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Betsy coil+resistor top end rounding
Betsy coil+resistor top end rounding
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Old 29th September 2020, 10:17 AM   #1
karloff70 is offline karloff70  United Kingdom
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Default Betsy coil+resistor top end rounding

Hi all,

I have built a small pair of open baffles with Wild Burro Betsy's and like them a lot. But I would love to wind down the top end a little. The 'too much' area is about 2.5kHz to 11kHz. Down by a couple of dB would likely do it at a guess. But in reality with one notch it would be more like a bell shaped dig into the area? Basically looking to flatten the response out by taking down 2.5 - 11 but that would take a flat top notch filter. Is that a thing achievable with some passive parts?

I am completely ape-like when it comes to passive parts values knowledge, by it seems the right size air coil plus the right size resistor could help here, even without a cap? Or with a cap?

Any help very appreciated indeed.
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Old 29th September 2020, 10:23 AM   #2
scottjoplin is offline scottjoplin  Wales
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You could do it passively before the amp by experimenting with this Baffle Step Compensation It's easily adjustable and scalable.
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Old 30th September 2020, 07:56 AM   #3
karloff70 is offline karloff70  United Kingdom
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Thank you, that looks interesting. Would give the option of setting the top amount by ear with a dial, I like that. But it will need a psu and more faff. Kind of keen to do this in an as minimal way as possible with just an air coil and resistor if I can get the harsh out a little that way.
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Old 30th September 2020, 09:42 AM   #4
GM is offline GM  United States
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Greets!

'Sounds' like CD horn EQ is what you're wanting, if so, then a parallel notch filter: Parallel]DIY Audio & Video Notch Filter Designer / Calculator Help

GM
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Old 30th September 2020, 10:17 AM   #5
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by karloff70 View Post
But it will need a psu and more faff.
Not necessarily, what's your source?
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Old 30th September 2020, 04:13 PM   #6
karloff70 is offline karloff70  United Kingdom
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The amp will be a 3875 gain clone and before that is a passive monitor controller and before that conversion.
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Old 30th September 2020, 04:15 PM   #7
karloff70 is offline karloff70  United Kingdom
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Quote:
Originally Posted by GM View Post
Greets!

'Sounds' like CD horn EQ is what you're wanting, if so, then a parallel notch filter: Parallel]DIY Audio & Video Notch Filter Designer / Calculator Help

GM
Nice! Thank you. Now, if I was only able to use that formula lol. If I was after something like. 2dB dip all the way from 2.5 to 10, what values would I need to use?
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Old 2nd October 2020, 06:05 AM   #8
GM is offline GM  United States
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You're welcome!

No clue, I solve acoustic problems with acoustic solutions and assumed one of the XO gurus would answer this Q. Frankly, surprised you can notice such a minimal broadband dip. Normally, just increasing toe-in or out solves such minor adjustments.

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Old 2nd October 2020, 08:13 AM   #9
jameshillj is offline jameshillj  Australia
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I think you may be looking for something called a 'speaker passive shelving filter' - it's included in the modern passive xover design packages but called response profiling or equalization, or something like that.

I haven't been able to find the old books on this but the Vance Dickason's "Loudspeaker Design Cookbook" will most probably have it - it's a pretty simple technique, once you get the idea.
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Old 2nd October 2020, 08:27 AM   #10
jameshillj is offline jameshillj  Australia
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Another one is the old book by G A Briggs (Wharfedale) - it's quite old now but just as relevant and explains the idea quite well - I think you can get it from Amazon, believe it or not!

Somewhere there's a site devoted exclusively to the Betsy driver and I think Caintuck Audio have done lots of work on this
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