Anechoically "flat to 20Hz" vs a 35-40 Hz roll-off

[Swerd]

There is no such thing as fast bass. In other words a low long wave low frequency will never have a sharp upstroke. To get that implies the addition of high frequency content.

The bottom line is that the system must have an excellent transient response to have natural realistic reproduction.

I completely agree with TLS Guy, transient response explains how time matters to bass behavior.

We have had this conversation before. I searched and found a previous thread where I took the effort to discuss how a speaker cabinet's Q is directly related to bass transient response. Cabinets with high Q result in bass that rings on and on, while low Q can result in bass that is well damped.

http://forums.audioholics.com/forums/threads/frequency-response-graphs.92881/#post-1062303

Qtc and transient response explain this better than "frequency response curves flat to 20 Hz…". Read it and tell me whether it helps you understand this better. At first, I found it hard to understand until I realized the transient response time gets longer as Qtc gets larger. The shape of the bass roll-off curve is directly linked to short (low Q) or long (high Q) transient responses.

Transient response isn't directly linked to bass deviations due to room reflections, but if bass comes from a sub woofer with a high Q cabinet design, its long ringing transient response will provide more time for the listener to be aware of unwanted standing waves. It will have more time to muddy over and obscure other sounds in the music that would be more easily heard with bass from a low Q cabinet.

 

[yepimonfire]

Interesting, I had not really thought much of in-room peaks causing an early roll-off. Makes sense!

I was sloppy to say 40Hz (35Hz is better), but used Jman's measurements for the Dayton SUB-1200 (below). This is before he was combining the port and the driver measurements into one curve, so we have to make some inferences, but the port starts to roll-off ~35Hz and the driver is falling fast at ~35Hz.

I have only heard the 1200. Do you feel the 1000 and the 1500 are equivalent designs, just with more (or less) extension/output, as expected from the size of the driver?

I'd say that's accurate. The amplifiers are slightly more powerful, but as we all know the difference between 100w and 100w is nothing, 150w is a measly 1.5dB gain all things the same. The sub 1500 is a hell of a lot more sensitive than the 1000. Listening to Jean Victor Guillou's pictures at an exhibition on the organ, which is a torture test for subs considering the recording seems to have unlimited bottom end, the driver barely moves at a volume of 100dB. Movies have been the same experience.

The amplifiers may seem a bit underpowered on paper, but even on the sub 1000 I managed to achieve 108 dB using low passed pink noise with no audible distortion or port noise. I haven't played around with the 1500 yet but I can only imagine that even in a large room one could easily achieve the 115dB required for reference listening peaks.



I still think there's something wrong with that measurement. Per a conversation with the PE tech, the port is tuned to 25hz, the drivers Fs is 25hz, and plugging the t/s parameters into a calculator along with the box volume and port diameter/length gives you an f3 of 25hz. Someone else took measurements on avsforum and got 25hz as well

Tuning a box and port above the Fs of a driver would be an incredibly stupid design decision that would create a "one note wonder". I hardly believe they would do that. Parts express has always been fair and honest with their low frequency ratings of their subs and speakers, as every one of them I've owned has measured -3dB at their claimed response.

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[yepimonfire]

I doubt that peaks cause early roll off. A peak in a higher freq range may just give the illusion of an earlier roll off. I don't see how a peak would change the lower response.

It wouldnt, just make it appear that way on a graph.

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[William Lemmerhirt]

It wouldnt, just make it appear that way on a graph.

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Ok. Could you explain exactly how this works then?

 

[KEW]

@TLSGuy and @Swerd. I was very much under the impression that transient response and impulse responses were what was relevant; but over the past year, discussion with ShadyJ and reading have me second-guessing this.
The following thread is directly on topic with my post and I am inclined to believe Josh Ricci has the best understanding of this.
It seems that he is saying that an earlier roll-off will always ensure an excellent transient response. I may be misinterpreting, but it seems like he is questioning the benefit of impulse/transient measurements as, in the end they are mostly reflecting the FR.

http://www.avsforum.com/forum/113-subwoofers-bass-transducers/2697241-what-best-measurement-subwoofer-tightness.html

 

[Swerd]

It seems that he is saying that an earlier roll-off will always ensure an excellent transient response. I may be misinterpreting, but it seems like he is questioning the benefit of impulse/transient measurements as, in the end they are mostly reflecting the FR.

http://www.avsforum.com/forum/113-subwoofers-bass-transducers/2697241-what-best-measurement-subwoofer-tightness.html

I don't have time now to read that over, but it was my impression that earlier roll-off is an indication of a low Q cabinet design, and a low Q design directly results in a short transient response. You can't get short transient times without a low Q (i.e. well damped) cabinet alignment.

 

[shadyJ]

@TLSGuy and @Swerd. I was very much under the impression that transient response and impulse responses were what was relevant; but over the past year, discussion with ShadyJ and reading have me second-guessing this.
The following thread is directly on topic with my post and I am inclined to believe Josh Ricci has the best understanding of this.
It seems that he is saying that an earlier roll-off will always ensure an excellent transient response. I may be misinterpreting, but it seems like he is questioning the benefit of impulse/transient measurements as, in the end they are mostly reflecting the FR.

http://www.avsforum.com/forum/113-subwoofers-bass-transducers/2697241-what-best-measurement-subwoofer-tightness.html

I don't think he is saying that an earlier roll-off ensures an excellent transient response. I think what he is saying that frequency responses that place more emphasis in upper bass will be perceived as tighter- that is if you don't know what the reproduced sound is supposed to sound like. In actuality, anything but a flat frequency response will necessarily have a worse transient response, because if your speaker system can not reproduce all frequencies at the same amplitude for a given input signal, that affects how the system behaves in the time domain as well.

 

[TLS Guy]

@TLSGuy and @Swerd. I was very much under the impression that transient response and impulse responses were what was relevant; but over the past year, discussion with ShadyJ and reading have me second-guessing this.
The following thread is directly on topic with my post and I am inclined to believe Josh Ricci has the best understanding of this.
It seems that he is saying that an earlier roll-off will always ensure an excellent transient response. I may be misinterpreting, but it seems like he is questioning the benefit of impulse/transient measurements as, in the end they are mostly reflecting the FR.

http://www.avsforum.com/forum/113-subwoofers-bass-transducers/2697241-what-best-measurement-subwoofer-tightness.html

Again we have a ton of confusion. Transient response and damping are not the same thing, but loosely related.

A good transient response implies a fast sharp upstroke. Damping implies it dies quickly.

Now to have a sharp spike on the impulse response then you have to have frequencies all the way from high to low. For instance a 1 KHz square wave requires perfect response to 20 KHz. So rolling off a sub will make its transient response look worse. In any event a bass wave form is long, so it take time to propagate. Remember phase can always be expressed in time. In fact to avoid you getting confused about this it would be much better if you thought about phase as time and not degrees.

Now loudspeakers are inherently resonant and again Q does imply an element of time. Loudspeakers can be reduced to the mechanical model of springs. A speaker cone on its suspension is obviously a spring. If the suspension is sloppy the driver is high Q if stiffer lower Q. Now the air in a sealed box is also springy. The box tuning of a reflex enclosure is a spring. Qts of a speaker is the interaction of the mechanical and electrical springiness of the driver. Total system Q is the interaction of the driver and its loading. Now system Q can not be lower than driver Qts. So Q determines how long the system keeps vibrating after an impulse. In other words how many cycles declining in amplitude until silence. It is that issue of time again.

Now it is generally accepted that at a Q of 0.5 or less the system will sound to the human ear non resonant. In other words the vibration will decrease in amplitude so fast the ear will perceive it as instantaneous.

So I will put up the impulse response of my dual lines. You will see there is a little time smear due to electronic crossover delays and group delays in the lines. This is a low Q system and even the eye does not see continuing vibrations to the impulse.

I have done my best to time align the design within the parameters of rolling off drivers to get a smooth frequency response. So in this system the extended bass response sounds so called "fast". Actually very fast and light.

Now this has an impact on room modes, as the absence of further cycles due to high Q does not continue to excite room modes. So it looks almost as good at the listening position.

In a sub, the issue is really damping. A sub does not produce high frequencies. However integration of the sub is vitally important and a big problem. My view is that a good integrated design will best a speaker and sub any day. Physical separation implies by its nature a trespass with time.

 

[yepimonfire]

It wouldnt, just make it appear that way on a graph.

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I tried placing a sub that had a f3 of 23hz in a small square room that was 12x12, being that the room was small and square all room modes in the bass region were greatly exaggerated. The two fundamental room modes were 40hz and 58hz, this caused a 15-20dB peak centering at 50hz sitting in the opposite corner of the sub. Sitting past the critical distance of one room mode but in the nearfield of another room mode (ie 70% from the back wall on the same side of the room as the sub) caused the two modes to be out of phase, giving me a 20 dB rolloff at 40hz. Sitting in the opposite corner of both room modes past the critical distance had the 20 dB peak at 50hz. If there is a 20 dB peak at 50hz, and a 12dB peak at 40hz, and 30hz and 20hz is 6dB and 12 dB down, it might as well be the roll off point since it would likely be below the threshold and subject to masking effects. The room I'm in now has a fundamental room mode of 40hz, I get about a 6dB spike centering at 40hz. Using the 40hz band on the eq in my receiver set to -6dB has completely flattened out the response, and the sub sounds deeper in extension because of it.

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[yepimonfire]

Wouldn't a low q sub with a response to 20hz require a very large cabinet/driver and a ton of amplification and possibly EQ to reach that low? Don't get me wrong, I personally choose sound quality and extension over form factor, after all I do have a 15" subwoofer sitting in a medium sized living room, makes a great 3rd end table. I just know that unfortunately, the majority of people don't want massive ugly speakers, which drives the market to where it is now.

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[William Lemmerhirt]

I tried placing a sub that had a f3 of 23hz in a small square room that was 12x12, being that the room was small and square all room modes in the bass region were greatly exaggerated. The two fundamental room modes were 40hz and 58hz, this caused a 15-20dB peak centering at 50hz sitting in the opposite corner of the sub. Sitting past the critical distance of one room mode but in the nearfield of another room mode (ie 70% from the back wall on the same side of the room as the sub) caused the two modes to be out of phase, giving me a 20 dB rolloff at 40hz. Sitting in the opposite corner of both room modes past the critical distance had the 20 dB peak at 50hz. If there is a 20 dB peak at 50hz, and a 12dB peak at 40hz, and 30hz and 20hz is 6dB and 12 dB down, it might as well be the roll off point since it would likely be below the threshold and subject to masking effects. The room I'm in now has a fundamental room mode of 40hz, I get about a 6dB spike centering at 40hz. Using the 40hz band on the eq in my receiver set to -6dB has completely flattened out the response, and the sub sounds deeper in extension because of it.

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Got any graphs?

 

[William Lemmerhirt]

Wouldn't a low q sub with a response to 20hz require a very large cabinet/driver and a ton of amplification and possibly EQ to reach that low? Don't get me wrong, I personally choose sound quality and extension over form factor, after all I do have a 15" subwoofer sitting in a medium sized living room, makes a great 3rd end table. I just know that unfortunately, the majority of people don't want massive ugly speakers, which drives the market to where it is now.

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No. It would likely need a large cabinet but that would depend on overall design and should reach 20hz then, as long as it's placed right. You're right, most people don't like "ugly" speakers, but I'm also sure end table placement doesn't yield the best response for a subwoofer at the LP.

 

[Verdinut]

I'd say that's accurate. The amplifiers are slightly more powerful, but as we all know the difference between 100w and 100w is nothing, 150w is a measly 1.5dB gain all things the same. The sub 1500 is a hell of a lot more sensitive than the 1000. Listening to Jean Victor Guillou's pictures at an exhibition on the organ, which is a torture test for subs considering the recording seems to have unlimited bottom end, the driver barely moves at a volume of 100dB. Movies have been the same experience.

The amplifiers may seem a bit underpowered on paper, but even on the sub 1000 I managed to achieve 108 dB using low passed pink noise with no audible distortion or port noise. I haven't played around with the 1500 yet but I can only imagine that even in a large room one could easily achieve the 115dB required for reference listening peaks.



I still think there's something wrong with that measurement. Per a conversation with the PE tech, the port is tuned to 25hz, the drivers Fs is 25hz, and plugging the t/s parameters into a calculator along with the box volume and port diameter/length gives you an f3 of 25hz. Someone else took measurements on avsforum and got 25hz as well

Tuning a box and port above the Fs of a driver would be an incredibly stupid design decision that would create a "one note wonder". I hardly believe they would do that. Parts express has always been fair and honest with their low frequency ratings of their subs and speakers, as every one of them I've owned has measured -3dB at their claimed response.

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Tuning a box above the Fs of the woofer is not necessarily stupid. It is absolutely necessary with a low Qts driver if you want to obtain a flat response curve with a lower frequency rolloff knee. You will also get a flat response if you tune lower but it will start to rolloff at a higher frequency. This lower tuning will provide extended bass but at the expense of that punch which we like in the low range.

For example, as I am more familiar with the Altec Lansing woofers, I built several cabinets using the A7 components, in the case of the 416-8C driver, here are the real facts:

Some Thiele/Small parameters: Fs: 23.9 - Qts: 0.26 -Vas: 643.9 liters

BassBox6 Pro recommends a bass reflex box with a net internal volume of 5.035 cf tuned at 33 Hz.
With this configuration, you would get a flat response down to the point where it starts to rolloff (100 Hz or so) and you would get an F3 at 49.6 Hz. This is the kind of response that you get with their very popular Valencia enclosures which were marketed in the 1960's. This driver is very efficient giving 99 dB for 1 Watt input at 4 feet but it doesn't go down low in a small enclosure.

It's a compromise. If you want it to go low to 20 Hz, you have to put it in a 20 cf enclosure but you lose in efficiency. IMO, for home use, the best configuration for that sort of low Qts driver is to use an equalized, the so called 6th Order assisted box alignment, where you can get an F3 at 28 Hz in a 7.6 cf box and possibly avoid the need of a subwoofer.

 

[Verdinut]

Wouldn't a low q sub with a response to 20hz require a very large cabinet/driver and a ton of amplification and possibly EQ to reach that low? Don't get me wrong, I personally choose sound quality and extension over form factor, after all I do have a 15" subwoofer sitting in a medium sized living room, makes a great 3rd end table. I just know that unfortunately, the majority of people don't want massive ugly speakers, which drives the market to where it is now.

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That is exactly what I said about the Altec driver.

 

[yepimonfire]

Tuning a box above the Fs of the woofer is not necessarily stupid. It is absolutely necessary with a low Qts driver if you want to obtain a flat response curve with a lower frequency rolloff knee. You will also get a flat response if you tune lower but it will start to rolloff at a higher frequency. This lower tuning will provide extended bass but at the expense of that punch which we like in the low range.

For example, as I am more familiar with the Altec Lansing woofers, I built several cabinets using the A7 components, in the case of the 416-8C driver, here are the real facts:

Some Thiele/Small parameters: Fs: 23.9 - Qts: 0.26 -Vas: 643.9 liters

BassBox6 Pro recommends a bass reflex box with a net internal volume of 5.035 cf tuned at 33 Hz.
With this configuration, you would get a flat response down to the point where it starts to rolloff (100 Hz or so) and you would get an F3 at 49.6 Hz. This is the kind of response that you get with their very popular Valencia enclosures which were marketed in the 1960's. This driver is very efficient giving 99 dB for 1 Watt input at 4 feet but it doesn't go down low in a small enclosure.

It's a compromise. If you want it to go low to 20 Hz, you have to put it in a 20 cf enclosure but you lose in efficiency. IMO, for home use, the best configuration for that sort of low Qts driver is to use an equalized, the so called 6th Order assisted box alignment, where you can get an F3 at 28 Hz in a 7.6 cf box and possibly avoid the need of a subwoofer.

I think for home theater purposes, where a response to 20hz would likely benefit from low q full range speakers and a sub crossed over at 40-50hz or so. I have noticed with large floor standers such as the polk monitor 70s I had at one time I got better, tighter bass without a sub but didn't get the same extension obviously (they were like -3dB at about 40hz or so). I have no idea what the q was but I know the cabinet volume was considerably greater than most consumer grade subs.

How would a sealed subwoofer that naturally rolls off at 40hz or so eq'ed flat to 20Hz sound? Too much distortion?

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[Verdinut]

I think that it would distort and you would need a very solid and heavy box. Could you imagine the compression inside the cabinet with long cone excursions?
Apart from the harmonic distortion, I would anticipate a non-linear distortion caused by the air compression and decompression factors.
To tell you frankly, I am a lot more familiar with bass reflex designs than closed boxes.
I would suggest that you contact TLS Guy who, I am sure, knows a lot more than I about sealed enclosures and should be able to answer your question.

I think for home theater purposes, where a response to 20hz would likely benefit from low q full range speakers and a sub crossed over at 40-50hz or so. I have noticed with large floor standers such as the polk monitor 70s I had at one time I got better, tighter bass without a sub but didn't get the same extension obviously (they were like -3dB at about 40hz or so). I have no idea what the q was but I know the cabinet volume was considerably greater than most consumer grade subs.

How would a sealed subwoofer that naturally rolls off at 40hz or so eq'ed flat to 20Hz sound? Too much distortion?

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I think that it would distort and you would need a very solid and heavy box. Could you imagine the compression inside the cabinet with long cone excursions? It would demand a lot of amplifier power.

Apart from the harmonic distortion, I would also anticipate a non-linear distortion caused by the huge air compression and decompression factors.

To tell you frankly, I am a lot more familiar with bass reflex designs than with
closed boxes.
I would suggest that you contact TLS Guy who, I am sure, knows a lot more than I about sealed enclosures and should be able to answer your question.
It would definitely be interesting to know his opinion on such hypothesis.
Cheers,

 

[shadyJ]

How would a sealed subwoofer that naturally rolls off at 40hz or so eq'ed flat to 20Hz sound? Too much distortion?

The distortion would only arise if the travel of the moving parts of the driver left the linear range of excursion. You can EQ the sealed sub flat to 20 Hz and get low distortion, at modest output levels, but when you turn up the volume, distortion will go up. The nature of the distortion will depend on the driver. You would normally see a heavy amount of odd-order distortions crop up, in an optimized driver design. I wouldn't be worried about the distortion so much as the driver bottoming out and messing up the former.

 

[shadyJ]

Apart from the harmonic distortion, I would also anticipate a non-linear distortion caused by the huge air compression and decompression factors.

Harmonic distortion is a non-linear distortion. I would expect distortion caused by air compression in a small enclosure to be mostly even-order harmonics.

 

[yepimonfire]

Got any graphs?

Unfortunately I didn't save the graphs.

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[Trell]

I'm too much of a newb to have enough experience to weigh in. My only experience with ported were a pair of Klipsch 10" subwoofers. My sealed SVS' blow them away. Not really a fair comparison though.

I am in the market for some new subs (got a diy project list together) and decided to go with a pair of 15" sealed subs, though ported isn't out of the question if the price is right. Either way I'm keeping an eye on this thread.

For sure have upgraded your subs

Having Some Issues With Localization

But only when I lean my chair aaaallll the way back! :p:p:p

forums.audioholics.com

You should be careful being that close to the subwoofer as it could give you a black eye