Zaph ZRT 2 way build; bass tuning question

[Flagenbush]

"Bracing and dampening a cabinet should follow these basic guidelines.

1. Bracing is designed to divide each panel so as to reduce its tendency to vibrate and move the vibration frequency point upward in the spectrum. A good rule is to divide each panel unequally. In other words, don't run a divider down the middle of panel and keep bracing no more than about 5" apart. That distance really depends on the wall thickness of the cabinet and the panel size."

Loren,

5" seems like a weird rule. Is that actual bracing that interconnects panel sides (ie front with left right and back)? Or are you referring to hardwood strips (say 3/4"x3/4") securely glued to the panel sides to break up vibration resonances? Putting interconnecting bracing behind speaker cones often creates unwanted impedance "glitches" or aberrations (D'Appolito, 1998). So, I can see 5" working with the strip method but hard to do interconnecting bracing with common midrange or larger driver sizes without creating possible impedance problems...

Glass or mineral fiber board products dampen very well, but I don't recommend them for ported (non sealed) speakers for health reasons.

Brian

[Mark33]

Hi,

I have an interest in this thread because I am in the process of building a ZRT using Madisound parts.

I have read somewhere that the area of shelf ventilation holes should not add up to less than the piston area of the driver, but have not been able to find anyone who can confirm this. As I understand it, there is no actual flow of air within the cabinet, just a pressure wave.

I cannot see anything in this thread to say that you have tried using the bass driver without a crossover to eliminate the possibility of a wiring problem?

[Flagenbush]

"As I understand it, there is no actual flow of air within the cabinet, just a pressure wave."

Mark,

In a closed system (sealed speaker cabinet) one could make a pretty good argument that there is no actual air flow and that there is simply a change in pressure (as you suggest). In open systems, ported speaker cabinets, the change in pressure produced by the bass driver does indeed move air in and out of the port (provided there is a free air pathway from the bass driver to the port). This can easily be verified by taping a small paper strip in front of the port and observing it move into and away from the port as the speaker is played and the driver pulsates in and out. This is most easily observed at less than 10 HZ and specialized software and hardware make it easier to confirm.

Trying the speaker with the bass driver in direct connect (absent a crossover) would certainly confirm if there is indeed a crossover problem. Pretty sure the Zaph pre-assembled crossovers come with a schematic and it would not hurt to verify connections are correct as well.

[Loren]

Yes, I meant that the bracing would be strips of wood or whatever dividing the panel into 5" or less segments. That is for a panel of 3/4" MDF. Thicker panels may not need to be so heavily braced.

I also use cross bracing in my cabinets from wall to wall, but not every 5" inches.

[Mark33]

>"As I understand it, there is no actual flow of air
>within the cabinet, just a pressure wave."
>
>Mark,
>
>In a closed system (sealed speaker cabinet) one could make a
>pretty good argument that there is no actual air flow and that
>there is simply a change in pressure (as you suggest). In
>open systems, ported speaker cabinets, the change in pressure
>produced by the bass driver does indeed move air in and out of
>the port (provided there is a free air pathway from the bass
>driver to the port). This can easily be verified by taping a
>small paper strip in front of the port and observing it move
>into and away from the port as the speaker is played and the
>driver pulsates in and out. This is most easily observed at
>less than 10 HZ and specialized software and hardware make it
>easier to confirm.
>

I still think it is only the mass of air in the port which moves. I might well be wrong, though. I wish someone could give a definitive answer about the minimum clear area which must be left in the internal bracing. I will do an impedance sweep on the finished speakers to check for problems, but it would be nice to know the rules.

[Flagenbush]

>I still think it is only the mass of air in the port which
>moves. I might well be wrong, though. I wish someone could
>give a definitive answer about the minimum clear area which
>must be left in the internal bracing. I will do an impedance
>sweep on the finished speakers to check for problems, but it
>would be nice to know the rules.

Mark,

That's it exactly... air has mass and it is that mass that enables sound pressure to travel, vibrate or oscillate. So, I'm pretty sure we are on the same page and its more a matter of splitting hairs and semantics, particularly with closed systems. In a ported speaker the transducer acts as a piston and air actually goes in and out of the port in response to the piston movement... just like a syringe. But, air mass (or water mass or rock mass, etc) is vital... sound does not travel in a vacuum, for instance, because there is no mass for the pressure wave to propagate through. Now, does sound make wind? In the strictest sense I would have to say no, but given enough discussion over a six pack of beer I might be convinced otherwise (perhaps at very low freqs... and one's definition of wind... solar wind versus "normal" wind... is there such a thing as sonic wind? I don't know... and does it really matter?). But, I think we can both agree that a piston creates wind in an open system much like a bellows because air is actually displaced.

As far as the minimum clear area for cross bracing... I can give you no definitive answer. Having it same size as the transducer as you suggest sounds good to me because, intuitively, it would at least be a safe conservative measure. Wish I could be more definitive on this... it may depend on transducer excursion limits and frequency limits of the transducer as well system Fs.

The beer is on me :)

Brian

[Reinocoabbada]

Im considering adding an additional mid-bass driver to add a little extra low end for the front.What drivers are you using and where are they installed?