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Title: Transient response?
Post by: duane massey on February 21, 2021, 01:31:43 pm
Just an idle question from a self-educated man: I understand how to read specs on speaker cabinets, and have been building cabinets for almost 50 years, so I should know the answer to this: is there any posted measurements in regards to the accuracy or transient response of a cabinet? Any way to compare boominess (maybe not the right term) at higher volume levels? We used to call it the "what goes in, comes out the same" goal, but we only had our ears back then, no test equipment.
Title: Re: Transient response?
Post by: Art Welter on February 21, 2021, 02:39:39 pm
Just an idle question from a self-educated man: I understand how to read specs on speaker cabinets, and have been building cabinets for almost 50 years, so I should know the answer to this: is there any posted measurements in regards to the accuracy or transient response of a cabinet? Any way to compare boominess (maybe not the right term) at higher volume levels? We used to call it the "what goes in, comes out the same" goal, but we only had our ears back then, no test equipment.
Spec sheet measurements don't directly indicate "Transient Response", though a smooth phase response and extended flat frequency response are good indicators. The ability to reproduce a recognizable square wave over a wide bandwidth is also a good indicator.

"Boominess", or "ringing", can be seen in waterfall or spectrograph measurements, showing energy storage vs time:

https://data-bass.com/#/articles/5cc0bc36a75a260004255c88?_k=25yqrk

Energy storage reduces, or "smears" transient impact.

Art
Title: Re: Transient response?
Post by: Martin Morris on February 21, 2021, 10:25:19 pm
Just an idle question from a self-educated man: I understand how to read specs on speaker cabinets, and have been building cabinets for almost 50 years, so I should know the answer to this: is there any posted measurements in regards to the accuracy or transient response of a cabinet? Any way to compare boominess (maybe not the right term) at higher volume levels? We used to call it the "what goes in, comes out the same" goal, but we only had our ears back then, no test equipment.

Duane,

Arta software has the Waterfall feature ... cheap too ... FREE

https://www.artalabs.hr/index.htm (https://www.artalabs.hr/index.htm)

cheers
Martin
Title: Re: Transient response?
Post by: John Roberts {JR} on February 21, 2021, 11:18:14 pm
Just an idle question from a self-educated man: I understand how to read specs on speaker cabinets, and have been building cabinets for almost 50 years, so I should know the answer to this: is there any posted measurements in regards to the accuracy or transient response of a cabinet? Any way to compare boominess (maybe not the right term) at higher volume levels? We used to call it the "what goes in, comes out the same" goal, but we only had our ears back then, no test equipment.
Since this is subwoofer forum I will ASSume limited frequency response.

Transient response can be objectively quantified by rise time, not sure how much it matters after the LPF of a sub.

JR
Title: Re: Transient response?
Post by: Ivan Beaver on February 22, 2021, 08:58:14 am
Since this is subwoofer forum I will ASSume limited frequency response.

Transient response can be objectively quantified by rise time, not sure how much it matters after the LPF of a sub.

JR
Yeah.  It is like drawing a line on the road.  The question is "when do you cross it"?  If you are walking that is pretty easy, but what if you in a tractor trailer?  Do you "cross it", then front touches the line?  but a little later you are still on the line, or when the rear of the trailer crosses it?  Or in the middle?

Higher freq are easier, but low freq present a whole new set of questions.

Even something like "arrival" of a low freq signal. Is it when the first part of the signal gets to you? or the peak?  Since low freq wavelengths can be very long, it gets into a whole different discussion.

Just look at the auto delay finders on various measurement platforms.  "If" they can give you a repeatable number, it is much longer than the distance you are away from the loudspeaker.  That is because they are adding the distance from the source AND the distance to the center part of the wavelength together.

Higher freq are much easier, because the wavelengths are much shorter.

And then you have the latency of the LP filter to add to the whole mess-------------
Title: Re: Transient response?
Post by: John Roberts {JR} on February 22, 2021, 09:25:07 am

And then you have the latency of the LP filter to add to the whole mess-------------
Better known as phase lag...

JR
Title: Re: Transient response?
Post by: duane massey on February 22, 2021, 10:08:11 am
Thanks, everyone. Back in "the day" we called it the "boom or thump" comparison. If you put on a recording of a heavy kick drum or thumping a mic, did the cabinet go "boom" or "thump"? We always strove for "thump", especially at higher volume levels. Built a lot of very large straight bass horns back then, and one of the biggest differences to our unscientific minds was the excursion of the woofers. Seemed to us that woofers in ported boxes really started flopping after a certain level, whereas the horns had significantly less excursion at the same output, and we assumed this was part of the boom vs bump that we were hearing. I will probably never build any horns of that magnitude again, so this is just idle curiosity on my part.
Title: Re: Transient response?
Post by: Ivan Beaver on February 22, 2021, 11:16:05 am
Thanks, everyone. Back in "the day" we called it the "boom or thump" comparison. If you put on a recording of a heavy kick drum or thumping a mic, did the cabinet go "boom" or "thump"? We always strove for "thump", especially at higher volume levels. Built a lot of very large straight bass horns back then, and one of the biggest differences to our unscientific minds was the excursion of the woofers. Seemed to us that woofers in ported boxes really started flopping after a certain level, whereas the horns had significantly less excursion at the same output, and we assumed this was part of the boom vs bump that we were hearing. I will probably never build any horns of that magnitude again, so this is just idle curiosity on my part.
Here is what I have found that is interesting, through various testing I have done. 

The "thump" or kick or punch is more due to a NON FLAT response.  Or one in which the upper part of the bass range is louder than the lower part of the response.  This can be due to either non proper alignment between tops and subs, eq boost, or just ragged response.

A flat accurate response will not sound as "punchy".

This can happen in a couple of different ways.  In horns,, there could be more horn gain at the upper end of the response than at the lower end (very common in shorter horns).

in front loaded cabinets this can often be harmonic distortion (which is simply higher freq that are not in the original signal-free sound if you think of it that way) or the rising response of the driver at higher freq of the bass range.

Most people have never looked at distortion with even a simple RTA.

Just put in a sine wave (preferably in the passband) at a low to moderate level, and look at the response on a RTA.  You should see a single spike (but there will be some skirts on the sides due to the way most RTAs overlap bands).

Now turn up the level and watch for freq that start to rise up that are harmonically related to the original (ie multiples of the original freq).  So if you put in 60Hz, you will see spikes at 120, 180, 240 etc.

The relative level of the other freq in relation to the original is the amount of distortion at those harmonics the cabinet is producing. 

This works well for full range cabinets as well.

Just don't get stupid or you can tear things up.
Title: Re: Transient response?
Post by: Mark Wilkinson on February 22, 2021, 11:28:12 am


Even something like "arrival" of a low freq signal. Is it when the first part of the signal gets to you? or the peak?  Since low freq wavelengths can be very long, it gets into a whole different discussion.

Just look at the auto delay finders on various measurement platforms.  "If" they can give you a repeatable number, it is much longer than the distance you are away from the loudspeaker.  That is because they are adding the distance from the source AND the distance to the center part of the wavelength together.

Higher freq are much easier, because the wavelengths are much shorter.



With all due respect, I don't think auto delay finders work like that...."adding the distance from the source AND the distance to the center part of the wavelength together."
(italics added to part i disagree with)

Because like you were saying just before that, when does the low freq arrive?  The first part of the wave, or the peak?
And the answer as I know it, is the first part of the wave, the very first initial rise of the wave.   
That's the time a good auto delay finder works to calculate, not the arrival of the peak of the wave.

My 2c...
Transient response predominantly equals frequency response.....flat full spectrum frequency response.
But even perfect frequency response can have it's transient response improved, when phase rotation/group delay are reduced/eliminated.

Perfect transient response is when the initial rise of all frequencies begins at the exact same time (which spreads their peaks out in time... )
This also gives a perfectly flat zero degree phase curve.  (not something likely to have with live sound, huh?)


Title: Re: Transient response?
Post by: Ivan Beaver on February 22, 2021, 12:54:59 pm
With all due respect, I don't think auto delay finders work like that...."adding the distance from the source AND the distance to the center part of the wavelength together."
(italics added to part i disagree with)

Because like you were saying just before that, when does the low freq arrive?  The first part of the wave, or the peak?
And the answer as I know it, is the first part of the wave, the very first initial rise of the wave.   
That's the time a good auto delay finder works to calculate, not the arrival of the peak of the wave.


So use a auto delay finder, with just a sub (no full range cabinets) with low pass filter engaged.  See what it tells you.  Now see if that distance is what the distance from the sub to the mic is.  I have never seen it be anywhere near close.

If you disengage the low pass filter, it will be more accurate, because there is more high freq information available (ie shorter wavelengths).  Of course the actual phase trace will tell you (depending on how it tilts) how close the measured distance is from the actual distance.  Of course you also have to take into account any digital delays (either actually set or AD/DA convertors).

It is not necessarily the peak, but is not the "onset" of the waveform getting there.
Title: Re: Transient response?
Post by: Michael Lawrence on February 22, 2021, 01:38:06 pm
I can tell you how it works in Smaart, which is an approach commonly implemented in other real-time analyzers as well. Typically your Delay Finder is just looking for the highest magnitude value peak in the IR (which is calculated as a realtime IFT of the TF). It finds the highest peak (absolute value, so if the largest peak is negative-going it'll still grab on to it) and then simply sorts out how much delay is needed to move that peak to t0. Optionally this can be done using ETC if desired, it might shift you a few samples either way.

https://imgur.com/ZslZDDr

Here that answer is "just less than 4 ms". (I am measuring relatively close to a lousy loudspeaker in a small reflective office.)
Once that delay is inserted:

https://imgur.com/TDD6ON1

As Ivan has pointed out we are now timed to the HF range in particular (flat-trending phase trace there) and the LF is arriving later (downward trend from left to right). The Live IR is biased towards high frequencies so it doesn't work very well for subs. That is for a few reasons but we can bandpass filter the IR if we want to lock onto a particular frequency range. For example, here is what we get with 125 Hz bandpass filter:

https://imgur.com/RSQdUmQ

After the filter is applied, it's the same game: find the peak in the IR. As you can see it's often not so clear cut and can be fooled by other arrivals from room boundaries and so forth, but our answer is now a full 15 ms later than it was before. If we insert that value into the measurement delay:
 
https://imgur.com/wvnfpmo

Now the phase trace is trending flat in that region (we are timed to that energy) and the higher frequencies are trending upward left to right (arriving earlier than that).

Thanks to the group delay of the LF there isn't one clear cut arrival time, as it's smeared out a bit - Ivan I really like your metaphor about the line on the road - , so the best we can do is to say "at what frequency." That's where the bandpassed IR trick comes in quite handy.

To clarify - we are not syncing to a particular point in the measurement signal's waveform - we are taking a source independent measurement. We are looking at the waveform of the impulse response of the system under test.
Title: Re: Transient response?
Post by: Mark Wilkinson on February 22, 2021, 02:24:15 pm
So use a auto delay finder, with just a sub (no full range cabinets) with low pass filter engaged.  See what it tells you.  Now see if that distance is what the distance from the sub to the mic is.  I have never seen it be anywhere near close.

If you disengage the low pass filter, it will be more accurate, because there is more high freq information available (ie shorter wavelengths).  Of course the actual phase trace will tell you (depending on how it tilts) how close the measured distance is from the actual distance.  Of course you also have to take into account any digital delays (either actually set or AD/DA convertors).

It is not necessarily the peak, but is not the "onset" of the waveform getting there.

Yep, I guess most all of us have seen how much an auto delay finder bounces around, when just measuring a low-passed sub.

I had a delay finder shootout comparing Smaart, Systune, and REW some time ago, where the test was to see how much each program varied through about a dozen 'finds'.
As expected, they all gave the same time, with essentially zero variance, when there was sufficient HF content.
But sub range of course got interesting....and plenty squirrely.

But back to onset vs peak...
I've found the better the transfer function measurement, the flatter the mag and phase of the measurement, 
that it becomes clear the programs are "trying" to make calculations that align onsets together.

"Trying"....because like you say, without enough HF content, the measurement programs don't have enough data to nail down timing.

An electrical transfer function of a full range, flat phase signal, will give a perfect looking Impulse Response, with let's say peak at t=0. 
(Like what we get running a transfer function, with  the exact same signal output on reference and measurement channels.)
 
Looking at that full-range Impulse with bandwidth limiting in place, shows the timings inherent for impulses of different octaves. 
Whatever  frequency range is chosen, the bandwidth limited impulse can be seen to have its onset at the t=0 timing of the full-range Impulse.
I've found REW is great for seeing this, it has more bench type analytics than Smaart.
I also find i get the same measurement results and timings using either program, so i do believe REW is just digging in a little deeper graphically to show how it works.

That timings are set by onsets is easy to see with such a clean full range impulse response, because the measurement program has all the data to make it all come together perfectly.

Cleary not the case with a sub.  But I think the point is, the program is trying to do for the sub the same thing it does with the clean full range impulse.
So the more the delay finder looks like it timed to peak rather than onset,  the crappier the measurement.
Title: Re: Transient response?
Post by: Michael Lawrence on February 22, 2021, 02:37:32 pm
Acquisition method is a big variable there.
Doing a sweep of a few seconds as in REW will net you a higher signal to noise ratio than a realtime analyzer's Live IR (which is made to be as fast and reactive as possible - 8K FFT with 4 averages by default in Smaart - which is enemy of averaging and longer acquisition times). If you flip Smaart over to IR mode and use either sweep or period-matched pseudo-random pink with a few averages you can trade in some acquisition time for really digging down deeper into the dynamic range. Here is 16K FFT, 0 averages, 32K FFT 8 averages and 256K FFT 8 averages all with period-matched pink.

https://imgur.com/yRqGUcU

We get the same answer in terms of frequency response which is why if you are just measuring to EQ / time align a PA, I am not going to use a slower acquisition method to increase SNR, I already have my answer. But if we are studying the room acoustics etc, the algorithms that calculate all those associated metrics are a lot happier and more accurate if we have a higher SNR in the measurement and it is worth the extra acquisition time.

Horses for courses.
Title: Re: Transient response?
Post by: Mark Wilkinson on February 23, 2021, 09:35:10 am
Acquisition method is a big variable there.
Doing a sweep of a few seconds as in REW will net you a higher signal to noise ratio than a realtime analyzer's Live IR (which is made to be as fast and reactive as possible - 8K FFT with 4 averages by default in Smaart - which is enemy of averaging and longer acquisition times). If you flip Smaart over to IR mode and use either sweep or period-matched pseudo-random pink with a few averages you can trade in some acquisition time for really digging down deeper into the dynamic range. Here is 16K FFT, 0 averages, 32K FFT 8 averages and 256K FFT 8 averages all with period-matched pink.

https://imgur.com/yRqGUcU

We get the same answer in terms of frequency response which is why if you are just measuring to EQ / time align a PA, I am not going to use a slower acquisition method to increase SNR, I already have my answer. But if we are studying the room acoustics etc, the algorithms that calculate all those associated metrics are a lot happier and more accurate if we have a higher SNR in the measurement and it is worth the extra acquisition time.

Horses for courses.

Hi Michael, thx for reply.

Yep, horses for courses. And please don't think i was saying REW is a better tool for finding sub timing.

My 'course' is always the same, that of a speaker builder trying to obtain the best quasi-anechoic measurements as possible (without a chamber other the great outdoors haha)
Haven't worked on room acoustic's in years.

So for my two horses, Smaart and REW, on their outdoor course, I've found I get more consistent sub timing with Smaart. 
It appears REW needs more HF spectral content than Smaart does, to do its transfer function math, with the same repeatability Smaart has. 
I don't know if this is due to Smaart's multi time windows, or to the temporal averaging capability.
I just know Smaart works better for low frequency work and is my go-to measurement program. (and that pink noise doesn't piss off neighbors like log swept sine sirens do lol)

What I like about REW is it lets' me look under the hood of the measurements, which I believe are probably much alike between programs. It's various high rez graphical breakdowns help, particularly for impulse responses, and other time domain looks. I often export IR's made in Smaart to REW to look into them deeper (it's easier to choose IR FFT size and averaging in Smaart.)

Anyway, apologize to the thread for swerving into technicalities regarding transient response, and even bringing up Smaart vs REW, etc.

But so help me, when i cut through all the horse crap audiophool impressions, and putting too much attention on measurements that don't matter cause they are buried so deep under SNR, or impossible to fix multiple acoustic source issues...etc
Well, simple mag and phase keep proving (to me anyway) that they are the gut science underneath it all that i can actually do something about....and the key to transient response.
I like to think my speaker builds have moved beyond 'punch' and into the world of 'slam'  ;D
Title: Re: Transient response?
Post by: Michael Lawrence on February 24, 2021, 10:15:00 am
Mark - no worries at all, it is definitely an interesting conversation, if derailed a bit from the original topic. I don't ever view it as a competition - at the end of the day you want to use the best tool to get the results you need. Simple as that.

m


Title: Re: Transient response?
Post by: Marcel de Graaf on February 28, 2021, 06:36:55 am
Hi All,

Wooo i catched this thread to late. This sort of threads keep me visiting this forum board.

There is an ongoing debate about the existence off punch, transiënt slam etc...... It keeps us interested because its recognizable when its there, but its still not defined with a measurement in a manner we can reprocedure it. Here`s my point of view.

When we notice a low frequency speaker has a lot off punch it`s mostly related to the high frequency and the distortion components of the speaker itself. Well it can sound musical to our ears, its not part off the original input signal. As the goal of a speaker system to reproduce the input source its techical wrong to have a source that has a signature at his own. All this signature is mostly attributed by the loudspeaker diaphragm.

A low frequency loudspeaker still can sound very musically (and much better to me) as it`s very fast and only producing low frequency content. Therefore the most important factor is to have a motor structure with a very low inductance and a rigid, non flexing cone. A example, the contrabass servodrive subwoofer use a motor that has the lowest inductance vs motor strenght, the system has very heavy riged diaphragms and still is the fastest, cleanest low frequency speaker i have ever heard. It`s still sound very fast even with steep low pass and high pass filters engaged. In terms of musical terms i would quote this as "slam" rather than punch.

A measurement number thats expressing the difference of the waveform (acoustic) vs the input source would be a more appropriate way to quantify this.

Gr. Marcel

     



Title: Re: Transient response?
Post by: Ivan Beaver on February 28, 2021, 12:05:34 pm
Hi All,

Wooo i catched this thread to late. This sort of threads keep me visiting this forum board.

There is an ongoing debate about the existence off punch, transiënt slam etc...... It keeps us interested because its recognizable when its there, but its still not defined with a measurement in a manner we can reprocedure it. Here`s my point of view.

When we notice a low frequency speaker has a lot off punch it`s mostly related to the high frequency and the distortion components of the speaker itself. Well it can sound musical to our ears, its not part off the original input signal. As the goal of a speaker system to reproduce the input source its techical wrong to have a source that has a signature at his own. All this signature is mostly attributed by the loudspeaker diaphragm.

A low frequency loudspeaker still can sound very musically (and much better to me) as it`s very fast and only producing low frequency content. Therefore the most important factor is to have a motor structure with a very low inductance and a rigid, non flexing cone. A example, the contrabass servodrive subwoofer use a motor that has the lowest inductance vs motor strenght, the system has very heavy riged diaphragms and still is the fastest, cleanest low frequency speaker i have ever heard. It`s still sound very fast even with steep low pass and high pass filters engaged. In terms of musical terms i would quote this as "slam" rather than punch.

A measurement number thats expressing the difference of the waveform (acoustic) vs the input source would be a more appropriate way to quantify this.

Gr. Marcel

   
A speaker that is a "faster" than another, is one that has a longer excursion with a given input voltage.

At any freq, the speaker will only move as fast as that freq.  At 60 hz (for example) all loudspeakers will move back and forth 60 times per second.  If they don't then something is REALLY REALLY wrong.

But one with a longer excursion per voltage will travel further, so it MUST go faster from one end of the excursion to the other.

Of course this extra excursion brings its own set of problems.
Title: Re: Transient response?
Post by: duane massey on March 01, 2021, 08:19:27 pm
A speaker that is a "faster" than another, is one that has a longer excursion with a given input voltage.

At any freq, the speaker will only move as fast as that freq.  At 60 hz (for example) all loudspeakers will move back and forth 60 times per second.  If they don't then something is REALLY REALLY wrong.

But one with a longer excursion per voltage will travel further, so it MUST go faster from one end of the excursion to the other.

Of course this extra excursion brings its own set of problems.
And this is kind of the question that I obviously didn't iterate well. Back in the 70's we built very, very large horns, straight horns with restricted throats. Compared to other designs the speaker excursions were very small to achieve what we perceived to be higher outputs, especially at lower freqs. The signal to them was hi-passed at 25hz and low-passed at 80hz. To my ears, there was no "overshoot" or "boominess", just a solid thud or thump. We were very low-tech, no measuring gear, so everything was relative to what we heard.
Most of the conversations here are well above my knowledge, but it has made fora very interesting dialog. Thanks!
Title: Re: Transient response?
Post by: MikeHarris on March 02, 2021, 02:01:57 am
been hesitant to bring up what had been a glaring issue to me.
some variable rails amplifiers...Crown MA for example..have difficulty with the leading edge of bass wave..notably kick drum attack.
i have seen over power related driver failure from using level to recover that feel.
Linea..Powersoft...Lab dont exhibit this
Title: Re: Transient response?
Post by: Marcel de Graaf on March 02, 2021, 03:47:43 pm
been hesitant to bring up what had been a glaring issue to me.
some variable rails amplifiers...Crown MA for example..have difficulty with the leading edge of bass wave..notably kick drum attack.
i have seen over power related driver failure from using level to recover that feel.
Linea..Powersoft...Lab dont exhibit this

I have experienced the same with some other amplifiers. One time i had the very solid reputable amplifer EV P3000 to my low frequency part and switch over
to a crest pro 9200. I couldn`t believe how much faster (if that is the correct word to use) and impact that amplifier gave to the system.   

Title: Re: Transient response?
Post by: MikeHarris on March 02, 2021, 04:16:23 pm
the Crest 9200 shamed the Crown too.
They did variable rails much better
Title: Re: Transient response?
Post by: duane massey on March 02, 2021, 04:52:53 pm
Interesting tidbit: when we built the 20hz horns in the mid 70's each one held 5 TAD 1602's. Each woofer was driven by approx 85 watts, and the excursion was so small that you had to shine a flashlight on the cone to even see the movement (if you could stand to squeeze into the throat while it was working).
Title: Re: Transient response?
Post by: Marcel de Graaf on March 04, 2021, 02:33:18 pm
Interesting tidbit: when we built the 20hz horns in the mid 70's each one held 5 TAD 1602's. Each woofer was driven by approx 85 watts, and the excursion was so small that you had to shine a flashlight on the cone to even see the movement (if you could stand to squeeze into the throat while it was working).

This is efficiency related. Hornloading a driver in the right conditions makes the driver have less excursion for a given output compared to direct/vented system. Its as Ivan mentioned if a speaker has more excursion for a certain frequency, than this speaker must be faster as a speaker with less excursion at the same frequency. Hornloading usually make`s the low frequency part sounding a lot cleaner as there is less distortion produced by the speaker.

We all know the classic 808 kick drum.  This has some high frequency content in the beginning of the waveform followed quickly by a decay off low frequencies. To ideal reproduce this kick drum (and make it absolute tight or "punchy") the high frequencies has to come from the same acoustic center as the low frequencies. I always wondered if it would not be a big  improvement for the listener as this full kickdrum is played back in a different track layer where only the full kickdrum is reproduced by a wider bandwidth subwoofer (multiple drivers). Maybe other problems occur.

Coming back to the low frequency driver itself. I always keep my eyes out for the highest -3db point of the motor structure itself. If you would dismantle the loudspeaker cone and suspension you are left with only the voice coil. This part has only the resistive part of the wire winding and the inductance formed by the coil. The formed circuit has some time delay on its own, usually called the electronic time constant in the world of servomotors. This time constant is the time the motor reached 63% of his max. current to its inital step response. The formule for the time response of the motor alone is L/R and this can be converted back to the real -3db frequency point of the loudspeaker, but be aware this usually not shown in a frequency chart of the loudspeaker, because directivity (and/or a combination from other effects) is make the speaker looking flat. The time constant of the servodrive subwoofer is incredible low.

And than there is the issue the inductance is not constant over its frequency range. It will always be a big can off worms. A good reading about the importance of the subject is in the following link; http://aespeakers.com/designing-for-low-distortion-lambda-001-motor/

gr. Marcel

 
Title: Re: Transient response?
Post by: Jim McKeveny on April 12, 2021, 12:04:34 pm


Transient response can be objectively quantified by rise time, not sure how much it matters after the LPF of a sub.

JR

Couple decades ago I came across a study that found that people are more sensitive to rarefaction than compression at low frequencies.(Wish I could find it now. It was in pre-internet engineering journal). This certainly implies that absolute polarity is a factor in the leading edge transient VLF experience.
Title: Re: Transient response?
Post by: Art Welter on April 12, 2021, 05:40:45 pm
Couple decades ago I came across a study that found that people are more sensitive to rarefaction than compression at low frequencies.(Wish I could find it now. It was in pre-internet engineering journal). This certainly implies that absolute polarity is a factor in the leading edge transient VLF experience.
Jim,

If you can find any scientific study that supports your implication, love to see it.

The "leading edge" transient of most VLF experiences is high frequency noise, like the kick drum waveform example below.
Reversing it's polarity, as between the top and bottom example will make no difference in the "experience" of it's VLF envelope.

That said, if a VLF waveform were highly asymmetric, and the speaker reproducing it had large amounts of even-order distortion, it's possible reversing polarity could be audible due to a level change.

Art




Title: Re: Transient response?
Post by: Ivan Beaver on April 13, 2021, 08:29:13 am
Couple decades ago I came across a study that found that people are more sensitive to rarefaction than compression at low frequencies.(Wish I could find it now. It was in pre-internet engineering journal). This certainly implies that absolute polarity is a factor in the leading edge transient VLF experience.
Years ago I did a test (based on some people telling me so), that JBL double scoops had more impact when the drivers went backwards with a + input.  The "idea" was that they loaded up the horn first, rather than hearing the front loaded first.

I totally understand how easily our ears are fooled (I have fooled myself quite often), but I swear they did sound punchier when wired in reverse.

With that being said, there are all kinds of places in the signal chain that could reverse the polarity of the signal, nullifying the movement.

I do question my findings back then (it was 25 years or so ago), as I have learned a lot since then that make me wonder about the test.  No I have not done it since.
Title: Re: Transient response?
Post by: Ivan Beaver on April 13, 2021, 08:32:12 am


That said, if a VLF waveform were highly asymmetric, and the speaker reproducing it had large amounts of even-order distortion, it's possible reversing polarity could be audible due to a level change.

Art
And just because you can hear it, does not make it better or worse.

The Hi futility market loves to embrace anything that "sounds different", as "It must be better".  Even if it is worse.  Just hearing a "change" is often a big deal.

If you "believe" a piece of gear is better, and it sounds different, then it MUST be better-right????????  HAHA
Title: Re: Transient response?
Post by: Jim McKeveny on April 13, 2021, 11:15:47 am

If you can find any scientific study that supports your implication, love to see it

I'd like to also. It was @1977-8. The "sub" woofer concept was just making the rounds - Infinity Servo-Statik, Fulton J's, Dahlquist Sub. I dove into the SUNY Stony Brook Engineering Library card catalog to see what research there might be on VLF. What came across was not so much the audio realm as military: shockwaves, non-lethal weapons, etc. The polarity difference wasn't about asymmetry in the source, but in the human response.

Title: Re: Transient response?
Post by: Jim McKeveny on April 13, 2021, 11:19:02 am
And just because you can hear it, does not make it better or worse.

The Hi futility market loves to embrace anything that "sounds different", as "It must be better".  Even if it is worse.  Just hearing a "change" is often a big deal.

If you "believe" a piece of gear is better, and it sounds different, then it MUST be better-right????????  HAHA

Agreed. This is what I call the "optometrist" effect. "Better? Or worse?...."  'Better now?" ....
Title: Re: Transient response?
Post by: Steve-White on April 13, 2021, 11:31:30 am
Years ago I did a test (based on some people telling me so), that JBL double scoops had more impact when the drivers went backwards with a + input.  The "idea" was that they loaded up the horn first, rather than hearing the front loaded first.

I totally understand how easily our ears are fooled (I have fooled myself quite often), but I swear they did sound punchier when wired in reverse.

With that being said, there are all kinds of places in the signal chain that could reverse the polarity of the signal, nullifying the movement.

I do question my findings back then (it was 25 years or so ago), as I have learned a lot since then that make me wonder about the test.  No I have not done it since.
Interesting.  I used to run a pair of single JBL rear horn loaded "scoops" per side in a DJ setup.  JBL E-140's in them, Phase Linear 400 for power with Altec 511 horns.

It could be the simple "Click Test" done with a battery when tuning the enclosures, i.e. how much damping material to stuff them with.  That's a good way to check how well the box works.  Kick drum attack of waveform as to what the amp sees with regards to polarity depends upon how it's mic'd - front or rear as far as the electrical polarity of the "hit".

I would like to listen to such a test and compare different LF designs - might learn something.  :)

Thinking back, the JBL + or red phase for DC was for the cone to pull in with a positive voltage applied to the red terminal which is the opposite to many other brands.
Title: Re: Transient response?
Post by: Art Welter on April 14, 2021, 03:24:41 pm
I used to run a pair of single JBL rear horn loaded "scoops" per side in a DJ setup.  JBL E-140's in them, Phase Linear 400 for power with Altec 511 horns.

Thinking back, the JBL + or red phase for DC was for the cone to pull in with a positive voltage applied to the red terminal which is the opposite to many other brands.
Altec changed their polarity conventions to the AES standard in the late 1960s, JBL continued with their "backwards" negative polarity on legacy woofers like the E-140.

A system or transducer is said to be negative if a positive-going voltage applied to its red (non-black) terminal causes a negative pressure at the output of the device. As of 2005, the following JBL woofers were still negative:
E110, E120, E130, E140, E155, LE8T, 2118, 2202, 2220, 2235, 2241, 2105, 2123,  2206, 2226, 2240, 2245.

However, in most cases, JBL loudspeaker systems, even if they make use of negative polarity transducers, were internally wired so that they “behave” as positive systems. That is, a positive signal at the 1/4" phone plug tip or red or positive terminal of the system, caused the low frequency cone to move outward.

Fun.



Title: Re: Transient response?
Post by: Ivan Beaver on April 15, 2021, 05:03:16 pm
Altec changed their polarity conventions to the AES standard in the late 1960s, JBL continued with their "backwards" negative polarity on legacy woofers like the E-140.

A system or transducer is said to be negative if a positive-going voltage applied to its red (non-black) terminal causes a negative pressure at the output of the device. As of 2005, the following JBL woofers were still negative:
E110, E120, E130, E140, E155, LE8T, 2118, 2202, 2220, 2235, 2241, 2105, 2123,  2206, 2226, 2240, 2245.

However, in most cases, JBL loudspeaker systems, even if they make use of negative polarity transducers, were internally wired so that they “behave” as positive systems. That is, a positive signal at the 1/4" phone plug tip or red or positive terminal of the system, caused the low frequency cone to move outward.

Fun.
I learned the hard way about JBLs backward polarity.

It is the first gig I did with all of my woofer cabinets.  Half were loaded with JBL and the other half with EV.

WHen I fired them all up, it wasn't as much bass as I needed or expected, so obviously I TURNED IT UP MORE.  What else do you do when you are young and stupid.

I had some replacement EV woofers on hand (just in case).  The guy providing the lights (who also owned a large PA in town) was helping me replace the drivers and he said "Did you know your JBLs are wired up backwards?".

He told me to take a battery to them after I got them reconed.

The lessons we learn the hard way.
Title: Re: Transient response?
Post by: Mike Caldwell on April 15, 2021, 08:55:21 pm
Altec changed their polarity conventions to the AES standard in the late 1960s, JBL continued with their "backwards" negative polarity on legacy woofers like the E-140.

A system or transducer is said to be negative if a positive-going voltage applied to its red (non-black) terminal causes a negative pressure at the output of the device. As of 2005, the following JBL woofers were still negative:
E110, E120, E130, E140, E155, LE8T, 2118, 2202, 2220, 2235, 2241, 2105, 2123,  2206, 2226, 2240, 2245.

However, in most cases, JBL loudspeaker systems, even if they make use of negative polarity transducers, were internally wired so that they “behave” as positive systems. That is, a positive signal at the 1/4" phone plug tip or red or positive terminal of the system, caused the low frequency cone to move outward.

Fun.

The models still in production from your list 2206, 2226, 2241 are still backwards just to to keep it less confusing when working with different eras of the same model.
Some thing applies to their compression drivers.

New JBL models note the standard polarity on the speaker as a reminder.
Title: Re: Transient response?
Post by: Steve-White on May 09, 2021, 01:35:10 pm
I learned the hard way about JBLs backward polarity.

It is the first gig I did with all of my woofer cabinets.  Half were loaded with JBL and the other half with EV.

When I fired them all up, it wasn't as much bass as I needed or expected, so obviously I TURNED IT UP MORE.  What else do you do when you are young and stupid.

I had some replacement EV woofers on hand (just in case).  The guy providing the lights (who also owned a large PA in town) was helping me replace the drivers and he said "Did you know your JBLs are wired up backwards?".

He told me to take a battery to them after I got them reconed.

The lessons we learn the hard way.

"Young and stupid" has an eerily familiar ring to it...  :)

The worst time I had with drivers was the initial year of running horns for mid-highs.  Altec 511 & 811's with I believe were 802D compression drivers on them.  Whatever crossover I was using I don't remember, but it was Altec passive.  After going though several diaphragms, I purchased my first electronic crossover, Ashly SC80.  Problem solved and the system sounded better to boot.

Then moving into 2" compression drivers and 90 x 40 fiberglass radial horns, meant I had lots more top end available, then the bottom end needed some upgrades to keep up.  Once LF components were upgraded to match the top end, came learning how to dial in the setup.  Sent a few 12" & 18" drivers to the promised land when learning how to setup limiters, system gain structure, and drive levels.

I enjoy reading through posts about how much amplifier for a given loudspeaker system or component and how some members comment on how much power they use.

For me, enough amp to burn down the stacks, then back it off around 2db and you're there.  The ones that mention they use astronomical amount of power, don't mention trips to the recone shop.  Which tells me they haven't hit the top end of the performance envelope - turn it up.  The only way to really know the limit is to push past it.  Talking passive speakers.

No idea if this applies to the pre-packaged powered stuff - but likely varies from brand to brand.