Crossover Design Changes Based on Horn Dispersion

[toddalin]

Your two inch port is tuning the cabinet to ~47Hz... not ideal for a subwoofer. I haven't studied those woofers, but I am sure you would be happier with a lower tuning frequency or perhaps a sealed box. Either modification will likely extend the bass and make it a bit truer sounding.

As for the extended midrange performance, I wouldn't count on a heavy coned sub to provide "quality" reproduction above a few hundred hertz... sure it will make noise at 700Hz and above, but it will also very likely sound pretty colored and wooly.

Another interesting thing about ported boxes that your mentioning tweeter holes has reminded me. I discovered that simply having four unfilled 1/4" holes for tweeter mounting can measurably change the tuning frequency.


Widget

Agreed that a 2" hole in the box is far from ideal, but was an easy trial. If I unblock the 3-3/4" hole on the back (that used to house the port), the tuning goes way up, the upper bass gets much louder, and the spectral balance really goes to he--.

Unforetunately, the woofer now partially blocks this port so the port tube (3-1/2" x 7") had to be removed from the cabinet and this port closed off.

"As for the extended midrange performance, I wouldn't count on a heavy coned sub to provide "quality" reproduction above a few hundred hertz... sure it will make noise at 700Hz and above, but it will also very likely sound pretty colored and wooly."

This is the 2205/2235 in the L200 cabinet (although at 1 meter) with one port blocked and no crossover in the system. Do you think this is any less wooley?

L200_2235_only.pdf (39.6 KB, 21 views)

[grumpy]

Do you think this is any less wooley?

I think that the WT10GTi is not a typical car subwoofer...
No real point in running it all the way up to 1KHz, but in a
sealed box, it will probably work OK. "Keeper"-type crossovers
might be overkill.

[Zilch]

"Keeper" was lifted from L200B and modified for three-way:

http://manuals.harman.com/JBL/HOM/Te...L200B%20ts.pdf

I don't believe we changed anything in the LF section, but Todd can verify.

JBL conjugates are rarely textbook Zobels, rather, custom and integral to the filters....

Edit: Here's the schematic. Todd runs the UHF directly rather than cascaded, as I recall:

http://audioheritage.org/vbulletin/s...6&postcount=62

The ones I built are here:

http://audioheritage.org/vbulletin/s...370#post105370

Footnote: A year and a half later, that system is still set up here. They were "Keepers," indeed....

[toddalin]

"Keeper" was lifted from L200B and modified for three-way:

http://manuals.harman.com/JBL/HOM/Te...L200B%20ts.pdf

I don't believe we changed anything in the LF section, but Todd can verify.

JBL conjugates are rarely textbook Zobels, rather, custom and integral to the filters....

Zilch is correct with minor exception:

The 7.5 ohm resistor in the Zobal network was reduced to 7 ohms due to lack of availability of the 7.5 ohm piece. I think that at the time I reviewed some of the other JBL crossovers and found a 6-7 ohm resistor used in the Zobal for a 2235 or maybe 136A.

The HF boost circuit (1 uF, 0.16 mH, 5 ohm) was omitted.

A 20 ohm 12 watt resistor was placed in parallel with the mid and high.

Other changes in the circuit would have no bearing on anything but include:

Addition of Theta Audio-Cap 0.1 uF by-pass caps on all caps

A 33 uF to replace the two 16.5 uFs in the Zobal network.

A 24 uF to replace the two 12 uFs in the LF

A 24 uF to replace the two 12 uFs in the HF

Two 8.2 uF to replace the 16.5 uF in the HF

The noted addition of the N7000 components using 0.5 mH inductors.

[Zilch]

Compare to Grumpy's results on Todd's driver(s) here:

http://audioheritage.org/vbulletin/a...1&d=1191219641

[grumpy]

Cool. With all of Todd's CV cabs semi-soffit mounted and two-wall
reinforcement, I doubt the port would be needed. L40 cab = 1.8ft3?

[Zilch]

L40 cab = 1.8ft3?

Seems I calculated it at 1.6 cuft some time ago.

http://audioheritage.org/vbulletin/s...152#post132152

In any case, this driver is eating up a substantial chunk....

[Zilch]

1) These are lease-breakers. If I crank them much more, it seems like the cabs will self-destruct. No sub required, but some better bracing certainly is.

2) Depth-wise, the drivers barely fit in L40, which is just under the recommended vented box size, 1.6 vs. 1.75 cuft. I might have to remove a patch of fiberglass from the rear in the area of the vent, as there's not much clearance there.

3) L40 tuning is too high; its 3" port is 7.5" long, whereas W10GTI specs say it should be more like 12". See the port response, where it's clear the wrong tuning is generating a boomy bump at the bottom end. I'll fix that with a 3" elbow and a short length of duct, as required.

4) High frequencies above 2 kHz sound nasty. It looks like crossing at 800 Hz is a good choice, and 1.2 kHz may be workable. I have some concerns about IM distortion, as the cone is really pumping to make the extended bass, but I also read somewhere that IM is fiction. Can't say I know what to listen for, actually.

5) It's 3110A and 3120A shown, the latter lowpass having too high "Q". AutoEQ immediately yanked the bump out, but the HF is apparently well handled for now:

[4313B]

1) These are lease-breakers. If I crank them much more, it seems like the cabs will self-destruct. No sub required, but some better bracing certainly is.

Yeah, they're too high Q for my taste, the old LE10H is about as high a Q as I want in a driver, but these W series are loads of "fun" in confined car spaces (kid's bedrooms too).

I'll fix that with a 3" elbow and a short length of duct, as required.

What kind of group delay are you going to get out of that?

[grumpy]

I don't really understand why sealed wouldn't be just fine...

[Zilch]

What kind of group delay are you going to get out of that?

Nasty, but still O.K., maybe. Red = vented, Blk = sealed:

[Zilch]

I don't really understand why sealed wouldn't be just fine...

EBP (Fs/Qes) says it's basically a closed-box driver.

Sealed is just fine with boundary reinforcement, as you suggested above, -10 dB @ ~24 Hz without it.

Vented is better for freefield, or plain ol' driving parents crazy, -10 dB @ 20 Hz. It's L100 boom moved down an octave.

These are not very efficient, 84 dB @ 1W, and are not going to take rated power at those frequencies, bottom, but vented (perhaps either,) will play mighty damn loud for a 10" driver down there....

[toddalin]

These are not very efficient, 84 dB @ 1W, and are not going to take rated power at those frequencies, bottom, but vented (perhaps either,) will play damn loud for a 10" driver down there....

Granted they are inefficient. Does 84 dB @ 1 watt consist of the standard 2.83 volts (into an 8 ohm load), or are you basing it on 3.46 volts into a 12 ohm load for a real 1 watt rating? I don't imagine you're running it at 3 ohms. Can you imagine two in a cabinet at 6 ohms with a 2425? Talk about mini goliaths.

[Zilch]

The 2.83 V spec over 3 Ohms is 2.67 Watts, if thats how they're spec'ing it. 1 Watt would be 4.26 dB lower, so I don't know who's zoomin' what with that.

I can never make sense of car audio numbers.

Where'd I get 84 dB? I clicked the "Calc" button for 1-W SPL in BB6P driver parameters, and it says 83.93 dB... :dont-know

[toddalin]

The 2.83 V spec over 3 Ohms is 2.67 Watts, if thats how they're spec'ing it. 1 Watt would be 4.26 dB lower, so I don't know who's zoomin' what with that.

I can never make sense of car audio numbers.... :dont-know

I thought that maybe the rating was a result of your personal measurements where you knew th input voltage and this would shed some light on it.

Spec sheet notes a sensitivity (2.83 V @ 1 M) of 92 dB. It doesn't say, but I assume that is into the 2.95 ohm load parallel wiring as some of the other spects are also based on the parallel wiring. That would equate to 2.71 watts and 86 dB at 11.8 ohm load series wiring.