This article will cover cassette tapes in depth, including their role in vintage boomboxes.

Cassette tapes were the CDs of the 80's.  They allowed us to carry our music in boomboxes, play recorded music in our cars, listen to music while jogging, etc.

Cassette tapes are basically a miniature reel-to-reel tape mechanism.  Its advantages are small size, quick load and unload and ease of portability.  Its disadvantages are slower speeds and poorer sound as compared to reel-reel decks.

Reel-reel decks offered excellent hi-fi, with frequency response and background noise ratios that rival CDs.  Cassette tapes were a compromise.

In simple terms, a cassette tape, like reel-reel, employ magnetic particles which are adhered onto a tape.  As the tape passes over a tape head, the particles are magnetized.  When that same tape is played back, the tape head picks up the magnetic information stored on the tape and it is transformed back into music.

A cassette tape travels at 1 7/8 inches per second across a tape head.  Therefore, in one second, a tape can only hold as much information as can be stored on a section of tape that is 1/4 inch wide and 1 7/8 inches long per each second.  By comparison, a reel-reel deck might play at 15 inches per second.  So, the reel-reel can store information on a section of tape that is 1/2 inches wide and 15 inches long per each second.  So, the reel-reel has 16 times the surface area of a cassette tape on which to store each second of music impulses.  This huge difference allows the reel-reel deck to offer a wider frequency response, higher dynamic range, less background noise, etc.

To improve cassette tape performance, high bias tapes were developed.  The high bias refers to the deck having to record and playback on a different bias frequency which would improve the cassette tape's treble response, overall smoothness and background noise level.  No bias is actually perfect. 

Normal bias refers to the basic cassette tape, which is like the tape used in reel-reel decks.  It does not require a special bias and can play back on any deck.  Some audiophiles prefered normal bias as it did not change the sound.  It sounded more flat and pure in their opinion.  That also depended on the quality of the tape.  A poor normal tape sounded awful, with dull highs and many drop-outs (loss of signal).  A high grade normal tape could sound quite good.

High bias  came in many formulations.  Ferrachrome, chrome, metal formulas.  Chrome was the most popular due to its price/performance ratio.  On the other hand, some blank metal tapes initally cost between $10-$20 each!  Each high bias tape supposedly offered wider frequency response, more dynamic range and lower background noise levels.  The degree of improvement varied greatly.  Because high bias tapes could handle a higher recording level, they were supposed to have lower background noise.  That was not always true.  one problem I always noticed is that the same high bias tape did not sound the same on all tape decks.  On one deck a tape might sound dull, while on another bright.  The tapes did not always match well with a particular tape deck or boombox.  In fact, many of the big brands of boomboxes and component decks began specifying which tape brands and types worked best with their equipment.

DOLBY LABS introduced noise reduction circuitry to reduce noise on cassette tapes.  Because cassette tapes move so much slower than reel-reel, there was less room to store information.  Less room meant a lower recording level.  The louder you record, the more magnetic particles you need.  If you record too loudly, you saturate the tape, meaning there are not enough magnetic particles to hold all the information.  Thus, the tape sounds distorted.  Reel-reels could store much more information per second, which translated into louder recording levels, which means less background noise and hiss.  So, noise reduction circuitry was introduced to try to suppress the background noise in cassette tapes. DOLBY B was the first and basic consumer noise reduction, found in component decks and in high-end boomboxes of the 80's.  Other DOLBY products such as DOLBY C and so on developed later.  Each supposedly worked better than its predecessor.  Some decks even featured very specific noise reduction windows in which a test signal was sent to set the noise reduction to optimum performance.  In my opinion, the noise reduction, like the high bias, did not always sound the same on every component.  I would find that tapes recorded with noise reduction might play better on some decks and boomboxes equipped with the appropriate circuitry than on others. 

Some vintage boomboxes, such as the high-end JVC, SONY, PANASONIC, PIONEER, AKAI, SANYO, TECHNICS, CROWN and so on offered tape deck mechanisms that could record and play as well as a component deck.  These boomboxes would feature noise reduction circuitry, high-bias tape options, wide frequency responses of as much as 30Hz to 19kHz and background noise levels of 55dB, 60dB or 65dB or better (noise reduction OFF). 

On the other hand, some of the so called holy grail boomboxes have very unsophisticated decks.  They might offer nothing more than a high-bias switch.  No noise reduction.  A narrower, more compressed frequency response and so on.  Tapes made on such units will, in my opinion, never sound as good as a tape made on some of the big name brands.  So, why some of these units are being touted as holy grails is a wonder.  It is surely not for their sophistication and audiophile qualities.  When playing a tape recorded with noise reduction on such an unsophisticated boombox, the tape will inevitably sound shrill or hoarse due to the lack of noise reduction circuitry.  Also, there will be much more hissing which is the inherent background noise of the tape itself.  Such unsophisticated boomboxes typically feature narrower deck frequency responses, which means much more compression and less detail.

In fact, some of those so-called holy grail boomboxes might be able to make tapes that sound OK on the boombox itself only because the boombox's performance is so much more compressed and compromised compared to a home audio system. 

On the other hand, a tape made on a high-end big name brand boombox that featured hi-fi specs and options will sound spectacular on a home audio system.  It may sound as good, or better, than a commercially bought prerecorded tape.  That's real high-fidelity, in my opinion.

I've owned boomboxes that touted cassette frequency responses of as high as 19kHz, as compared with 20kHz for a CD.  I've also owned component tape decks that claimed a 20kHz frequency response range.  A few decks even had switchable double speed which moved the tape at 3 3/4 inches per second.  One such deck claimed 25Hz to 22kHz frequency response at the higher speed. 

Compare those specs to some of the large boomboxes that are popular but unsophisticated.  They might offer frequency responses of 60Hz - 10kHz (approx).  Add to that the louder background noise level and hissing.  Terrible! 

These clunky holy grail boomboxes might not even have an a/c erase head.  That means the separate erase head is just a cheap permanent magnet that, in my experience, does not erase the tape as completely if you decide to re-record over the same tape again.

On the other hand, the big name sophisticated boomboxes might feature super hard permalloy heads which lasted for many many years.  One company even came out with a glass 'n x-tal head  which was touted as being so hard as to be able to retain its full fidelity performance for 17 years, if I remember correctly.  This is the difference between the quality high-end boomboxes and the big clunky unsophisticated ones.  This is why I don't believe all of the holy grail collectable boomboxes deserve to be called holy grails.  And why some of the really high fidelity boomboxes of the late 80's and early 90's should have been included.  It's one thing to call a vintage boombox a true collectable due to its sheer size.  But, size and performance were not always hand in hand.

For those who think cassette tapes are old dinosaurs that are useless, I doubt they realize how well some cassette decks could record and playback.  And, such decks did so with an analog signal, as compared to a computer altered digital signal employed in CD recordings.  There are still those who claim the analog recordings sound more natural and real. 

NOTES: 

I am not endorsing any particular brand.  I only mentioned some of the brands which I owned at one time or another.  I am refering to my own experiences with cassette tapes, boomboxes and component decks for this guide.

There were some other noise reduction circuitry being employed besides DOLBY LABS.  But, DOLBY was by far the most popular. 

 JVC tried its own noise reduction circuitry, found in some JVC deck's and boomboxes, either in addition to, or, instead of DOLBY.  But, JVC's noise reduction circuitry did not become popular that I can remember.

Some generic type noise reduction circuits also appeared.  They were labeled such names as DNR, for example.  They were supposed to be universal noise reduction circuits, able to reduce noise of any cassette tape.  In my opinion, they did not work exactly as touted either.