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Does dipole bass transmit less sound to neighboring rooms?

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#1
I've read that a dipole is a velocity source, not a pressure source. Does this mean the room is pressurized less with a dipole than when using a monopole source for bass? I would imagine a less pressurized room would transmit less sound to neighboring rooms, am I correct?
 

Juhazi

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#2
I haven't noticed any measurements. Most dipole speakers have problems to produce high spl down low, below 50Hz and I would like to think that this is the point. Measured sound pressure level inside the room is what counts, not the type of transducer.
 

AnalogSteph

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#3
I've read that a dipole is a velocity source, not a pressure source. Does this mean the room is pressurized less with a dipole than when using a monopole source for bass? I would imagine a less pressurized room would transmit less sound to neighboring rooms, am I correct?
Sounds reasonable enough. With a dipole you're interested in the amplitude at the lobes of its radiation pattern, while a conventional loudspeaker is almost omnidirectional at low frequencies.

Unfortunately, at frequency 0 a dipole inevitably is an acoustic short (no velocity, duh), resulting in a steep (4th order) bass dropoff. You can lengthen the path from front to back by making the baffle bigger, but for a sub that's not going to be small. Unsurprisingly, dipoles tend to need a lot of power and long throw at low frequencies. So not the most practical way of going about this, unless you are willing to go with in-wall mounting (as some people have done with subwoofer arrays).

Speaking of arrays, not allowing room modes to build up by absorbing bass at the back with an appropriate delay (i.e. a DBA) would have the same effect of "depressurizing" the room. Unfortunately setting up a DBA is neither cheap nor trivial, though I imagine you could make a decent approximation of one using closed box (CB) subs in the middle of the front and back wall.

Now before you consider going to these lengths, I would recommend experimenting with what you have. #1, try placing the sub right in the center of the room, and by that I mean in all dimensions. You may find that sub levels will go down quite a bit, especially when compared to a position on the floor near the wall or even corner. Some concepts like downfire subs deliberately make use of boundary effects to boost SPL output, at the expense of exciting a lot of room modes. Not relying on these implies using a larger, more powerful sub - probably a large BR or even larger CB depending on levels required.

What kind of sub and what kind of house construction are we talking about anyway? In a massive building the most severe issues may be related to room modes, while in a lightweight construction (which drains bass like nobody's business) the best thing to do may be getting the sub closer to the listening position.
 
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#6
I've mostly seen DIY full range dipoles, but here is a commercial offering with dipole bass from Jamo: https://www.jamo.com/products/r909

In my particular case, I already have a full range DIY dipole working in my apartment. I think this building would be considered lightweight construction. Space is tight, so the dipoles are closer to the wall than I would like. I'd prefer to move to a more traditional monopole but if the dipole bass is allowing me to listen louder without disturbing neighbors, I may want to stick to the dipole. In my current situation, I have a neighbor above, and a neighbor below me.

I just found this at linkwitzlab.com:
"The directional response of the ideal dipole is obtained with open baffle speakers at low frequencies. Note, that to obtain the same on-axis sound pressure level as from a monopole, a dipole needs to radiate only 1/3rd of the monopole's power into the room. This means 4.8 dB less contribution of the room's acoustic signature to the perceived sound. It might also mean 4.8 dB less sound for your neighbor, or that much more sound to you."

That makes sense to me, but I'm not sure if it applies below the schroeder frequency.
 
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#7
SL knows (knew RIP) his stuff...love my LXmini’s and LX521’s and for that matter my older Orion’s and Pluto’s too
 

Another Bob

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#10
But are they actually dipole at bass frequencies, or have they transitioned to omni? I could not find any measurements to answer the question.
Unless multiple drivers and fancy DSP techniques are in play (e.g. Kii), the radiation pattern is determined by the enclosure. A panel speaker or other dipole will not / can not change to monopole operation.
 

Blumlein 88

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#11
But are they actually dipole at bass frequencies, or have they transitioned to omni? I could not find any measurements to answer the question.
No they won't change to an omni. At lower frequencies the two sides they actually cancel out. The front and back side are out of phase. So when the wavelength begins to exceed the size of the baffle they start canceling output form one side vs the other. It isn't all at once. It will cause an output decrease at 6 db/octave. Plus if walls reflect some of the rear wave it is in phase at some frequencies with the forward radiation. This might lift some areas below where cancellation has occurred. Many ESL's boost this area one way or another to partly combat an early roll off.

So unlike a mono-pole which will become omnidirectional at lower frequencies, a bipole would cease having output at low enough frequencies.

EDIT to add: The cancellation begins when the baffle or width of the panel is half a wavelength. In open air conditions it would be - 3b at half that frequency and drop 6db/octave as frequency goes lower. In the case of some speakers I have and have had, this would begin at 226 hz for a 30 inch wide baffle. And be - 3db at 113 hz. This speaker has something of a blended built in boost of 12 db here. Which theoretically would allow it to have good output to 28 hz (which incidentally is what the maker claims).
 
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Juhazi

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#12
^Yep. The theoretical dipole cancellation 6dB/oct will not happen "ideally" in a small room, because of boundary effects. A room is basically a cube and bass waves practically gets boost/cancellation interferences from floor, front wall, nearest side wall and even ceiling. The summation of these reflected energies (SBIR) depends on distance and wavelength. A dipole woofer must always be equalized to give smooth response either on-axially or by room response (for low bass). This eq is most reasonable to assess by in-room measurements at the end-user's room - and with dsp. (Well, this applies to monopole bass too!)

Secondarily, below room's Schröder frequency(diffuse) standing waves/modes are very important to how we hear that sound- or measurement with long IR gating or RTA.

So , the debate of dipole vs. monopole vs. cardioid bass radiation pattern and in-room bass response is very complex.

Previously I linked to this study by kimmosto. It is titled "cardioid bass", but shows real life measurements of monopole vs. dipole bass speaker in the beginning. Also John Kreskowsky has lots of theory and practical of dipoles at his homepage most of all this page.
 
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Blumlein 88

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#13
^Yep. The theoretical dipole cancellation 6dB/oct will not happen "ideally" in a small room, because of boundary effects. A room is basically a cube and bass waves practically gets boost/cancellation interferences from floor, front wall, nearest side wall and even ceiling. The summation of these reflected energies (SBIR) depends on distance and wavelength. A dipole woofer must always be equalized to give smooth response either on-axially or by room response (for low bass). This eq is most reasonable to assess by in-room measurements at the end-user's room - and with dsp. (Well, this applies to monopole bass too!)

Secondarily, below room's Schröder frequency(diffuse) standing waves/modes are very important to how we hear that sound- or measurement with long IR gating or RTA.

So , the debate of dipole vs. monopole vs. cardioid bass radiation pattern and in-room bass response is very complex.

Previously I linked to this study by kimmosto. It is titled "cardioid bass", but shows real life measurements of monopole vs. dipole bass speaker in the beginning. Also John Kreskowsky has lots of theory and practical of dipoles at his homepage.
Very good links you posted. :)
 

edechamps

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#14
I've read that a dipole is a velocity source, not a pressure source. Does this mean the room is pressurized less with a dipole than when using a monopole source for bass? I would imagine a less pressurized room would transmit less sound to neighboring rooms, am I correct?
You ears sense pressure, not velocity. If you use a speaker that tends to produce less sound pressure at the listening position, you will increase the level to compensate until you reach the sound pressure level you usually listen at. At this point, the pressure at the listening position is the same as if you had used a different speaker. From there, I don't see any reason to believe less sound would be transmitted to neighbouring rooms.
 

DDF

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#15
You ears sense pressure, not velocity. If you use a speaker that tends to produce less sound pressure at the listening position, you will increase the level to compensate until you reach the sound pressure level you usually listen at. At this point, the pressure at the listening position is the same as if you had used a different speaker. From there, I don't see any reason to believe less sound would be transmitted to neighbouring rooms.
Dipole has higher directivity index than monopole so radiates less total sound power into the room for the same on axis SPL
 

Juhazi

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#16
Are you sure about the relevance of on-axis spl considering bass frequencies in-room? Isn't it the total radiated power (of low frequencies) that we also hear and measure in-room, below Schröder? Have you reference to what you claim?

I stand with edechamps that in-room spl (steady state, total radiated energy) is determinant to transmission of sound energy to the next room. But each wall has it's own transmission/damping characteristics and resonances. Room modes between adjacent walls in question must be also very important, and it has been shown by Linkwitz that a dipole bass is different to monopole in that respect.
 

DDF

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#17
For the same free field SPL on axis, dipole radiates less total power than monopole, by the definition of DI. If it radiates less power, then on average there is less energy to bleed next door.

Of course a situation could exist where the dipole needs to eq'ed louder at a given frequency because of room modes creating destructive interference at the listening location (which might not be seen by a monopole in that given instance), but that can happen for monopoles vs dipoles as well.

In room with modes, the dipole will energize fewer modes than the monopole due to its DI, hence the difference Linkwitz gets at. Some argue this is better for tonal balance at the listening location because "less modes is better" but that's an oversimplification and some (eg johnk) argue it can be worse since you don't get as much averaging (smoothing) across a greater plurality of independent modes. Which is better or requires more total total sound power at a given frequency in a given instance are of course dependent on the room, set up and specific radiation of the design but on average, the dipole DI makes it clear that a monopole will spill more sound power into the room for the same free field SPL on axis
 

Juhazi

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#18
^You keep saying "for the same free-field spl on-axis" But we have the speaker in a room here, that is my point! It is impossible to measure the free-field axial spl in a small room! (Well, we can set the mic there, but the bass response we get is always the steady state room response corresponding to total radiated spl, because we must use long IR gating)

We must suppose that the dipole bass and monopole bass are equalized to same room-spl, in this discussion.
 

TitaniumTroy

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#19
I have a shared wall with my duplex neighbor, in my computer room. He used to bang on the wall when my Monsoon 20000 hybrid planer's, conventional subwoofer would disturb him. Switched to all planer system via Magnepan Mini Maggies, haven't heard a peep from him since.

Everybody knows planers bass does not have as much slam as conventional, which is good for acoustical music. Not so much for rock and roll especially at higher volumes. I bought a second DWM bass module for my Mini Mags to increase bass output, one was not getting the job done.
 
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#20
Using bass traps reduces bass in the room and therefore the amount transmitted beyond it. That's also my experience. And there's a small bonus - it improves the listening experience!!!
 
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