T/S for DE250?

[dirkwright]

The data sheet provided by B&C does not list all of the T/S parameters for this driver. Anyone have them?

In order to cross over at the recommended frequency of 1.6kHz, I need a notch filter(s). There are two resonance peaks for this driver, according to their data sheet. So I need at least: Fs, Qes, Qts, and Re. I sent an email to them on Friday but have not heard back yet. Maybe it's holiday in Italy or something. I'm sure they'll get back to me eventually.

Also, does the electrical impedance change when a driver is coupled to a horn? I bought the ME20 horn to go with this driver.

[dirkwright]

Here's the DE250 datasheet.

[speaker dave]

Electrical impedance diffinitely changes when you put a compression driver on a horn. This is part and parcel to the high efficiency making the horn loading a significant part, as opposed to the typical woofer where low efficiency means that air load is fairly insignificant.

Thiele Small figures for a compression driver? They aren't typically given since woofer box modeling doesn't apply. (The system is not well represented by 2nd order highpass analogies.) What were you trying to do with them? How do you kow what notch filters you might need without measuring the driver on the particular horn you will use it with?

David S.

[dirkwright]

Originally Posted by speaker dave

Electrical impedance diffinitely changes when you put a compression driver on a horn. This is part and parcel to the high efficiency making the horn loading a significant part, as opposed to the typical woofer where low efficiency means that air load is fairly insignificant.

Thiele Small figures for a compression driver? They aren't typically given since woofer box modeling doesn't apply. (The system is not well represented by 2nd order highpass analogies.) What were you trying to do with them? How do you kow what notch filters you might need without measuring the driver on the particular horn you will use it with?

David S.

Well, it looks like I have to measure it while mounted on the horn. Assuming there is still a resonance peak in the same region as shown in the datasheet, then I'm going to need a notch filter as I wrote about above. I need the T/S parameters to design the series notch filter. The formulas are:

C= 0.1592/(Re x Fs x Qes), L= (0.1592 x Qes x Re)/Fs, and R = Re + (Qes x Re)/Qms

Huh, just realized I need Qms. Dang.

[AllenB]

I was going to describe my DE250 (mounted) impedance but I'll just attach this screenshot. I have alternated between using two and three notch filters, two for the main peaks and one purely for the response at the peak of hearing frequencies.

I can't say it will be ideal to use formulas here. The frequencies are so close that they'll interact and you need to design them as a team, and then you'll probably want to play with them in tailoring your response.

[AllenB]

Then after using two filters (other components removed for this plot).

[dirkwright]

Thank you! Yeah, this looks difficult, for sure. I have WT2 and TrueRTA so I can do a decent analysis I hope. I don't want to go active on this little project because I have a sweet 50 watt stereo integrated amp that I want to keep. I'll go active on the 3 way horn loaded system I have planned.

Speaking of WT2, I also have a pair of ME10's mounted on DE10's for another project. So, I checked out the impedance plot and T/S parameters for this combination. They are different from the manufacturers spec, but only Fs is very different. I had emailed B&C asking for the Fs of the DE10 driver, and they replied with 1.7kHz, which is about where the peak is in their plot. So, I measured Fs of 2.5kHz with the ME10 horns installed and the driver sitting on my desk aimed at the ceiling. One thing I don't get is the inductance change. I measured 0.4mH, and the data sheet says 0.1mH. I didn't think the horn would effect the inductance of the voice coil. Do compression drivers have to broken in like woofers?

I can't test the DE250 + ME20 yet since they have not arrived.

[dirkwright]

Originally Posted by AllenB

Then after using two filters (other components removed for this plot).

It looks like the peaks shifted also. This is starting to feel like mud wrestling with a greased pig.

[AllenB]

Originally Posted by dirkwright

Yeah, this looks difficult, for sure.

It's not so bad when you get the hang of it!

I have WT2 and TrueRTA so I can do a decent analysis I hope. I don't want to go active

I hope you don't think (as some misinformation would have you...) that an active system sidesteps dealing with driver issues, this would limit your success with active systems.

Fs is very different.

Compression drivers are a little different to dome tweeters. I cross mine over at 650Hz (first order).

It looks like the peaks shifted also. This is starting to feel like mud wrestling with a greased pig.

They didn't shift, my filters grazed the sides of them. It was a juggling act. I can't remember whether that's the best I could do with common values or I have fudged them a little to mod the response since the last revision. I highly recommend a crossover simulator. For this part alone you'll want impedance magnitude and impedance phase for each driver.

[dirkwright]

OK, which crossover simulator do you recommend? I also have WinSpeakerz, which is fine for boxes, but doesn't simulate crossovers as far as I know. I can calculate the values no problem, but simulating them with an actual driver impedance curve is something I don't seem to have.

Yes, I was under the impression that active systems didn't care about driver impedance, resonances, etc. Can you suggest some reading for me on this?