It appears that extraordinary claims are made on the manufacturers website regarding the Rythmik servo subwoofers and yet I don't see anything extraordinary about the test results that were carried out by an independent body on the Rythmik Audio DS12 subwoofer mounted in a 56L enclosure. 
http://www.hometheatershack.com/for...rythmik-audio-direct-servo-12-sealed-56l.html
For a servo controlled subwoofer I would have expected distortion performance much better than this and at least one order of magnitude better than the test results shown below.
The manufacturers website says the following:-
Can someone please explain these discrepancies ??
Am I missing something here or was this particular sample faulty ??
http://www.hometheatershack.com/for...rythmik-audio-direct-servo-12-sealed-56l.html
For a servo controlled subwoofer I would have expected distortion performance much better than this and at least one order of magnitude better than the test results shown below.
The manufacturers website says the following:-
Can someone please explain these discrepancies ??
Am I missing something here or was this particular sample faulty ??
An externally hosted image should be here but it was not working when we last tested it.
1. Look at post 10 in your linked thread.
2. It is a sensing coil feedback and slightly better results could perhaps be had with an accelerometer feedback sub.
2. It is a sensing coil feedback and slightly better results could perhaps be had with an accelerometer feedback sub.
Ron E said:
But the manufacturers website makes all of these claims about the drawbacks of accelerometer feedback when quite clearly, when properly implemented it is far superior to his own implementation.
The other issue is that winding a pickup coil around the main driving voice coil is thwart with problems. Namely the pickup coil is exposed to the same non linearities in field strength that the driving coil is exposed to. Also because of the close proximity of the pick up coil with the driving coil there are issues with mutual coupling. This may explain why this technique provides very little improvements at all.
The following test results are from a commercial sub woofer which uses an accelerometer. http://www.ultimateavmag.com/features/1004way/index4.html
An externally hosted image should be here but it was not working when we last tested it.
If you are lucky, the fellow who runs Rythmik may show up here. From time to time he has chimed in during my servo sub adventure.
For reference if anyone is interested:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=63397
For reference if anyone is interested:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=63397
snoopy have you....
asked the manufacturer about what you have found? I assume that you did not as you make no mention of any comment from them. They might have some insight regarding this issue.
asked the manufacturer about what you have found? I assume that you did not as you make no mention of any comment from them. They might have some insight regarding this issue.
snoopy said:
OK snoopy I am going to assume you are not trolling.
The commercial sub you linked to is an 18 inch driver and a $3000 sub. Because the ryhtmik is 8x cheaper we really need to normalize the comparison.
If the x-max is the same it sweeps 2.5 times as much air. This should buy well north of 6db - so your conservative first step should be to compare each level on the Rythmik the to the next higher level on the DD. Additionally in the tests linked the DD is 6db down at 20hz and 12db down at 15hz (the rythmik as tested is 2db down at 20hz and about 4db down at 15hz). Thus provided that the inputs were not scaled to get even output for the distortion tests, in the low frequencies (< 30hz) we really need to compare with approximately 10db differential between the drivers.
When comparing distortion at 25Hz with this adjustment--i.e. 90 compared to 100 and 95 compared to 105 compensating for both the change in swept volume and the difference in actual output--both drivers are within a few percent. At 20hz the larger driver and more expensive driver wins out...but you better believe that 2-3 rhytmik 15s would crush the DD.
None of this considers the possible difference in testing regimes. Because I am anal I read the regimes AND I went to find an overlapping test and found that the testing is not comparable.
The ULTIMATE AV tests place the mic .2-.5m but it appears that the normalize to 1 m becasue there is about a 6db difference between tests there and the home theatershack tests which use 2m placement-
http://www.ultimateavmag.com/news/050704yates/
For comparison the GENELEC HTS6 and the 7073A are identical speakers:
http://ultimateavmag.com/features/604way/index4.html
http://www.hometheatershack.com/forums/subwoofer-tests/984-genelec-7073a.html
Note that the shack test at 110db is significantly worse than the ULTIMATE AV test at 115.
hometheater, suggesting that the regimes result in greater than a 5db differential - likely the 6db from a difference between 1m and 2 m testing. Thus if I were to compare--adjusting for swept volume , test diffrence, and the possibility of different actual levels - I would start outwith a comparison that is between 12 and 16 db favoring the rythmik. Using these numbers at 90 db the rythmik is at 5% at 107 the DD18 is at 7% and at 115 it is at 10% -- pretty dang close.
In other words there a so many differences between the subs you chose to compare and the tests in which they are compared that to suggest that we know anything about the relative effectiveness of the tow servo systems is goofy. Well thats not exactly true we know the rhytmik system results in MUCH better low end extension and it has pretty good distortion for its bargain basement price.
Sean
Who kind of wishes he had been doing billable work for the last half hour.
seanzozo said:
What do you mean by trolling ??
Price notwithstanding and taking into account of the fact that I'm comparing a 12 inch sub to an 18 inch sub those exaggerated claims were made on the manufacturers website which has very little objective performance data to back up the claims.
I assume that in the Ultimate AV test the levels are adjusted so that 95 dB at 20 Hz means just that. In this case it would be easy to compare the distortion performance of other sub woofers even if they roll off earlier !!
Don't get me wrong if you look at some of the other tests on that site there are sub woofers with equally bad or worse performance than the Rythmik but then I don't suppose the designers make extraordinary claims about them !!
Re: snoopy have you....
Since the manufacturer's website did not have much in the way of objective tests I thought I might ask people here who have had experience with this product.
moray james said:
Since the manufacturer's website did not have much in the way of objective tests I thought I might ask people here who have had experience with this product.
Snoopy,
There is a 6db difference between the UltimateAVMag tests and the HTshack tests.
THE HTshack tests DO NOT adjust for level on the distortion tests - IKKA has specifically said this. In more recent tests, in order to avoid the confusion that results from people misreading the test like you have, IKKA identifies the sweeps by sweep number rather than DB. YOU MUST look at relative level to have the HD sweeps mean anything on HTShack. For example this means that with a flat sub like the Rythmik you need to compare the 90db line to the 100 db line for a different sub that is down 12db at 20hz.
It is very unlikely--though possible--that the UltimateAVMag tests do any different.
When compared correctly, the Rythmiks performance is actually quite good and lives up to the general tenor of the claims made by its manufacturer.
For example:
http://www.hometheatershack.com/forums/subwoofer-tests/8146-velodyne-spl-1200-mk2-new.html
This is a $1500 velodyne 12 inch driver - look at sweep 5 (the 105 db line) - it produces 88db at 20 hz - the distortion is 20%. The velodyne cannot produce more than 93 db at 25hz period.
go back to the rythmik
http://www.hometheatershack.com/for...rythmik-audio-direct-servo-12-sealed-56l.html
Note how the 90 db line produces 88db at 20hz - the distortion 10%. The Rythmik can produce >100db at 25hz.
So lets see
--1/3 the price (unless the velodynes shiny box is work $1k to you)
--15 db better extension at 20hz and half the distortion
--7 DB more useful output at 25hz
I certainly woudn't be ashamed if I was the manufacturer
OK so maybe that wasn't fair how about this:
http://www.hometheatershack.com/forums/subwoofer-tests/8159-diy-css-2xsdx15-sealed-140l-new.html
Two high excursion 15 inch drivers (which cost more without an amp than a Rythmik 15 kit)
orange line 90 db at 20 hz - 14% distortion
red line 95 db at 20 hz - 23% distortion
Rythmik 12
blue line 93 db at 20 hz - 22% distortion
The rythmik 15 would be:
--cheaper than two SDX15 and an amp by the price of an amp
--better two SDX15 subs in distortion at resonable levels
--would be roughly flat to 20hz rather than 10 db to 15 db down (this could be fixed with an Linkwitz transform, but the price of the amp just went up)
With regard to Rythmik's claims look here ->
http://www.rythmikaudio.com/output.html
Now go back to the maximum output chart on IKKA's test and add the 6db for going from a 2m to 1m measurement...wait they are almost identical - what an outlandish claim!
OK I am done...If it isn't obvious that the Rythmik is at least a good deal and well engineered -- then well I give up.
Sean
There is a 6db difference between the UltimateAVMag tests and the HTshack tests.
THE HTshack tests DO NOT adjust for level on the distortion tests - IKKA has specifically said this. In more recent tests, in order to avoid the confusion that results from people misreading the test like you have, IKKA identifies the sweeps by sweep number rather than DB. YOU MUST look at relative level to have the HD sweeps mean anything on HTShack. For example this means that with a flat sub like the Rythmik you need to compare the 90db line to the 100 db line for a different sub that is down 12db at 20hz.
It is very unlikely--though possible--that the UltimateAVMag tests do any different.
When compared correctly, the Rythmiks performance is actually quite good and lives up to the general tenor of the claims made by its manufacturer.
For example:
http://www.hometheatershack.com/forums/subwoofer-tests/8146-velodyne-spl-1200-mk2-new.html
This is a $1500 velodyne 12 inch driver - look at sweep 5 (the 105 db line) - it produces 88db at 20 hz - the distortion is 20%. The velodyne cannot produce more than 93 db at 25hz period.
go back to the rythmik
http://www.hometheatershack.com/for...rythmik-audio-direct-servo-12-sealed-56l.html
Note how the 90 db line produces 88db at 20hz - the distortion 10%. The Rythmik can produce >100db at 25hz.
So lets see
--1/3 the price (unless the velodynes shiny box is work $1k to you)
--15 db better extension at 20hz and half the distortion
--7 DB more useful output at 25hz
I certainly woudn't be ashamed if I was the manufacturer
OK so maybe that wasn't fair how about this:
http://www.hometheatershack.com/forums/subwoofer-tests/8159-diy-css-2xsdx15-sealed-140l-new.html
Two high excursion 15 inch drivers (which cost more without an amp than a Rythmik 15 kit)
orange line 90 db at 20 hz - 14% distortion
red line 95 db at 20 hz - 23% distortion
Rythmik 12
blue line 93 db at 20 hz - 22% distortion
The rythmik 15 would be:
--cheaper than two SDX15 and an amp by the price of an amp
--better two SDX15 subs in distortion at resonable levels
--would be roughly flat to 20hz rather than 10 db to 15 db down (this could be fixed with an Linkwitz transform, but the price of the amp just went up)
With regard to Rythmik's claims look here ->
http://www.rythmikaudio.com/output.html
Now go back to the maximum output chart on IKKA's test and add the 6db for going from a 2m to 1m measurement...wait they are almost identical - what an outlandish claim!
OK I am done...If it isn't obvious that the Rythmik is at least a good deal and well engineered -- then well I give up.
Sean
seanzozo said:
Forget about the Velodyne DD-18 then. That is not the issue here. Look at the THD level of the Rythmik subwoofer at 105 dB @ 30 Hz !! Surely you're not saying that this is good engineering ??
Now look at the claims made by the manufacturer !!
Where is the under 3% distortion as claimed ?? Am I missing something here or does anyone else see what I am seeing ??
seanzozo said:
Correct me if I'm wrong but the theatershack tests are done using ground plane measurements which incur a 6dB gain which is why the microphone is set at a distance of 2 meters and not 1. So the results have not been diminished as you claim they have 😉
A couple of things.
Rythmik audio has an adjustable F3, it was tested at 14Hz, if htshack tested at 28hz it would have significantly better distortion numbers. it is trading excursion for extension.
Second, The Rythmik is billed as a SQ sub not an SPL sub. Don't expect a 12" sealed sub to compete with 18" sealed subs, or 12" vented subs in a high spl test.
Third, The distortion by order test is much more indicative of SQ than distortion by db.
Fourth, I agree with what seanzozo said.
Rythmik audio has an adjustable F3, it was tested at 14Hz, if htshack tested at 28hz it would have significantly better distortion numbers. it is trading excursion for extension.
Second, The Rythmik is billed as a SQ sub not an SPL sub. Don't expect a 12" sealed sub to compete with 18" sealed subs, or 12" vented subs in a high spl test.
Third, The distortion by order test is much more indicative of SQ than distortion by db.
Fourth, I agree with what seanzozo said.
snoopy said:
snoopy,
You've decided to bash Brian and his subwoofers on this forum. You don't appear to have ever listening to, or measuring them yourself. You've decided to take this upon yourself without even asking your authority (Ilkka from hometheatershack) for his opinion on the results of his testing. And you ignore his posted comments, such as:
- The 12" sealed Rythmik Audio DS is generally a really good subwoofer. It has versatile settings for extension and shape of the frequency response, which both help to match the subwoofer and the room.
- The upper end stays really clean even when pushed really hard, but when listening to material with lots of high amplitude low frequencies (HT use), you will start to hear some amp clipping noises (ticking, crackling) at certain point.
- Brian decided not to use any amp limiters, which helps to preserve the maximum dynamic capability of the amp. But as you can see from the THD graph, distortion grows pretty large below 30 - 40 Hz when pushed hard. If one is using one of the lesser extension settings, naturally the low end compression and distortion are lowered too.
- You should notice that I used the lowest extension and low-Q settings in my tests, which make the compression and THD graphs look somewhat worse when compared to subwoofers with lesser extension.
- So always remember to check the real output and extension from the frequency response and maximum output graphs when making any comparisons.
The Rhythmik subwoofers are some of the best available for the price, and would show better than any pre-built items at 4 times the price. What's your beef with them?
Consider yourself corrected 😀!
snoopy,
I finally read your posted quote from the Rythmik site:
Where in that quote does it say that Rythmik subwoofers achieve 3% distortion at 100dB? And, would you seriously expect that every subwoofer in the range would achieve the same specification? I would find it much more realistic that this might be achieved in the largest subwoofer, using the reflex enclosure, and the 20Hz high-pass filter - not the smallest sealed enclosure that is sold by this company.
(This was supposed to be in the previous post, but I forgot it and tried to edit too late.)
I finally read your posted quote from the Rythmik site:
snoopy from the Rythmik website said:
Where in that quote does it say that Rythmik subwoofers achieve 3% distortion at 100dB? And, would you seriously expect that every subwoofer in the range would achieve the same specification? I would find it much more realistic that this might be achieved in the largest subwoofer, using the reflex enclosure, and the 20Hz high-pass filter - not the smallest sealed enclosure that is sold by this company.
(This was supposed to be in the previous post, but I forgot it and tried to edit too late.)
Cloth Ears said:
Excuse me !!! I did not set out to criticize any particular person in fact I never made reference to the guy who owns the company because I don't even know him or his name. I just saw what was written on his website and the test results from an independent tester which did not correlated very well with the claims being made. Even blind Freddy can see this !!
All things being equal, those tests run by hometheatershack were applied to a dozen other sub woofers so it is fair to make relative comparisons as another poster did even if you think those original tests are flawed.
My beef is that I don't condone misleading or false advertising of any sort. People like yourself should be thanking me for bringing this to everyones attention rather than trying to sweep it under the carpet.
snoopy said:
The company's been set up by one person, ipso facto, if you criticize the company, you criticize the person. But I understand that you didn't mean to...
snoopy said:
Unfortunately it isn't false or misleading. You just didn't read it properly. Your quote doesn't say that Rythmik subwoofers achieve any particular level of distortion. Only that "A well designed servo subwoofer will achieve distortion levels under 3% under the same conditions." Nowhere on the site does it claim 3% distortion at 100dB at 20Hz.
I also notice that you seemed to miss out the sections where Ilkka (of hometheatershack) praises the unit. And you still insist on using his test as the basis for your derogatory comments.
Continuing on in this vein indicates that you have some sort of serious problem in admitting your own mistake in misreading the stuff on the Rythmik website.
Re: Re: Extraordinary claims made about Rythmik Subwoofer !!
If it doesn't say this then the vendor of this product is essentially shooting himself in the foot by implying that his own product is NOT "well designed", using his own words.
The problem is that the claims made on the website are not backed up by any objective measurements and now that I have found some measurements done by an independent body, some people on this website are still in total denial !! I don't get it
Cloth Ears said:
If it doesn't say this then the vendor of this product is essentially shooting himself in the foot by implying that his own product is NOT "well designed", using his own words.
The problem is that the claims made on the website are not backed up by any objective measurements and now that I have found some measurements done by an independent body, some people on this website are still in total denial !! I don't get it
Cloth Ears said:
Yes I did read it properly and are you then saying that this criteria doesn't apply to his own product in which case it is a direct admission that his product is not "well designed", using his own words !! I quote again directly from the website:-
Cloth Ears said:
Which is why I invited comments from others regarding the objective measurements.
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