[Harp-L] Blowing out a harp (was Sound of Hohner)

[Mike Holcomb <mholcomb@xxxxxxxxxxxxxx>]

Mike Fugazzi wrote:

>How long does the average harp last some of you guys? 
>I've read that the longevity of harps is a concern a 
>lot of players take into consideration when purchasing 
>a harp. 

Run screaming Mike.  It's going to get really geeky here.

I wondered this too, because I really prefer special 20's for both sound
and comfort, and I've heard from many sources that they blow out quickly.

In my previous career, I was a reliability engineer.  Basically, you do a
lot of life testing of whatever product to study how long it will last. 
Because I had this background, and I was curious about the reliability of
harmonicas, I started keeping data on the Special 20's that I purchased.
Basically just which key, date of purchase, date of death, and which reed
failed.  Here's the data for my harps as of today's date:

Key	#	Purch Date	Death Date	Life	Reed
C	1	07/15/03			598	
D	1	10/06/03	02/01/05	484	4D
F	1	10/06/03			515	
A	1	10/06/03	07/18/04	286	5D
G	1	10/06/03	04/08/04	185	5D
Bb	1	03/13/04			356	
LoF	1	03/13/04			356	
E	1	03/31/04			338	
G	2	04/08/04			330	
A	2	07/18/04	02/26/05	223	5D
C	2	09/01/04			184	
B	1	10/26/04			129	
Ab	1	11/17/04			107	
Eb	1	11/19/04			105	
Db	1	12/17/04			 77	
F#	1	01/21/05			 42	
D	2	02/02/05			 30	

I'm not including in this data harp A-3 which I bought immediately after
A-2 croaked.  A-3 was a dud right out of the box (3 draw).  Now, this is
pretty uncontrolled because the different keys obviously get different
amounts of play.  But C-1 is my shirt pocket harmonica.  It's with me all
the time and gets played a lot.  I practice and gig with C-2, and have
generally only had one of each key at a time (with the exception of C).

When you are analyzing life data, you have to look at the age of the harps
still living along with the ones that died.  We know the life of D-1 was
484 days, but all we know about the life of C-1 is that it will be greater
than 598 days (provided it lives through today!).  This type of life
analysis gives you very different results than taking the average life of
the dead harps.  If you take the average life of the dead ones, you have
probably grossly underestimated the mean life.

Running the appropriate analysis, and fitting the data with a lognormal
life distribution, I calculate a mean life of 644 days.

Here is some more analysis from Minitab:

Table of Percentiles

		      95.0% Normal CI
Percent  Life(days)  Lower     Upper
      1       88      22	345
     10      190      90	402
     50      490     267	900
     90     1265     338       4735
     99     2739    3689      20347

What this means is that 1% of the Hohner Special 20's I buy will last 88
days or less.  10% will last 190 days or less.	50% will last 490 days or
less (and therefore 50% will last more than 490 days).	10% will last more
than 1265 days (3.5 years), and 1% will last more than 2739 days (7.5
years).  The confidence limits show just how terribly shaky these
predictions are.  And of course, these data only apply to me, based on how
hard and how much I play.

Coming down to me personally, if I always keep an arsenal of 14 harps (all
12 keys, plus Lo F, plus shirt pocket C harp), and the mean life is 644
days, I should expect to have to replace one about every 644/14 = 46 days
on average.  So even though the mean life is almost 2 years, it still
would seem to a working musician like you are replacing blown out harps
all the time.

--
Best regards,
Mike Holcomb