richie00boy said:
surely as the load impedance is the same due to the series/parallel arrangement, the overall power will then be the same, but 1/4 power to each driver.
Let's take it from the other angle, it is easier to explain that way.
I have not measured the follllowing, but have read of this effect and other posters on this forum with good reputation have vouched that the following is their experience as well.
Harry has one 8 ohm speaker in a certain size box. He runs one watt through it, and finds it is 90 dB@1W/1M throughout the bass range.
He takes four identical speakers and puts them into a box four times the volume. He arranges the 4 speakers not as a vertical array, but rather side-by-side as the following below:
00
00
Of course, he hooks them up in a series-parallel arrangement so the impedance for all four speakers together is 8 ohms.
He runs one watt through the box with 4 speakers.
He finds the 4 speaker box is 96 dB @ 1W/1M throughout the bass range.
Of course, if he wants to take the 4 speaker box and have it play at only 90 dB, he sends only 1/4 watt to the 4 speaker box. Each speaker in that 4 speaker box will therefore receive only 1/16 watt. That is if he wants the 4 speaker box to play at only 90 dB.
The effect seems to work well only as long as the wavelengths being played are considerably larger than the diameter of the woofers being used.
Does this make anything clearer? 🙂
PS: People who have built and measured these arrangements say that the actual effect is slightly less than 6 dB in practice, but the difference is negligible.
Raczynski has a good explanation of mutual coupling in this paper , including the math and examples. It's pretty much as Svante and KW have explained it.
The Edge baffle step software is very nice, but I was wondering if it was calculating the phase response as a minimum phase characteristic from the overall amplitude response or as the result of the sum of the driver and diffracted wavefronts.
Xdir looks cool also, but it might be useful to add a setback parameter for either of the drivers, as say for a compression hf driver.
Xdir looks cool also, but it might be useful to add a setback parameter for either of the drivers, as say for a compression hf driver.
Hybrid fourdoor said:
I think your question is what is better for you?
Well what do you want more than anything?
2 smaller sub boxes or one big one?
do you have the space for 1 big one?
i PERSONALLY would jump for 2 small 12 inch woofers,
if you ever damage one you want be left high and dry, if something happens to the 18 and it could, thats all your money wasted!
just to give you something else to think about Steren whats wrong with you today? you upset Tim Henman lost at Wembledone or What?
FWIW, if you orient the sub drivers perpendicular to the line of sight from the listening position, then intermodulation distortion (at the listening position) due to long excursion is largely minimized. Then with two smaller woofs on opposite ends of the box, you will have reaction cancelling and can have even harmonic cancellation if you orient the drivers in the same direction. Plus, I'm not a particular fan of room mode excitation, and I think more LF drivers arrayed somewhat in space are likely to deliver a less room dependent response characteristic to the listener. Plus you get generally a better approximation to ideally rigid cone behavior with two somewhat smaller drivers, everything else being equal.
Personally, I like two subs, ideally under the main speakers for stereo, but that arrangement is often not optimal or practical for other reasons. Of course, this would add up to four drivers, but OTOH, it's hard to have too much air moving capability at the bottom octave, IMO.🙂
For my HT SW's, I've bought sixteen 15mm Xmax 12" woofs which I plan to put into two 12 cu ft endtable style cabinets, if I ever get around to building them.
Personally, I like two subs, ideally under the main speakers for stereo, but that arrangement is often not optimal or practical for other reasons. Of course, this would add up to four drivers, but OTOH, it's hard to have too much air moving capability at the bottom octave, IMO.🙂
For my HT SW's, I've bought sixteen 15mm Xmax 12" woofs which I plan to put into two 12 cu ft endtable style cabinets, if I ever get around to building them.
thoriated said:
Edge subtracts the phase shift introduced by the perpendicular mic-to-baffle distance. You can test this by disabling the edge sources by using a sillily small baffle of 1x1 mm and put the driver off-baffle. The put the microphone symbol straight in front of the baffle and the phase shift will become zero.
XDir is a very quick hack, but you can imagine what would happen if you drew a line through the acoustic centres of the drivers. Then tilt your computer screen by the same amount. 😀
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