Damping Heresy cabinets?

[JonM]

Just picked up a pair of '83 Heresies (K22, K53, K77 drivers) that cosmetically match my '76 Khorns (oiled walnut/woven cane, not that it matters!). I'm Mortite-damping the plastic/fiberglass squawker horns (surprising difference - when I tap on the inside of the horns from the front with a screw driver, the undamped horn is much more resonant in the midrange than the damped horn. The "click" of the metal screwdriver tapping on the plastic of the horn is much more "plasticky" without the damping - I can finally see why damping would really make a difference - the resonance of the horn is right in the driver's operating range. I think I'm finally becoming a believer.)

I am wondering about damping the cabinet itself. A local hardware store sells 1/8" cork sheets, and it occurred to me that these plus some 3M spray adhesive would make sheets that could easily be applied to the inside of the cabinet panels, take up minimal volume in the cabinet, and possibly damp some cabinet wall resonances.

Does this idea (or using something like Dynamat) make any sense? Does anybody know what frequencies the Heresy cabinet walls resonate at - i.e., would they be damped by cork sheets or Dynamat? Has anyone tried it and either really liked or disliked the results? I hesitate to try it, because getting those cork sheets out would be a real pain, and I imagine the adhesive would be there permanently. Only if it's completely reversible or a real definite improvement would I consider it.

Thoughts?

[Malcolm]

IMHO damping Heresy cabinets is not necessary. It does not seem to be a popular tweak. Is there something you actually hear that you want to change?

I doubt 1/8" cork would do much. Dynamat would probably do much better. You may want to try filling part of the cabinet with fiberglass insulation instead. You can play with the amount to and see what it does to the sound. Some people replace the back panel with 3/4" MDF.

[JonM]

I guess I'm reacting to a woody, boxy sound in the upper bass/lower midrange. I don't know how much of this is due to cabinet resonances and how much is due to the Heresy's box simply being way too small for that woofer (resulting in freq response problems in the upper bass). (Is the Heresy II K24 woofer any better in that department than the K22 I have?)

I had a feeling a layer of cork won't do much. I've never worked with Dynamat, so I have no idea even what it's like. (My local car audio shop told me yesterday "car stereo season is over, so we're out of it". Maybe I'll try another shop a couple of towns over.)

I can certainly play with polyfill in the cabinet, and see what effect that has. At least I know that's reversible.

Oh, BTW, a second layer of mortite on the squawker horn does make a difference on top of a single layer. (Yeah,I was a skeptic!) The "tap test" between a single layer and a double layer made the difference clear. You guys have me convinced!

FWIW, ACE Hardware's version of rope caulk seems softer and more malleable than the Mortite brand. Very slightly stickier/gooier. Might actually work better.

[Malcolm]

If you are Heresys to your Klipschorns, remember that they are bound to sound a bit different below 700 Hz. Squawker goes to 400 Hz on Klipschorn, only 700 Hz on Heresy. There may not be much you can do about any difference due to that.

If the box is too small for the woofer, I would think it would be reflected in poor low end response rather than upper bass/lower midrange problems. Some people use the K-24 to try to get a little better bass.

I suggest starting with the fiberglass fill, not polyfill. Its nonflammable. The McIntosh folks did some tests years ago and found out it is not a good idea to use a flammable material for the fill. Under certain driver failure modes, the fill can be ignited.

You'll have to experiment with the amount of fill.

If that doesn't solve the problem, I suggest the MDF back panel.

One other relatively simple thing that can be done is to install one or more dowels from side to side and top to top, or stringers along the panels, to make the panels more rigid.

If that doesn't solve the problem, you could build new cabinets out of MDF or baltic birch.

[JonM]

Before the flames start, let me say up front that may will offend the sensibilities of some purists. It was an experiment, one with interesting results. I thought this audience might be interested.

I was thinking about this boxy resonant issue some more, looking at the K22, measuring the cabinets, and just thinkin'. Well, it turns out the cabinet volume of the Heresy is roughly the same as the acoustic suspension boxes of the '70s (I estimate 1.8 cubic feet or so). What if I put a woofer that was meant for a cabinet that size in place of the K22 (which needs a much bigger box)? I mean, what damage could it do if I just sort of snuck an AR or Advent woofer in there, you know, when nobody's looking? :-)

So I did! I had a couple of the original larger Advents collecting dust, so after a few preliminary measurements of frame sizes and the like, I popped out their woofers (the ones with the phenolic ring between the metal frame and the foam surround). I made 12" diameter, 1" wide circular gaskets from 1/16" cork sheet from my local ACE hardware store (hey, they stock the stuff, so here's a free plug!), and simply replaced the K22 with the Advent woofer, mounted right where the K22 went (even the screw holes lined up - it was meant to be!), with the cork gasket between the front of the woofer frame and the inside of the cabinet's front panel. No changes to the crossover, but I did put in the polyfill - all acoustic suspension speakers use it. (Yeah, Malcolm - I saw the McIntosh burned speaker experiments. I use 1 amp fast blow fuses in my speaker wires, so overheating like that is unlikely in my case, but your point is well taken.)

Okay, this is where the purists can stop reading. What I am about to say may upset them.

I really like the results. First, there's bass! Using the Stereophile test CD, with the Advent woofers, you get real bass to 30 Hz. The K22 poops out under 50 Hz. Next, that in-your-face lower midrange is gone. Voices are much more natural, much less boxy. There's a natural warmth to vocals now that's missing with the K22. But, unlike the larger Advent, with the Heresy, you still get the benefit of the horn mid and highs - dynamics and vibrancy the Advent tweeter never could deliver. (I think there's a nice synergy between toning down the tweeter by changing it's autoformer tap - that brings the highs back into balance with the mids - and a lower efficiency woofer, which raises the effective brightness and sparkle of the overall system.) The result is a speaker that is FUN to listen to! And isn't that what this is all about?

Okay, so I didn't do a TS analysis, and lord knows the cabinet isn't adequately sealed for true acoustic suspension operation. The woofers I chose are probably not optimum, and the crossover is probably wrong for the Advent woofer (it's DC resistance is 5 ohms, versus the K22's 7 ohms, and with the Klipsch inductor in series, who knows where it rolls off). But this was a freebie - it cost me $3 for the cork. And the results are quite excellent. I think a lot of people think the Heresy has the wrong woofer (or the K22/K24 have the wrong box). My ears now agree.

Now, what I don't know is what modern drivers would be a suitable alternative to my old Advents' woofers. You'd want something with similar TS parameters and the right frame size and screw hole locations. If anybody here could identify a suitable driver, or one even better matched than the ones I chose, then others could try this change, too. It is simple, completely reversible, and I think some of you will really like it. (I know, Paul Klipsch and Henry Kloss are both shaking their heads, but what the hey!)

[EvilMinion]

I hawk this all the time, but here goes...

I did the same thing to get better LF response out of my '85 Heresys. The enclosure measures out to around 1.78 cu. ft. minus the displacement of the drivers and crossover. I used the woofer from a JBL L100 (actually the 4311, it's a model 2213.. Same driver as a 123A though), and the Heresys have great bass now. They're not 20 Hz rumblers but they go into the 30s, and sound quite clean to me. They won't match the output of my Altecs but they'll get on up there. It was a worthwhile mod, by far.. I have $180 in the woofers, sold off the K-22s that were there because I didn't want em any more. I used a little long fiber material to fill the cabinets with, as well. Also cut some strips of thin foam to put around where the back of the cabinet screws down so it seals a little better. Keep in mind JBL has used an ack-basswards way of wiring them for awhile. Positive to the BLACK terminal drives the diaphragm forward. All in all it worked great. The white cone / black dust cap looks pretty cool peeking out of there, too. Another woofer I tried that I had good luck with was a Speakerlab W1208R. Those are hard to find, but it sounded good to me.

I'm gonna try to send a picture of them.

[jedro]

i used 1/2" fiberglass tacked to the sides & replaced the back panel with 3/4" mdf, all this is fluff, the key to the hereseys in my opinion is a simple wiring modification, won't cost a thing & is reversible if you don't like it, look for older posts on this bb for the mod & if you cannot find it email me

[JonM]

EvilMinion -

Actually, the 2213 looks like a good match. I ran its TS parameters through Rick Carlson's BoxPlot program, and the response looks good - a small 2 dB peak at 80 Hz, down 5 dB at 40 Hz, and 12 dB/octave rolloff below that.

The TS parameters for JBL woofers are available on the JBL website. For the 2213, the key parameters are:

fs - 25 Hz

Qts - 0.49

Qms - 8.5

Qes - .52

Vas - 235 liters

Xmax - 7.87 mm

Re - 4.4 ohms

Le - 0.6 mH

Mms - 85 grams

Is that driver still available from JBL? If not, its TS parameters give me a starting point to look at other drivers. Thanks for the tip!

[EvilMinion]

JonM,

Nope.. The 2213 hasn't been made in awhile, I don't believe. You can usually find a pair on ebay for around $150 to $200 a pair. I bought mine from a guy on there with the username "jblken", he did a fantastic job of packing them and shipping, good guy. Look for 2213s, or the 123A. It's the same woofer, just the 123A went in the home version of the 4311 monitor, the L100. It's difficult to mistake this woofer, though. I was lucky enough that my neighbor had a pair sitting around and he let me try them out. Not too long after that, I went on ebay and bought a pair, been really pleased with them. Just make sure the grilles stay on all the time if you have pets, as the surround is very tacky.

[JonM]

Oh, just a few last tweaks on my hybrid Heresies:

1. Connect the squawker/tweeter feed to lug #1 of the autoformer (lowest setting, -12 dB from the input), which to my ears provides a more natural balance with the inefficient acoustic suspension woofer. Not all woofers will need this reduction of the mid/highs - more efficient ones will not. The JBL woofer EvilMinion uses probably doesn't need this because it's more efficient than my Advent woofer.

2. Disconnect the 33 mfd capacitor across the woofer. That cap rolls of the high end of the woofer faster, but the Advent woofer was designed to go smoothly up to 1 kHz. I felt like I was missing midrange detail, harmonics of bass strings and the like. Letting the woofer go higher (and the difference is very clearly audible) restores what seemed to be missing.

Note - not all acoustic suspension woofers go that high. The NHT 1259 (a wonderful woofer) is good only to probably 250 Hz, and is not suitable for this application. The JBL woofer EvilMinion uses is rated to well over 1 kHz (in the JBL L100, it crossed over to the midrange at 1500 Hz), so it is. (And it looks cool!) I don't know if it would benefit from disconnecting that capacitor - EvilMinion, give it a try and see what you think.

Now, the resulting speaker needs a lot more power. Its efficiency relative to input power is set by the efficiency of that woofer, probably around 86 dB/watt. SETs need not apply. Does that eliminate the advantage of horns? No, because the big advantage of horns is their efficiency *at the input to the driver*. That means that the diaphragms don't move much for a given output, reducing distortion and dynamic compression. Adding a different woofer doesn't change that one bit for the midrange and tweeter. So you don't get the slam of a horn woofer, but you didn't have that with the original Heresy woofer. What you have with this combination is the low end extension of a good acoustic suspension woofer with the dynamic ease of horns in the mids and highs.

(EvilMinion - I added the foam strips along the back to get a better seal - thanks for that idea! I did something similar on the front around the woofer - a cork sheet wasn't doing it, but a poly foam camping pad from WalMart let me cut gaskets that are the right size and seal great. Too bad they're blue :-)

The Heresy is a terrific platform for this sort of experimentation - it's easy to get into, its layout is wide open, the woofer is a standard 12" size, and that autoformer makes it really easy to reset the midrange and tweeter levels (thanks, Klipschguy, for that idea in the first place!). This is to encourage those of you who enjoy this sort of stuff to dive in and see what you come up with.

[EvilMinion]

Jon,

If I shelved down the mid and tweeter anymore, I'd probably only do it another 3 db on these woofers. As is, I just run the bass boost on the receiver and it's about right. I love the sound. I never had any gripe with the mid or tweeters on these things and now that they've got good solid bass response, it's a wonderful thing. I'll also try to remember to disconnect that cap from the crossover, I'm curious as to what that might sound like, as well.

[JonM]

FWIW, I actually ran measurements on a Cornwall crossover, very similar to the Heresy crossover (bigger capacitor to the squawker, which goes a little lower than the Heresy's). Each autoformer tap is 3 dB down from the previous one.

Tap Level

5 Input

4 -3 dB

3 -6 dB

2 -9 dB

1 -12 dB

On the Heresy, the original squawker connection was at tap 2 and the tweeter was at tap 3. I dropped the tweeter initially to 2 to make it more balanced with the squawker, then dropped both of them to 1, to even them out with the inefficient woofer. Note that Cornwall has the squawker and tweeter one tap higher in level, to keep up with its more efficient woofer.

[EvilMinion]

Jon,

I'll have to look at the crossovers, that might be a worthwhile thing to try on mine. Maybe 3 db down and they'd be perfect. More like my Speakerlabs (which when set flat on the tone controls extend pretty damn far), only way more efficient.

[JonM]

For those who care, I'll try to attach a little picture of one Heresy with an Advent woofer installed (yes, that's a K-horn directly to the right). I really like the sound of the acoustic suspension woofer and those horns. Believe me, I am as surprised as anyone!