Open the page on the browser as usual. Then go to the URL and change 'Part2" to 'Part1' and hit Enter. Part one will open up !🙂
I already quoted the relevant snippet of #45 in my answer in #54.
Sorry @retearl for polluting this thread but Andrew is prone to be über-correct which is totally OK.... unless when he's actually wrong. I'll stop this now, readers may draw their own conclusions.
you can stay silent if you choose.
I have watched and contributed to a few Threads discussing this double cone area and the effect that has on SPL.
I think from memory all eventually agreed that doubling the driver count while maintaining the same total power input did achieve upto +3dB in SPL. But that was limited to a restricted frequency range and in some cases over a limited listening area.
This Thread has not taken account of those special conditions.
The Member simply stated that doubling the driver count while maintaining the same power input into each would give +6dB
That statement without the applicable conditions is wrong.
I have watched and contributed to a few Threads discussing this double cone area and the effect that has on SPL.
I think from memory all eventually agreed that doubling the driver count while maintaining the same total power input did achieve upto +3dB in SPL. But that was limited to a restricted frequency range and in some cases over a limited listening area.
This Thread has not taken account of those special conditions.
The Member simply stated that doubling the driver count while maintaining the same power input into each would give +6dB
That statement without the applicable conditions is wrong.
I would suggest, if you are all interested in educating people, to use schematics and a simulator where circuit voltage and current values are defined. That would be helpful and prevent any misunderstanding.
12" woofers build a big WMmtmMW
18" woofers build a BIG WMmTmMW 🙂
If you decide to use one amplifier per woofer, you can consider 4-ohm woofers(Re=3.2).
Otherwise, two 8-ohm(Re=6.4 ) woofers in parallel create a 3.2-ohm load which many power amps can drive with good efficiency.
Dayton sells the 12" RSS315HFA woofer in 4-ohm(Re=3.2) and 8-ohm(Re=6.4) versions
The SB34NRX75-6 is Re=4.2
18" woofers build a BIG WMmTmMW 🙂
If you decide to use one amplifier per woofer, you can consider 4-ohm woofers(Re=3.2).
Otherwise, two 8-ohm(Re=6.4 ) woofers in parallel create a 3.2-ohm load which many power amps can drive with good efficiency.
Dayton sells the 12" RSS315HFA woofer in 4-ohm(Re=3.2) and 8-ohm(Re=6.4) versions
The SB34NRX75-6 is Re=4.2
Attachments
Actually Andrew, my statement was meant to convey that there would also be a doubling of power as well, since both amplifiers run in parallel off the same output of the minidsp. I'll strive to be clearer next time.
From what I remember...
- 2 close-coupled drivers wired in series, driven from one amp - no change in SPL compared to 1 driver (doubled radiating area but doubled impedance)
- 2 close-coupled drivers wired in parallel, driven from one amp - +6 dB compared to 1 driver (halved impedance and doubled radiating area)
- 2 close-coupled drivers, driven from separate amps - +3 dB compared to 1 driver at same voltage (doubled radiating area)
Hopefully I'm not too far off the mark.
- 2 close-coupled drivers wired in series, driven from one amp - no change in SPL compared to 1 driver (doubled radiating area but doubled impedance)
- 2 close-coupled drivers wired in parallel, driven from one amp - +6 dB compared to 1 driver (halved impedance and doubled radiating area)
- 2 close-coupled drivers, driven from separate amps - +3 dB compared to 1 driver at same voltage (doubled radiating area)
Hopefully I'm not too far off the mark.
I can see that doubling the power sent to the bass speakers will increase the total SPL from the bass drivers by +3dB. There is no disagreement about that.
It's the extra +3dB that is only available if special circumstances allow that is the contentious part of your original statement.
The frequency range that this extra +3db becomes available rolls off very quickly as frequency is raised. It is available for most of the sub audio range, but that can't be heard. It's how far into the bass range that matters and here the spacing of the drivers has an effect that is being ignored.
Your statement is just fine.
You have added the special condition that needs to apply to get the extra +3dB.
All it needs is for KSTR and retearl to recognise that requirement and take account of it.
Anyone with an MTM want to do a couple of measurements of the woofers. 1 with one running and another with both running (wired in parallel).
It's cold and night here so I don't particularly want to do it. I would be very surprised if the result shows a narrowing of the difference in SPL as frequency increases.
Tony.
It's cold and night here so I don't particularly want to do it. I would be very surprised if the result shows a narrowing of the difference in SPL as frequency increases.
Tony.
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I only have 2 bass in my active system but it is a fundamental effect to mute one. May be the case with 2 / 4?
I know if the baffle is all square the baffle step boost will be higher up in frequency, therefor a separate width of each band is preferable when setting the levels.
I know if the baffle is all square the baffle step boost will be higher up in frequency, therefor a separate width of each band is preferable when setting the levels.
wrong
If the baffle is all square the baffle step boost will be higher up in frequency, therefor a separate width on the baffle for each band will balanace the amount of this effect over the frq spectra.
If the baffle is all square the baffle step boost will be higher up in frequency, therefor a separate width on the baffle for each band will balanace the amount of this effect over the frq spectra.
Have you seen these? https://www.google.co.uk/search?q=d...28-pnUAhXJAMAKHcyfC0kQsAQILg&biw=1200&bih=585
Have you ever measured it? I have, the first probably 30 years ago, just to confirm
the theory.
The reason why 2 drivers, driven with equal power (2X power in, or +3dB) produce an
increase of 6 dB in SPL is because the volume displaced (VD or vd(t) ) doubles. VD is
analogous to voltage, double the voltage in a circuit and the power increases by 6 dB.
Look up the equations for SPL calculated as a function of vd(t) and perhaps you will
understand this better.
Why does this happen? The efficiency goes up.
Mutual coupling that you hint at, is not the dominant effect, there are AES papers on this.
It may contribute a small fraction of a dB.
separate out the drivers as in a normal stereo system and you get the normal +3dB in SPL from the two sets of drivers having double the total input power.
That is the normal not close coupled arrangement.
Now bring the two speakers together so that the bass drivers become close coupled.
The level of the bass from the two speakers increases relative to the levels of the mid and treble.
That's good enough measurement for me, to prove that coupling is required to give the extra +3dB and it further proves that the spacing between the drivers limits the frequency band over which the coupling is effective.
It is this effect that is used to bring up the bass to correct for the bass roll-off that occurs when a small (relative to the wavelength) baffle is used and two small drivers become paralleled for the lowest frequencies.
That is the normal not close coupled arrangement.
Now bring the two speakers together so that the bass drivers become close coupled.
The level of the bass from the two speakers increases relative to the levels of the mid and treble.
That's good enough measurement for me, to prove that coupling is required to give the extra +3dB and it further proves that the spacing between the drivers limits the frequency band over which the coupling is effective.
It is this effect that is used to bring up the bass to correct for the bass roll-off that occurs when a small (relative to the wavelength) baffle is used and two small drivers become paralleled for the lowest frequencies.
I don't believe that you have ever measured this.
Go ask on the Parts Express forum, not going to waste my time here.
I've explained this many times in the last 30 years or more.
Go ask on the Parts Express forum, not going to waste my time here.
I've explained this many times in the last 30 years or more.
Looking into different woofers for the projects, I believe I'd consider using 15" woofers instead. It would truly be the ultimate, never question yourself decision. If you used 2 Parts Express Ultimax 15" woofers, they will give you -3dB at 29Hz with a box Q of .66. Easy to take that as low as you want to go with Linkwitz Transform, since these woofers have 19mm xmax & take 800 W. I calculated that a box 75in. x 18in. (same h & w dim. as Dunlavy VI) and 24in. deep (Dunlavy VI was 33in. deep), then allowing 60L total for a pair of 8" lower midranges, a pair of 4"upper midranges & tweeter. And this assumes a 1-1/2" wall thickness for the enclosure, so it's stout. Couple that with miniDSP & amps (even the LM3886 amps I use would give 102dB at seating position!) and you'd have "my ultimate" for a pair of speakers!
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