Rythmik or SVS?

[KEW]

A 12" woofer with moderate excursion ability with an f3 of 14 Hz will run out of throw very fast. Supposedly the servo mechanism compensates for the typical 12 dB/octave roll off of sealed subs, but I would not run the F12 in the mode with that kind of extension, it doesn't have the displacement for it. That would be asking a lot of even an 18" woofer. I don't think anyone should be buying a sealed sub with the expectation of getting a flat response to 20 Hz, and that includes the ULS-15 mk2- unless the sub were some kind of super sub like the Deep Sea Sound Mariana 24.

I agree with everything you say here, just wanted to point out that the specifications indicate that neither the SVS nor Rythmik specs show the kind of roll-off you described.

I don't think anyone should be buying a sealed sub with the expectation of getting a flat response to 20 Hz, and that includes the ULS-15 mk2- unless the sub were some kind of super sub like the Deep Sea Sound Mariana 24.

That is something I don't get. Everyone wants a sub that has a flat FR down to ~20Hz in an anechoic chamber, but once you get the boost from being in a room, you have a sub with significantly tipped up bass. I suspect if I had a ULS-15 mk2, I would run it in the "EQ2" operating mode (without the added extension).

When I compared the JLAudio E112's vs the Rythmik E15HP's, the JLAudios put out a lot more energy in the mid 20Hz range, but the Rythmiks really did dig down much deeper (HT content). Had I listened to them on separate occasions, I may have concluded the E112's had more depth, but instantly switching between it was obvious that the E15HP's had more gravitas, it just wasn't yelling "hey, look at me".
For music, the E112 is just too boomy. If I turned down the sub to where it did not boom (especially stuff like Maroon 5, which has some deep bass), it was down much too low for the normal-mid bass. Furthermore, Audyssey XT 32 would not sufficiently tame the E112's boominess.

As measured by Jman, the E112 (top) and E15HP (bottom) impulse responses look like this. It is pretty Clear that the E15HP is not making too much noise after it was supposed to have shut up, while the E112 resonates on. I believe this shows the boominess I was so disappointed with from the E112's:

Since SVS is in the discussion, here is the SB13Ultra (top) and SB1000 (bottom):

The SB13Ultra doesn't look too bad, but the SB1000 has a lot of overhang. I honestly don't know where the SB2000 would fall, but the Ultra has a lot of upgrades while the SB2000 is priced like a scale up from the 10" SB1000.

I would expect the F12 to mimic the impulse response of the E15HP because the servo (in a sealed box) seems to clamp things down. Output is the major advantage of the E15HP over the F12.

 

[shadyJ]

I agree with everything you say here, just wanted to point out that the specifications indicate that neither the SVS nor Rythmik specs show the kind of roll-off you described.

Their rolloff is due to a boost in deep frequencies. They wouldn't have to be pushed hard at all to compress to the natural response of the driver+enclosure. They will be made to hit maximum output below 30 Hz very fast. That is why I don't take their base response very seriously.

That is something I don't get. Everyone wants a sub that has a flat FR down to ~20Hz, but once you get the boost from being in a room, you have a sub with significantly tipped up bass. I suspect if I had a ULS-15 mk2, I would run it in the "EQ2" operating mode (without the added extension).

When I compared the JLAudio E112's vs the Rythmik E15HP's, the JLAudios put out a lot more energy in the mid 20Hz range, but the Rythmiks really did dig down much deeper (HT content). Had I listened to them on separate occasions, I may have concluded the E112's had more depth, but instantly switching between it was obvious that the E15HP's had more gravitas, it just wasn't yelling "hey, look at me".
For music, the E112 is just too boomy. If I turned down the sub to where it did not boom (especially stuff like Maroon 5, which has some deep bass), it was down much too low for the normal-mid bass. Furthermore, Audyssey XT 32 would not sufficiently tame the E112's boominess.

I don't think those charts measure what you think they do. 'Stored energy' is group delay, and in sealed subs a low end boost can generate group delay. However, I don't believe those charts are measuring group delay really. What would a perfect measurement look like in a chart like that? -Keep in mind that a 20 Hz cycle lasts 50 ms alone. Bass frequencies do not come and go in an instant. If you are interested in group delay, I would stick with Josh Ricci's measurements of group delay.

 

[KEW]

I believe a truly perfect sub would show nothing!
Since the test impulse is initiated by the same system that runs the mic, the measurement begins at the same time the impulse signal ends so the graph shows nothing of the impulse except the decay time.
The Rythmik E15HP is the best I have seen - fast decay and comparatively consistent across the frequencies:

 

[shadyJ]

Again, I don't think your interpretation of that data is correct. I think that, outside of room effects, simple frequency response is largely involved in those measurements, not so much group delay. Compare the spectrogram energy to the frequency response charts in the upper right window where there is a lot of energy vs where there is not a lot of energy in those charts. Also keep in mind that software was intended to measure room reverb time, not group delay. I am not so sure the ideal measurement would show nothing.

What's more, you said the E112 sounded boomy, and pointed to those spectragrams as evidence of that. The group delay of the E112 was measured by Josh Ricci, and nowhere was in its response was there a point where stored energy could have been humanly audible:

I think the difference you heard was not overhang but simple frequency response. I don't doubt that the Rythmik sub would have faster decay times either- I just don't believe that is what is mostly shown in those measurements, although there is some of that there. Compare the group delay of other subs that have been measured by both data-bass and home theater shack: the Aperion Bravus 12d II, the PSA XS15se. Compare the frequency responses of those subs to the spectragrams. What seems to be reflected is frequency response, although the delay of energy of the Bravus' passive radiators does seem to reveal itself in the spectrogram.

 

[Dr. Bob]

shadyJ, I don't think you're right to equate group delay with stored energy. According to here:
"In simple terms, group delay is the time it takes for an electrical input signal to become an acoustical output. It is frequency dependant and should ideally be zero seconds at all frequencies, but this is practically impossible."
So group delay would show up in the graphs as a shift to the right - indicating that the signal doesn't start at t=0 but at some later time.

Since the Fourier transform of an impulse is a flat spectrum, the graph should ideally show a thin red line on the left of the graph, and nothing else. This is very nearly what the Rythmik graph shows. The red/orange bulge protruding to the right in the E112's graph shows that there is significant energy at about 20 Hz that is hanging around longer, while the other frequencies have died out: stored energy. Orange is about 85 dB, so this would certainly be audible.

I'm not claiming to have any experience in these things: I've only owned one subwoofer in my life. But theoretically I'd expect any rightward protrusions in the graph to be heard as boominess - and that's what KEW is claiming to hear.

 

[Steve81]

Bill Fitzmaurice had mentioned a pearl of wisdom on this topic a while back a while back over at AVS.
http://www.avsforum.com/forum/113-subwoofers-bass-transducers/1478581-how-important-impulse-response.html#post23464901

Not terribly so. What the impulse mainly shows is how quickly inertia is overcome and the cone returns to rest after a single cycle pulse is applied. We don't listen to single cycle impulses, we listen to a continuous stream of impulses, and the inertial force is totally dwarfed by the electro-magnetic force provided by the motor. If the impulse response was really bad you'd hear it, but the frequency response would also point out the speaker deficiencies, and it would do so far more obviously. The main use of impulse response is to help identify what might be causing a really poor frequency response.

Food for thought.

 

[shadyJ]

shadyJ, I don't think you're right to equate group delay with stored energy. According to here:
"In simple terms, group delay is the time it takes for an electrical input signal to become an acoustical output. It is frequency dependant and should ideally be zero seconds at all frequencies, but this is practically impossible."
So group delay would show up in the graphs as a shift to the right - indicating that the signal doesn't start at t=0 but at some later time.

Since the Fourier transform of an impulse is a flat spectrum, the graph should ideally show a thin red line on the left of the graph, and nothing else. This is very nearly what the Rythmik graph shows. The red/orange bulge protruding to the right in the E112's graph shows that there is significant energy at about 20 Hz that is hanging around longer, while the other frequencies have died out: stored energy. Orange is about 85 dB, so this would certainly be audible.

I'm not claiming to have any experience in these things: I've only owned one subwoofer in my life. But theoretically I'd expect any rightward protrusions in the graph to be heard as boominess - and that's what KEW is claiming to hear.

Your cited definition of group delay sounds like another way of saying stored energy to me. Anyway 'stored energy' is how group delay was explained to me by people who understand the subject thoroughly.

One thing I am not certain about, is 0 in the t=0 before or after the signal is produced. The ideal response depends on what the test signal looks like. What would the spectrogram look like of a sub that can fully play back infrasonic frequencies, or to put it another way, what would the spectragram of a subwoofer that has a perfectly flat response from 1 to 250 Hz look like? If you look at the frequency response measurements in the upper right corner of those spectrograms, their energy levels do correspond to the energy levels in the spectrograms. So what is the difference between the delayed energy and the test signal? I sent XTZ an email with a few quick questions about the subject, maybe we will hear from them.

 

[its phillip]

Here's what data-bass has to say about the group delay measurement (and a few others):
http://www.data-bass.com/data?page=knowhow&type=0

10. A group delay graph is derived from previous measurements. This measurement indicates how much delay or storage of energy versus frequency is taking place in a system. Larger values in MS indicate more latency or energy delay.Ideally there would be zero group delay indicating an incredibly well damped system. In reality there is always some. Generally it is held that as long as the delay is below 1.5 cycles it is inaudible and most who claim to hear differences in delay between speakers would say that anything less than 1 cycle of delay is nothing to worry about. Additionally the deeper in frequency, the longer the wavelength and less sensitive our ears are to it the less audible a long group delay will be. Generally anything below 25-30Hz is not regarded as of much concern unless really bad. For example 40ms of delay at 25Hz is probably not a big deal and not very audible but 40ms of delay at 80Hz is going to be much more audible and of concern. Typically sealed, IB and other lower order systems offer the least amount of delay...Bass reflex systems typically have increased delay near the resonator tuning. Even higher order systems like horns and Bandpass enclosures can have more group delay and more complex delay plots. Additionally equalization and other signal processing, such as high pass filters and boost or parametric signal shaping can increase the group delay. Usually this measurements indicates nothing of concern unless the group delay is exceeding 1.5 cycles above 25Hz.

11. Waterfall and Spectrogram plot graphs are derived from previous measurements. These plots are both different ways of representing the amount of energy storage or decay rate in the systems. Resonances, ringing or other issues will show up with a long and slow decay rate. Look for frequencies that seem to hang around longer than the rest and seem to not want to decay away. For Waterfall graphs look for a response that drops off rapidly and cleanly by 25 to 30dB within the first 100ms. Unless there is a very obvious issue with ringing in a particular frequency band there is not usually anything of particular sonic consequence in these graphs. As with the group delay chart most of the energy storage will occur below 30Hz where it is not of much concern. Pay much more attention to issues higher up in frequency as they become much more audible than they are in the deepest bass.

 

[3db]

Here's what data-bass has to say about the group delay measurement (and a few others):
http://www.data-bass.com/data?page=knowhow&type=0

10. A group delay graph is derived from previous measurements. This measurement indicates how much delay or storage of energy versus frequency is taking place in a system. Larger values in MS indicate more latency or energy delay.Ideally there would be zero group delay indicating an incredibly well damped system. In reality there is always some. Generally it is held that as long as the delay is below 1.5 cycles it is inaudible and most who claim to hear differences in delay between speakers would say that anything less than 1 cycle of delay is nothing to worry about. Additionally the deeper in frequency, the longer the wavelength and less sensitive our ears are to it the less audible a long group delay will be. Generally anything below 25-30Hz is not regarded as of much concern unless really bad. For example 40ms of delay at 25Hz is probably not a big deal and not very audible but 40ms of delay at 80Hz is going to be much more audible and of concern. Typically sealed, IB and other lower order systems offer the least amount of delay...Bass reflex systems typically have increased delay near the resonator tuning. Even higher order systems like horns and Bandpass enclosures can have more group delay and more complex delay plots. Additionally equalization and other signal processing, such as high pass filters and boost or parametric signal shaping can increase the group delay. Usually this measurements indicates nothing of concern unless the group delay is exceeding 1.5 cycles above 25Hz.

11. Waterfall and Spectrogram plot graphs are derived from previous measurements. These plots are both different ways of representing the amount of energy storage or decay rate in the systems. Resonances, ringing or other issues will show up with a long and slow decay rate. Look for frequencies that seem to hang around longer than the rest and seem to not want to decay away. For Waterfall graphs look for a response that drops off rapidly and cleanly by 25 to 30dB within the first 100ms. Unless there is a very obvious issue with ringing in a particular frequency band there is not usually anything of particular sonic consequence in these graphs. As with the group delay chart most of the energy storage will occur below 30Hz where it is not of much concern. Pay much more attention to issues higher up in frequency as they become much more audible than they are in the deepest bass.

Based on that read, I believe KEW interpreted the results correctly and he further backed up his interpretations with his conclusions of what he heard. I don't understand why Shady keeps doing this!!

 

[shadyJ]

Based on that read, I believe KEW interpreted the results correctly and he further backed up his interpretations with his conclusions of what he heard. I don't understand why Shady keeps doing this!!

How does data-bass' explanation of group delay and their spectrogram explain the kind of measurements home theater shack is taking? They are measuring very different circumstances. Furthermore, how is KEW's interpretation correct when, in either measurement, the decay times of the E112 is below the threshold of human audibility?

 

[Dr. Bob]

I'm still confused about group delay, which seems to be being used in two different senses. However, I think I'm coming around to shadyJ's view.

The closest thing to an impulse input I could think of is a kick drum, so I looked up the frequency spectrum:

Notice that at the lowest frequency included (31 Hz), the time to decay to 85 dB is about 300 ms. So the 20-30 ms delay in Jman's plots (whether this is "group" delay or something else) is probably completely covered by the length of the input signal.

 

[3db]

How does data-bass' explanation of group delay and their spectrogram explain the kind of measurements home theater shack is taking? They are measuring very different circumstances. Furthermore, how is KEW's interpretation correct when, in either measurement, the decay times of the E112 is below the threshold of human audibility?

How do you explain the differences in what KEW heard?

 

[Steve81]

How do you explain the differences in what KEW heard?

Base frequency response and how well it meshes with KEW's room would be a fair guess. In my room, this was the starting point I chose to achieve a relatively flat response:


You can see how that differs from the E112, both in terms of how JL boosts the low end, as well as the behavior on the top end. If KEW's room is anything like mine, it wouldn't be hard to imagine the E112 sounding less than stellar without manually taking measurements & applying EQ.

 

[shadyJ]

I'm still confused about group delay, which seems to be being used in two different senses. However, I think I'm coming around to shadyJ's view.

The closest thing to an impulse input I could think of is a kick drum, so I looked up the frequency spectrum:

Notice that at the lowest frequency included (31 Hz), the time to decay to 85 dB is about 300 ms. So the 20-30 ms delay in Jman's plots (whether this is "group" delay or something else) is probably completely covered by the length of the input signal.

Wikipedia has a somewhat technical definition of group delay that does the job:
"In signal processing, group delay is a measure of the time delay of the amplitude envelopes of the various sinusoidalcomponents of a signal through a device under test, and is a function of frequency for each component."

Josh Ricci has this nice and succinct description of group delay taken from a discussion I had with him:
"It is a distortion of the timing of the signal. Delay indicates that signals in that bandwidth are developing a bit slower than at other parts of the bandwidth or ringing out longer which means that it takes the system some time to stop after the input signal has."

How it is reflected in the measurements from the Home Theater Shack is what I am trying to find out. I sent XTZ an email asking about it, but their server rejected my email. If those spectrograms are measuring both the signal and any delayed effects, then group delay will be obscured by quite a bit. It would be difficult to differentiate it from the regular frequency response output, so those charts wouldn't be very good at getting a sense over overhanging sound from the sub.

 

[KEW]

1
You can see how that differs from the E112, both in terms of how JL boosts the low end, as well as the behavior on the top end. If KEW's room is anything like mine, it wouldn't be hard to imagine the E112 sounding less than stellar without manually taking measurements & applying EQ.

Thanks for the info.
You specify manually taking measurements, I wonder why Audyssey (XT 32) did not tame the E112's? (I'm sure it did, some, but the Rythmiks are so much easier to listen to!)

 

[Steve81]

You specify manually taking measurements, I wonder why Audyssey (XT 32) did not tame the E112's? (I'm sure it did, some, but the Rythmiks are so much easier to listen to!)

IME, auto-EQ helps some, but it isn't a panacea. I know I had similar problems when I had the PB13; I ended up using the built in EQ and room compensation filters to correct the response before re-running Audyssey, and that helped a great deal.

 

[3db]

Base frequency response and how well it meshes with KEW's room would be a fair guess. In my room, this was the starting point I chose to achieve a relatively flat response:

View attachment 16670
You can see how that differs from the E112, both in terms of how JL boosts the low end, as well as the behavior on the top end. If KEW's room is anything like mine, it wouldn't be hard to imagine the E112 sounding less than stellar without manually taking measurements & applying EQ.

Thanks Steve. Are you saying that the output of the Rythmik is more linear than the E112?

 

[Steve81]

Thanks Steve. Are you saying that the output of the Rythmik is more linear than the E112?

In Kurt's room, I suspect that's the case.

 

[KEW]

Thanks Steve. Are you saying that the output of the Rythmik is more linear than the E112?

That is something I don't get. Everyone wants a sub that has a flat FR down to ~20Hz in an anechoic chamber, but once you get the boost from being in a room, you have a sub with significantly tipped up bass. I suspect if I had a ULS-15 mk2, I would run it in the "EQ2" operating mode (without the added extension).

The E112 FR is impressively linear down to ~20Hz, but those measurements are designed to mimic FR in an anechoic chamber.

IMHO, for subs, the only reason to measure this way is because it provides a consistent and repeatable measurement methodology. No normal residence has a room which does not add substantial room gain increasing as the frequency decreases.
Steve's chart of the "anechoic" response that results in a flat response after room gain would be a much better objective than an anechoically flat response. I am certain his room is a far better approximation of the typical listening room than an anechoic chamber!
"Anechoic" response Steve81 used to yield flat FR in his room:

Steve, please correct me if I am mistaken on any of this!

 

[TheWarrior]

The Schroeder Frequency helps define why Subwoofer measurements cannot be in-room: Below 250 hz, the room controls everything! Specific room dimensions that match quarter or full wave diameters, will resonate. So a given subwoofer will measure differently, in different rooms.