Greetings!
I've recently encountered some older articles about a particular subwoofer design by James Loudspeakers - their EMB line of subwoofers:
https://www.stereophile.com/subwoofers/904james/index.html
https://www.jamesloudspeaker.com/products/118
The "energy multiplier" sounds a bit ridiculous to me, but I guess this is just marketing talk. From what I could gather so far this seems to be a single-reflex bandpass enclosure that uses a passive radiator instead of a port or vent. However, since the front chamber is sealed, it seems to work more like an isobaric arrangement without the second motor unit.
What would be the advantages and disadvantages in this case other than potentially halving the Vas, resulting in a smaller enclosure? Has anyone experimented with this type of design before?
Ordered a few passive radiators to test this with the woofers I have laying around. I'm planning on testing with a small 4" TCP115-4 from Dayton and a bigger 8" subwoofer driver to see what the results will be. Trying to wrap my head around how to calculate the enclosures properly. Any and all advice would be very much appreciated!
I've recently encountered some older articles about a particular subwoofer design by James Loudspeakers - their EMB line of subwoofers:
https://www.stereophile.com/subwoofers/904james/index.html
https://www.jamesloudspeaker.com/products/118
The "energy multiplier" sounds a bit ridiculous to me, but I guess this is just marketing talk. From what I could gather so far this seems to be a single-reflex bandpass enclosure that uses a passive radiator instead of a port or vent. However, since the front chamber is sealed, it seems to work more like an isobaric arrangement without the second motor unit.
What would be the advantages and disadvantages in this case other than potentially halving the Vas, resulting in a smaller enclosure? Has anyone experimented with this type of design before?
Ordered a few passive radiators to test this with the woofers I have laying around. I'm planning on testing with a small 4" TCP115-4 from Dayton and a bigger 8" subwoofer driver to see what the results will be. Trying to wrap my head around how to calculate the enclosures properly. Any and all advice would be very much appreciated!
This is basic 4th order bandpass with passive radiator instead of port.
passive radiator behaves not much different than a port.
Although the cutoff rate is typically more steep with a passive radiator.
It has all the similar tradeoffs and benefits a typical bandpass 4th order has.
No the port is not powered, hence " passive" radiator
so it has no behavior or relevance to isobaric loading
For more successful passive radiator performance and low distortion.
Rule of thumb is 2x cone area of driver.
So if you used , say one 8" powered driver you would use 2x 8" passive radiators.
Since cone excursion of the passive radiator is rather high.
With any passive radiator port system. It is the general guide
to use 2x more passive for lower distortion.
To calculate is rather simple since Virtuix Cad has enclosure calculator
for 4th order bandpass, with normal vented port or passive radiator.
In enclosure designer they identify 4th order bandpass as
" Bandpass Type 1" with vent and
" Bandpass Type 1P " with passive radiator
Depending on your driver choice and what Qts value it has.
Hopefully Is more suited for just straight forward QB4
alignment if Qts is .3 or higher. If lower than .3 more suited for
BB4 or C4. So just match the bandpass to those basic alignments.
And not fart around with making up your own wild guesses like most do with sims.
That is the trick with Bandpass 4th order. They can be designed to have slightly more
output. Slightly being the word for more slightly more efficiency. Hence their energy multiplier
add copy. You basically get slightly louder, not magical "more bass" and the tradeoff with any
4th order ported or passive is less transient response, since your basically tuning higher for more output
or making the chamber smaller for more output. Hence low Qts is more desired driver.
.3 Qts or lower .4 or higher is waste of time. Low Qts basically a driver more friendly to smaller box.
Of course box ends up bigger with any bandpass for the second vented chamber.
passive radiator behaves not much different than a port.
Although the cutoff rate is typically more steep with a passive radiator.
It has all the similar tradeoffs and benefits a typical bandpass 4th order has.
No the port is not powered, hence " passive" radiator
so it has no behavior or relevance to isobaric loading
For more successful passive radiator performance and low distortion.
Rule of thumb is 2x cone area of driver.
So if you used , say one 8" powered driver you would use 2x 8" passive radiators.
Since cone excursion of the passive radiator is rather high.
With any passive radiator port system. It is the general guide
to use 2x more passive for lower distortion.
To calculate is rather simple since Virtuix Cad has enclosure calculator
for 4th order bandpass, with normal vented port or passive radiator.
In enclosure designer they identify 4th order bandpass as
" Bandpass Type 1" with vent and
" Bandpass Type 1P " with passive radiator
Depending on your driver choice and what Qts value it has.
Hopefully Is more suited for just straight forward QB4
alignment if Qts is .3 or higher. If lower than .3 more suited for
BB4 or C4. So just match the bandpass to those basic alignments.
And not fart around with making up your own wild guesses like most do with sims.
That is the trick with Bandpass 4th order. They can be designed to have slightly more
output. Slightly being the word for more slightly more efficiency. Hence their energy multiplier
add copy. You basically get slightly louder, not magical "more bass" and the tradeoff with any
4th order ported or passive is less transient response, since your basically tuning higher for more output
or making the chamber smaller for more output. Hence low Qts is more desired driver.
.3 Qts or lower .4 or higher is waste of time. Low Qts basically a driver more friendly to smaller box.
Of course box ends up bigger with any bandpass for the second vented chamber.
This helped me get the iso image out of my head.
From this page. Its got some good discussion but not specific to PRs.
audiojudgement.com/types-of-enclosures
Even more stuff to wrap your head around fourth order, then translate the port to pr.
https://audiojudgement.com/4th-order-bandpass-design/
Jeremy
From this page. Its got some good discussion but not specific to PRs.
audiojudgement.com/types-of-enclosures
Even more stuff to wrap your head around fourth order, then translate the port to pr.
https://audiojudgement.com/4th-order-bandpass-design/
Jeremy
Hi WhiteDragon, thanks for taking the time to respond!
I had no idea VituixCAD had this option, definitely will look into it and try it out.
You're right, apologies. I wasn't quite sure how to phrase it correctly. To my untrained eye the small front chamber looked more isobaric rather than bandpass.
Don't know where this rule of thumb originates from, but I encountered it frequently in many articles mentioning passive radiators. The notion of having at least double the cone area of the woofer when using PR's is a bit puzzling. Would you care to elaborate on that?
To my (admittedly limited) knowledge on this topic, the main concern seems to be with having at least double displacement capability (Vd) of the woofer. A passive radiator with the same cone area as the woofer, but with double Xmax/Xmech would theoretically work about the same as one with double the cone area and equal Xmax because both of those passives have the exact same Vd. Though in the extreme example of having the same Sd in a single passive radiator I would be veeery worried about transient response and possible distortion. Will try both and make measurements to see how it actually performs.
I had no idea VituixCAD had this option, definitely will look into it and try it out.
You're right, apologies. I wasn't quite sure how to phrase it correctly. To my untrained eye the small front chamber looked more isobaric rather than bandpass.
Don't know where this rule of thumb originates from, but I encountered it frequently in many articles mentioning passive radiators. The notion of having at least double the cone area of the woofer when using PR's is a bit puzzling. Would you care to elaborate on that?
To my (admittedly limited) knowledge on this topic, the main concern seems to be with having at least double displacement capability (Vd) of the woofer. A passive radiator with the same cone area as the woofer, but with double Xmax/Xmech would theoretically work about the same as one with double the cone area and equal Xmax because both of those passives have the exact same Vd. Though in the extreme example of having the same Sd in a single passive radiator I would be veeery worried about transient response and possible distortion. Will try both and make measurements to see how it actually performs.
No, I never exeprimented this active-passive design... I am currently working on an enclosure with the classic Isobaric configuration, with two active speakers.
But IMHO, I am not sure that this configuration belongs to a real Isobaric principle, since the front "Energy Multiplier" speaker is a passive radiator instead of an active speaker, even if it has a VAS too...
For me, it's rather a variant of what @jgaupel posted, where the port (at left) is replaced by the passive radiator (at right) :
Oh, and indeed : the "Energy Multiplier" muliplies absolutely nothing... Since it is a passive device, just like the port ! 😀
The probable advantages of using here a passive radiator instead of a port would be :
- filtering the internal resonances of the box.
- avoiding the airflow noises of the port.
The main problem with the James is the equal diameters of the devices used. Apparently, it does not sound very good for that reason.
If you use a PR one size larger, say a 12" PR and a active 10" woofer, then you can mount the woofer through the PR opening.
I designed a project called Overdrive10 with this setup, and feel it is an exceptionally well performing small subwoofer.
If you use a PR one size larger, say a 12" PR and a active 10" woofer, then you can mount the woofer through the PR opening.
I designed a project called Overdrive10 with this setup, and feel it is an exceptionally well performing small subwoofer.
Yep, PRs need approximately 2x the volume displacement of the main driver, or the PR will bottom out.
In ported systems, it's due to the PR acting at a lower frequency, but being driven to output the same SPL as the main driver. 4th order bandpass is a little more complex (the drivers will end up moving in-sync below the PR's resonance) but the principle applies.
At lower volumes, it sounds fine. It just sounds like a bottoming-out driver when you turn it up. The main driver will probably experience some weird loading as well.
As always, PRs often need added mass to get the resonance where you want it to be. This additional mass can run into the hundreds-of-grams, which mandates either a heavy cabinet or force-cancellation (use 2x PRs, placed on opposite sides of the cabinet) to ensure the finished product doesn't walk/skitter across the floor.
Chris
In ported systems, it's due to the PR acting at a lower frequency, but being driven to output the same SPL as the main driver. 4th order bandpass is a little more complex (the drivers will end up moving in-sync below the PR's resonance) but the principle applies.
At lower volumes, it sounds fine. It just sounds like a bottoming-out driver when you turn it up. The main driver will probably experience some weird loading as well.
As always, PRs often need added mass to get the resonance where you want it to be. This additional mass can run into the hundreds-of-grams, which mandates either a heavy cabinet or force-cancellation (use 2x PRs, placed on opposite sides of the cabinet) to ensure the finished product doesn't walk/skitter across the floor.
Chris
In a bandpass though, the mass required for the higher tuning is actually easier to get. You shrink the front chamber to raise the Fb, and hopefully don't need much mass to get it back to the required tuning. This way the PR is tightly coupled, and not much mass is needed more than spec.