The Advent Loudspeaker
- Thread starter Zilch
- Start date
Finding the one spot where stacked Advents play substantially like singles was certainly genuine speakergeek fun.
Heh, heh....
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rsfmotoman
Super Member
:scratch2:
As much as I love my Advents, that has been my experience with my NLA's (recapped). The imaging is ok but not stellar by any means.
My best illustration of classic combing from these Advent studies occurs in the "D'Appolito" configuration. Both speakers are upside-down, stacked vertically, and the listening axis is the upper tweeter, essentially midway between the two woofers. It's the bottom tweeter doing it, apparently:
Attachments
Get set up to do some measuring, then try to make sense of what you find.
There are thousands of hobbyists doing this now.... :yes:
SpruceMoose
Super Member
Thats Just Wrong!
What would Harry Pearson THINK?Thats Just Wrong!
:
Two Advent woofers, two years apart, #1 from 1974, and #2 from 1976, both with new refoams, their boominess substantially tamed by replacing the stock foam cabinet damping with R-19 fiberglass, heavy fill, but not stuffed, as suggested by Justw @ #18, above.
Compare to nearfield measurements with factory foam damping here:
http://audiokarma.org/forums/attachment.php?attachmentid=94451&d=1213056841
Configured as shown in #49, above, using Selenium D220Ti driver, modified EconoWave crossover, and JBL PT-D95HF-1 waveguide, response is flat +/- 2 dB out to 20 kHz:
Compare to stock utility OLA performance here:
http://audiokarma.org/forums/attachment.php?attachmentid=94510&d=1213066417
Cumulative Spectral Decay and Spectrogram:
Compare:
http://audiokarma.org/forums/attachment.php?attachmentid=94511&d=1213066417
http://audiokarma.org/forums/attachment.php?attachmentid=94512&d=1213066417
Compare to nearfield measurements with factory foam damping here:
http://audiokarma.org/forums/attachment.php?attachmentid=94451&d=1213056841
Configured as shown in #49, above, using Selenium D220Ti driver, modified EconoWave crossover, and JBL PT-D95HF-1 waveguide, response is flat +/- 2 dB out to 20 kHz:
Compare to stock utility OLA performance here:
http://audiokarma.org/forums/attachment.php?attachmentid=94510&d=1213066417
Cumulative Spectral Decay and Spectrogram:
Compare:
http://audiokarma.org/forums/attachment.php?attachmentid=94511&d=1213066417
http://audiokarma.org/forums/attachment.php?attachmentid=94512&d=1213066417
Attachments
markus
Master Procrastinator
ya know Zilch . . . I have 4 or 5 pairs of these Advents . . . I think one pair might get the Econo-Zilch-Wave treatment :thmbsp:
One pair of Walnut cabinets is far from perfect, so I wouldn't feel bad hot-rodding them. . .
and the change of the stuffing is DEFINITELY on the agenda
One pair of Walnut cabinets is far from perfect, so I wouldn't feel bad hot-rodding them. . .
and the change of the stuffing is DEFINITELY on the agenda
Do you perceive the low bass to be boomy and/or muddy, Markus, particularly when used with boundary reinforcement near a wall, like most are situated?
It's ironic, if true, that L100 and Advent were introduced at the same time with similar bass response, but L100 was branded "boomy" from the very begining for its artificial bass coloration. Stereophile also found the Smaller Advent to be underdamped at about where I have these tuned now. See Fig. 4 and text here:
http://www.stereophile.com/historical/506advent/index4.html
The Advent woofer's "problem" in the region of 1 kHz, whatever its origin, remains evident in the CSD, but the second-order lowpass filter in the EconoWave crossover has supressed it significantly. The midrange is now "cleaner" with respect to the characteristic resonances. Member Jackfish pointed out this issue in an earlier post here:
http://audiokarma.org/forums/showthread.php?p=1679375#post1679375
While I haven't done any polar dispersion measurements yet, it's a good bet from what I'm hearing that the known constant directivity performance of PT waveguides has more than overcome the deficiencies of the Advent fried-egg tweeter in this respect, as highlighted by John Atkinson in the Stereophile review measurements cited above:
We suddenly have excellent imaging here, but I'm setting up a more controlled A/B evaluation to verify this striking performance improvement to be real.
In any case, stay tuned; I'll post the waveguide part number and the crossover schematic once I'm done diddlin' with it here.... :yes:
jimbofish
for TRULY GREAT MUSIC
The grille sits somewhat forward of the drivers, and the size and shape of the opening in the Masonite behind the cloth comprises a "baffle" for the tweeter, particularly, as observed and measured by Atkinson.
I suspect there's a diffraction component to this, as well as the interference masking clearly shown in my initial measurements posted earlier in this thread. The grille is an integral part of the Advent "system."
I coined the phrase "Trompe l'Oreille" to describe it; the virtual image is an auditory "trick" played by various cues in the program, and the quality of that image relies upon the clarity and integrity of those cues. It doesn't happen if the cues aren't there or are ambiguous, and they're better on some recordings than others. I'm sometimes stunned by what appears on certain older recordings as consequence, apparently, of the recording technique and the fact that it was not adulterated during mixing or mastering.
I can certainly measure the sharpness of definition of an acoustic center between sources, but how that relates to imaging is indeterminate. I have not found much in the way of research by others relating to quantification of acoustic imaging.
It's there, it's easily smeared by reflections and degraded by phase anomalies, but it also collapses with small lateral displacements if too precisely defined. Toole teaches us that, in some degree, imaging and artificial soundstage within a room are reciprocal and mutually exclusive. I can easily generate a huge soundstage by spraying the room with dispersion, but the reproduced image becomes vague and diffuse, if it appears at all, which is why controlled directivity is considered a worthwhile element in image optimization.
Acheiving a true holographic image requires more precise control than generating a planar, 2D one. At the heart of imaging is phase localization, apparently, the rarified realm of psychoacoustic science.
Fun stuff.... :thmbsp:
jimbofish
for TRULY GREAT MUSIC
Is that what's happening with the stacked Advent system? :scratch2:
I had 10 or 12 tabs of all those graphs you mentioned earlier and my head was spinning by the time I got the end. You are a true scholar of your craft!:yes:
Well, I don't know, and probably won't until I get a second pair of originals here to stack and measure in the complete system configuration. Clearly, my results thus far do not support Pearson's contention that there is something unique about stacked Advents as opposed to other similar speakers used in this manner.
As to why I can't get even singles to image well, I still don't know, but I have confirmed with other listeners here that such is indeed the case with this original pair. I'm still working on it; recap is next.... :yes:
I would hazard a guess that they've got the tweeter playing pretty low. The woofer will be beaming and the tweeter suddenly throwing out a true hemispherical wave. So you'll get some reflections from boundaries from the tweeter side but not much from the woofer. Your brain probably can't reconcile the shift in the middle of the midrange so it just registers as "not quite right". The econo-wave probably comes pretty close to matching the tweeter dispersion to what the woofer's doing in that neighborhood some things hang together coherently.
'Course that's just me guessing.
Nice thread, Z.
Ray
Thank you, Ray. I'll keep workin' it.
I need to find more out about the actual transfer function of the originals, and will figure a way to get some leads out of the cabinets to accomplish that when I do the recap. We'll certainly want to see the "before and after" of that operation.
Your speculation brings forth this notion: George1355 suggested that there may be beneficial interferences resultant from stacking:
http://audiokarma.org/forums/showthread.php?p=1764895#post1764895
Conceivably, if the tweeter were effectively shut off by those in the extreme off-axis, the reflections would be less conflicting, and the imaging might actually improve. It's a long shot, but I'll check it out.... :yes:
Mighty low, apparently, at least before recapping.
Here's the ideographic data on Original Large Advent Utility S/N 249495 from Aug 11, 1976, using the stock crossover with the switch set to "Extended," all but woofer nearfield measured on tweeter axis.
Tweeter response without and with the grille installed:
Woofer, tweeter, and full range response:
Frequency response composite including woofer measured nearfield (1/4"):
Compare to the first look here:
http://audiokarma.org/forums/attachment.php?attachmentid=94510&d=1213066417
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KingBubba
"Too Much Stuff"
I've been reading this thread with personal interest for one reason. I have 2 pair of NLAs and I absolutely cannot stand the way they sound. I thought, a while back, that it was because I had not yet recapped them. I have since recapped them and my opinion is the same. My wife even makes the same comment I have about them. They are harsh and piercing to the ear. It makes little difference, IMO, which position the switch is placed. The sound is not sibilant or Ssssy. It is uncomfortably screechy. The bass is muted and not anywhere near boomy. I am very disappointed. I recently picked up and rehabbed a pair of L36s and I like the sound from them much better although they are a bit on the boomy side. My JBL LX600s are even better than the NLAs and the LXs are far from a great speaker, though fairly pleasing to listen to.
The recap was done because I thought the harshness was a product of bad caps. I even added a bypass cap to the equation thinking it would make a difference. I can hear little no difference between the before and after. I guess I'm one of the few that just don't really like the NLAs. I'm not one to try a redesign like Zilch is doing and since I am really quite pleased with my DCM collection and my JBLs I guess the Advents are probably out the door. Any opinions about my observations and feelings about NLAs would be appreciated.
Zilch, your attention to detail is incredible and, though I am one of the masses that don't mind a speaker with a bit of a bass boost and a receiver with a loudness button, I must say I appreciate your opinions and science work.
The recap was done because I thought the harshness was a product of bad caps. I even added a bypass cap to the equation thinking it would make a difference. I can hear little no difference between the before and after. I guess I'm one of the few that just don't really like the NLAs. I'm not one to try a redesign like Zilch is doing and since I am really quite pleased with my DCM collection and my JBLs I guess the Advents are probably out the door. Any opinions about my observations and feelings about NLAs would be appreciated.
Zilch, your attention to detail is incredible and, though I am one of the masses that don't mind a speaker with a bit of a bass boost and a receiver with a loudness button, I must say I appreciate your opinions and science work.
