Building a Heresy center - finally

[hwatkins]

Well folks, I am finally embarking on the great center channel experiment (after getting headaches thinking about the pitfalls) of creating a match for two pair of heresy in my HT/Music venue. Some of you may remember participating in answering my earlier 'testing the waters' message. I am repeating much of what I posted on audio asylum HE forum, so please excuse me if you also see it there. I have done extensive search of the forum and gotten some very good info.

I am decidedly a novice in DIY, but a voracious reader with an irritating focus when my mind is made up.

I am intent on building a new box to work as a center and to house the following - Klipsch 'E' crossover, K77 tweeter, K55-v w/700 horn and a woofer solution (my biggest issue). I have acquired the squawker and crossover and see little to stand in the way of finding a Tweeter that matches, my problem is what woofer(s) to use with the crossover (any any subsequent adjustments needed).

The woofers will also be dependent on the box size (I am doing this backwards - I have decided to start within a size range for the enclosure let's ballpark this as outside dimensions of 31" - 36" long,

10" high and 13" - 18" deep) and of course need to probably be in that 93 - 98 db efficiency range.

The 'shade tree' design is to mount the tweeter and squawker in traditional Heresy over and under with an 8 inch woofer on either side (I am very flexible here - maybe smaller woofer will do). My sub should fill very nicely from 100hz down (reciever crossover for bass will be set at 80hz). I am becoming more familiar (and confused at times) with pitfalls - enclosure size, venting, compression and on and on, but nothing has made me believe that any issue is insurmountable.

I do understand that any solution will be a compromise in some way - my primary objectives are(things I want to compromise the least) getting a mid and high freq tonal match for my other two pair of heresy, a smoothness in the lower freq from about 80hz to the cross over to the midrange, a crisp (non delayed) lower freq that is compatable with the horns and an attractive enclosure.

Way too much info and a little too few tech specs, but I thank you in advance for any input. Ideas on connecting the woofers (series/ parallel - although it looks like parallel is right for two), Impedence (I believe the E is for 16 ohms - and does it matter) expected by the crossover and a really silly need for crossover connections to each speaker (which tap to which speaker). I would normally open the back of my 1980 Hs to get connections, but they are in the ceiling and difficult to get to.

[hwatkins]

I have found schematics and wiring diagrams - so that is not needed.

[Malcolm]

I built something similar to what you are embarking on. So maybe my research can be of some help to you.

Type E crossover network is designed for an 8 ohm woofer.

Finding smaller woofers with high enough sensitivity is going to be your biggest problem. Options you might consider are:

* Replacement woofers from Klipsch for Academy or KV4

* Stephens Trusonic 80FR--shows up on eBay from time to time

* EV SP8B--shows up on eBay from time to time

* Any other high efficiency 8", 10", or 12" speakers--probably from 50's, 60's, 70's

Some kind of crossover tweak may be required. If you luck out and the two woofers you use together are with a couple dB of the original Heresy woofer, you probably won't hear a difference. If they are more efficient, all you need is a little additional resistance in the woofer circuit, either a small power resistor, or a replacement 2.5 mH inductor with higher DCR. If the woofer efficiency turns out lower than the original, you may need to change taps on the autotransformer, and maybe replace the capacitors, or pad the squawker driver and tweeter with resistors.

You may want to use a ported design to extend the bass response. The Heresy begins to roll off around 100 Hz and is 3 dB down by about 65 Hz. It is going to be hard to achieve the same response and efficiency with an acoustic suspension design using smaller woofers.

FWIW I used two 16 ohm 10" CTS alnico magnet woofers from the 70's. IMHO two 12" woofers would be even better.

Simplest way would seem to be to use Academy or KV4 woofers in box of same volume, same port size, etc.

[hwatkins]

Thanks Malcolm - that is very helpful, and I will be looking at your suggestions for speakers.

My research to this point is centering on an Eminence woofer - efficiency around 93db, which I figure I can attentuate the tweeter and squawker if need be with the existing taps on crossover - it may not be necessary.

When I run the specs on the Eminence Alpha 8 (using two speakers) I get a recommendation for a vented box. However, if I chose the closed box route and provide about 2.7 cubic feet, the spl at 70hz starts getting very close to the vented design (@100W vented SPL is 109.4 and closed SPL is 109)- below that the vented design is much better. At around 95hz the SPL becomes the same for either box. That said, the simplicity of a closed box (this being my first speaker) is appealing. I can make enough box modifications to make room for space needed. My biggest concern is that this is about 3db off from where the speaker flattens out - 300hz.

Since I am looking at running this as 'small' and let the SVS handle all info below 80hz, it seems to make some sense. What am I missing?

[hwatkins]

Um..Malcolm or anyone else - the Stephens is a 16 ohm unit - what issues do I face there?

[Malcolm]

Using 16 or 4 ohm woofers simplifies things. Two 16 ohm woofers in parallel present an 8 ohm load. Two 4 ohm woofers in series present an 8 ohm load. Two 8 ohm woofers will present a 4 ohm load wired in parallel, or a 16 ohm load wired in series.

When considering sensitivity, don't forget you have two woofers, not one.

I assume these are not going to go near a TV that is sensitive to magnetic fields. Otherwise you may want to consider using a woofer that is shielded or has an alnico horseshoe style magnet assembly.

[Frzninvt]

Why go through all the trouble of building a speaker and trying to get a tonal match, why not keep things simple and just use a fifth Heresy or buy an Academy? Geez.

[TBrennan]

You oughta be thinking about the speaker's directivity. The array you want to build will ahve some very strange directivity. It's understandable, you're just copying what most companies do. But they are far more concerned with having decent power handling and an unobtrusive box then in addressing directivity. Thus the glut of sideways psuedo d'Appolitos that plauge the center channel speaker market. Most of these speakers have a directivity pattern that is opposite of what is actually needed for good center channel performence.

If you want to do a Heresy type thing your best shot is to build a straight copy of a Heresy with it's 12" woof and just set the thing atop your TV upside-down or perhaps sideways. Of course compared to normal center speakers it will look weird but so what, it'll work better.

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