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
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.
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.
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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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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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.
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.
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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.
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.
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.
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
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
I have been using a 50Hz bass horn with a Vitavox K15/40 drivers. I don't get the extension, but it integrates and images well. Probably the time alignment issue takes this outside of any acceptable spec, however I have always wondered how direct radiators ever achieve time alignment (due to the phase shift that comes with flat response - which horns in the pass band in theory dont have). . The driver on the 425 horn is Yamaha JA6681B, and I have a Fountek ribbon tweeter next to it. Compared to a Fostex T900A horn tweeter I prefer the ribbon, bearing out what Lynn says, and may well go for the RAAL.
martin
An externally hosted image should be here but it was not working when we last tested it.
martin
Have you considered using a pair commercial grade ballbearing drawer slides? K&V make these and I believe they can be had in a 6" length. They can be mounted flat ... as in under your horn carriage ... so, directly attached to the woofer top panel. Slide horn in or out to suit
Hi Lynn
I hope you don't mind all the questions, but I guess everyone wants to lnow the thoughts of the master. I hope you don't mind if I add a few of my own.
As to box loading, IIRC you did consider open-baffle for the 'Beyond the Ariel' project, but what do you think of cardioid loading. To me it seems to be halfway between resistive vent and open baffle. Possibly a good compromise between them? I have read a lot of good comments about it.
Second, have you seen North Creek Music's MAPD driver loading technique? It looks very interesting and could work well, but needs a very large box. However if, as the advertising blurb states, and it does reduce suspension non-linearities, it could be interesting. It will just be impractical for a drivers with very large Vas (like my Tannoy DU386 with a Vas of 770 liters ).
Thanks again for putting up with all the questions.
Regards,
Deon
PS. I was curious to read your opinion on the MLTL. Is it just another form of TL, i.e. good?
I hope you don't mind all the questions, but I guess everyone wants to lnow the thoughts of the master.
I hope you don't mind if I add a few of my own.As to box loading, IIRC you did consider open-baffle for the 'Beyond the Ariel' project, but what do you think of cardioid loading. To me it seems to be halfway between resistive vent and open baffle. Possibly a good compromise between them? I have read a lot of good comments about it.
Second, have you seen North Creek Music's MAPD driver loading technique? It looks very interesting and could work well, but needs a very large box. However if, as the advertising blurb states, and it does reduce suspension non-linearities, it could be interesting. It will just be impractical for a drivers with very large Vas (like my Tannoy DU386 with a Vas of 770 liters
).Thanks again for putting up with all the questions.
Regards,
Deon
PS. I was curious to read your opinion on the MLTL. Is it just another form of TL, i.e. good?
How do you avoid rattles?Have you considered using a pair commercial grade ballbearing drawer slides? K&V make these and I believe they can be had in a 6" length. They can be mounted flat ... as in under your horn carriage ... so, directly attached to the woofer top panel. Slide horn in or out to suit
The tolerances in this type of drawer slide is very close. I wouldn't expect any rattles.
http://www.knapeandvogt.com/8800_Heavy-Duty_Full-Extension_Drawer_Slide.html?page=details.35#details
http://www.knapeandvogt.com/4100_Low_Profile_Box_Drawer_Slide.html?page=details.46
Other makers offer a similar designed slide. If you look at the section thru the slide (in the .pdf file) ball bearings are loaded in four places (bearings not shown). They are loaded where each section is curved to correspond with the curve of the mating section. The whole assembly is pretty tight. They offer a 12" length (in the heavy duty) and 8" (in the medium duty) but I'm pretty sure I've seen shorter.
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The exit angle of the 288 has been measured by Bjorn Kolbrek as being between 7 and 8 degrees. The AH425 is optimized for that angle. The Radian 745P and 745Neo is 4 degrees, according to the engineer I spoke with at Radian, which gives a very slight mismatch to the AH425 but I saw no time-domain artifacts when I measured the Radian/Azurahorn combination.
By measurement and audition, both the Altec/GPA 288 and the Radian 745Neo are excellent choices for the AH425, with very flat responses (+/- 1 dB) in the 700 Hz to 7 kHz range. No equalization was required - the system response is as flat as any soft-dome tweeter, but with 10~20 dB more headroom.
Martin of Azurahorn is using the rare Yamaha driver, and he's getting really good results as well.
By measurement and audition, both the Altec/GPA 288 and the Radian 745Neo are excellent choices for the AH425, with very flat responses (+/- 1 dB) in the 700 Hz to 7 kHz range. No equalization was required - the system response is as flat as any soft-dome tweeter, but with 10~20 dB more headroom.
Martin of Azurahorn is using the rare Yamaha driver, and he's getting really good results as well.