[Larpy]

I'm using Lii Audio F15 drivers as my main speakers and, just in the past two months, I've added stereo GR Research servo subs in H-frames.  For the most part, I'm delighted with the sound: with my Radio Shack SPL meter (calibrated to correct the meter's shortcomings in low bass and upper treble), I measure +/– 3 dBs from 25 Hz to 5K Hz, but between 6K and 7K there's a 6 dB spike.  I'd like to try building a notch filter to smooth this peak.  I haven't done this before and I'd like some guidance.

According to diyaudioandvideo.com's Parallel Notch Filter calculator, I should use a 1.87mH inductor and a 75uF capacitor.  As I understand it, this is a straightforward matter of adding the inductor and cap in parallel before the positive terminal of the F15 drivers.  A resistor (the calculator suggests a 2.65 ohm no matter what attenuation value I choose) also in parallel determines the amount of attenuation.

I ran a frequency sweep through GarageBand (I'm pretty low tech) using its parametric EQ to simulate a notch filter that attenuated 4 dBs at 6.3K with a Q of 5.0 and that smoothed out the peak fairly well.

Before I order parts (from Danny), I want to make sure what I'm planning makes sense.  Should I indeed use a parallel notch filter? With the above mentioned values for inductor and cap?  What resistance value will give me 5 dBs of attenuation?  According to Lii, the F15's impedance between 6K and 8K is 12-15 ohms.

Or is a series notch filter a better idea?  If so, why?

As I said, I'm a hobbyist who's comfortable building amps, but I'm brand new to DIY speaker building.  I appreciate any help you can offer.  Thanks. 

[Larpy]

I've been searching past posts in the GR circle that mention notch filters and found this one:

https://www.audiocircle.com/index.php?topic=103006.0

Reading that thread, it looks as though what I need is what Danny calls a "shunt filter" that sends the notch frequencies to ground.  So such a notch filter is not parallel but series, and in series from the positive terminal to the negative terminal of the speaker.

Am I understanding this correctly?  Or does Danny's advice in the thread above only apply to a notch filter added to a woofer/tweeter crossover and not a FR driver like I have?

If I use a parallel notch filter, I'll need a 75uF cap and, since it's in line with the FR driver, I hesitate to use something like a Solen cap, but 75uF is a hefty cap and serious money for a high quality cap.  So would using a shunt series filter allow me to use a lesser cap and not compromise the sound?

Playing with the parallel notch filter calculator, if I widen the bandwidth of the notch just a little, I can use a 40uF cap and a 1mH inductor.  That would be more reasonable for cost.

But I still don't understand if I should use either a parallel notch filter in line with the driver or a series filter to ground or if either one would work.

[Danny Richie]

I just measured one of those drivers last week for a customer. That was not a full range driver. It did have a peak at about 6kHz but it fell like a rock after that. There was no top end.

I wish I would have saved the raw driver measurements.

I designed a two way crossover for it and a large voice coil tweeter and it worked out pretty well.

[Larpy]

My pair peak at 6.5K but there's a flat shelf between 7K and 10K.  Around 11.5K they drop like a rock, with virtually no output at all above that.  But my ears can no longer hear 12.5K, so it's not a problem for me.

So I don't need a tweeter but a fix for the 6.5K peak.

I wonder if the pair you measured hadn't been fully broken in yet.  My pair sounded dreadful for the first 30 hours. 

[Danny Richie]

My pair peak at 6.5K but there's a flat shelf between 7K and 10K.  Around 11.5K they drop like a rock, with virtually no output at all above that.  But my ears can no longer hear 12.5K, so it's not a problem for me.

So I don't need a tweeter but a fix for the 6.5K peak.

I wonder if the pair you measured hadn't been fully broken in yet.  My pair sounded dreadful for the first 30 hours.

Burn in doesn't effect the measure frequency response. It can effect it a little below 200Hz, but that is way out of the range in question.

I can calculate a real notch filter for it though to fix the 6kHz peak.

[Larpy]

That would be great.  Thank you!

[Danny Richie]

That would be great.  Thank you!

Okay, I configured one from some measured impedance sweeps. I have all of the parts in stock and the cost is not very much. Just give me a call.

[alanhuth]

HI Danny,

In case you are tracking new posts here, this is the thread about Lii F15 notch filter. 

I want one. 

Thanks,

Alan Huth

[alanhuth]

Bump