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Old 25th October 2012, 06:54 PM   #8281
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Has anyone in this thread mentioned MMP (just made that up: Multiple Mistuned Ports), all slightly mistuned around the target tuning?
Dr. Geddes did this with his bandpass subs (though he recently switched to passive radiator).

Re-build any traditional single-port BR with multiple, mistuned ports that average (but none equal) the tuning of the single port.
Tweak until impedance looks good, sounds good.
This approach might work well when one has to use a smaller-than-ideal cabinet.

If someone out there has actually measured, or can model this approach, I'd like to know what was learned, such as practical span of tunings (1/3 octave, more?) If I had some free time . . .

Another alternative, (harder to tweak, but also pretty forgiving) is double-chamber reflex. Subjectively, the couple examples I've heard sounded more like a TL or large sealed than BR; well controlled & good extension.

-- Mark
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Old 25th October 2012, 06:58 PM   #8282
badman is offline badman  United States
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Quote:
Originally Posted by Tubamark View Post
Has anyone in this thread mentioned MMP (just made that up: Multiple Mistuned Ports), all slightly mistuned around the target tuning?
That's what my post above yours did. Works quite nicely.
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Old 25th October 2012, 09:58 PM   #8283
nuconz is offline nuconz  United States
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Quote:
Originally Posted by Tubamark View Post
Has anyone in this thread mentioned MMP (just made that up: Multiple Mistuned Ports), all slightly mistuned around the target tuning?
Dr. Geddes did this with his bandpass subs (though he recently switched to passive radiator).

Re-build any traditional single-port BR with multiple, mistuned ports that average (but none equal) the tuning of the single port.
Tweak until impedance looks good, sounds good.
This approach might work well when one has to use a smaller-than-ideal cabinet.

If someone out there has actually measured, or can model this approach, I'd like to know what was learned, such as practical span of tunings (1/3 octave, more?) If I had some free time . . .

Another alternative, (harder to tweak, but also pretty forgiving) is double-chamber reflex. Subjectively, the couple examples I've heard sounded more like a TL or large sealed than BR; well controlled & good extension.

-- Mark
sounds like the old distributed port arrangement.

some have used round, square, and triangular ports in the same enclosure. the karlson coupler might be better than these.

i have a pair of EPI speakers w/ 12" passive radiators that sound real good. the ESS amt1a speakers sounded great to me. they employed a 12" pr also. the original polk audio speakers employed the 12" pr in the larger units. many consumers liked these speakers except for the tweeter. for consumer audio sound, i prefer PR systems to vent.
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Old 25th October 2012, 10:13 PM   #8284
nuconz is offline nuconz  United States
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Default Hedlund w/ CSS WR125str

here are a couple of photos of these little 4-1/2" drivers in the large hedlund cabinets.

i'm not apologizing for the rough look of the hedlunds. they are over 20 years old and were built as prototypes. the builder gave them to me 2 years ago.

i originally installed the Pioneer BOFU in these and changed to the CSS this year.

they sound good. they are nowhere as efficient as the BOFU. wish they were about 93 db. but these are probably about 89 db since the two 16 ohm drivers are wired in parallel.

initially i installed just one 16 ohm driver in each cabinet before constructing the "faceplate" for the dual driver mounting. the left photo reflects this mounting. the right photo is of the two speakers in the cabinet.
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File Type: jpg SpeakersMountedInHedlund121006-1.jpg (617.0 KB, 696 views)
File Type: jpg SpeakersMountedInHedlund121006-2.jpg (680.1 KB, 674 views)
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Old 25th October 2012, 11:52 PM   #8285
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Quote:
Originally Posted by badman View Post
When are we going to see pics?
The cry of the Internet: "pics or it didn't happen".

Well, here's a picture of the Left speaker (they are mirror-imaged pairs). The woofer is on a panel that is slanted about 24~30 degrees, and the overall width is about 25". As you can see from the vent running up the left side, it's a half-Onken, with UltraTouch (recycled cotton blue jeans) filling in most of the vent.

The bass was a little thinner than I'd prefer, so the next go-round will have the vent on the floor, like the Ariel, except of course bigger.
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Old 26th October 2012, 12:28 AM   #8286
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The next version will be here in Colorado, so I can do the fine-tuning and ARTA measurements in my own living room.

In the absence of much literature on resistive-vent enclosures, it's important to measure the vent output and how it sums in-room with the woofer output. With the vent on the floor, the floor image becomes part of the vent, and affects system tuning.

I can tell how effective the vent damping is by looking at the spectra of the vent: if it's a single narrow peak, then the system is a conventional vented-box. As the vent output spectrally broadens, it becomes more like a TL. Changing the source impedance (with a 2-ohm series resistor) during the measurement phase will also reveal how sensitive the system is to dynamic Qts shifts, and to amplifier damping factor.

The system is designed to work with low to zero-feedback vacuum-tube amplifiers, and connected to the 8-ohm tap of the output transformer. That gives a source impedance in the 1~2 ohm range, and a slight mistuning when connected to high-damping-factor amplifiers with a Zout below 0.2 ohm. As mentioned before, this speaker is not intended for use with high-damping-factor Class AB transistor amplifiers - there are many other speakers that are more suitable.

Last edited by Lynn Olson; 26th October 2012 at 12:42 AM.
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Old 26th October 2012, 12:40 AM   #8287
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Lynn ... First to say, looks great, thanks. Would you hit the pic again with higher res, please. More detail can reveal a lot. Zene
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Old 26th October 2012, 12:55 AM   #8288
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Uh, that's all the detail there is; it was taken with an iPhone, and tweaked a bit in Photoshop to squeeze out more detail.

The woofer is surface-mounted, but there's no benefit to that except expediency when choosing different 15" woofers with different bolt circles. Now that I've settled on the GPA 416B Alnico 16-ohm woofer, I can mount the woofer in a rebate so the faceplate is flush with the front panel. Then again, maybe not, so the front panel is bit thicker at the most critical mounting location. Acoustically, there's no difference, since 700~750 Hz is as high as this woofer is going to go.

The asymmetry and use of 30-degree sub-panels is a diffraction-reducing measure; the alternative would be large-radii curved panels, but that might make construction a bit more difficult.

I haven't yet figured out an attractive-looking cradle for the compression driver; it needs to have about an inch of front-to-back travel so it can be time-aligned in-room (time-aligning partly depends on seating height).

The other reason for the slanted front panel is esthetic; rotating a big cabinet 24~30 degrees so it matches the angle of the AH425 looks kind of stupid. I don't mind rotating a slim speaker like the Ariel, which is only 8" wide, but a cabinet that is 25" wide is another story.

The speaker sounds best with the aim point about 1~2 feet in front of the listener, which is where the 24~30 angle comes from.
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Old 26th October 2012, 01:09 AM   #8289
badman is offline badman  United States
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Quote:
Originally Posted by Lynn Olson View Post
The cry of the Internet: "pics or it didn't happen".
Absolutely- and there's a good reason for that- a picture is worth a thousand words. And by my count, this thread owes us all about 500 pictures

Just playing, it's just very helpful to have a good image when we see how the theory gets applied in practice. I also use Ultratouch, though not immediately in the vent (the foam partially fills my vents as you see). The ultratouch is suspended between the ribs bracing the enclosure shell, and the rest of the bracing structure (so it's spaced about 1" away from the walls at any given point). By doing it this way, it encounters a higher velocity area than it would, pressed up against the enclosure walls where velocity is at its lowest.
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Old 26th October 2012, 01:56 AM   #8290
limono is offline limono  United States
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Altec 19 using 416 driver has 11 cu.ft , no wonder you have less bass than desired Personally , I'd just build another enclosure for 416 and add another 3-10 horn channels to it
Lynn , time is running out , you remember technicolor and you still play 15" plus horn ???
Did you ever hear what good midbass or at least upperbass horn does for music ? I think you need " a change of direction"
Rgrds, L
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