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February 12, 2018

Welcome back!  In part One of this series, we walked through confirming whether you have power all the way to the radio's power connector, and ended with the question, “Do you hear a slight 'thump' when you power on your radio?” 

If you do NOT hear anything resembling a 'thump' at power-up (let alone broadcast radio sounds), then it's time to have a go at the speaker.

Before we go any further, be advised that you may  share, re-post and use this article in its entirety only in your car club or other automotive forum or publication.  As a gentle reminder, please give credit where it's due (or else!): please cite this article's URL as your source and me as the article's author.  

Oh and being the over-thinker that I often am, I need to establish a couple of terms going forward in this article:

  • the term “speaker” applies to one or more speakers.  (Why? Because constant including the singular and plural spellings of words is distracting and gets annoying to write after a while.)

  • the term “radio” refers to any of the following words: the radio (duh), the tuner, the receiver, the “head unit”, the amp, and anything that actually drives signals at audio frequencies to the speakers for your listening pleasure.  (Why? Because it seems like there is a new way to describe the amplified source that lives in your dash (or glove compartment).)

  • the term “sounds” refers to music, talk radio, books-on-tape, podcasts, signals, or even dead air.  (Why? Because everyone listens to something, and these things all have one thing in common: acoustic waves move the air in ways that we know as what we like to listen to.)

And with that, let's get on with it already ( CRIPES! )...

The speaker in your Freedom Machine has one job in life: to convert electrical signals from the radio's output into acoustic waves that your ears interpret as sounds.  Not hearing a “thump” at power-up is probably a sign that either: the speaker has given up the ghost or the radio needs attention.  We will concentrate on the speaker as the culprit in this part of the series.

First things first: If you don't already own one, it is time for you to purchase a TSM (Technical Service Manual) for your ride.  In fact, buy TWO copies: one for the garage and one for the toolbox that you keep in the trunk.  You can find them on eBay or at swap meets.  Two VERY useful and fun sites that seem to be the same thing but actually aren't are these:  http://www.oldcarmanualproject.com/ and http://www.tocmp.com/ .  Bookmark them even if you already have a TSM.  The TSM will let provide specific instructions for accessing and removing (if need-be) the speaker.  With this resource at your disposal, it's time to access the speaker.

For the sake of discussion, the radio in my '64 Tempest quit making sounds on a roadtrip a few years back.  Upon arrival I set out to learn whodunnit.  Reaching up and actually feeling the speaker in this non-A/C car was pretty easy, but removing the glove compartment helped me see what the radio was blocking.  Turned out that it was worth the effort to remove the radio, too.  Besides, this gave me a chance to properly clean  everything as well as replace burnt-out light bulbs throughout the dashboard.  As an aside, bulbs that have been in place for decades collect dust.  Remove them all and clean them off with glass cleaner and a paper towel for a brighter instrument panel at night.  

In the image above, you will see what I found.  Fugly.  Upon closer inspection, the reason why it actually stopped producing any sound was that one of the tinsel leads broke free from its connection to the voice coil...an open circuit.  What really surprised me prior to that 'last straw' (given the ho-hum originality of everything) was that I actually had reasonable sound coming from this speaker at all, considering the condition of the rest of the cone.  I grabbed my DMM (see part 1 of this article series) and measured the DC resistance across the two speaker terminals – the display read “O.L”, which means an open circuit or infinite ohms.  Upon closer visual inspection, I could see the broken connection.  

By the way, let me include two sidebars for you here:

First, if electrical terminology such as resistance, impedance, and/or ohms either confuses you or makes your eyes glaze over, you'll find an interesting article on this topic posted in Matt's Madness that has a useful intro to these terms that's not too technical.  

Second, head back to Matt's Madness when you're done with this to find an illustrated article on the rehabilitation of the speaker shown in Figure 1.  In it, you will learn the anatomy of a loudspeaker and hopefully gain an appreciation for the companies that re-cone damaged or sun-baked speakers.

OK, back to the pursuit of tunes.  Besides a good vacuuming, bulb cleanup/replacement, and snugging down various nuts and screws that had gotten loose over the years, the re-coned speaker went back into its parking spot.  With the radio bolted down and the wiring connector plugged back in, I reconnected the negative battery cable I'd removed (this is cheap insurance, folks.  Get in the habit of doing this.), I hit the key and sound from the radio again filled the interior.  

But wait – suddenly the radio was putting out a LOT more sound than before, yet the re-cone was nothing more than an OEM-level job.  Although I always kind of figured that direct sunlight would negatively impact a speaker, I had no idea just how much so until I saw -and heard- for myself.  Unlike some, I am not a high-power stereo guy.  However, I do like to crank it when “right foot music” comes on, and I can say that the humble 10 watt AM radio is now quite capable.  But, to each his own.

In this anecdote, the culprit was a broken electrical connection (and heavily deteriorated cone, secondarily).  But other speaker-related culprits could have also been (and YOU may experience are): no electrical connection to the radio, a completely separated cone (from the frame around the perimeter), a bound-up voice coil (due to dust filling the thin, cylindrical region on either side of it, or a combination of these.  

If your ride has multiple speakers, prepare yourself for the need to face and remedy the “twist & tape” electrical connections that beginners (and hacks) too often make.  At each speaker, the impedance of each speaker and compare it to what the radio is designed to have.  Remember the 20% rule (again, refer to the Resistance and Impedance article).  There is no substitute for reliable electrical connections and healthy speakers.  Lastly, keep an open mind when you're troubleshooting a quiet radio in your Freedom Machine...and, also when you're ready to abandon it for something aftermarket.  

So now we have “thump”; In part 3 we are going to explore why there's no broadcast radio reception.  Until then, stay tuned.


“RediRad” Matt

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