No real surprises here, looking at the data. All drivers exhibit differences & these appear to fall roughly within the generally accepted tolerance levels of the industry for sample deviation. That's good to know / have confirmed.
Richidoo said:
Greets!
You'd want a small box, so D-Appolito's suggested 220"^3 net should be small enough, ergo its total internal Vb would include the volume of the circular cutout as well as the area inside the diaphragm. Calc its diameter (d2) from Sd and measure both the diameter of the base of the whizzer (d1) and its deck height (h), then:
Vcone = (1/3)*(pi/4)*h*(d1^2+d2^2+(d1*d2))
Ideally you'd subtract out the Vb of the whizzer from this also since your Vas measurement will only be as accurate how accurate the calc'd net Vb is. Then there's the matter of checking the sealing of the driver to the box, which normally requires the driver being driven by a very low frequency (VLF) to check for any air leaks, but with such a low mass diaphragm might not be a good idea.
That said, in the scheme of things a very accurate Vas isn't a requirement to designing excellent performing speakers (Qts dominates), so all things considered, your efficiency specs are well with the standard manufacturer's 10% tolerance to both between the drivers and the previous measurements, so we're good to go IMO.
GM
Richidoo said:
This should be the mechanical XO point between the main and whizzer cone, so should be at ~the same point on every D5NF of the same design.
GM
Richidoo said:
The Fostex FE126 & FE127 have a similar anomaly in about the same place.... and they have no whizzers. But they are about the same cone size.
dave
Greets!
OK, but this won't affect driver sealing since there's no rear vent to complete a path out of the box, though theoretically the gap's Vb should be accounted for in the test box's net Vb. I'm sure it's so tiny as to be irrelevant, so didn't bother to mention it.
GM
OK, but this won't affect driver sealing since there's no rear vent to complete a path out of the box, though theoretically the gap's Vb should be accounted for in the test box's net Vb. I'm sure it's so tiny as to be irrelevant, so didn't bother to mention it.
GM
planet10 said:
Greets!
Well, what can I say, there has to be a mechanical XO between the main cone and whizzer and there's no other phase 'wrap' shown in the Feastrex's impedance and since I know of no way to completely damp it down............
Anyway, from just looking at the 126E's pronounced curvilinear cone profile, I wonder if it's a reflection from the 'mouth' to the throat', like happens with a horn that doesn't have a smooth enough mouth transition.
GM
GM said:
Possibly. I can reduce the magnitude of this bump by about half with the damar trifoil + puzzlekoat part of the cone treatment.
dave
Hmm, is it a spike in the impedance or an actual phase 'wrap'? A spike would be easily damped as its just a break-up mode, but a phase 'wrap' typically requires some serous damping, like excessive stuffing in a TL.
GM
GM
When we go to measure the D5 Monster Alnico and the D5e field coil drivers, which both have the same cone and basket, but radially different magnet design, which parameters will remain the same and which ones will change?
I see no phase wrap in the impedance plot, but neither it, my monitor, or my eye's resolution is good enough to tell for sure, so for now those in the acoustic plot looks like either standing waves or break-up modes.
GM
GM
Richidoo said:
Thanks Rich, those are pretty close to what mine are also, less the additional testing. As for the box, I decided inverted mounting would be simpler to calculate the actual volume as it's now just the actual cubic space the cone section adds to the box. As the D5nf is has a fairly small Vas measurement now, probably less than 5 liters for a test box. Again, Keith (Larson) did not have any of the specs, just that it was a 5-inch driver. The box could also be made with the mounting baffle separate so you could add false panels to reduce the volume and allow other drivers to be mounted for testing. I might try the added weight using a penny to see how close they are with yours.
Regards, KM
Thanks. You guys make my head spin with the tech talk, but I blindly follow. No pranks allowed!! haha
To do the Vas sealed box test, you need to know the actual sealed AIR volume, right? The significant volume of D5 motor and basket should be calculated to subtract from box interior volume? Should the net air volume be close to the estimated Vas determined by damped mass method?
I will do it if the Maestros designing (my) Maiko say jump. 🙂
GM, wrt field coil affecting Qts, raising the coil energy should decrease Qts right? I prefered Joe's D9e coils cranked to max with Lamm tubes at RMAF. Maybe need less with an iron grip ss amp.
Joe are you gonna test them yourself? It is very easy, but you may wanna get WT3 from Parts Express, instead of WT2 which tests very slowly. Send them down here and me and Dennis will take care of that for ya! haha 😉
Spent a very enjoyable evening with the Freddie Changs last night. All the bracing and damping is gone, except for the crossbrace to mount the driver from the rear running side to side. I sealed up the old baffle mounting screwholes whish were bleeding to atmosphere. I lengthened speaker wires so I could move them out to 10 feet away from front wall, while sitting only 6 feet away from them. Reflective walls were 3-4x farther away than direct sound which eliminated most room effect. ohmygod. Bass is a little fluffy, and the pine box resonance is there, but jeepers, it is good. Looking forward to Maiko... hint hint...
Happy New Year everyone!
Rich
To do the Vas sealed box test, you need to know the actual sealed AIR volume, right? The significant volume of D5 motor and basket should be calculated to subtract from box interior volume? Should the net air volume be close to the estimated Vas determined by damped mass method?
I will do it if the Maestros designing (my) Maiko say jump. 🙂
GM, wrt field coil affecting Qts, raising the coil energy should decrease Qts right? I prefered Joe's D9e coils cranked to max with Lamm tubes at RMAF. Maybe need less with an iron grip ss amp.
Joe are you gonna test them yourself? It is very easy, but you may wanna get WT3 from Parts Express, instead of WT2 which tests very slowly. Send them down here and me and Dennis will take care of that for ya! haha 😉
Spent a very enjoyable evening with the Freddie Changs last night. All the bracing and damping is gone, except for the crossbrace to mount the driver from the rear running side to side. I sealed up the old baffle mounting screwholes whish were bleeding to atmosphere. I lengthened speaker wires so I could move them out to 10 feet away from front wall, while sitting only 6 feet away from them. Reflective walls were 3-4x farther away than direct sound which eliminated most room effect. ohmygod. Bass is a little fluffy, and the pine box resonance is there, but jeepers, it is good. Looking forward to Maiko... hint hint...
Happy New Year everyone!
Rich
Here's an interesting picture of the D5nf with the PB9... take by my photo buff friend...
An externally hosted image should be here but it was not working when we last tested it.
I have a friend here who designed the B & O Beolab 5 loudspeaker: http://www.ultraaudio.com/equipment/bang_olufsen_beolab_5.htm
He will be assisting me with measuring the D5e Type II and the other drivers as well. He has some fairly sophisticated test equipment. My understanding is that if you use a box of a known dimension (in this case we will be using a 1cu ft box) (One can calculate and subtract the volume of the yoke etc. acurately enough) and you have determined the fs, then the changes that occur by virtue of placing the driver in the box (esp. to the resonant frequency and the output at resonance) will enable one to calculate the parameters. Is that not correct?
Regarding changes with increased voltage to a field coil, I have been able to glean the following:
As voltage goes up:
BL increases
VAS increases
Qts decreases
Efficiency increases
He will be assisting me with measuring the D5e Type II and the other drivers as well. He has some fairly sophisticated test equipment. My understanding is that if you use a box of a known dimension (in this case we will be using a 1cu ft box) (One can calculate and subtract the volume of the yoke etc. acurately enough) and you have determined the fs, then the changes that occur by virtue of placing the driver in the box (esp. to the resonant frequency and the output at resonance) will enable one to calculate the parameters. Is that not correct?
Regarding changes with increased voltage to a field coil, I have been able to glean the following:
As voltage goes up:
BL increases
VAS increases
Qts decreases
Efficiency increases
The idea I had eliminates having to calculate the displacement of the yoke, magnet assembly, back of the cone, etc. If you turn the driver around so the front is mounted facing into the box, you simply add the small amount of the cone (which should be much easier to calculate) to the box volume. (I don't think the driver would know if he's turned around in this case.)
I would think Feastrex would have a drawing file showing the cone dimensions which could be used to calculate the cubic space from the front mounting surface to the resting position of the cone surface.... some geometry required.
Regards, KM
BTW - nice looking speakers there!
I would think Feastrex would have a drawing file showing the cone dimensions which could be used to calculate the cubic space from the front mounting surface to the resting position of the cone surface.... some geometry required.
Regards, KM
BTW - nice looking speakers there!
Happy New Year and all that jive!
Well, as I previously posted, if the box is small enough to significantly increase the driver's air load, then Vas can be calc'd and is considered the better of the two ways to measure it, but I don't see how you can derive the other T/S specs from it and 1 ft^3 is way too large to get an accurate Vas calc with these drivers based on its size in general and its WT measured Vas. Note too that the drivers should be well broken in WRT their suspension compliance for most accurate measurement, but then I'm sure your designer buddy knows all the details of T/S measurement of both small and large signals. 😉 For others, I recommend D'Appolito's book TESTING LOUDSPEAKERS.
Close, Vas is a mechanical compliance spec, so it doesn't change with field coil strength.
GM
Well, as I previously posted, if the box is small enough to significantly increase the driver's air load, then Vas can be calc'd and is considered the better of the two ways to measure it, but I don't see how you can derive the other T/S specs from it and 1 ft^3 is way too large to get an accurate Vas calc with these drivers based on its size in general and its WT measured Vas. Note too that the drivers should be well broken in WRT their suspension compliance for most accurate measurement, but then I'm sure your designer buddy knows all the details of T/S measurement of both small and large signals. 😉 For others, I recommend D'Appolito's book TESTING LOUDSPEAKERS.
Close, Vas is a mechanical compliance spec, so it doesn't change with field coil strength.
GM
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