FR125S Measurements and Filters

[lovechild]

I've come to the conclusion that the 0.1mH inductor is used for practicality rather than it being ideal (you're right, the smallest air core on madisound.com for example is 0.1mH). This might neccesitate a little unwinding if the rest of the values look ok.

Your opinion is appreciated as always.

hi vikash
my expierience with notch filter is also limited, but from the graphs your 8k notch looks fine to me, better than valis. I think that'd be worth a try as the high frequencies are a bit week for my taste - I have the components around, so maybe I will unwind one of my 0.1mHs the correct value and test it on the weekend.

...to bad I can't measure, so can only report what I hear.

When things get less insane here, sure! 🙂

thanks Geek, that would be great!

best, LC

 

[soongsc]

Hi George, it's just one driver. This isn't the final FR I'm working with atm. I am waiting to finish spraying the cabs, after which can line them both with foam and then measure the final FR of both.

It would be interesting to see how they sound. I have tried various notches to reduce cone breakup an other humps, but they always created lose of sound stage accuracy. Some times driver performance may vary from lot to lot, which is one more thing to consider.

One notch is the best when also combined with BSC to balance the whole audio spectrum.

 

[Vikash]

How would I combine the notch to include BSC? My baffle is 175mm wide (211mm including the bevelled edges) x 281 high.

There is no baffle step effect shown on any of the measurements I've seen so far. When measuring at 1m etc, shouldn't the baffle step show up?

 

[lovechild]

Bsc

I actually begin to think the the rise, starting at 600-700Hz is the bafflestep.

If you take the formular from TrueAudio
Baffle Step fb3 = 115 / WB (where WB is the baffle width in meters)
you get 638Hz for a 18cm baffle, that's about where the rise starts in your graph.

But that would mean the driver has a dip or series of dips in the upper midrange and the peak at 8k isn't that dramatic.

This would kind of strengthen GEEKs theory (or better experience) that when the midrange clears up, after an extraordinary long break-in period, all is fine.

or am I totaly off tracks now?!?

😕
LC

 

[Vikash]

Hmm, I guess on retrospection the ripple effect of baffle step is pretty clear from around 700Hz to 3kHz, which as you say means that there is a large dip in response 3kHz upward?

The bottom line being that no further BSC is required I guess.

 

[soongsc]

How would I combine the notch to include BSC? My baffle is 175mm wide (211mm including the bevelled edges) x 281 high.

There is no baffle step effect shown on any of the measurements I've seen so far. When measuring at 1m etc, shouldn't the baffle step show up?

The fact that MLS signals are not truely low frequency signals may be the reason why the baffle step does not show. Additionally, 1W testing is really not realistic, it's just good for sales.

The easiest way is to run "the Edge" to generate initial BSC values, add a cap just using listening to determine which sounds right, and then compensate the impedance.

Baffle diffraction ripples would normally be ignored. It does more harm than good to try to flatten those out.

 

[Geek]

thanks Geek, that would be great!

Ok, I've re-measured one of the two drivers today.

From my original measurements here, there has been a very slight (insignificant, IMO) change, other than in Fs:

After 3 hours:

Diver 1:
Fs: 68 Hz
Re: 7.1 ohms
Le: 0.297 mH
Z @ Res: 44.1 ohms
Qms: 4.35
Qes: 0.835
Qts: 0.7

After 200++ hours:

Diver 1:
Fs: 73 Hz
Re: 7.1 ohms
Le: 0.310 mH
Z @ Res: 44.1 ohms
Qms: 4.44
Qes: 0.854
Qts: 0.716

 

[Vikash]

Fs can barely be counted as changed (and has gone up).

In my measurements after 50-60 hours, Fs went down a tangible 15Hz (~20%) (VAS up by ~40%, Qts down by ~17%).

But T/S will not show up your percieved mid/top end break-in changes. I think LC was hoping for some FR graphs 😉

 

[lovechild]

I think LC was hoping for some FR graphs 😉

Yes, that's what LC was hoping to see.

Vikash, did you already do some listening with the notch filters?

LC

 

[Vikash]

Not yet. I finished spraying the primer yesterday. Hopfully I'll have it finished by the weekend to take final measurements and start on the filters...

 

[stappvargen]

Hi Vikash,

Maybe a stupid question but:
Why have you chosen a parallell notch filter instead of a series notch filter?

Regards,
Niclas

 

[Vikash]

Hi, a series notch filter as I understand it is used to reduce the impedence peak at Fs: http://www.speakerbuilding.com/content/1041/

 

[validator]

Hi,

thats right - a series notch is for impedance correction (upper picture) and parallel notch is the one we are talking about!
You don't have to look from the drivers point of view - it's the parts point of view. All parts are in parallel to each other and than in series to the driver.

Regards
Thorsten

 

[stappvargen]

Thank you both.

/Niclas

 

[soongsc]

Hi, a series notch filter as I understand it is used to reduce the impedence peak at Fs: http://www.speakerbuilding.com/content/1041/

This is the Zobel that goes in parallel with the driver for impedance correction.

 

[Vikash]

😕

A Zobel is used to correct the rising impedence at the upper range.

 

[lovechild]

As you're just talking about Zobels, when would a Zobel be usefull?

 

[Vikash]

A zobel will flatten the impedence rise caused as a result of VC inducance. This allows crossovers in that region to function better/more predictably.

http://www.trueaudio.com/st_zobel.htm

 

[lovechild]

Thanks!

 

[validator]

Hi,

to visualize Vikash's words hear a picture of a Zobel function. A Zobel can just be calculated with Le and Re.

For a series notch to control the impedance peak present at the resonant frequency you need the following data:
Driver DC Resistance (Re)
Driver Free Air Resonance (fs)
Driver Electrical Q (Qes)
Driver Mechanical Q (Qms)

Regards
Thorsten