[Gothover]

The band pass baffles signifigantly rolled of the hf, as expected, but but gained spl at lower frequencies, this gain and loading gave me the bass I was looking for, and required very little EQ.

As Gedde's noted in the thread, this design has alot in common with a conventional vented monopole subwoofer. I consider it a hybrid.

Dave

[Gothover]

L.B.A.T.      "Loaded Baffle Acoustic Transducer"

Dipole or Monopole?

Using the Eminence 15A as a reference:

The Eminence driver requires a sealed box at 5.3cuft to have an F3 of 47hz,
and a ported enclosure of 88cuft to have an F3 of 22hz, which tells me there
is definately more to this design, than a simply referring to is a conventional
monopole bass generator.

The bandpass open baffle is basically a loaded open baffle design, similar to the
loading of a horn driver but without the flair.

[Rudolf]

Can someone please explain the science behind this design?

Think of it as the front chamber of a ripole. The added airload in front of the cone will increase Mms, thereby reducing Fs and raising Qts. You will get a "hump" in the response curve around (the lowered) Fs. While this can be desirable, you will lose efficiency - massively. Since there is no rear chamber, the construction will tend towards a cardioid radiation pattern.
Added to that the front chamber will act as a Helmholtz resonator which can be tuned to some frequency. This will superimpose the above effect.

[Gothover]

Think of it as the front chamber of a ripole. The added airload in front of the cone will increase Mms, thereby reducing Fs and raising Qts. You will get a "hump" in the response curve around (the lowered) Fs. While this can be desirable, you will lose efficiency - massively. Since there is no rear chamber, the construction will tend towards a cardioid radiation pattern.
Added to that the front chamber will act as a Helmholtz resonator which can be tuned to some frequency. This will superimpose the above effect.

Thanks for the additional insight, it would certainly be nice to be able run sims on the LBAT design, rather than have to build and test, then modify and retest etc. Then again, I only learn the hard way.

Dave

[SteveRB]

love it.

what is the volume of the front chamber?

are the two woofers both sharing the front chamber or is there and internal panel separating two smaller chambers?

[Gothover]

love it.

what is the volume of the front chamber?

are the two woofers both sharing the front chamber or is there and internal panel separating two smaller chambers?

The woofers have independant chambers. I don't remember the chamber size, I would have to look at my notes.

Dave

[Gothover]

The Loaded Baffle Acoustic Transducer.

The L.B.A.T. has an orfice in the front and open baffle to the rear.

As the woofer attempts to move forward, the port creates a high pressure area which causes the wave to compress.
When the woofer changes direction , rarefaction occurs.


Dave Harris

[Rudolf]

Air waves are not air jets. Above picture shows a rather static and naive understanding of sound waves. You don't want to move air through your room, but to move waves through the air. Any "acceleration" of a wave through air would result in a change of frequency. It is called "doppler effect". I don't think that such an effect is intended here.

Rudolf

[Gothover]

Thank you Rudolf.

This crued drawing was merely and attempt to visually understand what is physically
taking place in the bass chamber.

Dave

[MJK]

Dave,

Very interesting speaker.

Interesting enough for me to get sucked into modifying a MathCad worksheet to simulate the geometry to try and understand how it works. After a couple of hours I found that the port adds a sharp Helmholtz resonance in the 100 to 300 Hz range, depending on the cavity dimensions, where the crossover is being made. It was tough to get a smooth transition between the woofer and the full range driver in my model, some pretty severe wiggles were generated.

I have not modeled your eact configuration, it could be done with some more effort, but I do not see much of an advantage of this concept over a basic U frame. Definitely a more challanging design and your speaker looks great. Not sure I am ready to make the extra effort.

Martin

[MJK]

 Delete

[Gothover]

Dave,

Very interesting speaker.

Interesting enough for me to get sucked into modifying a MathCad worksheet to simulate the geometry to try and understand how it works. After a couple of hours I found that the port adds a sharp Helmholtz resonance in the 100 to 300 Hz range, depending on the cavity dimensions, where the crossover is being made. It was tough to get a smooth transition between the woofer and the full range driver in my model, some pretty severe wiggles were generated.

I have not modeled your eact configuration, it could be done with some more effort, but I do not see much of an advantage of this concept over a basic U frame. Definitely a more challanging design and your speaker looks great. Not sure I am ready to make the extra effort.

Martin

Martin, thank you for your input.

This design may or may not have any advantages over a basic U frame, I have never ever heard one so cant even form an opinion about it.

I appreciate that you took the time to look over the design, your input is always welcome.

Dave 

[puppet]

Nice work Dave.

I'm interested in your impression of the AN drivers response mounted as you have it .. (U frame basically)

[Gothover]

I really could not be happier with the Audio Nirvana 10, it sounds very natural.

This driver works far better o-b than it ever did in a sealed or ported enclosure.

Dave

[puppet]

So the shrouding at the rear is of no consequence? Good to know.

[Gothover]

So the shrouding at the rear is of no consequence? Good to know.

The deep shroud actually made the drivers sound quite a bit smoother at higher levels. My original design only had 2 layers of mdf, the newest version has 6 layers.

 When I built the prototypes I simply added rings to the rear until I got the sound I was looking for, each ring changed the sound and in-room response just a little bit.

Dave

[studiotech]

Do you have a way to measure the AN driver?  I expect it to have ragged, peaky response up high.

Greg

[Gothover]

Do you have a way to measure the AN driver?  I expect it to have ragged, peaky response up high.

Greg

What kind of measurements are you looking for? I posted some FR measeurments earlier in this thread.

Dave

[Gothover]

Sorry, I guess I didn't post it.

I have and in room plot without EQ, the AN is running crossed at 200hz 1st order.




http://mysite.verizon.net/res12il11/sitebuildercontent/sitebuilderpictures/IMG_0692.JPG

[puppet]

The deep shroud actually made the drivers sound quite a bit smoother at higher levels. My original design only had 2 layers of mdf, the newest version has 6 layers.

 When I built the prototypes I simply added rings to the rear until I got the sound I was looking for, each ring changed the sound and in-room response just a little bit.

Dave

Of course. I've noticed this with a U frame build working here (woofer). From a design standpoint my mid range would need a degree of shrouding as well. I'll have to check this as well. Thanks.