How to Avoid/Reduce Feedback in Sound Systems

Principal cause of acoustic feedback

Most, if not all, of us have experienced hearing that piercing whistle from sound systems. What causes it and what can we do to minimize or eliminate it?

There are several types of feedback but in this case, the proper name is acoustic feedback, the type of feedback that you can hear. In simple terms, feedback happens when the sound from the speakers enters the microphone/s, goes through the mixers and amplifiers, out through the speakers and back into the microphone/s. In the case of guitars, the sound from the speakers make the guitar strings vibrate, which goes through the sound system, out the speakers, and vibrates the strings again. So, essentially, the sound is going 'round and 'round the sound system.

Feedback may be caused by microphones, guitar pickups, and other sound system inputs along with speakers. They can range in frequencies from a low rumble to an ear-splitting shriek.

So, how can you prevent your sound system from going into feedback?

Factors that can trigger feedback and solutions you can apply:

1 – System volume. The louder the sound, the more likely the sound will reach the microphone.

Solution: Reduce the volume and/or speak closer to the microphone so you can lower the volume. You can also use noise-cancelling microphones.

2 – Speaker to mic proximity. The closer the microphone is to the speaker, the more likely that feedback will occur.

Solution: Get the speakers as far away from the microphones as practically possible.

3 – Microphone is pointing at the speaker (the sound has a direct path toward the microphone).

Solution: Orient the speakers so they are pointing away from the microphones. It's easier to do by using unidirectional (a.k.a. cardiod) microphones.

speaker vs mic placement

4 – Room has a lot of reflective surfaces (even if the microphone is not pointing at the speaker, sound from the speaker can reach the microphone from reflections from the walls, floors, and ceilings).

Solution: Cover the walls, ceilings, and floors with sound absorbing materials. You can also install slats on the walls to break up reflections. Upholstered chairs will also help. If the chair is unoccupied, the upholstery will absorb sound. If the chair is occupied, the person sitting on it will absorb sound.

sound absorbers or sound diffusers on walls

5 – Room has parallel walls and parallel floor and ceiling. Sounds that bounce back and forth between parallel walls create "standing waves" that take longer to die down.

Solution: Same solution as #4. You can also build the room so that it doesn't have parallel walls, ceilings, and floors.

non-parallel walls (with sound proofing/diffusers)

Other solutions:

1 - Install "phase delay" equipment. These devices will shift the phase of the incoming sounds so that they will not generate "constructive interference" or sound that adds on to itself.

2 - Use a "cut-only" equalizer and a spectrum analyzer to reduce the frequencies where the feedback occurs. These are equalizers that don't have plus adjustments, only minus adjustments (the 0 dB is at the top of the sliders) and have bandwidths of 1/3-octave. When you increase the system volume and feedback starts to occur, you check the analyzer to find the frequency of the feedback and reduce the level of that frequency. Keep increasing the level and cutting the frequencies of the feedback until you attain your target system volume.

cut-only equalizer (A.K.A. room equalizer)

You can also use equalizers with cut and boost controls. The difference is, cut-only equalizers usually have a larger cut range than cut and boost types.

Urei brand room equalizer

Note: these days you can download a spectrum analyzer app to your phone. It should be accurate enough for general sound system adjustment.

Another Fake Proposal

email supposedly from Kindle Direct Publishing

I received another email with a proposal to convert my book into a movie. This time, it's from Kindle Direct Publishing. It's obviously fake because the sending address is amazon_submissions_at_gmail_com. Amazon using a gmail address?

Furthermore, my book is hardly a bestseller. If it was a bestseller, I'd understand if someone would contact me with a proposal such as this but it's nowhere near being even moderate seller.

Lastly, if some big movie production outfit really wanted to convert my book to a movie, I don't think they will ask me to submit a screenplay. Of course, they would offer to make the screenplay for me, which means I will have to pay for it. I would think a real proposal would be free.

If you're also a budding author and received something like this, don't believe it right away. Look at the sending address. If it's a gmail, yahoo, or other free, public email service, don't believe it.

Design Flub Fixed

 

Pinout diagram of Zilog Z80 microprocessor

Back around 1989, I received a request to fix an infusion pump, a device that allows medical staff to pump very small, and precise, amounts of fluids and medicines into patients.

I was told it would turn on but wouldn't start pumping. The display showed rubbish and pushing buttons didn't produce any response.

I opened the thing and quickly discovered a Z80 microprocessor, a computer chip that I had been studying for some time with the intention of building my own computer. I was very familiar with it.

From the description of the problem, it seemed as if the unit was not starting up properly. Opening the unit and checking pin 26 (the RESET pin), I found...nothing, the pin was floating (unconnected to anything).

The chip needs the RESET pin to be held at 0 volts for about a split-second after power-on to start the program at the beginning. If the chip is not reset, the program may start at a random line and the unit will likely hang or run erroneously.

A resistor, diode, and capacitor usually sufficed to do the job of resetting the chip but, in this case, there was nothing. I told the owner that I needed to buy the parts and would return the next day.

At home, I checked the Z80 user manual. While it explained what the reset pin was for and how to use it, the manual didn't say it could be left unconnected. Unfortunately, it also didn't say that a reset circuit was required. Anyway, I already had a course of action and I'd know after I put in the parts whether the unit would function or not.

The next day, I brought the parts, a soldering iron, and some soldering lead to the clients 's office and soldered in the parts. These was no provision on the board for them but there was enough space for me to put them in without difficulty. Once finished, I crossed my fingers and turned on the power.

Yes! The infusion pump's display gave an initial display and waited for an input. Someone set it up, inputted some parameters and pressed start. It worked! A few more tests and we declared the unit fit for use.

While basking in the thrill of a successful repair, I was concerned about the seeming design flaw in a commercial medical product. I told the client that they should inform the manufacturer about what we had found so they can recall the units already sold and have them updated. I went home fully expecting to soon receive a call from some engineer wanting more details. Unfortunately, there was none. They had either understood what the problem was and implemented the fix or they had discovered the issue themselves and were already putting out a recall order.

Anyway, this was just one of those repair jobs that sticks in my memory due to its unusual nature.

Zero Sales Since June 2023

 

Updated cover for U-1215 Smashwords version

Sales for U-1215 has become zero since June of this year. It's strange because I had consistent sales almost every month prior to this.

Quarterly sales of U-1215 from 2016 to 2023

I don't know what happened so I sent off an inquiry to Smashwords. They said that it's probably due to a "long tail distribution." What's that?

A long tail distribution is a type of statistical distribution that seems to explain what probably happened to my book.

A book may do very well at the beginning but over time, will start to slump, meaning sales will start to slow down. There may be many reasons why this happens so I won't try to give examples. Eventually, sales drops to a much lower level than at the start and it may drop down to zero or stay at a low level indefinitely.

If a book is very well written, sales may increase sharply and then plateau after some time. In this case the vertical part of the long tail refers to increase in sales rather than the total sales.

I'm not sure if this is the case with U-1215. If you look at the quarterly sales chart, sales started to increase in 2018 and did very well during the pandemic years (2020-2022). In 2022 it seemed as if the sales volume was starting to go down but in the first half of 2023, sales spiked (much to my delight) and suddenly dropped to zero (much to my disappointment).

Yesterday, in a bid to try and solve the problem, I changed the cover of U-1215 (Smashwords edition) to see if that will restore sales. 

The last sale was in June 2023. It's almost December 2023 and the sales report is still zero. Is this a long tail distribution phenomena? I have no idea. (".)

Update 08 Feb 2024: 

In December, I received a notification that I had a sale, six months after the last, and received $2.05 in my Paypal account. There have been no other sales since then. I need to write another novel but I'm not getting any ideas at the moment. (".)

Scam Alert! Film Adaptation Proposal

 

This would have been a perfect start to a day...if this were true.

I received this email today and, I have to admit, it got me excited...for a while. What author wouldn't be, right? You get an email from someone claiming to be from a film/television production company and proposing to turn your book into a film or television series. Wow! Hollywood, here I come!

As I read through the email, red flags started to wave. The first paragraph says it's from Rhiley Roads and yet, the email address is from Adam Mckay, the CEO of Hyperobject Industry. Furthermore, the email address uses a gmail extension. Curious. Shouldn't an official email come from a corporate email address?

I checked out Hyperobject Industries. It's a legit company run by Adam McKay and they've produced several movies and television series on Netflix. This email, however, uses the words "Hyperobject Industry" instead of "Hyperobject Industries." When you're representing a company, you can't afford to make mistakes like that.

I don't know how these companies work. Do they really read someone's book and just contact them offering to convert the book into a movie?

They also want to pitch the book at a Producer's Pitch Event in January 2024. I checked for the event and found a Hollywood Pitch Festival scheduled for December 2023. I don't know if this is the same or is it a different event.

The final red flag is that they want ME to make the synopsis, loglines, film treatment, and screenplay. That's not something an ordinary author would know how to make. Therefore, they propose to hire professional screen writers to do it for me. Guess who pays for those? Yup, me!

If they really wanted to make a film adaptation of my book, they would contact me properly and they would propose to pay me, not me pay them.

Still, getting a legit offer would be nice. I just have to remember to be realistic and wary of scam artists like this one. (",)

New Book - RTD Temperature vs Resistance Tables

RTD Temperature vs Resistance Tables

Those who know me know that I'm an instrumentation professional and I've been in the profession since 1985. One of the instruments that I've handled many times are RTDs, or Resistance Temperature Detectors. These are temperature measuring devices and are very popular in industries due to their accuracy, temperature range, and low drift. Handled and installed properly, they will last almost indefinitely.

RTDs operate on the principle that metals change their electrical resistance in response to temperature. This means that you can determine the temperature of the RTD by mea-suring its resistance.

Unfortunately, there many types of RTDs and each type has a different resistance at any given temperature. This is usually not a problem because instruments that use RTDs as a temperature measuring sensor perform the conversion of resistance to temperature internally.

However, if the instrumentation technician or engineer doesn't have such an instrument, and all he has is a digital multimeter or a resistance meter (devices that can measure resistance) or a resistance decade box (devices that can simulate resistance), he needs to know what resistance corresponds to what temperature. This book gives that information in the form of tables.

You can get these tables on the internet, yes, but you'll likely get only one table for one type of RTD. To get tables for other types, you'll need to perform several searches. Also, the smallest temperature interval you can get is 1°C. If you need to know the resistance of a fraction of a degree (e.g. 43.6°C), you'll need to perform a small calculation and you'll probably need a calculator.

This book gives the resistance values at temperatures ranging from -200 to 650 or 850°C for Pt100(385), Pt100(3916), Pt100(3926), Pt200(385), Pt500(385), and Pt1000(385), the most commonly used RTD types in use today. Furthermore, the book lists the resistances for temperatures at 0.1°C intervals. You're getting a very comprehensive source of information for temperature-to-resistance tables.

U-66 vs USS Buckley: Duel in the Atlantic (adaptation of a true story)

cover of U-66 vs USS Buckley

Just published my newest book, U-66 vs USS Buckley Duel in the Atlantic. It's a book that's been in the works for around seven years. 

Back in 2016, while I was researching for information about u-boats for my other book, U-1215, I came upon the story of U-66 and USS Buckley. The story I found was short so I went looking for more information about the event. The best source was from USS Buckley's after action report at the uboatarchive website. It detailed the almost minute-by-minute retelling of the whole battle.

With no thought of publishing the story as a book, I gathered every bit of information I could get and filed them in a folder in my computer. I went ahead and published U-1215 and forgot about U-66.

During the pandemic in 2020, the movie Greyhound came out. While watching it, the surface battle between the USS Greyhound and the u-boat struck me as very similar to the story of U-66 and USS Buckley. I decided to review the story and make it into a book.

I wanted to tell the story from both sides but all the information came from the American side. There was almost no information from the German side. I found an report on the interrogation of the captured survivors of U-66 but it offered very little information about the German side of the battle. There was no choice, I would have to invent some of the scenes.

Even though I decided to use my imagination about the German side of the story, I didn't want to abuse my artistic license but just coming up with sensional details. The scenes had to be plausible so as to be believeable. Besides, I didn't want to put "based on a true story" in the book. As far as I was concerned, it was to be a historical retelling of the event.

I started writing in 2022 (can't remember what month I started but it was around the last quarter of the year). I didn't concentrate on it, however. I was also busy trying to build my YouTube channels (Yes, plural) so I couldn't devote 100% of my time on it. I finished the book in July 2023.

With the book writing done, I needed to create a book cover image. I had a choice of two scenes: a front view of the destroyer escort and the u-boat side by side, blasting away at each other from what seemed point blank range (indeed, the battle did involve such distances). The second choice was an aerial view of the battle showing the two vessels maneuvering around the sea from the point of view of a US Navy aircraft that was watching the two gladiators duke it out below him.

Unfortunately, I couldn't find images that would work. I thought of hiring an artist but I couldn't afford them at this time. In the end, I decided to just put images of the destroyer escort and the u-boat side by side, empty of people and just lying there as if abandoned. If I could afford an artist in the future, I'll change the cover eventually.

The actual battle lasted only 16 minutes so the book is only 5,743 words, which qualifies it as a short story. Here's to hoping that it does as well, if not better, than U-1215, my best seller.