My Personal Audio Adventure |
|
|
|
|
|
Design C
This is my latest subwoofer. I redesigned the antipodal subwoofer (Design B below) to be "Push/Pull" after correspondence, about a year ago, with Siegfried Linkwitz. He made it clear to me that he felt I had removed a major advantage of the folded baffle dipole woofer (Design A below). By reconfiguring the drivers relative to each other I changed the subs operation from a "Push/Pull" design to a design which was not "Push/Pull". Push/Pull causes the cancellation of 2nd order distortion (please feel free to correct me if I got the order of distortion cancellation incorrect - I believe that I've seen it published as both "even" and "odd" in different publications and web sites - I would hope it to be congruent to a "Push/Pull" electrical amplifier circuit that automatically has it's 2nd order distortion canceled). So I spent about 2 weeks thinking about the Antipodal design and how I could change it to be "Push/Pull" while keeping it Antipodal. Earlier this year I finally finished the wood cutting and construction of the Push/Pull design. To build the Push/Pull Antipodal, I took apart the first antipodal design and modified it with new wood parts. I currently have the Unity Horn (acquired from Lambda Acoustics: http://www.lambdacoustics.com/) and sub crossed over at 300 hz (active 4th order on the sub with a Lambda/Unity passive 4th order crossover on the Unity). With extensive EQ on the sub, it has an f3 at the designated listing position of +/- 20 hz. The response changes as one moves around the room due to typical variable room acoustics. For a short discussion about cavity resonances, see Design A below. The design is wired for 8 ohms. I will try to publish a graph of the frequency response attainable at the central listening location sometime in the future. Unity Constant Directivity
Horns (Unity CDH, Unities or Unity Horn )
The Unities sound great to me, and they have only a very few hours on them - will they get better with use/break-in? They already do some things that the ESL63s will never do, like: 1) - wide dynamics (because they can play loud); 2) - high sound pressure levels (spl) and 3) - low distortion at high spl - I think I can hear this last attribute already. When I turn the volume up with peaks up to about 110 bd on really loud music, I can hear things that were previously masked by the louder sounds in the music as played on other speakers. I believe I've read that the sensitivity of our ears to different frequencies changes with respect to the sound pressure level of the frequency being heard. Lower volume sounds appear to be above some threshold where I can hear them, or maybe the Unities are more detailed than I and my wife realize when compared to our memory of the Quads. I believe that systems capable of doing well the three things listed above, can help all varieties of reproduced music sound closer to real and as the artist intended (these three things are related and maybe they are not really three individual things - it depends on how you understand and think about it). These three things are missing from the ESL63s at the volumes I want to have available for listening - maybe I just need a smaller room? Regarding imaging, I've never been into imaging - to me it is an artificial artifact, but sometimes it is there. I've not heard it at live performances, acoustic or amplified music, but it can be discussed as an artificial attribute. Imaging is different with the Unities as compared to the Quads. In some ways the Unities seem to image better than I and the wife remember the Quads imaging. The speaker radiation pattern has changed: from the ESL63's dipole radiation with it's direct sound plus front and rear reflections to the Unity's direct sound with few reflections. I've not listened to many horns; I have listened to some, most hurt my ears (crazy frequency response of poorly designed horns? I don't know), but the Unity's don't sound like the horns I've heard in the past. It depends on what tradeoffs you are willing to make. Both My wife and I are looking forward to listening to music on our Unity Horn -Push/Pull-Antipodal-Dipole (UPAD) sound system. All the listening to the Unities was done with my Wright Sound Company amps. I don't plan on listening to the Quads any time soon. So what other audio equipment
is connected in my system:
Future plans
Lambda Apollo woofer driver specs similar to: Pro Style Bass-Mid, Bass Horn
see at http://www.lambdacoustics.com/drivers/TD15M.html Once the woofers are in a baffle I plan to buy some wood veneers and some leather and try to make this creation attractive - I am obviously lucky that my wife appreciates the sound. August 18, 2001 |
|
ANTIPODAL FOLDED BAFFLE DIPOLE SUBWOOFER  
Design A next to Design B
The photographs of this speaker were taken while it was Under Construction - one side panel on each side of the speaker is missing - it was never completed. The panels can be seen on the Push/Pull Antipodal design (Design C above). I stopped construction to revise the design because Siegfried Linkwitz expressed concerns about it not being "Push/Pull". The output of the woofers at the sides would have been directed to the rear of the speaker when completed. The panels, once installed, would have created the characteristic dipole pressure null at the sides of the speaker - see Design C above for approximately how they would have appeared. July 27, 2000; August 18, 2001
|
|
Push/Pull SEMI-ANTIPODAL FOLDED BAFFLE DIPOLE SUBWOOFER  
This design was the result of discussions with Siegfried Linkwitz. If I remember correctly, these discussions, via e-mail, occurred near the end of 1999(?) prior to the publication of his wonderful "Linkwitz Lab" web site: http://www.linkwitzlab.com. I did not have his drawings to look at when I designed my subwoofer, but I did have his words of encouragement and instructions/direction. I didn't really know that I got it right until I saw his web site. I didn't discover his web site until after I had built my subwoofer (I think I saw something in a BASS LIST post that alerted me to it's existence). If I had known about Linkwitz's site prior to my subwoofer adventure, I would have been much more comfortable while I was designing and building my subwoofer project. The point I want to make is, if you are adventurous, that the comfort level for attempting such a project should be higher for you than it was for me. I was working in the dark, but I knew I could just start over if the subwoofer didn't meet my expectations. I hope that Linkwitz's site will further inspire those who are interested in dipole subwoofer design to create successful dipole designs of their own. I believe that Linkwitz's site has evolved, and I assume that it will continue to evolve. His web site is a great resource. My first folded baffle subwoofer is like a larger version of the Phoenix Dipole Woofer design he has published on his web site. I still have it sitting next to the "Push/Pull" Antipodal (Design C) - both are heavily equalized - but, to me and my wife, they sound fantastic together and with the Unity Horns. I have no reason to believe that the sound will degrade over time. Other speaker combinations with dipole subwoofers should sound great too, but if subwoofers based on my plans (see below) or similar plans are used, you may need some serious bass and room EQ. Mine do. I figure that the variable cavity depth on the speaker creates resonances in the frequency range from 300 Hz up to 600 Hz. It may resonate over this broad range since the cavities vary, or maybe there is a single resonance that is centered on an average cavity depth. I do not know, and I have not tested it to see where the sub resonates. This system is wired as a 2 ohm load - this has not presented any problems and the sound is fine, so far. I believe that wired as a 2 ohm load, the system should have at least 12 bd higher sensitivity than one of the drivers alone at 4 ohms. If we assume that the drivers are 87 db sensitive as has often been reported (published sensitivity is 90 bd for NHT 1259 (90 dB 2.83V/1m from Madisound web site - isn't 2.83V the voltage required for 1 watt at 8 ohms impedance), the system should be 99 db sensitive 1m. I don't know how this all actually washes out since the system is wired for a nominal 2 ohm load (based on the NHT 1259 driver nominal 4 ohm impedance), but it doesn't take much power to get the system woofing even with it being dipole. The cooling fins on the solid state subwoofer plate amp (KG-5230 from Stryke Audio) have not been noticeably hotter most of the time when I've compared them to the Push/Pull Antipodal design which is wired as an 8 ohm load (Design C above). Design A
If you want the plans I used to build these monsters, have access
to a large plotter and have AutoCad (you may be able to obtain plots from
a blueprint business which has AutoCad), I will send you electronic copies
of the plans. I plotted the drawings full scale, cut along the lines
and used the cut out pieces of paper as templates (I outlined the shapes
on the MDF and Baltic Birch Plywood). Beware that the plans are not
precisioin documents; if you undertake this project, you will need
to adjust some of the wood cuts to your actual project conditions even
if you are very precise at cutting wood. The baffles which I used
on all the projects are the same - they are just configured differently
(angled or straight - makes a different joint at corners) for the desired
function. If you want to use the NHT 1259, beware that it has been
reported that it makes some vent noise during large excursions. I
have not experienced this phenomenon, but I have eight woofers on a channel.
The woofers barely move most of the time, even during loud passages.
If there is significant vent noise, I may not be hearing it due to the
music masking it.
"Thank You" BASS List members who see this web page - I must thank all the people on the BASS List for the information which they freely share. By monitoring and lurking the list, I have learned much. The discussions on this list are invaluable to beginning to understand loudspeaker design. I've also been monitoring the Lambda DIY e-mail List (Lambda Drivers List) for quite a while too. Thank You to all those on that list who may see this web page. I have chosen my compromises,
and my adventure has just begun.
Other valuable and informative web sites which are not listed above that you might want to visit are: www.diysubwoofers.org
Good Luck on Your Adventure.
December 11, 1999; August 18, 2001; October 2, 2001 |
