I don't imply you try to confuse Allen ( it wasn't the case last time i refer to, only talking about different things or from a different pov).
But i think talking room acoustic in this context might be confusing. I might be wrong however.
But i think talking room acoustic in this context might be confusing. I might be wrong however.
I see. +3db comes from doubling woofers makes double spl. And more +3 db from halving resistance.Totally 6db. Right?
If connected in // yes ( two 8r in //= 4r) and if close enough for acoustic coupling to happen.
Eg: you plan to use the woofer up to 450hz: 343/450=0,76meter. 76/4~ 19cm. 76/3~ 25cm.
If center to center distance of drivers are within 19/25cm you'll have acoustic coupling up to 450hz.
Eg: you plan to use the woofer up to 450hz: 343/450=0,76meter. 76/4~ 19cm. 76/3~ 25cm.
If center to center distance of drivers are within 19/25cm you'll have acoustic coupling up to 450hz.
No. They add by +6dB even if the drivers are not near each other. Your term "acoustic coupling" implies that something happens when it does not.
What happens is that you get modal behaviour. The box creates diffraction. For a simple example say there are four corners and two drivers, now you have six sources of sound combining. The modes change with frequency. Here is an example..
Allen for both source to behave as one and only ( omnidirectional behavior to happen) these rules apply.
'Acoustic coupling' is a conservative term i've been introduced to while studying and i believe the guy i learned from ( he is a renowed designer in my country with university background).
Maybe i've lost the correct term in translation, maybe we talk about something different i don't know ( or we only disagree on a point and it's fine!).
What i talk about is described in fig3 p4 of this document:
http://www.xlrtechs.com/dbkeele.com...ear Phase Digital Crossover Flters Part 2.pdf
"The box create diffraction"
Yes as long as it is 3x bigger than wavelength of interest iirc ( this is the rule of thumb). It would ask something like 2m to be really annoying at 450hz.
And if the drivers are not too big it could combine to give an 'almost' omni behavior ( low value of Ka/low diffraction).
I wondered about their choice of 'tiny' woofer for the ls60 and i think it can explain their choice ( but here again i've no proof, only feeling).
It seems to be an answer Dave ( Planet 10) have choosen in Tysen and other design he built using this technique, maybe he thougts about it too ( or maybe it is something else).
'Acoustic coupling' is a conservative term i've been introduced to while studying and i believe the guy i learned from ( he is a renowed designer in my country with university background).
Maybe i've lost the correct term in translation, maybe we talk about something different i don't know ( or we only disagree on a point and it's fine!).
What i talk about is described in fig3 p4 of this document:
http://www.xlrtechs.com/dbkeele.com...ear Phase Digital Crossover Flters Part 2.pdf
"The box create diffraction"
Yes as long as it is 3x bigger than wavelength of interest iirc ( this is the rule of thumb). It would ask something like 2m to be really annoying at 450hz.
And if the drivers are not too big it could combine to give an 'almost' omni behavior ( low value of Ka/low diffraction).
I wondered about their choice of 'tiny' woofer for the ls60 and i think it can explain their choice ( but here again i've no proof, only feeling).
It seems to be an answer Dave ( Planet 10) have choosen in Tysen and other design he built using this technique, maybe he thougts about it too ( or maybe it is something else).
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I was clear to mention SPL, and the standard (+3dB)+(+3dB) discussion also implies SPL. The question did make me think of power, hence the simulations.
It's not so much the term, but how you used it. I searched the document for the word coupling and didn't find it.
Power will also be different from 1/4 wavelength if you have the drivers at 1/8 wavelength.
Ok. I think i got your point.
No, Keele didn't used the term but the graph describe what i understood as the term when it was explained to me.
No, Keele didn't used the term but the graph describe what i understood as the term when it was explained to me.
I think you are trying to describe coherent vs incoherent addition of sound sources.
Section 3 in this pdf explains it quite well
http://physics.bu.edu/py231/db3.pdf
And a good post from Tom Danley
https://www.audiosciencereview.com/...really-have-better-dynamics.25980/post-968327
Fluid this is spot on.
T. Danley's post is exactly what i'm talkin about and this have been named 'couplage acoustique [entre deux sources]' ( acoustic coupling [between two source]) in my native language during the course i had.
T. Danley's post is exactly what i'm talkin about and this have been named 'couplage acoustique [entre deux sources]' ( acoustic coupling [between two source]) in my native language during the course i had.
Indeed. So what we have here is coincident radiation of two sources.
(krivium, there is an old and common misconception which is often talked about, that if two drivers are at 1/4wl they 'feel' each other and create +3dB.. and this has incorrectly been called coupling)
(krivium, there is an old and common misconception which is often talked about, that if two drivers are at 1/4wl they 'feel' each other and create +3dB.. and this has incorrectly been called coupling)
Ok thank you Allen.
I wasn't aware of this 'drivers see themself' thing.
Weird approach but i could see the shortcut used to reach this wrong conclusion.
I wasn't aware of this 'drivers see themself' thing.
Weird approach but i could see the shortcut used to reach this wrong conclusion.
Basically, it comes down to how close the drivers are. If within that magical quarer wavelength they are coherent, otherwise not. It will be noted that this is very frequency dependent.
The higher the frequency the harder it is to get the drivers close enuff. A corallary of this is the 3 dB/ocatve roll-off of a line array due to HF cancelation.
dave
The higher the frequency the harder it is to get the drivers close enuff. A corallary of this is the 3 dB/ocatve roll-off of a line array due to HF cancelation.
dave
What are the benefits of back to back woofers? Only eliminating box resonances? Does soundstage become better? I am already very happy with single SB34NRX75-6 per cabinet but looking for something better. ( like all of us,because we are here )
And looking for flat surface woofers but could not find (because of waf) .Do they move less air because of lower surface area?
I am looking something like this but flat surface
https://tr.aliexpress.com/item/3294...101d91e16535138690404458ee994!66199451615!sea
I am looking something like this but flat surface
https://tr.aliexpress.com/item/3294...101d91e16535138690404458ee994!66199451615!sea
Push-push dramaticaly lowers the energy getting into the box, making for a more silent box. DDR also improves, you will hear more of the subtle detail (how much? Depends).
They are typically used at frequencies low enuff that they are omnidirectional, just like one woofer, but no baffle step.
dave
They are typically used at frequencies low enuff that they are omnidirectional, just like one woofer, but no baffle step.
dave
What is DDR? And I did not understand baffle step. Does one woofer like my sb34 always need baffle step correction ?
Downward dynamic Range. Less precisely the ability to reproduce small bits of information/detail
BaffleStep is the 2π to 4π transition that occurs when the frequencies get low enuff to wrap around the baffle with up to a 6dB loss in level below that frequency when on axis.
With push-push, the woofer on the other side also wraps and the loss is (near) perfectly filled in. Near, as limited by any FR variations from the shape of the enclosure.
These are the measurements Olson made for different shape baffles (single driver on the front)
dave
BaffleStep is the 2π to 4π transition that occurs when the frequencies get low enuff to wrap around the baffle with up to a 6dB loss in level below that frequency when on axis.
With push-push, the woofer on the other side also wraps and the loss is (near) perfectly filled in. Near, as limited by any FR variations from the shape of the enclosure.
These are the measurements Olson made for different shape baffles (single driver on the front)
dave
Here is a nice animation about "coupling" of bipole radiation, per distance at fixed frequency. Similar interference phenomenom happens whe separation is fixed but frequency changes. Spl spectrogram graph is another way of showing the effect of interference per frequency, from a single point in space. It clearly shows the first null and consequent ripples
https://www.acs.psu.edu/drussell/Demos/Bipole/Bipole-kd.html
Here you can change parameters of ripple tank http://www.falstad.com/ripple/
Basics http://salfordacoustics.co.uk/sound-waves/superposition/interference-from-two-point-sources
https://www.acs.psu.edu/drussell/Demos/Bipole/Bipole-kd.html
Here you can change parameters of ripple tank http://www.falstad.com/ripple/
Basics http://salfordacoustics.co.uk/sound-waves/superposition/interference-from-two-point-sources
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