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previous: John Fisher Ajay, I do have all kinds of Sp... -- 12/29/2002 4:26 PM View Thread

Re: Building a Bass Amp

12/29/2002 5:35 PM
Ajay
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Re: Building a Bass Amp
Hi John..PVA is white glue,it's used for holding tolex onto cabs,it's also known as plasticizer in the cement game,not quite sure how we managed before it was invented. The resin I spoke of is used to rigidize the cone,at bass freqs.the cone is shifting lots of air and they tend to "break up",go into nodes and antinodes,so by using resin it creates a rigid form that is still light enough to be sensitive at bass freqs. The PVA is used to add mass to the cone,this has the effect of lowering the resonant freq.The resonant freq. is really the lowest usable freq.of the speaker,without using EQ.If you use a normal guitar speaker (F.R.80Hz) then you'll need to use lots of bass EQ,you're trying to get a speaker to do something that it doesn't want to,if for example you put 10 watts into a speaker,then boost the bass by 10dB then the power at bass freqs.goes up to 100watts...by lowering the F.R. it makes the response flatter,needing less EQ..hence less power is dissipated in the voice coil,as a by product the speaker sounds a lot less peaky,all strings seem to have approx. the same energy.To test the speaker you can generate spot freqs.say 30,40,50,60,80 Hz thru a hi-fi amp to your chassis speaker mounted on a baffle.Oh and this should be done outside to prevent reflections!,then record using your best microphone,at about a yard from the cone,then spectrum analyze the results.This should give you a clue whether you have a bass speaker or not,a guitar speaker will drop off at about 70/80Hz a bass one should go lower...try using a goodish hi-fi speaker as a control,so that you have a reference point....sorry about the length of this reply...it's much easier to do than it is to describe!!! BW Ajay

 
Replies:
John Fisher Great! Thanks! I am going to get to... -- 12/29/2002 7:38 PM