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Old 12th July 2011, 09:54 AM   #1
awol66 is offline awol66  England
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Default Cabinet dimension advice

Ok , so this is my 1st post (apart from intro) so pls be gentle with me

Im hoping someone can help me with dimensions for cabs for these drivers

Audio Electronics BMR 180 . Nominal impedance : 15 Ohms , DC resistance :12 Ohms , Resonant Frequency :36 Hz

Frequency range : 30 Hz to 12000 Hz , Power : 90w Rms , Qms : 7.00 , Qes : 0.34 , Qts :0.32 , Vas : 31.8 litres

Chasis diameter : 184mm , Baffle cutout : 142mm . Used by JPW in their Ruby range of speakers .

Ive been trying to find the ideal size of horn so i could either start to think about how to fold it up a bit

or i did consider using the top 1/4 and making a pair of metronome cabs . I have looked at online caculators

but i must be putting the wrong numbers in the wrong boxes , jus cos ive got the specs dont mean i understand em.

I was looking for dimensions because my ability to build it is probably(definately) slightly better than my ability to

design it correctly , but any suggestions would be considered and appreciated .

I did consider calling this thread cabs for dummies , so if ya could bear that in mind an keep answers nice an simple

ta muchly
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Old 12th July 2011, 01:44 PM   #2
GM is offline GM  United States
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Quote:
Originally Posted by awol66 View Post
Ive been trying to find the ideal size of horn so i could either start to think about how to fold it up a bit ............
'Ideal' ? A theoretically 'ideal' horn for these specs would have only a ~6-212 Hz BW with a ~108 dB/m efficiency and be a small house in size, so I'm thinking you don't really mean 'ideal' literally. With [mid] bass horns, one usually figures out the largest dims one can afford, then see if it's large enough to meet the performance needs of the app [F3, F10] once any room gains are factored in.

GM
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Old 12th July 2011, 10:04 PM   #3
awol66 is offline awol66  England
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Thanks for the reply GM , my resonse might be a bit delayed cos we changing isp and our service is unreliable atm

ok , so i wasnt planning on actually building the full horn , but i thought that was my starting point , and then

presumably i would either scale the whole thing down to a useable size (i assume shrinking it would raise the BW (bandwidth?)

and reduce the efficiency ) or i use the upper section of the horn to construct a metronome design , I have built a pair of

metronomes for some hemp accouistic fr6.5 drivers and im very happy with the result , i was sorta hoping for something similar

that would make use of the BMR 180's lower frequency specs , i might need a tweeter with these , but my hearing is running out

around about the same frequency as the drivers do , the joys of middle age , as i start to afford and understand better quality

hifi , the bits that im listening to it with are getting beyond their best

If the specs suggest a completely different design pls feel free to let me know as i really am a beginner at this sorta thing .

the metronomes were built to dimensions supplied on the website (frugalhorn), i didnt work them out myself .

If im honest id like someone to chuck a bunch of numbers at me , attached to a rough plan an tell me ... " build these "

rite ill get this posted b4 my net crashes again , cheers
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Old 19th July 2011, 11:24 AM   #4
awol66 is offline awol66  England
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ok , so net is a bit more stable so i can keep up now (i hope)

Attachment 231735 i could just fit the drivers into these cabs

but i thought it would be better if they were used in an enclosure with the correct dimensions , and i dont think im going to

be able to work that out myself , which is why i posted this in the hope that some1 who could would give me a much more

accurate result.
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Old 19th July 2011, 11:36 AM   #5
sreten is online now sreten  United Kingdom
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Hi,

FWIW metal cone drivers are highly unlikely (unless they are Jordans)
to work well without a crossover due to higher frequency break up.
Very often a trap circuit is needed for the first large break up peak.

rgds, sreten.
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Old 19th July 2011, 12:55 PM   #6
awol66 is offline awol66  England
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lo sreten, thanks for the reply . FWIW ? sry i wasnt kidding when i said im a beginner at this

i seem to av messed up the posting a pic as well doh ...

wot im looking for to start with is a good idea of wot size cab i should be looking at ,

and if the metronome type idea is the right way to go , if there are much more suitable designs pls

feel free to point me in that direction. if i have to work out some of the dimensions myself my maths

is up to basics , but i dont understand the tuning of a cab or porting at all .

thanks for the help so far
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Old 19th July 2011, 01:05 PM   #7
awol66 is offline awol66  England
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http://www.diyaudio.com/forums/attac...-metronome.jpg

metronome pic i got wrong earlier
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Old 19th July 2011, 01:59 PM   #8
sreten is online now sreten  United Kingdom
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Hi, what online calculators are you referring to it the first post ?, rgds, sreten.

A Metronome I'd hazard would need to be very tall for a low Fs driver.
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Old 19th July 2011, 03:33 PM   #9
awol66 is offline awol66  England
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I didnt book mark any of the pages i looked at , i started from the free software thread on here an jus searched out from there , ishtek was 1 page dont recall the name of the prog , i spent several days dipping in an out of web pages as i got time but didnt get consistant answers or 1s that made sense to me anyway .
certainly nothing that jus said build it this big and this shape , which is wot im really looking for
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Old 19th July 2011, 04:52 PM   #10
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BMRally.jpg

ok this is one of the drivers im tryin to get sizes for ,(isnt it pretty ) the box its in at the mo used to be a bit of

furniture ,which ive used as a test box , its about 50litres in volume and doesnt seem to do these drivers justice in

the bass dept (i suppose a correctly sized port would help ), i tried the hempcones in these boxes and the bass

improved a lot with them in the metronome cab,which is why i was thinkin along similar lines. when i say improved

i dont mean louder, it seemed to get bigger and clearer, the ally cones have a lower freq response than the

hempcones by quite a bit , 30 hz as opposed to 45 , so i thought that would be even better bass
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