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Dirty-South Blues Harp forum: wail on! > Interaction of shells and elements.
Interaction of shells and elements.
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SuperBee
6963 posts
Jun 09, 2021
5:15 PM
This has been discussed before, but I've recently made a specific observation which builds on and is consistent with several other observations I've made over the last 5+ years, and it's enough for me to start believing I have sufficient weight of evidence to say there is an impact.

My belief is that in the case of Shure magnetic elements, the CR and CM types, they will have lower output in a JT30 shell than in a green bullet type of shell.

I've now noted this with at least 4 elements, moving in both directions.

I do not know why. I can speculate it could be about the space behind the element, the space in front of the element within the shell, or the way the mic sits in the hand and the shape and or volume of the resulting space between the harp and the element.
I don't have any data about crystal elements unfortunately. That could shed some light on the question of whether the size of the space behind the element is involved.
I also don't know whether the effect is the same for others or just me. If it's about the space in the hand, it could well just be something that applies to certain people, or is more of a factor for certain people.

I really don't know, but it's happened too many times with no exceptions that when I take a high output 520 or similar mic and transfer the element into a JT30 that resulting JT30 will have noticeably lower output and somewhat different character than the mic from which the element came.
Similarly I have had CM-equipped JT30s which I thought relatively tame. I had thought the element to blame, but been surprised to find the same element perform at a higher level in a Shure bullet.

I have read discussions about this before, and I think I've directly asked about it, but most advice received is that any impact is negligible at most.

I have also observed a difference in performance with these elements in a biscuit shell, but have not made as many swaps involving this type of shell.

I only have a couple of crystal elements and limited gasket S for these so have not tried swapping them between shell types.

I recently got my old brown bullet back in useable condition and this resulted in some reorganisation during which I observed this effect again, and it's too many times now. I'm convinced.
Ultimately it's not a big deal, but it interests me from a nerdy angle.
Prento
77 posts
Jun 09, 2021
5:54 PM
Hi Dave,
When you say a noticeable difference is it a negative thing, or just a case of having to turn the amp up a little to get the same response? Is there a tonal change, for example less bass response?
The reason I ask is that I have a 1970s cm in a 520dx shell that I’m thinking of transferring to an old Hohner blues blaster shell as the old Astatic crystal element is not overly strong. My cm does have quite a noticeably high and bassy output even when compared to my American D4T and pairs well with amps that have a weaker preamp section.
SuperBee
6964 posts
Jun 09, 2021
9:20 PM
Hi Prento. I think the tonal qualities are affected.
Years ago I bought a JT30 from an eBay seller in Maine. I was really happy with the deal, but the overall sound of the mic was disappointing. I thought the low end response was relatively weak. The element was a 99H86 made in 1959.
I removed the VC from the mic, but there was little change.
I later put that element into a 520SL and to my surprise the mic sounded great. It was much fuller and livelier than it had been in the JT.
Very recently I had a Shure bullet repaired and it came back to me loaded with a '64 CM. The person who put it together pointed out to me what a killer element it was, and when I tried it I had to agree. It was clearly the highest output of all my mics.
Before that mic had broken down it was loaded with a strong white CR and was the strongest mic I'd ever used. When it broke down I put the element into a JT30 and continued to use it. I felt it was never quite as good in the JT30 but I couldn't really go back and compare because the original shell had a malfunction.

Because I was sentimental about the original combination, I swapped the elements between those 2 shells.

To my surprise the performance factor followed the shells, not the elements.

I'd suspected this at times in the past and enquired if it was a "thing" but this was a clear demonstration. I think I'd never done a direct swap before using 2 very high output elements.

But I don't really know why and it might be personal.

I think the tonal aspect might be dependent on the particular element. There are definitely differences between elements. You might be able to compensate with volume and eq but I haven't really tried to measure that yet
dougharps
2258 posts
Jun 10, 2021
10:47 AM
Greg Heumann has a pdf covering the issue of amplified harp mics and briefly addresses the tonal effects of space in front of and behind a dynamic element in a bullet mic on page 13, 2nd paragraph.

All About Harmonica Microphones

I have a CM element in an Astatic biscuit mic and I think the bass may be reduced due to the shallow space behind the element, though I still really like the mic.
----------

Doug S.

Last Edited by dougharps on Jun 10, 2021 10:47 AM
wheel
687 posts
Jun 10, 2021
2:31 PM
Interesting observation. Thank you!
I've read somewhere that biggest sound out of the element you can get using Argonne mic body.
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Konstantin Kolesnichenko(Ukraine)
http://kolesnichenko-harmonica.com/
Millman500
3 posts
Jun 12, 2021
3:49 AM
Cool discovery. The problem with CM's is that they are exposed on the back, making the shell space crucial as opposed to sealed crystal elements....

Last Edited by Millman500 on Jun 12, 2021 4:02 AM
SuperBee
6970 posts
Jun 12, 2021
5:14 PM
I figure it's something like a speaker in a sealed cab and if there's not enough space it's gonna be affected, but it's also kinda hard for me to imagine the amount of space in a JT30 would be small enough to do that. There's definitely an effect though, maybe not huge but there's an edge these elements have in the 520 etc which is missing in the JT30.
I've got a EV605 shell which has a CM, and that thing has a monster low end response but it dies away quickly as the frequency rises. Now I'm wondering whether that phenom is also about the shell rather than the element.
jpmcbride
284 posts
Jun 12, 2021
7:50 PM
I'm an electrical engineer, and I've designed plenty of products with speakers in them. We used to struggle to get the volume we needed in our smaller hand-held products. I did a lot of testing and it was clear that space in front and behind of the speaker affected the volume, as did whether or not the space was sealed or open. But it wasn't a simple clear-cut relationship. We ended up using an audio engineer as a consultant and he did a lot of calculations and helped us figure out the optimal way to get the most sound out of our product. This was all related to speakers, but a microphone is really just a speaker operated in reverse. All of the same factors should apply.

I have another thread where I'm discussing putting a Shure CR element into the new Hohner Harp Blaster HB52 mic. I put that CR element into an Astatic Biscuit and the HB52 and it sounded different in each shell. Its brighter and louder in the HB52 than in the Biscuit.

So, in my experience, the shell makes a big difference. But its not always easy to predict. You just have to try it.




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Jim McBride
Bottle 'O Blues microphones
www.bottleoblues.com
SuperBee
6971 posts
Jun 13, 2021
1:16 AM
I wonder if I could effectively install a port into a JT 30 or biscuit shell. I've read that it's important to keep them sealed at the back to prevent feedback but I have zero first hand experience of this. I do have a spare jt30 style shell though, which has been drilled in back for a VC. Maybe I'll conduct an experiment


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