crossover question

[jaudere]

hello cranky. Thanks for that xlr thing. Was going to ask you about that. Btw are you always on line? your responses are very prompt. Did you see the snaps i have posted on the OB speaker thread? With this active crossover , few problems will pop up. 1) will have to buy a better cdp due to analogue thing. At present my sony is giving fair service with coax out. 2)i have multiple inputs into AVR: dvd player, pc & set top box of dish tv. So how can i do that through the active xo ? Is it possible by doing it in the following way? For tv, comp, connect my bookshelf pair to speaker A & mids ,highs & lows output of the xo to B. I think the A & B option is only for front speakers.

 

[jaudere]

hello cranky, i wont get disappointed so soon. If active xo is going to improve SQ and give me flexibility, then so be it. My LCD Monitor has built in speaker (view sonic 22"). Can live with that for the PC. Set top box can be connected to the older amp.(tv use is just about 40 min a day). So i can dedicate the AVR To single source. I dont want to go into the XLR thing. So i will need to search a bit more.

 

[jaudere]

Hi guys.

I am digging up this thread as I have another crossover related question.

Have a look at this cross over by Ahuja

Ahuja Radios

Ahuja Sound Solutions

What is this product exactly?

It says 1 way crossover. Do they mean to say High pass filter?

I have it with me. The quoted XO frequency is 4000Hz for 8 ohms but the Capacitor is 3.3 microF. If we go by the standard tables, this is a capacitor for 6000Hz for 8 ohms.
I don't understand what the coil is doing there and did not understand the R1 and R2 either.

I had connected a 4 ohm tweeter thinking that it will work as high pass filter at 8kHz (4Khz at 8 ohm should work as 8Khz at 4 ohm) but there was something greatly missing in the whole thing. So checked up the capacitor value. With 3.3 microF, it will work as high pass filter at 12kHz and that is why I was missing important data from the music. I used another XO with 4.7 microF capacitor and got the sound right.

 

[sashijoseph]

It is a 2nd order high pass filter(cap in series and coil in parallel with the HF driver).
So the correct formula for a 2nd order Butterworth is
f=0.1125/(ZxC) ===>0.1125/(8x(3.3/10^6)) = 4.2kHz

the resistor's are probably an L-pad attenuator for the tweeter.

 

[jaudere]

Thanks a lot. Can you please tell me how to find the value of the coil?
Secondly, what is the Z in the formula?
If I connect it with the 4 ohm tweeter,what will be the high pass point?
On output stage, it has a HF Terminal and LF Terminal. So through LF Terminal, does it feed full range sound to the low frequency driver?

Is there any way simple way that I can remove the attenuators together or one by one?

 

[sashijoseph]

For a 2nd order butterworth these are the formulae...
High pass : C = 0.1125/(ZxF)
L = (0.2251xZ)/F
where Z is the impedance of your HF driver and F is the xover frequency.
C will be in series with the driver and L in parallel.

Low Pass : formula remains the same,just swap Z with the impedance of your LF driver.
C will be in parallel with the driver and L in series.

For a 1st order Butterworth..
C = 0.159/(ZxF)
Z is the impedance of the HF driver and F the xover freq.
C is in series with the driver.

L = Z/(6.28xF)
again Z is the impedance of the LF driver
L is in series with the LF driver.

On output stage, it has a HF Terminal and LF Terminal. So through LF Terminal, does it feed full range sound to the low frequency driver?

looks so...why don't you decipher the schematic by looking at the pcb tracks? should be simple.

Is there any way simple way that I can remove the attenuators together or one by one?

if it's wired as an L-pad one of the resistors will be in series with the HF driver and the other in parallel.You may remove both and place a wire jumper in place of the series resistor.
but I think you would require some attenuation on the tweeter to match down to the (probably) lower sensitivity of the woofer.

Tell you what,do give the Passive Crossovers article at the ESP site a read to get you started on the tricky journey of passive xover design.
Passive Crossover Network Design

 

[quad]

From the Ahuja link (1 way crossover), it does look like the
LF output is the full range.

There are some simple online crossover calculators -

Passive Crossover Design Equations Formulas Calculator - Two Way Second Order Network Chebychev Bessel Butterworth Linkwitz-Riley
Crossover Design Chart and Inductance vs. Frequency Calculator(Low-pass)

 

[jaudere]

From the Ahuja link (1 way crossover), it does look like the
LF output is the full range.

There are some simple online crossover calculators -

Passive Crossover Design Equations Formulas Calculator - Two Way Second Order Network Chebychev Bessel Butterworth Linkwitz-Riley
Crossover Design Chart and Inductance vs. Frequency Calculator(Low-pass)

Thanks but my problem is bit different.
I already have a readymade cross over ripped from a 2 speaker whose specifications are not available. I wanted to find out the value of the inductar which is already there. I could have found it with the help of tables if i knew the impedance of the original speaker but even that is not available.

 

[jaudere]

which capacitor is better for Audio? Electrolytic or polyester?

Can I use 350V capacitor in place of 250 V? My amp is 60w RMS Into 4 Ohm. So i think anything above 50 V should be safe but is there any upper limit?

 

[navin advani]

I could have found it with the help of tables if i knew the impedance of the original speaker but even that is not available.

To find out the value of an unknown inductance one needs a bridge meter. see link below
http://www.aplab.com/pdfs/MT4090 - 200KHz LCR Meter.pdf

which capacitor is better for Audio? Electrolytic or polyester?

Can I use 350V capacitor in place of 250 V? My amp is 60w RMS Into 4 Ohm. So i think anything above 50 V should be safe but is there any upper limit?

Polystyene/Polyester caps are better for audio than electrolytic. Yes for this speaker even a 50VAC cap is adequate.

Where the value of the poly cap is not available (large values) one can use a large electrolytic cap and parallel it with a smaller poly cap for example 100uf elec // with 1uf poly.

 

[jaudere]

Thanks.
Is there any upper limit for for voltage for the cap?
I wanted to make a high pass filter at 8.5khz for 8 ohm tweeter. So the cap value is 2.2 uf. Such cap is not available. So I will be putting 2 caps of 4.7 in series to get a first order high pass filter at around 8500hz for 8 ohm. That is the lowest cap available locally.

 

[goldyrathore]

which capacitor is better for Audio? Electrolytic or polyester?

Can I use 350V capacitor in place of 250 V? My amp is 60w RMS Into 4 Ohm. So i think anything above 50 V should be safe but is there any upper limit?

Here is a quote from Rod Eliott
"If you are on a budget (decent caps at these values are expensive), one possibility is to use power-factor correction or induction motor start capacitors. These used to be oil-filled paper (some still are), and are much cheaper than "electronics shop" devices. I can vouch for the sound quality, as I use these to protect my tweeters - most are polypropylene are of film and foil construction, although metallised film is probably used as well. The stability and power handling will certainly be superior to that of bipolar electrolytics, and the high frequency response can be corrected (if necessary) by bypassing with a high grade polyester. I would expect that a 1uF bypass would suffice in most cases. "

Keltron and Tibcon are two local brands of such caps. These caps have MPP printed on them. You could start with these. Once you know the value that works best, you could replace with audio grade caps.

Also see http://www.hifivision.com/diy/14433...udspeaker-philips-fullrange-7.html#post214682 for use in xover.

Regards,
Goldy

 

[goldyrathore]

Thanks.
So the cap value is 2.2 uf. Such cap is not available.

Usual electrical shops carry MPP caps for fans staring from 2.2uf.
Regards,

Goldy

 

[jaudere]

Got 2 of those MPP CAPS from local electrical store. Brand Epcos (siemens technologies).
2.5uf: 8khz for 8 ohm and 16khz for 4ohm.

4 uf: 5khz for 8 ohm, 10khz for 4 ohm.
Tried both with 8 ohm and 4 ohm tweeter. Seems that 4 uf at 10khz suits best for my needs. That too is first order. So it should give useful output at least till 9khz.
Now I need to calculate my final impedance.
1)One 8 ohm speaker running without crossover.

2) 1 speaker 8 ohm through 250hz 2nd order low pass filter

3)one 4 ohm tweeter with 1st order high pass filter at 10khz.
All in parallel. Any guess of average impedance over full frequency range?
I have tried this combo with my marantz pm 6002. Ran it for 1 hour. No issues. At the most I can say that it became warm. It becomes this much warm with 8 ohm speakers also.

 

[jaudere]

spherical wheels instead of spikes.

Here is a wild guess. For speaker isolation, spikes are recommended.
I am a person who keeps on changing speaker position. Having spikes could be a headache for me.
Recently I visited a hardware shop for something else. There I saw this spherical wheel which is used under TV Trolleys. Being sphere(well almost), the point of contact will be single point which should serve well to isolate. It can be locked. So it wont move unnecessarily. When Unlocked, I can shift the speaker easily.
What is expert opinion on this idea?