You Want Stuffing With That?

[toddalin]

I have a dip/suckout in the 2251J cabinets at 800 Hz. Both cabinets do this and while the room is an influence, nearfield measurements would indicate something closer to home. I had checked with the published JBL spectrum and found no dip at this point in the driver's response.
https://lh3.googleusercontent.com/proxy/T67TiLIYrbt45b8lwSkDcZgIj60Wm0-jM2nAkt8XZpiyfOuReJZreW9ZRRMLWc27l1a9-Pq_QlLVDwtpJqn8y048_fwCph0WylcUG2M-NOQTyqf0VeR8jrkcMIggzwJW4Kz6LFogySCeUsynmIZ_cEq-CQ

I decided that this was potentially due to a cancellation of the wavelength due to the reflecting wave in the cabinet cancelling out the motion of the cone. There is no padding in the cabinet except for a piece of felt glued to the back wall. This is the nearfield spectrum with the driver through the crossover. Rob had mentioned that he thought the speakers were a bit bright in the upper midrange. This is probably what he was hearing. The dotted lines represent increments of 2.5 dB.
https://cimg7.ibsrv.net/gimg/www.corvetteforum.com-vbulletin/2000x1333/80-dsc_0002_f00f8f20d878a283e2fd2e289b1b8aadce6a7639. jpg
I theorized that by moving the back wall forward, but not taking up a lot of cabinet volume could potentially move the null up the scale because this represents a shorter wavelength and higher frequency on the bounce. Also, if the material were "soft" it would absorb some of this energy reducing the bounce.

I cut a couple pieces of 1-1/2" thick styrofoam and made them a tight fit on one of the the cabinets with the cut out for the port. This has to be two pieces to get them into the cabinet as the back is sealed. I put the speaker back in and everything else is just as it was in the first test. This is the result of adding the styrofoam. The lower end has come up considerably, the 800 Hz dip is reduced a bit, and the 1kHz+ peak is removed leveling this part of the spectrum to that below it. (There you go Rob.) The whole band is considerably smoother.

I will try removing the styrofoam and see if I can get similar/better results using some pink insulation sitting in the loft. The styrofoam is much harder to get the cabinet pattern right.

https://cimg3.ibsrv.net/gimg/www.corvetteforum.com-vbulletin/2000x1333/80-dsc_0004_e1aa40da2549b25abc7b93f70734f450ee00c197. jpg

[toddalin]

OK, I did the other box with fiberglass insulation and decided that not only was it far easier, it gave better results so I removed the styrofoam and redid the first box too. This is the spectrum from the first box in the same position that the other pics are of. Best yet!
https://cimg9.ibsrv.net/gimg/www.corvetteforum.com-vbulletin/2000x1333/80-dsc_0002_2__9d0e649bb1d8e84943df361a03f40d2264aa4c 40.jpg

[toddalin]

The stuffing really smoothed out the 2251J. The variance across its usable band went from ~5.7 dB to ~2.4 dB. These really do embarass the L200/300s and are more efficient to boot.

Note the definition, clarity of the vocals, and liveliness, even in a YouTube video. Also note that the bass that is MIA is in (not in) the disk and it is also MIA in the direct transfer to YouTube.


https://www.youtube.com/watch?v=aoD_JAMmrHE

[toddalin]

Oh Knots, it's raining today and who wants to go out in that?

Just a regular CD played on an Oppo95 through a Yamaha RX-Z9 Receiver in "CD Direct" mode with no sub, eq, digital processing, or room correction, physical or electronic. Recorded on a Nikon D750 SLR camera.


https://www.youtube.com/watch?v=oz9z9U6yNCQ

[toddalin]

Better to stay in and listen to The Boys in the Band.

https://www.youtube.com/watch?v=39UHD3mGwmc

[toddalin]

Stuffing the box increased the slope on the 2251J so I had to decrease the cap from 10.0 to 8.0 mfd to restore the integration to the Heil.

It's been said that a YouTube video is of no use in characterizing a systems sound. It's also been said that people can't produce speakers that are better than those offered by big firms, such as JBL.

Typical sound of an L300. You can go to lots of videos and you will still hear the characteristic mask in the vocal range proabably caused by trying to shove the fundemental range through a relatively heavy 15" woofer with a foam edge. And sure there's bass, but its bloated and just sort of rumbles along. In fact, it actually makes my desk speakers rattle.


https://youtu.be/UgmBBUo56Vs

[toddalin]

Now on the Mermans in "CD direct" played on an Oppo95 through a Yamaha RX-Z9 RECEIVER. No digital processing, eq, or room correction.

Bass is now "discript" and natural. (My computer speakers "hit" but do not rattle.) Vocals are clear and presence is vastly improved. Dynamics are vastly improved. Too bad you can't hear the 3D soundstage and imaging in the recording.

These are >3 dB more efficient and can handle over twice the power of the L300s. They can play very loud very clean if desired.


https://youtu.be/W66SQS1wDUA

[DerekTheGreat]

I dig the '57 and '63ish Corvettes. ;)

[toddalin]

After I replaced the cap on the 2251J, going from 10 to 8 mF and opening the rear port (that was previously taped off), this is the new nearfield spectrum for it with the grill on. This uses the standard scale typically used in other test displays. You can see why the 2251 presents a nice coherent midrange in that it includes the entirety of the fundemental range for vocals and most instruments crossing over to the Heil just above this.

I will try to add more insulation to the side walls and see if I can completely alleviate the slight dip at ~800 Hz. Ultimately, this may not be desireable because the room seems to accenuate the 1kHz band in the sweet spot.

https://cimg7.ibsrv.net/gimg/www.corvetteforum.com-vbulletin/2000x1333/80-dsc_0005_d7bb7ebb86b9955f5b165661ae0d2e9271d5e404. jpg

[toddalin]

I dig the '57 and '63ish Corvettes. ;)

Should look in the garage.

https://cimg6.ibsrv.net/gimg/www.corvetteforum.com-vbulletin/800x533/80-image_65f4fd124529759d8fb9d623ca1db5629f7e4a89.png

[DerekTheGreat]

Wow, is that yours? Very nice example of a '64. If a wore a hat, it would be off to the body and paint people who worked on that fine piece of machinery. Just wow. Always loved those wheels too.

[toddalin]

Wow, is that yours? Very nice example of a '64. If a wore a hat, it would be off to the body and paint people who worked on that fine piece of machinery. Just wow. Always loved those wheels too.

Yes, we traded our boat (25' flybridge sedan) for it back in ~1984-1985.

The wheels are actually of my own doing and they are not the Corvette knock-offs, though that's what they resemble. They are actually 1" wider and lighter with better brake cooling. They are also a whole lot safer than the knock-offs. BTW, the paint job cost me $14K almost 10 years ago.

[BMWCCA]

She sure is pretty! :applaud: