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Home » Sponsored » Pi Speakers » 4 pi, oh my! (pi 4)
| Re: 4 pi, oh my! [message #66278 is a reply to message #66257] |
Wed, 23 February 2011 09:55   |
EL Jack
Messages: 5
Registered: February 2011
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Esquire |
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| Bill Epstein wrote on Tue, 22 February 2011 17:10 | | EL Jack wrote on Tue, 22 February 2011 13:48 | All standard: Eminence drivers and the base crossovers.
I have previously built a small 2-way but the veneer was not entirely successful. I'll need some help to decide what to do, but I'm inclined to go with a basic black paint.
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I think you'll find that painting plywood or MDF is more work than veneer.
For $75 you can buy a 4x8 sheet of NBL (no black line) walnut, cherry or oak veneer from tape-ease.com. One sheet will do the front, top and sides of both speakers. Use the method described by Bob Brines for gluing it on http://www.brinesacoustics.com/Pages/Articles/Cabinet_Construction/Construction.html
You don't have to trim with a router, a sharp block plane or even a utility knife will do fine to get within an 1/8th, then sand flush.
Enjoy! (and go JBL and B&C as soon as you can!)
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Thanks Bill - as you've figured out, I'm "Mr Black" from AA, and please accept my thanks for pointing out these speakers to me.
I'll check out the veneer method you mention. I previously did it a much more difficult way (with the guidance of a friend who is a woodworker but not much of a finisher...).
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| Re: 4 pi, oh my! [message #66279 is a reply to message #66276] |
Wed, 23 February 2011 14:25 |
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Wayne Parham
Messages: 18783
Registered: January 2001
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Illuminati (33rd Degree) |
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I agree with Bill, the quality difference in the 150Hz to 1.5kHz range is noticeable with the upgraded midwoofer. That's the reason for the upgrade, and the reason why I think the woofer is the most important part to upgrade. Tweeter is second, because while it is smoother, I think the improvement is a little less "important" than the midwoofer upgrade. Both woofer and tweeter upgrades are worthwhile though.
This is true for both the three π and four π loudspeakers. Both have good quality midwoofers in the stock build, but the upgraded midwoofers are higher quality "best of class" parts. The difference is largely due to shorting rings being used in the upgraded parts, which makes the motors more linear and decreases distortion. The material and shape of the cones in the upgraded midwoofers also helps reduce breakup, with the end result being smoother midrange with less distortion.
If you're just casually listening for a few minutes at a time, the differences are subtle. You can hear a difference, but it definitely isn't night and day. It's when you really sit down and listen that you notice the quality improvements from the upgraded parts the most. I guess that's subjective, but my point is you shouldn't take this to mean the stock parts suck and the upgraded parts are the only things worth having. That's not the case. The stock speakers sound great. It's just the upgraded versions make the speaker go from a "great speaker" to what I consider to be a "best of class speaker". It's a good-better-best deal with the stock builds being "better than most" and the upgraded builds being the "best".
There is one last thing worth mentioning. There is a difference in the electro-mechanical parameters of any loudspeaker driven at one watt than there is when driven at ten watts, and it shifts even more at a hundred watts. At high power levels, voice coil resistance increases and this tends to shift the speaker towards an underdamped electrical alignment. Voice coil heating tends to lift the low bass, sometimes causing excessive peaking. At low power levels, the voice coil is cool so there is more electrical damping but the suspension of prosound speakers (designed for several hundred watts) is often stiffer. This change of compliance tends to reduce low bass output. All my designs are made so that they won't get peaky at high power levels, providing good response from flea power to full tilt, but some shift a little more, some a little less. Most shift from moderately overdamped to slightly overdamped, some from slightly overdamped to slightly underdamped.
One thing I've noticed about the 2226 is that it is stiffer than you expect at low power levels. Even though T/S parameters are technically small signal values, JBL rated the 2226 with values that are more representative of how the speakers acts at about 10% power, i.e. ~60 watts. If you take a JBL 2226 and connect it to your handy-dandy T/S woofer tester, you'll find compliance is a lot smaller than the published figure. That's because the woofer tester is sending it about a tenth of a watt for an input signal, and the electro-mechanical properties are much different than it will be at higher power levels. Personally, I think it was a good idea to publish T/S specs for this woofer that are representative of how it acts at moderate power levels, because this is how the driver is going to be used most of the time. But most manufacturers publish specs that are more in line with what you'll actually measure with less than a watt drive signal.
What this means from a real-world perspective in terms of loudspeaker performance is the four π using the Omega 15 produces more output below 100Hz at low power levels than the version with the 2226. As power levels increase, the alignment shifts and brings up the bottom end but at very low power levels, there is less bass output from the 2226. So if you're running low power tube amps, this might be something to consider. If you're using subs, it really doesn't matter. The improvement in midrange quality makes it worthwhile to upgrade, in my opinion, even with the slightly reduced bass output. But I did think it worth mentioning.
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| Re: 4 pi, oh my! [message #66304 is a reply to message #66242] |
Thu, 24 February 2011 22:05 |
Doc Jr 8156
Messages: 26
Registered: May 2009
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Chancellor |
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Welcome, Mr. Black. I'm glad you are enjoying your 4Pis now. As Bill said, upgrade to the JBL 2226 and B&C 250 will just add enjoyment every time you fire up your 4 Pi's. With mine, I use triodes and pentodes SET (3-8 watts maximum) as well as puss pull amps (35 watts) even vintage receivers (Macintosh, Marantz, Sansui, Pioneer, andYamaha) I collected through the years and it never cease to amaze me how loud and clean the sound reproduction these speakers are capable of. I even enjoy them when using SS amps. However, just for kicks if you have an opportunity, try a class D amp (100 watts) and you will hear what the fuss regarding the JBL's are all about. I have 5 different single driver speakers and a Linkwitz Orion with all the whistles but I enjoy my 4 Pi speakers no less than any of those. Lets thank Wayne for the joy these speakers are giving us. The Pi speakers need more and better exposure so more people can enjoy them specially those who love low power tube amps. Godspeed.
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| Re: 4 pi, oh my! [message #69230 is a reply to message #69228] |
Mon, 29 August 2011 09:57 |
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Wayne Parham
Messages: 18783
Registered: January 2001
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Illuminati (33rd Degree) |
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The 7° tilt angle you see in the photos of my setup was chosen largely because the first crossovers put the forward lobe angled downward slightly. Not much, like 5° or so. The nulls were about 15° above the speaker and 25° below. That's why I had stands made with 7° angle, making the nulls be at 23° up and 18° down. The crossover has been changed since then, and the forward lobe is more centered. But I kept the stands, because even with the centered forward lobe, I still like some tilt-back.
This is very much a perfectionist thing, because that tiny shift didn't make any difference at all. The forward lobe is clean over a very useful range, 90° wide and 40° tall. I've seen "waveguide" speakers with an ultra-thin "strata" lobe, like 15° - only 7.5° above and below the centerline. On those, any shift can move you outside the window, into the nulls or outside into the secondary lobes. But all models of π speakers have tall enough (40°) vertical pattern to be useful, and HF output outside that falls off pretty sharply, which really helps reduce ceiling slap.
Personally, even with the centerline of the forward lobe pointing straight ahead, I find I still like 3° to 5° tilt-back on the stands. This is just about right to cover floor to standing height at normal listening distance, 5 to 10 feet back. The forward lobe spans about 1.8 feet above and below the centerline at five feet, about 3.5 feet above and below the speaker ten feet back. When you angle it back some, this pattern shifts upward by that amount.
We don't want ceiling slap - it's more objectionable than a floor reflection at high-frequency - but then again, the floor is usually carpeted, so the biggest problem from floor reflection is usually in the lower midrange (which we cure with flanking subs). Still, the floor is a closer boundary than the ceiling, and the speaker is directional enough at HF that even with some tilt-back, you just don't get ceiling slap until you're pretty far away.
So in the end, I like the stands to provide 3° to 5° tilt-back. It helps cradle the speakers too, because they can sit back on the backrest, a lip that's about an inch tall.
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| Re: 4 pi, oh my! [message #69244 is a reply to message #69243] |
Tue, 30 August 2011 08:43 |
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Wayne Parham
Messages: 18783
Registered: January 2001
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Illuminati (33rd Degree) |
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I recommend Baltic Birch or medium density fiberboard. MDF is tonally neutral, without a single natural fiber resonance because it is a semi-homogenous mix of wood pulp fibers suspended in glue. It's really a glueboard. However, it isn't all that strong and is easily chipped, especially on corners and edges. It also soaks up wood like a sponge, and then expands. Baltic Birch holds up better, especially in humid environments or when transported a lot. It is almost as tonally neutral, and is usually free of internal voids. Voids are what make most other plywood product unusable for speaker cabinets, because where there are voids, there is usually debris inside which buzzes.
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