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I'm experimenting with waveguide + cardioid woofer at the moment (ER18DXT and the 27TBCD-DXT tweeter). Even though I'm in a different category from Lynn's efficiency figures and design preferences there is something to be said about the nature of the sound in this configuration. The difference from conventional speaker boxes is striking and the sound is very immediate, unobstructed.
Working with open baffle is very challenging though, I underestimated the challenge.
Working with open baffle is very challenging though, I underestimated the challenge.
I could not agree more. We are running a pair of Rythmik 15" per side crossed around 60Hz at the studio and I am also running a stereo pair of 15" at home with my open baffles. We tried higher crossover points in both places and 70-80Hz was too high IMHO. I did not intend to runs subs at home and started out with Lambda Dipole 15s in the baffles, but they could not give me what I was looking for, so I swapped those out for some low Q B&C woofers and added the Rythmik subs in PVC plumbing tubes directly behind the baffles.
Greg
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They are pretty groovy, I love them. As big a scary as they look, they don't sound that way at all, they just get out of the way of the sound, the music and the emotions. Not perfect, but still my favorite.
I am not disagreeing with you either. The point I am trying to make is don't over think this, build it first, then you might discover you have madly fallen in love with music again, then after you have spent considerable time with it tweak it the way you want.
I have been guilty in the past of trying to perfect designs before even starting them then find that a year has passed without having started it, then another great design comes along and it all starts again. Yes you could consider building a slot loaded open baffle sub to add to this. You might find though building Lynn's speaker brings you so much enjoyment there is no need for a sub.
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I have had the complete opposite experience. I don't want to hijack this thread so I will leave it at that
Although I'm not always on the same page as Dr. Geddes, I agree about the desirability for multiple subs scattered around the room - three or four, for example.
One of the more annoying things about 2-speaker stereo is the conflict between speaker locations for smoothest bass and the speaker locations for best imaging. It is very unlikely these will be the same, and I personally prefer to optimize image quality, and use other methods to smooth out the bass. This is where multiple subs come in handy - and the more subs you use, the less acoustic power they need to radiate, since you're not trying to push power into an acoustic null.
Since it is pointless to drive a low-efficiency, heavy-cone subwoofer with a tube amp, that's where well-designed Class AB or Class D transistor amps come in. There's not much sensation of timbre below 80 Hz, and certainly hardly any at all below 40 Hz. The natural superiority of transistor amps in driving shaker tables - one of the first industrial applications for the Crown DC300 - is just as good for driving a subwoofer.
I have no idea if servo feedback is audibly cleaner than a non-feedback setup, partly because perception of IM and THD in the sub-80 Hz region is fairly low (compared to the much more critical region between 1~5 kHz). Maybe it sounds better, maybe it doesn't. Subwoofer drivers are all woefully inefficient and need lots of power to do their task. Again, the more you use, the less power each one needs.
As for my own setup, it's kind of a hassle to sample the input of the Karna amplifier for the subwoofer drive without sonic contamination. Sure, I can build yet another box that has JFET-input buffers to drive the subs and associated amps & lowpass crossovers, but first I want to complete my own pair of the new loudspeakers.
As for the resistive-vent enclosure for the Altec/GPA 416B Alnico, it uses a slot vent like the Onken or Fonken. Unlike the Onken or Fonken, it uses a single wide vent at the base of the cabinet, instead of two going up the left and right sides. I thank Planet10 for providing assistance on likely alignments and vent geometries - resistive vent enclosures are not well documented in the literature. In subjective terms, box frequencies between 30 and 35 Hz sounded good, just a bit lower than standard alignments. There's also the option of lining one side of the vent with carpeting, which provided additional resistive loss.
The reason to use a resistive vent versus a conventional vented-box is twofold: a conventional VB is quite sensitive to amplifier source impedance as well as dynamic variations in BL product for the driver. In a conventional 4th-order acoustical highpass filter (which is what a VB is), more than 90% of the filter damping is provided by the amplifier. In addition, this amplifier damping is "seen" through the BL product of the loudspeaker, which is not that linear. The "L" of BL product is the length of the voice, which of course is constant, but the "B" are the magnetic lines of force that cut through the voice coil - and this does vary, even for underhung voice coils.
As with the Ariel, both the enclosure alignment and crossover architecture are optimized for source impedances in the 1~2 ohm range, which is typical for direct-heated triode amplifiers that do not use feedback. Since there are zillions of Class AB high-feedback transistor amplifiers with ample (100~1000W) power, there are other speakers (typically less efficient) that are better matches for them. The new loudspeaker is optimized for moderate-power vacuum-tube amps in the 4~60 watt range, which covers most tube amps.
One of the more annoying things about 2-speaker stereo is the conflict between speaker locations for smoothest bass and the speaker locations for best imaging. It is very unlikely these will be the same, and I personally prefer to optimize image quality, and use other methods to smooth out the bass. This is where multiple subs come in handy - and the more subs you use, the less acoustic power they need to radiate, since you're not trying to push power into an acoustic null.
Since it is pointless to drive a low-efficiency, heavy-cone subwoofer with a tube amp, that's where well-designed Class AB or Class D transistor amps come in. There's not much sensation of timbre below 80 Hz, and certainly hardly any at all below 40 Hz. The natural superiority of transistor amps in driving shaker tables - one of the first industrial applications for the Crown DC300 - is just as good for driving a subwoofer.
I have no idea if servo feedback is audibly cleaner than a non-feedback setup, partly because perception of IM and THD in the sub-80 Hz region is fairly low (compared to the much more critical region between 1~5 kHz). Maybe it sounds better, maybe it doesn't. Subwoofer drivers are all woefully inefficient and need lots of power to do their task. Again, the more you use, the less power each one needs.
As for my own setup, it's kind of a hassle to sample the input of the Karna amplifier for the subwoofer drive without sonic contamination. Sure, I can build yet another box that has JFET-input buffers to drive the subs and associated amps & lowpass crossovers, but first I want to complete my own pair of the new loudspeakers.
As for the resistive-vent enclosure for the Altec/GPA 416B Alnico, it uses a slot vent like the Onken or Fonken. Unlike the Onken or Fonken, it uses a single wide vent at the base of the cabinet, instead of two going up the left and right sides. I thank Planet10 for providing assistance on likely alignments and vent geometries - resistive vent enclosures are not well documented in the literature. In subjective terms, box frequencies between 30 and 35 Hz sounded good, just a bit lower than standard alignments. There's also the option of lining one side of the vent with carpeting, which provided additional resistive loss.
The reason to use a resistive vent versus a conventional vented-box is twofold: a conventional VB is quite sensitive to amplifier source impedance as well as dynamic variations in BL product for the driver. In a conventional 4th-order acoustical highpass filter (which is what a VB is), more than 90% of the filter damping is provided by the amplifier. In addition, this amplifier damping is "seen" through the BL product of the loudspeaker, which is not that linear. The "L" of BL product is the length of the voice, which of course is constant, but the "B" are the magnetic lines of force that cut through the voice coil - and this does vary, even for underhung voice coils.
As with the Ariel, both the enclosure alignment and crossover architecture are optimized for source impedances in the 1~2 ohm range, which is typical for direct-heated triode amplifiers that do not use feedback. Since there are zillions of Class AB high-feedback transistor amplifiers with ample (100~1000W) power, there are other speakers (typically less efficient) that are better matches for them. The new loudspeaker is optimized for moderate-power vacuum-tube amps in the 4~60 watt range, which covers most tube amps.
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In my view the old days of a single speaker wire and a crossover have long gone, with the simply massive leap in available pro-audio digital crossovers it's now possible to do a very effective and economical trip-amp arrangement.
For instance with a 24bit/96kHz conversion to digital piped into a digital crossover can then drive a small tube amp for the tweeter, a medium tube amp for the midrange and then a solid state amp for the bass/sub.
For CD's etc you can of course merely up-convert to 88.2 or 96kHz for the crossover. In that way you get each transducer properly driven directly from real amps, and push the awkward crossover technology into the digital domain, which can then be tweaked at will for the perfect sound, corrected for rooms as required with a DEQ unit - still in the digital domain.
This approach then also allows you to use the Open-Baffle technology with some decent correction for the response as required - so the baffle etc can be focussed on reducing stored energy rather than ultimate response curves.
Just my thoughts on the quest for the ultimate loudspeaker!
Funny how the big Altec multicells look so intimidating but actually sound sweet and gentle. Not that you want to get the EQ wrong - like all horns, they want to be treated with respect, and that means getting the EQ and crossover just right. Horns certainly have a way of letting you know when the crossover is too low or the EQ is wrong.
Hi Lynn
As far as the subs go, there is no need to develop your own amps. The Rhythmic Audio subwoofer solution comes with their own amps, which have the servo-feedback circuitry built in. The amps have built-in adjustments for 'Delay/Phase', 'Crossover (frequency)', and 'Level'. It has a further switchable parametric equalizer with adjustments for 'Gain', 'Bandwith', and 'Frequency'. I am not affliated, just a fan.
As far as the main speakers are concerned, I was thinking that the depth of the mid-bass box can be reduced to reduce the volume and so reduce the low bass output. The front dimensions must be kept the same so not to affect the XO. An different alternative would be an open baffle or a lossy cardoid box that will limit low bass output. Just my thoughts.
Enjoy,
Deon
As far as the subs go, there is no need to develop your own amps. The Rhythmic Audio subwoofer solution comes with their own amps, which have the servo-feedback circuitry built in. The amps have built-in adjustments for 'Delay/Phase', 'Crossover (frequency)', and 'Level'. It has a further switchable parametric equalizer with adjustments for 'Gain', 'Bandwith', and 'Frequency'. I am not affliated, just a fan.
As far as the main speakers are concerned, I was thinking that the depth of the mid-bass box can be reduced to reduce the volume and so reduce the low bass output. The front dimensions must be kept the same so not to affect the XO. An different alternative would be an open baffle or a lossy cardoid box that will limit low bass output. Just my thoughts.
Enjoy,
Deon
Forgot to add: the Rhythmic Audio system even corrects for things such as memory distortion. Here is a link to the Rhythmic Audio website:
Rhythmic Audio products page
Enjoy,
Deon
Rhythmic Audio products page
Enjoy,
Deon
Also forgot to add, the RA subs also have toggle-switch adjustments for the steepness of the XO slope (12dB/24dB), a rumble filter, adjustment for low frequency extention (14Hz,20Hz,28Hz), and damping (lo,mid,hi).
Greg, I'm curious to know what was your experience with the adjustments. How easy or how hard, and how different for the different venues and needs (studio vs. home).
Thanks,
Deon
Greg, I'm curious to know what was your experience with the adjustments. How easy or how hard, and how different for the different venues and needs (studio vs. home).
Thanks,
Deon
The problem with VLF distortion is that it happens at frequencies where the ear is much more sensitive, and can easily appear louder than the signal itself:
Woofer measurements
Well, we've ended up with pretty much the same settings at my home and the studio. Max extension(14Hz), highest damping setting(this switch has a tremendous effect and can take the subs from typical floppy sounding to super controlled and tight) and about 60hz crossover. I should note though, that at the studio we are using the BSS Omnidrove that controls the mains(Lambda and Beyma TPL-150) for crossover and EQ functions for the subs. At my home, I use the built-in crossover and parametric EQ on the Rythmik plate amps.
I've also heard others claim that the Rythmik stuff is just average or not that good. Well, it's all up to integration, isn't it. If you don't get them adjusted and mated with the speakers very well, of course the resulting outcome might not sound that good. Properly implemented, these subs are excellent.
Also of tremendous sound and quality would be Dannys take on open baffle servo subs over at GR Research. He is partnered with Brian at Rythmik on these. I've heard them several times and they are superb and dig really deep. He uses them successfully with his open baffle, high efficiency models with no problem, so in practice, low efficiency open baffle drivers are working just fine with nearly 100db/spl sensitivity speakers.
I also have to note that Bob Katz of Chesky Records and masterng fame has heard the subs and is impressed as well. Once he hard the mains, he thought they might be the best large monitors he's ever heard in a studio setting. Now they we added the subs, we are possibly surpassing the sound of his own mastering studio. I used to be an assistant for him many years ago and he is local in town here in Orlando.
Greg
What multiple subs do is to use lower energy to excite multiple modes so that the energy is scattered. This can improve performance such that you do not hear the concentrated peak or dip. The tradeoff is that the low frequency phase is now not coherent with the nature of the original musical instrument which may contain complex spectrum. What I have not tried is the double bass array arrangement which seems like a more technically desirable solution. Has anyone had any experience with it?
Wow serendipity. I was just getting around to asking about this and above is my answer.
An amp like mine with a Susan-Parker Zeus output power stage, also with no global feedback, and with the output transformer wired in 2:1 mode has an output Z of 1 ohm (right in the pocket). With a nominal 16 ohm load, the power output is ~26 Watts, again in the pocket.
This speaker is looking good.
In 4:1 mode, output is ~7.5 Watts, but the output Z is 0.25 ohms, perhaps too low. However, if only half of the windings are used, then output Z can be 0.5 ohms. Output Z easily can be brought up to the 1~2 range in 4:1 mode by using resistors instead of external links to wire up the 4:1 mode. If 7.5 Watts is enough (it should be), then the 4:1 OPT mode with the external resistor used as a link could be the best match because 4:1 mode measures the cleanest.
resistive-vent enclosure for the Altec/GPA 416B Alnico
Hi Lynn
are there more details about your resistive-vent enclosure for the Altec/GPA 416B Alnico documented somewhere ?
i am also intrigued by the concept but cannot find a lot of information .
so if you could shed some more light on that concept , and the results your are getting, that would be much appreciated .
regards
malcolm
Hi Lynn
are there more details about your resistive-vent enclosure for the Altec/GPA 416B Alnico documented somewhere ?
i am also intrigued by the concept but cannot find a lot of information .
so if you could shed some more light on that concept , and the results your are getting, that would be much appreciated .
regards
malcolm