Yeah, well, ok?
How will you do it two the front and 2 on the back - where is the driver??
The driver should at least be equidistant from the PRs... I would expect.
Technically, or theoretically, the air in the box is all "one" mass, but in reality (and based on real tests that I have made) this is *extremely* far from true. The air pressure on even a single PR is far from even. The suspension of the PR serves to integrate the forces into a single axis motion.
With these very small PRs, it is possible that they will not be moving in concert. This is possible, but I have not tested it.
I was referring to the excursion limit of the driver wrt SPL.
But yes, the excursion of the PR needs to be substantially larger than that of the driver, and increases as the Fp is lowered.
Should be a fun build. Wish the driver(s) were a fair bit less expensive, they are neat! I would have loved to have things like this a number of decades back, as I was heavy into experimenting with small high performance drivers, mostly in arrays but a few with a single or dual and a PR... This sort of driver would have been a dream build.
Oh, btw, if you have the driver on one wall, I'd consider the PRs to the left and right walls... aiming up or down is NG for any of them, imo.
How will you do it two the front and 2 on the back - where is the driver??
The driver should at least be equidistant from the PRs... I would expect.
Technically, or theoretically, the air in the box is all "one" mass, but in reality (and based on real tests that I have made) this is *extremely* far from true. The air pressure on even a single PR is far from even. The suspension of the PR serves to integrate the forces into a single axis motion.
With these very small PRs, it is possible that they will not be moving in concert. This is possible, but I have not tested it.
I was referring to the excursion limit of the driver wrt SPL.
But yes, the excursion of the PR needs to be substantially larger than that of the driver, and increases as the Fp is lowered.
Should be a fun build. Wish the driver(s) were a fair bit less expensive, they are neat! I would have loved to have things like this a number of decades back, as I was heavy into experimenting with small high performance drivers, mostly in arrays but a few with a single or dual and a PR... This sort of driver would have been a dream build.
Oh, btw, if you have the driver on one wall, I'd consider the PRs to the left and right walls... aiming up or down is NG for any of them, imo.
This is the setup that I was thinking initially, as the full range drivers take up the dead space either side of the isobaric clamshell. Having the PR be on 4 sides of a box is viable, and would be the coolest looking way if this was stand alone, but there would be no good place for the FR speakers to go.
I feel that the drastically small volume of air inside will help keep all of the PR's in sync. I should get the components early this week, Then I can knock up some test enclosures.
This is not a good plan for good sound.
The small baffle on the FRs = big baffle step issues and diffraction.
The sub drivers on top (or bottom) are working against gravity, meaning that they will not be happy except in the near term.
Ur way better off with a box that will be deep enough to take a pair of 6.5" PRs or even a pair (or single) 8" PR on a side (or two sides depending on how many PRs).
Are you just standing a tiny FR box on top of ur "sub" cabinet?
I'd put the isobaric facing out and the PRs left and right sides.
If the FR are detachable, consider some sort of larger baffle for them, maybe fold out.
_-_-
again, what is the design goal? just small size and boom & sizzle (a la Bose?)
The small baffle on the FRs = big baffle step issues and diffraction.
The sub drivers on top (or bottom) are working against gravity, meaning that they will not be happy except in the near term.
Ur way better off with a box that will be deep enough to take a pair of 6.5" PRs or even a pair (or single) 8" PR on a side (or two sides depending on how many PRs).
Are you just standing a tiny FR box on top of ur "sub" cabinet?
I'd put the isobaric facing out and the PRs left and right sides.
If the FR are detachable, consider some sort of larger baffle for them, maybe fold out.
_-_-
again, what is the design goal? just small size and boom & sizzle (a la Bose?)
Purpose: taking the heavy passive radiator approach, like some of the compact bluetooth speakers do, to make a full range speaker (including sub bass) that can be moved very easily, the sillyness of the size is one of the draws for the project. I am aware that using larger elements will make a better sounding speaker, though audiophile requirements are not needed for this project. I mainly would like people to be impressed by the fullness of a speaker that could easily fit in a typical backpack. This could be referred to as boom as sizzle, though of course we would be aiming for more if the constraints will allow for it.
I do not see the issue of the drivers working against gravity. This will only apply a DC force to the drivers, displacing their resting position by just over 10um. I would imagine manufacturing anomalies cause a bigger deflection.
I absolutely agree with you on the FR placement issue. The problem is that there will not be much space for the baffle. I want to avoid moving parts as in this design vibration noise is very likely. The FR will be fixed to the box to minimise the deployment hassle.
I can correct for the baffle step in the active crossover somewhat easily. Though the peculiarities in the off axis response will remain of course.
Thanks for your input btw bear, I like hearing more experienced opinions and ideas.
I do not see the issue of the drivers working against gravity. This will only apply a DC force to the drivers, displacing their resting position by just over 10um. I would imagine manufacturing anomalies cause a bigger deflection.
I absolutely agree with you on the FR placement issue. The problem is that there will not be much space for the baffle. I want to avoid moving parts as in this design vibration noise is very likely. The FR will be fixed to the box to minimise the deployment hassle.
I can correct for the baffle step in the active crossover somewhat easily. Though the peculiarities in the off axis response will remain of course.
Thanks for your input btw bear, I like hearing more experienced opinions and ideas.
The passive radiator mass works against two "springs", the air spring and the suspension spring. The effects of gravity on an upward facing PR will be different than one facing forward (which is basically unaffected by gravity), they won't respond exactly the same, resulting in an acoustical waveform biased towards the + or - portion of the signal, which will vary with frequency. In addition, the upward facing PR will sag over time, the suspension will become progressively more non-linear as the PR takes a downward "set".
I have a lightweight downfiring "sub" in my kitchen, it has sagged about 2mm over the last 10 years- having not measured it "before" and "after", it still sounds OK at the levels I use it, but I'd expect it wouldn't perform "as new" at high levels, as it would be pushed past Xmax easier on the forward excursion than rear.
I once did a similar thing just to see how much noise it would make. 4-15" passives and one TC 10" woofer, it was not what I would call a success. In fact the only productive thing to come out of that was that I found a bug in BassBox Pro, it was exaggerating the gain from adding additional passive radiators. I also learnt that passives are not all that great; the surrounds will cave in and the cones will rock sideways if pushed. I was plugging the woofer into the 120V AC and the box was tuned to 60Hz so I was not entirely surprised, but still disappointed...
Ok this thing is on the road, CAD for the sub enclusure is done in essence, just need to add some nut traps and the like to secure the removable bottom.
I got some more plywood, so I will not have a shortage of that tomorrow, though my amplifiers are still not here, so I am going to have to do my best hacking around with some spare amplifiers that I have from some old projects.
For cutting the baffles, I have a laser cutter in the lab, so that is taken care of, as well as all those finger joints!
So I have them up and running. They definitely go deep, strong output down to the 30's. They are definitely small, 30cm long. They are definitely inefficient, excursion limits me to back ground music level volume. Point proven
With some additional care in measurement, I should be able to smooth out the peaks that could be causing the over excursion. It is interesting because they sound like really large speakers, just small enough to get into a rucksack, and incapable of starting a party
Once I get the amplifiers installed properly (when they arrive), I will do some tests in our DSP lab, perhaps with a bit of social engineering I may be able to use a proper calibrated mic and measurement tools with all the trimmings.
Primarily I feel that getting them in a normal room will make all the difference. The lab that I am working in is 15-20m long and 8m(ish) wide, with high ceilings. So no chance of meaningful cabin gain there lol. When it is neat I can do some in (normal) room testing with some much more modest equipment.
Primarily I feel that getting them in a normal room will make all the difference. The lab that I am working in is 15-20m long and 8m(ish) wide, with high ceilings. So no chance of meaningful cabin gain there lol. When it is neat I can do some in (normal) room testing with some much more modest equipment.
This is a nice little tweeter Vifa OX20SC00-04 3/4" Fabric Dome Tweeter.
To integrate it, just make a simple xover set at 3KHz or so, and make sure you mount the tweeter as close to the full range as you can manage.
To get levels right, you will need to make measurements. The tweeter is much more efficient than the fr, so you need to pad it down.
Edit: only do it when you are not happy with the sound as it is, since it takes quite a bit of effort to get it right.
To integrate it, just make a simple xover set at 3KHz or so, and make sure you mount the tweeter as close to the full range as you can manage.
To get levels right, you will need to make measurements. The tweeter is much more efficient than the fr, so you need to pad it down.
Edit: only do it when you are not happy with the sound as it is, since it takes quite a bit of effort to get it right.
I have some dayton nd20FA-6 on hand actually, they are surface mount as well actually. After a bit of listening, still with the system un-balanced, I agree that the high end is a little muted, especially compared to the very present low end. Sounds like playing a 360p video on youtube on well ballanced speakers, not bad, just not fully sharp. I will see what I can achieve with the EQ first, as mini DSP makes that very quick to iterate.
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