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 1 
 on: Today at 10:20:40 am 
Started by Mike Sokol - Last post by John Roberts {JR}
Is autoformer a real word in the US?


Steve.
I always thought it was a word,  :-[ ?

Here's a TMI autoformer story...  Back when Peavey entered the fixed install market where most install power amps use output voltage step up transformers to hit the nominal 70V/100V constant voltage (misnomer) sound distribution. Substituting autoformers for those output transformers would not only reduce significant weight, size, power loss, and cost, but the audio frequency response and distortion would even be better.

While it should have been a win-win-win-win....., it was a lose when the customers rejected them. The primary downside to autoformer outputs is that they are not completely floating. Apparently inadvertent ground shorts to one side or the other of 70V audio lines is pretty common. With a transformer's floating output, the short is ignored and the beat goes on. With an autoformer if the hot side is shorted (50-50 chance), the music stops and a difficult (expensive) service call is required. Further an amp upgrade in an old install from a previous transformer output model might not work as expected, until wiring is fixed, and lastly the install technicians didn't need to pay any attention to which output wire was which.

The install market was (is?) conservative and resistant to change so Peavey had an uphill battle even with no identifiable differences to point to. Since the customer is always right, we re-engineered the entire line to use the larger, heavier, less efficient, transformers. (ouch   :o ). That is a lot of copper and iron that arguable wasn't really needed.

JR

 2 
 on: Today at 10:12:41 am 
Started by Tim Bulin - Last post by Paul G. OBrien
I could do 95% of my shows with a pair of DM112s and a single DM118, and it would sound really good.
Then that is what you buy gear for. 

Unfortunately, most of my customers want to see those 15s sitting on top of the subs...bigger footprint, more of a "whoa" factor I guess.
No they don't, if you actually polled people most wouln't care and from those that do have an opinion there would be as many that say smaller or invisible speakers would be better.

Maybe I'm just paranoid about it, but, I lost a big show last summer to a guy with a truckload of SA and Rockville speakers(and it did not sound good).
Yes you are being paranoid of change, and guess what you will probably get that event back next summer.

 3 
 on: Today at 10:04:43 am 
Started by Josh Billings - Last post by Simon Lewis
Most applied acoustics texts will cover "sound transmission through partitions" in some depth...
At very low frequencies, the stiffness of the partition is the dominant effect, followed by the partition resonance at slightly higher frequencies.
This website has some good coverage on the issue... http://www.sekon.cc/acoustics/SoundTransmission/index.htm

 4 
 on: Today at 09:55:17 am 
Started by Charles Prabhu - Last post by Ken Cross
It sounds like you want to connect 2 amplifier outputs to (3) 8-ohm speakers. Or you want to bridge amplifiers and connect them to 3 parallel speakers.
If that is your question, yes it may work but your amp spec doesn't show you output going below 4 ohms when bridged.  If you connect all 3 speakers in parallel, you should have an impedance of 2.66 ohms. Be careful if you bridge the amplifier you will have an output with plenty of power to damage your speakers. From the specs, it looks like you should be able to power all 3 speakers from a single channel of the amplifier. (that would be my choice.)

Just to clarify: are the speakers to be used in a single cluster or distributed into other locations. I ask because if they are in a cluster and you run 3 on one channel and one on another, then you need to worry about matching the phase of the speakers.

Ken

 5 
 on: Today at 09:50:37 am 
Started by Karl Winkler - Last post by Jason Glass
I went to Jason, Pete, and Henry's seminar yesterday and thought it was really great. Everyone did a good job contributing useful information, and the time wasn't sufficient for the content, which is a good problem to have.

Thanks for that, and for this great forum.
Thank you, Dan! I'm glad you enjoyed it, and it was a pleasure to meet you.

Sent from my Nexus 5 using Tapatalk


 6 
 on: Today at 09:24:43 am 
Started by Josh Billings - Last post by Tom Danley
My buddy has a venue and has neighbors that are getting a little fussy with the subwoofer kick thumping. I'm looking for someone in the Southern California area that can help consult with them on what needs to be done to get their exterior sound bleed under control.

Was considering suggesting a cardiod sub array, but not sure if that will really help.

Hit me up via PM or feel free to reply on here

Josh Billings

In the 80’s I got tired of being called by the police in the middle of the night when we were doing life testing of the Servodrive subwoofers at Intersonics. It only took a few trips in the middle of the night to shut it off before a solution was imperative.

Some solutions have been described already but this might be helpful too.
Obviously sound is pressure, pressure which alternates positive and negative and at say 132dB, this represents an alternating  peak pressure of about 2 pounds per square foot of area.  This force is felt by say a wall and it is the walls mass and stiffness and the duration the pressure is applied that determines how far that wall will move in and out in response.  That movement-radiates the attenuated sound on the other side.

There is a complication too, stiffness and mass are opposite reactive forces and when paired as in a wall (or a loudspeaker cone in a box), one also has a resonance or resonant frequency. As in other parts of audio, the sharpness of that resonance is the Q and by adding things which have mechanical resistance (like drywall, construction adhesive etc) the Q of a resonance can be lowered / broadened. 
 In a room a diaphragm like wall resonance usually produces a suck out and not a peak as instead of a ridged boundary, it has give and losses.  The “limp mass” mentioned reduces the stiffness and any significant resonance but increases the mechanical losses so that the act of simply moving the barrier dissipates a lot of the energy.   
Another approach that works higher in frequency is various densities of fiberglass panels, these have a large amount of acoustic friction on the pressure as it propagates through it.

Anyway, at Intersonics we made a “death room” which had about 35dB of attenuation at 40Hz and lots more above and that ended the police calls and late night trips to shut it down.

It was a basic design I took from a sound control handbook and it went like this.

The header and footer was a 2x6, the studs were 2x4’s that were alternated so that the inside and outside walls were not connected other than at the top and bottom.  The 2x4’s were covered with ¼ luan (cheap)  plywood glued to the 2x4’s and then 5/8 drywall inside and out glued and screwed.  The roof was the same construction and basically set on top like a cap and under the footers and between the roof and walls was carpet as a seal.
There was a 90 degree L aluminum in each corner top to bottom and the door had the same construction and sealed with foam tape and carpet.   To make it nicer for testing non-subwoofers, we hung heavy shag carpet on (spaced just away from) the walls.
In your case, you might want to play band passed pink noise and go outside and see if there is a “hot spot” on the building that could be treated on the inside with a similar or other barrier.
Hope that helps
Tom

 7 
 on: Today at 09:15:40 am 
Started by Karl Winkler - Last post by Dan Mortensen
I went to Jason, Pete, and Henry's seminar yesterday and thought it was really great. Everyone did a good job contributing useful information, and the time wasn't sufficient for the content, which is a good problem to have.

Thanks for that, and for this great forum.

 8 
 on: Today at 08:10:29 am 
Started by Tim Bulin - Last post by David Allred
Unfortunately, most of my customers want to see those 15s sitting on top of the subs...bigger footprint, more of a "whoa" factor I guess. 


who is your market?  College frats?

 9 
 on: Today at 08:00:44 am 
Started by Nathan Riddle - Last post by David Allred
I haven't? [and no i'm not trying to 'play dumb' or be sarcastic, I'm really questioning my experience here]

Ratings? Meaning of the hardware? Is the below quote of myself not sufficient? [seriously not trying to be an a$$ about this, i'm actually questioning the validity of my statements as 'proof' of the ratings/expected loads]
 
Also, was the 100-300lbs not enough info? Should I be specifying torque?

Again, I am NOT trying to be sarcastic. I want to know so that if/when* I talk to an engineer about specifications for loading truss on a wall in the future (because it WILL happen again) I want to not sound like an idiot...

Agreed, tension isn't good. But I was willing to calculate the tension given the torque (moment) on the truss from a perpendicular loading at a distance away from the wall rising to sheer force down & compression on the bottom of the truss and tension along the top.

Giving rise to 6x clamps along the top (unistrut being found to be a better material in-between truss and wall for allowing expansion/compression) & 2 along teh bottom (because they will be under compression less is needed.

Also, thorough bolts were determined to be the best, inwhich case when mounting the unistrut would be much safer and could get away with only 2. But if using wedge lag bolts then 6 along the top would probably be better off. Albeit much harder to get straight and make the truss mount correctly.

Agreed. I thought I was stating my case well and providing the design specs of the hardware in question. I now believe that assumption to be incorrect given Mr. Rees's questioning of the layout.

This flows into my next thought.

I have mishandled stating my case clearly. Sorry all.

Sometimes you have the design in your head and it's too simple to forget others don't. I try to think about that when posting on a forum, but I'm not perfect...

Hopefully the attachment work.

Does that drum shield have a ceiling? :o 
What about the drummer supporting the middle section like a Carmen Miranda hat.  Would definitely require a chin strap.  Talk about a mover. 8)

 10 
 on: Today at 07:05:10 am 
Started by Mike Sokol - Last post by Mike Sokol
Is autoformer a real word in the US?

Steve.

Nope... It's a registered trademark.

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