Nelson Pass: The Slot Loaded Open Baffle Project

[Nelson Pass]

Originally Posted by GRollins

Oh for cryin' out loud...

Hi Grey! You can see why I haven't had the time to finish the reply to
your email.

As you can also see, I probably did you a favor.......

[dlr]

Originally Posted by Nelson Pass

I say that clearly that the acoustic load is asymmetric front vs back. There
are other examples of such things - How about a horn without an enclosure
behind the driver? Clearly it works, and it works because the acoustic
load on the diaphragm is not symmetric.

The problem I have in considering this (assuming it's correct for sake of argument) is that if this is true, this would introduce distortion due to the asymmetry. Seems unlikely to be the case, partly because the loading on a driver is the sum of the load on both sides, one side undergoing positive pressurization while the other side is undergoing negative, simultaneously for each half-cycle with each side providing the same magnitude no matter the direction of movement. I just don't see how asymmetric loading is the issue unless it truly does result in asymmetric movement of the driver diaphragm which would not be desirable.

Dave

[CLS]

Originally Posted by Radugazon

Have you measured the FS ?

After two more pages of talking, I gues it's time to get back to the real thing.

The parameters of the woofers when they're nude on swings near floor (not entirely the same as in free-air due to more load near boundary, but close enough):




And those with them on the slot loaded OB:



Their fs drop with slightly higher Qts.

[Godzilla]

I'm just curious how the things will sound?

[bocama]

Originally Posted by kropf

To follow up my previous post (#119). The implication is that the driver diaphragm actually will move less for a particular SPL than the same driver in free space must move. I submit that this is the source of most of the disagreement on the subject.

Jeremy

But that is not the case at all. The effect you describe is the same as if you were closer to a speaker the same energy is concentrated in a smaller area but that does not have a effect if you are not very close to the slot

[Zen Mod]

well ........ just deleted at least 15 sentences , realizing that my peanut sized brain can't put it in any practical way ...... so just one thought certainly stays -

PWK's famous line (that PWK , who certainly wasn't humorless bastardo type ) , in which he was saying that world now needs just one proper 5-watt amp - later became complemented with : "and one of my big button badges in every room " ...

[bocama]

Originally Posted by Nelson Pass

Oh no......

JBL Control SB-2 Slot-Loaded Vented Subwoofer

from the text
"This subwoofer features a unique concept in passive attenuation".
Not that I pretend to understand marketing speak especially in english

[CLS]

Originally Posted by Godzilla

I'm just curious how the things will sound?

In my incomplete mockup, I'd say pretty good.

Lack of front baffle area makes it much less efficient than expected. And I got a 7~8dB dipole peak problem around 200-250Hz range. (I fixed that with digital EQ for the time being.)

Other than those, it sounds pretty good. Very clean and deep. I heard new sounds in one of my old CD during breif listening last night, some sub-bass noises, quiet but clear. Such LF --- air vibrations -- delivers an illusion that it's pressurizing the room, but of course it's not.

This low level performance fit my current requirement very well. I haven't tried higher SPL, yet, as the rest of the speaker is still under construstion.

[Salas]

Originally Posted by bocama

from the text
"This subwoofer features a unique concept in passive attenuation".
Not that I pretend to understand marketing speak especially in english

Low pass filter action of the baffle in front of the driver they mean.

[Salas]

Originally Posted by CLS

Such LF --- air vibrations -- delivers an illusion that it's pressurizing the room, but of course it's not.

Hmm, can it also be due to the air column of a slot driving the room's air always resistively.

Originally Posted by CLS

Lack of front baffle area makes it much less efficient than expected.

Its the air pocket mass loading the cone also. That's why Fs drops. So to lose some efficiency due to that also, goes with the territory.