Always interesting to see why so many do measurements inside as oppose to dragging outside and doing GP ...
I've researched, engineered and built what I think are some very good OB speakers (Bob's Website click on Audio, then Aurium Waveguide), and I think I can explain why (perhaps the main reasons) they generally sound better than non-OB speakers. First I have to say that evaluating speakers well requires a good understanding of the problems associated with the recording process, and acoustics in general, besides the usual stuff. You have to be able to put things in context. There are MANY variables involved.
Above about 1kHZ we perceive image location primarily by amplitude comparisons, left to right. Below about 1kHZ we perceive image locations primarily by timing comparisons, left to right (or vice versa). Inter-aural crosstalk needs to happen only once in the reproduction process (usually in the recording process), or image actuation is largely destroyed below about 1kHZ. Inter-aural crosstalk usually happens a second time during playback with two speakers. Our "ear-brain" mechanism gets lost trying to perceive two sets of info that don't correlate. Any sense of image actuation below about 1kHZ that we may think we perceive is likely by luck and due to the listening room acoustics being stimulated. OB speakers will grab that bull by the horns and generate a much better "substitute" imaging information in that region below about 1kHZ. A big step away from conventional "fidelity" as we've come to think of it, yet a more real sounding (real feeling) listening experience.
I've been experimenting with the Carver "Holographic Generator" circuit for decades, and more recently have built a Polk style Holographic Soundbar, and yes, your head has to be perfectly centered to find out what you've been missing when it comes to imaging, but then IMO it's undeniable. Perhaps because the lower you go in frequency, the more we perceive the energies in a "feeling" way rather than a more abstract way (for lack of a better term).
When your imaging becomes "wideband" rather than just above 1kHZ (as with the conventional system), I find that other things aren't nearly as important. The system could have a poor frequency response, maybe a little audible distortion, and if the imaging is wideband I'll feel a presence that makes the experience what I'm really after. I'll enjoy the listening experience considerably more. With good quality recordings (especially binaural involving a variation of a head mic pair), I'll hear and feel a whole different acoustical environment, which can be quite fun.
Now days some softwares do "time panning" that works with high-end reverbs to create a whole wideband soundscape that really comes to life with any variation of inter-aural cancellation during playback through speakers.
For decades I've been building speaker systems, and always set them up for best imaging at a sweet spot. I'd listen a little bit back from the third corner of the equalateral triangle type thing. My older brother Ron who knows darn little about anything technical has often provided a better listening experience with his McIntosh ML-1's, which has bothered me. I eventually realized that the thing he figured out intuitively and does differently than me, is that he separates the speakers a lot more, with little interest in any kind of sweet spot. He generally goes for maximum practical separation of the speakers in the room. What I think this achieves is to throw away imaging accuracy above about 1kHZ, in return for room acoustics generated, fake but surprisingly effective imaging info below 1kHZ. The presentation "feels" better and more real on the bottom line with most recordings. (This is where you're sure I'm getting off topic)
With well designed OB speakers at least 3 ft. out from any walls, I find that I can get a big part of both worlds; good imaging above 1kHZ in the sweet spot area, and a significantly improved "sense of imaging" below 1kHZ. The rear emission of the OB speakers bounces around the room in a way that re-creates the lower midrange timing info. Not strictly "real" from a purists point of view, but usually way better than nothing. Embeded reverbs take on a 3-D nature, and everything has a more distinct sense of place in the soundstage presentation.
One might ask, "Is this fake imaging info really good enough for me?" I find it's a lot better than un-usable imaging info below a kHZ, and the recording process is riddled with all kinds of problems associated with imaging 99% of the time anyway. Sometimes it's nice to be able to largely effectively fix a poor recording process.
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Bob,
I understand what you are saying but all I can think of when I imagine a system with that wide soundstage like that is a Bose 901 system and the huge sound without the definition. You are really creating something that was never really in the recording. As far as the binoral sound recording they are so few tha it is just a novelty to most. If I could soffit mount a system flush with the front wall with a live end dead end as used in the studio that would be my ideal system in a room to listen to most music, but that seldom is really done.
A.Wayne,
Your right that if you don't have an anechoic chamber to test speakers there is nothing like taking the speakers outside and burying them flush in the ground or 40 feet up on a pole pointed up. But once a speaker is already made and finished in a box it is time to put it in a room and see what you got. Then it becomes all about the room and room placement, I wish that wasn't the case but it is. And how often does a wife or girlfriend for that matter let you put your speakers out in the room a minimum from any walls? If you have your man cave, or a cave-women who lets you do as you please you got it made. My current designs are intended to be used as nearfield monitors though they will easily fill a room with sound. Definitely not going to be PCFrank sound though, not going to happen! I don't know of any other self powered speakers that contain two discrete amplifiers, active crossovers and based on the Slewmaster thread amplifiers. Headroom will not be a problem, keeping your hearing may be though!
I understand what you are saying but all I can think of when I imagine a system with that wide soundstage like that is a Bose 901 system and the huge sound without the definition. You are really creating something that was never really in the recording. As far as the binoral sound recording they are so few tha it is just a novelty to most. If I could soffit mount a system flush with the front wall with a live end dead end as used in the studio that would be my ideal system in a room to listen to most music, but that seldom is really done.
A.Wayne,
Your right that if you don't have an anechoic chamber to test speakers there is nothing like taking the speakers outside and burying them flush in the ground or 40 feet up on a pole pointed up. But once a speaker is already made and finished in a box it is time to put it in a room and see what you got. Then it becomes all about the room and room placement, I wish that wasn't the case but it is. And how often does a wife or girlfriend for that matter let you put your speakers out in the room a minimum from any walls? If you have your man cave, or a cave-women who lets you do as you please you got it made. My current designs are intended to be used as nearfield monitors though they will easily fill a room with sound. Definitely not going to be PCFrank sound though, not going to happen! I don't know of any other self powered speakers that contain two discrete amplifiers, active crossovers and based on the Slewmaster thread amplifiers. Headroom will not be a problem, keeping your hearing may be though!
Tsk, I wonder what this "PCFrank sound" is? What I find strange is the combination of "intended to be used as nearfield monitors though they will easily fill a room with sound.", implying a rather 'small' sound, along with "keeping your hearing may be (a problem) though!", implying somewhat raucous characteristics - sounds to me a bit like those active pro monitors I spent a day running around vetting ... 
The "big" sound, holographic, 3D, however you want to describe it - is there on the recording, always, and it's up to the playback system to extract it. There are probably a million ways of doing it, but personally I've found that very boring looking, conventional setups, with nothing box speakers will do it - but the sound has be extremely clean for it to happen ...
The "big" sound, holographic, 3D, however you want to describe it - is there on the recording, always, and it's up to the playback system to extract it. There are probably a million ways of doing it, but personally I've found that very boring looking, conventional setups, with nothing box speakers will do it - but the sound has be extremely clean for it to happen ...
I never liked the Bose 901's. My OB's actually have very good definition. Imaging is as good as I've heard, or better. Needing to have them 3 ft. out from any walls can be a problem unless you've got a fairly large room. Getting a wife to put up with them too. As far as creating something that was not in the recording, true, but what OB's create may be what the recording engineer and musician wish they could have delivered. I found it interesting that being OB didn't at all get in the way of the Carver type hologram circuit working. I guess because of the amount of difference in the delays involved, our brains process them separately (125uS vs 6mS).
I have never seen a DI measurement of such a large speaker from a DIYer before. How did you measure the DI? If it's the horizontal DI, do you have a rotating turntable that can support that speaker? Also, you are showing the DI at low frequencies as well. How did you measure it so low?
I heard Gary Pimm's OB subs for the first time a few years ago. They sounded fantastic. If I remember right, they consisted of two 15" drivers in a compact folded baffle enclosure, equalized for desired response, and powered by their own tube amp.
My bass cabinets (70 Hz downward) are 5 cu ft enclosures with a TD15H in front and 15" passive radiators on both side walls. They are tuned to 23 Hz, and powered by plate amps.
I have been planning to eventually retire the plate amps and instead use my Parasound HC1500A amp and QSC DSP-30 so I can further optimize their in-room performance. If there is a (reversible) way to experiment with an OB approach using what I have on hand, I would be curious.
I am quite pleased with what I am hearing right now, though, so I'm not in a hurry to make changes.
Gary Dahl
This sounds great to me, to get the compactness WAF etc and yet be able to deliver down to a 23 Hz tuning. Like too with Gary Pimms impression on you, when you have the mental tools and audio skills and been there and done most things you can find a number of ways to get something you can and want to live with a while.
I like transmission lines, but I would like to try a dual winged i.e paired open baffle set up with a sealed baffle woofer in between, with say 20 Hz tuning. These all require a big room even if the set up is kept relatively small. And I would run them solid state AB
I'm pretty sure your describing Bi-pole, and not specifically Open Baffle. I think the holographic sound your talking about can be achieved with front and rear facing sealed and ported designs as well. A broader sound scape image but not as strictly defined.
Please correct me if I'm wrong, but as far as I know, di-pole, bi-pole and open baffle (OB) are all generally the same thing. The thing about the interaural cancellation "Holographic Generator" optional function is that it doesn't work very good if there are substantial reflections off the side walls of the listening room. That effectively creates more non-corrolated crosstalk. But di-poles or OB's have cancellation at their sides due to diffraction which increases as you go down in frequency below about 1kHZ, so the inter-aural cancellation actually works better with OB's in the frequency range that you're trying to do something about (lower midrange), than with sealed or ported boxes. Even without the inter-aural cancellation function engaged, less side wall reflection gives a cleaner lower midrange sound; more of what's in the recording. These speakers I built actually do imaging extremely well with a decent recording. It's only diffuse or blurry if the recording causes that somehow.
Hi,
The work of Linkwitz is well known and highly regarded, of course.
Actually I went in the beginning of this thread and found some your designs of open baffles that were directing the way to beyond at that time.
Impressive. But ...
Did you actually build any of these big dipoles ?
And did you measure them in your room to determine the real equalisation requirements ?
And, most importantly of all, did you listen to these dipoles ?
You do realise these are nothing close to Orion. Orion has small baffle, small drivers, low Qts. They were chosen by Linkwitz for Orion driven by the obsession of having constant directivity.
With his baffle and driver selections, the equalisation requirements become as they are, for Orion. But your drawings are not like Orions...
18" + 15" dipole
.
JoshK,
Thinking how to accurately answer your question.
Bob,
I would think that the radiation pattern would be very different from an OB and a system with both a front and rear facing speaker that are in phase vs the out of phase output of an OB. With the open back you are just letting the rear out of phase radiation bounce of the wall and the only thing keeping that wave from cancellation of the front wave directly at lower and not that low are the side baffles on a U shaped enclosure. It goes so against the design of infinite baffles and closed box design and I just have never seen the reason to use the open back with the poor low frequency response due to the cancellation effects. I would rather use two opposed in phase drivers in a closed sealed enclosure if that was the object to use the rear wall as a reflective surface, Just my opinion here I'll say.
Thinking how to accurately answer your question.
Bob,
I would think that the radiation pattern would be very different from an OB and a system with both a front and rear facing speaker that are in phase vs the out of phase output of an OB. With the open back you are just letting the rear out of phase radiation bounce of the wall and the only thing keeping that wave from cancellation of the front wave directly at lower and not that low are the side baffles on a U shaped enclosure. It goes so against the design of infinite baffles and closed box design and I just have never seen the reason to use the open back with the poor low frequency response due to the cancellation effects. I would rather use two opposed in phase drivers in a closed sealed enclosure if that was the object to use the rear wall as a reflective surface, Just my opinion here I'll say.
A bipole has both forward-facing and rearward-facing drivers, wired in phase.
A dipole has both forward-facing and rearward-facing drivers, wired out of phase.
An open baffle functions as a dipole (front and rear surfaces of the same drivers are inherently out of phase), but of course there is no enclosure.
Gary Dahl
A dipole has both forward-facing and rearward-facing drivers, wired out of phase.
An open baffle functions as a dipole (front and rear surfaces of the same drivers are inherently out of phase), but of course there is no enclosure.
Gary Dahl
Hey Bob,
With dipole/open back, the sound going rearward is out-of-phase with the front wave.
With bipole, the rearward firing wave is in-phase with the front wave.
Bipole does not come around and cancel like a dipole does.