Rythmik 12 or 15

Brian (or anyone else),

I was wondering if I could get a bit of advise on subs.

I'm in an approximately 3700 cubic foot room, but will have a "near-field" sub placement (sub directly behind couch on one side directed in - me sitting on the couch ~ 5ft away). Though my room is large, my entire 7.1 setup is on one end (one, 1/3rd of the room), and I don't really care about the sound performance on the other 2/3rds of the room.

Would a 12" be sufficient without anything nasty (like clipping) for up to about 100db? Technically, I have space for the 15", but I'd really prefer to not go that large unless you just think that's what I need in my case? FWIW's, my SB12+ doesnt have any issues playing to my demands, but I believe it has a bigger amp? (425 bash)

Also.... I own a SB12+. Are you pretty confident that when I compare your sub to my current one, that the end result is that my SB12 will go on ebay, and I wont return the Rythmik? :-) To be real, could I tell a difference? I do have a HSU test tone disk, btw.

Thanks,

Az.

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Originally Posted by azanon

Brian (or anyone else),

I was wondering if I could get a bit of advise on subs.

I'm in an approximately 3700 cubic foot room, but will have a "near-field" sub placement (sub directly behind couch on one side directed in - me sitting on the couch ~ 5ft away). Though my room is large, my entire 7.1 setup is on one end (one, 1/3rd of the room), and I don't really care about the sound performance on the other 2/3rds of the room.

Would a 12" be sufficient without anything nasty (like clipping) for up to about 100db? Technically, I have space for the 15", but I'd really prefer to not go that large unless you just think that's what I need in my case? FWIW's, my SB12+ doesnt have any issues playing to my demands, but I believe it has a bigger amp? (425 bash)

Also.... I own a SB12+. Are you pretty confident that when I compare your sub to my current one, that the end result is that my SB12 will go on ebay, and I wont return the Rythmik? :-) To be real, could I tell a difference? I do have a HSU test tone disk, btw.

Thanks,

Az.

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I believe Ilkka has measured SB12+ and our 12" has better output and better extension. Furthermore, there are customers of ours who had SB12+ and they not only comfirmed the above two points, they also commented ours sound better. If you are happy with SB12+'s output, our F12 won't disappoint you. If you'd like to have something that is 3db or more higher output than SB12+, then I would recommend 15" sub to be on the safe side. The main downside with SB12 (hopefully SVS understand it) is the enclosure size is just too small. This is because internal volume of enclosure does not scale down well with external volume. So when a manufacturer uses an overly small enclosure, we can expect the output takes a toll because internal volume (the number that really affects low frequency efficiency) will look even much smaller. So advantage of that 425WRMS is completely evaporated with a smaller enclosure. Another victim of overly small enclosure is Velodyne DD12.

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Originally Posted by RythmikAudio

I believe Ilkka has measured SB12+ and our 12" has better output and better extension. Furthermore, there are customers of ours who had SB12+ and they not only comfirmed the above two points, they also commented ours sound better. If you are happy with SB12+'s output, our F12 won't disappoint you. If you'd like to have something that is 3db or more higher output than SB12+, then I would recommend 15" sub to be on the safe side. The main downside with SB12 (hopefully SVS understand it) is the enclosure size is just too small. This is because internal volume of enclosure does not scale down well with external volume. So when a manufacturer uses an overly small enclosure, we can expect the output takes a toll because internal volume (the number that really affects low frequency efficiency) will look even much smaller. So advantage of that 425WRMS is completely evaporated with a smaller enclosure. Another victim of overly small enclosure is Velodyne DD12.

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I did stop by Ilkka, and there's one graph I'm assuming I'm not understanding based on what others have said.

On the Total Harmonic Distortion (THD) graph of the Rythmik 12, it shows it going "off the chart" (above 30%) at 24hz and anything below that frequency and 100db. When I pull up the same graph by Ilkka for the SB-12, it shows approximately 22% THD, then distortion actually falling for frequencies lower than that, at 100db/24hz. I assuming I'm reading that wrong somehow, because that graph would tell me that below 24hz, there's major distortion issues with a Rythmik?

Re: the extra 3db with the 15, I might just have to risk it with the 12. Seems like mathematically (from a stats point of view), there's no significant difference in volume between a sub that can play with negligible distortion at >100db, and one that can do an extra 3db more. I'm equating significant difference with > 5% difference in clear volume.

If my numbers are right here, that's an extra 69% in volume (size) for <3% increase in clear volume (between an F12 and 15). From my point of view, that seems like bad scaling the other way around (internal enclosure vs. external volume). Somewhere along the way, seems like enclosure size has to go up exponentially for a linear (or worse) increase in clear volume.

Your thoughts?

azanon, those graphs can be tricky to read. You must look at both the THD graphs and the output sweeps graphs at the same time to properly interpret them. Or you could just look at this chart:

http://www.hometheatershack.com/foru...formation.html

That chart tells you the maximum clean output for each sub at various frequencies.

Also, a 3dB increase is no joke. Since sound is logarithmic, 3dB does not correlate to a 3% increase in volume. It's actually much more than that. If you double the amount of amplifier power a sub has, you get a 3dB increase. It takes two identical subwoofers placed next to each just to get a 6dB increase.

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Originally Posted by Mike^S

azanon, those graphs can be tricky to read. You must look at both the THD graphs and the output sweeps graphs at the same time to properly interpret them. Or you could just look at this chart:

http://www.hometheatershack.com/foru...formation.html

That chart tells you the maximum clean output for each sub at various frequencies.

Also, a 3dB increase is no joke. Since sound is logarithmic, 3dB does not correlate to a 3% increase in volume. It's actually much more than that. If you double the amount of amplifier power a sub has, you get a 3dB increase. It takes two identical subwoofers placed next to each just to get a 6dB increase.

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Thanks Mike. I knew the output for the SB-12 was a lot lower at those low frequencies. I just didn't know if those THD graphs were saying - "not a lot of output with SB-12 at lower frequencies, but for what there is, its low(er) distortion".

But yeah i see on that "compliation" graph, it clears that up for me.

I also knew, more or less, that you had to double amp power just to get a small increase in decibels. But I always concluded from that the opposite way of thinking - get a reasonable amount of watts, then don't worry about it anymore because the returns are diminishing.

I googled and found a site here that says a roughly 10db increase will be perceived by us as doubling the sound volume. http://www.windpower.org/en/tour/env/db/dbdef.htm So about 33% more volume for that increase in size. That seems more reasonable.

Hmm, maybe I didn't interpret that graph as wrong as I thought. Found a clip of Ilkka's quick comments:

DIY Rythmik Audio Direct Servo 12" sealed 56L
Extremely good extension. Very versatile frequency response adjustments. Can be used in larger and also in smaller rooms. Upper end of the frequency response rolls off above ~70 Hz. Quite high max SPL, but high deep bass distortion due to amp clipping. Brian says that he doesn’t want to use any limiters, but lets the amp clip/limit the output instead, so it doesn’t limit the dynamics. Low upper bass distortion, so the servo does its job well. Upper bass distortion mainly 2nd order distortion. Quite high deep bass power compression. Low group delay and fast decay. Good price/performance ratio.

http://www.hometheatershack.com/foru...html#post45289

BTW, I'm going to Iilka because you guys keep bringing him up.

So which is it, extremely low as Dave says in the product listing or is it high? I'm really just trying to understand, this is not a troll attempt. I'm asking because I'm actually considering this product.

Ilkka offers some extended thoughts in the Rythmik results thread:

http://www.hometheatershack.com/foru...html#post48248

I've had the D-15 for almost a week now and have not yet noticed any clipping noises when playing extremely loud HT (14hz, high damping). However, I have not tried turning the other speakers off to listen for it. What I do notice are all the loose things in the room rattling. :rolleyes:

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Originally Posted by azanon

So which is it, extremely low as Dave says in the product listing or is it high? I'm really just trying to understand, this is not a troll attempt. I'm asking because I'm actually considering this product.

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I need to do some damage control here :-)

As much as I like to quote Ilkka's result, I do think he didn't do a good job explaining the results. The source of confusion is the db label on the curve. A curve labelled 100db can be easily misinterpreted as 100db at every frequency. But it is clearly not. Actually, the subwoofer with the least extension actually measures best in distortion. As a result, most of the DIY subwoofer with -3db at 40hz measure better than others. The labelling is so misleading that one member of AVS forum even quoted two SDX15 in a 140L sealed has output of 120db at 20hz with distortion of blah blah... I remind him that 120db curve has such a severe roll-off that it has only 105db left at 20hz. Ilkka was never able to get 120db output them.


Back to SB12plus vs Directservo, the curve labelled as 100db and 105db actually only has 87db output and you can see it clearly saturates. When that happens, all the harmonic distortion figure is meaningless because it enters another area called amplitude modulation distortion (or compression). We need to measure how far off they are from the supposed output level. Even if we just check the distortion for fun, that 87db at 20hz has a 20% distortion. Our 12" has 95db max output. That is 8db more than SB12plus. In addition, our output curve giving 87db output at 20hz is actually labelled as 90db and the distortion is 10%. At 30hz, the max output of SB12 plus saturates at 97db. With distortion curve close to 18%. Ours distortion at 95db (30hz)is 5% and at 100db, the distortion is 10%. So we can interpolate the distortion at 97db is around 7%. Ours eventually will saturate at 105db. Again that is 8db difference. 8db is actually 6.25x in power. That means if the driver in SB12 plus driver were not the limiting factor, it will need 425*6.25=2650WRMS to match our output. That is more than what can be attributed to by the 33% increase in enclosure volume.

Again, in terms of distortion reduction, ours is about 2.5x smaller than SB12plus and that is also 8db. 2.5x in amplitude is 6.25x in power. In addition, our distortion is mostly 2nd order which is mellow and less harsh. SB12plus has more higher order distortion which is more audible (as a result of our loudness curve). The calculation above does not consider that aspect of distortion audibility. At 95db curve, we have 1% distortion at 40hz, and SB12plus has 6% distortion.

Harmonic distortion is not the only type of distortion. It is the easiest to measure and has been quoted more often. I have mentioned amplitude modulation distortion. Memory effect (or hysteresis) is another type. None of them are measured by Ilkka. Another issue is the perceived bass speed and articulation, which is affected by factors such as Qts value. Our Qts value is 0.3 in enclosure. That is 3x lower than other nonservo subs.

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Originally Posted by RythmikAudio

I need to do some damage control here :-)

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I'm really just trying to understand, not slander your product. I've said a few times now I'm a novice on these things, and just a hobbyist who enjoys great music. I assure you, if i actually could discover something sinister in this field, 100 other experts would have long since beat me to the punch.

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Originally Posted by azanon

I'm really just trying to understand, not slander your product. I've said a few times now I'm a novice on these things, and just a hobbyist who enjoys great music. I assure you, if i actually could discover something sinister in this field, 100 other experts would have long since beat me to the punch.

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Don't worry about this. You are not the only one who reads those curves your way. As I have explained, it is very natural. Members of other non-manufacturer forums have raised similar question, not to mention those who are in your situation but never ask questions and go get a different subwoofer. In those forums, I cannot say anything more than suggesting that they should read the output curve and distortion curve together to get a better idea. Here I would like to leave a response as a record so that members and customers in the future have something to refer to. In short, this is not a damage from you or other members, instead, it is a colateral damage from a very professional review. I was hoping everyone can read it right and it is clearly not.

Several members have asked me about the reviews. I have no problem sending them to reviewers expressing purly subjective evaluation such as those in TAS or Stereophile (even though Stereophile also presents measurement). For reviewer as technical as Ilkka, I actually have to interpret the results to the customers. I discussed this with him and he replied he presented objective data and it is up to the readers to interpret what they mean. That is what I am doing now. Then there are other reviewers actually rank the products as 1,2,3... For those reviewers, I would think a review collectively from 500 customers is just as valuable as, if not more than, a review from 3 guys who determine the ranking of the products.

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Originally Posted by Mike^S

azanon, those graphs can be tricky to read. You must look at both the THD graphs and the output sweeps graphs at the same time to properly interpret them. Or you could just look at this chart:

http://www.hometheatershack.com/foru...formation.html

That chart tells you the maximum clean output for each sub at various frequencies.

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Can someone enlighten me on how to interpret the chart?

Firstly, what is "max clean output"? Is clean defined by reference to % distortion or something else?

I assume the figure in each column is in dB units?

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Originally Posted by jbjb

Can someone enlighten me on how to interpret the chart?

Firstly, what is "max clean output"? Is clean defined by reference to % distortion or something else?

I assume the figure in each column is in dB units?

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Unless Brian(RythmikAudio) sees this thread again...I suggest you contact him and ask.

But for the second two questions...the answer is yes and yes. :)

Thanks again Curtis.