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In Reply to: Thanks for the Augie Versus Dayton IB Insights, Etc. Re: Kurt, I'd like to ask your advice about... posted by Dr Deville on February 16, 2007 at 13:13:11:
Hi George,In my OB projects, I always tried to keep the crossover frequency below 200Hz or so, if the FR or wide-band driver could go that low on the given baffle. It is difficult to set the crossover point much lower than that, because most FR or WB drivers on a baffle of a reasonable size would start to roll off around there.
Have you bought the FX120 drivers yet? I have a pair of FX120's and I like them. Another small wizzerless FR driver for OB application that I can recommend is the TangBand W4-1320SB (the "bamboo-fiber-cone" driver). Just this morning I was listening to a pair on small OB's augmented in the bass with a subwoofer, and I was again impressed by how good the sound was from those little inexpensive drivers. Compared to the FX120, the TB driver has crispier highs. I'm going to try the FX120's on the same baffles, and I'll let you know how they compare to the TB bamboo drivers in that configuration.
I have to say, however, that my thinking about OB has changed somewhat, now that I've tried a clone of Linkwitz's PLUTO speakers. As good as the OB sound of the TB bamboo drivers is in terms of soundstage and imaging, which is about as good as what I've gotten from all the FR drivers I've tried, it is no match to the sound of the PLUTO-clone speakers in those respects. Even my wife, who is not an audiophile, said that she preferred the PLUTO-clone speakers to the TangBand OB speakers (both were put in the same locations and used the same subwoofer to add bass), because she could clearly tell where the instruments were playing when listening to the PLUTO-clone, while the TB OB speakers did not give such a clear picture.
I am not saying that I’m giving up on OB or that omni-directional is the way to go. Nevertheless, I now think that it takes more than putting a good FR driver on a baffle to get great sound. I’ve ordered some new drivers so that I can do some experiments to verify one idea I have.
In this regards, if you have the time, I’d encourage you to also make clones of the PLUTO speakers. They will serve as a useful benchmark/reference for gauging all other speakers in terms of soundstage and imaging.
Best,
Kurt
Follow Ups:
Hi Kurt,I'd like to continue our discussion, if you have the time. I feel bad about hijacking this thread, so if you have an idea of where this would be more appropriate, I'd be glad to move there.
"I have to say, however, that my thinking about OB has changed somewhat, now that I've tried a clone of Linkwitz's PLUTO speakers. As good as the OB sound of the TB bamboo drivers is in terms of soundstage and imaging, which is about as good as what I've gotten from all the FR drivers I've tried, it is no match to the sound of the PLUTO-clone speakers in those respects. Even my wife, who is not an audiophile, said that she preferred the PLUTO-clone speakers to the TangBand OB speakers (both were put in the same locations and used the same subwoofer to add bass), because she could clearly tell where the instruments were playing when listening to the PLUTO-clone, while the TB OB speakers did not give such a clear picture."
I find this very interesting, and have been puzzling over it. Particularly because Seigfried Linkwitz gushed over the improvement in his Orions when he added a rear-firing tweeter, changing them from conventional front-radiating to dipole in the treble.
One thought--how close to you have your speakers to the walls? SL talks about the necessity of having the speakers at least 3' away, so that reflections are delayed enough that the brain processes them as ambience, and not smeared imaging.
If your speakers are close to the walls, that might explain why you find a front-radiating speaker to have better imaging than an open baffle. I'm guessing they are not that close, and I'll have to ponder more. That's not a bad thing.
I'll also be curious to learn your comparisioin of the Fostex with the TB. I'm thinking that treble peak on the TB might be a resonance, which pushes me towards the Fostexes, since I can always boost treble another way.
Thanks, and have fun,
George
Hi George,I doubt that Russ would mind us having a discussion about OB off his thread.
The PLUTO-clones and the OB speakers are both placed about 5.5 feet from the backwall. Neither system is listenable (to my ears) if pushed too close to the backwall. Even at 3 feet from the wall they did not produce a soundstage that is anywhere close to what I used to get in the 1400 SQFT basement of my old house in Illinois. By the way, the PLUTO is supposed to be omni-directional up to 3000Hz, even though the tweeter is front-firing. I've not measured how high the back radiation of the OB speaker goes.
One thing I noticed about the sound from the PLUTO-clones is that there is a bit "hollowness" or "softness" in human voices compared to the sound of OB. Not sure whether this is due to the omni-directionality (perhaps too much reflected sound in the midrange) or mainly a frequency response issue. I got a similar impression, however, when I listened to my "ball" speakers that have nine 4" FR drivers distributed on each multi-faceted enclosure. More investigation is needed.
I compared the TB bamboo drivers with the FX120's using the same baffles yesterday. The FX120 was smooth and full-sounding, but compared with the TB it appeared to lack sparkles in the high and not have as good clarity. The additional energy in the highs given by the TB driver also seemed to produce a better delineated soundstage that is easier to "see into." Perhaps some people would prefer the fuller sound of the FX120, but to my ears the FX120's in the given room and on the given baffles were not as exciting to listen to as the TB drivers. Thus, if I were to pick one, I'd go for the TB driver. I don't think you'd be seriously disappointed by the TB drivers on OB.
Best,
Kurt
Hi Kurt,It's good to "hear" of your satisfaction with the Tang Band W4-1320SB . I'm still a little leary of that sharp little peak between 15K and 20K, since I suspect sharp changes in frequency response represent non-linear behavior, like cone breakup, interference, or resonance. Do you think that's a reasonable suspicion in general?
Of course I am splitting hair, since the peak is so small, but since I'm planning on equalizing the output, I can always give the FX120 a little more "zing" if need be. These are all just musings on my part, and your experiences are very helpful.
I see you're using passive (speaker-level)1st order crossovers in your Pluto clones, do you use that with your OB setups? I think the Plutos have a XO somewhere in the midrange, which I'd like to avoid. Do you have a guesstimate of where yours is. I'm leaning towards a digital crossover to experiment with, and because I want to try line-level crossovers. I remember hearing the difference between active and passive crossovers with the old Magneplanar Tympani s, and the improvement was dramatic and beautiful.
This is fascinating and fun--there are so many variables, even when trying for a relatively simple solution.
Thanks again for taking the time to share your thoughts and experiences--fun and helpful.
Best,
George
Hi George,I think it is reasonable to suspect that a sharp change in the response of a mechanica/electrical/acoustic system means that it is going through a resonance or mode transition of some sort.
I don't know how "bad" the peak in the response of the TB driver really is. It doesn't look too bad compared to the peaks and valleys in the repsonse curves of many famous FR drivers, but I agree that it would nicer if it could be avoided.
As to cone break-up modes and resonances, are you thinking that a 5" paper cone like the FX120 will maintain pistonic motion all the way to 20KHz? There are break-up modes, and the question is how well the resonances are controlled. In this regard, I wonder how the response curve of FX120 will look like without smoothing.
I used first-order speaker-level crossover in the PLUTO clones because it was easy to put the speakers together quickly that way. Nevertheless, the first-order crossover was selected also because I thought that it should be relatively benign in terms of phase rotation as compared to a 4th-order active. I was shooting for a crossover frequency around 1200Hz. Even though the crossover was in the midrange, I was hoping that the transition was not be as objectionable as it would be with a 4th-order crossover.
With my OB projects, I normally do not use any speaker-level high-pass filter (i.e. a cap) on the FR driver. In some projects, I run the FR driver wide open, and add bass using a powered subwoofer with a 2nd-order low-pass. In other projects that use separate woofers, I use a 4th order active crossover and biamp the FR and the woofer. When I played with the Audax PR170MO with a tweeter, I did use a cap on the tweeter.
You are right that there are so many variables in designing a speaker system, and the problem is that the effects of some variables are not well understood, let alone well-controlled.
Best,
Kurt
Hey Kurt,Thanks again for the thoughtful reply. I'm enjoying the back and forth, and appreciate you taking the time with a newbie. Your reasoning seems valid to me--my sympathies. But--doubtless partially due to my inexperience--I want to try a slightly different variation.
In particular, I take your point that any paper cone speaker (or any speaker, I imagine) will have breakup modes, and that one brand's frequency response curve might be smoother than another brand's simply due to measurement techniques.
Granted that, my preference is to err towards smooth rather than crisp. Add to that I will be driving my FR with a SET amp, which has a relatively high output impedence, aka a very low damping factor. Paul Joppa asserts that this causes an SET's output to decrease less than a high-damping amp's when a FR driver's load impedence rises in the bass and treble--boosting them. So I'm thinking the lower-treble speaker might work better with an SET. Any thoughts?
Of course I had my mind set on the FX120, and after a while I might bring myself around. Half the price is a nice incentive, and I will have equalization available. Any thoughts on the 3" Jordans? The specs and buzz look good.
I'm also leaning toward an active crossover for three reasons--I want to hear if it sounds better than a passive, I want ease of experimentation, and I want to unburden my FR's SET amp.
Regarding that--is your dislike of fourth-order crossovers due to their inherent, ideal qualities, or the fact that implementing them with analog/passive components mucks up the signal? My understanding is very shallow here, but I'm under the impression that their theoretical qualities are excellent.
So many thoughts, so many variables. My strategy is to try to keep an open mind. And, as Einstein said "Things should be made as simple as possible, but no simpler."
Thanks again for your experiences and thoughts.
George
Hi George,It's my pleasure to chat with you about speakers. I think most others at this forum have already forgotten about this thread so perhaps you don't have to keep feeling guilty about hijacking. ;-)
Since you had your mind set on the FX120, go ahead and try it. I know that feeling of wanting a particular toy. ;-)
As to SET, you can treat the output impedance of the amp and the speaker impedance as forming a voltage divider. Thus, when the speaker impedance gets higher either towards the low frequency resonance or in the high range, the speaker gets more of the amp output. For most drivers, this will have the effect of boosting both the bass and the treble. It's like pushing in the "Loud" button on a receiver. In other words, the amp becomes a tone-control, and the effect is speaker dependant. In the case of FX120, I don't think that is an effective way to fix the HF rolloff, as the impedance rise is too gradual to compensate for the rolloff. You'd end up with a rising response in the mid and most of the high and then the rolloff before reaching 20KHz. Perhaps you'd like such a tonal balance, but it is not flat, which I think is what you desire theoretically.
I don't dislike 4th-order crossovers per se. Nevertheless, I am not certain about how the increased phase distortion associated with a high-order crossover might impact the sound so I'd rather keep the crossover simple. Linkwitz, however, thought that the phase distortion of a LR4 crossover is not audible at either 100Hz or 1400Hz. http://www.linkwitzlab.com/phs-dist.htm
Well, I guess we have extended this thread long enough. Time for you to build something! Let us know how the FX120 OB project turns out.
Best,
Kurt
Hey Kurt,Build something??!!?? Surely you jest! ;)
Actually, I'm building the preamp and SET FR amp now, but won't put the speakers together until i sojorn to MI this spring--I plan to use them to keep me relatively sane in the hovel I am remodeling.
Besides, I find the research delicious foreplay, where anything is possible, before dealing with cold, cruel reality.
Thanks for the Linkwitz link--his site is fascinating. It's interesting that he found phase distortion in his analog 4th-order crossover inaudible. I'm planning on using a digital XO, which I believe will have none of the phase distortion, though naturally it's own compromises. And I'm hoping the sharp slopes will minimize interference between the drivers. The prospect of combining new and old tech in a new way excites me.
The digital XO will also provide equalization, another one of those varibles.
I'll certainly report on my experiences, but that'll be a good while from now.
Feel free to comment if you like, and thanks and good luck!
Best,
George
Hi Kurt,Thanks for taking the time to write your helpful and informative reply. You've given me some things to ponder. I'd like to go open baffle for ease of construction and experimentation and reduced room-interaction, but I do take your suggestion seriously. In the meantime, I hope I can impose on you for a quick question or two:
What drivers does Linkwitz use in his Pluto, and/or you in your Pluto clone? So far I haven't seen them mentioned--if that's proprietary information, I understand.
No, I haven't bought the FX120 yet, and, not having the speaker to audition, am certainly open to suggestions. In saying the Tang Band W4-1320SB has crispier treble, I'm assuming that is better? Their frequency response chart certainly looks nicely smooth and level, and similar to the FX120. Half the price is nice too.
And could you point me to a description of your setup? I'd like to compare it to what I'm contemplating. Again, if my sieve-like memory has forgotten, please accept my apologies.
Thanks again for your very helpful replies.
Best,
George
Hi George:I got addicted to the OB approach years ago after putting a pair of Fostex FE83 on cardboard baffles and added a subwoofer for bass. I was floored by the spaciousness and richness of the sound from such a simple setup. I've had numerous OB projects ever since, using various FR or WB drivers, ranging from 69 cents each to over 2 thousand dollars a pair. They all sounded quite different, aside from the common attributes of OB sound. Ease of construction and experimentation is definitely a major factor that makes this approach so interesting to me. Nevertheless, even back then when I tried OB speakers for the first time, I suspected that the room-filling soundstage was due to, rather than in lieu of, room interaction.
Linkwitz's PLUTO uses a 5.25" Peerless woofer and a 2" wide-range driver by Aura. The drivers and construction of the speaker are described here: http://www.linkwitzlab.com/Pluto/construction.htm
When I read about this design, one thing that struck me was that the size of the 5.25" woofer was selected for bass extension so that the speakers could (with some heavy EQing) be produce some bass, but a smaller woofer might be better if omni-directionality is the goal. A smaller woofer in a smaller housing can be omni-directional to a much higher frequency (i.e., the baffle step transition happens at a higher frequency range) at the expense of bass extension. I thouhgt that pushing the baffle step transition up could allow a simpler crossover to be used, and the better omni-directionality might enhance the sound. So, instead of using a 5.25" woofer, I decided to use a 3" driver. Since I happened to have several Fostex FF85K drivers lying around, I decided to use them. Like the original PLUTO, my clones also use ABS plastic pipes for housing. The sealed enclosure for th FF85K is made of a 3" pipe coupling and a 8"-long piece of 3" pipe, with a top wooden plate with a routed hole for the driver and a wooden base plate. The Aura "tweeter" is in a sealed enclosure made of a 1.5" pipe coupling and a 4"-long piece of 1.5" pipe, and an end plate. The Aura driver is pushed into the opening of the 1.5" coupling with a strip of cardboard wrapped around it as a gasket. The tweeter housing is supported on a 1.5"-high piece of wood glued to the top plate of the woofer housing, such that the tweeter faces the listener while the woofer fires upward, just like the original PLUTO design. The crossover uses simple 1st-order elements, with a 15 uF cap in series with the tweeter and a 1.6mH coil in series with the woofer, both drivers being connected in the positive phase. I have to emphasis that the cap and coil values were calculated based on some guesstimates and were intended for a quick-and-dirty project, and the resulting sound could be far from optimal. No other components for level-matching or response shaping are used. Since a 3" driver in a sealed enclosure is not going to give any bass, I use a subwoofer (the same subwoofer I used years ago with the FE83) to fill in the bottom end.
As to the comparison between FX120 and the TB bamboo driver, the TB driver does seem to put out more energy in the highs. In this regard, the TB driver sounds more airy and detailed than most of the FR drivers I've tried. I am about to make new adaptor plates for mounting the FX120's on the baffles, and I'll provide my impression after comparing the two drivers on the same baffle. By the way, those baffle are nothing special. I built them using the material I found in my garage. They are 20" wide, about 35" tall, and have side panels about 8" at the top and 12" at the bottom. The side panels support the baffle and give it a bit tilt up towards the listener. The driver is mounted with its center at about 10" from the baffle top edge and offset from the baffle centerline by 2". I use the subwoofer to add bass.
Best,
Kurt
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