MOX in parallell with a 1 mH inductor for the B200

Rafal · « **Reply #120 on:** 11 Jan 2007, 01:40 pm »

Do you guys ever find that you end up playing your B200 OB louder without the filter? I had Tannoy System 800A active studio monitors before (which have an incredibely flat freq. response) and I think that I am playing mu B200 OB louder (at least that's what my wife tells me). I have the bottom end supported by a sub and I'm wondering if there is a some sort of mid range recess (louder low and high frequency). It is more noticable on jazz recording with a trumpet (like Miles Davis). Do you think a filter would help?

On other note, does anyone know where I could get a full frequency (20hz to 20 KHz) test tone CD?

Vinnie R. · « **Reply #121 on:** 11 Jan 2007, 02:52 pm »

Hi Rafal,

Quote

Do you guys ever find that you end up playing your B200 OB louder without the filter?

I find that I play it louder *with* the filter. The sound is more balanced to me with the BSC, so I can really turn up the volume and enjoy it.

Best regards,

Vinnie

scorpion · « **Reply #122 on:** 11 Jan 2007, 08:54 pm »

Rafal,

You could try this one: http://www.nch.com.au/tonegen/index.html . Works fine!

/Erling

markC · « **Reply #123 on:** 11 Jan 2007, 10:23 pm »

I agree with Vinnie; With the BSC in place, It takes "the sting" out of the upper mids, (which I found very exciting for a while, but soon became a little irritating). With the BSC I play louder, as the mids are tamed down compared to the low end response. It's cheap to try-just buy some budget inductors and resistors and try it out. If you prefer the new sound, then you can replace the elcheapos with high quality parts; if you don't like it as well, you'll only be out a few bucks.

Biarritz · « **Reply #124 on:** 13 Jan 2007, 09:53 am »

Hi,

I have been following this discussion and the Gravity Well of a Dark Star for a while. I found some very interesting information there. 6 Months ago I bought the B200. At first I placed them a vioght pipe enclosure that I build for my Philips 9710. Meanwhile I was thinking about putting them in an open baffle like the Visaton NoBox.

Since my listening room is not very big, I decided to go for some small enclosure and used the Omega 8 as an example. The measurements of my enclosures are a bit different then the Omega 8, but the volume is this about same as are the double vents from Scan Speak.

When I had them up and running I like the sound, but it was to bright for my taste. First I build a 10" sealed sub to support the lower frequencies and when I read about this thread, I decided to try a correction circuit and the results were very satisfying.

I decided to have them measured. My local DIY speaker part supplier www.speakerland.nl has a professional measurement room and last Wednesday my speakers were placed in front of the mic. They were measured with and without the correction circuit (8 Ohm MOX and 1 mH inductor). I was very happy with the results of the correction circuit.

You can see it on my website at http://www.cadillac.demon.nl/Project_B200.htm

konut · « **Reply #125 on:** 13 Jan 2007, 12:31 pm »

Welcome Biarritz! Very well done all the way around! A most informative first post. Its a shame you couldn't get a FR and phase plot with the capacitor in place. aa

scorpion · « **Reply #126 on:** 13 Jan 2007, 04:00 pm »

Biarritz,

It is nice to have more measurements of the B200. Your results are very much in line with german independent measurements and apply to OB B200s also. It shows too that Visaton's own measurements rather underestimate the treble rise and that the correction LR-circuit restores balance appropiately. Very good !

An aperiodic enclosure is quite suitable for the B200 but it does need correction too. You should enjoy the brilliant B200 sound like the rest of us.

/Erling

markC · « **Reply #127 on:** 14 Jan 2007, 03:15 pm »

Try a zobel on the b200 and that impedance curve will flatten out nicely. It allows the LR circuit to really do it's job.

Biarritz · « **Reply #128 on:** 14 Jan 2007, 06:58 pm »

Scorpion:
I hope these measurements is some good food for you all.
Perhaps in the near future I will try a open baffle for this speaker. As you may have seen on my website I have tried this concept with my vintage Richard Allan speaker. My wife liked them too since they could be folded together and put away in a corner. My problem was how to add bass power without using those large woofers. Integrating this speaker with a closed sub is much easier I think.

MarkC:
I will try a zobel. 6,8 Ohm + 47uF like in the Visaton designs. My EL34 triode Push Pull amp (soon to be KT88) will probably like that very much.

Konut:
Perhaps in a few months when I have enough listening hours to get to know the new setup I will have them measured again.

scorpion · « **Reply #129 on:** 14 Jan 2007, 10:56 pm »

Biarritz,

Measurements are always good to have. On page 10 in this thread there are some simulations which I performed for various LRC and Zobel combinations that I think will give a reasonable picture of what this kind of circuit will do to frequency response of the B200. Perhaps you saw it already.

/Erling

markC · « **Reply #130 on:** 15 Jan 2007, 01:28 am »

Quote from: Biarritz on 14 Jan 2007, 06:58 pm

MarkC:
I will try a zobel. 6,8 Ohm + 47uF like in the Visaton designs. My EL34 triode Push Pull amp (soon to be KT88) will probably like that very much.

My calculations, (O.K computer's calculations), suggest a 6.2 ohmR and a20ufC.
I used a Mills 12W resistor and a Solen cap. Fairly inexpensive.
I also have a notch filter targeted at 13.5K. This really takes out the beaming of the driver.
And then there's the Visaton G25FFL tweeters......

scorpion · « **Reply #131 on:** 15 Jan 2007, 10:37 am »

My Zobel (5.6 ohms 8 mikroF) was calculated from measured Re and Le for my elements I then used Rod Elliot's
( http://sound.westhost.com/lr-passive.htm#3.1.1 ) formula to find the values.

/Erling

markC · « **Reply #132 on:** 15 Jan 2007, 10:47 pm »

Hmmm...
Quite different outcomes. I used a zobel calculator and plugged in the published values. The results were then added to a P-Spice software program to confirm results.
What were the measured values for re and le from your drivers if I may ask?

scorpion · « **Reply #133 on:** 17 Jan 2007, 11:17 am »

markC,

I remeasured my elements. They are very alike with Re = 5.3 ohms and Le = 0.28. This would point to 5.6 ohm (nearest value i resistor series) + 10 mikroF for the Zobel according to the formula. Can voice coil induction change with use ?

/Erling

markC · « **Reply #134 on:** 18 Jan 2007, 10:42 pm »

I don't believe inductance could or should change with break-in. Your measurements are quite different than the published specs. Especially the inductance. A difference between the published .5 mH and an actual of .28 mH is substantial. I'm currently experimenting with high pass x-over values and I couldn't believe the difference in sound when changing between a .025 mH and a .05 mH inductor. So if the voice coil inductance is off by .22 mH, this is something to seriously think about. I guess I'm going to have to break down and buy an LCR meter.
Plugging in your measured values to the calculator that I used, I get 10 uf and 6.6 ohms. Very close to your calcs.

MJK · « **Reply #135 on:** 19 Jan 2007, 01:40 am »

Quote

Can voice coil induction change with use ?

I doubt it. But voice coil inductance changes with frequency by quite a bit. An LCR meter will only give a value at one frequency, or maybe a couple depending on the cost of the meter, so you will be fooling yourself a little bit by using this single value. The best way I have found for designing a Zobel is to measure the raw driver using my LAUD set-up and then import the impedance curve into a program that can do some math, I use MathCad but Excel would also work. Then I iterate the Zobel values and calculate the new combined impedance until I produce a reasonably flat and resistive (zero phase) curve, these are the values of the Zobel components that I then look to buy and use.

JohninCR · « **Reply #136 on:** 19 Jan 2007, 02:08 am »

What does a flattened impedance do in terms of audible response? Is it just the impact on phase or does it affect amplitude too?

MJK · « **Reply #137 on:** 19 Jan 2007, 02:36 am »

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What does a flattened impedance do in terms of audible response? Is it just the impact on phase or does it affect amplitude too?

It should have no impact on audible response. The voltage at the driver terminals is unchanged by adding a Zobel network so the SPL response should be the same. By flattening the impedance, the Zobel allows any filter upstream to be designed based on a constant resistance and should in theory produce a predictable change in SPL response when the filter is added into the system. That has been my experience when using Zobels in my full driver speakers with passive correction circuits and SS amps.

scorpion · « **Reply #138 on:** 19 Jan 2007, 09:41 am »

Good to have a lesson on these matters. Pity the rules of thumb don't apply. My meter uses 900 Hz for measurements, 2 % accuracy according to specs. Regarding the B200 Visaton claims 0.5 mH, I measured 0.28 and Hobby HiFi and Klang & Ton (well reputed German magazines) both measured 0.18 mH. This is a great spread. One don't really know what to trust. Is there any approved standard for Le measurements ? And will voice coil inductance vary that much with frequency ?

/Erling

MJK · « **Reply #139 on:** 19 Jan 2007, 11:38 am »

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Is there any approved standard for Le measurements ?

I have no idea. I measure the impedance of my drivers as a function of frequency and work with that actual data.

Quote

And will voice coil inductance vary that much with frequency ?

I took a quick look at a couple of the drivers I have measured and a factor of two variation with frequency seems possible. So if I were to look at a range of 0.18 to 0.28 mH or 0.28 to 0.5 mH that seems plausible, but 0.18 to 0.5 mH seems a little wide of a range. I have not worked with this driver so I really can't say for sure, maybe if you designed your Zobel based on the average of the readings it would be close enough, a Zobel is fairly forgiving.