Null and Void at 630 and it Hertz!

[toddalin]

Ahh, the ever continuing saga and quest for a flat, pleasing sound.

Those who have been following my "Keeper" crossover threads know that I've been fighting a (loosing) battle to get some sembalance of a flat frequency response, especially through the critical vocal range. To this end, I built crossovers that should be an ideal match for the components.

When that failed, the woofers were redone (less than 2-year old authentic JBL cones and remagnetized last Monday) and test out perfectly normal as per a 2235 specs using Woofer Tester-2. Nice strong BL factor too now (23.5)! Thanks for coming by last night Dave (Grumpy), so we could test this out.

The problem appears to be a null at about 630 Hz. The null is down about 11 dB from the average signal and is fairly sharp in contour.

Thinking it may still have been the crossovers, they were rewired from their original configuration (smaller Zobal cap and bigger Zobal resistor) to pass more highs to no real avail. The 11 dB null persisted.

The crossovers were rewired again changing both caps (from 24 mF and 33 mF on the Zobal per JBL N200B specs to 15 mF and 24 mF on the Zobal) again to no avail. (Still have the same null.)

OK, lets' be really sure it's not the crossover. When the woofer is connected directly to the speaker tap..., a 10-11 dB null at 630 Hz.

This is smack dab in the critical portion of the vocal range. In fact, when playing pink noise, (and looking into the void), as soon as you speak, that 630 band comes on nice and strong.

We can only conclude that it is not the crossover, but some manifestation of the woofer in its environment. (Yes, I made sure that all eqs were off.)

Does anyone have any ideas on trying to determine what could cause such a drastic "suck-out" right at about 630 Hz?

[toddalin]

That's weird?? Wave length at 630Hz is 21 1/2 inches. So half wave is 10 3/4

You have anything at 32" from them or some multiple where you could get a strong reflection to null it out??

What happens in the middle of the room??

How high is the center of the woofer off the floor?? If it was 16" off the floor there and back would be 1 1/2 wavelength so it would be 180 or out of phase.

Just a shot in the dark that's quite a null. That's kinda high to be a room placement issue.

Rob

Don't think so.

[toddalin]

Well maybe you do. The L300 cabinet isn't all that much different with the woofer spacing with a L200 if I remember right. Your are on pedestals that look higher than stock. What do you get when you measure them?? Figure there and back you only need 16" off the floor.

Could simply not be the issue but it couldn't hurt to check.

Rob

? = ~14"

I really don't think that's the problem.

[toddalin]

I connected the Behringer directly to the 2205/2235, turned the pink noise up to -13, laid the mic on the floor and the speaker pretty much exhibited the classic 2235 response pattern. Surely I was on to something!

This then led me to believe that there could be a problem with the Yamaha (RX-Z9 http://www.yamaha.com/yec/products/p...1&CTID=5000300) invoking it's own sonic signiture, even with all eqs turned off. OK, possible progress! This would make sense because I replaced the 130A shortly after replacing the A1 with the Z9.

I dragged out the old Yamaha (DSP-A1 http://www.yamaha.com/yec/products/p...1&CTID=5002600) and ran the Bnger directly into the amp input by-passing all processing.

But no... As soon as I raise the mic off of the floor..., there's that drop-out in the 500-650 range. I've tried pillows on the floor and around the speaker, again to no avail.

So, as long as the mic is on the floor, no problem (except it doesn't pick up the tweeter).

I guess I'm just going to have to lay on the floor when I listen. Got to be a better solution.

[grumpy]

yeah... thought mic on the floor might separate "floor bounce" issues from other effects...
I don't really want to haul a 4430 over (yet).

goofing w/ parametric EQ in the Behringer -did- put back energy in the nulled area;
wasn't in an effect or tape loop, so only noise was listened to in this mode.

Still wonder about the L200 cab... Q measured pretty high IIRC, & rear panel cancellation
distance would be about right ( case of 'glass being 1/2 full? ).

[Tim Rinkerman]

I wouldn't trust what a Behringer device was telling me if my life depended on it....

[toddalin]

I wouldn't trust what a Behringer device was telling me if my life depended on it....

The Bngr only confirms what the ear doesn't hear (at least in this case). The vocal suck-out is very obvious as Grumpy can atest.

[edgewound]

Shove a big 'ol slab of R30 directly behind the woofer in the cabinet to see if that mitigates any rear cabinet wall cancellation. Is the rear cabinet wall rigidly braced?

[toddalin]

yeah... thought mic on the floor might separate "floor bounce" issues from other effects...
I don't really want to haul a 4430 over (yet).

goofing w/ parametric EQ in the Behringer -did- put back energy in the nulled area;
wasn't in an effect or tape loop, so only noise was listened to in this mode.

Still wonder about the L200 cab... Q measured pretty high IIRC, & rear panel cancellation
distance would be about right ( case of 'glass being 1/2 full? ).

If this is related to rear panel cancelation, there is something that can be done. Originally the crossovers (or something) bolted to the back brace. There are still screw holes there. A piece of thin plywood could be bolted in place and would only slightly reduce the overall cabinet volume. The reflection distance to the back of the woofer would be altered slightly.

[toddalin]

Shove a big 'ol slab of R30 directly behind the woofer in the cabinet to see if that mitigates any rear cabinet wall cancellation. Is the rear cabinet wall rigidly braced?

Typical JBL L200 cabinet. There is a brace behind the woofer that runs side-to-side along the back wall. There are also front-to-rear braces along the side walls.

[grumpy]

Shove a big 'ol slab of R30 directly behind the woofer in the cabinet

The vocal suck-out is very obvious as Grumpy can atest

I wouldn't trust what a Behringer device was telling me if my life depended on it....

Works well enough as a "for indication only" device. I've calibrated a B-mic vs a $$
Earthworks measurement mic and it's certainly flat enough to represent the wide-ish null in
the FR around 600Hz. ... and my life doesn't depend on it. -grumpy

(got started late & the main test was woofer BL after re-mag... other equipment was left @home.)

[toddalin]

Shove a big 'ol slab of R30 directly behind the woofer in the cabinet to see if that mitigates any rear cabinet wall cancellation. Is the rear cabinet wall rigidly braced?

If this is the case, wouldn't we also see the suck-out with the mic lying on the floor? I mean, wouldn't it be there at any mic position?

Also, it is manifested in the center channel cabinet, and that's a completely different cabinet (which is another reason I was thinking it may have been the Yamaha).

[4313B]

I don't really want to haul a 4430 over (yet).

Bring over a regular 2235H and bolt it in his boxes if you're so inclined and test it.

I guess I'm just going to have to lay on the floor when I listen. Got to be a better solution.

You're incredibly persistent, I'll say that much. I would have bagged the whole mess, sold a vette and bought a pair of Everest II's instead. You have what appears to be a really nice room and you would probably do well to invest in today's equivalent of the Hartsfield.

[edgewound]

If this is the case, wouldn't we also see the suck-out with the mic lying on the floor? I mean, wouldn't it be there at any mic position?

Also, it is manifested in the center channel cabinet, and that's a completely different cabinet (which is another reason I was thinking it may have been the Yamaha).

Todd,

Please allow me to be perfectly frank with you.

You now have a reasonably modern foundation to build a very capable system around your "2231" woofers (2205 core + 2235H recone kit).

It seems to me you still have LE175 mids and those god awful sounding(by today's standards) 075/2402 ear bleeding bullets that will never get you a pleasing high end response unless you have total HF hearing loss and need that shrill tweeter to get any semblance of "treble".

Do yourself a favor if you're going to stick with the furniture that you have.

"Upgrade" to a 2425/2426 or LE85/2420/2421 on an "OSAR" waveguide horn and a 2404H-1 or 2405 tweeter and see if that helps. To be perfectly honest with you, you are completely wasting your time with the mids and highs that you've got. While you're at it....build a crossover that that would be somewhat like a 4333. Somewhere here you have to let go of all the frustration that you are experiencing with what you've got and send good money after good components without trying to reinvent the wheel. All the tools are right here for the taking.

Get rid of those "bullets". Somembody on eBay will take them off your hands to mate with a D/K/E130 PA system.

Sorry to be so blunt...I want you to enjoy the music....not bang your head against the wall.

[4313B]

Or just ask Zilch about the 2452H-SL and his favorite waveguide.