From victora@mda.vnd.TEK.COM Thu Sep 12 16:07:44 1996 Return-Path: Received: from inet2.tek.com (inet2.tek.com [134.62.48.22]) by ursula.ee.pdx.edu (8.7.5/CATastrophe-2/10/96-P) with SMTP id QAA05949; Thu, 12 Sep 1996 16:07:43 -0700 (PDT) for Received: by inet2.tek.com id ; Thu, 12 Sep 1996 16:07:31 -0700 Received: from tektronix.tek.com(134.62.48.24) by inet2 via smap (V1.3) id sma023258; Thu Sep 12 16:07:18 1996 Received: from tekgen.bv.tek.com (tekgen.bv.tek.com [128.181.44.33]) by tektronix.tek.com (8.7.5/8.7.3) with SMTP id QAA12869 for ; Thu, 12 Sep 1996 16:08:58 -0700 (PDT) Received: from Ariel 3 (ariel3.vnd.tek.com) by tekgen.bv.tek.com (4.1/8.0) id AA06791; Thu, 12 Sep 96 16:07:11 PDT Message-Id: <9609122307.AA06791@tekgen.bv.tek.com> Date: Thu, 12 Sep 96 16:09:30 -0700 From: "Victor J. Albert" Organization: Tektronix X-Mailer: Mozilla 1.1 (Windows; U; 16bit) Mime-Version: 1.0 To: thunder5@ee.pdx.edu Subject: Car Transfer Functions Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=us-ascii Status: RO X-Status: "Grizz @ MTX Technical" wrote: >Danny Bishop wrote: >>Grizz @ MTX Technical wrote: >>> >>> Frankd@Venter.und.ac.za (Immortal) wrote: >>> > >>> >When setting up a car for SPL , I have heard that the subs should >>> >be tuned to the resonant frequency of the car . >>> >What exactly does this mean? >>> >Also how does this relate to the transfer function of a car? >>> >and how would I find it (Tranfer function that is) >>> > >>> >Thanx DLF >>> > >>> The transfer function is a >>> nightmare to calculate accurately. A simple understanding of the >>> term will allow you to "guesstimate" at where the t.f. begins for a >>> given vehicle. We know that the gain is at 12 dB @ octave and starts >>> at different frequencies. For example, a two-seater sports car or >>> mini p/u may start at around 80-90Hz while a full-size van may start >>> at around 30-40Hz. Obviously the bottom octave will be reinforced >>> much stronger in a smaller vehicle. This also means that in a smaller >>> vehicle, you can get away with tuning at a higher frequency in a smaller >>> enclosure. A large vehicle will need a larger/lower-tuned box to play >>> lower anechoically to make up for little transfer function benefit. >> >> >>As I was lead to beleive the Tranfer function begins basically at the >>first mode of the vehicle. To calculate this you should measure the >>longest point to point length of the interior of the vehicle. Then a >>little math --- 565 / l' = x Hz (basically 565 is gain by the speed of >>sound and quarter waves and all sorts of tech stuff.. for more read a >>book called -- THE MASTER HANDBOOK O ACOUSTICS -- ISBN 0-8306-4437-7) >>Anyway most sedans will give you a transfer function beginning at 90 or >>so Hz. This means that everything below that point rises in frequency >>by 12 db per octave. To build your bass boomer you should try and build >>a box for your subwoofers that will make the best use of this extra free >>bass... but obviously you can't get a sub that will give you any serious >>SPL down really low (20 HZ) and that is where the transfer function >>would theroretically make the most difference. So the trick is to model >>lots and lots and lots of box woofer combinations to try and find the >>lowest high dB system you can find. One box that gives 130db at 50Hz >>may not be as good as one that gives 129 dB at 45 Hz !! (MOST computer >>programs will not take into account transfer function but many will >>allow you to build in an eq response, or something like it.. this will >>make the whole process a lot quicker.) >> >>Hope some of this helps you >> >>Danny Bishop >>dbishop@world.net >> >>Sales Support >>Eurovox Australia > > > >Agreed. However, one simple measurement doesn't give you an accurate >answer. That's one way to "guesstimate" that seems to work well. The >problem with only one measurement is that you have no idea how much >volume is in the vehicle. What if the vehicle was not only 10'long, >but 10' wide as well (seriously unlikely)? I'm sure you know what I >mean. :^) > >Grizz Archer >MTX Technical > >