Question for Todd W. & BobR - C.D. horns

[Richard C.]

Hello all,

I am trying to find out how bad this "apparent apex" problem is:

BobR said:
"Todd has previously mentioned the problem of `apparent apex' in constant-directivity horns caused by the axial displacement of horizontal and vertical breakpoints but that may or may not be objectionable to you."

I have been reading on this subject, and I came across a "white paper" from Peavey on their new quadratic throat CD horn design. Peavey says that the standard CD horn is flawed, but they don't say how bad it really sounds!

I know the horiz and vert break points inside the throat are at different points, but what does this (apparent apex problem) "really" sound like, and what would be the worst sound source that would show this up? Does a CD horn sound equally flawed up close and at a distance? Is it something that only certain people can hear? Is it something that most people live with and don't mind?

I know many people that are bothered by multi-cell lobe patterns, and wouldn't EVER even listen to one. But, on this hostboard, there are several people that must just overlook this little flaw - and love these multi-cell horns for ALL the other advantages.

Richard C.

[Todd W. White]

Well, first I wouldn't trust ANYTHING Peavey says about anything!

Secondly, The problem is you can hear the problem with CD horns as the apparent location of the source of the sound coming from it shifts up and down the throat with frequency. It IS hearable and it IS very annoying.

Multicellular horns don't have this problem, and the lobing people say they don't like, while it IS there, is not really noticeable in real listening environments.

[joyspring]

Richard C:

Todd summed up the `apparent apex' problem quite nicely; it simply refers to the perception that the apex (or origin of the coverage angle) differs in both horizontal and vertical planes.

In most domestic situations where listening positions are fixed, it may be noticeable. However, in a public address installation with horn clusters, the divergent apices are much more prominent.

If you're not moving about in your listening space, chances are good that you will not notice the problem.

Todd:

"Well, first I wouldn't trust ANYTHING Peavey says about anything!"

Peavey's early products (very derivative products, mind you) have earned them a poor reputation that persists to this day...

Having said that, Peavey is now quite an innovator in pro audio and musical instruments (particularly their MIDI products) and represents excellent value in midrange pro audio/ MI markets.

Charles Hughes' AES preprint ("A Generalized Horn Design to Optimize Directivity Control & Wavefront Curvature," Audio Engineering Society, Preprint #5016, September 1999) is an excellent analysis of how the problems of attaining even power response while avoiding apparent apex problems of earlier constant-directivity horns and maintaining a pleasing straight-walled rectangular aspect mouth are approached and solved. The Peavey .pdf that Richard C mentions is a very nice tip of the hat to its predecessors from Keele (EV), Altec and JBL, demonstrating the evolution from the original EV CD horn to Peavey's current waveguide offering.

Solid analysis and very trustworthy engineering from a cutting edge US manufacturer.

As I mentioned in an earlier post, for critical listening applications, horns (at least those that provide significant acoustical loading) are now an anacronism; in monitoring systems still utilising compression drivers (generally very high output systems), waveguides have entirely replaced horns if the current offerings from JBL, Quested, Genelec et al. over the past decade are any clue. Having 3-8 dB lower second- and third-harmonic distortion while maintaining even power response without `apparent apex' is a *very* significant benefit.

BobR

[Richard C.]

Todd,

In particular, I would like to know if the MR931-12 used in the Model 14 & 9842 has this problem. Someone told me that ?this Mantaray horn? is not a ?true? CD horn. It sure looks like a CD horn, and ALL of the Altec literature on this horn states that it has ?constant directivity?. The visible breakpoints inside the MR931-12 horn aren?t like the kind we see in the typical large format CD horn with the long parallel walled throat (which puts the horizontal and vertical apexes several inches apart). My MR931-12?s have a very different throat. It looks like the two apexes are at the same place (the screen on the driver).

BobR,

I thought that the Peavey white paper was very well written. There wasn?t much hype. I hate the way some reviews are written ? mostly BS. I would much rather read a paper written by a technical person (engineer, technician), than a marketing person. I would guess that the EV horn that he was eluding to, was the SM120 used in the early Eliminator (Sentry ???).

I know that EV and Peavey are sore subjects on the Altec hostboard, probably because these are two of many companies that helped put Altec out of business.

BobR,
Do you have to compose your message on a word processor, and than copy it into the dialog box on the hostboard, or do you type extremely fast? Some of your posts are quite long and thought out. I have had two of my replies lost because I took too long to compose the message. I have Hi-speed DSL, so it appears to be a problem with the hostboard. I try to post, the page refreshes, and it comes back to a blank dialog box. Everything is gone! It might take me 30 minutes or so, I guess it times out.

Richard C.

[joyspring]

Richard C:

"I hate the way some reviews are written ? mostly BS. I would much rather read a paper written by a technical person (engineer, technician), than a marketing person."

I agree wholeheartedly.

"I know that EV and Peavey are sore subjects on the Altec hostboard, probably because these are two of many companies that helped put Altec out of business."

Peavey targeted a totally different market segment altogether (the low-mid end sound reinforcement market) - I believe they had little to do with Altec's demise.

Altec failed because the management decided to live on past glory (i.e. - Academy standards, etc.) and did not fully support research and development (or at least give them enough latitude in marketing decisions).

Hence, EV, JBL et al. easily surpassed Altec, particularly in the 1970s.

"Do you have to compose your message on a word processor, and than copy it into the dialog box on the hostboard, or do you type extremely fast? ...I have had two of my replies lost because I took too long to compose the message."

I do type quickly ;-) judging from some of the grammar mistakes I often make. I actually use the dialogue box in my browser, which is Mozilla on Linux (Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.2)).

I suspect that this message board software relies on cookies to determine session state though I haven't thoroughly investigated this. You may have cookies disabled in your browser - this may be a security feature of the browser.

BobR