The Blackbird: a center channel to match SR71's

[lunchmoney]

Here's a center channel I just completed to match my SR71 mains.

I call it The Blackbird, a nod to the SR71 Blackbird jet.

It uses the same drivers as the SR71:

SEAS ER18RNX Woofer




SEAS 27TDFC Tweeter




Here is an approximated crossover design that Zaph (John Krutke) very kindly provided me with. It's important to note that some of the values will change. I am currently voicing and will be posting the final design in a few days. Because of the peculiar spot in which the speaker will live (AV cabinet and TV making for nearly an infinite baffle-like situation, see pix below), the final crossover design will be dialed in for my particular setup. Your results may vary. Note that the horizontal lobing is nearly perfectly symmetrical, despite the assymetrical driver layout. The SR71 was a great speaker to start with, since it's vertical lobing is almost perfectly symmetrical.




Here are some images of the design. All 3/4" mdf. Note that the flange of the tweeter is trimmed in order to get the tweeter as close as possible to the woofer. 2" Precision Port facing out the back, just like the SR71. Outer dimensions are 21.75" wide X 8.125" high X 10.75" deep. Internal volume is .5 cubic feet, not including the sealed off chamber for the crossover (to the left of the tweeter). There will eventually be a grill over it for baby-proofing reasons, by sheer coincidence the PE 1 cu ft MTM grill is a perfect fit. The small panel on the back will be for accessing the crossover. In general, aesthetics are of no concern, as it will be buried in an AV cabinet, all that will be seen is the PE grill.














Conclusion: Awesome center channel. Very detailed, yet forgiving enough for less than perfect sources (i.e. cable TV). Matches the SR71's extremely well. If you've ever heard SR71's, enough said. Most of the credit here should go to Zaph for his fantastic SR71 design. If you're looking for a center channel to match you SR71's, or just a great center channel for that matter, I highly recommend it.

[lunchmoney]

Here are some pictures from the build:

[BOBinGA]

Another quality build from the Lunchmoney factory.
Keep 'um comin'

-Bob

[Txgrizzly]

is the removable panel on the back for your crossover? i also like the insets for the magnets for the front speaker cover...
i also like your CNC style setup on your drill press to get your cutouts. how much space do you have between the spindle and the pillar to spin your work material?

[lunchmoney]

yes, the removable panel is for the crossover compartment... here's a pic:

[lunchmoney]

Here's the final crossover schematic:

[SpeakerGuy]

Does it sound good? One thing I like to use for testing center channels is the scene in Blackhawk Down where the main character is talking in a hanger.

[lunchmoney]

So after more than a week of listening, here are my impressions....

I am VERY pleased. Thrilled ya might say.

It's a perfect match for the SR71's. If you've heard how good SR71's are, you could stop right here. Enough said.

Vocals are very detailed, without being harsh or fatiguing. They are high-passed, so I can't comment much on bass response, but mid-bass is very full and satisfying. One thing I've always liked about SR71's are their super smooth, non-fatiguing sound, and the Blackbird follows suit.

Compared to the Tritrix center channel I was using before? No comparison. Much more detailed and clean sounding, much fuller mid-bass, much less fatiguing. Better in every way. That's saying a lot, since I have much love for the Tritrix.

This cost me about $200 to build, soup to nuts. Clearly this would absolutely lay waste to a store-bought speaker anywhere near that price. You might be pushing 1k to do better, seriously.

Overall, an SR71 + Blackbird front stage is simply awesome. Not a really huge, BIG speaker sound, but amazingly clean and detailed due to awfully nice SEAS drivers. Add a sub, and it's just amazing. I'm currently using a modest Dayton Ref 10" in a 1 cu ft sealed enclosure, and I'm more than happy.

Thanks for tuning in, and it is my sincere hope that others may use this info to build their own!

Cheers!

Dan

[lunchmoney]

Here's a dimensioned drawing of the final design

[crisscross]

Great build. I am building Mark's ER18 build and I think this will go great with it.

[Bent]

regarding the SEAS 27TDFC, is the flange made of something that is easily mahcined such as you did to decrease spacing?

[lunchmoney]

regarding the SEAS 27TDFC, is the flange made of something that is easily mahcined such as you did to decrease spacing?

Yes, the flange is an easily machinable plastic. ABS I believe.

I scored it, rough cut on a bandsaw, then a final pass by hand with a dremel.

You could easily do the whole thing with a dremel though.

If I were to do it again, I would have taken the flange off of the tweeter, mounted it in the already-milled tweeter recess, mount it in themilling machine, then let it be cut simultaneous to the woofer flange recess.

Too bad this didn't occur to me before it was already done :roll:

[SpeakerGuy]

LM: thanks for your response.

To anybody building this, or another design with a machined tweeter faceplate - no need to remove the faceplate, just cover the dome with a little circle of paper + some masking tape. If the dome protrudes from the faceplate, then something like a plastic cap taped on will keep the sawdust out. A router bit will make a nice clean cut - but you might get a little melted plastic bits left, that can either be scraped off with a little piece of wood or lightly sanded (just don't scratch the FRONT of the faceplate when you do that).

If you don't hear any unpleasant sibilance or "chestiness" (beyond what's actually there in the recording), and voices are quite clear - then based on your evaluation I don't think there would be anything to be gained by buying a "high end" center channel.

The only area that might be improved would be slight/modest improvement through stiffer/damped enclosure walls.

I'd be very curious to hear the difference between SR-71 / ER18DXT. I do have both types of tweeters and one pair of ER18 woofers... I suppose I'll keep my eyes out for another pair used - you don't see them being sold often (must be because of how good they are )

Thanks for sharing the design, seems like one I'd recommend - hopefully people could HEAR it before they let the sideways TM appearance bother them.

[fbov]

So after more than a week of listening, here are my impressions........Vocals are very detailed, without being harsh or fatiguing. ...Compared to the Tritrix center channel I was using before? No comparison. Much more detailed and clean sounding, much fuller mid-bass, much less fatiguing. Better in every way. ...This cost me about $200 to build, soup to nuts....

...If you don't hear any unpleasant sibilance or "chestiness" (beyond what's actually there in the recording), and voices are quite clear - then based on your evaluation I don't think there would be anything to be gained by buying a "high end" center channel....

I mentioned to Lunch on another thread (at PE?) that I've recently upgraded from a "vertical-only" sideways MTM (NatP) to a true MTM CC (Modula MTM CC), as he has to a sideways TM CC in this design. What I find curious is that a change in horizontal FR uniformity would affect vocal quality and speach recognition on axis. This was the immediate and most enduring difference I noticed. I find it curious that both of you report hearing the same differences.

At $200, this design is a great value for those who don't need the extra few dB of an MTM.

Have fun,
Frank

[lunchmoney]

The only area that might be improved would be slight/modest improvement through stiffer/damped enclosure walls.

The walls are quite stiff, note the fairly through bracing. I can't hear even a hint of panel resonance.

Damped enclosure walls I've never tried. They are lined quite well with sound deadening materials, but not any actual constrained damping layer. Maybe I'll try that on my next project.

[lunchmoney]

I mentioned to Lunch on another thread (at PE?) that I've recently upgraded from a "vertical-only" sideways MTM (NatP) to a true MTM CC (Modula MTM CC), as he has to a sideways TM CC in this design. What I find curious is that a change in horizontal FR uniformity would affect vocal quality and speach recognition on axis. This was the immediate and most enduring difference I noticed. I find it curious that both of you report hearing the same differences.

At $200, this design is a great value for those who don't need the extra few dB of an MTM.

Have fun,
Frank

Hmmm... well, comparing the Blackbird TM to the Tritrix MTM is so vastly apples to oranges that I don't think you could claim that the improvement was due to TM vs MTM.

The drivers in the Blackbird are so much better that you really can't really draw any conclusion about the TM vs MTM... you'd really have to compare speakers with similar drivers.

Even with your NatP vs Modula comparison, it's still tough to compare, since their crossovers are different.

Science requires more control over the variables

On a side note, there's not even the slightest hint of asymmetrical sound coming out of the Blackbird, despite its asymmetrical driver layout. If you sat more than 2' away from it, you wouldn't be able to tell what side the tweeter was on. Makes you wonder how many center channels are symmetrical only for aesthetic reasons, and actually suffer because of it.