Enclosure for (2) Dayton Audio ND91-4 and (1) Peerless 830878 3-1/2" Passive Radiator

[jtice]

Enclosure for (2) Dayton Audio ND91-4 and (1) Peerless 830878 3-1/2" Passive Radiator

I am thinking about building a single speaker that uses two Dayton Audio ND91-4 Drivers and one Peerless 830878 3-1/2" Passive Radiator.

Ive read that people have had success with using a single ND91 in a vented 0.04 cu. ft. enclosure.
So, would it work out well if I made a 0.08 cu. ft. enclosure with two ND91s and one 830878 radiator?

Never used a passive radiator before, so just curious how that effects the enclosure requirements.

OR,,,
am I better off just doing a 0.08 cu. ft. enclosure with a typical tube port?
If so, can anyone provide me with what size/length I would need? Prefer to use easy to get PVC pipe.
Or I could do a slot port actually. Front facing.

Links to the driver and radiator...
Dayton Audio ND91-4
Peerless by Tymphany 830878 3-1/2" Passive Radiator

 

[chris661]

PR volume displacement should be roughly equal to 2x the volume of the main driver(s). In this case, a single 3.5" PR isn't going to keep up with the main drivers. You'll get a lot of distortion before the main drivers are really trying.

Chris

 

[TBTL]

Ported is not possible with these ND91 woofers, a port will not fit. Passive radiators behave like ports but will always fit.

 

[Prosny]

Also, if I may, Dayton Audio itself does better suited radiators for its own drivers. They have similar names to the active drivers, but end with PR. I would have a look, if I recollect correctly they even have a 5-1/4” version

 

[jtice]

Thanks guys, just looked into the Dayton radiators, and they do indeed seem to be a much better fit.
The ND90-PR is perfectly matched to one ND91 driver.
But yea, looks like I would definitely need two radiators with two drivers.
Or, I could use a single ND140-PR 5 1/4" which would be over twice the volume of the two drivers, which might fit my design better.

 

[xrk971]

Typically you want the PR to have about twice the Sd of the main driver. It needs to be modeled to get the best performance and many PR's have a bolt that lets you attach washers for added mass. Also, you can use any driver with voice coil, if it has the right TS params to be a PR. Then the voicecoil can be left open or a resistor can be connected to form an electromagnetic damper (brake) for tighter but less deep bass. Useful for cheap/budget drivers to turn into PR's which can sometimes be hard to find.

 

[jtice]

Did you mean Vd? Not Sd?
I ask because it says this on the Dayton PR specs...
Tip: As a general rule, the passive radiator(s) should have at least double the displacement of air (Vd) as the active woofer(s)/subwoofer(s) in the system.
To calculate Vd: Sd x Xmax = Vd

Does it hurt to be over twice the Vd?
Two ND-91s would be 279.68 Vd (559.36 for double)
A single ND140-PR is 779.4

The ND91 specs say 0.01 cu. ft. for sealed and 0.04 cu. ft. for vented.
If I use a passive radiator, I should use the vented volume, correct?

 

[xrk971]

Assuming same linear displacement, double Sd is double Vd. This would be the case if both cones have similar suspension stifness. If the PR hasa very soft suspension then same Sd would require 2x the displacement. This is not a good idea as high displacement is usually higher distortion.