Rythmik Audio FV15-HP Data-Bass test results - Page 6 - AVS Forum
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post #151 of 172 Old 06-27-2011, 11:42 AM
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Thank you for the kind words monomer!

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post #152 of 172 Old 06-27-2011, 11:54 AM
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Quote:
Originally Posted by DS-21 View Post
What you're saying is, in effect, that as long as there's enough power on tap, your system will in fact compensate for power compression.
This is what Brian is trying to say, but as you noted he is referring more to low-to-moderate playback levels before the subwoofer amp/driver/ports/etc. run out of steam or reach their physical limits. And there is no free lunch. By needing to use more amplifier power to compensate, the result is less wide dynamic range. So, like almost all things related to subwoofer design, there is a tradeoff involved.

One valid question is, how relevant is thermal memory effect at low-to-moderate listening levels with a non-servo subwoofer? ie. how much does the frequency response change over time at these low-to-moderate listening levels (after having just listened at high listening levels), and how does this effect change based on the design of the driver voice coil and based on the alignment of the subwoofer? When I get a chance, I will check the frequency response in our demo room to see how much it changes when sweeping from low level to high level and back to low level using non-servo subwoofer.

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post #153 of 172 Old 06-27-2011, 05:16 PM
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As promised, attached are some frequency response sweeps that I performed in our demo room using a 15" non-servo vented subwoofer. I did sweeps at 80dB, 90dB, 100dB, and 110dB (the point at which the whole room was shaking like crazy, and there was up to 2dB output compression at some frequencies) in succession. Then I immediately re-did the sweep at 80dB, 90dB, 100dB in succession. As you can see, the frequency response is essentially identical between the first run and second run. All things considered, the thermal memory effect with a non-servo subwoofer seems to depend on individual design details, and at least in this sample case seems to have very minimal effect on the measured frequency response. Certainly a very interesting and thought-provoking debate though.

Sincerely,

 

Thermal Compression.PDF 22.814453125k . file

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post #154 of 172 Old 06-27-2011, 05:57 PM
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post #155 of 172 Old 06-27-2011, 06:45 PM
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Quote:
Originally Posted by Pete_Hsu View Post

As promised, attached are some frequency response sweeps that I performed in our demo room using a 15" non-servo vented subwoofer. I did sweeps at 80dB, 90dB, 100dB, and 110dB (the point at which the whole room was shaking like crazy, and there was up to 2dB output compression at some frequencies) in succession. Then I immediately re-did the sweep at 80dB, 90dB, 100dB in succession. As you can see, the frequency response is essentially identical between the first run and second run. All things considered, the thermal memory effect with a non-servo subwoofer seems to depend on individual design details, and at least in this sample case seems to have very minimal effect on the measured frequency response. Certainly a very interesting and thought-provoking debate though.

Sincerely,

Am I missing the attachments?
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post #156 of 172 Old 06-27-2011, 09:13 PM
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Quote:
Originally Posted by Pete_Hsu View Post

As promised, attached are some frequency response sweeps that I performed in our demo room using a 15" non-servo vented subwoofer. I did sweeps at 80dB, 90dB, 100dB, and 110dB (the point at which the whole room was shaking like crazy, and there was up to 2dB output compression at some frequencies) in succession. Then I immediately re-did the sweep at 80dB, 90dB, 100dB in succession. As you can see, the frequency response is essentially identical between the first run and second run. All things considered, the thermal memory effect with a non-servo subwoofer seems to depend on individual design details, and at least in this sample case seems to have very minimal effect on the measured frequency response. Certainly a very interesting and thought-provoking debate though.

Sincerely,

Pete,

Thanks for doing the test. But the memory effect is not static. It is not between sweeps. Memory effect happens in real time, on the fly. I asked Josh to do a test like that is to make use of existing testing tools. But the best way to observe thermal memory is to device a special waveform that emulates the dynamic changing nature of music. I come up with a simple waveform with two signal strengths at 80hz to represent alternating strong and weak signal in music. The correct waveform is supposed to look like this with two distinctive signal levels.

The same waveform is repeated for 8 times consecutively without interrupt. I call each an 1/8th waveform.

Now, the nonservo first 1/8th waveform looks like this



Notice the large signal strength continue to go down due to compression and then it hands off to the small signal in the 2nd 1/8th waveform.



Two interesting things happen here. First, the small signal will go through an expansion (opposite of compression as the beginning temperature is higher and then it gradually cool down). And then after that another period of large signal comes in. Note there the initial strength of the large signal will depend on how long it has been in the small signal (or cool down) period. That creates a highly complex memory effect that is very undesirable. So in real world, the temperature goes through this heat up and then cool down and corresponds to this compression and then expansion process. Here I use small signal as an alternative signal. If I had use a signal that consumes very little current and yet cause large cone excursion (such as the signal located at the impedance peak point), you can imagine that yet creates a different compression/expansion pattern because the temperature recovers very fast.

To conclude here. I add 3rd 1/8th waveform.



and last 1/8th waveform



Note the scale now has dropped 10%.

Here I want to demonstrate is that compression and thermal memory effect is a complex behavior.

One the other hand, the first and last 1/8th waveform for servo

and
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post #157 of 172 Old 06-27-2011, 09:19 PM
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I had no idea that HSU & Rhythmik were on such friendly terms. It's almost like they're not even competitors. The last thing I expected was to see Pete explaining aspects of Brian's servo sub in a Rythmik thread and then illustrating how a HSU sub (presumably) does not suffer from thermally induced compression. Brian must be verklempt at such comraderie. Me, I'm thinking this is like Stevie Wonder's song, Ebony and Ivory. I hope Brian returns the favor when Ricci gets around to evaluating the HSU sub.

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post #158 of 172 Old 06-28-2011, 04:23 AM
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Pete - you seem to have a thing for comparing your VTF-15 (or a non-vented 15" sub anyhow) to the Rythmik!

Instead of posting your internal sweeps here, feel free to send the VTF-15H to Ricci for the battery of tests as Brian did. They seem to be of pretty good quality as you've pointed out...

 

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Quote:
Originally Posted by pbc View Post

Pete - you seem to have a thing for comparing your VTF-15 (or a non-vented 15" sub anyhow) to the Rythmik!

Instead of posting your internal sweeps here, feel free to send the VTF-15H to Ricci for the battery of tests as Brian did. They seem to be of pretty good quality as you've pointed out...

Good luck!

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post #160 of 172 Old 06-28-2011, 05:28 AM
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As I have mentioned, what we called linear system is actually called "linear time-invariant" system. Therefore anything that can lead to time variant behavior is put in as a spec in the playback system. For instance, in the old LP days, the turntable has WOW and Flutter spec and in the CD/DVD world we have jitter spec. Some audiophile are after super clock chip in CD/DVD player. The purpose there is to get the lowest jitter. But the time invariant part of subwoofer is very significant. In the past, engineers just either don't have a solution for it, or don't know how to quantify it, or both.
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post #161 of 172 Old 06-28-2011, 05:45 AM
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Quote:
Originally Posted by pbc View Post

Pete - you seem to have a thing for comparing your VTF-15 (or a non-vented 15" sub anyhow) to the Rythmik!

Instead of posting your internal sweeps here, feel free to send the VTF-15H to Ricci for the battery of tests as Brian did. They seem to be of pretty good quality as you've pointed out...

Somehow I don't see that happening. How many times can a certain 15" non-servo sub stand getting beaten up by the Rythmik? It may fare better in objective tests against some lower-priced competitors.
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post #162 of 172 Old 06-28-2011, 06:08 AM
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Originally Posted by mojomike View Post

Somehow I don't see that happening. How many times can a certain 15" non-servo sub stand getting beaten up by the Rythmik? It may fare better in objective tests against some lower-priced competitors.

That is mostly the limitation of tests. As many have said before, if you can hear the difference and yet they test the same (with "objective" tests), then we have not used the right test. If your only objective is getting low distortion, then you need to know how many different types of distortions are there and which are benign distortions (distortion that is time invariant and can be modeled by polynomial) and which are bad distortion (that is time variant, cannot be modeled by simple polynomial). The shortcoming of distortion test is it cannot differentiate the two. It is up to the engineers to dissect it and analyze it and read between the charts. What do we need engineers for?
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post #163 of 172 Old 06-28-2011, 06:50 AM
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Quote:
Originally Posted by mojomike View Post

Somehow I don't see that happening. How many times can a certain 15" non-servo sub stand getting beaten up by the Rythmik? It may fare better in objective tests against some lower-priced competitors.

Only one way of knowing how it would fare though ... sounds like we'll soon have the Epik Empire and the eD A7S-450 ID offerings added in due time by Josh.

People can then at least use these tests to judge the pros/cons of each design as well as whether the extra $$$ for Sub X vs Sub Y is "worth" it to them since as we know there is rarely/never a "1:1" relationship between extra performance to extra dollars.

 

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post #164 of 172 Old 06-28-2011, 07:06 AM
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Quote:
Originally Posted by Rythmik View Post

Pete,

Thanks for doing the test. But the memory effect is not static. It is not between sweeps. Memory effect happens in real time, on the fly. I asked Josh to do a test like that is to make use of existing testing tools. But the best way to observe thermal memory is to device a special waveform that emulates the dynamic changing nature of music. I come up with a simple waveform with two signal strengths at 80hz to represent alternating strong and weak signal in music. The correct waveform is supposed to look like this with two distinctive signal levels.

The same waveform is repeated for 8 times consecutively without interrupt. I call each an 1/8th waveform.

Now, the nonservo first 1/8th waveform looks like this



Notice the large signal strength continue to go down due to compression and then it hands off to the small signal in the 2nd 1/8th waveform.



Two interesting things happen here. First, the small signal will go through an expansion (opposite of compression as the beginning temperature is higher and then it gradually cool down). And then after that another period of large signal comes in. Note there the initial strength of the large signal will depend on how long it has been in the small signal (or cool down) period. That creates a highly complex memory effect that is very undesirable. So in real world, the temperature goes through this heat up and then cool down and corresponds to this compression and then expansion process. Here I use small signal as an alternative signal. If I had use a signal that consumes very little current and yet cause large cone excursion (such as the signal located at the impedance peak point), you can imagine that yet creates a different compression/expansion pattern because the temperature recovers very fast.

To conclude here. I add 3rd 1/8th waveform.



and last 1/8th waveform



Note the scale now has dropped 10%.

Here I want to demonstrate is that compression and thermal memory effect is a complex behavior.

One the other hand, the first and last 1/8th waveform for servo

and




Why does the servo chart use about 1/2 the voltage of the non servo chart?
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post #165 of 172 Old 06-28-2011, 07:34 AM
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Quote:
Originally Posted by J_Palmer_Cass View Post

Why does the servo chart use about 1/2 the voltage of the non servo chart?

Good question, these are tests that I've done in 2006. I accidentally left the attenuator switch (for my data acquisition system) for the servo at 2x position. I have never bothered to post these. But I really want to clarify what we are looking for for thermal memory/compression. It is still a good illustration of what thermal memory is about. The idea is we have discussed the compression, but we've never discussed the expansion part. What goes up must come down.

I still have the 60hz comparison and the levels do match between servo and nonservo. I will find a time to post them too.
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post #166 of 172 Old 06-28-2011, 09:21 AM
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Great stuff...and very interesting.

This thread certainly has its twists and turns.

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post #167 of 172 Old 06-28-2011, 12:06 PM
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Hi Brian,

Quote:
Originally Posted by Rythmik View Post
Pete,

Thanks for doing the test. But the memory effect is not static. It is not between sweeps.
My pleasure, and thanks for the clarification. I wasn't looking at how the frequency response changes at different sweep levels, but rather was looking to see how the frequency response changes when starting at low sweep levels, increasing to very high sweep levels, and then going back to low sweep levels (ie. the "rev2" sweeps). I did the sweeps this way because you mentioned a few days ago that you wanted to show the frequency response of the subwoofer in this manner to illustrate lack of thermal memory effect (link here: http://www.avsforum.com/avs-vb/showt...1#post20614751 ).

Interestingly enough, looking back at post #1, in the 1 port mode (but not in the 2 port mode), it looks like the frequency response sweep at 90dB did change by up to 1-2dB at some frequencies when the sweep was re-run. What is that exactly, some extra wind or background noise?

Doing very high SPL sweeps ends up to be somewhat of a torture test in terms of heating up the voice coil, whereas most music and movie bass program material is very short-term in duration. It's nice that servo can adjust for response variations over time, but of course as with all things related to subwoofer design there are always tradeoffs involved. Intuitively, at least when looking at non-servo designs, the thermal memory effect would seem to be influenced by the overall driver/enclosure/amp design. All things considered, like many different measurements this is not something that is easy for the customer to comprehend nor quantify with respect to real world program material.

Anyway, it's very nice to be able to discuss in a friendly and productive manner. At some point and on some level, even as competitors it's nice to be courteous and respectful and understanding of differences in our designs.

Sincerely,

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post #168 of 172 Old 06-28-2011, 06:19 PM
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Wow!!.... Congrats to Mr. Hsu and Brian!... No words..... Both are CHAMPIONS!...
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post #169 of 172 Old 06-28-2011, 08:02 PM
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So Pete, are you inferring that a 'properly' (without limitation) designed subwoofer wouldn't benefit significantly from a servo design?

Additionally, if the above is true, then are servo designs only beneficial when there must be comprises made (either due to size, driver limitations, cost, etc.)?


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post #170 of 172 Old 06-28-2011, 11:19 PM
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Here is the nonservo 60hz. First 1/8th waveform



Second 1/8th waveform



and the last one




And servo. First 1/8th waveform



and last 1/8th waveform



The compression of 60hz is not as bad as 80hz. But they are still visible by eyes.
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post #171 of 172 Old 06-28-2011, 11:28 PM
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Quote:
Originally Posted by Pete_Hsu View Post

Hi Brian,
My pleasure, and thanks for the clarification. I wasn't looking at how the frequency response changes at different sweep levels, but rather was looking to see how the frequency response changes when starting at low sweep levels, increasing to very high sweep levels, and then going back to low sweep levels (ie. the "rev2" sweeps). I did the sweeps this way because you mentioned a few days ago that you wanted to show the frequency response of the subwoofer in this manner to illustrate lack of thermal memory effect (link here: http://www.avsforum.com/avs-vb/showt...1#post20614751 ).

Yes I did. I think I know why in vented subs, such a method may not work as well in demonstrating thermal memory. The tail of the sweep is at very low frequency and for vented sub, that is below the port tuning frequency, where the impedance becomes very large. So the tail of the sweep is at the frequency band that can cause a lot of cone excursion and yet consume very little current. And that can wipe out the memory effect we want to observe. But for sealed subs, it is not so lucky, because the lower end normally is the most power demanding area. We will see what Ricci has got with other subs. As for vented subs, the sweep may need to stop at the port tuning frequency to be able to observe the effect. But that just add a lot of hassel to the test.

Quote:


Interestingly enough, looking back at post #1, in the 1 port mode (but not in the 2 port mode), it looks like the frequency response sweep at 90dB did change by up to 1-2dB at some frequencies when the sweep was re-run. What is that exactly, some extra wind or background noise?

Those are from the noise. Ricci's tests has more wiggles because he used only minimal smoothing. The results from AVTalk and Ilkka looked smoother simply because they used heavy smoothing. I agree with Ricci's approach to give us more of the raw data using as little post processing as possible.
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post #172 of 172 Old 06-29-2011, 06:52 AM - Thread Starter
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Correct...The small uptick on the repeat 90db sweep in 1 port mode below 13hz is probably environmental noise. Being outdoors very low frequency noise from: Airplanes, cars, trucks, wind, trains and heavy machinery can rear its head. The 90 db sweep has the lowest signal to background noise ratio and most subs roll off heavily below 20hz anyway. The Rythmik is actually better in 1 port configuration in that regard than most. You can see this same sort of thing in some of the power compression sweeps where the base level has the lowest octave of frequencies down into the background noise. Also it is not possible to average multiple sweeps, which can average out this sort of thing, during the power compression test because it would cause even more heating and the highest sweep level is always pretty rough on the sub so you don't want to repeat that 4 times in a row. Hmmmm...I guess I could average only the lowest or lowest 2 sweep levels where the sub is loafing...

There is no smoothing at all on the majority of this data. Most measurements that you see will have anywhere from 1/12 to 1/3rd octave smoothing. It does make things a lot easier to digest but you lose resolution and information. A trade off.


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