What are the threads on a 1" horn

[AZJimC]

Hi, again,
I was wondering, and thought, these guys would know more than likely. I was looking at some horn's for PA use, and their drivers, like the 1" throat threaded screw on type. One of them said it is 1 3/8" 18 TPI. I guess these are not tapered? I was wondering if flanges to put on home made horns are available pretty cheap, or if I could use a 1" or 1.25" nominal pipe threaded flange? I know one of you have messed with these before, so tell me what you know.

Thanks,
Jim

[PRR]

I'm sure it isn't pipe-thread, nor any kind of standard outside the cheap horn racket.

On one wood horn, I started with a 1.375" counterbore, used a rubber drain washer to seal the driver to the horn, and used a 1x3 and two lag-bolts to clamp the driver onto the horn.

A wiser man would buy a standard adapter from threaded horn to 3-bolt flange:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-322
Selenium ADF25-25 Horn Adapter - Your Price: $2.57 - In Stock 

"This is cheap plastic (but very functional) making it easy to drill to fit the JBL 3 bolt pattern. However a point to note is this matches the Altec Lancing 3 bolt 1.5 inch horn configuration."

" Please consider replacing this with the multi-pattern aluminum adapter made by P-Audio (model # PC-25)..."



http://www.loudspeakersplus.com/html/paudioadapters.html

http://www.loudspeakersplus.com/product.asp?specific=jokmlpi4
P Audio PC-25
Single adapter converts 1" screw-on driver to a 1" bolt-on horn.
Your Price: $12.00

http://www.paudiothailand.com/pdf/products/PC-25.pdf

[AZJimC]

Great, thanks!  never thought to search "adapter". That was exactly what I wanted, but had no idea they made bolt on to threaded adapters. Too bad it is more costly than a plumbing flange, though the plastic is likely cheaper. Maybe I should get the plumbing industry to make some, in cast iron, :-)

Thanks,
Jim

[PRR]

> the 1" throat threaded screw on type.

I been out of the racket a while.

But traditional Theater (good) drivers are flange. Screw-on was the provence of stuff like you see in M*A*S*H: reentrant tin horns with not much over an octave of speech bandwidth. Screw-on does not prove the driver is crap. There are some very fine screw-ons; in many cases they are small brothers to the Big Boys. But the interface defines a market segment where the customers are not buying sound Quality, just Quantity. Horns per buck.

Flange horns are traditionally hundreds of dollars. Tin reentrants are under $100, and the driver costs less than the tin. So why would you use a cheap-crap driver on a high-price horn? And since few companies made both types, why would they sell an adapter to allow use of another brand's parts?

And IIRC most of the screw-on drivers are NOT 1 inch exit.

I know one of the exits on a EV 1829 is 3/4". That's the "bass" exit. On 10"x20" horn it was rated down to 150Hz, and this is a little 2" diaphragm. It NEEDS high compression to make high-volume bass without absurd diaphragm excursion. To use it into a 500Hz 1" horn, you need over 1.5 inches of flare to maintain design compression down to 500Hz; 5 inches of flare to pull 150Hz out usefully. Above 1KHz though, the mismatch is tolerable. And since in modern high-level Rock And Roll (even some Polka and Folk), you don't run even true 1" drivers below 1KHz, what the heck.

I made a lot of pizza money with 1829s and wooden horns. Response above 8KHz is much less important than a good spread around 3KHz. And the no-top-octave phenolic diaphragms were hard to kill.

[Frankenamp]

There has been a little crossover (pun intended) with tweeter horn types for the most basic reason. $.
As you so correctly stated- the big boys (Altec & JBL, fer example) made flange horns and a lot of 'em. Lots of VOTT's got sold off when theaters upgraded their sound systems and Joe Rocker scores a sweet deal for his PA system... Dosent understand limiting or clipping... and frys his 811 or 375 drivers (fill in yer favorite profanity)! them things are expensive! (daayuuummm) Joe finds out that he can get an EV University, or Peavey screw-on driver for less than the cost of a replacement diaphragm assembly. Joe dont want clean or clear, he wants loud and cheap. It behooved the manufacturers to make an adapter to fit throw-away drivers to the otherwise good horns.

[AZJimC]

I made a lot of pizza money with 1829s and wooden horns.

That was the reason for the question, I saw some cheap screw-ons and my budget is non existent, so I thought, build a big horn, and put a threaded adapter on it, and pop on a cheap driver, and crossover the thing about 1k+ with a 2nd order crossover, and that should do it for my needs right now.

What about a single wide mouth horn with two drivers? Bad idea? I note I have not seen any likt that commercially made, but I'm not sure why.

Thanks ya'll,
Jim

[Frankenamp]

http://www.l-acoustics.com/manuels/dV-DOSC%20dV-SUB%20Manual%20V3%200605.pdf

Look at page 11 of the pdf.

The basic idea behind the Vdosc line array tweeter horns is that there are two drivers feeding each horn and each horn is placed as close as physically possible on a vertical plane basically a long thin strip horn. The midrange drivers feed from the sides and are quasi-horn-loaded in that the the midrange horn is a continuation of the tweeter horn assembly. The mid-tweeter assembly functions from about 200 Hz to 16 kHz with a crossover at about 1.6K.

Here is an elegant low-dollar variation: it operates from about 3kHz to 20 kHz.
http://www.billfitzmaurice.net/OmniTop12.html
http://www.billfitzmaurice.net/DR280.html

[PRR]

> single wide mouth horn with two drivers? Bad idea?

Draw me a picture.

If you mean what I think you mean: It's frowned upon.

When you have ONE sound source, you know where it is.

If you have two sources in VERY different places, your sub-mind understands what's happening, sorta.

Two sources which are close but not coincident mess-up the sound field and confound the mind.

Nevertheless, it is widely done. There is a too-popular configuration for the center speaker of a home theater rig which is two 5" woofers about 10" on center. If you sit SMACK on the centerline (and if the woofs match), the field is strong and solid; everybody else hears different comb-filtering and top-loss, even mirages.

And everybody stacks all sorts of speakers. The "line array" fad gives an alternative, but bad old random-stack is always in fashion, even if never in phase.

As Frank says, it can be done well. Look at 1930s theater horns. A Y-throat was a common option for high level or particularly for high-reliability horns.

Note that, since any useful compression driver is already well-coupled, two drivers is the same efficiency and only 3dB higher maximum output.

Do you know how to plot a sorta-exponential horn? And transcribe it to slab-wood and band-saw? I used to do that a lot, sometimes for cash. But there are many opinions about horns and I am reluctant to get involved when I am very rusty on my rule-o-thumb magic-numbers.

Do you have an idea what your COVERAGE should be? It just-happened that radial exponential horns worked sorta-well in traditional vaudeville halls. They are disasters in typical dives, which is part of why I made my own and then just gave-up the business.

[AZJimC]

Draw me a picture.

I did draw you a pic, but scanner is locking up, so, I'll describe it. A wide horn, horizontally, say a mouth about 8"x 20-24 wide, that goes back to a throat wide enough to hold two drivers side by side. Main reason is I want to have two in series to sort out the ohms the way I want it. I have done no plotting for the horn, but I intended to use a pair of the really cheap 1" drivers on eBay.

Thanks Frank, that pdf is a good read, I never got what they mean by the "target" and the horn area equaling 80% of the target area. Surely they are not meaning the intended coverage? I can't see their horns equaling that much. That system is way bigger than I need or want, well, maybe want. I do understand the same principals apply.

My use will be maybe down to 6-800hz and I'll let the 12" & 15" cover the lower end. Even 1khz would be a good cutoff for mine, considering how cheap the drivers are, I would not want to have them doing anything that might make them growl. There is a guy here selling up to 14 Yamaha BR12 units from his club. He wants 100 each, and they have a horn, and a 12", and the horn is supposed to have a much better driver than I would be getting on eBay. I don't know how I will afford as many of these as I'd want, but time will tell I guess.

Later, and thanks PRR too,

JimC

[PRR]

> A wide horn, horizontally

Why?

In most dives, you want wide horizontal pattern, narrow vertical pattern.

A narrow pattern MUST use a large dimension.

A wide pattern can be smaller. It can be larger, but usually not the best use of transport.

I really don't think you want to run screw-drivers much below 1KHz.

> I want to have two in series to sort out the ohms

No! Air is much trickier than electricity. Get the ACOUSTICS right; don't gimmick the acoustics to make your electrical system add-up.

Anyway, any good horn is SO much more efficient than any box-woofer that horn impedance doesn't matter. I routinely drove 16 ohm horns with 4 ohms of woofer... the 4:1 "mis"-match roughly corrects the difference in efficiency. Horns tend to be over 10% at crossover, and woofs rarely beat 2%.

You need to decide if you want Pattern Control or you want the rising directivity and falling room response of a plain exponential. If you want honky-horns, I'm outa here.

If you want 60-90 degree beamwidth over several octaves: your mouth can be near 13,000/F where F is your lowest frequency. Construct a cone (usually a pyramid) back, until you reach 1,600/F. Now go to an exponential taper. The area halves every 1,000/F of length until you reach driver size.

To favor better high-end dispersion in one axis (usually horizontal), the transition from conical to exponential may be at a magic area instead of a magic width. Compute 1,600/F, then square that. Bring your pyramid back to this area. Change mouth size or pyramid angles slightly, so the transition section is tall and narrow. A 1" wide transition will give good dispersion well up the audio spectrum, and seems to mate a 1" throat with a flat-exponential, but leads to an awkwardly tall transition section. 1.5" is a good compromise, and you can find clean 2x4 lumber (or 2 slabs of 3/4" stock).

This (below) works very well above 900Hz, and can be wood-butchered from a yard of nice 2x4 stud and a quarter sheet of well-bonded 1/2" sheathing, with a sabersaw and some Liquid Nailz. The horn-throat is cut to 1/2" tall in 1.5" wood, you then rat-tail to approximate a 1" circle. Neat-freaks will of course want to putty-up the corners to taper 1.5" to 1", but it really does not hurt to have this short ugly transition.

[AZJimC]

PRR,
Thanks much man, that is in my budget, and I already have the wood, and, of course the tools, much better than a saber saw available to me. I was noticing the side-top on there, which way would the dispersion go?

Also, the 2x4's I get are very soft, so should they be coated with something harder in the throat, like sheet aluminum, to stop certain frequencies from being absorbed?

Would it change the taper a lot to taper the height from 1.5" 10 1"? I can plane the 2 by down on one side if so. When you say 1600/F is that the Freq center, or highest, or cutoff? I can do the calcs, just need to know what I am shooting for here.

I agree fully about the 1k+ for the 1" driver, especially the ones I will be using. I'll be lucky to get a metal housed one, and not a cheesy plastic one. These are 8 ohms, and I never thought about correcting for efficiency with impedance, but that makes sense. I'll likely end up with 8 ohm horns, and a total of 2 ohm woofers, 4 for the 12's and 4 for the 15"s. that will keep my amp loaded well. Is there any reason not to use 2 0f these, per side, at about 15 degrees spread for better horizontal dispersion?

Again,
Thanks much,
Jim

[Frankenamp]

(sorry for the late reply, my monitor took a dump and the new one is on a slow truck from Tennissee)

With all the work you are wanting to put in to this system, I'm wondering what is gonna be the use- Bass Guitar or PA?

With all the sweat and sawdust you have available you could do better by building a modern horn. Direct Radiators are between 3-5% efficient, and horns are 7-10%, sometimes better. If you want to go with a higher crossover frequency of about 3-3.5K, a stack of peizo horns melded and crossfired will give you a horizontal dispersion of 120* and pretty tight vertical dispersion. One guy I know of wouldn't believe it until he put a melded array up against his big JBL loaded horns. after listening and measuring the performance (RTA), he put the JBL's up on ebay. Note: not all piezos are created equal.

If I am to assume that you wish to use the 12's as mid-bass, and the 15's as subs (assuming you already have them) you might want to go horn loaded all the way. Aside from the requisite amps, all you need really is the speakers, an active crossover network and a speaker management system with a brick wall (zero attack) limiter. Lot of guys have good luck with the Behringer DCX/DEQ setup for cheap thrills, or one of the better Driverack (not the entry unit- dosen't have the brick wall). Don't bother with a passive crossover, for the cost of parts alone, you can get a decent used Rane crossover. Give it a thought. ;)

[AZJimC]

This is for a PA, 20 Chan Board, 2x600W amp built in. I'll have to make the amps and horns for later, For now, I am using a 4x12 box for each side, so I must make a pair or quad of anything to get the mid and top out. I'll have to go passive on the crossover, and later, I'll build the loaded horn for the bottom, and likely get an amp or two along the way, as I find bargains, (read broken, needing fixed)

Thanks, again, but I still wonder about two of the plywood jobs a side? That seems a match for the 4x12's

Jim

[Frankenamp]

OK, another apology for slow replies- using a borrowed (SWMBO's) puter...
does your setup allow for inserting a crossover to allow one side to do the lows and the other side to do highs? This would be a help.
Are you wanting to use the 12's? If so what are the T/S parameters?

[AZJimC]

hmmm, where to start?

The 12's I am using now are celestions in a marshal type slant cabinet. Not that I intend to use these, but for now it is all I have. I am trying to put together just enough to do a small area, and practice, which I have a pair of old Yamaha 3 ways with a 12, a 10, and 5 tweets, for monitors. I have a small about 150w amp for monitors, so the two 600w are free for fronts. I need to load them to 2 ohms for max power, and that is about where I am now. I figured two horns on each side, 8 ohms each, and one 4x12 cabinet at 4ohms can get me by for a while. Later I'll add two sub boxes, probably a pair of 15's, and an amp for them. Then I'll be halfway to a active crossover, and another amp for 3 ways.

Since I find deals on broken equipment, I never know what I'll come across, but that kind of dictates what I have to use for now, till cash flow is better. I just saw a BK amp, something-140 today that is working ok I may be able to get to replace the sleezy amp I am using for monitors, but I might be able to get a good 3way active crossover in that deal too.

The speakers I have available now other than the 4x12 celestion boxes, are those Chinese Lexons. I still have no specs on them, but I don't have to pay a lot to get a few of them, at least the 4 15" subs. I really want the 4x12's for guitar back asap though, so I would have to build something similar to replace them, maybe the 12' lexons, again no specs available yet.

I am trying to sell some studio equipment for a friend, Rane eq's, one of them realtime eq, and much midi stuff, including 3 units made by JL Cooper for recording board automation, a MAGI IIRC. Also older ProTools interfaces, Quads I believe. Selling this stuff, 3 racks full, would help me get $ for other PA stuff. He also has the amp, and crossover, and chinese speakers, likely for free if I sell some of the other stuff.

I do have guitars, and a few amps to swap for PA stuff, but that would be the same, take what I can get for a good deal. Anyone want a 24 yr old Martin D-28? That would get my cash flow going again, but I won't sell that for less than it's current value, due to the future value. Rather keep it till I can get what I want from it. Really, just rather keep it, :-)

Thanks Frank,

Jim

[Frankenamp]

Oh Man, DON'T sell the Martin! A friend of mine got one for a sweet price because he knew a guy with a dealer's license... still more than I could afford- once in a lifetime thing. As for using the 12's, I think you might want to look at a couple of Bill Fitzmaurice designs: for the tops look at the O-Top 2-12 or 1-12. As a temporary stopgap measure, you might be able to adapt one of the Omni-Subs to work with what you have, but it wont be perfect... You are wanting to put a lot of sweat and sawdust into some pro audio PA bins, lets get the biggest bang you can. Look up threads on the melded peizo array. If you can get your 12's to make it up to 3Khz, you are home free because peizos don't need a crossover and turn on somewhere between 3k and 3.5k. One peizo by itself will sound like crap, but an array will make a believer outta youse. Once you get things in order and get the recommended drivers you will be pleasantly surprised. Maybe even shocked. Even if you want to try out the array with the 4x12's it might worth it. For the price of a couple of decent screw-on drivers, you can get a couple dozen peizos, slice 'em and dice 'em into a test rig... Check the posts for which peizos are good (there are some bad ones out there like the Pyles).

Just to give you an idea for subs on the cheap, MCM makes an 8" with and Xmax of about 16mm that regularly goes on sale for 25 bucks it only takes about a hundred watts, but four or six in AT (auto tuba) horns will make some noise. The T24's will work with the MCM 55-1745 10" but the Xmax (4mm or 6mm) isn't enough to do much. I personally heard a stack of AT's loaded with HL10's. The test started at about 5.56v (mike was at two meters) loud even then, we gave up at 20 volts because our fillings were about to vibrate loose. (basic difference between the MCM 8 and the Eminence HL10 is that the HL10 will take 300 watts RMS and the MCM will take about 120. I have a couple in a horn designed for HT that gets about 60 per driver, never needed even that (to loosen yer kidney stones) ;) Still waiting for the wife's cat to hide in it (so I can play the intro to Pvt. Ryan) ;D

[AZJimC]

OK, Since piezos are cheap, and I'll likely want some anyway, what could 6 or 12 a side hurt? I can give that a shot, with my 12's now, and maybe a single horn per side. I would be interested in an idea of the impedance curves for the piezos.

Now, if I build a horn for the subs, or actually the low mids, how will that effect the driver's ability to reproduce highs, like from 1.5k to 5-6k? Won't a horn on them reduce their higher range, of course depending on the design of the horn? Or should I not worry, and let the piezos do all that they will do well, alone? I figured as much overlap as I could make is a good deal? or no? I'll have to use inductor/Cap filtering to make the boxes behave as expected, except with regard to the piezos, as they handle that themselves yes? Then I don't count their impedance until they kick in? Am I over analyzing this?

The Martin(s) and older fenders, guitars and amps, are my savings account, or the interest bearing part of it anyway. Not really ready to cash them in, but if I can get a good current price, and possibly get another, and have a bit of increase left, then I'd do it. I know quite a few bluegrass players, and can sometimes do quite well, if I happen to find the right deal.

Gotta get to doing something while I feel up to it, so,

Later,
JimC

[Frankenamp]

http://www.billfitzmaurice.com/OmniTop12.html
That's the link to the Otop 12. Also shows the unit with both the compression horn and the peizo melded array. It's a short, straight horn as you can see, you'll want to do an impedance curve on the prospective driver to get the proper component values. The published values are for the Eminince Definimax 2512 neo driver which is about as good a driver as you can get for that design. (You can spend more $, but nothing else is better due to diminishing returns on yer dollar) It is one of the few designs that will work fairly well with a non-optimum driver, (better than any commercially available system at several times the price) but loaded with the recommended driver, the only thing better is one of the DR series- which requires good wood skills, and the exact driver. Give it a look. 

Peizos are voltage driven- they don't use much current and below 3,000 Hz they have high impedance which effectively turns them off below 3-3.5K. this is why they don't use a conventional crossover. On the other hand, you may need to use a 4 ohm 25 watt resister in series with the array because some cheap amps put out noise at supersonic frequencies and will oscellate and fry due to low impedance at those frequencies.

[PRR]

> Won't a horn on them reduce their higher range, of course depending on the design of the horn?

The horn is everything. Many things are possible. Many of them are too difficult.

A 12" cone, below 600Hz, is just flapping. It can't grab air well. Large simple horns can significantly improve efficiency. A horn can be very effective at very low frequency if it is big enough, larger than an Econoline.

Above 600Hz, it grabs air well. A simple large-throat horn will not improve power efficiency above 600Hz. You can get more output on-axis with directivity; by 1,200 or 2,400Hz the 12" cone has "too much" directivity for most indoor applications and a simple horn won't help.

The efficiency is falling all across the audio band due to MASS. Above 600Hz, if we could improve the acoustic resistance, we could raise efficiency. The way to do this is to work a large diaphragm into a small tube, which can be expanded to a large mouth and a whole world. A 2" throat driver has a 4" diaphragm, 4:1 compression. This can buy 4 times the efficiency or 4 times the cut-off frequency.

But when you work a 12" cone (10" diaphragm) into a 5" mouth by simply bolting it to plywood, you have up to 50 cubic inches of trapped air. This "spring" works against the cone mass and resonates. You may estimate the resonance by simple extrapolation of Fs and Vas. For typical 12" cones it works out near 500Hz-1KHz. The resonance is well damped and loaded by the horn throat, but above resonance the horn flaps and very little acoustic power gets to the throat.

The trapped air is not necessary, just an accident of available parts. HF horns have a compression plug to fill the space. They generally leave barely enough clearance for the diaphragm to move. This shifts front resonance up another octave or three, depending how hard you want to work and how daring you are. Somewhere in that range, you also have to take account of phase-shift: the distance across a large perfect cone becomes multiple half-wavelengths and tends to destructive interference. A paper cone has phase-shift from coil to rim even before you try to bring all the zones together in a small throat.

Both Community and E-V worked on large cones for high compression midranges. I think the project killed Community (they re-appeared with generic boxes) and E-V seems to be trying to dump their driver in the autosound market.

On a smaller scale, I designed and built a huge compression horn for a 4" driver which with 1 Watt was VERY LOUD 600Hz-3KHz. From the top tech balcony, it would shout over power-tools on the stage in a 600-seat theater; partly efficiency and partly by extreme directivity. This had no plug in the trapped space in front of the cone, and the drop-off above 3KHz was quite remarkable.

Bill has followed a different path to horn design. Some of his claims are intriguing, better than I'd expect from a glance at his available plans, but I've not bothered to reverse-engineer his ideas. There are some interesting synergies in horn detailing, he's certainly an energetic builder, and his results say he's found a few tricks.

[PRR]

I do generally agree with the ARRAY of Piezo. The stock piezos are cheap-cheap-cheap and quite nasty, because everything has been trimmed to a minimum. A 4x3 array of the square horns, just tying their mounting-holes together with wire to form an arc-front, eliminates the "honk/squeak" and the crappy directivity, gives a solid clean midrange above crystal resonance.

> they have high impedance which effectively turns them off below 3-3.5K.

The specific cut-off is piezo-disk resonance. The center drives the diaphragm and the rim is unrestrained. At high frequency the rim mass exceeds diaphragm loading, the rim is stationary and the diaphragm moves. At low frequency the diaphragm stiffness exceeds rim mass and the rim flaps free. A slow impedance sweep through the cutoff zone will find the resonance. If you open the works and touch or restrain the piezo disk, you can shift the resonance, though I was not able to get more than a half-octave useful extension, and even that was not practical off the test-bench. The low-cut is very sharp.

They won't put-out sound below ~~3KHz, and can stand quite high voltages, but that disk is still flapping. In very high power systems, it can be wise to use a high-pass filter so they only get voltage at frequencies they can use. This can't be the "series cap" we use on dynamic tweeters, because the driver is a capacitor too. A C-R filter works. A C-L-R filter works better. It is convenient to use a standard 2.5KHz 12dB/Oct L-C passive crossover loaded with a dummy resistor.

> some cheap amps ...will oscellate and fry due to low impedance at those frequencies.

That's the flip-side of piezo-arrays. They are capacitors: Impedance is infinite at DC and zero at infinite frequency. One piezo is designed to have a tolerable impedance at the top of the audio band. IIRC: At 20KHz the small ones run 50 ohms and the large ones fall near 10 ohms. My 4x3 array fell to 4 ohms at 20KHz and 1 ohm at 80KHz. Many amplifiers (not just the cheap ones) may be distressed with such loading, it eats-up NFB margin. A series resistor protects the amp, but adds a top roll-off. Many-many-piezo arrays may start to droop in the top of the audio band.

[Frankenamp]

Splaying peizos is a no-no (comb filtering) this does not happen if they are cross fired, and you can get 120+ degrees of dispersion. If you don't get reputable drivers one must do a sweep of each driver to find out if it quacks (diaphragm hitting something it's not supposed to) or risk a nasty sounding array. Series/parallel arraying will keep the voltage to each driver at a reasonable level. Bill uses some tweaks to a conical horn (flare rates...) and gets pretty good results. I have a pair of 8's in a 13 foot horn that get to about 22 Hz (above 100+ dB) with an Adcom 60 watt amp). You are correct- mouth area is everything! with horns the f3 of an array is lower than a single horn. Even the Labhorn is required to use an array of four to get the published response. The trick is to have the horn lenght to support the mouth area. Horns tend to shift the resonant freq down because the air mass tends to make the cone seem heavier than it is. (Which is why early bass horn models used 'reactance nulling' (small rear chamber to push the resonance back up.)