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Focal TBM beryllium help want a back chamber
Focal TBM beryllium help want a back chamber
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Old 15th September 2021, 04:32 AM   #1
Oabeieo is offline Oabeieo  United States
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Default Focal TBM beryllium help want a back chamber

Hi guys ,

I am doing a project I have a 5 way linear phase active system
Using minidsp and 12ch amps

I have all focal utopia drivers , I just swapped into the focals and I came from a mix of dynaudio and stevens audio.

The stevens tweeter is a 1Ē soft dome with a back chamber.

The focal be has either a open back or a cap that makes it a sealed back. With open back fs is 250hz with the cap itís 1500hz


That said , I installed the focals , all the drivers perform as expected except this tweeter. Coming from the stevens , I wish it had similar dispersion as the stevens. The stevens seems to have more energy in the forward lobe and had more equal energy as my listening position has unequal path lengths.

Making a back chamber for the focal would be a cinch. Super easy.

How do I know how big to make it and will it make it have similar dispersion as the stevens

Thanks in advance
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Old 15th September 2021, 04:44 AM   #2
GM is offline GM  United States
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Different size drivers have differing polar responses, so will only match up over a portion of their BW. Need the Focal's T/S specs to calculate a cap.
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Old 15th September 2021, 04:54 AM   #3
5th element is offline 5th element  United Kingdom
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And a rear chamber won't affect the focals dispersion either.
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Old 15th September 2021, 04:59 AM   #4
Oabeieo is offline Oabeieo  United States
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Quote:
Originally Posted by 5th element View Post
And a rear chamber won't affect the focals dispersion either.
Ahh I didn’t know that .... maybe I’ll try with cap off

Quote:
Originally Posted by GM View Post
Different size drivers have differing polar responses, so will only match up over a portion of their BW. Need the Focal's T/S specs to calculate a cap.

Thanks here’s a link to the driver lmk what you think I should do
https://www.focal.com/sites/www.foca...utopia_tbm.pdf

Last edited by Oabeieo; 15th September 2021 at 05:08 AM.
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Old 15th September 2021, 05:04 AM   #5
Oabeieo is offline Oabeieo  United States
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So if it won’t change dispersion..... what exactly is the point of low fs

If I take the cap off and run open back, will it affect power handling and will it affect anything else if I only need to cross over at 3K....

I’m using a shallow second order slope with a Q of .7
So it digs kind of far down but I don’t know I don’t know what I’m trying to ask I just liked the way that the soft dome sounded better as far as dispersion

This has amazing sound quality.... it’s just different..... maybe it’s just a tuning thing
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Old 15th September 2021, 05:31 AM   #6
GM is offline GM  United States
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Originally Posted by 5th element View Post
And a rear chamber won't affect the focals dispersion either.
Tis true. Frankly wasn't sure what he was trying to tell us, so assumed the Focal was OB since it was the only way for it to cause problems since the tweeter is sealed.......
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Old 15th September 2021, 05:53 AM   #7
GM is offline GM  United States
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Quote:
Originally Posted by Oabeieo View Post
Thanks hereís a link to the driver lmk what you think I should do
https://www.focal.com/sites/www.foca...utopia_tbm.pdf
You're welcome, though didn't realize both are tweeters, so with no info on the Stevens and precious little for the Focal, can't really offer any suggestions, though normally the one with the wider dispersion would need a waveguide [WG] to narrow it up to match the narrower tweeter.

No clue what 'IAL' stands for, but I'd use the low Fs for a > 4 kHz 1st order XO.

Yes, it will affect power handling since excursion increases 4x/octave, hence the 4 octave minimum for the 1st order [250*2^4].
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Old 15th September 2021, 07:05 AM   #8
Oabeieo is offline Oabeieo  United States
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Thank you!!!

Here’s the page for the stevens

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Old 15th September 2021, 07:24 AM   #9
Oabeieo is offline Oabeieo  United States
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Okay so the stevens is a fs of 650hz

The focal with no cap is 250hz fs

So maybe I’ll try just the cap off first and see what it does

I think that IAL means Infinite baffle (guessing)

So what about the done shape , the focal is inverted M shape

Could that be affecting its dispersion a little ?

It’s not bad ..... actually the focal most might say is more accurate, I just wish it had the dispersion of the stevens but had the focal sound.....

Maybe it’s a lost cause and what I’m asking is wrong

As someone pointed out the back chamber doesn’t affect dispersion
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Old 15th September 2021, 08:55 AM   #10
5th element is offline 5th element  United Kingdom
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The main thing that affects the focals dispersion is that it's a metal dome. Fabric domes breakup in the upper octave and this gives them better off axis response. I'm not entirely sure what to expect from the inverted dome of the focal though.

Metal domes usually have phase shields in front of them, for protection and for improving their off axis response. The focal Be dome doesn't have this. You could try tilting the treble up to add some sparkle and see if that helps.
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