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

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!

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

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