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Multi-Way Conventional loudspeakers with crossovers

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Old 24th August 2012, 04:53 PM   #7841
boris81 is offline boris81  United States
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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.
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Old 24th August 2012, 09:08 PM   #7842
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I'm not disagreeing with that. But when referring specifically to the Rhythmic Audio subs with their motional feedback, they will be better in the bass than just about any non-assisted woofer. And I still contend that relieving the midbass from frequencies below circa 60Hz, which is below the area where tone is developed, will have benefits higher up. JMHO. YMMV.

Deon
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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Old 24th August 2012, 09:49 PM   #7843
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I do have a soft spot for Altec multicells. They sound completely different - I mean really different - than the traditional Altec sectoral horns.
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.
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Old 24th August 2012, 10:29 PM   #7844
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Originally Posted by DeonC View Post
I'm not disagreeing with that. But when referring specifically to the Rhythmic Audio subs with their motional feedback, they will be better in the bass than just about any non-assisted woofer. And I still contend that relieving the midbass from frequencies below circa 60Hz, which is below the area where tone is developed, will have benefits higher up. JMHO. YMMV.

Deon
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.

Last edited by Melon Head; 24th August 2012 at 10:41 PM.
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Old 24th August 2012, 10:39 PM   #7845
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Originally Posted by boris81 View Post
Working with open baffle is very challenging though, I underestimated the challenge.
I have had the complete opposite experience. I don't want to hijack this thread so I will leave it at that
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Old 24th August 2012, 11:04 PM   #7846
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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.

Last edited by Lynn Olson; 24th August 2012 at 11:30 PM.
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Old 24th August 2012, 11:57 PM   #7847
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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.
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!
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Old 24th August 2012, 11:58 PM   #7848
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Originally Posted by Pano View Post
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.
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.
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Old 25th August 2012, 12:34 AM   #7849
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Yes, very true. I guess we've both been there, suffered thru that.
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Old 25th August 2012, 07:13 AM   #7850
DeonC is offline DeonC  South Africa
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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
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