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Home » Sponsored » Pi Speakers » Help please ... from the bottom up (Four Pi questions)
| Re: Help please ... from the bottom up [message #59559 is a reply to message #59558] |
Tue, 30 June 2009 16:15   |
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Wayne Parham
Messages: 18723
Registered: January 2001
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Illuminati (33rd Degree) |
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Response for the tower two π speaker looks like this:
This is a pseudo-anechoic measurement, so the bass isn't shown. The towers have nice, deep, full bass though. To put numbers on it, f3 is 40Hz and f10 is about 30Hz.
Its impedance curve is very benign, works well with tube amps. All my speakers are this way. They're all high-efficiency designs that have impedance characteristics that work well with tube amps.
All of my speakers were designed with build simplicity in mind (except the 12π hornsub). Models one, two, three and four are all just boxes with a few holes cut in them. You can literally cutout the pieces to build one in a half hour, and have the box completely assembled in an hour. Most people wouldn't race through it like that though, and take a little more time.
The six, seven and eight π models take a little more planning. Parts cutout and assembly is not entirely trivial, mostly because these models include a midhorn. There are also more parts, more things involved. But still, as horn loudspeakers go, these are relatively simple designs, all straight sided horns that are pretty easy to cut and fit. They're made that way both for their directivity and for their ease of construction. I'd say a six, seven or eight π takes a few hours for cutout and another few hours for assembly. The beginner will likely cut and try a few midhorn panels before they get some that fit the way they want.
Things like routed grooves for recessed driver mounting are nice extra touches that aren't necessary, but add to the aesthetics. That adds to build time. Same with the finish. You can use all butt joints and paint the box and it will sound just as good as if you use mitered edges and/or add exotic wood veneer and a dozen coats or hand rubbed tung oil. Painted finishes take a day or two, but hand rubbed tung oil takes a day drying time between coats. So as you can see, time to finish is mostly determined by the quality of finish.
You didn't ask, but I'll give you some personal impressions and comparisons between models. Others may have a different take, but this is how I feel about each of the speakers in the line. I designed each and every one with an intended purpose, and each were done with passion. They're all perfect for their intended application, in my mind. Each represents the best choices I could make for the goals they were intended for.
As for the two we've been talking about, it's hard to really compare the two π tower with the four π speaker, especially in its best trim. They're made for two different purposes, although both are made to sound great and be satisfying to listen to (and look at). I will say this though - My own personal speakers are two π towers and four π's. Those are the models I listen to the most, literally for several hours a day. The towers are in my bedroom and the four π's are in my main listening room. Both are setup for two channel audio as well as for home theater. The four π's are augmented with three π subs, which provide deeper extension and more importantly, smooth room modes.
I also have seven π cornerhorns with all the best options (2226/DE250) and they're my favorite speakers. They do magic like no other speakers I've ever heard. Sadly, my main listening room isn't right for cornerhorns so they are in my office. I listen to them a lot there too, but they're really just for background music. I'm always working when I use them, not doing critical listening. It does tend to improve the quality of my work, because I am not eager to leave the office. 
To me, the one π and two π models are excellent for surround speakers or as mains in small rooms, bedrooms, anywhere that a good quality secondary system is desired. They're also perfect speakers for a starter hifi for high-school or college kids. Response is flat and these speakers have a pure sound. Crystal clarity without sounding shouty. Bass response is good below 100Hz, but not by much.
The two π tower speaker is all that but it has deep bass. It is actually more full sounding than some of my larger models. This model sounds just like the one and two in the midrange and treble, but it has deeper, fuller bass.
The three π and four π models both offer horn loading and uniform directivity. They have excellent directional characteristics, with almost the same response off-axis as on-axis. You can move left or right of the loudspeaker as much as 45° and they sound very much the same. Likewise, movement up or down is acceptable and response stays the same within over a 40° arc, above and below the speaker 20°. No speaker with a cone woofer and soft-dome tweeter can come anywhere close to this, in fact, many other speakers with horns that boast constant directivity don't do this well.
I didn't chose the HF horn solely because of its constant directivity, in fact, I've tended to use radial horns and other similar flares like what are now starting to be called waveguides. My loudspeaker designs are whole system designs, not overly optimized in one area at the expense of others. So for example, I've never used a constant directivity horn with sharp edges for pattern control. Mine are all very smooth, providing nice horizontal coverage and well behaved verticals. This holds true for all of my larger models, the three π and four π two-way loudspeakers as well as the six, seven and eight π models.
The three π and four π speakers are both designed to crossover from midwoofer to tweeter where horizontal directivity matches. This happens at the frequency where the woofer has begun to beam, typically around 1kHz for woofers of this size. For that reason, the woofer selection is critical - it must be capable of smooth midrange sound. The cones must be well damped. The crossover is carefully designed with the geometry of the speaker in mind to set the vertical nulls out far enough above and below the speaker to give a nice large clean forward lobe. All in all, it's a very good design approach, in my opinion, combining good directional characteristics, high efficiency and low distortion in a relatively small package.
The six π and seven π speakers are designed to provide constant directivity all the way through the audio band, at least down to the Schroeder frequency where room modes begin to dominate. Unlike the three π and four π speakers, which have collapsing directivity through the midrange, the π cornerhorns have constant directivity throughout. This makes unsurpassed uniformity of the reverberent field, as perfect spectral balance as you could have. They also are physically situated back into corners where they are somewhat unobtrusive, even with their larger size.
The eight π is a sort of blending of the two approaches, with some characteristics of the three π and four π and some of the six π and seven π speakers. It's a two-way design, but it uses a midhorn and can be placed in a corner, like the cornerhorns. This forces the radiation pattern into an eighth-space pattern, just like the cornerhorns. The midhorn driver is reflex loaded in the bass range, so it doubles as a woofer.
Placement of these speakers is part of their magic. More information can be found in the following threads. There are some other links in the thread too, so be sure and follow through.
At the low end of the band, I employ overdamped alignments in all my speakers. What this means is the rolloff is slow and gradual, much like a sealed box speaker. Venting gives a bit deeper extension and it reduces excursion, which tends to reduce distortion. Those are reasons enough to use venting, even if overdamped like a sealed box.
Vented cabinets have more phase movement in the bottom octave than sealed cabinets, but room modes tend to swamp the response below the Schroeder frequency anyway. This makes the moving phase of a vented cabinet completely irrelevant indoors, so the added bass extension is a benefit for which there is no penalty.
I like to add subs to the larger models in order to further reduce room modes as well as increase extension. Being high efficiency designs, they have trade-offs in terms of size verses extension. A 3ft3 to 5ft3 box is not necessarily a small box, but for a high efficiency speaker, it's not that big either. You'll definitely have output to 40Hz, but it's rolled off. Nice smooth rolloff, bass enough to sound good without subs but perfect for blending with subs. Makes for a nice upgrade path. Build the mains first, add subs later. More information about the multi-sub configuration can be found in the following link:
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