as in vinyl, with what he thought was a good rendition of a thunderstorm. The two, inside and outside, were at the same level in the living room, including the house shaking and the window glass obviously bowing. Of course a small amount of EQ and a 600 watt crown amp will do this, but look at the pictures, see if you think it is possible.

And this is clean enough to pick out any bass viol, from an orchestral group and follow it , without strain.

Bud
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Old 17th September 2009, 11:24 PM   #6017
Pano is offline Pano  United States
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Thanks for the great pix, Bud - and the story.

BTW, that's cotton batting insulation on the back - the blue stuff. For those who want to know....
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Old 18th September 2009, 12:10 AM   #6018
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BTW, that's cotton batting insulation on the back - the blue stuff. For those who want to know....
Something like 85% recycled denim (that is a lot of blue jeans) ... Bob (at CSS) is selling managable quantities of the 1/2" (5/8") stuff. A god send. We are now using it in place of the vinatge cotton or woll felt we had been using. We are still working our way thru a full bat of 3 1/2". The microTowers use this. Good stuff.

http://www.bondedlogic.com/

dave
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Old 18th September 2009, 12:48 AM   #6019
BudP is offline BudP  United States
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To give credit where it is due, the math behind much of Gary's work comes from our own John K at this site. http://www.musicanddesign.com/index.html So, if you want to explore other cardioid bass schemes, make sure you get the real information.

Bud
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Old 18th September 2009, 01:17 AM   #6020
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Well, that last post certainly set the cat amongst the pigeons!

I'm not married to any one approach - but I do think it's useful to partition deep bass (20~80 Hz) from the 80~800 Hz range. The solutions are different, and the interactions with the room are different as well. Deep bass is mostly below the lowest-frequency room mode, and is the domain of Hoffman's Iron Law, which is inescapable.

Setting aside the choice of technology, the dominant problems in the 80~800 Hz range are room modes, followed by box modes and panel vibration. The drivers are inherently flat, since they are in the piston band, so they are essentially blameless here. There are worries about delta-inductance and arcana of magnet construction, but those are minor compared to room modes, box modes, and panel vibration.

If anyone doubts that box modes or panel vibration are audible, by the way, just put your ear against the side panel of conventional loudspeaker, listen for a while with bass-range or vocal music, than move back to your chair. The droning coloration you heard while listening to the box will still be audible from the sitting position - in fact, now that you know what it sounds like, you won't be able to ignore it!

The marvelous thing about OB's is that this coloration is finally, and wonderfully, all gone. But the increase in excursion (below baffle peak) is no small matter. The added excursion (compared to a closed box) is another 6 dB per octave - of course, it can equalized and additional watts thrown at it, but the extra distortion is there to stay (unless servo feedback is used). The OB increase in excursion is [Ion top of[/I] the normal 12 dB increase in excursion per octave of a closed-box speaker.

Ideally, this would be offset by an increase in cone area - but as you can imagine, the cone area necessary to keep excursion low at the lowest frequencies would truly be immense - the size of a wall.

The baffle peak is a little troubling as well. It is caused by the rear wave coming around the baffle to the front - so it appears in the time domain as well as the frequency domain. Subjectively, it is much less offensive than box modes and panel vibrations, because those have much higher Q's and take a lot longer to ring down to zero - that's the droning sound you hear coming from the side of a conventional box.

Each type of approach has measurable, and with listening practice, audible faults. Once you know what box modes and panel vibrations sounds like, they are hard to accept. Once you get used to the effortless quality of horn-loaded bass - especially with piano and symphonic music - direct-radiators don't sound as good. Different people are sensitized to different types of coloration, thus the preference for different types of loudspeakers, electronics, and source materials.

I have had the misfortune of working with loudspeakers for a while, and notice odd sounds that most others don't hear. That doesn't increase my appreciation of hifi, it makes more difficult to listen, since much of the time all I'm aware of is a checklist of faults. The objectivists might say that it's all in my head - and well, yes, it [I]is[/I} all my head, since I can't hear what others are hearing. Who's head would it be in, anyway, if not my own? How can I imagine what anyone else is hearing? I'm not good at that kind of thing.

Less facetiously, I usually hear an improvement when a measurable fault is corrected - although not always. I'm not very sensitive to phase distortion, and others are. Some people go nuts when the absolute phase (of both channels) is inverted, but all I hear is a subtle - sometimes very subtle - timbral change on some instruments, less than a change in seating position, or a track-to-track difference in EQ.

What I do hear - in other words, what I care about when listening to a loudspeaker - are cabinet colorations, as well as fairly obvious dynamic-range limitations. These appear to be the major tradeoffs.
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