Resistor help please

[Filterlab]

Hi chaps.

I've just got back into hi-fi and I'm fiddling around with customised speakers (lots of fun!). Anyway, it's been frickin' ages since I've dabbled in electronics so I'm rather rusty.

I'm looking to add a separately enclosed pair of ribbon tweeters to my custom builds. I have the circuit ready in terms of high pass (5Khz 12dB roll off 8Ohms), but the sensitivity of the tweeters is 98dB whereas the custom builds are 91dB. Obviously this is going to sound a bit treble peaky to say the least and I'm looking for a 7dB attenuation.

I keep getting in a muddle with my resistor calculations and I've received conflicting information as to where in the circuit they should go. Can one of you knowledgeable peeps add the resistors into the diagram below for me please? I'd rather not get into adding L-pads as I'd like the values fixed to match the custom builds.

Ta! :)

http://i192.photobucket.com/albums/z121/Filterlab/12db5KHz.jpg

[Marco]

Nice to see you popping in again, mate. Hope life is treating you well :)

Marco.

[Filterlab]

Hello!

Yep ta, busy though! This place looks very nice and busy.

How's you and Del?

[Martinh]

Hi Rob,

I'm not sure of your exact figure, but if you look at this page you will see how to calculate the resistor value for the tweeter impedence and required attenuation.

http://www.diyaudio.com/forums/multi-way/189847-introduction-designing-crossovers-without-measurement-2.html

BTW it's a great guide for constructing and tweaking crossovers.

Edit: I reckon you'll need a series resistor around the same value as your tweeter impedence. Also note on page 1 of the guide the need to add a parallel resistor across the tweeter to flatten the tweeters impedence.

Cheers,

[Marco]

Hello!

Yep ta, busy though! This place looks very nice and busy.

How's you and Del?

You're always busy, matey, so nothing new there! :eyebrows:

We're cool, thanks. Del's up to her eyes in marking homework from her college pupils (she's a college lecturer now, dunno if you knew).

Yup - we've looked after the old place for you, dude - nothing else would do considering all the work you put into it! Maybe now that it's wintertime, we'll see you checking in more often. Hope so :cool:

Marco.

[Filterlab]

Thanks Martin H, now sorted. That gave me the layout I needed and I realised I was using the Butterworth crossover design. Added the resistors as below with 4.43Ω and 6.46Ω values (or as near as) to achieve the 7dB attenuation. I found a resistor value calculation table too which may help other folks (who are as thick as me when it comes to electronics!). :)

8 Ohm, 12dB second order, 5 KHz high pass crossover with 7dB attenuation.

http://i192.photobucket.com/albums/z121/Filterlab/12dbsecondorderhighpassfiltercrossover5Khz8Ohms7dB Attenuation.png

http://i192.photobucket.com/albums/z121/Filterlab/Resistorvalues.png

[Martinh]

That's probably a good starting point, although you need to take into account the tweeter in parallel with the 6.4 ohm resistor will increase the attenuation a bit.

Using the method in the guide and assuming an 8 ohm tweeter, I get:

R parallel 6.4 ohms.
Capacitor ~ 4.4 microfarads
Inductor ~ 0.23 mH
R series 3.6 or 4.7 ohms

Not far off :)

BTW do you use a circuit diagram software for those schematics?

[John]

Welcome back Rob great to see you posting again

[awkwardbydesign]

Thanks Martin H, now sorted. That gave me the layout I needed and I realised I was using the Butterworth crossover design. Added the resistors as below with 4.43Ω and 6.46Ω values (or as near as) to achieve the 7dB attenuation. I found a resistor value calculation table too which may help other folks (who are as thick as me when it comes to electronics!). :)

8 Ohm, 12dB second order, 5 KHz high pass crossover with 7dB attenuation.

http://i192.photobucket.com/albums/z121/Filterlab/12dbsecondorderhighpassfiltercrossover5Khz8Ohms7dB Attenuation.png

http://i192.photobucket.com/albums/z121/Filterlab/Resistorvalues.png
Wouldn't putting the 6.46ohm resistor there halve the impedance? And then to retain the same xover frequency, you would need to double the capacitor and halve the inductor? Approximate figures only. Or does it make no difference, one resistor before and one after the xover?

[Martinh]

Wouldn't putting the 6.46ohm resistor there halve the impedance? And then to retain the same xover frequency, you would need to double the capacitor and halve the inductor? Approximate figures only. Or does it make no difference, one resistor before and one after the xover?

Yes, that's what my calcs indicate.

I may be wrong though :scratch:

Cheers,

[Filterlab]

Wouldn't putting the 6.46ohm resistor there halve the impedance? And then to retain the same xover frequency, you would need to double the capacitor and halve the inductor? Approximate figures only. Or does it make no difference, one resistor before and one after the xover?


Yes, that's what my calcs indicate.

I may be wrong though :scratch:

Cheers,

So should I put the resistors in series before the capacitor - or just change the cap and inductor values to the ones suggested by Martin? It's an 8 Ohm tweeter by the way.

[Filterlab]

I did the diagram with Pages by the way. It's Apple's word processor which happens to have layout design built in.

[Martinh]

I'm pretty sure the circuit layout should stay as it is.

Can anyone else double-check my figures?

[Filterlab]

I'm pretty sure the circuit layout should stay as it is.


That's what I thought, it seems to be the norm so to speak. I really don't want to burn out a pair of brand new ribbon tweeters so I want to get it right! :)

[awkwardbydesign]

I hope someone can give a definitive answer to my question, as it would help me too. Preferably an answer that I can actually understand! (That will dumb it down nicely)

[Filterlab]

I think I'll just go down the L-Pad route. At least I can set the tweeter level to 'just right' without all the faffing about with resistors. Assuming that there's no resistors in the circuit, the high pass is correct is it not?

[Stratmangler]

The L Pad is a resistive divider network.
You'd be as well to use an L Pad to fine tune the attenuation requirement, then measure the potentiometer resistances and replace the L Pad with fixed resistors.

It also help to remember that sometimes less is more - the hifi aspects may be reduced, but sweet music (as opposed to a hifi sound) can flow from a properly aligned set of drivers

[Martinh]

My calculation is as follows:

6.4 ohm resistor in parallel with 8 ohm tweeter, gives 3.6 ohms impedence for the two together.

Capacitor value equals the inverse of this impedence value x 12.6 x crossover frequency.

1 divided by 3.6 x 12.6 x 5000 = 4.4 micro F

Inductor value equals impedence value divided by 3.15 times the crossover frequency

3.6 divided by 3.15 x 5000 = 0.00023 or .23 mH

Then for the series resistor, you use a value equal to the tweeter/parallel resistor for -6db of attenuation. So if you go to the next size down, you should achieve around -7 db. This resistor will need to be tweaked to fine tune the tweeter level and it should not affect the crossover frequency.

These rule of thumb calcs are based upon the steps in the article I linked to.

Hope this helps,

[Martinh]

I think I'll just go down the L-Pad route. At least I can set the tweeter level to 'just right' without all the faffing about with resistors. Assuming that there's no resistors in the circuit, the high pass is correct is it not?


Yes, without the resistors, the high pass looks correct for an 8 ohm tweeter.

Are you thinking of one of these for the attenuation?

http://www.ebay.co.uk/itm/L-Pad-Attenuator-50W-8-Ohm-Wirewound-Volume-Control-/230650651940?ssPageName=STORE:HTMLBUILDER:SIMPLEIT EM&refid=store

They look interesting.

[Filterlab]

The L Pad is a resistive divider network.
You'd be as well to use an L Pad to fine tune the attenuation requirement, then measure the potentiometer resistances and replace the L Pad with fixed resistors.

It also help to remember that sometimes less is more - the hifi aspects may be reduced, but sweet music (as opposed to a hifi sound) can flow from a properly aligned set of drivers

My thoughts precisely, plus it gives the advantage of fiddling to get it 'right' (i.e. music, not hi-fi!). :)


Yes, without the resistors, the high pass looks correct for an 8 ohm tweeter.

Are you thinking of one of these for the attenuation?

http://www.ebay.co.uk/itm/L-Pad-Attenuator-50W-8-Ohm-Wirewound-Volume-Control-/230650651940?ssPageName=STORE:HTMLBUILDER:SIMPLEIT EM&refid=store

They look interesting.

Exactly those Martin!

However, I just spoke to the chap at Connect Audio (who sells the tweeters) and he told me that the crossover sits at the start of the circuit and the attenuation comes after, as thus. He gave me the values to accomplish the fixed attenuation for my requirements:

http://i192.photobucket.com/albums/z121/Filterlab/5KHz12dBsecondorderhighpassfilter8Ohm-revised.png

However, I'm liking the L-Pad route more now and then do as Stratmangler suggested.

[Filterlab]

Anyhow, I've just got to wait for my Scandyna The Drops to sell first. :)

Cheeky link to my eBay auction right here - click it Click It CLICK IT! (http://www.ebay.co.uk/itm/190743101903?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1586.l2649)

[The Grand Wazoo]

Hi Rob,
Nice to see you - I hope all is well with you & yours.
I've been admiring the minimalism that your avatar displays for quite some time now!

[Filterlab]

Hi Rob,
Nice to see you - I hope all is well with you & yours.
I've been admiring the minimalism that your avatar displays for quite some time now!

Hello Chris!

All is good thanks, starting to settle down now. I'll do a proper 'returned' post in Abstract Chat later on. :)

That avatar is the album cover from my next release - however I started it in 2010 and I've still only completed three tracks with another waiting for copyright problems to be sorted. Not a priority at the mo!

How's you matey?

[The Grand Wazoo]

Yes, I'm fine thanks - all the better for not working today!
My comment on the minimalism of your avatar was a bit of a joke as the image doesn't seem to be showing. I liked the one I was able to see!

[Martinh]

Exactly those Martin!




They look pretty handy, even if its just to to tweak the level and then substitute fixed resistors later.

I was thinking of putting some of those into my speakers to adjust the woofer crossover. It would adjust the amount of forwardness to the sound. One Way for laid back and the other for edge of the seat.

[Filterlab]

Yes, I'm fine thanks - all the better for not working today!
My comment on the minimalism of your avatar was a bit of a joke as the image doesn't seem to be showing. I liked the one I was able to see!

Oh, I see. :) It's showing for me. How odd!

The proof.... :D

http://i192.photobucket.com/albums/z121/Filterlab/ScreenShot2012-10-22at190404.png


They look pretty handy, even if its just to to tweak the level and then substitute fixed resistors later.

I was thinking of putting some of those into my speakers to adjust the woofer crossover. It would adjust the amount of forwardness to the sound. One Way for laid back and the other for edge of the seat.

I think it's the simplest in terms of circuitry and it does add that tweakiness which audiophiles are always a bit fond of. I'll have a think, I'll probably end up on the L-Pad route though.

[awkwardbydesign]

Anyhow, I've just got to wait for my Scandyna The Drops to sell first. :)

Cheeky link to my eBay auction right here - click it Click It CLICK IT! (http://www.ebay.co.uk/itm/190743101903?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1586.l2649)
Aww, those are so cute!

[awkwardbydesign]

Yes, without the resistors, the high pass looks correct for an 8 ohm tweeter.

Are you thinking of one of these for the attenuation?

http://www.ebay.co.uk/itm/L-Pad-Attenuator-50W-8-Ohm-Wirewound-Volume-Control-/230650651940?ssPageName=STORE:HTMLBUILDER:SIMPLEIT EM&refid=store

They look interesting.
Bear in mind, these assume that your tweeters are actually 8 ohm. Most drivers are somewhat different.

[Marco]

I'll do a proper 'returned' post in Abstract Chat later on. :)


Ahem... :popcorn: :popcorn: ;)

Marco.

[Filterlab]

Ahem... :popcorn: :popcorn: ;)

Marco.

Ooops! You know what I'm like, up to my neck in it, and now with a baby too...

I'll do one either later this evening or tomorrow morning. ;)

[Marco]

Lol - no worries, matey. I know the score, dude... Whenever you get a chance :)

Marco.

[Filterlab]

Aww, those are so cute!

Thanks man, like little aliens they are - aliens that kick butt hard! :booty:

[Filterlab]

Ok, I have many parts in my possession; L-Pads, terminals, silver plated copper wire, red acrylic cubes for mounting - but no tweeters or crossover components yet.

I decided to go for an 18dB crossover rather than a 12dB as it seems to be recommended for ribbons, certainly safer anyway. I can't wait to get them built and up and running. Hopefully Mr. Postie will deliver the main components tomorrow . :)

[Filterlab]

I'll do a circuit diagram of the 18dBs when I have a mo. :)

[kininigin]

Hi rob,

Can you check your messages,i sent you a pm a while ago regarding repairing an ipod touch.

Do you still do that sort of thing? :cool:

[Filterlab]

Hi rob,

Can you check your messages,i sent you a pm a while ago regarding repairing an ipod touch.

Do you still do that sort of thing? :cool:

Hello!

Nothing in my inbox, but it's something I can do no problem. PM me again. :)

[kininigin]

Cool,pm sent.