The Official "Can It Measure Well and Not Sound Good Thread?" - Page 7 - AVS Forum
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post #181 of 195 Old 05-24-2012, 05:23 AM
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Originally Posted by MIkeDuke View Post

I am probably swimming in the deep end here but what the hell. Not sure if this has been mentioned, but don't we have to make sure the sub is measured properly in the first place before we can make an assumption on how it would sound?

Certainly. Any good reviewer in this area would normally state their methodology and equipment. If you look at Ricci and Ilkka they are quite upfront about this. So people know the measurements are done properly.
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post #182 of 195 Old 05-24-2012, 05:42 AM
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Originally Posted by jchong View Post

Certainly. Any good reviewer in this area would normally state their methodology and equipment. If you look at Ricci and Ilkka they are quite upfront about this. So people know the measurements are done properly.

I agree. Those two do seem to be some of the best, most complete type pf reviews I have read. My issue was that the people who reviewed the sub I mentioned did not realize it was a ported sub. Despite the huge flared port on the back of the sub. So it's not that they did not state their methodology, because they did. It's just that IMHO they were short on following the details of knowing what kind of sub they were measuring. That's all. I know it's hard work doing this type of work. But if we are saying that we can almost tell how a sub will sound, and act in our rooms, and a lot of the time we wont have the ability to hear all of the subs in our room, I just think it's important to do it right. Otherwise it's just a best guess on what it might be doing.

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post #183 of 195 Old 05-24-2012, 06:32 AM
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Originally Posted by mojomike View Post

In comparing the response between sealed and ported modes, we can see that there is a different shape from about 70hz on down. In the sealed mode, there is a rolloff that subtly begins at about 70hz. The shape from this point and below is different enough to give a different sound. Which is more accurate would depond on the characteristics of your room as well as your setup.


Yes, you are exactly correct, and I was incorrect when I said:

Quote:


The two modes should look the same above the port tune, and they do. The difference is how they decay at, and around, the port tune.

While the decay looks very similar above the tune point, the other differences are in the frequency response... the roll-off points and the slope of the roll-offs.

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post #184 of 195 Old 05-24-2012, 06:55 AM
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Originally Posted by mojomike View Post

In comparing the response between sealed and ported modes, we can see that there is a different shape from about 70hz on down. In the sealed mode, there is a rolloff that subtly begins at about 70hz. The shape from this point and below is different enough to give a different sound. Which is more accurate would depond on the characteristics of your room as well as your setup.

Ah yes, I forgot about the diff in the FR curve. I suppose the earlier roll off for the sealed mode makes it sound cleaner perceptually?
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post #185 of 195 Old 05-24-2012, 07:39 AM
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Originally Posted by jchong View Post

Ah yes, I forgot about the diff in the FR curve. I suppose the earlier roll off for the sealed mode makes it sound cleaner perceptually?

Depending on the room acoustics or perhaps taste, it might sound "cleaner" or "quicker" or possibly on the other hand "thin" or "weak." To determine which is actually more accurate, you would need in-room frequency charts.
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post #186 of 195 Old 05-24-2012, 09:02 AM
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Originally Posted by MIkeDuke View Post


I agree. Those two do seem to be some of the best, most complete type pf reviews I have read. My issue was that the people who reviewed the sub I mentioned did not realize it was a ported sub. Despite the huge flared port on the back of the sub. So it's not that they did not state their methodology, because they did. It's just that IMHO they were short on following the details of knowing what kind of sub they were measuring. That's all. I know it's hard work doing this type of work. But if we are saying that we can almost tell how a sub will sound, and act in our rooms, and a lot of the time we wont have the ability to hear all of the subs in our room, I just think it's important to do it right. Otherwise it's just a best guess on what it might be doing.

Afaik the tests are conducted at one or two meters outdoors so the contribution of the port is essentially captured. You can see a lot of discussion re how to accurately measure a ported sub in connection with the audioholics review(s) of the big ported Hsu. Ricci did fairly extensive testing to figure out how best to test subs with multiple powered drivers. IIRC differences between orientTions are on the order of one dB.

You will hear both driver and port on any sub. Depending on orientation and the room relative contributions may possibly differ slightly but you can't measure potential room effects simply because every room and every placement will differ.

If testing were being done in the very near field (an inch or less, typically indoors) you might need to take a separate measurement of the port and mathmatically combine them like Stereophile does for its speaker tests. But for subs tested at one or two meters outdoors I don't know how you would combine port and driver measurements. The main test already hears the port. You would have to use math to deduct the port output from the original measurement then add the port back in which seems counterproductive to me.
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post #187 of 195 Old 05-24-2012, 11:58 AM
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Originally Posted by craig john View Post

Hi jchong,

I could certainly do this, but I am going to pass on this request for 3 reasons:

1. IMO, the graphs speak for themselves. I chose these graphs as examples of different FR's only, not to make "examples" out of any of these subs.

2. There are many owners of these subs on the forum. I don't wish to offend any of those owners. More importantly, I don't think the point of this thread is to discuss the SQ of individual subs.

3. The graphs speak for themselves.

The OP said:



I posted graphs showing extension, (Low), output, (Loud) and FR, (Flat). IOW, everything the OP asked for except distortion, (Clean), graphs, (which are nonetheless available on the Data-Bass website.)

The baseline "sound signature" of each of those subs can be gleaned from the graphs. Nonetheless, how any specific sub will sound in any particular room will be a function of the room, the listening position and the optimization efforts the owner/installer has gone to to optimize the "transfer function" of that sub to the LP. Even a marginally performing sub can be made to sound good by installation optimization. However, NO sub can go beyond it's performance capabilities and physical limitations, and these will always be determined by the "baseline" outdoor, GP measurements.

For example, a sub with a -3 dB point of 25 Hz will never have deeper extension than 25 Hz, no matter how it is installed in a room. Even if you add multiples of that same sub, the combined response will still have a -3 dB point of 25 Hz. The maximum output at 25 Hz will go up, but the roll-off below that will stay the same. If you want deeper extension than 25 Hz, you need a subwoofer with deeper extension, pure, plain and simple.

I will also state that I think the difference in "transient response" between sealed subs and "vented" subs is clearly audible. For example, here is the transient response of the SVS PB13 Ultra in sealed mode:



and here is the response of the exact same sub in 15 Hz "ported" mode:



The LF roll-off is obviously different, but the decay time difference is, IMO, going to be much more audible than the LF roll off. The LF roll off can be compensated with an LF boost, (i.e., a Linkwitz transform circuit.) The slow decay time can not be compensated for with any current technology, and that slow decay will muddy the sound of the bass, and interfere with the response all the way up into the midrange.

Craig

this is starting to make more sense to me now. if you have FR graphs WITH decay time graphs (transient response), you might be able to tell how good or bad a sub will sound

but a FR graph ALONE will not tell you how "accurately" a subwoofer will reproduce the sound of an acoustic stand-up double-bass

i'm glad we got that cleared up

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post #188 of 195 Old 05-24-2012, 12:19 PM
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Originally Posted by otk View Post

this is starting to make more sense to me now. if you have FR graphs WITH decay time graphs (transient response), you might be able to tell how good or bad a sub will sound

but a FR graph ALONE will not tell you how "accurately" a subwoofer will reproduce the sound of an acoustic stand-up double-bass

i'm glad we got that cleared up

Clearly in ported mode it has a longer decay time but look at the frequency and spl, is this even noticed? Can we even feel if something is happening at 85-90 dBs at 10-20hz?
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post #189 of 195 Old 05-24-2012, 08:00 PM
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Originally Posted by MKtheater View Post

Clearly in ported mode it has a longer decay time

But this only applies at port tuning right? In the context of a double bass, where the lowest note is around 31Hz the port isn't going to affect the transient response if I understand it correctly.

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... but look at the frequency and spl, is this even noticed? Can we even feel if something is happening at 85-90 dBs at 10-20hz?

Are you referring to the listening threshold for low freq? If so, I think 90dB is audible down to 15Hz. At 20Hz, it needs to be about 82dB to be audible. This is going by the charts posted by Keith Yates:

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post #190 of 195 Old 05-24-2012, 08:03 PM
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Originally Posted by otk View Post

this is starting to make more sense to me now. if you have FR graphs WITH decay time graphs (transient response), you might be able to tell how good or bad a sub will sound

but a FR graph ALONE will not tell you how "accurately" a subwoofer will reproduce the sound of an acoustic stand-up double-bass

I wonder how relevant is distortion in predicting how accurate a sub will sound?

The reviews also include a distortion graph and the CEA-2010 table also gives distortion numbers.
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post #191 of 195 Old 05-24-2012, 09:08 PM
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What I was saying was that in ported mode the longer decay times are at 90 dBs and below and from 18hz and lower. So will we even notice the difference between ported and sealed in reality? Now put these in a room and now the sealed will take better advantage of the room gain and the extension might be noticed at a reasonable level.
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post #192 of 195 Old 05-24-2012, 09:22 PM
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Originally Posted by MKtheater View Post

What I was saying was that in ported mode the longer decay times are at 90 dBs and below and from 18hz and lower. So will we even notice the difference between ported and sealed in reality? Now put these in a room and now the sealed will take better advantage of the room gain and the extension might be noticed at a reasonable level.

I see what you mean. Looking at the waterfall, it seems most of the signals are completely decayed by 150ms. At 18Hz though, at 150ms it still seems as if the signal is at 90dB. At 300ms, it is at 73dB.

The audible threshold for 18Hz is 84dB, so going by the waterfall perhaps still audible out to 200ms?

Hope my interpretation is right. Corrections welcomed since I still need to learn more about this.
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post #193 of 195 Old 05-25-2012, 04:58 AM
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Originally Posted by JHAz View Post

Afaik the tests are conducted at one or two meters outdoors so the contribution of the port is essentially captured. You can see a lot of discussion re how to accurately measure a ported sub in connection with the audioholics review(s) of the big ported Hsu. Ricci did fairly extensive testing to figure out how best to test subs with multiple powered drivers. IIRC differences between orientTions are on the order of one dB.

You will hear both driver and port on any sub. Depending on orientation and the room relative contributions may possibly differ slightly but you can't measure potential room effects simply because every room and every placement will differ.

If testing were being done in the very near field (an inch or less, typically indoors) you might need to take a separate measurement of the port and mathmatically combine them like Stereophile does for its speaker tests. But for subs tested at one or two meters outdoors I don't know how you would combine port and driver measurements. The main test already hears the port. You would have to use math to deduct the port output from the original measurement then add the port back in which seems counterproductive to me.

Thanks for the explanation. That does make sense. The tests showed it to have an incredible amount of SPL capabilities, at least IMHO. But it also had a very high -3db point when measured outside(which was explained very well by the testers though) whereas many other, much smaller and less powerful subs had a lower -3db point when measured outside. But then I was told that the -3db point when listed outside was really meaningless because this sub will be put inside a room and will most likely have some sort of EQ attached to it to give you what ever curve you want.

As I said, I have heard this sub before and at a store and at one point I was watching a movie so loud that I was told it was shaking the 30,000 cf building I was in. I think if you were to look at the graphs and charts of this sub people would probably dismiss it because of its distortion numbers. But it was one of the only subs that could handle a 115db sweep and hit a max of 118, outside, at around 65Hz. I can honestly say that it is still one of the best sounding subs I have experienced but again, if you look at only the charts, people might dismiss it. But again, thanks for the explanation.

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post #194 of 195 Old 05-25-2012, 07:30 AM
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Originally Posted by MIkeDuke View Post

Thanks for the explanation. That does make sense. The tests showed it to have an incredible amount of SPL capabilities, at least IMHO. But it also had a very high -3db point when measured outside(which was explained very well by the testers though) whereas many other, much smaller and less powerful subs had a lower -3db point when measured outside. But then I was told that the -3db point when listed outside was really meaningless because this sub will be put inside a room and will most likely have some sort of EQ attached to it to give you what ever curve you want.

As I said, I have heard this sub before and at a store and at one point I was watching a movie so loud that I was told it was shaking the 30,000 cf building I was in. I think if you were to look at the graphs and charts of this sub people would probably dismiss it because of its distortion numbers. But it was one of the only subs that could handle a 115db sweep and hit a max of 118, outside, at around 65Hz. I can honestly say that it is still one of the best sounding subs I have experienced but again, if you look at only the charts, people might dismiss it. But again, thanks for the explanation.

Mike, as the person responsible for those measurements on AV;Talk, I would like to make a few points.

Firstly, we made a mistake. Had I known this was a ported sub, I would have had the guys turn it round 90 degrees so both port and driver were equidistant from the mic. If you have any idea of the logistics of one of these testing sessions, it is not easy to test half a dozen subs in an afternoon. It's a lot of work. There has to be a division of labour. In this case, I was sat 100m or so away from the sub operating the test rig while my colleagues were responsible for manhandling the various subs in and out of boxes. From that distance, there was no way for me to realise this was a ported sub. I had no prior notice of exactly which subs were going to turn up on the day. The UK sales manager from Focal-JM Lab was on hand and he never mentioned this was a ported sub and none of those doing the "humping" mentioned it. It was only when I went hunting for the manufacturer specs on the web to publish the results that I realised our mistake.

Yes, the wrong orientation would have made a small difference to the overall measurements. The port is effectively 24.9" further away from the mic than the driver. At a guess you might expect to get 2-3dB more output at the extreme low end of the frequency response with the sub turned sideways. But it's not an order of magnitude difference.

Part of me says, this is like looking a gift horse in the mouth and nit picking over measurements that no-one had paid any money for and therefore has no right to expect perfection. We do however take great pains to try and get things right but slipped up on this occasion. I'm sure if you look hard enough you will find slips in Ilkka's and Ricci's work.

In terms of the original point of this thread, it seems to me that an essential point is being missed here in terms of the perception of sound vs objective measurement. The ear and brain do not operate in the same way as a spectrum analyser. Psychoacoustic effects come into play and are important.

While a flat frequency response and zero distortion may represent the ideal situation for any reproduction system, no real-world subwoofer gets anywhere close.

The important issue is the way in which a particular design falls short of that ideal and the way that shortfall is perceived by the listener vs another design.

Some people may think objective measurements like THD% provide useful guidance on what something sounds like, but in reality a particular THD% number doesn't correlate with perceived sound quality at all. Also, THD% as measured ground-plane will be rather different when measured in-room. We actually need a better objective metric for distortion than THD%.
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post #195 of 195 Old 05-25-2012, 07:48 AM
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CJ,
Thanks for that post. It was most informative. I was not trying to be an ass. If I came off that way I am sorry. I was just meaning to say that even when people try and extrapolate how a speaker, or in this case a sub, might act in their room, it is important to know that it was measured "the right way". I fully understand that all of these tests are very difficult and time consuming. I guess I let my bias get the best of me. Yes, I am human. I have heard this sub many many times. It seemed to me to be a great sub. The specs seemed to indicate that it was a great sub. Also, back then, all I looked at was how low a sub went and I figured that the lower was the better sub.

All of this measuring and data analysis is way more than I can do so please don't take my points as being %100 negative. I just brought it up because I felt since I have heard this sub many times and it always sounded great to me, that I should bring it up. If all I had to go on was the -3db mark, I would not even consider this a sub woofer. I was unfortunately hung up on that number. I just wanted to try and make the point that there is more to what a person might think a sub woofer might sound like and act like then what the numbers might tell us. Again, I meant no disrespect to you or any other tester out there .

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