Passive radiator speakers… really a benefit?? To bassreflex speaker design

[sarumbear]

it is ? that would require insanely large boxes.

It was a continuation of the negative sentence. I’m sorry that I was not clear. 20Hz port/resonance/tuning is not the norm.

 

[Maciek]

Not noted yet but no port "chuffing" with a PR.

No chuffing but You may get out of displacement, same issue but in general yes, its easier to do a PR design than a state of the art BR, like if You wanted to follow what Kef did on LS50. If You can fit a BR large enough to keep air speed down than its fine even with a straight pipe.

 

[Maciek]

See its like with everything in audio, solve one problem and You run into another. Of course its more sensible to tune for say 25-30 hz and avoid the extreme weight and related sag but its not unusual to do it. If I remember well this PR was sold in two flavours, one with 200 grams of factory added weight and the other with 400 grams exactly for the purpose of hitting 20 hz notes.

It was a continuation of the negative sentence. I’m sorry that I was not clear. 20Hz port/resonance tuning is not the norm.

 

[fpitas]

When you use a PR you also get a response null below the tuning frequency. That may or may not matter to you, but it does add group delay and (even more) possibility of over-excursion.

 

[sarumbear]

When you use a PR you also get a response null below the tuning frequency. That may or may not matter to you, but it does add group delay and more possibility of over-excursion.

Wouldn’t you get the same from a port?

 

[fpitas]

Wouldn’t you get the same from a port?

Not the extra null. The over-excursion, yes.

 

[sarumbear]

Not the extra null. The over-excursion, yes.

I appreciate if you explain further or point to a source for me to understand what you mean. Thank you.

 

[fpitas]

The Subwoofer DIY Page - Passive Radiator Systems

 

[sarumbear]

The Subwoofer DIY Page - Passive Radiator Systems

Thank you. However, as the document says that null is very much below the resonance that I can’t imagine if it’s audible at all, especially when the speaker at those frequencies is normally generating very high distortion.

 

[fpitas]

Thank you. However, as the document says that null is very much below the resonance that I can’t imagine if it’s audible at all, especially when the speaker at a whole is normally generating around very high distortion.

My problem is the extra group delay. I've proven to myself I can hear the group delay of ported, and I tune ported carefully for minimum group delay to sound the most like sealed. Other than that, I'll comment that PRs are a whole lot more expensive than ports!

 

[Haflermichi]

Why would you think that? No port, no chuffing. Period.
Proper design and use is another matter.

 

[Maciek]

If You can hear group delay then You tune it too high. The lower we go the less sensivitive we are to distortion in frequency and phase. This is another reason to use PRs at very low tuning frequencies. In such case this null that You wrote about and in general steeper cutoff below Fb comapared to BR play in Your favour, as You dont have to filter the subsonic frequencies.

My problem is the extra group delay. I've proven to myself I can hear the group delay of ported, and I tune ported carefully for minimum group delay to sound the most like sealed. Other than that, I'll comment that PRs are a whole lot more expensive than ports!

 

[fpitas]

If You can hear group delay then You tune it too high. The lower we go the less sensivitive we are to distortion in frequency and phase. This is another reason to use PRs at very low tuning frequencies. In such case this null that You wrote about and in general steeper cutoff below Fb comapared to BR play in Your favour, as You dont have to filter the subsonic frequencies.

You're saying the box doesn't unload the cone there?

 

[MAB]

It is typical to add mass to Passive Radiators, and nothing mentioned here is unusual or mis-applied. And the added mass and tunings are actually not extreme, especially if you have multiple passive radiators, they are just proper resonant system. I use two Seas L26 passives with per L26 woofer, with 240 gram added mass per radiator, and it's not extreme at all, it's just a passive radiator that acts like two 10" ports and air mass equivalent to the total mass of the radiator, which is rather ideal. No port noises or resonances too. And if I wanted to eliminate any possibility of the over-excursion of the PRs I would use four per active, in which case I would need to add around 500 grams of mass, which also would not be extreme. Probably the only extreme part is the cost of the four radiators.

 

[jhaider]

I think you are an order of magnitude off. Can you show a PR that has such high moving mass? Here is an 11" model:

See here:

https://cdn.head-fi.org/a/10134596.pdf

The Peerless XLS application note designs are probably the most well-known set of PR subwoofer designs in audio hobbyist circles.

 

[mhardy6647]

In terms of PRs and port chuffing -- did I miss my window of opportunity to mention how common, in decades past, port noise complaint was?

 

[OldHvyMec]

Woofers usually have way lighter cones compared to PR which cas easly carry 300-500 grams of weight.

Actually no. The voice coil and cone can easily outweigh a PR. The spider return/centering spring is the key to PRs. I use 10-18" PRs
I seldom add several washers. Most of the new PRs are not very sensitive. The issue with very sensitive PRs they historically don't hold up well
because of the light spring and foam surrounds vs Butyl rubber surrounds and dual spider returns. I like tuning with disk to a point (if need)
and adding pliable putty until I get a boom. Then remove just enough to remove the boom. I like the weight that's accessible from the front
vs the back, too.

Your stuck with fixed ports and it better sound good in every room. LOL It can't. PRs can require a little maintenance just like any active
driver. BOTH move, both require, rotation, surround maintenance, connection service if it's not mechanically joined and spot soldered
and of course fastener retorque. A weight adjustment as time goes on (you (remove weight). I remove putty about every 2 years. If the sub is moved,
it is re-tuned to that room, that amp and cables. Add putty until it booms and remove it until it stops.. Then EQ the room.

A different idea all together. Servo subs, Bass columns (as couplers) and room treatment (Helmholtz resonators). The best I've found
for just about any reproduction. Just add a good monitor, I like small planars and ribbons. TM, MTM, LS, and hybrid line source.

 

[Haflermichi]

In terms of PRs and port chuffing -- did I miss my window of opportunity to mention how common, in decades past, port noise complaint was?

Haha! I got that. But back on topic. In my mind the major benefit to using a PR over BR per the OP's original question.
Small, ported boxes+high cone excursion to squeeze bass out=port chuffing. Wait a minute. Roth was right after all...

 

[DVDdoug]

If you are building a speaker you should be able to find software to model/compare/predict the performance of various designs. Of course with PR you are more limited to whatever passive radiators you can find, whereas you can design and build any port dimensions, or you might find that sealed works better in your situation. (The software I've used, WinISD, doesn't do PR designs.)

If you are buying, then it's usually best to consider the speaker a "black box" and choose the one that has the best performance (considering price and size, and whatever considerations) and don't worry about how the manufacturer accomplishes it.

 

[Blumlein 88]

I have seen designs where a complete speaker larger than needed for passive was used for the passive radiator and damping was adjustable by shorting it with variable resistance.

Vandersteen had an odd arrangement they called an active coupler. It acted as a passive radiator, but the voice-coil was fed very low frequencies so below the passive tuning it became actively driven.