horn top splaying

Hi all,

I've just registered to this forum, so I'll start with a few words about my involvement in this hobby. I've been reading on here since eight years or so. Back then, me and a couple of friends on a tight budget had some great fun building a punisher from MDF, later a pair of MBH115s. Around then I discovered hornresp and got acces to a nice workshop. I chewed around on expanding the usable range of the HD15 design and finally built a pair 15" BPH6's with a ported back chamber, but shaped like a W-bin.

Loud and punchy but lacking low-end, so I redesigned them into a 18" version using PD186 and built 6 pieces. I built a pair of Limmer P3 in a horizontal layout to go on top of them.

Well that works very well! I think the P3 is generally considered a good design and I can only recommend it. But I am struck by this fever some of you might kow ;-) so i'm thinking of doubling up the amount of BPH6 bassbins to 6 per side. And then, correct me if I'm wrong, I think I'm entering a stage where one hornloaded top per side is not going to match the bass anymore.

Generally speaking, when using multiple tops per side in a horizontal row, you'd say you need narrow dispersion, about 30-40 degrees. Three pcs of 40 degree tops a side would be perfect, 120 degrees in total. Wouldn't you?

Reading around about CD-Horns and horn dispersion in general, tinkering with horn-resp a bit, I'm trying to get an idea of what can be done. I'm an RF engineer and I'm familiar with the theory.

So now to my question of how to properly splay tops:

In the lower-mid range up to ~500 Hz, normal-sized speakers don't beam, they just couple. A horizontal row of three tops has wavelength-like dimensions in this frequency range so the resulting dispersion will have cancellation zeros off-axis. For example a 150cm wide horizontal row should have its first zero at around 100 Hz at 90 degrees of axis.

Entering the upper mid range, >500Hz, where speakers do beam. As I understand it, you'd be trying to splay the tops so that each -6dB off-axis response overlaps with the next. Splay angle then equals coverage angle. If I recall correctly, large Funktion One (or Turbo) speaker clusters are set up so, that each person in the audience has only one top bin pointed at him.

For a 3-top 120-degree cluster you'd then need three 40-degree tops a side.

Now there don't seem to be many of those 40 degree top bins. I am confused. For example, a Turbosound TSE-111 has 70 degrees of horizontal coverage. If you'd try to splay those bins, having each bin cover 70 degrees of the audience, you'd have 70 degrees of splay angle between them. Ugly! More over, you could not use more than two of those tops per side without either breaking the 'rule' or having more than 180 degrees of coverage. Maybe that 'rule' (coverage=splay angle) is not correct?

TMS2 and TMS3, that are based on the same mid-horn, are usually splayed only 10 degrees or so. In the TSE-111 datasheet, there's a sketch of the flying hardware, showing ~35 degrees horizontal splay.

Another example is the Limmer 308, which has a well-documented coverage of 60 degrees. You can find the coverage graphs on a resellers' website. (Other manufacturers should take an example and publish those colored graphs as well). Anyhow, you could only use two Limmer 308s a side to get 120 degree coverage, as I understand it.

Where am I going wrong? No-one splays top bins by 60 degrees. Is it generally accepted to have cancellation and comb-filtering all over the place? How do you guys splay?

I'm hoping on a nice and nerdy discussion!
Thanks in advance and have a nice day,
Robert

fourway hornloaded wrote: Maybe my first post was a little too long. I will try to summarize: When using multiple tops per side, * Which horizontal dispersion do such tops need to have? * Which splay angle do you tend to use? I've posted some pictures of my system with the Limmer P3 tops in the 'show off your sound system II' thread. Robert

This will vary with the room you are setting up in, and the tops you are using - there isn't a definitive right answer to this one really!

If you have a wide, shallow room, you're likely to need wider dispersion than if you have a long, narrow room....

fourway hornloaded wrote: Is it generally accepted to have cancellation and comb-filtering all over the place?

This inevitably happens no matter what, it's just up to the brochure and marketing of your particular system as to how bad the effects are 

And the 2386 is not even anywhere near constant directivity. When i saw your post i was just about to post a topic about large format 2'' horns. 

Thanks for explaining the crossover/beamwidht thing Teun! You seem to work with quite a few different mid-hi bins. I was thinking along the fully hornloaded route, although double-15" top bins like you mention, crossed my mind as well. Though it's clear to me that larger bins are the ones that have narrow dispersion, I am just so tempted to build something smaller. Take for example Funktion One Res3, if you'd leave out the 18" horn, you'd have a nice little  65cm x 65cm bin doing 180 upwards with 50 degrees of horizontal coverage. I'm not sure what to believe though. The double-12" horns you were talking about, for example, do not seem to reach less than 60 degrees below 800 Hz, even though they are large:
http://www.loudspeakers.de/daten/limmer/lim-302.jpg
http://lsv-achenbach.de/daten/limmer.htm

As for 2" cd horns without diffraction slot: did you see Limmer 243? I don't want to sound like a complete limmer fan here, but his dispersion plots look nice. I had a look at the JBL 2385 after reading your post... and got the point. 'so much for constant directivity'.

Your double-12 seem to be quite brutal if they outplay such expensive compression drivers. I reckon you're in quite a different ball park then. Myself, I'd like to play around with small-dispersion paper-cone mid-horns in the future. After reading Volvotreter, Keele, Geddes and especially Peavy's 'quadratic-throath' paper, I'm actually not put down. We all know Martin, Turbo, F1, Föhn, Limmer and even RCF have been very succesfull with paper-cone mids. Now recently if you have to believe Peavy and Geddes, the whole horn-business seems to steer away from cd-horns, knowing you aren't going to get constant directivity anyway, and turn towards conical horns, with maybe a little curvy bend at the mouth to avoid too large a mismatch. Conical horns have narrower dispersion than similarly sized exponentials. Especially in a multi-way system you should be able to cut off such a horn before dispersion gets too narrow, or at least before the first transversal reflections in the mouth occur. Conical is of course very DIY-friendly. Well, that doesn't solve the problem of finding a narrow horn for your high-frequency compression driver, of course. Unless you'd want to make that yourself too.

Right now I'm figuring if this high-fi conical thingie, I mean oblate spheroid and the like, are going to work equally well with narrower dispersion. Because neither Peavy nor the hifi guys seem to do anything narrower than 90 degrees. A narrow conical horn might very well turn out to sound like a megaphone... because it actually 'is' one.

What is with elliptical, what can it do? The XT 1464 you mention is elliptical. Hornresp doesn't simulate it. On the forums, they're all into that type of horn.

Proper mouth termination is the key not having megaphone sound.

I'm using quadratic throat 80x40 horn with 630mm x 330mm mouth and BMS4594, horn is terminated with about 75mm radius to the outside air, xo at 900Hz. Horn is about 270mm deep

Two 670mm deep straight mid-bass horns below with 18 sound 12ND930. Whole cabinet is 800mm deep.

Result is 110dB/W above 150Hz after eq:ing the peaks down

Btw horn response doesn't take account if your horn's axial geometry is a square, ellipse or round. Or bent like bass horns. Only expansion rate counts here.

Ellipse is best (most hifi, at least for me) compromise to have H and V in different angles. My small pa uses Faital FH144 and LTH142 combo, really sweet sound compared to Beyma 380M+TD164.

And Teun, that 600Hz horn must be quite huge to give acceptable loading down to 300Hz:ish. Not that you wouldn't know that already but is it practical...


edit:Sorry got bit carried OT

I would try to make the high horns with 40 horizontal first and modifying them so long they would comb as little as possible, after that mate them with normal 2x 12" BR low mid section with cabinet so narrow as possible to achieve good coupling up to about 800Hz. This would dictate the cabinet width somewhere 360mm. EV phoenix 2122 as example. Form follows function.

my 2p


Edited by AndyWave - 04 April 2014 at 7:42am