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JinMTVT 13th July 2004 05:59 AM

Subwoofer amplifier goals and decisions ..
I've been searching for a good thread that lists all the information
on building a sub/bass amplifier and it's constraints ...

So i would like to ask you all knowledge people ,
to list and talk about the details implicated in building a
good subwoofer amplifier in general
( not for a particular sub unit )

What are the limitations in this kind of amplifier?

What can we "cut" to save because of absence of high frequencies ( this amp needs to be good working up to 1KHz max)

Wich is the best method for low Hz power and precision ?

From what i read, our ears do not perceive good resolution in the 500hz and lower region, so could we compromise sound qualiyt for Oumph and power without any perceived degradation in sound quality ?

what kind of design is best suited for this application...

and also specify electronics that require special needs for lower Hz region ( PSU requirements? sotrage caps? wiring ? current? )

Thanks all for your time!

hunter audio 13th July 2004 12:29 PM


for starters you have to take into consideration the driver - your amp should be rated way higher than the driver - to avoid clipping damage to the driver

next is the input circuitry consideration - this is where i find most people turning a blind eye a powered sub is not an amp and spk in a box

you have to be good at the input circuitry - 24 db cross over beow 200 hz + active bass linear correction network + a good quality parametric equalizer + a bass boost

if you opt for the linear bass correction network it will give you linear bass spl upto 20 hz that requires heavy amplification + power supply

best choice for such an amp will be a rugged - mosfet - more in parallel the better regardless of the power rating

the power supply should be bifiliar winding primary + secondary = with 2 bridge rectifiers and lots of capacitance 1,00,000 for starters per rail

and the va best at 2 X (times) the power rating

if you go in for all this the next would be the box - you need a real rock solid enclosure

then you can really push lows as much as you like


transducer design engineer

JinMTVT 14th July 2004 12:04 AM

thank you for the info! :)

I don't really understand what you are talking about in terms of input low pass with quality harder to realise than a high pass filter?

personally my next project for sub is a 15 or 18" transfer line
with an external amplifier ( might just sit on top of it )
something in the 8 to 10' long enclosure ..typical taper TL design

i do not have any good resssources for the driver yet, so i do not know of any specs ..

this will be ultimatl played in conjunction of a pair of ESL pannels
for md and highs, and the crossover point shoould be set in the 500hz region ( 500 to 700hz )

Capacitance storage is really needed that much ?
why is bass harder to drive than highs?

is it because of the excursion of the drivers that asks for more current?

paralell mosfet is a la "slone" optimos design right?
this is a trade off for power on higher distort?

is there any parts of amplification that we do not need to take care of when working only with sub 1Khz ?

thanks again

cunningham 14th July 2004 01:03 AM

low freq. amp design
A good sub amp is usually direct coupled to the speaker. Best to use op-amps for the active low-pass filters for the input, can make the Fc adjustable with a pot. Most sub woofers don't respond well above 100Hz, and as freq. increases, so does the inductance reactance of the speaker coil. The most important thing is that it has a stable DC bias. If you use an OP-AMP for the differential amp stage, a very stable DC bias is possible, and you get no :hot:
Don't expect to get high freq. responce from an OP-AMP diff. circuit on account of the slew rate. But for low freq., this may work well.

Anyway this can seriously simplify your project. :D

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