Scaling a HL sub?
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URL: https://forum.speakerplans.com/forum_posts.asp?TID=2555
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Topic: Scaling a HL sub?
Posted By: gaston_pdu
Subject: Scaling a HL sub?
Date Posted: 05 September 2005 at 1:07pm
| I just want to know, what could happen if I just simple scale an 18'' Horn Loaded Sub (like 184) to use it with an 8''. Only intended for home sub, just that. Would it work properly?, Deeper and louder than the same 8'' driver into a BR cab?. The driver is around here, so i will use it. Is a very very cheap subwoofer, 40 U$S the couple, hehe. cheers! |
Replies:
Posted By: Dave Slater
Date Posted: 05 September 2005 at 2:57pm
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can't be done put simply it's the length of the horn that determines the lowest frequency possible take the 18" super scooper for example its path length is 2.22m a horn is a quarter wavelength resonator which basically means it resonates at a frequency 4 times its path length 344m/s (speed of sound) divided by 8.88m (4 times the path length) gives a frequency of 38Hz the reason that plan states that putting 4 scoops together gives you a cut off of 30Hz is because the mouths couple together and having a larger mouth increases the lowend spl output however it's not as simple as keeping the same length and mouth area the throat and front chamber combination acts as a low pass filter allowing you to tune the high end response (larger volume = lower cutoff) the throat also controls the overall spl output (a smaller throat creates more air pressure but too small has a negative effect and can destroy the driver) the rear chamber allows you to balance the cone excursion on its limits at the tuning frequency (again a larger volume = a lower frequency) simply scaling a design wont work as each horn has to be tuned for a particular set of driver parameters best bet is to read up on horn design at this website - http://melhuish.org/audio/horndesign.html - http://melhuish.org/audio/horndesign.html download horn response - http://www.users.bigpond.com/dmcbean/ - http://www.users.bigpond.com/dmcbean/ read the help manual and play around with your driver work on corner loading your horn (0.5 Pi in horn response) as you'll be able to reduce the size of mouth and to some degree the path length yet still maintain the low frequencies you desire have fun!
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Posted By: Tom Umney
Date Posted: 06 September 2005 at 10:33am
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http://www.lsv-achenbach.de/plaene/plan_bpvissub.htm - http://www.lsv-achenbach.de/plaene/plan_bpvissub.htm Kompakter Bandpass-Subwoofer mit Visaton GF200 bestückt. Hier ist die aktiver Version gezeigt. Die Maße der Öffnungen für das Aktivmodul sind auf die Module von Thommessen angepasst. Als Reflexöffnung dient ein IT HP100 mit Trompetenförmiger Öffnung um Strömungsgeräusche zu verringern. Seitenansicht Ansicht von unten mit abgenommenem Boden
Theres plans for an 8 inch bandpass instead. |
Posted By: Centauri
Date Posted: 06 September 2005 at 12:04pm
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As Dave said, scaling won't work. If you have a look at Bill Fitzmaurice's http://www.billfitzmaurice.com/plans/product_info.php/products_id/11 - Tuba18 , http://www.billfitzmaurice.com/plans/product_info.php/products_id/23 - TableTuba and http://www.billfitzmaurice.com/plans/product_info.php/products_id/7 - Autotuba
cabinets (all use an 8" driver), you will see that a long path length
is still used. The smaller mouth area will mean corner loading
(placing box in a room corner) will be needed to keep the low end
efficiency up. Even if you don't actually make one of those
boxes, they give you an idea of what is required. Cheers Graeme |