Passive Radiators

[GordonW]

I am thinking of replacing the single 6th order vented bandpass box in my Nissan truck, with a pair of slightly smaller bandpass boxes (for stereo bass).

The only issue, is that the ports required to do that, would be prohibitively big, and take up WAY to much box volume. In fact, the current box was about as small as could be done, and still have reasonably low vent velocity. Using slot or pipe vents in an even smaller enclosure- well, that just ain't gonna cut it...

So- I am planning to do a pair of passive-radiator 6th order bandpass:

View attachment 2870135


Each box will have an internally mounted 7" woofer (probably a Dayton Audio), and a 7" passive radiator tuning the front chamber, and a second 7" passive radiator tuning the rear chamber. Should be able to get down to 22 Hz f3 (!) before cabin gain is considered- and even lower, in vehicle. With two of these, it should be PLENTY of output (should be about the same as a pair of 10" in sealed boxes, only with more low end extension). And the boxes will only be about 7.5" tall... leaving plenty of space behind the front seat in the truck, for tools, luggage or other stuff...

Regards,
Gordon.

Well, this project has changed.

I decided to make the cabinets, where they sit on top of the plastic compartments on each side of the rear area (where the jack and such live), right against the jump seats on each side. Here's a cross-sectional diagram of what it's going to look like:



The "cutout" in the bottom corner, will allow the box to sit on top of the plastic compartments. I think I can actually attach some hooks on the sides of the box, to use the seatbelts for the original jump seats back there, to hold these in place- which will allow easy access to the jack and tools, whenever needed. This also allows the middle space behind the front seats, to be completely empty- nothing will have to sit on top of the boxes.

This is using some different drivers now- the Dayton DS165-4 6.5" subwoofer, and a pair of the Dayton DS215 8" passive radiators, per box. It will actually go lower than the box I originally spec'd out. And the cool thing? With the 8" passive radiator- the cutout is 7.125" diameter- larger than the outer diameter of the woofer. I can remove the woofer through the passive radiator hole, if needed. No need to disassemble the box- just remove the PR, then remove the woofer...

Regards,
Gordon.

 

[Lavane]

Well, this project has changed.

I decided to make the cabinets, where they sit on top of the plastic compartments on each side of the rear area (where the jack and such live), right against the jump seats on each side. Here's a cross-sectional diagram of what it's going to look like:

View attachment 3318676

The "cutout" in the bottom corner, will allow the box to sit on top of the plastic compartments. I think I can actually attach some hooks on the sides of the box, to use the seatbelts for the original jump seats back there, to hold these in place- which will allow easy access to the jack and tools, whenever needed. This also allows the middle space behind the front seats, to be completely empty- nothing will have to sit on top of the boxes.

This is using some different drivers now- the Dayton DS165-4 6.5" subwoofer, and a pair of the Dayton DS215 8" passive radiators, per box. It will actually go lower than the box I originally spec'd out. And the cool thing? With the 8" passive radiator- the cutout is 7.125" diameter- larger than the outer diameter of the woofer. I can remove the woofer through the passive radiator hole, if needed. No need to disassemble the box- just remove the PR, then remove the woofer...

Regards,
Gordon.

Very cool. Catching the back wave from the subwoofer with one of the PR's.

 

[GordonW]

Very cool. Catching the back wave from the subwoofer with one of the PR's.

Yes. PR vented front AND rear cabinets (6th order bandpass).

Regards,
Gordon.

 

[Rick Owen]

Yes. PR vented front AND rear cabinets (6th order bandpass).

Regards,
Gordon.

Interesting, why is the volume to the PR's different? Very curious.

 

[GordonW]

Interesting, why is the volume to the PR's different? Very curious.

Different woofers require different ratios of front chamber to rear chamber volume, to give a specified bandwidth and frequency response range, in a bandpass enc;losure.

With these woofers- if the chambers in this box were the same size- the bandwidth would be way too narrow. It would be almost a "one note bass" box. Great, if you want to do "sound competition", but terrible for playing music.

There is no "magic ratio" of chamber volumes- each speaker in each application, has a different alignment, that works best.

As it is- this box is flat from about 22Hz to about 78Hz, f3 on each end. To get that, it required a chamber of 0.12 cubic feet for the small chamber, and 0.65 cubic feet for the large chamber. Small chamber is tuned to about 55Hz, and the large one to about 22Hz.

The great thing about using passive radiators in a box like this? It's EASILY tune-able in the vehicle. If I have too much upper bass? Make the small chamber passive radiator heavier, to tune it to a lower frequency. Not enough low bass "weight"? Remove a bit of weight from the large chamber passive radiator, to tune it to a higher frequency. Much easier than changing port length- it's literally just bolting and unbolting metal washer weights from the back of the radiators.

Regards,
Gordon.

 

[Lavane]

Different woofers require different ratios of front chamber to rear chamber volume, to give a specified bandwidth and frequency response range, in a bandpass enc;losure.

With these woofers- if the chambers in this box were the same size- the bandwidth would be way too narrow. It would be almost a "one note bass" box. Great, if you want to do "sound competition", but terrible for playing music.

There is no "magic ratio" of chamber volumes- each speaker in each application, has a different alignment, that works best.

As it is- this box is flat from about 22Hz to about 78Hz, f3 on each end. To get that, it required a chamber of 0.12 cubic feet for the small chamber, and 0.65 cubic feet for the large chamber. Small chamber is tuned to about 55Hz, and the large one to about 22Hz.

The great thing about using passive radiators in a box like this? It's EASILY tune-able in the vehicle. If I have too much upper bass? Make the small chamber passive radiator heavier, to tune it to a lower frequency. Not enough low bass "weight"? Remove a bit of weight from the large chamber passive radiator, to tune it to a higher frequency. Much easier than changing port length- it's literally just bolting and unbolting metal washer weights from the back of the radiators.

Regards,
Gordon.

I've seen passive radiators with a wing nut on the back. I guess it's used to stiffen up the cone, allowing more or less movement?

 

[Rick Owen]

I've seen passive radiators with a wing nut on the back. I guess it's used to stiffen up the cone, allowing more or less movement?

It's there to facilitate adding weight, usually in the form of metal washers.

 

[Rick Owen]

Different woofers require different ratios of front chamber to rear chamber volume, to give a specified bandwidth and frequency response range, in a bandpass enc;losure.

With these woofers- if the chambers in this box were the same size- the bandwidth would be way too narrow. It would be almost a "one note bass" box. Great, if you want to do "sound competition", but terrible for playing music.

There is no "magic ratio" of chamber volumes- each speaker in each application, has a different alignment, that works best.

As it is- this box is flat from about 22Hz to about 78Hz, f3 on each end. To get that, it required a chamber of 0.12 cubic feet for the small chamber, and 0.65 cubic feet for the large chamber. Small chamber is tuned to about 55Hz, and the large one to about 22Hz.

The great thing about using passive radiators in a box like this? It's EASILY tune-able in the vehicle. If I have too much upper bass? Make the small chamber passive radiator heavier, to tune it to a lower frequency. Not enough low bass "weight"? Remove a bit of weight from the large chamber passive radiator, to tune it to a higher frequency. Much easier than changing port length- it's literally just bolting and unbolting metal washer weights from the back of the radiators.

Regards,
Gordon.

Ok, you are confusing me a bit, as I see only one woofer, and two PR's, (each with a different chamber volume). My best guess that is that each chamber is tuned to a different Frequency, and this is effect is extending the frequency response?

 

[Lavane]

It's there to facilitate adding weight, usually in the form of metal washers.

Thanks. I looked a few up. They do have one or more thick metal slugs depending on the PR model.

 

[GordonW]

Ok, you are confusing me a bit, as I see only one woofer, and two PR's, (each with a different chamber volume). My best guess that is that each chamber is tuned to a different Frequency, and this is effect is extending the frequency response?

Yes, a bandpass box has to have the two chambers tuned to different frequencies. That allows the phase shift of the higher frequency chamber, to cancel out the phase shift of the woofer (relative to the other chamber, the output of the woofer is at 180 degrees/inverted polarity). In this frequency range- the output of the two vents adds together, to boost sensitivity.

Regards,
Gordon.

 

[Rick Owen]

Yes, a bandpass box has to have the two chambers tuned to different frequencies. That allows the phase shift of the higher frequency chamber, to cancel out the phase shift of the woofer (relative to the other chamber, the output of the woofer is at 180 degrees/inverted polarity). In this frequency range- the output of the two vents adds together, to boost sensitivity.

Regards,
Gordon.

Very interesting, could this be done to an enclosure that has two woofers mounted Isobarically?

 

[GordonW]

Very interesting, could this be done to an enclosure that has two woofers mounted Isobarically?

I'm not sure I am understanding the question.

Yes, it is possible to make an isobaric loaded bandpass enclosure.

But, the isobaric woofers would be directly coupled to each other (using a sealed "tunnel" between them, of as small air volume as possible, for true "isobaric" operation), and the bandpass enclosure chambers would be on either side of the isobaric-loaded drivers.

Here's what that basically would be configured like, in a general theoretical sense:



Regards,
Gordon.

 

[Lavane]

I'm not sure I am understanding the question.

Yes, it is possible to make an isobaric loaded bandpass enclosure.

But, the isobaric woofers would be directly coupled to each other (using a sealed "tunnel" between them, of as small air volume as possible, for true "isobaric" operation), and the bandpass enclosure chambers would be on either side of the isobaric-loaded drivers.

Here's what that basically would be configured like, in a general theoretical sense:

View attachment 3320876

Regards,
Gordon.

How would this be wired? One woofer for each channel? Wired out of phase from each other?

 

[GordonW]

How would this be wired? One woofer for each channel? Wired out of phase from each other?

One woofer would have to be in inverted polarity, to the other, so they would act in "push-pull".

For it truly to act as an isobaric enclosure- both woofers would need to be fed the exact same signal. A stereo signal would cause issues, due to the difference between the signal on the two channels- a change in effective box tuning, distortion, and such.

Regards,
Gordon.

 

[Lavane]

One woofer would have to be in inverted polarity, to the other, so they would act in "push-pull".

For it truly to act as an isobaric enclosure- both woofers would need to be fed the exact same signal. A stereo signal would cause issues, due to the difference between the signal on the two channels- a change in effective box tuning, distortion, and such.

Regards,
Gordon.

Thanks.

 

[Rick Owen]

I'm not sure I am understanding the question.

Yes, it is possible to make an isobaric loaded bandpass enclosure.

But, the isobaric woofers would be directly coupled to each other (using a sealed "tunnel" between them, of as small air volume as possible, for true "isobaric" operation), and the bandpass enclosure chambers would be on either side of the isobaric-loaded drivers.

Here's what that basically would be configured like, in a general theoretical sense:

View attachment 3320876

Regards,
Gordon.

Ahh, ok, no way to pull this off in my currently configured enclosures, but I do have another pair I could play with.

Any idea how it might would with a pair of these:

 

[GordonW]

Well, this project has changed.

I decided to make the cabinets, where they sit on top of the plastic compartments on each side of the rear area (where the jack and such live), right against the jump seats on each side. Here's a cross-sectional diagram of what it's going to look like:

View attachment 3318676

The "cutout" in the bottom corner, will allow the box to sit on top of the plastic compartments. I think I can actually attach some hooks on the sides of the box, to use the seatbelts for the original jump seats back there, to hold these in place- which will allow easy access to the jack and tools, whenever needed. This also allows the middle space behind the front seats, to be completely empty- nothing will have to sit on top of the boxes.

This is using some different drivers now- the Dayton DS165-4 6.5" subwoofer, and a pair of the Dayton DS215 8" passive radiators, per box. It will actually go lower than the box I originally spec'd out. And the cool thing? With the 8" passive radiator- the cutout is 7.125" diameter- larger than the outer diameter of the woofer. I can remove the woofer through the passive radiator hole, if needed. No need to disassemble the box- just remove the PR, then remove the woofer...

Regards,
Gordon.

I got these running today.

I had to make one change- it was going to be difficult, to put enough mass onto the Dayton DS215 passive radiators, to get a low enough tuning frequency in the larger chamber. I remembered having a pair of home-made passive radiators made from old Peavey Scorpion 10" frames, using a disc of 1/2" MDF, an Advent 9" foam surround, and a couple cylinder-shape MDF discs, cut to fit a flat spider. That MDF was far heavier than the Dayton radiator started with, proportionally to to the cone area- so, it was much easier to tune for the right box frequency.

The difference between these, and the previous port-vented bandpass enclosure? HOLY COW. A LOT more "effortless" sounding. Better transients, more impact. Actually having more than enough vent area, makes a huge difference. Even though the amp is producing LESS power driving the two new enclosures (it was bridged onto a single 4 ohm cabinet before, now it's a 4 ohm cabinet per channel, in stereo, which should be just slightly higher than half the power, total as bridged mode)- it's got a lot more usable output. Less distortion than before, and it absolutely shakes everything in the truck, on organ pedal tones. All on about maybe 45 watts per woofer.

Between having the bass be stereo now (I can clearly hear better stereo image and less localization of the bass compared to the previous mono sub), and better dynamics- this is a lot better sound. And between the two cabinets- they only occupy maybe 40% more space (the original cabinet was just over 1 cubic foot total- these are both about 0.75 cubic feet each) than the first one- and due to the fact that they sit on top of the jack storage area- the usable storage area is virtually unchanged. Major improvement, overall.

Regards,
Gordon.