Zilch's AK Design Collaborative - Econowave Speaker

[Kegger]

Thanks Skywave,:thmbsp:

 

[skywave-rider]

I think Wayne would say the nulls are helpful in that they serve to "punctuate," to quote him, the vertical pattern, providing less energy into the ceiling and floor.

:yes:

Well from what I can tell there's a point of diminishing return. As long as the distance is close enough to push the nulls outside the horn's normal pattern there's no point in driving them farther out as there's no acoustic output for them to affect at wider angles.

The ultimate solution to the issue we're discussing is zero center to center distance which is a coaxial design. In that configuration the nulls we're discussing disappear entirely because the path length is the same for all frequencies and angles.

Coaxials are a whole different wormcan, however.

 

[Bauhausler]

I think Wayne would say the nulls are helpful in that they serve to "punctuate," to quote him, the vertical pattern, providing less energy into the ceiling and floor.

:yes:

He did say that, but as I understand it that only applies to frequencies within the crossover region. When the resulting notch coincides with the outside edge of the horn's pattern, those frequencies drop off more dramatically out of pattern.

That's the theory, anyway. It's all dependent on the actual acoustic phase of the wavefronts, and that involves the physical characteristics of the sources. I suppose that can be derived for the horn from the published phase characteristics of the WG and driver, but there's no general case for the woofer. I would expect a light/stiff woofer (LE8) and a heavy/loose woofer (Large Advent) to perform quite differently at 1600 hz.

 

[skywave-rider]

The phase cancellation, creating the nulls, results from energy in the frequency range both drivers are playing. That is, the crossover region. Otherwise, the drivers don't interact.

I believe how the woofers react, regarding the nulls, relates only to their output at given frequency in the crossover range. Those factors would affect the phase and summation.

The point I was trying to make is that, from what I learned from Mr. Pi, the horn pattern can be made more precise and that helps reduce floor ceiling bounces (why we like horizontally asymmetrical horns.) And that also contributes to better power response, but I'm still getting that fixed in my head.

 

[Zilch]

He did say that, but as I understand it that only applies to frequencies within the crossover region. When the resulting notch coincides with the outside edge of the horn's pattern, those frequencies drop off more dramatically out of pattern.

Above the crossover frequency, assuming it's high enough, the waveguide takes control. That's what constant directivity is about, the "flat line" in Wayne's graphs.

Again, it's not absolute, though. There's still energy at wider angles, but progressively diminished with increasing angle and frequency. See Geddes's measurements of EconoWave vertical polar response. The "cutoff," and spec of the waveguide, is defined by the angle at which the output is -6 dB relative to on-axis.

The woofer's directivity is defined by the diameter of its piston. With a much smaller woofer, you'd want a higher crossover frequency so that its dispersion matched that of the waveguide in the horizontal....

 

[Bauhausler]

I think I'm at the 'now we''l just have to see' point. Choosing an appropriate spacing, cabinet and (I hope) woofer is the best I can do for now.

I just finished re-foaming 4 large Advent metal basket woofers. Two will go to repair a pair of New Large Advent speakers for a friend and 2 will go into my EWGLA project. I'm planning to use Utility cabinets. In order to get the driver spacing and positions I want I think I'm going to drop a new baffle on top of the stock one. I'll cut a board to fit inside the cabinet's front rim, mark and cut the driver cutouts, cut away interfering portions of the original baffle and glue/screw the new baffle down.
Since these will probably be mounted on short stands I want the WG as close to the top of the cab as possible, preferably with the upper rim reaching the cabinet's top surface. I'll place the woofer directly below the WG. I'd rather optimize the positioning of the drivers for midrange and treble performance than couple the woofer near the floor for boundary reinforcement of the lowest frequencies. This places the woofer within an inch either way of the center of the baffle.
I need to get those cabs today and assess the lumber situation.

 

[skywave-rider]

Bauhausler,
I had to cut off the old baffle leaving "tabs" for the new as well. Mine will never be pretty.

Requesting more pics.

 

[dnewma04]

Geddes Summa, for example, has a round horn that prohibits close vertical spacing between drivers. As a result, the anti-phase nulls start at 7.5 degrees. That's such a narrow angle that the null forms straight in front of the speaker for 12 feet back! It is absolutely imperitive that these speakers be mounted in such a way that they favor upward angles, because on a stand or wall mounting virtually ensures the listener will be treated to deep 10-15dB notches between 1.0kHz and 1.5kHz. No matter how good the rest of its performance is, if you're sitting in a null, response is bad.

I have a lot of respect for Earl Geddes, but until and unless this issue is addressed using an asymmetrical horn with shorter vertical dimension, the narrow null angles impose a serious performance penalty, in my opinion. That is why I do not use or recommend round horns for an application like this.

If my math is correct and my understanding of the Summa and it's vertical polar plots is also correct, it has a null at 7.5 degrees down from the center of the speaker system. At a couple of meters that would put it on axis with the woofer or approximately 9-9.5" down from the center point. At 12', you be looking at a null that would be at the base of the enclosure. I cannot fathom how under normal circumstances, this could possibly pose an issue? Perhaps, if you bought the speakers without understanding of proper placement, or directions on placement, you might end up putting them on stands that were tall enough to put you in a null at the listening position if you were in close quarters but it would take some rather odd speaker placement to mess it up. I certainly wouldn't plan on putting the Summas on something like a 2 foot stand and sit very close, or a 3' stand at 12' and think it would be an optimum listening position.

Maybe I'm just reading your post wrong? Your insinuation seems to be akin to saying that dipoles are a poor choice of speaker format because if you place them very near the back wall in the room, they don't perform well.

 

[Bauhausler]

If my math is correct and my understanding of the Summa and it's vertical polar plots is also correct, it has a null at 7.5 degrees down from the center of the speaker system. At a couple of meters that would put it on axis with the woofer or approximately 9-9.5" down from the center point. At 12', you be looking at a null that would be at the base of the enclosure. I cannot fathom how under normal circumstances, this could possibly pose an issue? Perhaps, if you bought the speakers without understanding of proper placement, or directions on placement, you might end up putting them on stands that were tall enough to put you in a null at the listening position if you were in close quarters but it would take some rather odd speaker placement to mess it up. I certainly wouldn't plan on putting the Summas on something like a 2 foot stand and sit very close, or a 3' stand at 12' and think it would be an optimum listening position.

Maybe I'm just reading your post wrong? Your insinuation seems to be akin to saying that dipoles are a poor choice of speaker format because if you place them very near the back wall in the room, they don't perform well.

Consider that the radiation pattern is not straight forward (horizontal). In cases where the HF driver is above - and importantly - behind the LF driver the pattern is tilted upward. The null from the lower edge of the horn may in fact be projecting straight forward and the null from the upper edge of the horn may be at +15 degrees from horizontal. That would make sitting right in front of the speaker sound very unnatural in the crossover region which is obviously bad.

The point that he makes is that a narrow angle between the nulls means that only a very small part of the forward radiation pattern of the horn can be unaffected by the drastic spl dips caused by cancellations in teh crossover region.

 

[Zilch]

There's some advantage or value in having a constant directivity system with a total useful vertical beamwidth of 15°?

 

[dnewma04]

In the case of the Summa, it isn't 15 degrees. It's simply 7.5 degrees down from the vertical with the downward null, 22.5 on the upward null giving an effective pattern of 30 degrees vertically. For home, it seems quite good/effective. Sure, more coverage *could* be better, but it doesnt appear to be a problem unless you tried to make it one.

 

[Zilch]

30° would be considered "beamy" by most standards, and the on-axis response anomaly is certainly also a significant issue.

The point is, why steadfastly maintain that axisymmetric is the superior approach, when its limitations preclude constructing a system with a more desireable vertical beamwidth?

Geddes ALSO claims he could mitigate the on-axis response anomaly in an axiasymmetric design. Why, then, stick with a design which precludes use in the conventional manner?

The answer may simply be that's not what he's making and selling. The mold for the better design would have to be made using more sophisticated technology than he has available in his garage.

His own measurements indicate that EconoWave is the superior performer, for $10 apiece....

 

[dnewma04]

At 12', from the center of the speaker, we have -19" to + 57". For a floor placed speaker or one on a short stand, we'd have a coverage area of shin level to well above most people's standing listening height. At 6', it does shrink the area to 3' or so. Placement would be critical at 6', not so much at more typical listening distances.

I believe that Geddes acknowledges that alternative designs could fix the issues, but the "issues" aren't issues in terms of his speakers performance in his intended use. If fixing a null at the ankles is critical, maybe he doesn't anticipate people listening while laying on the floor and for the sake of this discussion, we are? Also, why is the on-axis anomaly a problem if they are designed to be listened to off-axis?

If it ain't broke and all...

I thought his own measurements showed the PT waveguide measured more like a diffraction horn than a waveguide?

 

[Zilch]

I thought his own measurements showed the PT waveguide measured more like a diffraction horn than a waveguide?

Bottom line of that was that Geddes has a specific interpretation of the term "Waveguide" narrowly defined by his work only. All else is "Non-Waveguide." He claims to have coined the term, and is thus entitled to define it. The industry does not accept his definition, and others have demonstrated that he did not, in fact, coin the term.

For the comparison of EconoWave to his waveguide, he set the performance criteria. E'Wave not only met those, but bettered the performance of his device in many, if not most, respects.... :yes:

 

[dnewma04]

Interesting interpretation.

 

[Zilch]

Interesting interpretation.

It's documented in two threads over on the DIY forum. Problem is, you have to wade through a plethora of ego-wars to get at the specifics. I could NOT get anyone to discuss the data, despite that being the thread topic. Everyone apparently saw it as springboard for prosecution of their own agendas.... :thumbsdn:

 

[Russellc]

It's documented in two threads over on the DIY forum. Problem is, you have to wade through a plethora of ego-wars to get at the specifics. I could NOT get anyone to discuss the data, despite that being the thread topic. Everyone apparently saw it as springboard for prosecution of their own agendas.... :thumbsdn:

Not to mention the fact loads of people here are happy ( I dont think anyone has been disappointed here) with the results and are spending very little money, while his followers are out 1200 and I havent seen a happy camper yet.

Russellc

 

[dnewma04]

Let's be fair, what he is sending out (so far) has been pretty shoddy without a doubt from a construction standpoint. The performance of the finished products (Summas) have received nearly universally rave reviews. There were a few posts on some hifi forums indicating that at the RMAF, they found his speakers "boring" but it's a tough setting to make any real judgements, and boring often turns into satisfying while exciting turns into ear piercing and unliveable quickly in many rooms. Anyone who has listened to his set up with properly implemented sub-bass has come away with the impression that it was the best, or near the best sounding system they have ever come across.

Geddes is a huge PITA to deal with, but he knows his **** more thoroughly than anyone and his speakers show it.

Not taking anything away from the EWG, I bet the different variations sound excellent and sometime within the next 6 months or so, I will be building my own. I don't anticipate they will perform at or near the same level as the Summas, however.

 

[Wayne Parham]

Vertical pattern

I have a lot of respect for Earl and have visited with him several times over the years. Our design philosophoies are very similar, so much so that five years ago I considered building an elliptical horn just like what Earl often talks about. I make wood horns on a CNC machine so I could have easily made them. I eventually decided to do my own, but it is similar to what Geddes describes in many ways. We build similar speakers and embrace similar design philosophies, with a few exceptions.

The thing is, and I've said it many times, is that I think it is a mistake to match a 90 degree round horn to a direct radiating midwoofer because of the vertical nulls. I won't restate the reasons as I think everyone reading this understands them. They're written elsewhere in this thread. Even Earl has admitted it would be better to reduce vertical pattern and to decrease the vertical distance, both things an asymmetrical horn makes possible.

You say "why does it matter" and my response would be it matters because it is an improvement. One of the main advantages of uniform directivity is spectral balance in the reverberent field. Reflections from the floor and ceiling contribute to the reverberent field.

Not only that, but Earl admitted himself that there were applications where people had installed his speakers in clubs high on the walls, avove the listeners. This means the nulls aren't "at the ankles" but rather throughout the entire listening area. Earl should have informed them to mount the speakers upside down, in my opinion. It appears he simply overlooked or ignored the vertical pattern. While I agree that uniform response is more important along the horizontal plane, as I've said before, it doesn't matter much if you're sitting in a vertical null.

This is not intended as an insult. I respect Earl a lot and his speakers sound good. But I must admit that I don't think they sound better than other similar speakers with good horns. I prefer those with asymmetrical horns, and I can definitely hear a difference when I move from sitting to standing and move around the room. I think those with good asymmetrical horns just sound better, less phasey and more natural.

 

[dnewma04]

Wayne, there is no doubt that the vertical nulls "could" make a difference and if Earl doesn't provide recommendations that would prevent misplacement on a purchasers part, then shame on him. In a "normal" home setting, the limited downward coverage likely wouldn't present an serious/audible issue. Using an asymmetrical horn would likely open up placement options to some degree and not alter performance in other areas. So yes, it *could* be considered an improvement. But, it's entirely possible that the added cost would result in no identifiable difference by a significant majority of purchasers. I can understand where he wouldn't be excited about trying to tool that up for an improvement that could be realized by just simply moving the speaker from an improperly placed position to a proper one.

The Summa was probably the best high efficiency speaker I have come across. For a while, I thought it was the Unity horn based Lambda speakers I heard, but over time, I think long term listening would make me lean towards the Summas. I sure would like to hear both in my room with my gear.