Lynn's rehab? Oh, you meant speakers.I've become comfortable numb.
John - you should have a New Years Resolution to be a bit more congenial.
There were points in this thread that were quite interesting. I think that Lynn learned some things, not all what he expected and that seems to have set him back. Thats R&D.
I agree with Dr. Geddes' summary. The heavy equalization requirements of dipoles offset much of the attraction, particularly since I'm only interested in developing a loudspeaker for use with low-power triode amplifiers.
People who are using Class AB or Class D transistor amplifiers have many more choices in loudspeakers, since 200~300 watt transistor amps are readily available at moderate prices. In the Class A direct-heated triode world, 15 watts is a lot of power, and 60 watts is starting to get up there for PP pentodes running in Class AB. Tube watts are expensive watts, and EQ and multi-amping just make them that much more expensive. It hasn't escaped my notice that many of the dipole builders have ended up going down the path of professional SR practice, with multi-amp arrays, and digital EQ and crossovers.
It might sound mundane, but I'm considering a resistive-vented enclosure for an Altec/GPA 416 and/or AESpeakers TD15M. Planet10 has suggested starting with a 4.5 cubic foot resistive-vent enclosure and seeing how that works out. I'm also examining Jeff Markwart's cabinet plans for the Altec Model 19, with its 6.5 cubic foot vented enclosure for the 416 driver. The appeal of a resistive-vent alignment is that it is less sensitive to dynamic Qts variations than a classical vented alignment (at the expense of ultimate bass reach). This is important with DHT amplifiers, since damping factors can range from 2 to 5, depending on the selection of output tube and transformer primary values.
Since I started this thread nearly three years ago, there is now much more information about horn and waveguide design - thanks to Dr. Geddes, Bjorn Kolbrek, JMMLC, and many, many others who have generously contributed here in the DIYaudio forums.
People who are using Class AB or Class D transistor amplifiers have many more choices in loudspeakers, since 200~300 watt transistor amps are readily available at moderate prices. In the Class A direct-heated triode world, 15 watts is a lot of power, and 60 watts is starting to get up there for PP pentodes running in Class AB. Tube watts are expensive watts, and EQ and multi-amping just make them that much more expensive. It hasn't escaped my notice that many of the dipole builders have ended up going down the path of professional SR practice, with multi-amp arrays, and digital EQ and crossovers.
It might sound mundane, but I'm considering a resistive-vented enclosure for an Altec/GPA 416 and/or AESpeakers TD15M. Planet10 has suggested starting with a 4.5 cubic foot resistive-vent enclosure and seeing how that works out. I'm also examining Jeff Markwart's cabinet plans for the Altec Model 19, with its 6.5 cubic foot vented enclosure for the 416 driver. The appeal of a resistive-vent alignment is that it is less sensitive to dynamic Qts variations than a classical vented alignment (at the expense of ultimate bass reach). This is important with DHT amplifiers, since damping factors can range from 2 to 5, depending on the selection of output tube and transformer primary values.
Since I started this thread nearly three years ago, there is now much more information about horn and waveguide design - thanks to Dr. Geddes, Bjorn Kolbrek, JMMLC, and many, many others who have generously contributed here in the DIYaudio forums.
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My speakers will run off an I-Pod! And closed box is virtually immune to driver Qts variations. Might be something in what I do - Ya-Think?
There are subtle differences between closed-box and resistive-vent designs, and I'd like to explore them. The Altec/GPA 416 is also 6.5% efficient in Theile/Small terms, and that translates to about 100 dB/metre, give or take a dB or two. Just about enough for a 15-watt amplifier.
It is surprising how influential the Lansing Iconic turned out to be, with a 15" woofer and a compression driver and horn on top. Even the selection of crossover frequencies - 800 Hz - turns out to be much the same, more than seventy years later.
It is surprising how influential the Lansing Iconic turned out to be, with a 15" woofer and a compression driver and horn on top. Even the selection of crossover frequencies - 800 Hz - turns out to be much the same, more than seventy years later.
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Might be something in what I do - Ya-Think?
Yeah, I was just going to say, we are getting pretty close to your speakers...
In all fairness to Earl, he used to go both ways...sealed and ported.
and while they may not theoretically be ideal, the GPA 604 Series III is a very good value, (terrific sounding with a good crossover), and works in a variety of enclosures including configured as a dipole quite well. You just end up building a Quad 57 size baffle if you go the dipole route and add subs if you want them. This is too big for me so I have them in 110 liters (aperiodic) vented.
Chris
p.s. In general I much prefer the sound of sealed bass, but with what I running at home right now, sealed doesn't provide any.
and while they may not theoretically be ideal, the GPA 604 Series III is a very good value, (terrific sounding with a good crossover), and works in a variety of enclosures including configured as a dipole quite well. You just end up building a Quad 57 size baffle if you go the dipole route and add subs if you want them. This is too big for me so I have them in 110 liters (aperiodic) vented.
Chris
p.s. In general I much prefer the sound of sealed bass, but with what I running at home right now, sealed doesn't provide any.
Hi Lynn,
Have you evaluated (compared) the sound qualities of bass produced by tube or solid state amps in a properly setup active system? Do you prefer tube (or SET) to handle the bass in such system?
As to the multiple drawbacks of dipole, in system integration, actually it's not essential to have multi-amp "arrays", not that scary. 2-way active (4 channels of amplification in total) can already free up a lot of burden either way - that means an even simpler and 'purer' amp circuit can be used in the delicacy mid-high section.
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I found that people tend to stick with high damping amps and 'twist' other portion of the system to suit it. Or it seems the both ends of most given systems stay very 'stubborn' -- speaker components and amps hold their basic damping characters without much changes. In most cases the box tunings are inserted between them to get a proper system Q by adding another spring-mass resonant sub-system. Maybe we can call this a necessary evil, but sometimes it's not that necessary.
Hi Q woofers are utilized by some people on dipole applications while some others dislike the weak motors. When low Q woofers are used, massive EQ is inevitably applied and disliked by (more or less) the previous camp and others don't like dipole at all.
Oh well, why don't we give up the constant voltage output charactor of 'ordinary' amps? This frees up a lot of possibilities to set up a 'dreamed' system.
I can understand the 'conveniences' in combinations of amps with constant voltage O/P and low damping speakers for commercial products. But we DIYers don't have to constrain ourselves in that concept.
I'm using dipole bass, with woofer of Qts=0.3 and small baffles. My digital EQ is set flat under 160Hz. Compensation is done by 1st order passive xover in line level. And the amp driving the bass has an output impedance of 20 Ohm.
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Look to the Monacore SP-38/300N in about a 1.3 cubic foot aperiodic enclosure. (..low cost, good performance.)
For something similar to the Monacore but alnico, consider the Weber 15A200 (basically a nos jensen) in about a 1.7 cubic foot aperiodic enclosure.
For more low freq. extension, a little more eff., and a much higher price, consider the Olimpia Audio W416 in about 2.3 cubic foot aperiodic enclosure.
The target Qtc. (I *think*) should be about 1.2 factoring in aperiodic sp-loss, some gain from the impedance interaction, and some baffle-step loss.
To get more extension you can also go the dual-chamber route, with the added "expense" of additional volume for both the "main" chamber and the slightly larger secondary chamber. Qtc. should be lower for this design (in the "main" chamber), and you probably should factor in some baffle step compensation.
Here is a design (PDF link) using the dual-chamber approach:
http://user.faktiskt.se/M_N/WD25T_Part1.pdf
LINK problems.. see search link here (2nd one down):
http://www.google.com/search?client...=hp&q=hifi+world+aperiodic&btnG=Google+Search
The Qts of that driver is .41 btw.. with an fs around 25 (89 db).
Look to Spica's minimum phase crossover (..Bessel 4th order on the low-pass and 1st order for the high-pass). It provides some additional acoustic center off-set for the horn as well (..so it won't need to protrude out quite as far from the speaker's front). It should also "clip" the problem upper freq. range from the 15" and the JMLC flared horn should handle the 1st order reasonably well provided it's crossed at the right freq.. (..considering the low freq. of the horn and the amount of round-over I'm guessing around 900 Hz.)
Stereophile: Spica TC-60 loudspeaker
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John - you should have a New Years Resolution to be a bit more congenial.
I was being congenial.
Well I'm currently running Altec 416-8A drivers in the VOTT 828 bass cabinet. (the bass part of the A7). That's a net box volume of about 12 cubic feet - 340L.
The original box needs a lot of bracing and damping, but that's not hard to do.
Getting the port size and tuning right makes a BIG difference in the sound. Tuned right it has the clean sound of a sealed box, but with more low end.
(hint, the original box is tuned over an octave too high)
I'll be interested to see what Lynn does with the GPA 416 in a smaller box.
The original box needs a lot of bracing and damping, but that's not hard to do.
Getting the port size and tuning right makes a BIG difference in the sound. Tuned right it has the clean sound of a sealed box, but with more low end.
(hint, the original box is tuned over an octave too high)
I'll be interested to see what Lynn does with the GPA 416 in a smaller box.
I have a little bit of experience with time-aligned speakers - the Audionics LO-2 was designed before the introduction of the Spica TC-50, and had better square-wave response. I usually avoid 1st-order highpass filters due to poor excursion control - by lowering the Q of 2nd and 3rd-order highpass filters, I can reduce the amount of time-domain overshoot without exacting too great a cost in excursion control. The antique LO-2 (circa 1979) used a low-Q 2nd-order filter, and it worked fine - certainly sounded better than the 1st-order filter I tried at first, which had pretty obvious tweeter overload, not my favorite sound.
Many years later, I expected the Klipsch Chorus to be a real monster thanks to the PA-grade plastic horns, but much to my surprise, it dropped into place in a couple of days. Kind of unexpected, with drivers that rough. I could of twiddled with it for a longer period of time, but speaker recycling quickly reaches diminishing returns. (First you redesign the crossover - then replace the HF drivers - then the bass driver - and when you're done, all that's left of the original speaker are the cabinet and speaker terminals.)
The MF horn retained its 3rd-order highpass filter, but as you can see from the impulse and group-delay responses, I was able to coax pretty decent time response out of it. Although it's cool in a technical kind of way, I wonder if this isn't the audio equivalent of riding a unicycle - a crowd pleaser, but not exactly practical transportation.
Although this kind of response sure looks pretty in MLSSA, I'm not too sure what it correlates with subjectively. But if you can do it for free, well, why not? We all like nice-looking graphs.
The main advantages of resistive-vent enclosures are fairly subtle - lowered sensitivity to driver Qts shifts (desirable for unknown-output-impedance tube amps), and a freedom from a zero in the response around 1 Hz (due to unavoidable box leaks, or Ql). The examplar for this breed of cat is the Dynaco A25, but I have a rather different purpose in mind.
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From listening tests, Ipod output is inverted. I hope you noticed it. Makes big difference. Also, Ipod performs poorly unless the charger is plugged in. Improved power source improves sound. In the end, Ipod could really sound impressive, much to my surprise.My speakers will run off an I-Pod! And closed box is virtually immune to driver Qts variations. Might be something in what I do - Ya-Think?
I've run my speakers off headphone amps. Kinda fun. That's the thing about efficient speakers, it takes so little power to make some sound.
There is a fellow over on the Altec forum building an AM radio with a horn and driver. No power used except what comes over the air! Basically the old crystal set with a very efficient speaker.
There is a fellow over on the Altec forum building an AM radio with a horn and driver. No power used except what comes over the air! Basically the old crystal set with a very efficient speaker.
I just wanted to add a point to the one you think I missed.
I'd also like to get speakers with as high effeciency as I can get. I also realize then the electronics also need to be improved significantly, and the cost goes up fast.
Hello Lynn,
If you go on this rather more conservative path, why not consider something a la Audiokinesis design? Meaning a dipole, dual 15" drivers back to back.
Pros: lower distorsion, higher sensitivity (right in the 102dB ballpark), higher power handling (possible low-end eq for the little excursion of TD15M), dipole radiation pattern.
Cons: probably larger volume (although now a closed box can be imagined), very creative design to minimize and absorb edge diffractions (the sides will be wider, similar to a monopole speaker), and possible distorsion effects due to double cone pressure interaction (although this is not really documented).
Did I summed up this well?
If you go on this rather more conservative path, why not consider something a la Audiokinesis design? Meaning a dipole, dual 15" drivers back to back.
Pros: lower distorsion, higher sensitivity (right in the 102dB ballpark), higher power handling (possible low-end eq for the little excursion of TD15M), dipole radiation pattern.
Cons: probably larger volume (although now a closed box can be imagined), very creative design to minimize and absorb edge diffractions (the sides will be wider, similar to a monopole speaker), and possible distorsion effects due to double cone pressure interaction (although this is not really documented).
Did I summed up this well?
I would to follow someone doing that!!! I have 4 TD 12" drivers unused and many, many waveguides/CDs in my garage.
The TD15M doesnt go that low though, Maybe the TD15S series is a better choice.
Doug20,
I second a design using similar bipole principles that Duke of AudioKinesis uses in his Planitarium Beta speakers.
Even though I have not heard the Beta bipole speaker. I have heard the Dream Maker on two different occassions at audio shows. And I can say that they do a great job in giving a full and blanced soundfield that closely mimics electrostatic speakers.
I feel the Dream Maker to be one of the more realistically sounding speakers that I have heard. As always, my opinion is subjective. So, take it with a grain of salt.
Duke is a class act, and could bring something valuable to this discussion.
Are you reading this Duke?
NW
I second a design using similar bipole principles that Duke of AudioKinesis uses in his Planitarium Beta speakers.
Even though I have not heard the Beta bipole speaker. I have heard the Dream Maker on two different occassions at audio shows. And I can say that they do a great job in giving a full and blanced soundfield that closely mimics electrostatic speakers.
I feel the Dream Maker to be one of the more realistically sounding speakers that I have heard. As always, my opinion is subjective. So, take it with a grain of salt.
Duke is a class act, and could bring something valuable to this discussion.
Are you reading this Duke?
NW
