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PostPosted: Mon Jun 26, 2017 6:17 pm 
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Rich4349 wrote:
" I think part of the smoother response is due to using wider cabs (and thus bigger air chamber for the driver, just like a 'normal' sealed sub) and not only the increasing front surface of the cabs."

Does the smoothing come from the larger horn, larger driver chamber, or both? A larger horn (seems to) offer lower resistance to the air mass, so it would *seem* like a SMALLER rear chamber would be needed to tighten up cone movement and "smooth" things out. (I realize you cannot deduce audio engineering!)


Better lower response comes from a bigger horn mouth, that's why cornerloading and v-plating is so beneficial and do herds of 8 or more work the best in half space. (no walls)
Quote:
Horn loudspeakers minimise the impedance mismatch between diaphragm and the air, by acting as an acoustical transformer. The horn flare provides a controlled expanding wavefront to transform relatively small diaphragm movement into a large air movement, and with careful design efficiencies of well over 100dB/W/m are easily achieved. Unfortunately, bass is again a problem, since the circumference of the mouth should be equal to the wavelength of the lowest frequency to be reproduced. At 20Hz, this means a circumference of over 17 metres, and for a square horn (less than ideal, but smaller than circular) that means 4.3 metres per side! http://sound.whsites.net/subcon.htm#s4

17 meters ~ 57 feet

Your reasoning for a smaller chamber compared to a close sub seems logical to me, but I'm new to this and don't have a complete picture of all variables involved. I'm just starting to see some interaction between them.

The very high Mmd (moving mass) of the gto804 might also be a reason that a smaller chamber is not that big of a penalty or even better compared to the 3010lf and 3012lf which have a very low Mmd and to me look the happiest in wide boxes.

I'd love to see some comments on air chamber sizing and influence on output.

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PostPosted: Tue Jun 27, 2017 9:20 am 
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I understand the relationship between mouth size and high pass dB, as well as horn path length and high pass hz itself. (Thanks, Bill!)

My question was regarding cabinet width, chamber volume, and smoothness of response.

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PostPosted: Tue Jun 27, 2017 9:28 am 
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The cabinet width in and of itself is inconsequential. From a design standpoint it has to be made wider to make the mouth larger for higher sensitivity at the low end of the pass band. But if you go too wide the throat is too large for proper loading of the driver and the rear chamber is too large for reactance annulling. That's why a range of acceptable widths is specified.


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PostPosted: Tue Jun 27, 2017 3:48 pm 
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Think wrote:
Amps put out Voltage, not Watts.
Amps also put out current in amperage. In essence, amps do put out watts, but you can't measure watts on the fly, because watts is a calculation derived by multiplying volts and amperage.

You limit drivers to volts.
Yes.

So when you start with cold speakers and set the voltage limits and the temps go up, the resistence goes up
Yes, sort of. Even a "cold" driver will have different impedance at different frequencies.

and lowers the power output of the amp
No No NO! The change in impedance alters the other variables in amp output, ie voltage and amperage.

and thus the sound output.
The lowering in sound output is not due to the amplifier. It is due to the decreased ability of the driver to convert electrical energy into sound efficiently, due to power compression. The decrease in output is relative . It only occurs in power compression.


You could then turn up the voltage but you soon will hit thermal limit as doubling voltage will quadruple power output.(W)

Never! The voltage limit is the voltage limit.

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PostPosted: Tue Jun 27, 2017 4:17 pm 
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Grant Bunter wrote:
So when you start with cold speakers and set the voltage limits and the temps go up, the resistence goes up.
It does, and it is the DCR, not impedance. A property of wire is that as temperature goes up so does resistance. The reverse is also true, making possible superconductivity.
How it impacts us is that when DCR goes up sensitivity goes down. If there was a practical method of significantly better cooling the voice coil sensitivity wouldn't go down, but there isn't one. If there was we'd be using it. What does work is using enough speakers so that you're not near the limits of their capability.


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PostPosted: Thu Jun 29, 2017 10:31 am 
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Bill Fitzmaurice wrote:
Grant Bunter wrote:
So when you start with cold speakers and set the voltage limits and the temps go up, the resistence goes up.
It does, and it is the DCR, not impedance. A property of wire is that as temperature goes up so does resistance. The reverse is also true, making possible superconductivity.
How it impacts us is that when DCR goes up sensitivity goes down. If there was a practical method of significantly better cooling the voice coil sensitivity wouldn't go down, but there isn't one. If there was we'd be using it. What does work is using enough speakers so that you're not near the limits of their capability.


DCR is the resitence of the wire used as/in the voicecoil in a driver which raises in resistance as the temperature goes up?

So if we limit on voltage, and temps and resistence go up, a warm or hot driver draws less power from the amp then a cold driver.

Is the raising DCR the primal cause for power compression?

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PostPosted: Thu Jun 29, 2017 11:17 am 
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Think wrote:
Is the raising DCR the primal cause for power compression?
No. It's the only cause.


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PostPosted: Thu Jun 29, 2017 2:34 pm 
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Think wrote:
So if we limit on voltage, and temps and resistence go up, a warm or hot driver draws less power from the amp then a cold driver.


:horse: :horse: :horse: :wall: :wall: :wall:

Drivers don't draw power.
Amplifiers deliver power.

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Built:
2 x DR 250 (melded array) with March 2012 plans.
4 x 20" BP102 T39's, 2 x 28" 3012lf loaded underway.
3 x WH8 with melded array.
Bunter's Audio and Lighting "like"s would be most appreciated...


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PostPosted: Thu Jun 29, 2017 6:45 pm 
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Grant Bunter wrote:
Think wrote:
So if we limit on voltage, and temps and resistence go up, a warm or hot driver draws less power from the amp then a cold driver.


:horse: :horse: :horse: :wall: :wall: :wall:

Drivers don't draw power.
Amplifiers deliver power.


Receive instead of draw then........

I think your way of reacting is not very constructive nor positive. :cop:


@Bill Fitzmaurice; thank you for clearing this up.

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Last edited by Think on Thu Jun 29, 2017 7:40 pm, edited 1 time in total.

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PostPosted: Thu Jun 29, 2017 7:00 pm 
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Bill Fitzmaurice wrote:
The cabinet width in and of itself is inconsequential. From a design standpoint it has to be made wider to make the mouth larger for higher sensitivity at the low end of the pass band. But if you go too wide the throat is too large for proper loading of the driver and the rear chamber is too large for reactance annulling. That's why a range of acceptable widths is specified.


I found this: viewtopic.php?f=28&t=23964&hilit=reducer+panel&start=30#p266378
" Just like when you tune a ported box too low, low freq efficiency suffers. That is what the reducer plate in the plans does."

Which makes clear to me that chamber reducers can be used, the size of the driver chamber does matter and does not have to be as wide as the cab.


About temperature influence on drivers: http://adamjhill.com/AJHILL/wp-content/ ... tation.pdf

Quote:
8. Conclusion
Through research, simulation and experimentation, it is clear that voice coil temperature
affects the performance of a loudspeaker. The majority of these effects occur due to the direct
relationship between the voice coil temperature and DC resistance. The change in DC
resistance can affect the majority of performance parameters including electrical impedance,
efficiency and axial SPL. The increase in DC resistance also causes certain low frequency
values (around 110 Hz in the tested loudspeaker) to increase in amplitude as temperature
rises. This can be attributed to the changes in the electrical impedance and quality factor
around the nearby resonant frequency (90 Hz in this case).
Aside from the DC resistance relationship, the voice coil temperature also causes the
enclosed air in a loudspeaker to rise in temperature. This will bring a rise in the speed of
sound inside the enclosure, causing the response pattern to shift upwards with temperature.
While the low frequency range is largely unaffected by the voice coil temperature, high
frequencies experience a significant decrease in amplitude. This is likely due to the change in
stiffness of the enclosed air making it harder for the driver to move at high velocities without
any lag.
The most interesting frequency range affected by voice coil temperature is a mid-range band.
The explanation presented in this paper is that this drop in amplitude is due to the resonant
modes due to the enclosure dimensions. These modes interact to cause significant drops in
this frequency range that become more visible as the voice coil temperature rises.

Tested was a 125W 8 inch driver with a 35W amp and voicecoil temps got 76C / 169F See page 46 for measurements; interesing to see is that the back plate of the driver is hotter then the coil.
Page 50 shows a 1kHz dip when the driver is warm.

According to http://sound.whsites.net/lr-passive.htm#s3.3 voicecoils get even hotter like 150C and all passive crossovers suffer from rising temps to.

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PostPosted: Sun Jul 02, 2017 5:15 am 
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Chamber reducers,
Only apply to Drivers that have a certain value (or lower) in Fs, ie usually the lab 12.
It's in the plans.

VC temp:
The quote you pasted seems almost irrelevant in that it talks more about mid and high frequency effects, yet much of your time here has been about subs, ie below say 100Hz.

Still good to see you've found something that tells you it's about the driver rather than the amplifier.

All in all it's always about having enough cabs to deliver the SPL you require without flogging them to the point where temperature becomes an issue.
And believe me, I know about temperature. My ambient median summertime temperature is 40+ degrees C...

_________________
Built:
2 x DR 250 (melded array) with March 2012 plans.
4 x 20" BP102 T39's, 2 x 28" 3012lf loaded underway.
3 x WH8 with melded array.
Bunter's Audio and Lighting "like"s would be most appreciated...


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PostPosted: Sun Jul 02, 2017 7:56 am 
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Quote:
Which makes clear to me that chamber reducers can be used, the size of the driver chamber does matter and does not have to be as wide as the cab.
Yes, yes, and yes, but probably not for the reasons you think. The reason is reactance annulling. I won't go into detail, as even those experienced in horn design can be confused where reactance annulling is concerned. The very term used to describe the effect is misleading, as for decades designers knew what was happening but not why, so the cause was incorrectly identified.


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PostPosted: Tue Jul 04, 2017 7:12 am 
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Grant Bunter wrote:
Think wrote:
Amps put out Voltage, not Watts.
Amps also put out current in amperage. In essence, amps do put out watts, but you can't measure watts on the fly, because watts is a calculation derived by multiplying volts and amperage.


Amplifiers output power in watts, which is most easily (roughly) calculated by multiplying measured output voltage and measured output impedance load. Current, measured in amperes (amps), is most easily derived in this paradigm by dividing output voltage by impedance or output power by voltage. I say "roughly" because it's a much more complicated function dependent upon the frequency spectrum of the output. The way I have described it here works accurately only for sine waves, not program content.

While the term "amperage" is in common usage and has a definition in Webster's, it has no IEEE definition, along with "Wattage" and "supercalifragilisticexpialidocious." The sound of ALL of them is quite atrocious from an engineering perspective.

This is a nice representation of the four way relationship that is Ohm's law.
Image

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PostPosted: Sun Jul 16, 2017 4:00 am 
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The amps 'offers' a voltage (V). This is primal, so amps output voltage. (This is why a limiters limit volts.)

Then needs a load (R) to 'take'or transfer the power to.

Depending on the resistence of the load, a certain current (amperage) (I) will 'flow'.

Amps only output power (W) when a load is present. The ammount of power the amp can put out depends on the load.

Depending on the load, the amp will be able to put out power.

The maximum power depends on the potential (!!!) to deliver power by the amp and the resistence of the load and the maximum power the load can take.

example: if you connect a 5W speaker to an 2000W amp, the amp wil not be able to deliver more then 100W or so for a very short moment, because the driver burns out and the load is gone.

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PostPosted: Sun Jul 16, 2017 4:17 am 
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Bill Fitzmaurice wrote:
Quote:
Which makes clear to me that chamber reducers can be used, the size of the driver chamber does matter and does not have to be as wide as the cab.
Yes, yes, and yes, but probably not for the reasons you think. The reason is reactance annulling. I won't go into detail, as even those experienced in horn design can be confused where reactance annulling is concerned. The very term used to describe the effect is misleading, as for decades designers knew what was happening but not why, so the cause was incorrectly identified.


Thx, I have a much clearer picture now of the variables in play even if I don't know how they interact precisely.

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