Extraordinary claims made about Rythmik Subwoofer !!

[snoopy]

Originally posted by moray james
because you sound like a man with a bone to pick. I may be totally wrong about this but that is the impression that you give to me. So if you are an engineer with a fair amount of experience with electro acoustics why don't you discuss your concerns with the engineer who designed the product that you are concerned about? You can have a rational discussion and you both might learn something. I do not see the point in what it is that you are doing now. You are dumping on a product and the designer has no chance to defend his design. Is that how you do business in the engineering job you have now?

What is the bone I have to pick ??

Instead of defending the indefensible why don't you ask the proprietor of the said product to step up to plate and offer a plausible explanation for all on this forum to see ??

That is not asking a lot is it !!!

[moray james]

I have no interest in asking the designers anythig. You are the one who questions the product. You refuse to go to the source (the designer) and to discuss the issues that you have with this product with the one person who knows the product better than anyone else. This has become a strange mission, I do not see the point of this thread any longer. Perhaps the moderator would not mind stepping in at this point. A cooling off period might be useful.

[Cloth Ears]

Originally posted by snoopy
Instead of defending the indefensible why don't you ask the proprietor of the said product to step up to plate and offer a plausible explanation for all on this forum to see ??

That is not asking a lot is it !!!

OK, the driver itself. To produce 100dB at 20Hz from this driver in a 56l sealed box would require a peak to peak excursion of around 36mm, slightly over xmax. It would also require a steady 400W to produce that much motive power, well over the drivers' claimed power handing ability. Thus, this driver would not be able to meet the "criteria" that you claim the manufacturer claims.

Try the DS1500 driver instead. To produce 100dB at 20Hz from this driver in a 125l sealed box would require a peak to peak excursion of around 23mm, roughly 2/3 xmax. It would only require a steady 120W to produce that much motive power, well within the drivers' claimed power handing ability. Thus, this driver may be able to meet the "criteria" - at least it certainly wouldn't melt.

You see, it appears to me that you want every driver/box/amplifer combination from Rythmik to meet the "criteria". It's quite possible that one or more of the larger combinations can meet that "criteria", but obviously they have not been tested - only the smallest box/driver/amplifier was.

I don't expect the 7" drivers on my Elacs to play flat down to 20Hz. I don't expect the 12" Lambdas that I have in my DIY sealed (spookily - 56l) bass boxes to play flat down to that level either. With a bit of EQ and not too much amplification, they will (+0/-2dB). But if I'm playing music (or have the HT up) loud, then I turn the EQ down (or off). There's only so much you can do with a 12" single driver. With a 15" reflex or 15" + PR, or 2x12 + PR (or 2) the 3% distortion @100dB @20Hz "criteria" might be achievable.

If you cannot see that the proprietor has absolutely nothing to gain from attempting to "defending the indefensible", then I guess you cannot. You could probably try mailing him to ask this question, but I would not be doing it myself, as all the people I know of are quite satisfied with his products (Ilkka included).

I hope this is a better debating type response!

[Brett]

Snoopy, I have no interest in Rhythmic subs, never owned one or have an interest in owning one (because I'm going to use something else).

However, I do find the quote you posted from their website unsettling, and if I were interested in the product and made the comparison on a tech basis as you did, I would be a bit shy about ordering one. I do not believe there is any malicious intent, just poor wording.

[snoopy]

Originally posted by Cloth Ears


If you cannot see that the proprietor has absolutely nothing to gain from attempting to "defending the indefensible", then I guess you cannot. You could probably try mailing him to ask this question, but I would not be doing it myself, as all the people I know of are quite satisfied with his products (Ilkka included).

I hope this is a better debating type response!

Sure I could have asked the proprietor and I originally was going to do that but then I thought someone on DIY forum would be able to clear it up quickly but as you can see it has become quite controversial.

And like you said to get a 12 inch driver to deliver the goods at high SPL in a sealed enclosure is no mean feat unless you use some sort of distortion reducing techniques such as a servo which is essentially the claim made by Rythmik.

[Eva]

The truth is that the distortion plots are completely deceiving for an expensive driver with motional feedback and such a claimed lineal excursion capability, even if only results above 35Hz are considered.

However, given the extremely low sensitivity of such drivers, the problem is more likely to be that the 350W amplifier is running out of power below 50Hz at 105dB (example: 350W are 25dB, the driver may be 87dB/W and the sealed box may cause it to be already -7dB at 50Hz, 87-7+25=105dB).

Note that large bass horns routinely provide 105dB with less than 10 watts of input power and sub 1% THD down to 30Hz or lower. SPL over 120dB with THD in the 1% range is easily obtained. This really makes me ask myself if all this ultra-expensive long-excursion and servo technology is worth the effort. It has never been for me.

[agent.5]

Originally posted by Eva


Note that large bass horns routinely provide 105dB with less than 10 watts of input power and sub 1% THD down to 30Hz or lower. SPL over 120dB with THD in the 1% range is easily obtained. This really makes me ask myself if all this ultra-expensive long-excursion and servo technology is worth the effort. It has never been for me. [/B]

Large is the keyword here, I suppose.

[snoopy]

Originally posted by Eva
The truth is that the distortion plots are completely deceiving for an expensive driver with motional feedback and such a claimed lineal excursion capability, even if only results above 35Hz are considered.

However, given the extremely low sensitivity of such drivers, the problem is more likely to be that the 350W amplifier is running out of power below 50Hz at 105dB (example: 350W are 25dB, the driver may be 87dB/W and the sealed box may cause it to be already -7dB at 50Hz, 87-7+25=105dB).

I'd go along with that except at the 90dB and 95dB marks the performance is fairly ordinary which I wouldn't have thought to be attributable to amplifier overloading.

[Eva]

Ambient noise is probably resulting in increased THD at lower SPL.

[seanzozo]

Originally posted by snoopy


I'd go along with that except at the 90dB and 95dB marks the performance is fairly ordinary which I wouldn't have thought to be attributable to amplifier overloading.

Any sealed driver that is equalized (through servo, linkwitz transform or otherwise) flat to 20hz has VERY different power requirements at 20hz than in the midband. Thus 90-95db might require significant power ... in a sealed sub it is by no means "ordinary."

Using basta to simulate a 12" with the rhythmik parameters requires 24db gain over 2.83 V to hit 95db at 2m with a ground plane. (which is 400+ W)

I hate to get back into it, but at the time the marketing for rhythmik's website was written (years ago - and because it is one guy the site changes little) the 12" was available in a vented format. A vented 12" tuned to 20hz would use 1/5 the power and ~1/10 the excursion at 20hz and would likely hit 100db 1m with a ground plane at low distortion.

Snoopy - If you add the word vented to the statement that got your panties in a wad - the statement is accurate
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The sealed servo sub gets you a small footprint sub with reasonable distortion, low group delay and excellent extension.

The vented servo sub gets you a medium footprint sub with low distortion, high group delay, and excellent extension

A hornsub gets you enormous footprint, vanishingly low distortion, and moderate to poor extenstion unless equalized.

ALL OF THESE can be well engineered ... even if one statistic is better or worse than another... it is a question of tradeoffs ... or "horses for courses"


Sean