Sadly, John Kreskovky's
"The Room Mode simulator for rectangular rooms"
Room Mode Simulator
is currently down.
Think you could drop him a line if you like.
In his tech notes you can find a qualitative explanation to the effect of front wall (any boundary actually...) placement for monopole and dipole speakers
Boundary effects
There are loooots of goodies to read through in his Tech-Studies page
http://www.musicanddesign.com/tech.html
Michael
"The Room Mode simulator for rectangular rooms"
Room Mode Simulator
is currently down.
Think you could drop him a line if you like.
In his tech notes you can find a qualitative explanation to the effect of front wall (any boundary actually...) placement for monopole and dipole speakers
Boundary effects
There are loooots of goodies to read through in his Tech-Studies page
http://www.musicanddesign.com/tech.html
Michael
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Sorry, last time I went though this exercise in a somewhat rigorous fashion it was before I had measurment gear. The physics don't change much, though.
Since you're crossing to the H baffles fairly high and have independent amp channels for the 21" have you considered running this as a five way? (As I recall you're using the Fireface 800, which IIRC has 10 independent analog outs.) I was thinking over my much more modest four way plans this morning and concluded there should be some localization benefit from crossing the lower driver in a sub pair separately from the upper one. In your case I'd be tempted to experiment with crossing in the side sub pair lower than the center sub pair too.
Depends on how much cancellation there is of the subs' front and back waves at the driver strings. Since the hanging drivers are in the H baffles' nulls I wouldn't expect a lot of phase modulation distortion; knowing Erik he's probably already measured the subs' SPL at the mains.
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Nice link. Somehow I missed that one.
As something of an aside, my experience with rear ported box speakers is, unsurprisingly, they tend to behave more like dipoles than Kreskovsky's box or cardiod curves. Particularly if the ports are right behind the drivers so the box starts to approximate an H baffle. The walls I was listening to weren't as damped as Erik's and it was some years ago, but my memory of the sound is in good agreement with the midbass honk of John's dipole curve and not with the monopole+cardioid combination one would expect of a sealed box speaker transitioning through baffle step. I've a hunch Erik's got enough wall and ceiling damping placement will be more about room modes and am curious to see what his findings are.
Tonight I moved the entire setup almost 1 meter further into the room.... didnt have much effect, the only positive thing was that the bass was a little less affected by the secondary mode in the length direction of the room.
I also found that the main dipoles dont like to have the large sub's too close, there are strange things happening below 300 Hz.
So... I moved the subwoofers a bit back against the wall again. I couldnt hear any significant change doing that.
An other thing I tested that DID affect the bass "slam" and "attack" quite a lot was to XO even higher between the sub's and the 8-inchers (170 Hz), and to play a little with the target frequency response. A slight rise in bass reponse from 200 Hz and down proved to be quite effective.
I also found that the main dipoles dont like to have the large sub's too close, there are strange things happening below 300 Hz.
So... I moved the subwoofers a bit back against the wall again. I couldnt hear any significant change doing that.
An other thing I tested that DID affect the bass "slam" and "attack" quite a lot was to XO even higher between the sub's and the 8-inchers (170 Hz), and to play a little with the target frequency response. A slight rise in bass reponse from 200 Hz and down proved to be quite effective.
If these are bad idea apologies for that,
There are bungee, shock or elastic stretch cords.
These drivers can be hooked by the chords, also (more aesthetic and has a more energy storing capacity)
You know the bamboo curtain like this http://www.fullmaxhk.com/custom/Bamboo_Curtain.jpg
What do you think about to use it as baffle
if we apply such a curtain to the Erik's system(maybe two layer)
What will be the probably results (no rattle, linear FR ?)
There are bungee, shock or elastic stretch cords.
These drivers can be hooked by the chords, also (more aesthetic and has a more energy storing capacity)
You know the bamboo curtain like this http://www.fullmaxhk.com/custom/Bamboo_Curtain.jpg
What do you think about to use it as baffle
if we apply such a curtain to the Erik's system(maybe two layer)
What will be the probably results (no rattle, linear FR ?)
I'm sure there are several good ways to suspend/hang the drivers. I just chose the first, cheapest and best I came up with, and it proved to work well. Its also very easy to install.
As for the bamboo curtain, I'm a bit in doubt. Its kinda semi-transparent acoustically, and probably wont work that well as a baffle. On the other hand, I dont want a baffle either, since one of my goals is to operate the drivers below the dipole peak. That means no baffle, or very small baffle.
As for the bamboo curtain, I'm a bit in doubt. Its kinda semi-transparent acoustically, and probably wont work that well as a baffle. On the other hand, I dont want a baffle either, since one of my goals is to operate the drivers below the dipole peak. That means no baffle, or very small baffle.
Have not measured, but there is very little bass where the main dipoles are placed. The H-baffles dont have a clearly defined off-axis null, but the level is probably 10 dB or more down at the side compared to the front.
Will measure!
Teaser.....
An externally hosted image should be here but it was not working when we last tested it.
The H-baffles have arrived, and I'm going to set them up in the room tonight. I will try a distributed placement first, to see how that affects the room modes.
An other thought is that placing the subs like this should create a phantom image in the middle between the two subs for each channel. This phantom image will be where the main speaker are located. This should be beneficial for the overall stereo image or what? Any experience on this, folks?
An other thought is that placing the subs like this should create a phantom image in the middle between the two subs for each channel. This phantom image will be where the main speaker are located. This should be beneficial for the overall stereo image or what? Any experience on this, folks?
An externally hosted image should be here but it was not working when we last tested it.
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Changed the plan a little bit. Gonna try this layout tonight!
An externally hosted image should be here but it was not working when we last tested it.
I'm not finished with everything regarding the new sub's yet, but I can tell you that the distributed setup shown on the sketch in post #753 works very well. Each pair of woofers is able to create a phantom image between them, right at the point where the main dipoles are located. Very nice! Those who think bass cant be localized should come and listen for themselves.
What the....??
An externally hosted image should be here but it was not working when we last tested it.
