Help me understand time domain effects

Some time ago, a speaker company starting with D... produced a set of tower speakers that was reviewed on Stereo Review (around 1993). The most notable aspect of the speakers was the streo imaging, even when standing in front of one speaker, the review said that the streo soundstage was still intact.

I understand this has to do with time domain effects, but at this time it is time domain effects and not stereo sound stage effects that I am concerned with.

This software may help: | Acoustic Sciences Corporation

What I have read so far simply does not help. Apart from frequency response what else is there to consider in a speaker array, and room response?

This one may help as well: http://www.bigstonaudio.com/tdtheory.html
 
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Time and frequency are inextricably linked. The frequency response through the inverse Fourier transform, is the impulse response in time. The Fourier transform of the impulse response, is the frequency response.

So a peak or dip in FR at X Hz correspond to a feature at 1/X Hz in seconds, and vice versa.

Ideally we want a flat FR and an infinite peak of short duration equivalent to the inverse bandwidth of the frequency response in time.

It's a huge subject and I think it may be instructive to play with easy experiments and have hands on training and self teaching rather than just reading on the theory.

I am assuming you are talking about Dunlavy speakers. It's ok to mention names. :)

Yes, they are known for superb time domain response and are actually a rare example of a transient perfect speaker. Transient perfext speakers play percussive sounds most realistically and can play square waves properly. They can be identified with a Step Response that looks like a right triangle.

Back to hands on self training. Go and download a copy of Room EQ Wizard (REW) software. It's what most folks on diyAudio use to take measurements of speakers. Install it and start using it to take measurements of your speaker - any speaker will do even the one on the laptop or PC speaker. Any mic will do for teaching even the built in one on the computer.

REW - Room EQ Wizard Room Acoustics Software

The important thing is take a measurment of a speaker then post analyze it with all the tools a your fingertips to see the relationships between the frequency and time domain. The instruction manual is well written and contains theory and even references to technical papers used for the algorithms in REW.

If you really want get into designing and building good sounding speakers a calibrated mic is a must have item. It is a great tool and one of the most important things you need to have as a speaker designer.

Play with REW, read up on Fast Fourier transform, ask questions.

Read Siegfried Linkwitz's website - all of it. He is a superb teacher and has put a tremendous wealth of info up with great diagrams and explanations.

Linkwitz Lab - Loudspeaker Design

Good luck.
 
Time domain behaviour has been one of the highest points on my agenda. To get there I used a specific type of speakers to be able to get there. Well, at least in my mind.
It's an interesting subject and so far, after having build my speakers and obtained a high degree of time coherency I still feel it's a valuable asset for a loudspeaker to have.
An interesting read would be the papers linked in the first post of this thread:
http://www.diyaudio.com/forums/full-range/284916-room-correction-speaker-correction-what-can-we-do-dsp-power-now-availabl.html

Intrigued by these papers I tried the demo version of that software in my living room with my speakers. The plot that came out looked like this:
TDA_3D.jpg


If you are indeed talking about the works of John Dunlavy here, he has been a mayor influence on my views on time coherency. I chose a different set of compromises to get there. Most of my journey is covered in my (huge) thread: http://www.diyaudio.com/forums/full-range/242171-making-two-towers-25-driver-full-range-line-array.html

Stereophile has published an interview with John Dunlavy which is also food for thought.
Loudspeaker designer John Dunlavy: By the Numbers... | Stereophile.com

I've read all I could get my hands on written by Mr. Dunlavy. Very educational. Here's another group of documents containing a lot of material from Mr. Dunlavy:
Legacy Whisper Dunlavy SC V opinions - Page 16 - AVS Forum | Home Theater Discussions And Reviews

And for even more, his paper on the subject of loudspeakers:
Legacy Whisper Dunlavy SC V opinions - Page 10 - AVS Forum | Home Theater Discussions And Reviews
Look for the post by "Shocked One" 1/3 down on that thread that contains the paper by Mr. Dunlavy on: "Loudspeaker Accuracy".

While I agree on the excellence and wealth of material on Mr. Linkwitz's site, I don't see the time coherence as high on his agenda as it was on my own to be honest.
 

eriksquires

Member
2013-05-10 4:11 pm
Some time ago, a speaker company starting with D... produced a set of tower speakers that was reviewed on Stereo Review (around 1993). The most notable aspect of the speakers was the streo imaging, even when standing in front of one speaker, the review said that the streo soundstage was still intact.

I understand this has to do with time domain effects, but at this time it is time domain effects and not stereo sound stage effects that I am concerned with.

I'm not sure this particular feature is as much time as dispersion, and depends on exactly what the reviewer meant by Soundstage.

There's really in my mind, two ways in which reveiwers mean this. One is the more general sense of being able to hear sounds coming from between the speakers. A second sense is that they feel they can locate the precise location of instruments in the 2D space, and maybe the 3D space between the speakers.

In the first place, it's a more general sense of knowing the bass is playing to the right of the drums. In the second it's a sense of an acoustic instrument taking up space 1 foot back and 2 feet in from the right speaker.

So, I'll assume he meant the first, general sense. This is not about having perfect time domain results as much as having wide dispersion that varies evenly with the frequency. That is, you could have a narrow speaker that you can't hear at all when close to the other, or you could have a speaker with some frequencies that at an angle are out of balance with the rest.

The Magico S1 Mk IIs are a great example of the first sense as well. Wide and even dispersion so that anywhere you sit you have a general sense of the soundstage.

There is also a great debate about what is "perfect" enough. For some, perfect means that one driver blends in perfectly with the next even if the step response is not a triangle but a series of impulses. To them (and me) what's important is the blending from one signal to the next. Here's an example.

Step_Response.jpg


I think in general, this would be considered a very good step response, but not time-aligned. If it were time aligned, the first pulse at the left would be gone, and the big triangle shape to the right would be better defined.

Personally, I think a great step response is a good thing, but I've heard imaging come and go with step responses not nearly as good, so I'm not sure that this particular feature is THE way to get good imaging. Maybe I need to do more listening and reading. :)

Best,


Erik
 
From Stereophile measurements, here is the Dunalvy SC IV Step Reponse:

D4afig08.jpg


Here it is playing square waves:

D4afig09.jpg


For comparison, here is the measured step response at listening position for Wesayso's line arrays:

impulsestep.jpg


Possibly the best I have ever seen. Look at how far out it goes.

Imaging has to do more with phase coherency than with step response. For phase coherency, you want it to deviate as little from a nominal value as possible.

Here is measured phase at listening position and FR from Wesayso's LA:

linpas.jpg


I can't even fathom in my mind how good and coherent that would sound if I could actually hear it with my ears!

Interested in getting results like this? Use full range drivers and some DRC processing, room treatments, and lots of elbow grease - it's all there and within reach!

More info here: http://www.diyaudio.com/forums/full...er-full-range-line-array-127.html#post4382188
 
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Pan

Member
2002-09-19 3:52 pm
Time and frequency are inextricably linked. The frequency response through the inverse Fourier transform, is the impulse response in time. The Fourier transform of the impulse response, is the frequency response.

So a peak or dip in FR at X Hz correspond to a feature at 1/X Hz in seconds, and vice versa.

The impulse response will give you information about frequency response and phase/time response.

The frequency response (without the company of phase response) can not give you information about time domain behaviour unless the system is minimum phase which most speakers are not.
 
Quite a few detailled responses, which will take some time to understand: but the encouragement to experiment is appreciated - I need to create some space on my HP Pavilion to install the required software.

The speakers I mentioned - found the article - are the "DCM Time WIndow Three Loudspeaker System" - reviewed in Stereo Review Magazine.

Quote

"Since its founding nearly twenty years ago, DCM Corporation concentrated on designing loudspeakers whos acoustic output is as 'time coherent' as possible in order to create a stable, well-defined stereo images ove a wide listening area"

Another review here

DCM Time Window Seven Floorstanding Speakers reviews - Audioreview.com

Welcome to DCM Speakers
 
The Linkwitze site is great. He describes what we want from Stereo reporduction thus:

3.2 Optimal Stereo reproduction
The magic occurs when the loudspeakers seemingly disappear from the sound scene, to the point where one is inclined to ask: what are these two contraptions in front of me doing? Figure 11. All that is perceived is a phantom scene. A scene, which is not hard bounded by loudspeakers, softly windowed and extends behind and above the speakers. While there is a sweet spot, namely the apex of an equilateral triangle, the scene does not collapse into the nearest speaker upon moving to one side, but stays between the speakers with a perspective similar to what one would hear at a concert sitting to the side.

The-Magic-in-2-Channel-Sound
 
Those sound like nice speakers although I could not find the "time window 7"
On the website. Do you have a link to the specs? The other products all have a straight front baffle, and one immediate clue is that without either a physical stepped offset of the tweeter/woofer or use of a waveguide on the tweeter, it will be almost impossible to have a time aligned speaker system without active DSP.

What mic do you plan to use?
 
I just looked at some video of that Time Window 7 speaker on Youtube. My first impression is that it's a 2 sided speaker utilizing reflections to create envelopment. But that's just a first impression. The port on it makes me doubt it's time coherency though.
But without knowing more it would be unfair of me to judge them.

One of my favourite quotes on the effects of stereo:
There is another way of thinking about this: the loudspeakers serve as the first "early reflections" of a (phantom) sound source whose direct sound we didn't hear. Because our brain is good at filling in the missing blanks, it "infers" where that phantom source must be and THAT "inference" is what we actually perceive, or think we "hear."
Source: Moulton Laboratories :: The Brave New World: Loudspeakers to the Left of Us! Loudspeakers to the Right of Us!

Make the "reflections" we do hear (or loudspeakers) behave good enough in the room you are in and you will get the results as in that quote from Linkwitz.
All that is left is the music. I cannot point to the location of my speakers with my eyes closed, even though I know quite well where they should be.
 
Time Windows

Those sound like nice speakers although I could not find the "time window 7"
On the website. Do you have a link to the specs? The other products all have a straight front baffle, and one immediate clue is that without either a physical stepped offset of the tweeter/woofer or use of a waveguide on the tweeter, it will be almost impossible to have a time aligned speaker system without active DSP.

What mic do you plan to use?

Time Window 7 or such speakers must be older ones that are no longer produced. If you want to see the internals, Google "DCM time window 3" and you get some images of speakers with 2 sets of speakers at 90 degrees.

I will post the specs from the magazine article - is it ok to screenshot the section of the article - copyrights and so on - ed?

Time - aligned speaker system - time to get to the basics on speakers in a new topic.

What mic- I hav a headphone set with a microphone will start with that.
 
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Your speakers are great

I just looked at some video of that Time Window 7 speaker on Youtube. My first impression is that it's a 2 sided speaker utilizing reflections to create envelopment. But that's just a first impression. The port on it makes me doubt it's time coherency though.
But without knowing more it would be unfair of me to judge them.

One of my favourite quotes on the effects of stereo:

Source: Moulton Laboratories :: The Brave New World: Loudspeakers to the Left of Us! Loudspeakers to the Right of Us!

Make the "reflections" we do hear (or loudspeakers) behave good enough in the room you are in and you will get the results as in that quote from Linkwitz.
All that is left is the music. I cannot point to the location of my speakers with my eyes closed, even though I know quite well where they should be.

I followed some of your incredible speaker posts. Unfortunately I have to get to basics to understand all of this, yes I will try audio analysis - I have already found some audio software and will be trying it out as soon as possible.

This audio stuff is complex. I started out looking for a replacement for my sound system and after dissatisfaction with commercial products I am experimenting on my own now.
 
Hmm, not sure what you want explained about 'time domain effects'. I mean to accurately reproduce a signal requires that everything arrives at the same time with a flat frequency response and in the correct phase, so the highest frequency arrives first with each lower frequency increasingly delayed and since there's usually one or more XOs, their delays have to be factored in also to preserve the proper phase.

Physically, the driver's vertical locations shift backwards with increasing frequency and with increasing XO phase rotation [if applicable].

GM
 
Hmm, not sure what you want explained about 'time domain effects'. I mean to accurately reproduce a signal requires that everything arrives at the same time with a flat frequency response and in the correct phase, so the highest frequency arrives first with each lower frequency increasingly delayed and since there's usually one or more XOs, their delays have to be factored in also to preserve the proper phase.

Physically, the driver's vertical locations shift backwards with increasing frequency and with increasing XO phase rotation [if applicable].

GM

Well OK, then, then physically how to allow for this - the tweeters have to be furhter back in the cabinet than the woofers? How about crossovers, can crossover delay also be compensated for by speaker placement?

Can the shifting of the cone of a speaker driver be negated by making the cone fixed and allowing the coil to move? ( I think this was tried in a Time Domain speaker produced by Fujitsu?

http://www.fujitsu-ten.com/business/technicaljournal/pdf/33-2.pdf
 
Huh, that egg speaker story about time alignment is crazy! A single 3" fullrange is tilted/shifted for what! Crazy!

BasicHIFI1, please study modern loudspeakers construction principles well fist, eg. the RoomEQWizard Help section. The program downloads for free and is not large. You don't have to have any hardware (calibrated mics etc.) in the beginning.

Some good sources for down-to-earth basic principles of loudspeakers here
Frontiers
Speaker Design Works
The Art of Speaker Design
 
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Well OK, then, then physically how to allow for this - the tweeters have to be furhter back in the cabinet than the woofers? How about crossovers, can crossover delay also be compensated for by speaker placement?

Can the shifting of the cone of a speaker driver be negated by making the cone fixed and allowing the coil to move? ( I think this was tried in a Time Domain speaker produced by Fujitsu?

http://www.fujitsu-ten.com/business/technicaljournal/pdf/33-2.pdf

Well, the easy way is to use a wide BW point source [cone] woofer and HF compression horn speaker like the pioneers of audio arrived at. ;) Otherwise, a sloping or stepped baffle, stacked individual speaker boxes or a combination thereof, etc., can be used: http://www.6moons.com/industryfeatures/rmaf05paul/2.jpg
http://crev.vo.llnwd.net/o42/audioreview/images/products/product_121090.jpg

A more complex, but superior, way is to create a two or way horn like Danley Sound Labs' SH50 Synergy horn and add a separate sub system.

Yes, for every slope order add another 90 deg [1/4 WL] of delay, so for 4th order offset they are in phase, but have a 1 Hz frequency offset.

You're describing the diaphragms of early compression horn drivers, so as for driver, speaker design in general and modern design in particular, you really need to take Juhazi's advice, then ask for clarifications if need be.

GM
 

AllenB

Moderator
Paid Member
2008-10-18 11:31 am
can crossover delay also be compensated for by speaker placement?
Yes and no. A fixed distance, which means a fixed delay, means a different amount of phase shift at different frequencies.

Not that driver placement is worth a hill of beans if you don't do the important stuff, like getting the right amount of sound out into the right places in a smooth way across the spectrum. Driver placement can help to achieve this because it keeps things simple (geometrically).

Having the drivers time aligned, 'just because..', shouldn't figure high on your list of priorities.
 
Well, the easy way is to use a wide BW point source [cone] woofer and HF compression horn speaker like the pioneers of audio arrived at. ;) Otherwise, a sloping or stepped baffle, stacked individual speaker boxes or a combination thereof, etc., can be used: http://www.6moons.com/industryfeatures/rmaf05paul/2.jpg
http://crev.vo.llnwd.net/o42/audioreview/images/products/product_121090.jpg

A more complex, but superior, way is to create a two or way horn like Danley Sound Labs' SH50 Synergy horn and add a separate sub system.

Yes, for every slope order add another 90 deg [1/4 WL] of delay, so for 4th order offset they are in phase, but have a 1 Hz frequency offset.

You're describing the diaphragms of early compression horn drivers, so as for driver, speaker design in general and modern design in particular, you really need to take Juhazi's advice, then ask for clarifications if need be.

GM

Downloaded and reading : http://www.roomeqwizard.com/REWhelp.pdf