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In Reply to: RE: Observable Woofer Cone Movement posted by John Elison on April 20, 2015 at 13:17:25
"The Thiels have a sealed enclosure with a passive radiator"
Doesn't the presence of a passive radiator make the Thiels bass reflex speakers? They simply use a passive radiator instead of the air in a port to take advantage of the back wave from the woofer.
JE
Follow Ups:
The Thiel woofer and passive radiator act like an acoustic suspension speaker when playing vinyl. There isn't much low frequency movement or pumping at all. Compared to the ported woofer in my B&W speaker, the Thiel CS3.7 is virtually motionless.
With all respects, "what a speaker acts like," i.e. a person's subjective conclusions from their observations, is not determinative of the type of speaker it is.
Your Thiels are bass reflex speakers, albeit ones that use a passive radiator instead of a slug of air in a port for their reflex tuning.
Any woofer will have a characteristic roll off in its low frequency extension. In general terms, whether used in a sealed box enclosure or in a reflex box, a woofer can be made that will provide the same amount of energy. That is, there will be the same amount of "area under the curve." You cannot make bass energy out of nothing. A well made bass reflex speaker takes some of the area under the curve that is extreme bass and moves it higher in frequency. This has the effect of moving the bass roll off lower in frequency, giving more apparent bass, but rolling off the bass much more steeply thereafter. A sealed box will have deeper bass, but the bass will not seem as prominent.
Below is a link to a Stereophile Review (bless JA, all the work he puts in, and his generosity in publishing these reviews!) that shows your Thiels to have a classic bass reflex roll-off. I'm sure the bass you experience in your room is deep, tight and tuneful.
JE
You are free to believe anything you want, but the Thiel's enclosure is sealed. That is a fact.
I agree, your speakers are sealed. They are also bass reflex speakers.
I said your speakers were: "bass reflex speakers, albeit ones that use a passive radiator instead of a slug of air in a port for their reflex tuning." A passive radiator will not work unless the speaker is "sealed." However, using a passive radiator to augment the bass gives the speaker a bass-reflex alignment.
Again, look at that Stereophile review. Figure six shows how both the woofer and the passive radiator contribute to the overall bass response. The passive radiator's power comes from the back, or reflex, wave of the woofer. Remember, we cannot create bass out of nothing.
Note how at the frequencies where the passive radiator (the red trace) is at its highest, the frequencies of the woofer (the blue trace) are at their lowest. This would also happen if the speaker had a woofer and a port. In one case, the woofer would be causing a diaphragm to vibrate, in the other a column of air.
Note also how steeply the overall frequency response rolls off below the "elbow" in the curve. A true "sealed box" (in acoustic terms) design would have a shallower roll off, but one that had an "elbow" higher in frequency.
This is really all academic and has nothing to do with how a speaker sounds. I'm sure there are stellar and infernal examples of both designs to be had. I'm also pretty sure your Thiels sound great. Enjoy them, even if they are not an "acoustically sealed" box!
JE
You're right; they sound great!
Another think I like about them is the woofer and passive radiator don't respond to ultra low frequencies when playing vinyl.
Thanks,
John Elison
Hey John,
As knowledgeable as you are in several areas, Jaundiced Ear is correct on this point. Whether a port-and-duct or a passive radiator, the design is bass reflex.
:)
Regardless of how they're labeled, the only thing that matters to me is how my Thiel speakers perform. With regard to woofer pumping from vinyl they perform like acoustic suspension speakers. All ported speakers I've owned exhibited significant woofer pumping when playing vinyl records, but the Thiels don't. Apparently, passive radiators provide the best of both worlds.
Best regards,
John Elison
nt
I expected the Thiels to pump with vinyl, but they don't, so I'm happy.
John,
This probably has nothing to do with having a passive radiator rather than a port. A system that is direct coupled all the way from cartridge to driver should pump from vinyl regardless of driver loading. If it doesn't, it's likely that something in your signal path is not direct coupled. Probably your phono stage or line stage. But Thiel's use a complex crossover, so there might be a series cap in there.
Dave
You should be happy with them whether they pump on vinyl or not!
JE
JE
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