Dipole bass array

[gainphile]

This is to give +6db output compared to typical 2x woofer h-frame dipole setup, while keeping the system reasonably small.

Depth should be kept between 30-40cm to give useful output 120Hz and below.



Any comments ?

[454Casull]

Looks like a doubled-up W-frame. Not that there's anything wrong with that, but the drivers should have a fairly stiff suspension to be able to play in that orientation, and you probably want to rotate them every 6 months (arbitrary number) or so.

[gainphile]

Yes it is. I've been thinking of stacked w-frame, but did not like the width. With this configuration the front baffle is kept narrow at around 30cm with 10" woofers.

Are you talking about driver suspension sag? is this a problem?

[planet10]

6dB?

4x vrs 2x gives 3 dB more efficiency and maybe more available power depending on how they are wired,

This is a concept i came up a long while ago....



Push-Push Dipole Concept

This keeps the drivers oriented in a way that gravity doesn't drag them down. I'd at least reorient things so that the drivers are firing sideways.

dave

[gainphile]

Originally Posted by planet10

6dB?

dave

yes, according to SL

The sound pressure p at some distance from the source is proportional to the square root of radiated acoustic power.

p ~ (Pa)1/2 ~ vp Ap

When the piston area Ap is doubled and the piston velocity vp stays unchanged, then the pressure doubles (20 log (2) = 6 dB).

In summary, when two identical drivers are connected in parallel and driven with constant voltage, then twice the electrical power is consumed (+3 dB), the radiated acoustic power is increased by a factor of four (+6 dB), and the free space sound pressure level is doubled (+6 dB) at a given distance.

The horizontal w-frame is an option but at the cost of wider baffle which degrades polar response for an 8" driver.

[planet10]

Note that 3 dB of that "then twice the electrical power is consumed (+3 dB)" is from doubling the power delivered by assuming a constant voltgae source, so in your situation, you have 16 ohm woofers and are wiring for 4 ohms and you amplifier is capable of doubling power into 4 ohms.

The more likely situation is that you have 8 ohm woofers, and you'll be series/parallel, which (given a constant V amp) nets you 0 dB (but 3 dB more efficiency)

dave

[Nuuk]

Some of you guys must have very large listening rooms! I've got more than enough bass with single 15 inch woofers (Hawthorne Augies) per channel.

[jerome69]

Very good idea Keep the 10" woofer.

I just rotate the twin W dipole sub in order to have the higher sub ouput in front of the baffle.

[john k...]

Originally Posted by planet10

Note that 3 dB of that "then twice the electrical power is consumed (+3 dB)" is from doubling the power delivered by assuming a constant voltgae source, so in your situation, you have 16 ohm woofers and are wiring for 4 ohms and you amplifier is capable of doubling power into 4 ohms.

The more likely situation is that you have 8 ohm woofers, and you'll be series/parallel, which (given a constant V amp) nets you 0 dB (but 3 dB more efficiency)

dave

Correct. 4 driver in series/parallel gives: 1) No gain in voltage sensitivity of two in parallel. 2) 3dB increase in efficiency. 3) 6dB increase ins max SPL capability.

[cuibono]

When I did something similar, I used a second set of amps to get +3dB, instead of wiring them all series-parallel. Not sure if it is worth it though...

Something to consider is the distortion profile of your drivers - you probably want more output lower in frequency, but the two cases I've looked at, at the low end of the dipole woofer's passband, distortion rises rapidly. So high, that more drivers wouldn't help. These are high qts drivers, maybe low qts with low fs values (<25Hz) wouldn't have this problem?