B&C DE250 comparison on XT1086

[kstrain]

This observation, accrued over a period of months, may be of help to others looking for a 1" compression driver. The post is meant for those who have the ability to measure and correct the response themselves: no curves or designs are given.

I bought the ND1060 with the XT1086 horn in the hope they would match well, but DE250s that I already had turn out to be a much better solution (may have claimed they are good, but there are few comparisons).

Various RTA measurements were made on an XT1086 horn. The source was from a 0.5 ohm, purely resistive.
The horn was stuffed with absorbing material to reduce cavity resonances.**

The ND1060 was a good fit to the horn with minimal throat discontinuity. The DE250 required more filler to avoid a small but worrying gap.

RTA resolution ranged from 1/6h to 1/48th octave at various locations. (I'm not going to post graphs as they would be non-standard and easily misleading.)

The contrast in the smoothness of response between these drivers was surprisingly large (and repeatable). The ND1060 was tried first and showed multiple significant resonant features: a mixture of relatively high-Q resonances and comb/notch structures. The big surprize I had later on was that DE250 was very much smoother with only a few low-Q features, one not very pronounced notch feature and no sign of combing. (The drivers were exchanged a couple of times as a check.)

Equalising to about +/- 1 dB at 1/12th octave resolution from 1.5 kHz to 15KHz is relatively simple with the DE250 but far beyond my ability with the ND1060.

The measurements fit with listening experience - the ND1060 sounded unnatural on vocal sibilants no matter what EQ I tried (over a substantial time, i.e. months, while the DE250s sounded quite good on the first attempt, with just 3 biquadratic stages plus overall high pass and compensation for HF droop (CD horn and stuffing).

So I add another voice favouring the DE250.

Ken

** Thanks to Dr Geddes for the inspiration to damp the cavity modes, with a bit of thought it seems possible to do this quite well even with a (gentle) diffraction horn like the XT1086.

[tinitus]

Fore a smallish waveguide there is another you may want to try

BMS 2193 fiberglass horn...cost around 40 EUR

My plan is to mount it on the back of a baffle with additional roundings

[Brett]

Thanks Ken.
I am going to use the XT1086 in the sides and rears of my HT (mains will use something else) with the DE250's as I already have them, so your post is reassuring. I have a spunky new measurement mic to test with too.

What did you use as damping material inside the horns?

[noah katz]

"I am going to use the XT1086 in the sides and rears of my HT"

Interesting. Are they not good enough for mains use?

CD is nice in having even power response, but what about the directivity?

I have contemplated CD, or however close an 8" B&C coaxial approaches it, and aiming them upward for diffusion.

What freq is your XO?

[Brett]

Originally posted by noah katz
"I am going to use the XT1086 in the sides and rears of my HT"

Interesting. Are they not good enough for mains use?

I have something else for the mains.

Originally posted by noah katz
CD is nice in having even power response, but what about the directivity?

I have been experimenting and like the directivity better than the other options I've tried such as Sonab OA5s

Originally posted by noah katz
What freq is your XO?

Boxes are still being built, so final numbers are not set, but 1k2 seems to work pretty well.

[D OB G]

kstrain, how did you manage to stuff the XT1086s?
I've succesfully managed open-cell foam in a Parts Express waveguide, but I can't see a way to do it effectively, and symmetrically, with these waveguides.

David

[kstrain]

Originally posted by Brett

What did you use as damping material inside the horns?

Brett,

after concluding that it would be hard to get the right foam in the correct shape I tried some old loudspeaker wadding. It was unused because I did not think it very good for its intended purpose, due to it not absorbing as much as other wadding. I've had it for years and am not sure what it is (dark colour, less dense than normal wadding) .

I estimated that a few dB loss would be helpful but still easy to EQ, and kept in mind where the reflections would be most strong (at the driver, at the mouth and at the abrupt change in slope) when positioning the wadding.

I started by putting some wadding into the throat section (in the first ~5cm) until I could see just a little loss at high frequency, then used the density of that as a guide to loosely filling the rest of the volume with wadding, finally with a sheet of it right over the mouth, extending just beyond the edge.

When I started I thought I'd have too much loss, but this does not seem to be the case. Also it was easy to match a pair, the pieces used were paired and the horns are almost filled so it all stays in place.

Actually measuring the benefit is not easy and I'm mainly just convincing myself that a few dB of loss must help damp any modes there are, without significant reduction of maximum output (after digital EQ).

Might be worth a go with any wadding you have around, particularly when you can measure the loss - you can't really go far wrong there.

Oh, and of course you have some special foam to compare with to know how much loss to add ...

Ken

[Brett]

Cheers for that. I guess I'll just have to try some things and experiment. I've just got a new measurement mic from IBF Akustic in Germany and need to decide on ARTA or Soundeasy and start taking measurements.

Originally posted by kstrain
Oh, and of course you have some special foam to compare with to know how much loss to add ...

Had: they were returned.

[hasselbaink]

Interesting subject. I wonder if anyone has measurements of the DE250 (or similar) in the XT1086 wave guide?

And are 18Sound compression drivers really that bad in their own wave guides!?

Kris

[D OB G]

I haven't fitted my XT1086s yet (with DE250), but I was concerned about how much they rang when tapped.

I have covered the ribbed surface with children's non-setting modelling clay (called plasticine or "fun clay" in Aus).

There's over a kilo per waveguide there now, and they ain't ringing no more.

David