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RE: Tweeter difference problem with 3.3Rs and more

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In Reply to: RE: Tweeter difference problem with 3.3Rs and more posted by Davy on August 27, 2010 at 07:48:02

Wimas are very good, improvement over that will be more costly. You did good.

It seems to me that you are liking the second order crossovers better than the 3rd order butterworth - which sounds "heavy" to you. I take it to mean that you are getting bass overhang at higher crossover frequencies, and a gap in the midbass when using lower crossover frequencies.

So I suggest you take the second order as a starting point, and figure out how you want it aligned and then we can calculate an equivalent PLLXO with a volume control - I would suggest a Bourns cermet for best bass (there is also a series of cermets made by a Vishay subsidiary who's name escapes me but might be easier to get a hold of in the UK), or a wirewound pot (these are normally multiturn and are less convenient but sound just as good if not better). The next best thin are PEC carbon pots. Do not get log (audio) tapers, but linear ones, they sound way better. But you will want to keep the Behringer to optimize the next room or position.

Resistors, for bass - stick to metal film or wirewound. The 0.6 Watt are likely to be just fine, but I would only use them where a higher rated metal film or wirewound are not available. After all, this is a pro audio device and can output 20 volts - most of which you are intending on burning (93.6%).

The problem with the moth is the audio taper pot, which is a variable resistor, and does not sound good with significant attenuation. It also has contacts that are subject to oxidation, but are internal, so can not be cleaned. Making a successful log taper pot is very difficult because of the necessarily variable width of the trace.

Follow Ups:

RE: Tweeter difference problem with 3.3Rs and more - Davy 13:59:44 08/27/10 (3)
Hi Satie,
Sorry for the delay in replying, - had to get a bit of afternoon emergency shut eye again!
So that�s great about the Wimas, - had no idea they were decent. I look forward to putting those in my PLLXO on Sunday, so I have all Wima caps in it.

Yes you are dead right about the 3rd order Butterworth, - at higher crossover freqnecuies, - by that I mean up to about 250 Hz, the sound is too heavy and not right, like this the mid/treble sounds shut in and not transparent, - and looses air etc. And when you put the freq down there is hole in the midbass liek you say and also the lower mid start to become a bit too absent.

Using second order Bessel at about 205-215 Hz and a higher volume level really does blend better to my ears, - the highs , transparency, sparkle and the midrange are all better. Maybe LR might be even better � I did not try it yet. Butterworth 2nd order was no good, too heavy again.

I still have to test out the parametric EQ properly on the 3rd order Butterworth, - I might be able to get it to blend a lot better using that, - there is potential there for sure.
I find it odd the 3rd order Butterworth does not sound right as this is the filter Magnepan recommend in all the manuals I�ve read with these type of 3 series (I read the MGIII, MGIIIa, and MG3.5 manuals). The 3.5 looks very similar to the 3.3 (the passive crossover design looks the same schematic, - just slighly different values used). And in the 3.5 manual it says to use 200Hz LP 3rd order and 200Hz HP 2nd order when using an active crossover, and the stock passive crososver freqs are quoted at 200Hz LP 3rd order and 300Hz HP 2nd order at the end of the manual. I am not sure if the 200Hz HP 2nd order is a typo, - it could be. In the MGIII and MGIIIa manual the active and passive crossover freqneucies the manual says are the same so it could be a typo in the 3.5 manual,
Anyway, I�ve asked Magnepan if they have the 3.3R manual or can let me know the settings it states, - just in case they are quite a bit different from what I am using. Perhaps if they don�t have it I can track down another owner that can tell me the settings the manual says so I can make doubly sure!

Will try out the L-pad using the wirewounds after I�ve got the right values!, eventually! Looking forward to that. I am going to aim for aournd 12dB for use with the Quad on the bass. and about 6dB for using the NAD on the bass, to eliminate any hiss.
Thanks again for that. Did not reaslise it was so easy to do an L-Pad.

The idea of building a 2nd order LP crossover with a level control sounds very cool, - will do more testing but I am sure it will work as the 2nd order already Bessel sounds good and I didn�t even try LR yet. That�s good I could use the higher gain Quad 606 on the bass with attenuation and the lower gain NAD going straight through to the mid/treble, and adjust the level on the bass only to get it to match.
The question is would the Butterworth 3rd order be better with a bit of tweaking with the EQ?, - not sure but I�ll see, - I understand 3rd order is not viable to build a PLLXO with ease though!

When you say I should figure out how I want my LP 2nd order PLXSO aligned do you mean Orthogonal and all that stuff?! How do I go about that and test with the Behringer what�s best, - is it the phase I have to adjust?

There is a high end audio parts store online here called hificollective,
http://www.hificollective.co.uk/
They are a bit pricey but I�ll see what they have with regards to pots etc. They do flashy resistors like Shinkos and Audio Note Tantulums, and they also do Black Gates etc.

A Technics SL1600MK2 is finishing on Ebay Germany pretty soon (one with a broken auto mechamism but is sound otherwise), - I am going to try to get it. There is also a SL17000MK2 which might go very cheap as the guy says it doesn't even spin (and the Auto doesn't work either!) Should I give the 1700 a miss if it doesn't even turn or do you reckon it could be easily fixable?(probably not I guess, - by me anyway!)
Goona get one of these for sure though, I want some dynamics from LP!, - thanks again for leading me to these decks!
All the best.
Colin
- RE: Tweeter difference problem with 3.3Rs and more - Satie 15:04:58 08/27/10 (2)
  Part of your problem matching up with the Behringer sounds like a phase problem. Remember that unless you adjust phase the Behringer will be at 0 while the phase ON THE PLLXO changes from -180 below the crossover frequency to about 0 an octave or two above it. That means you will get cancellation at some point around the crossover frequency. So try the 3rd order again and adjust phase to match the PLLXO as well as you can along with the crossover frequency. So yes, we are talking phase, polarity and orthogonality.
  
  The LR is steeper than the Butterworth, so you will probably have a similar problem - but perhaps more of it.
  
  Magnepan often suggests using second order crossovers as an alternative to the third order low passes when using an active crossover. I think this is in part because the bass is always set up as third order LP because of the great demands it puts on power amps and that it is easier to drive a third order than a second order since the odd order crossovers (at speaker level) position the current phase at 90 degrees to the voltage phase, so that the power envelope is less likely to be breached - and you have less of a chance of clipping.
  
  For cermets and wire wound pots, in linear taper, you need to look to places like digikey, molex or Arrow electronics distributors since these are not used in audio but in instrumentation.
  - RE: Tweeter difference problem with 3.3Rs and more - Davy 15:35:52 08/27/10 (1)
    Hi Satie,
    Thanks again for the great info, Many Thanks for the phase explanation, - makes sort of sense to me! (for once), - Yes I need to adjust the phase then when using the 3rd order Butterworth LP to get the crossover point to sound right, and play with the freqnecueis. So when I adjust the phase do I just try all the way from 0 to 180? It works in steps of 5 degree inrements. Should I test at like 0, 45, 90, 135 and 180 or just tune by ear? Never done this before.
    The LR I was taking about trying with the Behringer was for 2nd order like you suggested earlier today, - not tried it yet, only Bessel and Butterworth. Bessel worked better.
    
    So is this why the 2nd order LP seems to blend better with the 3.3Rs at the moment? Is the phase setting less of an issue with that, - I guess it is easier to blend 2nd order LP with a 2nd order HP, than using a 3rd order LP with 2nd order HP.
    
    Thanks as well for the very interesting explanation of why Magnepan use 3rd order in the bass as its easier on the amp than 2nd order. Is this mainly true in single drive speaker level passive mode?, - if you hook the bass amp directly up to the panel in active or PLLXO is a second order LP crossover less of a problem? I understand now why the stock 2.7 is hard to drive as its 2nd order in the bass.
    
    Thanks for the info on where to look for pots, - will get on it.
    Cheers again,
    Colin
    - RE: Tweeter difference problem with 3.3Rs and more - Satie 10:35:51 08/28/10 (0)
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