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awol66 12th July 2011 09:54 AM

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 :)

GM 12th July 2011 01:44 PM


Originally Posted by awol66 (
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.


awol66 12th July 2011 10:04 PM

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 :)

awol66 19th July 2011 11:24 AM

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.

sreten 19th July 2011 11:36 AM


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.

awol66 19th July 2011 12:55 PM

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

awol66 19th July 2011 01:05 PM

metronome pic i got wrong earlier :)

sreten 19th July 2011 01:59 PM

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.

awol66 19th July 2011 03:33 PM

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

awol66 19th July 2011 04:52 PM

1 Attachment(s)
Attachment 231781

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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