Passive high pass filter app. 60 hz

emosms

Member
2010-09-28 1:19 am
Hi,

I am designing a 2 + 1 home system.

The main floorstanders use cheep 10'' whizzers, no T/S parameters.
Rated as 55 Hz - 5 kHz, that's all..
They are paper cone. I know what to expect, more or less, having 8'' units from the same brand.
It is pretty ok and darn simple with a tweeter added.

The subwoofer is going to be one 10'' Coral driver.
In a 38 liter box I get a nice round curve:
~0 db/ 50 hz, f3 ~29-30hz, -8 db/20hz

I can linearize it somehow with my amp's variable loudness.

The point is that I don't want to feed that frequency into the main speakers.
So, for a simple 6db/oct high pass @ 60 hZ (hope it will save them enough) I need some 330 uF capacitor.

What capacitor should I use? Should it be non-polar?
I have some polar electrolytes rated 300 and above volts.

p.s.
The sub is going to be active anyway. Fed into hot input or via the amp's headphone jack.
So, I can apply some filter (to linearize a bit 25/30 to 50 hz) in the active sub and not pushing all drives from the amp, but then I have to do the active filter myself.

Anyway, the active sub will have variable freq low pas and a simple volume pot - in order to align the sub unit with the floor standers properly.
I want to minimize the control manipulation in the sub and control bass through the main amplifier (amp's bass and variable loudness).

Regards !
 
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emosms

Member
2010-09-28 1:19 am
Use non-polar capacitors. Much cheaper solution is line-level RC high-pass filter after the volume pot. Formula for the RC filter is the same, R is amplifier input impedance.

Line level filter would be problematic for the main speakers/ main amp. Have to put a seporate device with seporate power supply into the amp loop.
It will also reduce the amp controls bass which goes to feed the active sub.

Most easier would be to push less bass from the main amp and turn a bit up the active sub
 

giralfino

Member
2009-02-28 9:20 pm
The point is that I don't want to feed that frequency into the main speakers.
So, for a simple 6db/oct high pass @ 60 hZ (hope it will save them enough) I need some 330 uF capacitor.
The point is that a single cap won't give you the desired high pass at that frequency. Play with a crossover simulator (PCD, XSim), importing a FR and impedance, and see what happens. (Hint: a mess, as the HP filter interacts with the impedance peak of the driver).
60Hz HP should be done at line level.

Ralf

Caps for crossover need to be non polar, as the current is AC
 

freddi

Member
Paid Member
2005-08-16 4:21 pm
an inline speaker level cap can be a good way to get more bass out of a sealed box at the cost of higher excursion and a good way to muck up things - especially with strong motor and vented system. If your Coral's amp can tolerate lower impedance then a swamping resistor across the speaker would help smooth out the impedance peaks. A high impedance amp such as tube with little negative feedback won't work as well as ~constant voltage types when intentionally trying to get the boost.

ck3NOwQ.gif
 
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Line level filter would be problematic for the main speakers/ main amp. Have to put a seporate device with seporate power supply into the amp loop.
It will also reduce the amp controls bass which goes to feed the active sub.
No need for separate power supply, just make Y divider - output from audio source (CD player, PC) divide in two interconnect cables: one to the subwoofer amp input, other to the input of the main stereo amplifier. After the volume pot of the stereo amp, on the "hot" wire solder serial capacitor on each channel. If the amp input impedance is, say, R=47 K, then for f=60 Hz you need C=56 nF - very small and very cheap. Varying resistivity of the volume pot will have some interactivity with the high-pass filter, but if you use 5 - 10 K pot everything will be OK.
 

emosms

Member
2010-09-28 1:19 am
Thx all !
I rethinked what I want to achieve.
In order to spare the full range from low frequencies (loudness control), I can adjust the bass response on the active sub only.

So, Linkwitz transformer in the active sub, to equalize response (20 - 50 hz range)
The spreadsheet calculator (I found one) shows that with a chosen sub driver, box volume 35L it needs +13db adjustment, which is ok.
Eventually I could aim for equalisation in the 25 - 50 hz range, seems enough.

Then I have to design the stages for the active-sub preamp, which is another study and another forum category..

In general, modules, sub preamp:

0. I can have 2 x 16 volts from the PT - do I need electronic stabilization?
1. Input buffer, sum of L + R channel
2. Eventually a hot input as well.
3. Low pass filter, order, type (Q factor)
4. Low pass - variable cut off or switch preset frequencies. Problems with variable cut-off and filter Q
5. Linkwitz transformer - hope that the spreadhseet is ok.. :)
6. Need for buffer between stages, impendance at low pass filter/linkwitz output (yes, I don't know well the basics)
7. Simple pot or impendace match bufer after the linkwitz
8. Resulting phase shift of all stages
9. A stage for 90" phase shift - I've seen that on active subs.
10. Passive filter for driver's impedance load stabilization - Needed at all?
 
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Hi, sorry but I don't undertstand :

( it seems the same thing as yesterday as a greek member questioned about equalizers etc and in the end he realized that by lowering the volume and boosting the bass he achieved a nice sound :confused: )

Ok for all the signal conditioning for bass, but what about the original question:

DO my ( cheap, horrible ) fullrange behave well at full power or not ?
How can I prevent from modulating the cone movement done by bass frequency ?
 

emosms

Member
2010-09-28 1:19 am
The full range is pretty ok.
I wont listen it at full power, not nice. 2 x 15 W rms from 10 inchers is more than enough.

If I want deep bass, I want it at relatively low SPL (so that f.ex. people can hear each other talking)
If I boost bass - I risk to damage the fullrange.
If I dont want that much bass DEEP bass, not boomy bass - turn off the sub.

The fullrange whizzers can give a plenty of boomy bass, pretty much as anything you buy, regardles of price.

10'' cheap whizzer in 40 liters is still much better and more natural than 6.5'' in a 2 or 3 way crossover.
The issue is SPL (and ability for bass) vs Speaker and enclosure size.
 
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emosms

Member
2010-09-28 1:19 am
I am used to that. A friend has pair of whizzers from 1965:
- 12 inch/15ohm, made in my country. Rated 12.5 wats RMS !!!
So not top level, no T/S parameters.

We listen them up to moderate level.
Actually, they can reproduce very low and deep bass to some extent, noticeable, in a very undersized enclosure of 32 L.
Whit some piece of PVC pipe with length... set by trial and error.
We just know we should not push them hard towards the down range much more than we hear with no EQ or Loudness.
Except if listen to a very very low volume.

So, in my case I want to be able to push the low range a bit more :)

Consider the bang for the buck factor.
I compared 10 inch whizzers to 6.5'' ok quality full range or midbass speakers from established manufacturer, T/S parameters included.
Still, you will have some tiny speakers that cost at least twice ( I am afraid, more than twice...).

So I definatelly preffer to get much bigger speaker operated at half the rated power.
btw, they are rated 80W, i guess they are 30, maximum 40 w RMS (absolutely maximum)
 
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