What is the plastic horn in this PA speaker accomplishing?

thesamhill

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I have a small pa speaker I use as a monitor for solo acoustic gigs. I don't love the sound, it's got a weird peaky artificial sound.

The unit is this:



It's got a plastic piezo horn in it. It looks pretty much exactly like this:

https://www.parts-express.com/Goldwood-GT-1025-3-x-7-Wide-Dispersion-Piezo-Horn-Mid-Tweeter-280-062

It's soldered straight to the bigger speaker lugs with a resistor on the white wire side. The instructions on the website say it can be wired without crossover, but needs a 47 ohm resistor which is what I believe it has (pic of resistor attached)

I'd kind of like to know if the unit sounds better without this horn in it. If not, then it's either the amp or the big speaker and prob not worth messing with any more. But if so maybe an old eq pedal would make it more palatable.

What do I need to do to take this horn out of the circuit? Can I just take it out? Or would that still possibly lead to an issue with resistance?
 

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Dacious

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The horn is looking after high frequencies - not needed for electric guitar but certainly is for acoustics and human voices and woodwind or brass or flutes. You can disconnect it and see if you prefer the tone, but the odds are it may sound dull and lose punch.

You certainly can use an eq pedal on the line to it to pull down the highs. You can also try increasing the value of the resistor by 10-20%, Don't go.past 100 ohms.
 
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Peegoo

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You also need to make sure to match the Ohms impedance of the speaker cab to the amp. If the amp needs to see 8 Ohms, and taking the tweeter out of the loop changes the speaker cab from 8 Ohms to 4 Ohms, that can be bad when running the amp up past 6 or 7 on the volume.
 

Jon Snell

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You also need to make sure to match the Ohms impedance of the speaker cab to the amp. If the amp needs to see 8 Ohms, and taking the tweeter out of the loop changes the speaker cab from 8 Ohms to 4 Ohms, that can be bad when running the amp up past 6 or 7 on the volume.
Incorrect!
Removing the piezo horn will increase the impedance of the speaker cabinet by a very small amount above 5kHZ or so. Not the other way around. Probably not even measurable.

The resistor in series with the horn does three things;
Reduces the ear shattering horrible noise produced by the piezo horn, stops a solid state amplifier from seing a near short circuit at high frequencies and attenuates the horn slightly.

Piezo horns have a logrithmic load resistance. Depending on the size of the cell, at 1kHZ they will measure 100 Ohms or greater, at 20kHZ the appear almost short circuit as a load. Hence the resistor.
They are also used as an ultrasonic transducer, (speaker), in rodent or bird scaring devices at around 40kHZ.

Update; added wiring schematic to clarify.
 

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thesamhill

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Thanks all! I'll update if I get any results worth noting.

This is giving me some perspective on why tone matters for performances when the audience doesn't care. It's tough to get into the performance when your monitor is saying you sound like an icepicky, plasticky mess.

A better monitor might be the end solution but I like to at least try to work with what I've got before I move on, so I appreciate all the assistance.
 

schmee

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Those cheap piezo horns are terrible creating a buzzy high EQ. You can try just direct to the speaker bypassing the crossover & horn. Many PA type cabs have pretty warm sounding speakers though. But some are fine.
 

wabashslim

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All of the above, and - piezos have infinite DC resistance, IOW they'll appear open if you measure them with an ohmmeter, unless of course some other circuitry in/around them is at play. The amp sees them similar to capacitors. I've seen them wired directly across the speaker, no resistor. And because their own low-frequency response is nil no crossover is needed. I personally think you'll end up buying a better monitor after experimenting with this one.
 

Bill Moore

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They do brighten things up!
Back in the day when we were using 4-12 columns for PA speakers, (think Shure Vocalmaster, and others), I built a couple of boxes with 2 Radio Shack piezos in each, and paralleled them with the 4-12's. There was a little more clarity, but it was great to finally get PA speakers with midrange horns!
 

PhredE

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Similar to what wabashslim says, it is not at all uncommon for many bass amp/cabinet builders to use a simple (usually 'cheap'!) piezo wired in parallel for all the high frequency output.
Simple, cheap and works reasonably well.

No reason that couldn't be done for guitar but all that higher frequency stuff is generally not sought by guitarists.
 

thesamhill

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Update:

Pulling that horn out made a huge difference. Maybe I got a bad one or something. It sounded a lot lot better without it.

So with the 10" speaker and an EQ setting that boosted the treble (the "soft" preset in VLC player if you're playing along with the home game), I played Cherokee by John Moreland through the headphone jack on my phone, through a stereo-to-mono adapter, and into the line in. That's the closest thing I had on my phone to what I'd want to use the monitor for- ie solo acoustic gigs.

It sounded dark, and mushy in the higher vocal range, but for a monitor I could def get along with it. Dark is better than artificial and plasticky.

After that I hooked up a plain old stereo speaker- a Dayton Audio B652, a speaker that I already know I like- just to see what it did. It is 6 ohms, not 8 and rated for 40 watts not 50, but I didn't crank it. Just had a listen at "that's a bit loud for this time of night, honey" levels.

It sounded pretty good imo. Def better than I thought it would and good enough to make it seem like the amp in the unit isn't a total write-off.

I think I have some other stereo speakers around here that are rated high enough watts to push the volume a bit. Will update again when I find and test. But I'm feeling more hopeful that I can find a driver combo that can make this a suitable monitor for looping at solo gigs.

In the meantime feel free to speak up if I'm about to fry myself :)
 

thesamhill

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Update 2:

I'm sure you're all following me learning "speakers for dummies" with breathless interest so here's another update :)

I took the actual horn apart. It looks like one of the screws was overtightened and the receiver barrel part that it screws into was shattered. There were plastic shards all over the inside of the housing. Two of the other 4 screws were loose.

I took it apart, shook out the shards, tightened it up, and reassembled.

And... it's better! I think I get what the horn is doing now.

The horn isn't really acting like another speaker driver. It's more like salt on a steak. The actual flavor is coming from the main driver, and the horn is kind of sprinkling some brightness into things that helps the overall sound image resolve.

That's kind of unexpected. It's also kind of interesting.

This monitor is essentially a 50w SS amp with a 10" speaker and a piezo horn. It happens that I have an SS bass amp around in case a bassist wanders into a jam session, and I think it's exactly that- a 50w SS amp with a 10" speaker.

I wonder if I could build a switchable piezo horn circuit into that amp and create an emergency backup PA box.

I can't imagine it would sound great, but having suboptimal sound quality for an evening beats driving an hour away to play a solo acoustic gig, setting up, then having to tear down and go home without getting paid coz the PA died and you didn't have a backup.
 

Dacious

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Many bass amps are exactly like that with a switchable horn..in that case you use the horn to save the driver whilst playing slap bass. The bass driver does not like the sharp transients and you'll cook the voicecoil.
 

Boreas

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Stuff a sock in it! Adjust sock to taste.

Horns are pretty good at dispersing high end, which wants to travel in a straight line. So I would lean toward not removing it from the circuit permanently.
 
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thesamhill

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Stuff a sock in it!

Whaddya know, that's the same advice my wife gave me. And here I thought she was just telling me to shut up :)

I did end up replacing the horn in the monitor after I took it apart. It's still a cheap monitor but then, I still have no ear for tone so that kind of works out. That will probably stay that way until the horn fails again.

I also ordered another horn to test out on the bass amp I have. I'll probably put that on a switch if it sounds ok. That's not a super urgent project tho. I might try to play a little guitar at some point, too lol
 




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