D.I.Y. plate reverb

words, photo and audio by: Telegraphy

The first artificial audio effect to produced a reverberation sound is known as the echo chamber. A sound source and microphone are placed in a large caverness room which allows persistence of sound to be heard. This persistence of sound is created by bouncing the sound source audio off highly reflective surfaces of the chamber, this is heard as a reverberation. This is by far the best reverb effect one could produce and the most expensive.

 A cheaper way to produce reverberation is to use what is known as a  plate reverb.  This device is best described as having similar physical characteristics to an audio speaker. While working on the same principal as a speaker, the plate reverb can produce reverberations better in quality then it's digital counterparts. Historically, this device has been used in studios since the early 1960's      

The concept of a plate reverb is quite simple. An electromagnet, like the one found on a audio speaker, is directly or indirectly coupled to the center of a piece of sheet of metal. Audio from a sound source is fed into this electromagnet (voice coil) which will physically vibrate the piece of sheet metal (plate). These audio vibrations are echoed many times, echos which are in fact persistence of audio. The amount of persistence (reverberation) is determined by  the physical
characteristics of the plate. These characteristics many include  length, height, and stiffness of the piece of sheet metal. Once reverberation has been set off in the plate itself, it then needs to be detected. This is accomplish by directly or indirectly coupling microphones to the plate. The micophones pickup the reverberations and sends them back to to be mixed  with the original "dry" audio.


  The following article is a step by step
description of a home built plate reverb

  The cost of building this plate reverb was around 
$150. All materials needed (excluding electronics) were obtained at my local Lowes home hardware store. Electronics on the other hand, were from RadioShack.

materials used

 Step 1: You can't have a plate reverb just hanging around without a proper home. The first order of business is to construct a frame from which the plate hangs from
. I used 8 foot sections of galvanized slotted angle iron which has many holes in it. These holes are perfect for a quick and painless assembly. Two of these sections is good enough for this project. Cutting the proper lengths was a breeze with a simple hack saw. Now that all four sections are to length, it was time to make four corner bracket plates. These brackets are used to make the frame ridged. 1/32 aluminum sheet metal cut with a band saw into a triangle shape. Three 9/32 holes drilled like so are all that is needed. Attaching the corners brackets to the four lengths of angle iron was made by using 1/4-20 nuts and bolts. Now that the frame is ridged length wise, it was time to construct cross members to make the frame ridged radially. 1/2 aluminum angle stock is strong enough to do the job. Arranging them in a "V" patten prohibits the frame from twisting.

  Oh yea.....I forgot...
 You can't have a frame just laying around all day doing nothing - Thats what men are for. This frame is going to need some feet to stand on. Using the last of the galvanized stock, I cut to length small sections and then I made two of the same corner brackets I made earlier. Connecting the feet to the frame in the same fashion as the

frame corners

  Step 2:   What's all of this hanging around non-sense. Speakers don't hang around - That's what teenagers are for. Using the last of the two 8 foot sections of aluminum angle stock, I cut to length two vertical mounting brackets. This will hold the driver in place.

  Step 3: You didn't think I would forget about the most important piece of them all. Without it, we would have to name it the "Air-verb". Anyhow - Now I know that there are many different opinions out there on what type of plate material to use and how thick it should be to produce a certain sound quality. For that, I will leave it up to you to do your own research and decide based on what you want.


                                            Just in case your wondering what I used:
At Lowes home hardware, they had in stock a 3 ft x 2 ft plated steel sheet metal. The thickness of this sheet metal is 26 AWG which is roughly .016 inch. This is quite thin in a reverb point of view. But I wanted something that would easily reverberate at low frequencies. So my theory is that the thinner the plate is, the more easily it will vibrate at lower frequencies.
 Having about 2 inches of space between the frame and the plate, gave ample lee way to use medium strength springs to suspend the plate from the frame. I used four 3/4 inch heavy gauge springs for this project - it's enough tension to ensure good persistence. Before the plate can be installed, the corners must be reinforced. If the corners are not strengthened, the immense tension exerted by the springs will eventually ware out the corners. Using four more 1/32 aluminum triangles (yes, that's the last of the dreaded triangles.) I drilled four small holes on each triangle to accompany four revives, plus another 9/32 hole for the mounting nut and bolt. Duplicating the holes onto the plate was a breeze with a sheet metal hole puncher.

  This next step takes a bit of elbow grease - tensioning  the springs. This requires patience, strength and a third hand to keep the frame from moving (unless your like me who uses his knee, head, foot or any other available extremity instead). Use your knee folks, it's simpler. The first spring is the easiest - no tension. The second spring (of coarse) is much more difficult. I tensioned the spring on the opposite corners from the starting one. Using a pry bar of some sort to pull the spring to the mounting hardware, I bolted them down and took a breather.

 Step 4:
Now folks, I know what your thinking. You can't just connect the output leads of your mixer directly to the plate and expect it to perform. No, you need a driver of some sort. There are different methods for driving a plate reverb. The method I'm using in this project involves directly connecting a speaks voice coil to the plate itself. Again, there are many different opinions out there regarding how to drive and detect audio too and from a plate reverb. So as another disclaimer, I will let you do your own research.     

                                               Just in case your wondering what I used:
  I wasn't about to spend another $150 for a brand new speaker, only to have it disemboweled for it's precious voice coil. One good thing about being a man is that you tend to hang on to things (like your ex who treated you badly...please come back baby!!). I had speakers laying around - not expensive ones but they had voice coils. These in particular were old Chrysler automotive 8 ohm speakers. I wanted to directly couple the speakers voice coil to the plate itself. This required some manly modification to the speaker.
   How to disembowel a speaker:
(the ionosonde way)
           1: Ripe out cone body. Use hobby knife to cut away cone right down to the dust cover.  "Making first incision"
           2: Cut away dust cover (being careful not to cut into the voice coil or the spider. DOING SO WILL RESULT IN COMPLETE DEATH. ) "nurse Mary, please hand me the forceps".
           3: Using what ever tool at your disposable, cut away speaker basket taking care not to cut away the connection terminals.(I used sheet metal nippers) "this limb needs to be removed, cut off saw nurse Mary"     
           4: Remove terminals leaving the metal mounting tabs( I'll use these as the voice coil mounts) "O.K. sutcher up the patient nurse Mary - My bill will be in the mail"



Now that I had a working voice coil (driver) ready for mounting on the plate reverb unit, it is time to fabricate a coupling link that will directly connect the driver to the plate. But first, I need to do something with this mess I made while performing that gruesome surgery on our patient. A quick sweeping with my trusty broom and......wait a minute - broom - broom handle... Perfect! A broom handle is the right size for making a driver coupling link. Just cut off about 1 1/2 inches of the broom handle (the length depends on the distance your driver will be away from the plate)  - file or sand one end to size for a slip fit into the voice coil. Glue the coupling to the voice coil. It is essential to be cautious while gluing. If glue seeps down into the gaps between the coil and the magnet, then you essentially made yourself a nifty refrigerator door magnet. In other words, the driver won't work if the coil and magnet are glued together. After the glue has dried, mount the driver to the frame. If the coupling link length is correct, it should lightly touch the plate. If the plate is bowed outward, then the coupling link is to long.

 Drivers in place and ready to use. All that is left is the pickups. Again, there are many different opinions out there of what type of pickups to use and how to use them. Everybody has different needs to fulfill in their reverb project. It just isn't right for me to tell you what my opinion is(sorry folks). But........


                                                 Just in case your wondering what I used:
  Piss...hey you....What if I told you that Radio Shack has had a secrete only known to musicians for many years. You would say to yourself, "Telegraphy your crazy!!", has you search through those pro-audio gear catalog's looking at $100+ acoustic pickups. Well just between you and me (and keep this on the down-low) Radio Shack sells pickups for $4.49 each. They don't label them as such but instead their called Piezo Elements 1500-3000 Hz model: 273 073  The sound quality of this devices are great for the price.

Taking those $4.49 acoustic pickups (Piezo Elements) out of their packages, I realized that these pickups didn't look like your average piezo element.Well for starters, the elements are buried inside a blast proof, geek proof, flame resistant, and radiation proof  -  black plastic case. To extract this rare element, you need a good sharp hobby knife, a skrew driver, and most of all - patience. All you have to do is pry open the top with a skrew driver (sounds easy enough. Boy are you in for a treat). Down inside of it's impregnable case is the piezo element. It's almost press fitted down in there, so your going to need a hobby knife to gently pry it loss. 

Attaching them to the plate reverb is straight forward but keep in mind - Yes for the last time. Everybody, say it with me. "There are many different opinions out there of where to place these elements on the plate". So please, do your own research. Knowledge is power.  The most complicated and scientific of these opinions, is to find out where on the plate the wave front anti-node of certain frequencies are. Oh, yea I forgot.....
                                             Just in case your wondering where I placed them:
  Attaching them at equal distances from the ends and having them placed on opposite faces of the plate works for me. The reason why I placed them on opposite faces is to "simulate stereo". Remember that we're only using one driver (mono). Now it would be cool if I had enough room, time and money to have two plate reverbs; one for each channel.


 After wiring up the driver into an audio source and running the pickups into a low noise pre-amp, it was time to test this plate reverb out !

                                                          Here's an audio sample. Enjoy.

Ann Arbor Hash Bash 2013

words, photo and audio by: Telegraphy

"Hemp - Hemp - Hooray!
                                                Unknown Hash Bash protester 2013

Ahh, Ann arbor. The college town of all college towns. This Michigan mid-sized city is home to the University of Michigan, one of Americas finer college. Besides the usual traditional college curriculum, more unconventional courses are offered, such as - Zombie Survival and How to be Gay: Male Homosexuality and Initiation. But I didn't travel 50 miles from my home on the east side of Detroit just to expand my intellect in higher education (wow, all of these pun words - "expand" "intellect" "HIGHER". You can see where this is going folks.) no, I came here on this typical gray spring day that you often find here in Michigan to observe and hopefully decipher one of Ann Arbors finest attractions - The Ann Arbor Hash Bash.

  This annual event has been attracting stoners (like a newly found hidden smoking spot) since 1972. At first, it was intended to be a celebratory gathering which brought public awareness to the Michigan Supreme Court decision on  March 9th 1972, declaring the law used to imprison activist John Sinclair on marijuana possession charges,  unconstitutional. Since then, it has grown into a protest march against federal and state marijuana laws with the intent to completely eradicate the pot prohibition. This yearly event is held on every first Saturday of April on the steps of the University of Michigan's Diag  (/ˈd.æɡ/ DY-ag) which is a large open space in the middle of the university's central campus. The main event is at "high noon" with various key note speakers rallying a crowd of thousands. This event has grown year by year in attendants and so has the thick cloud of pot smoke hovering above them.

    So as I hurtled down the highway on my way to this event, the first bump in the road hit me like Fat Dab - Detroit construction. "It's only April" I said. "Construction season isn't supposed of started yet". As conscientious Detroit drivers knows, Michigan has two seasons: Winter and road construction season. Crawling my way through this tragic traffic, constantly shifting gears from first too second on my well warn 1999 VW Jetta, I started to wonder, because when ever I'm in a Detroit traffic jam; to keep my cool I often ponder on cosmic issues. "Does the Hash Bash still have that revolutionary spirit that was so prevalent during the 1960's and 70's, even in this modern internet based society we call America or is it just a good excuse for twenty-somethings to go to get high?". I mean a question like this real helps to releave a lot of stress from the out-numbered offensively driven trucks that infest I-94  

 Finaly after an hour drive, I arrived in Ann Arbor. Exploring the city trying to find a good parking spot is more akin to finding the mythical pot of gold at the end of the rainbow. It was impossible! Almost all parking spots were ether metered or permit parking only and I wasn't about to wast my time running back and forth feeding a hungry meter like a stoner after a hard days smoke-a-thon. Thirty minutes of searching and almost ready to give up, I finally found a free parking spot. A mere three blocks away from the Diag, it was one of those miracle parking spots you only hear about in urban legend stories. Quickly reserving my free parking I headed out to the Diag. Having a half an hour before the festivities, it gave me ample time to relish in the atmosphere. Oh, I'm not saying where I found that free "legal" parking spot.

  Grabbing a cup of tea in the coffee house across the street from the U of M campus, I headed up the long straight walkway to the center campus Diag. It was cloudy and cold with an occasional lite northerly breeze that made it feel more like winter at the steps of Diag. Good thing I was smart enough to bring along a nice hot cup of tea. Even with the cold Michigan weather at hand, it certainly didn't keep the stoners away as we'll find out later on. Even at 11:30 am, there was already copious amounts of people, standing around, smoking, sometimes occasionally dancing to rhythmic beat of various drum circles that were sporadically stationed throughout the Diag.

 Roaming around the crowd, I started to familiarize myself with the vast collection of different people who were in attendance. Trying to piece together what type of person would come to an event like this and why. My mind was blown away to see so many different generations, races, creeds and political view points being represented here. Hippies - Yea, they were there, dreads and all. College jocks - Dude, Bro. They were there in force. Freaks - Eh, few and far between but if you glanced over the top of the crowd, you will notice the unmistakeable site of a  mohawk jetting out like a soar thumb ( like a undercover cop car). Straight edged clean cut students -  Again, just think undercover cop car. Speaking of police."Two". What does two have to do with Ann Arbor's finest? Well the whole time I was there, I only counted a total of two police officers and they were standing well away from the crowd, almost to the point where you had to question yourself as to what's the point of the police having a presents there at all. Maybe they were afraid of getting a contact buzz ?                                        

 By 12:00 am "high noon" the crowd grew at an overwhelming rate. With twenty-somethings flocking in large groups down the side walks towards the Diag, you get a sense that this is going to get interesting. The Hash Bash got under way in what I thought was quite unusual. You would think that the customary way of starting such an event would be to light up a ceremonial joint. Not here! This is Ann Arbor, we still respect our constitutional rights. Everyone in the audience put down their joints or what ever they were smoking, faced the American flag perched up high on the flag pole in the middle of the Diag, as a young lady sang The National Anthem. As it ended, cheers rang out from the crowd, and the mass conflagrantion of organic material continued.

  With vairous key note speakers gathered above the crowd on the steps, their rallying voices blaring through P.A. system, passing the microphone around so each one get his or her chance to voice their concerns on subjects such as - cannabis economics - marijuana prohibition repeal - hemp industry - and more. Notable speakers that really set the crowds joints on fire was: Michigan State Rep. Jeff Irwin, who spoke about completely legalizing marijuana. 

 During these rallying speeches, other activities of an illicit nature was taking place. The whole Diag was up in smoke. A constant barrage of white puffs of smoke flew away, carried by the wind. This interesting aroma saturated the crowd. A mixer of different strains of pot, marijuana, dope, bud, call it what you will , it was like being in the epicenter of a hurricane. The confusion of all these different smells overloading your sense of smell. Everywhere you looked, there was someone smoking a joint, a bowl, I even caught a glimpse of a young gorgeous blond girl smoking out of a huge glass bong. They don't care, they'll do it out in the open, "This is the Hash Bash - smoking's legal", one protester suggested to me as he took a big hit off of a massive blunt. And all the while those two Ann Arbor police officers I told you about earlier; they were still there, away from the crow. Just observing I would imagine.

  After a while of being subjected to ounce after ounce of second hand smoke from the audience, I started to fell different. Almost euphoric. Spending that much time in the middle of Michigan's largest smoke-out, definitely has some side effects. All of the sudden in stead of my attention being focused on the speakers, it was now in hyper A.D.D. mode. I tell you that girl standing ontop of that wall has the most sexiest socks I've ever seen.......Sorry, back to the story at hand. Yea, A.D.D. and I think the hole crowd was feeling the same way. But in the mist of all this smoke, were people who were genuinely interested in what the speakers had to say. One of them was a middle aged man who's there every year holding a novelty American flag with the stars substituted as pot leafs or the hippie who's photogenic oversize bowl rises eyebrows and let us not forget the young man of the street and his cardboard sign signifying free handouts. But most importantly what I found out as the effects of the pot smoke wore off, as I stood there looking around in the middle of a smoke infused crowd, a small group of people in front of me broke apart to revile what was once hidden by them. Like Moses and the parting of the sea. An answer that was well hidden the whole time I was there. Like uncovering of a great mystery, there it was, the answer I've been looking for - a lone medical marijuana patient in a wheelchair. Looking decrepit, maybe hurting but with a big smile on his face and as he exhales a big puff of smoke I realize who and why they come to the Ann Arbor Hash Bash.