Something stirs in the Undergrowth

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Ali Tait
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#2566 Re: Something stirs in the Undergrowth

Post by Ali Tait »

It is, thanks.
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#2567 Re: Something stirs in the Undergrowth

Post by IslandPink »

chris661 wrote: Mon May 18, 2020 3:38 pm 1. 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.

2. 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.
Still catching up.... been slaving away all day at the kitchen table, as usual ...

1. No, my enthusiasm was curbed after the last horn build !
There are always endpoints, may be more than one, and depends on the number of dimensions.
The OB set-up still demands some experimentation to see if the twin FX120's could be replaced by a Lii Audio 8" - this should give me better bass and lower-mids, as I wouldn't have to pad the Supravoxes down. That's pending opening-up of travel etc.

2. The Yuichi horn together with a ribbon is more than interesting, it's so much better than even good cones in the upper mids, it cannot be ignored long-term. If I was going to experiment with anything like a direct driver underneath, it would have to start from a low-Q driver operating in the velocity-controlled region ( ie. upslope ) with low group delay. I said maybe 416B as an option earlier , but I think FE208Ez is more logical at least down to 150Hz . At some point the excursion will get too much, for reasonable volume, at which point the EQ would have to drop off steeply.
Whether this would bridge the gap to the tapped horn, that can go to at least 100Hz, not sure.
I should be able to get some idea using Hornresp, and a big sealed enclosure.
Proximity has its problems - but I can leave this to some listening experiments I think - I did hear some superb results, at one point, with the Azurahorn and the B&C driver, with the horn hanging over the front of the 8" driver.
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#2568 Re: Something stirs in the Undergrowth

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steve s wrote: Fri May 15, 2020 7:54 pm To me they are coloured to some degree and only as good as the driver..
Definitely true, the driver has to be good. One problem is that the centre of the cone, and dustcap, take over rather too much as frequency goes up, and if the driver fires straight down the horn, your response carries on far above where the sim says it rolls off. I have found that firing sideways into the throat is very helpful to cancel/mix some of that unwanted HF, but also, even in that case, a phase plug in front of the cone cleans things up. Definitely the FE208Ez is the best driver I've used for a horn in this range, I tried at least four.
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#2569 Re: Something stirs in the Undergrowth

Post by IslandPink »

Well this experiment has legs - this is FE208Ez on a big volume ( ie. IB ) driven by about 12.5W , gets 100dB at 100Hz with excursion just under 2mm ( Xmax = 2.5mm ) . Would be less in real life on a small baffle at 100Hz, but worth a try some time.
FE208Ez_limit_100Hz.JPG
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#2570 Re: Something stirs in the Undergrowth

Post by vinylnvalves »

For my two penneth on DSP processing, my experience has been minidsp and the Nadja. I used REW but found it too automated, preferring to use Holm Impulse or Arta to take the measurements and then build the crossovers up from scratch myself mainly using IIR’s which are fine for normal crossovers but you will not achieve linear phase. Linear phase is one of those debated topics on which the learned disagree. I heard the linear phase demo by Linn at Scalford a number of years back and it was clearly better than the non linear phase crossover on the same speakers. However I take this with a pinch of salt, as Linn salesmen are like Kirby vacuum cleaner salesmen, so what we were comparing against may have been poor.
I have been investigated more powerful systems so can do FIR’s at a reasonable sample rate. Studio systems are out of my budget. So looking at I5 plug computers. One of the best DSP front ends is Sigma studio which was free for use with AD DSP chipsets. There are lots of other diy codes as well as the ones Chris has mentioned. The following is a cheap way of dipping you toe into digital processing.https://www.audiophonics.fr/en/dsp-modu ... 12690.html
My logic for speaker building hasn’t changed since I was building passive crossovers. I only use drivers with reasonable flat responses and only use their linear frequency range, minimising the manipulation. I am only currently using the DSP for bass duties with “pass through” for the AMT’s. If you are happy that your top end is well aligned, I would suggest that you only a DSP for the bottom end, and maybe the powersoft amps are the ticket, others have used the Berhringer Nuke amps. I do find a KW per channel keeps the Supravox 15” drivers under control :D
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#2571 Re: Something stirs in the Undergrowth

Post by Ali Tait »

I use aN INuke Behringer amp for the 18” Goldwoods on the Bastanis, DSP at 200hz. Mid is a 12” driver, likely an Eminence, which is run open but mechanically damped. Tweeter is a compression driver run with 2.5uf first order cover, changed from 1uf after Mark’s measurements. Works well to my ears.
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#2572 Re: Something stirs in the Undergrowth

Post by chris661 »

IslandPink wrote: Mon May 18, 2020 7:24 pm
chris661 wrote: Mon May 18, 2020 3:38 pm 1. 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.

2. 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.
Still catching up.... been slaving away all day at the kitchen table, as usual ...

1. No, my enthusiasm was curbed after the last horn build !
There are always endpoints, may be more than one, and depends on the number of dimensions.
The OB set-up still demands some experimentation to see if the twin FX120's could be replaced by a Lii Audio 8" - this should give me better bass and lower-mids, as I wouldn't have to pad the Supravoxes down. That's pending opening-up of travel etc.

2. The Yuichi horn together with a ribbon is more than interesting, it's so much better than even good cones in the upper mids, it cannot be ignored long-term. If I was going to experiment with anything like a direct driver underneath, it would have to start from a low-Q driver operating in the velocity-controlled region ( ie. upslope ) with low group delay. I said maybe 416B as an option earlier , but I think FE208Ez is more logical at least down to 150Hz . At some point the excursion will get too much, for reasonable volume, at which point the EQ would have to drop off steeply.
Whether this would bridge the gap to the tapped horn, that can go to at least 100Hz, not sure.
I should be able to get some idea using Hornresp, and a big sealed enclosure.
Proximity has its problems - but I can leave this to some listening experiments I think - I did hear some superb results, at one point, with the Azurahorn and the B&C driver, with the horn hanging over the front of the 8" driver.
1 - Fair enough

2 - It sounds like the future system should revolve around that horn, then. Am I right in thinking you've got the Supravox 285 GMF driver? If so, the datasheet looks pretty promising for running that driver up to about 1kHz (Supravox specifically mention mating it with a 1" HF driver), in which case you would get rid of a crossover point and some headaches.
A large-format midbass combined with a good compression driver is a nice approach to a HiFi system IMO.

Do you have a cabinet that you could mount the Supravox drivers in?
The reason I ask is that combining a horn with an OB leads to a very odd presentation. I should know, because I've tried it. My OB was a 3-way design with an EV DH1a (excellent HF driver) on a horn, a Faital 10FH520 and a Beyma 15P1200Nd. The mids and bass had a very different sound to the HF, and I think that was down to how the room was being excited - the room behind the speakers was only receiving (and reflecting back to me) mids and bass, while the HF was only going forwards towards me. The frequency response etc was good, but the sound was still wrong.
It appears that Linkwitz found similar, and included a rear-facing HF driver in his LX521s: https://www.linkwitzlab.com/LX521/Description.htm

Based on that, I'd suggest that the radiation pattern ought to be consistent across the range, whether dipole or monopole. If you'd like to keep the HF horn, then it seems to me that the next step is a really really good cabinet for those Supravox drivers. Occasionally, you hear of speakers that "don't sound like a box", and they typically employ extensive internal treatments to break up standing waves, absorb reflections, and ensure the panels don't radiate delayed energy into the room.
Plenty of bracing and internal lining are the way forwards IMO.

Attached is an impedance graph I took of my Faital 10HX230 cabinets. The internal treatment was pretty straightforward: 1/2" wool underlay, and plenty of it. IIRC, it was three layers at the top and bottom, two layers down each side, and one layer on the back (the back panel also has a metal handle inset, which provides an uneven surface). The results, IMO, speak for themselves. It went from lots of little resonances, particularly the 700Hz one, to having them all damped out nicely.
The frequency response also improved - the ports are at the bottom of the baffle, and had problems with midrange leakage. With the added absorption, there's less midrange bouncing around inside the cabinets, so less to leak out of the ports. This had a knock-on effect on the frequency response - there was an obvious peak/dip combo around 700Hz, which vanished with treatments. Much better.

I have heard people say that internal treatments "kill the sound", and what I think has happened is that the midrange leakage has contributed some "liveliness" to the sound, which would then be missing. YMMV.

I suspect that impedance curves of other box loudspeakers could be quite revealing.

Chris
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#2573 Re: Something stirs in the Undergrowth

Post by IslandPink »

chris661 wrote: Tue May 19, 2020 11:40 am
1. It sounds like the future system should revolve around that horn, then. Am I right in thinking you've got the Supravox 285 GMF driver? If so, the datasheet looks pretty promising for running that driver up to about 1kHz (Supravox specifically mention mating it with a 1" HF driver), in which case you would get rid of a crossover point and some headaches.
2. A large-format midbass combined with a good compression driver is a nice approach to a HiFi system IMO.

3. Do you have a cabinet that you could mount the Supravox drivers in?
1. Yes but I've just explained that if we want a low phase-shift midrange, then the alternative to a horn is a very low Qts driver that can be equalised to flat using FIR. That's why I was talking about the FE208Ez. The Supravox is a very good but mass-loaded driver in the region, Qts is just under 0.4.

2. It's 'nice' but not good enough - this is almost where I started, about 9 years ago.

3. No, I converted it into a nice three-shelf rack for turntable and amps !
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#2574 Re: Something stirs in the Undergrowth

Post by chris661 »

1 - That's not the only alternative. We could also take a flat driver and flatten the phase if FIR is being deployed.

2 - Fair enough. Do you remember if it was the driver or the implementation?

3 - Oh well.

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#2575 Re: Something stirs in the Undergrowth

Post by IslandPink »

There are some more points I should respond to, but let me just get down what Tom Danley explained, a few years ago , I was able to find the document, which Martin Seddon ( Azurahorn) sent me :
( I'll do it in two chunks ) -

"Hi all

I am not sure how many Joes are in the "its all magic" camp and how many
are interested in how things really work but so far as how a woofer
really works, this has been known for some time. Authors like Benson,
Heyser have written very good books and papers on the subject.
At least from being able to model / predict the performance of a real
speaker from its electroacoustic equivalent circuit, there are no
missing links or mysteries, just a few things mfr.'s chose not to
explain and or things some choose not to look at..
Perhaps this explanation will help.

The number one misconception about woofers is that moving mass has
something to do with "speed" of response or its high frequency limit.
It does not, at least directly.
What mass affects is efficiency and also the shape of the low frequency
roll off.

A radiator that is small compared to the wavelength it is producing,
experiences an increasing acoustic load with increasing frequency (one
of the few places on sees a frequency dependent resistance with out a
reactance).  That radiator in an infinite baffle, driven at a constant
velocity
will produce a +6 dB oct rising response because its radiation
efficiency increases with frequency.
To make a driver like this have "flat response", we must roll off the
voltage response 6 dB per octave, one pole.
This is done by having a much larger amount of mass or weaker motor, such
that above some point velocity control is lost and then with increasing
frequency, the velocity falls 6 dB oct. It is this range, where the
velocity falls 6 dB /oct that one has flat response.
Electrically, this speaker looks like and acts like an R/C filter, the R
is the coil R+the amplifier source is R, and the C is the moving mass of the
speaker reflected through the motor, which looks /acts like a capacitor.

Since the moving part is the C, it is the voltage across it (the voltage
/velocity output) which falls 6 dB /oct, which is cancelled out by the
changing radiation resistance and now gives flat response.  The -90
degree phase shift of the slope is not cancelled out as the radiation
resistance is pure resistance.  Changing the size of the C (moving mass)
has no effect on the slope angle, just its level and starting point....."
"Once you find out ... the Circumstances ; then you can go out"
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#2576 Re: Something stirs in the Undergrowth

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"..99% of the people do not realize that when a point source has flat
response, its mid band acoustic phase lags behind the input signal by
about -90 degrees (once all fixed time delays are accounted for). This
broad band lag is equal to a time delay whose amount increases with
decreasing frequency.    This -90 degree operation is how some of the
simpler measuring systems "determine" acoustic phase, it is a Hilbert
transform of the amplitude and at low frequencies for a simple piston,
this is a safe assumption.

Consider how a normal "perfect" speaker spreads out a signal in time.
Make an imaginary signal that has equal amplitude content from 100 Hz to
25 Hz, a specific waveshape which has this property.
Take an imaginary perfect flat response speaker who's upper and lower
cutoffs are way past our needed bandwidth.
This mass controlled "flat" response speaker has a  -90 degree lag or
delay, at 100 Hz the phase shift is equal to a source 2.83 feet behind
the speaker cone, at 50 Hz, the delay is equal to 5.66 feet, at 25 Hz is
equal to 11.32 feet and so on.
This test signal's wave shape defines the input "time" of each frequency
component.
When reproduced, the highest frequency component at 100 Hz emerges from
the radiator 2.5 ms AFTER the signal arrived at the driver terminals.
At 50 Hz, this component emerges 5 ms AFTER the signal hit the terminals
and at 25 Hz, the signal emerges after 10 ms and so on.
With the driver spreading the signals frequency components out in time,
it is simply not possible to retain the same waveshape as the input
signal, lower frequencies arrive progressively later in time than the
original signal..  Any signal reproduced is done so with the spectrum
rearranged in time by the drivers acoustic phase response.

If one had a driver which had a very strong motor or a normal motor but
very low moving mass, ( ed. low Qts ) one gets an "over damped" response.
This term is from filter design meaning that it is not optimally flat,
excessively damped, rolling off too soon and gradually
Should the  slope of the response reach 6 dB per octave, the driver is
operating in the Velocity controlled mode, while the response is not
flat, the acoustic phase DOES track the input signal
(zero degrees) and
the different frequency components are not spread out in time.
The waveshape of the input signal is more closely replicated as the
frequency components are in the original "time" although the amplitudes
are off 6 dB/oct.   Each 3 dB /oct change in the slope produces a 45
degree change in phase.

An over damped response more closely retains the time information where
a flat amplitude response cannot "
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#2577 Re: Something stirs in the Undergrowth

Post by cv »

Thanks for reposting that Mark. Probably the single most important post in the history of the joelist!
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#2578 Re: Something stirs in the Undergrowth

Post by steve s »

I agree. Thats made me think..
So if I understand that correctly mark
A horn bass speaker 12' long would have similar phase shifts as a 'flat' bass driver at 25 hz

The type of speakers I prefer I know have a rising response, but also have less phase shift.
Or lag behind the music less.. which could explain or relate to slow or fast sounding bass ( I know it's supposedly all fast..)
Hopefully Scott will have a view on this?
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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#2579 Re: Something stirs in the Undergrowth

Post by IslandPink »

steve s wrote: Thu May 21, 2020 8:55 pm 1. I agree. Thats made me think..

2. So if I understand that correctly mark
A horn bass speaker 12' long would have similar phase shifts as a 'flat' bass driver at 25 hz

3. The type of speakers I prefer I know have a rising response, but also have less phase shift.
Or lag behind the music less.. which could explain or relate to slow or fast sounding bass ( I know it's supposedly all fast..)
1. It's good, innit ?

2. I don't think that follows. A horn within its proper loading band, which depends on length and mouth size, has flat amplitude and no ( or minimal ) group delay. Now, a 12' horn could only be resistive down to about 50Hz, assuming the mouth size is pretty big, that's one thing....but there's not really a correspondence to a mass-loaded bass driver at 25Hz.

3. Yes, I was thinking of your OB experiments over the years, actually. I have had experiences listening to low-Q mid drivers on OB or unloaded, where you get lots of tone and dynamics, but the frequency response is tipped-up. After some time, your ears/brain can sort-of compensate, or fill in the missing bass if it's there at lower amplitude.
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#2580 Re: Something stirs in the Undergrowth

Post by steve s »

With regard to the horn, with a folded horn the sound would have to still travel the 12 ' to get out of the horn giving the same time delay ?
Regarding open baffle and tone I completely agree
I've implemented mine using a low order crossover and using more surface area. Along with the semi open baffle or whatever you want to call it.. It seems to work well I also feel the bass is well balanced. It's a difficult thing to measure
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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