Horn vs. Waveguide

[Wayne Parham]

Problem is the directivity of the JBL has gone to hell by 2khz. Which means you should cross considerably higher.

All these speakers have gone to hell by 2kHz, that's the point. It almost doesn't matter that a horn retain CD in the vertical unless the pattern is narrow enough that it is within the null angle. Outside the nulls, there be dragons. 🙂

Best to keep those vertical nulls far apart. Too close together and they become part of the sound field you hear.

CD will still have considerable room influence. And whether a person is designing for wide dispersion or narrow, you must still aim for even and smooth response off axis, no matter the actual level, don't you agree? That's where I have concerns with matching drivers with very different directivity. Although I must say that sins in the vertical domain are not near as bad as in the horizontal, and at least there the JBL is about the same directivity as the woofer.

I agree that smooth response and uniform horizontal beamwidth are very important but I am not so quick to dismiss the vertical. Nor would I want an axisymmetrical horn unless my goal was a very directional beamwidth, like 40° or less. Personally, I think having 90° coverage in the horizontal is important for home hifi. I wouldn't want the vertical coverage nearly this high though.

The ceiling reflection can be really bad, and most people don't treat their ceilings. Even if they do, it never hurts to reduce HF in this direction. It is usually the closest boundary except the floor. For the same reason, I think wall-to-wall carpeting is good.

As you've realized, there is a big notch at the vertical null angle. But don't make the mistake of thinking output beyond the nulls is "OK". It is not. The two sound sources move further and further out of phase, and so they develop weird interference patterns of hot and dark spots, depending on angle and frequency.

You know, I think most of us interested in this stuff agree that uniform beamwidth is a good thing. Remember, though, that all the speakers we're talking about here have collapsing DI through most of the audio band. Only the high frequencies approach CD, and even then, only in the horizontal.

I think that's pretty good because it at least provides coverage through the room and with reasonably good spectral balance. Imaging is good too because of various things, including the Haas effect. However, if you really want to go towards CD, try a configuration that adds a midhorn and put the speakers in corners. A larger midhorn can provide directivity much lower than the tweeter can, and corner placement sets the directivity all the way down to the Schroeder frequency. Below that, use multisubs.

 

[Patrick Bateman]

This is why Earl diffuses the ceiling reflection and damps the floor bounce, right? Ask him. If he could be making a successful axi-asymmetric version of his waveguide, he'd be doing it.




And this you consider "no compromise?"




You're comparing the JBL vertical to the Geddes horizontal. Ask Earl to post his vertical response system polars, and I believe we'll see a different picture. He earlier refused to do it in the Nathan thread here, as I recall.

Notwithstanding the apples and oranges issue, it's easily seen that at 30� the JBL horizontal is doing just as well.

You are posting vertical polars for what JBL product, please?




Has it? Here's Earl's measurement of the JBL waveguide vertical polars, and despite it being a 50� axi-asymmetric, it's doing nearly as well at 30�:

All of my data is from the manufacturer's themselves. You can download it yourself. I posted it on the forum because many of the people reading this thread would be interested in comparing the two "waveguide" profiles.

JBL offers two types of PT waveguides. One is optimized, and one is compromised. All the pics of the econo-wave use the compromised model.

Here's a verbatim quote from the JBL literature:

"PT waveguides are grouped into two families. The first is “compact”, and second is “optimized cover-
age/rotatable”. Compact PT waveguides balance performance in
favor of small overall package size. Frequency response is optimal, distortion is superbly low, depth is minimized for use where a shallow enclosure is required. Beamwidth and directivity are optimal in the horizontal plane. Vertical beamwidth and directivity are optimized to provide a good match with JBL low frequency and midrange transducers; however, vertical pattern control does not extend as low as optimized coverage PT waveguides."

Here's the link, from JBL's own library:
http://www.jblpro.com/catalog/support/getfile.aspx?docid=277&doctype=3

While I'm happy to congratulate you on a successful loudspeaker project, I believe you are doing your students a disservice when you slander the Geddes product as if the JBL waveguide is a superior waveguide. The JBL may be superior in price, and it may be superior in size. But even JBL itself acknowledges that it's a compromised design that sacrifices directivity control. It's right there in their literature.

 

[Wayne Parham]

..."Frequency response is optimal, distortion is superbly low, depth is minimized for use where a shallow enclosure is required. Beamwidth and directivity are optimal in the horizontal plane. Vertical beamwidth and directivity are optimized to provide a good match with JBL low frequency and midrange transducers; however, vertical pattern control does not extend as low as optimized coverage PT waveguides."

I think I'll just say this just one more time because I don't want to sound like a broken record. Besides, I don't use PT waveguides or round OS waveguides.

However, I do think it's worthwhile to think about this issue.

All of the loudspeaker systems we're discussing on this thread are compromised in the vertical.

Even if the horn / waveguide has vertical pattern control, if the nulls fall within the beamwidth, it doesn't matter much. The nulls cut the vertical pattern in half, with the sound outside the nulls being undesirable because it is so far out of phase (in the crossover region) and produces excessive ceiling reflections at HF.

The smaller rectangular waveguides don't have vertical pattern control low enough, so beamwidth increases down low. If the change in directivity is abrupt, it causes ripples in response where the directivity change occurs.

Both are bad things, pick your poison.

I'd rather have a horn / waveguide that allowed tight spacing to move the nulls out, and to limit the HF at large vertical angles. I'd prefer that its collapsing vertical directivity be gradual to avoid ripples in response in the middle of the passband.

I'd actually really rather that it have CD in the vertical, but stay within the nulls. We may get close to that with an elliptical, but it will be tough.

Just my last 2¢ on this subject. Sorry if I sound like a broken record. We now return you to your regularly scheduled programming. 🙂

 

[augerpro]

You're comparing the JBL vertical to the Geddes horizontal. Ask Earl to post his vertical response system polars, and I believe we'll see a different picture. He earlier refused to do it in the Nathan thread here, as I recall.

And you're comparing a system response to the response of a single device. That's not exactly apples to apples is it Zilch? The vertical polar of Geddes waveguides is obviously the same as the horizontal. How could it not be? It's a circle. Now the system response is obviously not the same as just the waveguide, but then neither would the system response be the same for the JBL compared to just the horn.

Has it? Here's Earl's measurement of the JBL waveguide vertical polars, and despite it being a 50° axi-asymmetric, it's doing nearly as well at 30°

I dunno man...I see it losing pattern control-i.e. the response is flaring-at about 2500hz, and it's completely lost at 1800hz. What do you see? Also all the zig-zagging response with peaks and nulls that change with frequency and direction are probably wall reflections. Foam could probably help here as you don't see this behavior with Earl's WG's.

I agree that smooth response and uniform horizontal beamwidth are very important but I am not so quick to dismiss the vertical.

I don't think anything I've said dismisses the vertical axis. Quite the contrary. I don't think we're that far a part, I guess I could sum up my position in that while you attempt to maximize vertical DI (at least for the tweeter) to reduce room influence, I'm saying you can't do it perfectly, and you still need to keep the response smooth there.

However, if you really want to go towards CD, try a configuration that adds a midhorn and put the speakers in corners. A larger midhorn can provide directivity much lower than the tweeter can, and corner placement sets the directivity all the way down to the Schroeder frequency. Below that, use multisubs.

Cool idea

Now I don't have a horse in this race. I just want a factual and logical comparison from all sides. What we need is more evidence and less spin. As some of you know I'm doing a roundup of various drivers including some of the more promising horns/waveguides. I'm working on a methodology to get an accurate representation of horn performance. I've offered Earl a chance to send one of his 12" waveguides. Hopefully he'll accept.

 

[noah katz]

“The nulls cut the vertical pattern in half, with the sound outside the nulls being undesirable because it is so far out of phase (in the crossover region) and produces excessive ceiling reflections at HF.”

How do you define HF? The nulls only occur in the overlap region where both drivers operate, so at HF where only the tweeter is operating the issue goes away.

“I'd actually really rather that it have CD in the vertical, but stay within the nulls. We may get close to that with an elliptical, but it will be tough.”

CTC distance could be reduced by using, say, a pair of 6” drivers next to each other instead of a single 12”.

Missed this before:

“BTW pushing drivers apart increases vertical directivity, not pushing them together.”

If you look at a narrow range of freq I guess you could call it that, but in general it just makes a mess of polar response, as Wayne has discussed.

 

[ZilchLab]

While I'm happy to congratulate you on a successful loudspeaker project, I believe you are doing your students a disservice when you slander the Geddes product as if the JBL waveguide is a superior waveguide.

I've slandered nothing. Despite Earl's summary dismissal of the JBL PT waveguide, his own measurements demonstrate that it IS superior to his offerings in many respects. It'd be good if everybody got past that an on to substantive issues.

And you're comparing a system response to the response of a single device. That's not exactly apples to apples is it Zilch? The vertical polar of Geddes waveguides is obviously the same as the horizontal. How could it not be? It's a circle. Now the system response is obviously not the same as just the waveguide, but then neither would the system response be the same for the JBL compared to just the horn.

My point exactly. We can't compare the vertical system responses, because they are not available for the Geddes products.

I dunno man...I see it losing pattern control-i.e. the response is flaring-at about 2500hz, and it's completely lost at 1800hz. What do you see? Also all the zig-zagging response with peaks and nulls that change with frequency and direction are probably wall reflections. Foam could probably help here as you don't see this behavior with Earl's WG's.

It's quasi-anechoic in all of them, I believe, so wall reflections are not an issue, I wouldn't think. You're going to have to be more specific which curves you're talking about, as I'm not following you here.

I don't think anything I've said dismisses the vertical axis. Quite the contrary. I don't think we're that far a part, I guess I could sum up my position in that while you attempt to maximize vertical DI (at least for the tweeter) to reduce room influence, I'm saying you can't do it perfectly, and you still need to keep the response smooth there.

At what point is it simply no longer a factor with respect to perceived spectral balance? If y'all start up with the AR/Allison "dominant reverberant field" thing, I'm outta here....

 

[Patrick Bateman]

I've slandered nothing. Despite Earl's summary dismissal of the JBL PT waveguide, his own measurements demonstrate that it IS superior to his offerings in many respects. It'd be good if everybody got past that an on to substantive issues.

The JBL is cheaper and it's smaller. As a waveguide, it's inferior.

This gets back to the Mustang LX vs Porsche debate.

A Mustang LX may be cheaper than a Porsche, but to declare it superior because it's "superior in many respects" is pure fantasy.

By the way, when did you listen to a Geddes design?

I own JBL speakers, I own Gedlee Summas, and I've listened to the PT waveguides that you're so fond of.

 

[doug20]

The JBL is cheaper and it's smaller. As a waveguide, it's inferior.

This gets back to the Mustang LX vs Porsche debate.

A Mustang LX may be cheaper than a Porsche, but to declare it superior because it's "superior in many respects" is pure fantasy.

By the way, when did you listen to a Geddes design?

I own JBL speakers, I own Gedlee Summas, and I've listened to the PT waveguides that you're so fond of.

Why do you assume that someone is trying to replace what Geddes is doing? No one is even competing with him on this, we are DIYers, he sells speakers....hmmmm.

This whole car analogy isnt meaningful because no one has ever posted that the econo-waveguide choices are equal or better then Geddes designs.

The point here is that we are DIYer and we are looking for alternatives to just purchasing some KIT. Anyone can do that and its not really DIY!! People like Zilch think outside of the box and find value in things that few realized there was value.

If you want to use the car analogy, think of it this way....

Sure the Geddes designs maybe the Porsche of waveguide designs but you should consider the fact more people buy a Mustang in a year then Porsche and they are extremely happy with their mustang performance.

You heard the PT guide so does it have value (ie like a Mustang vs a Porsche)? Im not asking if it matches the Summas just that it has value.

 

[augerpro]

My point exactly. We can't compare the vertical system responses, because they are not available for the Geddes products.

We don't have system responses for the JBL either! Just the horn itself! Which is all anyone is trying to compare. You seemed like a straight shooter and I hope I'm misunderstanding you, because this kind spin doctoring word play is making me lose any respect I had for you. I hope I'm just not reading you correctly.

It's quasi-anechoic in all of them, I believe, so wall reflections are not an issue, I wouldn't think. You're going to have to be more specific which curves you're talking about, as I'm not following you here.

The walls of the horn are causing major interference as you move off axis. Not talking about the walls of the room it was measured in.

 

[ZilchLab]

A Mustang LX may be cheaper than a Porsche, but to declare it superior because it's "superior in many respects" is pure fantasy.

I don't know where you come up with this. Show me where, in all of the posts I ever made, I have asserted that anything is superior to the Geddes products in that larger sense?

We're simply dealing with the objective facts here, I do believe....

 

[ZilchLab]

We don't have system responses for the JBL either! Just the horn itself! Which is all anyone is trying to compare.

See #607. Those are system curves, and the Geddes vertical is conspicuously MIA. Further, the JBL system posted for comparison is indefinite. Is that JRX? Which model?

You heard the PT guide so does it have value (ie like a Mustang vs a Porsche)? Im not asking if it matches the Summas just that it has value.

Whether or not he's heard the PT waveguide is indeterminate at this point, actually. Best we know, he's heard MPRO, a JBL sound reinforcement speaker, and we haven't yet determined what that horn/waveguide is....

 

[Patrick Bateman]

Why do you assume that someone is trying to replace what Geddes is doing? No one is even competing with him on this, we are DIYers, he sells speakers....hmmmm.

Hey I love DIY just as much as the next guy. Look at my profile, I post here all the time. And I've been doing it for years.

Don't you ever get to that point when you realize that some things are better left to the pros?

Earl Geddes wrote the book on waveguides, literally.

http://www.aes.org/e-lib/browse.cfm?elib=8173

The idea that Earl is getting rich by selling kits is just silly. When I met him, he'd driven TWO THOUSAND miles with the Summas in the back of his car, just to demo them.

If he was doing this for a profit motive, wouldn't he hire someone to set up the speakers? Or better yet, just go to work for JBL?

As for the Porsche vs Mustang comparison, I agree that there's a lot of merit in affordable designs. That is why I spent my own money on the JBL M-Pro. Take a look at the data that I posted; it illustrates that the M-Pro has a waveguide that's superior to the "PT Waveguide", and that the Summa is superior to both.

The whole idea of a waveguide is to well... control a wave right? And the M-Pro has consistent coverage for almost five octaves. The design with the PT waveguide is all over the map.

But the PT waveguide IS cheap, absolutely. If cost is your main criteria, it looks like this:

Econo-wave > JBL M-Pro > Summa

If controlled directivity is your goal, here's the pecking order:

Summa > JBL M-Pro > Econo-wave

This whole car analogy isnt meaningful because no one has ever posted that the econo-waveguide choices are equal or better then Geddes designs.

The point here is that we are DIYer and we are looking for alternatives to just purchasing some KIT. Anyone can do that and its not really DIY!! People like Zilch think outside of the box and find value in things that few realized there was value.

If you want to use the car analogy, think of it this way....

Sure the Geddes designs maybe the Porsche of waveguide designs but you should consider the fact more people buy a Mustang in a year then Porsche and they are extremely happy with their mustang performance.

You heard the PT guide so does it have value (ie like a Mustang vs a Porsche)? Im not asking if it matches the Summas just that it has value.

I listened to a pair of speakers which used the PT waveguide, and they had all the characteristics of a horn. Great dynamics, huge sensitivity, and that weird tizzy treble. You know what I mean? Where it sounds like the highs are tilted up, but you can't get rid of it with an EQ?

That's the sound of HOMs.

Here are a few speakers I've listened to that DIDN'T have that sound:

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All three of these have something in common...

 

[augerpro]

See #607. Those are system curves, and the Geddes vertical is conspicuously MIA. Further, the JBL system posted for comparison is indefinite. Is that JRX? Which model?

Ah so there is! I was mistaken. But are we trying to compare waveguides, or are we trying to compare baffles, woofers, and crossover slopes? The more stuff you add, the harder it is to compare apples to apples. BTW I hope you aren't using those graphs to back up your position on the JBL waveguide's superiority. The one polars I saw weren't that bad given the price, but these system plots make it look kinda crummy. But it's hard to say what the cause is as some of the major problems are around the crossover. And I'm referring to the horizontal plots.

 

[Patrick Bateman]

See #607. Those are system curves, and the Geddes vertical is conspicuously MIA. Further, the JBL system posted for comparison is indefinite. Is that JRX? Which model?




Whether or not he's heard the PT waveguide is indeterminate at this point, actually. Best we know, he's heard MPRO, a JBL sound reinforcement speaker, and we haven't yet determined what that horn/waveguide is....

The best way to compare the three waveguides is by using three speakers that are similar formats.

All three speakers are two-ways with so-called "waveguides." Each one has a 15" woofer. The JBL AC2215 has a compact PT Waveguide with a coverage of 60 x 40 degrees. Froogle lists it for $800. The JBL M-Pro 415 has a full-sized waveguide (it's close to oblate spheroidal, but not quite) with a coverage of 70 x 70 degrees. Froogle lists it for $400. The Summa has a full sized OS waveguide with a coverage of 90 x 90 degrees. It lists for $3000.

 

[NEO Dan]

Interesting comparison you've got going here
Cost no object Geddes Summa
JBL MPro 70° x 70° WG, you can't buy, but you don't like the throt size anyway.
JBL PT Series 90° x 60°, The $10 Econo-Waveguide

I'd like to suggest an alternative $10 JBL PT Waveguide, I think for the $$$ could be a better option for the DIY crowd. Not perfect, just better 🙂

http://www.jblproservice.com/pdf/MRX Series/MRX515.pdf

http://www.jblpro.com/catalog/general/Product.aspx?PId=51&MId=3

http://www.jblpro.com/catalog/support/getfile.aspx?doctype=3&docid=597

 

[ZilchLab]

The whole idea of a waveguide is to well... control a wave right? And the M-Pro has consistent coverage for almost five octaves. The design with the PT waveguide is all over the map.

You're not getting this, apparently, if you believe that posting the system beamwidth plots of an axi-asymmetric JBL PT product is indicative of its inferiority to axisymmetric Geddes designs. You don't even know the vertical beamwidth of the Geddes products for the comparison.

On the other hand, here are the system plots of three axisymmetric implementations of the same JBL product:

http://www.jblpro.com/catalog/support/getfile.aspx?doctype=3&docid=663

http://www.jblpro.com/catalog/support/getfile.aspx?doctype=3&docid=645

http://www.jblpro.com/catalog/support/getfile.aspx?doctype=3&docid=654

May we see the Geddes system verticals, please?

All three of these have something in common...

Uhmmm, oblate spheroidism, maybe?

Ah so there is! I was mistaken. But are we trying to compare waveguides, or are we trying to compare baffles, woofers, and crossover slopes? The more stuff you add, the harder it is to compare apples to apples.

Yeah, I didn't do it. That's Patrick trying to convince everyone that he's made the right purchase decision, is all.

 

[Patrick Bateman]

Interesting comparison you've got going here
Cost no object Geddes Summa
JBL MPro 70� x 70� WG, you can't buy, but you don't like the throt size anyway.
JBL PT Series 90� x 60�, The $10 Econo-Waveguide

I'd like to suggest an alternative $10 JBL PT Waveguide, I think for the $$$ could be a better option for the DIY crowd. Not perfect, just better 🙂

http://www.jblproservice.com/pdf/MRX Series/MRX515.pdf

http://www.jblpro.com/catalog/general/Product.aspx?PId=51&MId=3

http://www.jblpro.com/catalog/support/getfile.aspx?doctype=3&docid=597

Are you sure that's a "progressive transition waveguide?"

It looks like a real waveguide to me. It has constant coverage, it doesn't beam at high frequencies, the vertical axis isn't squashed...

Looks a lot like the waveguide in the MP415, which is very good IMHO.

Couldn't find any references at JBL that referred to it as a PT waveguide:

http://www.google.com/search?q=mrx515+"progressive+transition"+site:jblpro.com

 

[catapult]

Hey Brandon,

I really look forward to your test of the JBL with some foam. To my eye, its CD behavior as shown in Dr. Geddes's measurements looks 'good enough,' certainly better than the graphs Patrick posted purporting to show how crummy the horn is. 😉 The bigger problem as I see it is the sharp edges at the mouth creating reflections and ripples in the response. I'd think a foam plug should help a whole bunch with that as a reflection from mouth to throat and back to mouth would have to pass through the foam twice.

 

[NEO Dan]

OK maybe it is not a PT WG. I'll look more into that. Thanks for bringing it to my attention.

What is up with your quote of my post? Are you pasting to/from a text editor? Whatever it is it's mangling things to unreadable state...

 

[ZilchLab]

OK maybe it is not a PT WG. I'll look more into that. Thanks for bringing it to my attention.

No matter, I just posted some PTs that are even better.... 😉