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active crossover?

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Death By Bass

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**broken link removed**

in Figure 1B, what is the reason for the low pass section being connected in series with the low pass section of the bandbass section?

that is all :D
 

Nigel Goodwin

Super Moderator
Most Helpful Member
It gives a little extra attenuation of bass frequencies to the HF unit, and it costs nothing to do - so why not?. In practice I doubt it would make any real difference?, but it doesn't cost anything!.
 

Death By Bass

New Member
I'm wanting to do a 4 way, highpass, two bandpass, and low pass. So, I dont think I'll connect the lowpass in series with the bandpass... keep them totally seperate :)

thanks.
 

dknguyen

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No reason. It's probably what they had available. Or maybe the op-amps needed different output ranges so they were two types of op-amps used and they had different power supplies so couldn't be stuck into the same package. I don't know about this for sure since I just glossed over the article. Or maybe to help isolate noise between the op-amps.
 
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dknguyen

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I saw that circuit during my glossing. Theoretically it makes no difference if you use a single op-amp, dual, triple, quad, or whatever. It's probably what they had lying around (single and dual-op amps are both probably more common than quad, and you have too many ICs if you use single-opamps, so they used dual).

Don't worry about it too much.
 

Nigel Goodwin

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Death By Bass said:
is there a reason they are using dual opamps, instead of quad?

As suggested, it's simply down to layout problems, and what you have available - technically it makes no difference.

One obvious reason for using dual opamps is so you can build a modular system, with each filter section on it's own board - as each sections uses two opamps, a dual is perfect for that - and a quad would be too big!.

If you're building it all on one board?, use quads, doubles, singles, whatever you like - or a mix of all three?.
 

Death By Bass

New Member
I dont really know what crossover frequencies I want...

my original design seemed alright, but I'l thinking I should do the tweeters higher (they reccomend 3500Hz at atleast 12dB per octave)

and I haven't actually chosen the midrange yet :p lol
 

Nigel Goodwin

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Most Helpful Member
Death By Bass said:
I dont really know what crossover frequencies I want...

my original design seemed alright, but I'l thinking I should do the tweeters higher (they reccomend 3500Hz at atleast 12dB per octave)

and I haven't actually chosen the midrange yet :p lol

Are you trying to do PA or HiFi?, and why do you want four way?.
 

Death By Bass

New Member
Nigel Goodwin said:
Are you trying to do PA or HiFi?, and why do you want four way?.

car... :D

3 way active fronts, and the subwoofas in the boot :p

looking at running Vifa tweeters up front, unknown mids as of yet (looking for a 4inch) and 8inch Peerless midwoofers, and unknown subs... :)
 

Dr.EM

New Member
At a guess the sub frequency could be under 90Hz, the woofer under 600Hz, the mid under 4Khz and the tweeter anything above this. It's nice to use a 24dB on the sub at least.

As Nigel pointed out though, 4-way is uncommon because it is usually unnessecery. My old Hi-Fi speakers were 3 way and my new ones are 2 way. The new ones are FAR better and will go much louder. The old one is let down by a poor quality midrange, and that will always be a problem with multiway systems. You'll need well matching drivers (in terms of tonality, sensitivity and freq range covered). This is likely to cost you more and is also likely to be hard to achieve a good setup. My advice would be just woofer tweeter and a sub.
 

Death By Bass

New Member
I want as much bass upfront as possible, hence the choice of 8inch woofers upfront, crossed over at 70Hz. Then ofcourse, the 8's wont go high enough to cross directly to the tweeters, so a 4inch midrange was decided upon, crossed to a smallish dome tweeter...
 

audioguru

Well-Known Member
Most Helpful Member
Your 8 inch woofers won't have any output below about 100Hz up front in a car. There isn't enough space for an enclosure for such big speakers to produce low frequencies. Therefore most cars use 6.5 inch speakers in the doors. Use 120Hz to crossover to the sub-woofer.
Many 8 inch woofers have a peak at about 5kHz. 6.5 inch speakers have a peak at about 6kHz. Either woofer works fine without a midrange and with a fairly large tweeter (one inch dome) that can go down to 4kHz.
 

Nigel Goodwin

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Most Helpful Member
Death By Bass said:
I want as much bass upfront as possible, hence the choice of 8inch woofers upfront, crossed over at 70Hz. Then ofcourse, the 8's wont go high enough to cross directly to the tweeters, so a 4inch midrange was decided upon, crossed to a smallish dome tweeter...

Well a sub-woofer doesn't really count as one of the drivers, as you only have one of them. But as for the rest?, two drivers should be fine, and probably far better than trying to use three - check out many of the best speakers in the word, they are often two way rather than three way.

Main problem with a car though is the small internal space, it's too small to get decent bass reproduction, which is why all you get is a single note boom-boom noise!. Like Audioguru says, 8 inch drivers would probably be a waste of time - for that matter why not use passive crossovers?, with the exception of the sub-woofer, where an electronic one would be an advantage.
 

Death By Bass

New Member
Nigel Goodwin said:
Main problem with a car though is the small internal space, it's too small to get decent bass reproduction, which is why all you get is a single note boom-boom noise!.

thats not true, but anyway...

Nigel Goodwin said:
Like Audioguru says, 8 inch drivers would probably be a waste of time - for that matter why not use passive crossovers?, with the exception of the sub-woofer, where an electronic one would be an advantage.

10 litres sealed, will give me a -3dB point of around 80Hz, which is low enough for me... the parts for passive crossovers will cost me as much as a 4 channel amp to run the mids, and tweets actively would... plus, its alot more difficult to get frequencies accurate, with impedance rise and such...
 

audioguru

Well-Known Member
Most Helpful Member
Where in a car will you find 10 liters per side up front for woofer speaker enclosures?
 

Death By Bass

New Member
audioguru said:
Where in a car will you find 10 liters per side up front for woofer speaker enclosures?

in the doors....

**broken link removed**

fibreglass over the map pockets, and there's alot of mounting depth behind the stock 4inch speakers...

or, if that fails, even mounting the woofers free air should give a -3dB point of 85Hz...

:)
 
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