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PostPosted: November 20th, 2017, 7:45 pm 
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chris1973 wrote:
Roscoe Primrose wrote:
Cogito wrote:
Thanks Tom and Walt.

The box calculations based on T/s parameters seem to be an approximation under some "assumed" conditions. By that I mean, there doesn't seem to be any allowance for
1. Input power

Bassbox says you can put 100 watts in there and not exceed Xmax. I don't know if you know what 100 watts is, but 100 watts is a lot of power!


At what frequency and what xMax?


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PostPosted: November 20th, 2017, 7:47 pm 
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chris1973 wrote:
So, I'm not sure about what the engineers say about this:

My information defines fc as the box resonance, and f3 as the low end rolloff.

From this I would assume that if fc is above f3, it is a competing signal with the bandwidth of information the driver is supposed to be faithfully reproducing in a flat manner, hence detrimental to the performance of the system.


However, if fc is belowb f3, the resonance is producing gain in a place where you are losing gain from the natural rolloff of the system, and therefore might be beneficial in extending the low end response of the system altogether.

Chris


CHris:

What is Fc? I have never seen that in a list of TS parameters. Thanks.


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PostPosted: November 23rd, 2017, 6:40 pm 
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Posts: 375
Roscoe Primrose wrote:
Cogito wrote:
Thanks Tom and Walt.

The box calculations based on T/s parameters seem to be an approximation under some "assumed" conditions. By that I mean, there doesn't seem to be any allowance for
1. Input power

Not relevant. Performance should be independent of power until you run out of linear excursion or the voice coil gets hot enough to create power compression.

Roscoe


Roscoe,
Right on, but this article also says, performance can vary when played loud, within in the limits of the speakers T/s parameters.

http://www.fohonline.com/ci/31-tech-feature/12614-klippel-plots-going-beyond-the-thiele-small-parameters.html

Quote:
The Thiele-Small (T-S) parameters now provided on every driver datasheet do not provide insight into how drivers perform when the music is pumping and the drivers are required to produce a lot of output. Loudspeaker drivers are messy devices, producing more distortion than the rest of the audio signal chain combined. The T-S parameters do not capture any of that messy behavior or provide insights into whether one driver will have cleaner performance than another.
...
...
One key limitation of the T-S parameters is that they are “small signal” parameters, which means that they accurately capture the performance of the loudspeaker at low output volume. Further, the parameters have fixed values. They do not change for the driver based on different input levels. This is not indicative of the mechanical reality of drivers, where the electromechanical parameters of loudspeakers change during a gig.

For example, loudspeakers are bad at turning electricity into sound and the remaining electrical energy is dissipated as heat. This heat raises the temperature of the driver voice coil and magnet structure. As the voice coil temperature rises, physics dictates that the voice coil wire does not conduct as effectively, and this causes the driver voice coil resistance to increase. The thermal change in the driver results in a shift to multiple T-S parameters. This shift is not quantified by the numbers on the datasheet, which were probably measured at room temperature.

_________________
Shashi


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PostPosted: November 23rd, 2017, 7:56 pm 
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Joined: October 21st, 2013, 6:53 pm
Posts: 226
tomp wrote:
chris1973 wrote:
So, I'm not sure about what the engineers say about this:

My information defines fc as the box resonance, and f3 as the low end rolloff.

From this I would assume that if fc is above f3, it is a competing signal with the bandwidth of information the driver is supposed to be faithfully reproducing in a flat manner, hence detrimental to the performance of the system.


However, if fc is belowb f3, the resonance is producing gain in a place where you are losing gain from the natural rolloff of the system, and therefore might be beneficial in extending the low end response of the system altogether.

Chris


CHris:

What is Fc? I have never seen that in a list of TS parameters. Thanks.


Fc is box resonance as defined by Vance Dickason in the LDC. it's Qtc x fs over Qts


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PostPosted: November 23rd, 2017, 8:06 pm 
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At what frequency and what xMax?[/quote]

Bassbox tells me at 100 watts, this driver is producing 10mm of excursion @20 cycles. It peaks out at 11 mm down at 10 cycles. I assume that, if the signal goes this low, this would all be audible, even though it's below f3.


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PostPosted: November 23rd, 2017, 8:21 pm 
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This all brings up another issue I didn't understand until I had an amplifier with meters on it.I would hope somebody else chimes in on the issue:

We buy speakers that have 100-200 watt capability, and a lot of us buy amplifiers that can exceed 100-200 watts, but depending on your speakers, your actual listening level probably starts hurting before you reach 50-60 watt peaks. Despite this we still seem to think those 200watt specifications, and 110+db simulations we get from them, are of any practical importance.


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PostPosted: November 24th, 2017, 10:01 am 
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Joined: February 28th, 2013, 3:31 pm
Posts: 790
Cogito wrote:
Roscoe Primrose wrote:
Cogito wrote:
Thanks Tom and Walt.

The box calculations based on T/s parameters seem to be an approximation under some "assumed" conditions. By that I mean, there doesn't seem to be any allowance for
1. Input power

Not relevant. Performance should be independent of power until you run out of linear excursion or the voice coil gets hot enough to create power compression.

Roscoe


Roscoe,
Right on, but this article also says, performance can vary when played loud, within in the limits of the speakers T/s parameters.

http://www.fohonline.com/ci/31-tech-feature/12614-klippel-plots-going-beyond-the-thiele-small-parameters.html

Quote:
The Thiele-Small (T-S) parameters now provided on every driver datasheet do not provide insight into how drivers perform when the music is pumping and the drivers are required to produce a lot of output. Loudspeaker drivers are messy devices, producing more distortion than the rest of the audio signal chain combined. The T-S parameters do not capture any of that messy behavior or provide insights into whether one driver will have cleaner performance than another.
...
...
One key limitation of the T-S parameters is that they are “small signal” parameters, which means that they accurately capture the performance of the loudspeaker at low output volume. Further, the parameters have fixed values. They do not change for the driver based on different input levels. This is not indicative of the mechanical reality of drivers, where the electromechanical parameters of loudspeakers change during a gig.

For example, loudspeakers are bad at turning electricity into sound and the remaining electrical energy is dissipated as heat. This heat raises the temperature of the driver voice coil and magnet structure. As the voice coil temperature rises, physics dictates that the voice coil wire does not conduct as effectively, and this causes the driver voice coil resistance to increase. The thermal change in the driver results in a shift to multiple T-S parameters. This shift is not quantified by the numbers on the datasheet, which were probably measured at room temperature.

Good article, but he starts mixing up distortion with other parameters such as resonant frequency. At the end of the day all are important but should be looked at separately. You can then make a value judgment about what is most important to you. BTW, the Klippel sight has a huge amount of information. I don't think there is anyone else that has the depth of knowledge about dynamic drivers that he has.


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PostPosted: November 24th, 2017, 10:36 am 
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Posts: 790
chris1973 wrote:
tomp wrote:
chris1973 wrote:
So, I'm not sure about what the engineers say about this:

My information defines fc as the box resonance, and f3 as the low end rolloff.

From this I would assume that if fc is above f3, it is a competing signal with the bandwidth of information the driver is supposed to be faithfully reproducing in a flat manner, hence detrimental to the performance of the system.


However, if fc is belowb f3, the resonance is producing gain in a place where you are losing gain from the natural rolloff of the system, and therefore might be beneficial in extending the low end response of the system altogether.

Chris


CHris:

What is Fc? I have never seen that in a list of TS parameters. Thanks.


Fc is box resonance as defined by Vance Dickason in the LDC. it's Qtc x fs over Qts


Thanks Chris. Hope your Thanksgiving went well. I'm still trying to digest all the goodies we had.

The term Fc is interesting. I'm still away for the holiday so I don't have access to my SDC but looking it up on the web I see several definitions for Fc, Fb, and even an Fcb. We could combine those with Fs and come up with Fcbs. That way we could watch it all on TV. :lol: I'm including an interesting chart of terms I found. There is another parameter that may trump all the others that I saw on that chart, SAF. Seriously, I try to separate the various factors out so that I can make the unavoidable compromises that are necessary. Mixing resonant frequency and Q might tell you what the output is at any given frequency but by separating them you can tell what the "qualitative" effect of those two parameters are. For example, if you have a small box with a resulting higher Q and higher Fb (or Fc if you chose that semantic) although the bass will not go as low, it may seem to have more bass because of the bump. That is a common ploy used in small montors to create an image of more bass. Is it real low bass? No, but it might be satisfying. If you have an idea of what all the individual parameters are and how they are affected by box size you can make better decisions.

Now to really get folks pissed off at me. In my not so humble opinion, with the drivers that are available today you are really putting yourself at a disadvantage by relying totally on passive box alignments. Even if you want to stay with passive crossovers you can still smooth out the low bass respose and possible extend it if you have sufficient linear volume displacment in the driver and also sufficient amplifier power. I'm including an example of that process in my main system. With EQ, at my listening position which is 11 feet from the subs, the response is flat to 10 Hz. Since the 4 DVC 15 drivers have so much linear volume displacement, the distortion barely exceeds 5% at the higest point. This measurement was taken with only half of the subs working for a comparison with the single 18" Ultimax kit I was testing for the magazine. In reality it represents a measured 106 dB at that level.

The best part of this discussion is that we seem to have gotten the creative juices flowing and that is always a good thing. Now back to digesting food rather than audio information.


Attachments:
Definitions of Audio Terms.pdf [56.51 KiB]
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DVC 15 in distortion with DEQX EQ at listening position to 50Hz.png
DVC 15 in distortion with DEQX EQ at listening position to 50Hz.png [ 3.53 KiB | Viewed 1619 times ]
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PostPosted: November 24th, 2017, 10:49 am 
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Joined: February 28th, 2013, 3:31 pm
Posts: 790
chris1973 wrote:
This all brings up another issue I didn't understand until I had an amplifier with meters on it.I would hope somebody else chimes in on the issue:

We buy speakers that have 100-200 watt capability, and a lot of us buy amplifiers that can exceed 100-200 watts, but depending on your speakers, your actual listening level probably starts hurting before you reach 50-60 watt peaks. Despite this we still seem to think those 200watt specifications, and 110+db simulations we get from them, are of any practical importance.


Chris:

Off the top of my head, three things pop up. First, if you are using meters you may not be seeing true short term peaks. A scope would tell you that. If the amp is really clipping, the clipping behavior of the amp will determine how bad the distortion is. That is why many low power class A single ended amps reach way beyond their rated power. They generally clip in a very benign way. Their actual distortions are not as objectionable.

The second thing is that the drivers (or in rare cases the crossover components) may be distorting. You would have to see the driver distortion vs power input to determine that, Some drivers have very low distortion untill you reach Xmax and then go ballistic. Others have distortion levels that climb more gradually.

The third thing that is often overlooked is your ears. At some point not only does the level sound unrealistic, you can push your ears into a non-linear region.

Anyone else have other ideas?


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PostPosted: November 28th, 2017, 6:55 pm 
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With EQ, at my listening position which is 11 feet from the subs, the response is flat to 10 Hz. Since the 4 DVC 15 drivers have so much linear volume displacement, the distortion barely exceeds 5% at the higest point. This measurement was taken with only half of the subs working for a comparison with the single 18" Ultimax kit I was testing for the magazine. In reality it represents a measured 106 dB at that level.[/quote]

So getting to 10 cycles with really low distortion sounds interesting, but does anybody really need 106db in their listening room???
I'm not playing devils advocate, or passing a judgement in the form of a question. I'm asking because I really don't know!

I am actually a little bit more intrigued by something called "sound intensity", I have also heard it referred to as "sound power", as opposed to "sound pressure". Can anybody tell me anything about that?
Chris


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