Rebuilding Coral 3-Ways (B20FU20-51FW, W4-1052SD, GT-1005)

[zach_t]

Hello all, here are some pics of my latest project. I am rebuilding a pair of Coral 3-way speakers. I will reuse the cabinets and want to keep the same design theory. The Coral’s originally has a full range 10” driver, no crossover. A 4” midrange with a high-pass capacitor and a resistor in series with the driver. Finally a horn tweeter with a same value high pass capacitor as the midrange.

Drivers for my project I choice the 8” Pioneer B20FU20-51FW (http://www.parts-express.com//pe/showdetl.cfm?&Partnumber=290-045), the 4" Tang Band W4-1052SD (http://www.parts-express.com/pe/showdetl.cfm?Partnumber=264-828) for midrange and the Goldwood GT-1005 Wide Dispersion Piezo Tweeter (http://www.parts-express.com/pe/showdetl.cfm?Partnumber=270-011).

I built a prototype box before hacking into the real cabinets (which are in excellent shape). Same external dimensions as the actual Coral boxes. This is a prototype enclosure, no bracing, no adhesive in the joints, no caulk in the seams, no lining, no stuffing, no driver gaskets, etc. The blue painters tape helps seal any gaps at the joints.

From some initial in-room measurements (want to take some more), the TB 4” should roll-off around 1.5 kHz and the piezo should handle 5 kHz and up. I took measurements with the speaker in one location and the mic in four typical listening locations.

In regards to sound, tough to say. I listened to both the 8” and the 4” full-range. The 8” sounds a little hollow and muffled in my opinion (some of this may have been the enclosure). The 4” sounds nice, vocals were much more clear. Lacking bass naturally, but not objectionable for the material I was listening to. So far, I am impressed with this little 4” driver. I am concerned that with the current scheme, the 8” will handle most vocals and the 4” will handle most harmonics. The vocals from the 8” so far are not that impressive, IMHO. I am sure they will improve with enclosure bracing and stuffing.

Both alignments are sealed with a Qtc of 0.68 (couldn’t do that again if I tried, purely luck). The 8” has an F3 of 67-Hz (using actual measured T/S parameters). The 4” has an F3 of 92-Hz using factory specs.

[Chris Roemer]

I built a prototype box before hacking into the real cabinets (which are in excellent shape). Same external dimensions as the actual Coral boxes. This is a prototype enclosure, no bracing, no adhesive in the joints, no caulk in the seams, no lining, no stuffing, no driver gaskets, etc. The blue painters tape helps seal any gaps at the joints.

From some initial in-room measurements (want to take some more), the TB 4” should roll-off around 1.5 kHz and the piezo should handle 5 kHz and up. I took measurements with the speaker in one location and the mic in four typical listening locations.

In regards to sound, tough to say. I listened to both the 8” and the 4” full-range. The 8” sounds a little hollow and muffled in my opinion (some of this may have been the enclosure). The 4” sounds nice, vocals were much more clear. Lacking bass naturally, but not objectionable for the material I was listening to. So far, I am impressed with this little 4” driver. I am concerned that with the current scheme, the 8” will handle most vocals and the 4” will handle most harmonics. The vocals from the 8” so far are not that impressive, IMHO. I am sure they will improve with enclosure bracing and stuffing.

Both alignments are sealed with a Qtc of 0.68 (couldn’t do that again if I tried, purely luck). The 8” has an F3 of 67-Hz (using actual measured T/S parameters). The 4” has an F3 of 92-Hz using factory specs.[/QUOTE]

You're not asking any questions. If you were, I'd say you can probably do better. There's a LOT of overlap there (which causes combing issues). Why not let the TB play a bit lower and low pass the woofer since you don't like the sound of vocals coming out of it anyway. Then roll off the top of the tweeter and let a litttle Dayton Neo do the work of the Piezo. Also, align the mid and tweet vertically, not offset to the side as on your box. Also, you could turn the box sideways, making it deeper than wide. Also, you could vent or use a woofer capable of at least 50 Hz, if not 40 or even 35.

chris

[zach_t]

Hi Chris, yup, no questions. More of an FYI or build thread. I reserve the right to ask questions later though! :) My original intent was just to keep the same design intent as the Coral, just do it better with newer drivers. Crossover comp0nets should be minimal, so I will give ti try and see what happens. I will be posting some in-room responses shortly (ran out of time this morning). I am reusing the current cabinets, so not enough volume (even going from 10" to 8") for venting. I do plan on adding some internal bracing and lining the Coral cabinets when I rebuild the front baffles.

If everything goes together correctly, I should have a good in-room response out to 10 kHz. Question is, how will it sound? I will have wait and see on that. I may be pleasantly surprised.

[zach_t]

Here is the in room response for the 8" Pioneer B20FU20-51FW.

Front Baffle: approx. 13" wide by 21.25" tall
Speaker Position: Constant for all four measurements
Mic Position(s): 4 unique positions. 4 positions at typical listening locations.
Input Level: Constant for all four mic positions.
Smoothing: 1/6 octave

[zach_t]

Here is the in room response for the 4" Tang Band W4-1052SD.

Same conditions as last post.

- Input level may vary slightly, so you can't compare output magnitude.
- Microphone position is not 100% repeatable, so there is some error there when comparing between drivers.

[zach_t]

Here is the in room response for the Goldwood GT-1005 Wide Dispersion Piezo Tweeter.

Same conditions as last post.

- Input level may vary slightly, so you can't compare output magnitude.
- Microphone position is not 100% repeatable, so there is some error there when comparing between drivers.

NOTE: you can here the suckout around 5 kHz in the test tones. I think I recall seeing a fix for this somewhere. Like adding epoxy to the backside of the horn.