Reflections and Tapped Horns

[4pyros]

Can sound wave reflections from solid objects in frount of a set of subs, damage the speaker cones in tapped horns?


In other words, Should I worry about setting up tapped horn subs along the main road leading into a major casino with cars, trucks, and buses passing within feet in frount of the subs?

Andy

 

[chris661]

I wouldn't worry too much about it. As a truck passes by, the pressure wave you feel is such a low frequency that the TH would act as a short-circuit: it'd push on both sides of the cone at pretty much the same time, so the forces would pretty much cancel.

 

[4pyros]

the pressure wave you feel is such a low frequency that the TH would act as a short-circuit

Sorry Chris I do not under stand what you mean by "such a low frequency" would that not make the sound wave longer and more susceptible to reflections?

 

[chris661]

When driven below the lowest tuning, tapped horns provide almost no resistance to airflow, right?

It makes sense (to me, at least) that, if it was to be excited externally, it would have similar tuning properties. ie, if the TH has a lowest tuning at 30Hz, an external source of 20Hz would excite both sides of the cone pretty much at the same time, in much the same way as the driver itself would run out of excursion at 20Hz pretty quick: at those wavelengths, the cabinet disappears.

HTH

Chris

PS - I may have it completely wrong, and would happily admit that if anyone comes along with a better answer.

 

[weltersys]

Can sound wave reflections off nearby solid objects damage the speaker cones in tapped horns?


In other words, Should I worry about setting up tapped horn subs along the main road leading into a major casino with cars, trucks, and buses passing within feet of the subs?

Andy

Andy,

Passing vehicles create a temporary boundary that can increase level, but will not cause any damage.
If you park a bus alongside your stack, it will increase forward output more than 3 dB.
Did you ever determine what voltage to limit your amplifiers to prevent overexcursion of your 3015LFs?

Art

 

[4pyros]

OK I rephrased my question. To say the vehicles are passing right in front of the speakers not passing along side them.
Meaning the sound wave is coming back to the cab from the front.
Does that make a differance?

 

[4pyros]

Andy,

Passing vehicles create a temporary boundary that can increase level, but will not cause any damage.
If you park a bus alongside your stack, it will increase forward output more than 3 dB.
Did you ever determine what voltage to limit your amplifiers to prevent overexcursion of your 3015LFs?

Art

Walt;
I started out the year with the limiter set to -8db and low end set to 40hz.
Unfortunately sometime during the year the settings ended up back at default. 0db limit and 20hz low pass.
The cones are damaged again but not as bad as last time.
I still need to physically check excursion. I may be able to do that tomorrow.
Andy

 

[weltersys]

OK I rephrased my question. It say the vehicles are passing right in front of the speakers not passing along side them.
Meaning the sound wave is coming back to the cab from the front.
Does that make a differance?

No.
Neither will people standing in front of the cabinets.
To much excursion from driving the speakers too hard will damage cones, as you have already found.

Explosives in close proximity to horn loaded speakers can damage cones, but it has to be really loud, like 180 dB, and really close, like a flash pot on top of the cabinet.

Art

 

[djk]

Pyro is more likely to blow HF drivers.

 

[epa]

i think the pressure of a passing truck is negligible,compared to the pressure inside the th @ full power.
a formula 1 car or nascar,dragster ect, maybe,if they get close enough.

 

[weltersys]

Pyro is more likely to blow HF drivers.

Back in the day, Reo Speedwagon toured with DB sound.
One of their pyro guys had the idea of mixing two different brands of powder together at a large stadium show, as it turned out the sum was greater than the parts.

The concussion mortar had an iron base about 6" x 6", the downward thrust from the explosion was enough to drive it through 3/4" of fiberglass coated Baltic Birch on the cabinet it sat on.

Although the FOH and monitor engineer had muted all the open microphones, around sixteen 15" drivers loaded in FLH horns in close proximity to the "event" suffered ripped cones and/or smashed voice coil formers, but no HF drivers were blown, and they were as close to ground zero as the LF drivers that blew.

At any rate, with "normal" pyrotechnics, DB sound had not had any problems with driver loss (as long as they muted the PA before the big bombs), the one described was a doozy, and not repeated.

 

[djk]

I had problems with Pyro tearing the Nomex voice-coil formers on Altec 288s right where they attach to the dome. The LF drivers never failed, but I never saw a situation as what you described (insanity).

I'll have to ask Bruce Knight from DB about that era, he lives locally.

 

[4pyros]

Alright guys my system is set up outdoors hundreds of feet from the pyro and facing away from the launch site, so I dont think thats it.
I made a little power meter and hooked up the subs.
It seems they could could have been inadvertently over powerd.
I was seeing over 500 watts depending on how much bass was in the songs.
I must have done something wroung calculating the attenuation needed to keep the power under the speakers rating.
I think it was because the calculations assumed the 28db input setting was being used on the amps, but I have been using the 1.2 volt setting assuming that matched the output of the Xover.
Is anyone willing to double cheak all the calculations for me?

 

[tinitus]

because you post good info, but of more value to other PA guys, I moved you to PA systems

hope you are ok with that


moderation

 

[4pyros]

because you post good info, but of more value to other PA guys, I moved you to PA systems

hope you are ok with that


moderation

Thats fine

 

[weltersys]

I think it was because the calculations assumed the 28db input setting was being used on the amps, but I have been using the 1.2 volt setting assuming that matched the output of the Xover.
Is anyone willing to double cheak all the calculations for me?

Andy,

Why do you keep looking for numerical calculations that won't address your loudspeaker problem?
As I wrote you the last time you "tenderized" your cones, simply run pink noise, back down your limiters until you see the cones don't exceed Xmax, done.

Well, "done" as long as the limiters are not set to "0" and LP to 20 Hz again .

 

[weltersys]

I had problems with Pyro tearing the Nomex voice-coil formers on Altec 288s right where they attach to the dome. The LF drivers never failed, but I never saw a situation as what you described (insanity).

I'll have to ask Bruce Knight from DB about that era, he lives locally.

DJK,

That might have been a glue problem aggravated by the pyro.

If you were like most of us at the time, you may have been using "protection" series capacitors, which removes the amplifier damping, allowing the diaphragm to move more freely when subjected to high SPL coming in from the outside.

Dave Rat was breaking TAD diaphragms just from the SPL of the adjacent woofers (while testing with the HF unpowered) until he removed the caps.

 

[djk]

"That might have been a glue problem aggravated by the pyro."

No, the Nomex tore, not the adhesive. The problem seemed to be the amplifier driving the diaphragm forward while the overpressure from the pyro drove the dome backwards, the dome seemed stretched as well. No cap in that setup, direct connected to a Crest 3501 IIRC. Switched to JBL 2441 after that, they didn't sound as good, but they held up better (under pyro). The former Nomex former is much heavier on the JBL than the Altec, but the HF on the large Altec is more like a good 1" driver.

 

[4pyros]

Why do you keep looking for numerical calculations that won't address your loudspeaker problem?

Out of curiosity.

simply run pink noise, back down your limiters until you see the cones don't exceed Xmax

I did not have the time or place to do that before. I will do it now.

 

[ClackS02]

Can sound wave reflections from solid objects in frount of a set of subs, damage the speaker cones in tapped horns?


In other words, Should I worry about setting up tapped horn subs along the main road leading into a major casino with cars, trucks, and buses passing within feet in frount of the subs?

Andy

As long as you are not using delicate speakers such as ribbon tweeters you should be fine !