Something stirs in the Undergrowth

Dedicated to those large boxes at one end of the room
User avatar
Nick
Site Admin
Posts: 15709
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#2551 Re: Something stirs in the Undergrowth

Post by Nick »

Yep, like Mark did for a few seconds I was thinking in terms of optics where solids have a slower speed of propagation. Unfortunately reality gets in the way again.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
SimonC
Old Hand
Posts: 545
Joined: Mon Sep 24, 2007 11:34 am
Location: West Yorkshire

#2552 Re: Something stirs in the Undergrowth

Post by SimonC »

IslandPink wrote: Fri May 15, 2020 8:38 pm One key feature of this mode of operation is that the cone's motion lags by 90 degrees ( phase ) from the voltage. So you might think that the phase is flat over that bandwidth, too ?
Don't forget the cones motion is driven only by the current flowing in the voice coil, not the voltage, and this current is 90 deg out of phase with the voltage for an inductor. I'm trying to figure out how this phase changes with frequency in the way that Tom Danley's post is explaining.
It jumps from talking about phase in relation to voltage to phase in relation to time mid paragraph and I'm trying to get my head around this...
User avatar
Nick
Site Admin
Posts: 15709
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#2553 Re: Something stirs in the Undergrowth

Post by Nick »

not the voltage, and this current is 90 deg out of phase with the voltage for an inductor.
Yes, but the voice coil is not a inductor, its a motor, so the power factor angle will be less than 90.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
User avatar
IslandPink
Amstrad Tower of Power
Posts: 10041
Joined: Tue May 29, 2007 7:01 pm
Location: Denbigh, N.Wales

#2554 Re: Something stirs in the Undergrowth

Post by IslandPink »

The voice coil inductance is relatively low in a speaker drive unit's typical operating band - it becomes important higher up where it limits the HF extension.

Struggling to find relevant info here, everything seems difficult today, the Tom Danley comment is stored on my work machine, I did a detailed comment about the Guy Sergeant horn a while back (Steve) on my thread but can't find it despite searching various terms. Just having another bad day :(
"Once you find out ... the Circumstances ; then you can go out"
vinylnvalves
Old Hand
Posts: 1074
Joined: Sat Jan 26, 2013 12:08 pm

#2555 Re: Something stirs in the Undergrowth

Post by vinylnvalves »

Answering Nicks question of what horns bring to the party I think is key here. From my perspective for me two things efficiency which means the driver doesn’t have to move far for a given db, which reduces the IM distortion. Secondly direction control, which I think is the most important, a nice sweet spot where you put your listening chair. Now for a bass horn.... I don’t see any benefit going below the schroeder frequency for your room. The efficiency for bass duties can be achieved by multiple bass drivers, some of the best bottom end sounding systems I have heard are wall of drivers types mainly OB with 3 or 4 15” drivers per channel.
If you have a massive room then you will have different design requirements. Regarding Guy Sargents horn rig at Scalford, yes it sounded nice, it had dynamics and micro detail. It was time aligned so the horn of the bass horn was about 12 ft on front of the others. It was in a 40ft room, where PA style systems are required.
SimonC
Old Hand
Posts: 545
Joined: Mon Sep 24, 2007 11:34 am
Location: West Yorkshire

#2556 Re: Something stirs in the Undergrowth

Post by SimonC »

Nick wrote: Sat May 16, 2020 10:14 pm
not the voltage, and this current is 90 deg out of phase with the voltage for an inductor.
Yes, but the voice coil is not a inductor, its a motor, so the power factor angle will be less than 90.
Sorry if you are teaching me to suck eggs here, its 30 years+ since I last did any AC theory.

Yes, but does it really change that much with the frequency? Inferring from the impeadance curve it will change rapidly around Fs, but once you are past that then its almost flat, or very gently rising for most of its working region and the power factor would also follow suit. (I take that back, it looks like the PF wanders around all over the place https://forum.speakerplans.com/power-fa ... page1.html)

Reading back the original post now I've had a nights sleep, I think the reason I'm struggling to follow the point its trying to make is that it jumps from power factor phase, to acoustic phase and then onto transient performance in one bound. Its compressed about 300 pages of Bjorn and Thomas's book into into one paragraph and my brain can't keep up.
chris661
Shed dweller
Posts: 2556
Joined: Mon Feb 22, 2010 7:29 am
Location: Sheffield

#2557 Re: Something stirs in the Undergrowth

Post by chris661 »

IslandPink wrote: Fri May 15, 2020 8:38 pm
chris661 wrote: Fri May 15, 2020 2:41 pm In response to point 1, I think it's worth noting that direct radiators also have a flat phase response across their linear range. You seem to be avoiding the obvious solution, then - what's wrong with putting drivers in a box?
Not so fast, young fella .
( I really must find Tom Danley's Joelist posting, and extract some of the gold from it to post on here.
Now, this may have been Tom quoting knowledge that came from people like Harry Olson) :
A cone driver when it's operating linearly ( amplitude ) is balancing the cone mass against increasing radiation resistance as the dispersion angle reduces.
One key feature of this mode of operation is that the cone's motion lags by 90 degrees ( phase ) from the voltage. So you might think that the phase is flat over that bandwidth, too ?
No, because the time for one cycle ( wave ) varies by a factor of 3 or 4 across the flat band of a cone driver. Hence the time lag for one quarter of a cycle ( 90°) is also NOT a constant value. So, there's a slow phase shift from high to low frequency, the lower frequencies lagging behind slightly in time. This implies the transient response of a good driver on a sealed box, within its flat band, is not as good as a horn.

Lots of good comment here, will take me a while to catch up.
Just a thought: you've made a small error in your post above, which is this: you've said that there's a constant phase lag, and then said that, because the frequency changes, the delay changes (true) and therefore the phase changes, which is false.
Constant phase angle = varying group delay, and constant group delay = varying phase angle.

Seems to me that the radiation resistance bit above directly contradicts the idea that speakers are minimum-phase devices.

Chris
User avatar
IslandPink
Amstrad Tower of Power
Posts: 10041
Joined: Tue May 29, 2007 7:01 pm
Location: Denbigh, N.Wales

#2558 Re: Something stirs in the Undergrowth

Post by IslandPink »

vinylnvalves wrote: Sun May 17, 2020 8:30 am 1. I don’t see any benefit going below the schroeder frequency for your room. The efficiency for bass duties can be achieved by multiple bass drivers, some of the best bottom end sounding systems I have heard are wall of drivers types mainly OB with 3 or 4 15” drivers per channel.

2. Regarding Guy Sargents horn rig at Scalford, yes it sounded nice, it had dynamics and micro detail. It was time aligned so the horn of the bass horn was about 12 ft on front of the others. It was in a 40ft room, where PA style systems are required.
1. What's the Schroeder frequency, Steve ?
ps. I know Dietmar Hampel has said that one of the advantages of very big horns like the 12A, 15A is that lower midrange frequencies like 200-300Hz become directional, which reduces room interaction. I would very much like to hear his system, but it's probably never going to happen !

2. I think Steve's point was that he didn't like Guy's horns. I had some misgivings about the type of driver, length, expansion etc. If I could find any info on them , pictures etc, again, I would comment further.
"Once you find out ... the Circumstances ; then you can go out"
vinylnvalves
Old Hand
Posts: 1074
Joined: Sat Jan 26, 2013 12:08 pm

#2559 Re: Something stirs in the Undergrowth

Post by vinylnvalves »

The Schröder frequency is when directionality became academic in a room due to the wave length, its around 200hz for an average 14ft room. Below this freq you apparently cannot tell where the bass source is. It logic behind subs, especially swarm multiple subs.
User avatar
IslandPink
Amstrad Tower of Power
Posts: 10041
Joined: Tue May 29, 2007 7:01 pm
Location: Denbigh, N.Wales

#2560 Re: Something stirs in the Undergrowth

Post by IslandPink »

chris661 wrote: Sun May 17, 2020 11:01 am
1. Just a thought: you've made a small error in your post above, which is this: you've said that there's a constant phase lag, and then said that, because the frequency changes, the delay changes (true) and therefore the phase changes, which is false.
2. Constant phase angle = varying group delay, and constant group delay = varying phase angle.

3. Seems to me that the radiation resistance bit above directly contradicts the idea that speakers are minimum-phase devices.
1. Good point, but still not sure there isn't a phase shift. By the time the waves are launched into the air, there could be. I mean - does the peak of an 800Hz wave, launched at the same time as a 100Hz wave line up properly ? I'm not sure it does, if there is a quarter-wave lag on each.

2. Well : group delay = first derivative ( slope ) of phase

3. I'm still not confident enough that I understand 'minimum phase', need to read up again. I'll let someone else comment.
"Once you find out ... the Circumstances ; then you can go out"
JamesD
Old Hand
Posts: 997
Joined: Tue Oct 09, 2007 4:26 pm
Location: North Yorkshire

#2561 Re: Something stirs in the Undergrowth

Post by JamesD »

Thoughts on using the term phase applied to natural sounds including speech and music:

For me talking about phase over wide frequency ranges doesn't make a lot of sense as it means different values at each discrete frequency you choose to define it at. Group delay does make sense as its applicable to each and every frequency. This particularly applies to natural sounds where pure sign waves don't occur on their own. Sine waves appear either from test signals or as a result of analysis, not discretely from the sound source so phase is essentially undefined until analysis is performed. Group delay is always measurable without further analysis - particularly given the impulsive nature of a lot of natural sound. I would say we are looking for constant group delay across the whole loudspeaker and particularly across any crossover region...

One reason I like open baffles and sealed boxes with a system Q of 0.567 which takes care of the bottom end response but puts big demands on the driver to get down into the bottom octave (16Hz to 32 Hz or 20Hz to 40Hz - depending on where you want to start :-)) Still not sure how you maintain this throughout the rest of the frequency range or with horns...

Whilst its true that Group delay is the first derivative of the phase angle this is with respect to angular frequency and hence a different value for each value of angular frequency - were back to not being able to define a single value across a range of frequencies...

Hope this helps a little...
User avatar
IslandPink
Amstrad Tower of Power
Posts: 10041
Joined: Tue May 29, 2007 7:01 pm
Location: Denbigh, N.Wales

#2562 Re: Something stirs in the Undergrowth

Post by IslandPink »

Not ... quite... but that doesn't mean it won't help when I read it several times again !... the likelihood being, any lack of merit (to me) is overwhelmingly due to me not understanding it, rather than your comments being confusing ! :D
It's fair to say, right now I have no clear understanding of what to build ( if at all ) next, as regards horns, as before I had some drive to go through the pain of building the next horn idea, based on a feeling that THIS ONE would work out ; however this has been successively eroded and the current dismal world situation has drained me of enthusiasm for a new project - paradoxically - despite potentially having a bit more time at home !
"Once you find out ... the Circumstances ; then you can go out"
chris661
Shed dweller
Posts: 2556
Joined: Mon Feb 22, 2010 7:29 am
Location: Sheffield

#2563 Re: Something stirs in the Undergrowth

Post by chris661 »

Sorry Mark, it wasn't my intention to curb your enthusiasm.
This has been a long and interesting journey to follow, but it would be nice if there was an endpoint in sight. It feels like this discussion is starting to reveal a target to hit, though, which is constructive.

It seems to me that you're perhaps more sensitive than most to (or just better at spotting) phase shifts.

Based on that, my go-to would be FIR-based DSP, which means you could take a system and alter the phase response to your liking while having the option of steep crossover slopes if they're needed. I can see, though, that DSP isn't something that everyone wants. IMO, high-quality digital gear is "good enough", but others will always disagree.

I think a 3-way system with first-order crossovers could also work, but you'd have to be really careful to pick drivers that are smooth and flat over a wide bandwidth, and (in the case of the mids and tweeters) don't mind receiving quite a lot of low-frequency signals.
Based on the gear you have around at the moment, I'd be thinking of something like the nice 12" bass drivers you have, running up to about 400Hz to meet a Fostex FX120, and those up to, say, 2kHz crossing to a good dome tweeter. I think a set of drivers like those would work well with first-order crossovers with minimal extra work. Cabinet-wise, I'm visualising something like the Yamaha NS1000 monitors.

The Yuchi horn you have is interesting, but I fear its implementation - to get decent polar response, you want the drivers acoustically fairly close together. That would mean the FX120s are sitting close to the compression driver, and will suffer from near reflections from the walls of the horn, as well as diffraction at the edge of the horn mouth.
A work-around might be to align the FX120s closer to the mouth of the HF horn, but to implement some kind of delay (DSP would make this easy) to time align them again. Another work-around would be to simply apply lots of absorbing material to the underside of the HF horn, killing off any reflections.

Remember: reflection = path length difference = time difference = phase shift.

When I make the journey over to you, of course I'll bring the rack of Powersoft amps for some FIR processing, but if you'd like me to bring, say, the FE126eN drivers you heard a while ago, just let me know. We'll have 10x channels of amplifier to play with, so a 5-way stereo system is on the cards. The amps can also implement all the usual IIR (analogue) filters, so we could try the first-order 3-way if you like.

Cheers,
Chris
User avatar
Ali Tait
Eternally single
Posts: 4374
Joined: Fri Jun 08, 2007 8:10 pm
Location: Galashiels

#2564 Re: Something stirs in the Undergrowth

Post by Ali Tait »

Chris, what’s available that provides FIR based processing and what are the costs please?
chris661
Shed dweller
Posts: 2556
Joined: Mon Feb 22, 2010 7:29 am
Location: Sheffield

#2565 Re: Something stirs in the Undergrowth

Post by chris661 »

Ali,

My amp rack has 3x Powersoft amps. Here's one of them: https://www.powersoft.com/en/products/t ... eries/t604

I have 1x T604 (6KW, 4ch), 1x T602 (6KW, 2ch) and 1x T304 (3KW, 4ch). RRPs are between £2000 and £3200 +VAT, depending on which amp you want (obviously, lower power and channel count = cheaper). However, you can get very significant discounts on those prices. I can't post publicly what I paid for them, but it was a lot less than that.
I went through these guys: https://www.cuk-audio.com/ and found them easy to work with.

I decided to go for those amps because they pack a lot of power, DSP and monitoring into a small space - the stack of amps is the size of your average AV receiver, and yet there's 10x amp channels, DSP, and a lot of power there. The density of the technology is impressive, and that's a good chunk of what I was paying for.
It ends up a useful tool in this situation (ie, take a load of DSP and amplifiers to someone's house to play HiFi for the day), but I wouldn't necessarily suggest that Mark goes out and buys a rack of Powersoft.


There are other options for FIR processing. For example, EQ APO (https://sourceforge.net/projects/equalizerapo/) is free, and will run on most Windows machines. It sits between the media player and the physical output device, and lets you do all sorts of neat stuff - including FIR processing. The interface is pretty straightforward, too, and I'd recommend playing with that software to anyone that's interested in this stuff. If you have a multi-channel soundcard (I expect one of those cheap 5.1 cards would do for a bit of playing around), you can also set it up for active crossovers.

To implement the FIR processing, you'll need something that can make the impulse files that EQ APO is expecting. Remember, an impulse response can contain a frequency and phase response curve within a .wav audio file - that's pretty useful: you can program an EQ curve and phase curve, export as a .wav, and import it into whatever. I use RePhase for this. You get a couple of graphic EQs, as well as a crossover section, tell it how many taps you want it to use and how long it can sit there and optimise, and it'll spit out a file. You can have an impulse response file (which makes EQ APO happy) or an old-fashioned CSV (comma separated variable) file, which my Powersoft amps understand.
RePhase shows you the measurement you've imported in one colour, and what the measurement will look like with the finished filter in another. Useful stuff, and it lets you optimise a bit before firing up the stereo to listen.


So, the workflow for a HiFi system with a PC source would be:
1 - Measure the speaker (or system) using REW. Take a few measurements, do some averaging, figure out what can be fixed with EQ work.
2 - Export the measurement from REW into RePhase.
3 - Using RePhase, create an impulse file (containing your adjustments)
4 - Import that impulse file into EQ APO
5 - Enjoy the music

Hope that's useful.

Chris
Post Reply