Extraordinary claims made about Rythmik Subwoofer !!

[snoopy]

Originally posted by Cloth Ears


Nope.

They listened and learned, made their own experiments and measurements and drew conclusions from what they learned. Whether they had qualifications or not does not actually matter, it's how they went about what they did that counts. The fact that they had engineering qualifications means that they knew that it was best to "listen and learn, make their own experiments and measurements and draw conclusions from what they learn".

Where in the original papers by Thiele and Small is there any emphasis on the analysis of a loudspeaker enclosure by listening to it ?? Can you explain how Theile or Small derived the small signal electro acoustical system response function by listening to various different speaker systems ??

To really understand the details in Thiele or Small's papers requires understanding of engineering circuit analysis and the dynamics of mechanical and acoustical systems. To say otherwise is just displaying your ignorance.

[jlharden]

huh?? Thiele & Small correlated measurable electrical and mechanical driver parameters into a basis for predicting loudspeaker behaviour......

What an oddity this has become.......

[snoopy]

Originally posted by jlharden
huh?? Thiele & Small correlated measurable electrical and mechanical driver parameters into a basis for predicting loudspeaker behaviour......

What an oddity this has become.......

They didn't derive the parameters from listening tests as some people are implying.

[infinia]

Hi
The sub as tested Did Not use the servo feedback loop to reduce distortion. The one he tested used the Linkwitz Transform circuit only.
Quote from the Rythmic web site
"The kit consists of a 370w amp (A370 SE) with a Linkwitz transform circuit a board, and a DS12 driver without servo feedback. With the Linkwitz Transform circuit we can get a better bass extension than what natural physics gives us. "


The LT circuit places great demands on excursion and amplifier power (ie potentially higher IMD) and trading this for a limited amount of frequency extension.


Besides it's normal for marketing to make broad sweeping statements or puffery of their products. You cannot use these statements in a technical argument unless lawyers are involved.

Cease fire now folks, hahaha.

[pjpoes]

I was under the impression, having read the ht shack bit, that the sub was one using the servo feedback. Rhythmik offers both, and I would have thought that would have been made clear in the review. In fact, the tester makes the claim that the servo does appear to be working, so again, I must assume it was a servo unit.

I still stand by that the claims made my Rhythmik are perfectly acceptable given that they dont ever state the conditions for which it must be true. They do sell a subwoofer, in fact, more than one subwoofer which I would wager can do what they claim. It just so happens that the single 12" subwoofer with servo, in a sealed enclosure, under these particular test conditions (completely free air-no loading) could not meet the claims. However, as has been mentioned, they don't make this claim as something that must be met free air. The claim is less specific, so if, for instance, they were to be sued for false advertising, they could easily argue that the claim was meant to include in room loading.

As I've mentioned numerous times, I don't care what type of technology you use, a normal vented or sealed enclosure with a 12" woofer can not easily achieve 100db's at 20hz, in free air, with low distortion without a lot of amplifier power. This also means that the speaker must be capable of huge amounts of linear cone travel, and have huge thermal limits. A servo can help make a cones travel more linear, but I would argue that, in a real room, there are better ways to achieve it. As Zaph mentions in one of his writeups, low excursion woofers have less distortion than long excursion woofers. This of course means, used within their linear range, but still, if you need more linear range, just use more woofers.

If you did have a ported enclosure, that would change things some. At the port tuning, 20hz in the case of this argument, the cone would be at minimal motion, and thus, minimal distortion. This is actually seen very easily in the distortion graphs on the HT Shack website, as the ported units generally have a notch in the distortion around the same area as the tuning frequency. This is how my subwoofer achieves this claim. I special version of the TC 3000 subwoofer in a 5 cubic foot enclosure tuned to around 20-21hz. In my particular enclosure it only requires roughly 75 watts to achieve 100db's at 20hz, but if I seal the enclosure, that number increases by close to ten fold. As I recall I measured over 50 volts when I ran some tests a while back, at the time trying to show the efficiency difference of a ported system at low frequencies. This Rhythmik sub, which I believe at least used to have its drivers made for them by TC Sounds, would be in a similar boat. However, as I recall, they were based on the TC2000 not 3000, and would have been of the more typical small box parameters, and thus more limited.

oh and there is nothing unmusical about a ported subwoofer tuned to 20hz. In car audio competitions you tune to the cars resonant frequency, typically between 50 and 70hz. This makes for a peaky response, which is what you are referring to, but is quite different from a subwoofer tuned to 20 hz. The Bandpass designs only take this further by tuning to a very narrow point, especially the 6th and 8th order designs, which allow roughly 6-10 db's of gain at that point, but very sharp fall off on either side. That is nonmusical.

[infinia]

Originally posted by pjpoes
I was under the impression, having read the ht shack bit, that the sub was one using the servo feedback. Rhythmik offers both, and I would have thought that would have been made clear in the review. In fact, the tester makes the claim that the servo does appear to be working, so again, I must assume it was a servo unit.

His first post under test conditions, he talks about eq settings which says he has the kit with the LT option, and this option does not use servo feedback according to the vendor.
I missed the part where the tester claims about the servo working, besides how would he know unless he disconnected it or compared it to a similar setup without it.
Regards,

[badman]

Originally posted by infinia
Hi
The sub as tested Did Not use the servo feedback loop to reduce distortion. The one he tested used the Linkwitz Transform circuit only.
Quote from the Rythmic web site
"The kit consists of a 370w amp (A370 SE) with a Linkwitz transform circuit a board, and a DS12 driver without servo feedback. With the Linkwitz Transform circuit we can get a better bass extension than what natural physics gives us. "

Wow, look at that

[pjpoes]

Originally posted by infinia


His first post under test conditions, he talks about eq settings which says he has the kit with the LT option, and this option does not use servo feedback according to the vendor.
I missed the part where the tester claims about the servo working, besides how would he know unless he disconnected it or compared it to a similar setup without it.
Regards,

I still think you are incorrect. What I see him talking about is the dampening and extension switches, which are a feature of the servo system, not the LT. I believe this was a servo sub tested, not an LT. However, your main point about the LT is still true of the servo. When it comes right down to it, a servo is nothing more than an active "smart" LT.

[pjpoes]

Originally posted by infinia


His first post under test conditions, he talks about eq settings which says he has the kit with the LT option, and this option does not use servo feedback according to the vendor.
I missed the part where the tester claims about the servo working, besides how would he know unless he disconnected it or compared it to a similar setup without it.
Regards,

I still think you are incorrect. What I see him talking about is the dampening and extension switches, which are a feature of the servo system, and the LT. I believe this was a servo sub tested, not an LT. However, your main point about the LT is still true of the servo. When it comes right down to it, a servo is nothing more than an active "smart" LT.

[infinia]

Originally posted by pjpoes



I still think you are incorrect.

Wow I really cannot believe this, now you want to argue with me.
Some peoples kids.... just can't let it go. Now I remember why I took 6 mo. away from this forum.