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-   -   simple bass boost circuit (http://www.diyaudio.com/forums/solid-state/9025-simple-bass-boost-circuit.html)

deepanger 25th December 2002 01:19 AM

simple bass boost circuit
 
hi,
just wondering if ican make a simple bass boost circuit that can
drive 40watt rms speaker..
something we can call a (one band "bass" equalizer), i think its
a simple design,, so any ideas?!

Nelson Pass 25th December 2002 06:06 AM

One of my favorites is called the "hump & bump", which is
a classic Sallen-Kelly type 2 pole high pass filter where you
crank the gain up on the op amp until the positive feedback
creates a peak. Typically I get from 0 to 12 dB fairly sharp
boost at the peak frequency, and then it falls off sharply
at frequencies below that. With care, you can get more gain
than that, but figures below 10 dB sound best.

You also can make it out of a conventional non-inverting
power amp. If somebody else doesn't post the schematic
before Thursday, I will.

:santa2:

deepanger 25th December 2002 10:43 AM

u say its a high pass filter?!
the required is a bass boost > low freq.
anyway it can be modifieded , can u post the schematic.?

GRollins 25th December 2002 02:40 PM

Nelson is correct, it's a high pass. The trick is that the circuit is set for something like, say, 12 or 15Hz.
Think of a woofer cabinet with a Q higher than .707. There will be a hump before the bass rolls off. The higher the Q, the higher the hump.
This is the same thing except done electronically. The objective is to set the rising response of the circuit against the falling response of the woofer. Ideally, adding the two will produce flat response down to some arbitrarily low frequency where the circuit begins to fall off. Linkwitz did a nice paper on this years ago which is (I think) available on his website. Do a Google search on Linkwitz and speakers and see what you come up with for a URL.
There are two limitations to this strategy. The first is that it consumes horrific amounts of power from your amplifier. You'll need a pretty hefty hunk of amp if you intend to play loud. The other is that a driver designed to go down to 30Hz or so is only going to have a certain amount of cone excursion. If you start driving it an octave deeper than it was meant to go, you're going to find yourself bottoming voice coils real fast. And they'll start sounding real loose and rubbery long before that, as you'll be out of linear cone excursion.
That said, it sounds great as long as you remember that there are limitations.

Grey

Nelson Pass 25th December 2002 06:26 PM

This goes back a long way. I was using it at ESS in '73.

Generally we select the peak for the point at which the
woofer starts rolling off. When you increase the Q of the
filter, the frequency of the peak rises, so you want to
account for that.

Typically, I set the gain for 6 dB or so at the frequency
where the woofer is down 6 dB. You can go for higher
boost, but the transient response starts to suffer.

Higher than 18 dB, and you've got a nice oscillator.

Interestingly, when you kick this filter in, the woofer cone
stops moving so much, since it removes subsonics while
you're at it.

palesha 26th December 2002 06:24 AM

Happy Christmas!
Nice & interesting discussion on bass boost. Give schematics along with tips to get it matched to different speaker boxes. Also let know whether it will be ok for sealed, vented etc.

deepanger 26th December 2002 04:35 PM

thanx replying everyone,
actually am aNewbie in the audio amps so i didnt understand
most of the terms and ideas posted,, ijust want something simple
and clear and after lets see how it can be upgraded or modifieded
into something better.
lets c some schematics 1st..
thanx again.

GRollins 27th December 2002 01:48 PM

Schematics and formulas are provided in the Linkwitz paper. Read it before continuing. This is not a trivial project. It assumes, among other things, that you know the actual performance of the speaker that you intend to use. Printed specs are useless for this. You'll need an accurate response curve in order to know what frquencies to plug into the formulas. Even then it may take a bit of cut and try to get things settled in properly. No one publishes the Q of a finished speaker, for instance. You'll have to diddle the values a bit to get flat response. It took me two or three iterations to get it right the last time I did this, though the results (at low to moderate volumes) were well worth it.
I wouldn't recommend using a circuit like this for a vented box. In general, sealed boxes are best if you intend to start playing with the incoming signal.

Grey

deepanger 27th December 2002 02:01 PM

Quote:

Originally posted by GRollins
Schematics and formulas are provided in the Linkwitz paper. Read it before continuing. This is not a trivial project. It assumes, among other things, that you know the actual performance of the speaker that you intend to use. Printed specs are useless for this. You'll need an accurate response curve in order to know what frquencies to plug into the formulas. Even then it may take a bit of cut and try to get things settled in properly. No one publishes the Q of a finished speaker, for instance. You'll have to diddle the values a bit to get flat response. It took me two or three iterations to get it right the last time I did this, though the results (at low to moderate volumes) were well worth it.
I wouldn't recommend using a circuit like this for a vented box. In general, sealed boxes are best if you intend to start playing with the incoming signal.

Grey

actually i intended to use this on my 6x9 coaxials (40rms, 130max)
from ma 1st post i didnt mean to use it as an amp. to drive those
big subs. , ijust wanna it to enhance (boost) the low freq. in my
car coaxials abit. , the same function as those equalizers, but u can call it a (one band eq.) ..u get the point?

deepanger 28th December 2002 12:35 PM

where r ya all?!
need help this!..:xeye:


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