Roll off midrange acoustically by lowering box volume - diyAudio
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Old 18th December 2008, 12:00 PM   #1
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Default Roll off midrange acoustically by lowering box volume

Hello friends.

I will be using the Accuton C173N-T6-90 6.5" Midrange driver. 93.2dB.

Znom 6 ohm, Re 6.5 ohm, fs 73Hz, Qms 6.54, Qes .32, Qts .30, Mms 15.75, Cms .3 mm/N, Sd 145 cm2, Vas 8.8 ltrs.

I would like to build the midrange enclosure as to naturally rolloff the low end at around 200Hz. I can experiment, but what volume should I start at to cut the fewest cuts for my experiment boxes?. The unit has a natural rolloff at 110Hz; if that means anything. I would like to get away from using a large Cap at the low end.

Thanking you in advance
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Old 18th December 2008, 12:20 PM   #2
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anywhere from 2-5l sealed should do. 2l gives Qtc of .7 and -3dB around 175Hz. Pushing closer to 5l brings the Qtc to around .5 and the f3 to 200Hz

Edit: reread your title, around 1l will also bring the f3 to around 200Hz but with a bump in the reponse and a high Qtc. I would go for the 5l box in preference if space allows
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Old 18th December 2008, 12:25 PM   #3
tinitus is offline tinitus  Europe
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Basicly I think you have a good idea

-3db will be around 200hz which will suit butterworth
If you want Linkwitz you will have -6db around 150hz
Not much you can do about it
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Old 18th December 2008, 12:25 PM   #4
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I think 1.72L will give you a f3 of 170hz That is if you don't have
any seriese resistance . Now if you have to add a Lpad to lower
the effency things get a lot different!
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Old 18th December 2008, 01:59 PM   #5
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good idea excerpt if your solid state amp one day have a broke/ damage and put istantanyously big DC on your precious accuton!
So you have to replace woofers and midwoofers also

P.S.: maybe you have a tube amp so ignore my post

Cheers,
Paolo
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Old 18th December 2008, 03:43 PM   #6
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Thank you all for your quick responses.

I am using a tubed amp, the Atma-Sphere MA1 mklll OTL.

I was going to use a series resistor for a reason; The tweeter is the Accuton C25N-6-13, 1", with 92dB. The C173N is 93.2dB. Is this a difference I should worry about?.

What would the series resistor do to my acoustic low end rolloff idea?.

My original calculation has 1.5 l?. Where would that put my f3?.

I think I need an LCR for the cone breakup at 4500Hz, will that make a difference?.
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Old 18th December 2008, 03:49 PM   #7
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Is it the Atma-sphere OCL also ?

Paolo
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Old 18th December 2008, 05:14 PM   #8
tinitus is offline tinitus  Europe
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Quote:
Originally posted by Cousin Billy
Thank you all for your quick responses.

I was going to use a series resistor for a reason; The tweeter is the Accuton C25N-6-13, 1", with 92dB. The C173N is 93.2dB. Is this a difference I should worry about?.


Sensitivity match is no problem...you may even need padding down the tweeter, but may depend on other things like crossover design, or actual real life sensitivity etc.
Reason is that you will cross the mid below 200hz, hence you will need to make some BSC on the mid, which means it may be down around 90db at cross point to tweeter

A different option would be if the woofer could compensate fore the BSC both below and above mids rolloff, but it may be real tricky and be the cause of phase problems

There would be good reasons to cross the mid a bit higher, maybe just above 300hz...and then use a woofer section with sensitivity higher than the mid, though it may not be easy to make such a woofer section

Another option could be 2.5 way with addition of another but different driver... a small woofer with specs making it play lower than the "mid"...may not be that easy either
I am hoping to make something similar with bigger 18"/12" pro woofers...have not tried it yet

Appology if it sounds confusing, but thats because it really isnt that easy, either way
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Old 18th December 2008, 06:17 PM   #9
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Quote:
Originally posted by inertial
Is it the Atma-sphere OCL also ?

Paolo

A quick look on the Atma-Sphere website, I'm not expert of electronics,
and there is not mentioned OCL word , but I thik it is so because the double independent floating power supplies, no need of output capacitor I suppose.
They claim the output stage is "ultra-safe", I hope for you you do not have to experiments the opposite ( rare) case !

One more: one of the function of the rear volume is to absorb the rear wave; the more volume ( stuffed) the better.

Cheers,
Paolo
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Old 18th December 2008, 06:49 PM   #10
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Billy, a series resistor or an amplifier with a high output impedience will cause the QTS to be higher.
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