Re: [Harp-L] removing the bars from SP20's (was Micro Mart Sprue Cutter)

[Vern <jevern@xxxxxxx>]

I'll move from my position that the bars "do not affect acoustical performance" to Rick's "slight, bordering on imperceptible (difference)" ...not a huge concession!

Vern
 
On Jan 22, 2011, at 9:07 PM, captron100@xxxxxxx wrote:

> 
> Vern wrote: 
> ......the supports that run across the chambers....are there to keep the partitions from warping while the comb cools 
> immediately after de-molding.  Although they serve no purpose after the comb has cooled, they do not affect the acoustical 
> performance of the harp...
> 
> 
>  A few years ago, renowned harp expert, Hohner's Rick Epping, said that removing bars 1 thru 6 may improve the harp's tone. 
> So whenever I worked on my SP20's, i did it.  It is quick and easy.  If i remember correctly, i think I removed the bars and any residual 
> burrs with an Exacto knife.  See Rick's post below.
> 
> Date: Fri, 6 Jul 2007 
> From: "rick epping" <rickepping@xxxxxxxxx>
> Subject: Re: [Harp-L] comb design/structure
> To: harp-l@xxxxxxxxxx
> In 1994, when adapting the design of Special 20 comb for Hohner's Chinese Richter models like the Pocket 
> Pal and Bluesband, I conducted tests on Special 20 combs, comparing their performance with and without the
> reinforcing bars.  I thought I found a very slight difference between them, with the reeds in the lower cells having 
> a slightly better tone without the bars and those in the higher cells having a slightly better response with
> the bars. I believe the high reeds benefit from the presence of the bars because the bars raise the resonant frequency 
> of the cells, bringing them closer to the reeds'  natural frequencies.  So when setting up a Special 20 I will often remove the 
> bars from cells 1-6 and leave those in cells 7-10.  For the design of the injection mold for the Chinese models I
> gave the connecting bars a more aerodynamic, lanceolate profile, which I found to also slightly improve performance.
> 
> The amount of difference between the designs - bars or no bars, rectangular-or lanceolate-profiled, I found to be slight,
> bordering on imperceptible. But it's the sum of all the little things that can add up to a good harp.
> As my father used to say to me when I was a kid, sweeping up the sawdust in his cabinet shop on Saturdays, "Take care 
> of the corners and the middle will take care of itself."
> Best regards,
> Rick
> 
> 
>