BillFitzmaurice.info

...in the garbage behind a large venue in the process of remodeling.

Photos are attached. Observations are as follows:

1. They are trapezoidal in shape, with rails mounted on opposing sides. This makes me think they are designed for use in a line array.

2. The installed drivers are 18", making me think that they must be subs.

3. Doing some digging around, I think that they could be characterized as "ported horns:" The front of the driver is orthogonal to the long port at the edge, and parallel to the trapezoidal side of the cabinet. The channel that they face is about 4 inches wide, as shown in the photos.

4. There is also a rectangular port in the front of the cabinet.

5. There is no dampening material inside the cabinet, making me think that it cannot be bass-reflex design.

My questions are as follows:

1. I am a DJ who plays smaller venues and I have two of these cabinets. Are they potentially of any use individually or as a pair?

2. If running one cabinet, would I want to run it on the side, with the long port along the floor for coupling? Or another orientation?

3. If running a pair, would I want to put the long ports next to each other to achieve a coupling of the cabinets? Would a coupling plate help, as described for Bill's designs?

Comments, suggestions, and answers are all welcome. These may not be the best subs in the world but the price is right and I am having fun thinking about how I might experiment with them.

Thanks,

CDM

garbage find?! Sweet!

cafedumonde wrote: ↑Thu Sep 06, 2018 6:37 pm
Comments, suggestions, and answers are all welcome. These may not be the best subs in the world but the price is right and I am having fun thinking about how I might experiment with them.

They may not be the best but it says right on the label that they are the finest !!!

Go ahead and experiment with them. Those are definitely reflex subs, around here we would call them slot loaded reflex, there may be other names for that design but they used to be common. Our local regional sound company here still uses a variation of that design.

I would calculate the area of the box and the side ports and put that into a program like winISD to model the tuning frequency of the cabinet. That will let you know where to place a high pass filter at as below that freq the cabinet wouldn't load the driver and over-excursion could happen.

My only concern is that driver looks more recent than the box does. Non sound techs usually replace blown drivers with something that they think looks better by the wattage numbers or x-max, often not realizing that ALL the thiel/small parameters are important for good performance. Just throwing a high wattage driver in the box to replace the blown one is a crap shoot at best. It may or may not perform well.

Its not shown in the photos but the drivers bear the same label as the cabinets. I expect that they are a white-label driver from another manufacturer, with the origin obscured. However, This means that they are likely original.

Thanks for all of the comments so far!!

How much do you figure they weight?

What are the cabinets' dimensions?

I tried to hook up both cabinets this morning but only got a momentary pop from one of them. I was going to open them up anyway.

The weigh about 90 pounds, with the current drivers installed.

The cabinets are trapezoidal, with the front face measuring 23.5 x 23.5 and the rear face 19.5 x 23.5. they are 23.5 deep.
Accounting for the width of the slot (4.75") and the thickness of the plywood, I estimate the volume behind the driver at 3.67 cubic feet.

The port is rectangular and measures 6.25w x 4.25h x 3.75d

Comparing the volume behind the driver to ones from other bass reflex designs that I have, it just over one cubic foot less. Of course the other designs do not have the slot.

Could someone characterize the tradeoff between volume and putting a slot in front of the driver? Is there a theory on why the slot is beneficial?

Thanks,

CDM

?? Especially interested in the theory of why the slot is beneficial.

Thanks,

CDM

The slot makes it into a band pass design.

Thanks Bill.

Does the orientation of the box matter? For example with the slot parallel to the floor vs. orthogonal? Can the boxes be coupled when run as a pair when the slots are next to each other?

I assume that your guidance on room placement still applies.

CDM

A sub is a sub, the rules for one apply to all.

Seems like it's more of a bass reflex than anything else. I'm no expert on bandpass designs but as a 6th order bandpass the tuning would seem to be rediculously wrong as there's no tuned port to speak of, it's literally just open on one side.

Look closely: That's a port. It has depth.

Which one are you talking about? I know there's an actual small rectangular port, but I'm not convinced the BFM horn mouth looking thing is a actual tuned port.