Horn beaming

[Robh3606]

As Ian surmised, I was thinking of the older style horns, my 511b’s, which have a reputation for beaming in the higher frequencies. I can only expect that to increase when I try to augment their HF performance with the BMS drivers.

I am not sure I undertand you correctly but it simply does not matter what driver you use. To do anything really significant as far as directivity is concerned you will have to use a tweeter with these older style horns. They use their directivity to compensate for the compression drivers natural rolloff to give you reasonably flat on axis response. The DI of the horn cannot be changed or compensated for.

Rob

[Zilch]

Agreeing with Rob, the 511s beam in the VHF, and that is fixed by the horn geometry. In my cursory analysis of that, it seems as long as you have line-of-sight down the throat to the driver exit, you're within the beam. 075/2402 beams worse, in my experience with both, but I'd have to do polar measurements to quantify it.

The Altec beamwidth specs stop at 8 kHz, where it's ~45° vertical and flattening, though the DI is still rising:

http://www.altecpro.com/pdfs/vintage...0HF%20Horn.pdf

With respect to imaging, it's clear from the measurements I've done and posted here that BMS seems to have the manufactring variables well under control; it's not uncommon for the FR curves of even unselected pairs to virtually superimpose....

[Ian Mackenzie]

I think you missed his point.

That Jorg was saying was because the BMS has a more extended HF the beaming maybe more obvious (subjectively) than with a driver with limited HF response.

The data in the John Eargle Sound Recording handbook is far more understandable

[Zilch]

The Altecs aren't shown in Eargle's Sound Reinforcement book, but the JBL radials fall to 30° above 10 kHz, then rise to just under 40° at 20 kHz.

MY point is that, with respect to vertical beaming they're likely equivalent to or better than the UHF drivers often recommended here, and so nobody has to read between the lines, that includes 077/2405, as well:

http://www.jblpro.com/pages/pub/components/2405.pdf

So, my response to Jorg's "I can only expect the beaming to increase" is, no, it will be rather the same as occurs without extended HF, as I read the specs, and I don't see any advantage to using a separate UHF driver in this particular regard.

Just now reviewing Eargle at Ian's prompt, I note as a sidebar that the slant-plate lens collapses to 10° at 10 kHz, rendering its utility for HF extension extremely limited by comparison....

[Ian Mackenzie]

Lobes as distinct from directivity.

[Mr. Widget]

Yes, similiar, but the two sides must have constant power response (the FR can't be changing with angle,) while the SPL changes in a precise manner to maintain balance, i.e., the two sources must vary reciprocally with lateral movement of the listener(s).

I guess I am not following you. Are you saying that a constant power response is necessary for a speaker to create a believable “sonic trompe l'oreille”?

The Everest I manual...
H2600/3100 horns...

Odd that you would bring up these horns... in the world of horns they are quite unique and while some love them and they do some interesting things, they are certainly not the best horns out there for creating a believable image.


Widget

[Mr. Widget]

So, my response to Jorg's "I can only expect the beaming to increase" is, no, it will be rather the same as occurs without extended HF, as I read the specs, and I don't see any advantage to using a separate UHF driver in this particular regard.

I think Jorg was suggesting that the Altec horn will continue to narrow it's beam width with increasing frequency. Since the BMS is likely to reproduce higher frequencies it would seem logical that the beaming would increase.

In this case a tweeter should help. A smaller diameter driver with a smaller horn will likely beam less... if that is the goal.

Personally I tend to sit on axis with all horn systems so in a room with even slightly controlled side reflections the beaming isn't all that big of a problem. I am not suggesting that beaming is never an issue and that the beaming of say an 075 is acceptable... that is a bit extreme.


Widget

[Robh3606]

I think you missed his point.

That Jorg was saying was because the BMS has a more extended HF the beaming maybe more obvious (subjectively) than with a driver with limited HF response.

Hello Ian

I did thanks for the clarification. And yes I think he is correct.

Rob

[Zilch]

Lobes as distinct from directivity.

I'm not seeing any lobing in the JBL radials, at least not in the horizontal:

http://www.lansingheritage.org/html/...dial-horns.htm

Please provide a specific reference evidencing lobing in the vertical for disucssion.

I think Jorg was suggesting that the Altec horn will continue to narrow it's beam width with increasing frequency. Since the BMS is likely to reproduce higher frequencies it would seem logical that the beaming would increase.

That's my point. What specs and descriptions I have been able to find indicate that the beamwidth is generally flat above 5 kHz, and in the case of the JBLs, actually widens a bit at the extreme high end, thus concluding that Jorg's concern may be unwarranted.

Frankly, I was expecting otherwise, and having prior experience with exponentials, was surprised (and pleased) to discover that 511 and 811 supported VHF extension so well when I worked with them in the Valencia project.

[Earl K]

Back to Jorgs' initial question.

I can understand why poor off-axis response would matter in a venue,

- Even this assumption can be proved wrong / or minimized to the point of it being a non-starter if working in an environment that has a certain amount of sound absorbtion on the walls / or in a home or control room by employing some version of a LEDE setup . ( LEDE = " Live End Dead End " ).
- I have a version of LEDE setup here in my narrow living room ( Dead End around the first 4' of the speakers ) . This controls just about all the most siginificant off-axis colorations by damping down the initial reflections ( that destroy intelligibility ) .
- My speakers are also surrounded by foam that more or less butt up to the sides of the cabinets. They are actually 4' high, floor standing foam bass traps which were purchased last decade from Auralex. This setup is a form of a fake soffit mounting that free-stands 3 ft out from the back wall. I can sense immediately destructive diffraction effects occuring when I remove any of this foam. This all looks like hell / but it works acoustical wonders ( once again, enhancing imaging ) .

but in a dedicated listening room does a narrow "sweet spot" matter much?

- Not much at all in my experience if everything else is done with a dollup of acoustic design.
- My round Selenium Exponentional horns certainly do beam. At first I didn't think much beaming was happening in any significant way / but when I went and actually measured the 6 db down points vs frequency , it was quite apparent the horn acted just like one would predict. These nominal 45° horns ( yes that is narrow ) are toed in so that the horizontal 6 db down point ( more or less ) goes down the room parallel to the wall .
- The kicker is / it just doesn't sound beamy within a narrow room. ( Horns are @ 6 ft between centers / with each center occuring about 24" off either side wall .
- It's impossible ( once the speakers are properly toed-in ) to find a spot where one isn't looking directly at significant portions of both horns' phase plugs .
- From this setup, I've been rewarded by achieving ( to use a Tony Gee phrase ) ; "bowling alley" imaging ( ie; very, very deep ) .

This room wouldn't be used for entertaining. Wouldn't beaming improve imaging as there would be less reflected sound from adjacent surfaces?

- It has been my experience that contructive beaming will enhance imaging .
- One should choose a horn that works for the given room ( just like we do the sound contracting business ) . This portion of the sound business knows it's only destructive ( for intelligibilty ) to bounce acoustic energy off reflective surfaces. One must have good intelligibilty before one can expect to achieve some reasonable imaging .

- "Phase coherence" also helps ( as has been pointed out ). My 2-way MTMs are time aligned / and it does make a difference . Though I wouldn't trade time-alignment for proper horn coverage and acoustic room treatments .
- Absolute phase ( or polarity ) also makes a difference to all this. I just won't build a system that sucks and blows at the same time ( just to achieve a smooth crossover point ) .

<> Earl K

[Mr. Widget]

That's my point. What specs and descriptions I have been able to find indicate that the beamwidth is generally flat above 5 kHz, and in the case of the JBLs, actually widens a bit at the extreme high end, thus concluding that Jorg's concern is unwarranted...

So you are saying that between 5KHz and 20KHz the pattern does not narrow for the Altec? I find that hard to believe.

This polar plot of a classic radial horn by JBL, the JBL 2350, clearly shows narrowing at 10KHz... I'd assume even greater beaming beyond that.


Widget

[Mr. Widget]

- Absolute phase ( or polarity ) also makes a difference to all this. I just won't build a system that sucks and blows at the same time ( just to achieve a smooth crossover point ) .

Now that's a whole different can of worms! Certainly worthy of a thread someday.


Widget

[Earl K]

- The defined directivity horns combine that with amplitude compensation.
- The SPL increases off-axis inwardly to maintain L/R balance off center.

An increase in SPL towards the center of any horn is called beaming in my vernacular .

It's a "trompe l'oreille" that works to effectively generate a phantom center image from different listening positions. I believe it was abandoned in favor of a center channel, which does a better job of that, and also sells more speakers.

- "Trompe L'Orielle" ??? This appears to be a "fancy-pants" way of stating that JBL now likes some beaming to occur from their $50,000 plus systems.

- I know if had a pair of H4338 horns, I'd be experimenting with 30° to 60° entry throats ( to clad onto that 90° bell section ) , so that I too could have some "Trompe L'Orielle" ( or beam induced imaging , as we blue-collared types might just call it ).

[Earl K]

Why am I bothering to talk about beaming right now ( just before my holidays ) ?

- Because I'd like to see a bit of beaming built into the Project May horn .

[Zilch]

So you are saying that between 5KHz and 20KHz the pattern does not narrow for the Altec? I find that hard to believe.

I don't know, as Altec specs only to 8 kHz.

However, here's what Eargle says, as I cited above:

[O.K., "Generally flat from 8 kHz," then.... ]