MWalt
Super Member
OK...Got it. Thanks, man. The nuts and bolts to this are easy for me. It's the electronics side of the house where I am completely clueless. :scratch2:
If I pull this off it will be proof positive that anybody can do a waveguide
EconoWaveguide Utility Large Advent Build Thread
- Thread starter Bauhausler
- Start date
OK...Got it. Thanks, man. The nuts and bolts to this are easy for me. It's the electronics side of the house where I am completely clueless. :scratch2:
If I pull this off it will be proof positive that anybody can do a waveguide
Bauhausler
Rational Subjectivist
I have a NLA build under way for a friend. He had a plastics shop make custom grilles to clear the WG. I have not seen them yet. Pix when they arrive.
Altair
New Member
Hi, I've been reading this thread with great interest.
I will be trying this mod on one of my 4 pairs of Advents.
However, I have not seen any mention of this but I'm concerned that the integration of the new waveguide and its large driver might reduce the internal volume of the speakers to the point that the Qtc gets excessively high.
Have you encountered this effect in your mods ?
Do you know what actually is the Qtc of the speakers before the mod, for the older and the newer models ? I suspect it must be close to 1.
I would be interested in modifying my boxes to get the Qtc down to around .8 or .7 to remove the small bass peak, by adding a small extension at the back of the box. At the same time, I would probably put the crossover on the outside, for easy tweaking.
To your knowledge, has someone already tried this before ?
Thanks in advance, your comments will be taken into consideration.
altair
I will be trying this mod on one of my 4 pairs of Advents.
However, I have not seen any mention of this but I'm concerned that the integration of the new waveguide and its large driver might reduce the internal volume of the speakers to the point that the Qtc gets excessively high.
Have you encountered this effect in your mods ?
Do you know what actually is the Qtc of the speakers before the mod, for the older and the newer models ? I suspect it must be close to 1.
I would be interested in modifying my boxes to get the Qtc down to around .8 or .7 to remove the small bass peak, by adding a small extension at the back of the box. At the same time, I would probably put the crossover on the outside, for easy tweaking.
To your knowledge, has someone already tried this before ?
Thanks in advance, your comments will be taken into consideration.
altair
cubby01
aka Buck
I've wondered the same thing. I don't know this but my assumption is that this is kinda fixed with the amount of fiberglass fill that is used. The fiberglass acts to virtually enlarge the speaker enclosure. In other words the optimum amount of stuffing for the modified (smaller volume) enclosure might be a bit more than the unmodified enclosure in order to reach the same 'virtual' volume.
Bauhausler
Rational Subjectivist
PETEB knows a lot about Advents and I hope he can contribute. I've Ewaved 2 pairs and have another underway. The total volume that the driver and WG occupy inside the cabinet is about 1L, which should have no audible effect.
Some hints for getting the best bass quality out of Advents - maybe you know this already:
Make sure the woofers have the right foam surrounds. The Fs should be under 20. Too stiff foam will raise the Fs to 35 - 40 and they won't sound right.
Use fiberglass, even in speakers that originally had foam stuffing. The difference is profound and has been documented.
I think Ewaved Advents are great. I wouldn't go back to the Fried Eggs. I'm in the process of 'upgrading' to Ewaved DQ-10s.
Altair
New Member
Thanks for the replies,
I should have mentionned that I had already refilled all my speakers with fiberglass many years ago, and they are fully filled, not packed, but just full, except for immediately behind the woofer. I am therefore assuming that I already have the maximum amount of filling, and I still detect a small bass peak before the rolloff.
The foam surrounds have also been changed at that time with the replacements from Rick? Cobb that are the correct 17mm ones.
Recently I happened to find a picture (attached) of the 5012 speaker alongside a NLA, and the 5012 seem to have slightly larger dimensions. That's what made me believe that the older boxes were marginally small.
It would be very interesting to have someone calculate the required box volume from the woofer specs that you (and others) have measured. That way we could compare with the actual volume and determine what action has to be taken to optimize the box.
altair
I should have mentionned that I had already refilled all my speakers with fiberglass many years ago, and they are fully filled, not packed, but just full, except for immediately behind the woofer. I am therefore assuming that I already have the maximum amount of filling, and I still detect a small bass peak before the rolloff.
The foam surrounds have also been changed at that time with the replacements from Rick? Cobb that are the correct 17mm ones.
Recently I happened to find a picture (attached) of the 5012 speaker alongside a NLA, and the 5012 seem to have slightly larger dimensions. That's what made me believe that the older boxes were marginally small.
It would be very interesting to have someone calculate the required box volume from the woofer specs that you (and others) have measured. That way we could compare with the actual volume and determine what action has to be taken to optimize the box.
altair
Attachments
Bauhausler
Rational Subjectivist
Rick sells the correct foams, so it's likely that your woofers are in spec.
I've run the Large Advent woofer specs through WinISD. The program specifies quite a large box (3X the Advent's size, IIRC) for optimum bottom end. It's my understanding that there's a danger of exceeding Xmax if the box is too large and high levels of LF are fed to the woofer. The smaller box reduces this danger.
I doubt that any audible improvement in the bass would be gained by box volume increases less than 50%.
As for the bump that you hear, you could try increasing the density of the fiberglass fill to see if that brings it down. I have a 70hz bump in-room, but it's due to the room's 36' X 24' X 8' dimensions, and no amount of speaker fiddling will get rid of it.
Personally, if more bass was needed rather than altering the original speaker boxes I'd add a mono powered sub. There are benefits to having a 3rd bass source in the room.
Altair
New Member
Wow, I never thought that the ideal enclosure size would be as large as 3X the actual box. I think I'll study speaker design an download WinISD.
In the meantime, I will transform one of my pairs into an E-wave. That will give me the chance to try different stuffing densities.
Another question if I may;
In the main E-wave thread, I remember reading about using a 6 x 6 waveguide in place of the 6 x 12 one, but that it might require a slight mod to the crossover.
But I've never found any reference to the actual mod involved.
A 6 x 6 would fit better in my NLA with the rounded corners.
Another option would be the 8 x 8 but again I haven't seen an application report. Have you ?
Thanks again for your comments,
really appreciated.
altair
In the meantime, I will transform one of my pairs into an E-wave. That will give me the chance to try different stuffing densities.
Another question if I may;
In the main E-wave thread, I remember reading about using a 6 x 6 waveguide in place of the 6 x 12 one, but that it might require a slight mod to the crossover.
But I've never found any reference to the actual mod involved.
A 6 x 6 would fit better in my NLA with the rounded corners.
Another option would be the 8 x 8 but again I haven't seen an application report. Have you ?
Thanks again for your comments,
really appreciated.
altair
Altair
New Member
Great !
So no mods to the crossover are needed for the 8 x 8 ?
And none for the 6 x 6 either ?
Now I just have to try to convince JBL to send a pair to Canada :worried:
I heard they weren't doing that...
With the increasing popularity of these EWs, someone is going to have to organize distribution of WGs soon :yes:
Thanks Zilch
So no mods to the crossover are needed for the 8 x 8 ?
And none for the 6 x 6 either ?
Now I just have to try to convince JBL to send a pair to Canada :worried:
I heard they weren't doing that...
With the increasing popularity of these EWs, someone is going to have to organize distribution of WGs soon :yes:
Thanks Zilch
QFT. I can speak from numerous experiences, that both of these statements are completely on-track.
Regards,
Gordon.
Hi, you ask about enclosure volume as related to Fc and Qtc and we should look at how sensitive these parameters are to box volume. Also, you mention an optimum volume - this is a concept that many modern simulation packages rely on to provide an "ideal" box size, however it is flawed or at least not so simple. If you read the original papers for the Acoustic suspension design it suggested that the box should be ten times stiffer than the total suspension compliance. This would be expressed, with T&S parameters as Vb = Vas/10, however it was later noted that it was too difficult to make such loose suspensions and the factor was typically 3 to 5 in acoustic suspension systems of the 1970s. It really is not critical to have the 10X factor.
What is more important is to have the correct Fc, and Qtc as intended by the designer. It is interesting that once the air spring is the dominant spring constant the suspension stiffness value is not critical as long as it is large. The air spring resonates with the cone mass to determine Fc, and cone mass is much easier to control. Also, note that Fc is square law with box volume, you'd have to make the box 4 times bigger to lower Fc by a factor of 2, thus the exact box volume is not critical. The programs that suggest a box volume often target a Qtc of .5 or .7 and may not account for the effective lowering of Qmc with stuffing. Kloss was looking for a Qtc closer to 1, it usually measures around .8 to .9 and it can be fine tuned by placing more or less damping material behind the driver. Also, remember that the amplitude response is -6dB at Fc for Qtc = .5, -3dB for .7, and 0db, with slight broad peaking above Fc for a Qtc of 1.0. -6dB is one fourth the power and one gives up significant low bass output for this lower Q. The system will sound significantly different with significant changes in Qtc.
To answer your question - no you do not have to worry about the volume taken up by the horn for an E-wave mod. Early LAs had 3 layers of fiberglass and it essentially filled the box right up to behind the woofer. the woofer actually compressed the fiberglass a bit.
They went back to fiberglass in the 5002/12 however the pieces were folded and placed above and below the woofer with an open space behind the woofer - you can see the back wall when you remove the woofer. Remember that many of these had the Jensen revised woofer and perhaps this was required to obtain the target Qtc. I measured a pair and reported Qtc at the CSP - don't recall the exact value but it was not significantly different from the typical .8 to .9.
Altair
New Member
Thanks Pete for this extensively detailed answer.
I think I will do the e-wave mod as specified, then see if it has changed the bass response in my room.
Actually, I have excellent response down to at least 25-30 Hz, of course it is dropping fast and the level is quite low, but I can "feel" the lower notes, something that is pretty impressive for speakers that size, and I'm not willing to loose that. It might be caused by a beneficial room/speaker combination.
It's just that I also have a bass peak at around 40-50 Hz, and this is surely caused by a Qtc > .8 If I could just eliminate this peak (by enlarging the box ?), then the bass would be completely satisfying. I might also try filling up the boxes with a bit more fiberglas but they are already quite full.
I'm targeting a Qtc of .7 ideally.
Thanks again.
I think I will do the e-wave mod as specified, then see if it has changed the bass response in my room.
Actually, I have excellent response down to at least 25-30 Hz, of course it is dropping fast and the level is quite low, but I can "feel" the lower notes, something that is pretty impressive for speakers that size, and I'm not willing to loose that. It might be caused by a beneficial room/speaker combination.
It's just that I also have a bass peak at around 40-50 Hz, and this is surely caused by a Qtc > .8 If I could just eliminate this peak (by enlarging the box ?), then the bass would be completely satisfying. I might also try filling up the boxes with a bit more fiberglas but they are already quite full.
I'm targeting a Qtc of .7 ideally.
Thanks again.
They play as low as AR3a, according to my measurements; the curves virtually superimpose:
http://www.audiokarma.org/forums/showthread.php?p=2979087#post2979087
And the bump? That was Kloss's "Special Sauce."
[Switch to higher density fiberglass to tame it, maybe.... ]
http://www.audiokarma.org/forums/showthread.php?p=2979087#post2979087
And the bump? That was Kloss's "Special Sauce."
[Switch to higher density fiberglass to tame it, maybe....
]
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On what basis do you come to the conclusion that you are getting 25 - 30 Hz? RTA, test CD, source material that you know?
No a peak around 40 to 50 is not likely due to a small change in Qtc, it is more likely a room mode. An active parametric EQ or room treatment would be the way to fix it.
More fiberglass and a lower DCR woofer inductor are ways to lower Qtc. However, the current inductor has fairly low resistance and there is a point of diminishing returns - don't bother if you use a tube amp.
What amps are you using and how many watts?
OK... then, what about a BIG passive notch filter ?
Is this doable, or am I dreaming
Not doable - values would be too large.
Measure, figure out what the problem really is, then an active EQ if you have a large peak.