Extraordinary claims made about Rythmik Subwoofer !!

[snoopy]

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/foru...ealed-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:-

Direct Servo technology: why do we need it?
Conventional subwoofers have extremely high distortion. Well regarded conventional subwoofers typically have measured distortion levels exceeding 15% at 20 Hz at 100 dB. This includes many subwoofers costing more than US $3000. We think this is far too high. A well designed servo subwoofer will achieve distortion levels under 3% under the same conditions.

Can someone please explain these discrepancies ??

Am I missing something here or was this particular sample faulty ??

[Ron E]

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.

[snoopy]

Originally posted by Ron E
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.

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/feature...ay/index4.html

[dswiston]

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:

Servo-feedback Subwoofer

[moray james]

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.

[seanzozo]

Originally posted by snoopy

The following test results are from a commercial sub woofer which uses an accelerometer. http://www.ultimateavmag.com/feature...ay/index4.html

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/foru...lec-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.

[snoopy]

Originally posted by seanzozo


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.

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 !!

[snoopy]

Originally posted by moray james
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.

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.

[seanzozo]

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/foru...0-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/foru...ealed-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/foru...-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

[Cloth Ears]

Originally posted by seanzozo
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

Hear! Hear!

Is that up to an hours billable now?