Hi 5th Element.
Yesterday I worked on a Kicad design for the TPA3251 that I was going to post in the class-D thread but got sidetracked on the speaker design in this thread
I understand using the TPA single ended isn't as good as BTL mode, however it is very attractive to use this chip in a 2.1 mode for a very compact amp and the power rating is perfect for this use (20w for the desktops, 120W for the BTL sub with linkwitz reinforcement). Also I'm not sure the 2nd order distortion is going to be an issue with SE with very low power use for nearfield and not as critical for the higher power sub, and I will be using larger low-ESR caps on the power supply rails near the chip which will ameliorate the 2nd order harmonic issue with this chip. Open to suggestions though as I don't have experience with this particular chip yet.
I got 5 samples from TI so its not a big stretch to add a second TPA chip so that the desktop units are BTL and the sub could even be PBTL although a bit of an overkill power wise....
Yesterday I worked on a Kicad design for the TPA3251 that I was going to post in the class-D thread but got sidetracked on the speaker design in this thread
I understand using the TPA single ended isn't as good as BTL mode, however it is very attractive to use this chip in a 2.1 mode for a very compact amp and the power rating is perfect for this use (20w for the desktops, 120W for the BTL sub with linkwitz reinforcement). Also I'm not sure the 2nd order distortion is going to be an issue with SE with very low power use for nearfield and not as critical for the higher power sub, and I will be using larger low-ESR caps on the power supply rails near the chip which will ameliorate the 2nd order harmonic issue with this chip. Open to suggestions though as I don't have experience with this particular chip yet.
I got 5 samples from TI so its not a big stretch to add a second TPA chip so that the desktop units are BTL and the sub could even be PBTL although a bit of an overkill power wise....
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Dear planet10 please realize a minimum phase device that any frq response variation from flat ideal not being low Q in amplitude change, and that means peaks and dips variations plus system and individual drivers stop bands roll off slopes, will beside the perceived change in amplitude energy also change frq dependent release timing too. That is group delay and don't look at it with a 50mS vertical scale when errors is >1kHz and up zoom in and you will see how frq dependent notes from a instrument chord in replayed recording will be manipulated in release time. Sum of this is output signal will be distorted compared input signal and very clear visual looking at IR/SR transient plots or try feed system with square waves verse a system with out those variations. Had frq response amplitude changes been a nicer low Q or FIR based then input verse output changes would be better. Also in this talk we above worst manipulating room modes and you should be very lucky to prove that room reflection actual in lucky way at listening position repair frq response and phase timing errors.
Allow me saying such subjective predictions based on data as long as you pop in subjective and declare other drivers to miss low level detail compared your favorites and not backing up with data that show you actual have managed improve drivers data verse original datasheet or other shared measurement resources.
OK have done a bit more research on aperiodic, I agree with Dave it is a suitable design for the parameters I'm aiming for. It will aid transient response especially in the bass, helps with the rear reflections and flattens the impedance curve around resonance but the tradeoff is a higher F3 (albeit in a smaller box).
So to be able to select an appropriate driver and box, this is what I have gleaned from reading up:
- A driver designed for sealed boxes. Qes between 0.6 and 1, driver Qtc below 0.5
- Box size is small about 1/3 Vas.
- Vent size: ¾ the size of the cone, just a hole not a tube
- Dampen the cabinet with thick stuffing but leave a clear acoustic path from the driver to the vent
- Adjust stuffing in vent to reduce the impedance peak (watch for introducing a second resonant peak)
- Vent position, immediately behind the driver to help remove reflections (important for thin cones)
- Design the box for a system Qt of 0.9 (drops about 0.2 with the vent) for a total of 0.7
I still have to select a driver with a low Fo/F3 and reasonable xmax so still limited to the drivers available.
Is there anything else I need to consider for an aperiodic design for a nearfield speaker?
Thanks for all the help so far.
So to be able to select an appropriate driver and box, this is what I have gleaned from reading up:
- A driver designed for sealed boxes. Qes between 0.6 and 1, driver Qtc below 0.5
- Box size is small about 1/3 Vas.
- Vent size: ¾ the size of the cone, just a hole not a tube
- Dampen the cabinet with thick stuffing but leave a clear acoustic path from the driver to the vent
- Adjust stuffing in vent to reduce the impedance peak (watch for introducing a second resonant peak)
- Vent position, immediately behind the driver to help remove reflections (important for thin cones)
- Design the box for a system Qt of 0.9 (drops about 0.2 with the vent) for a total of 0.7
I still have to select a driver with a low Fo/F3 and reasonable xmax so still limited to the drivers available.
Is there anything else I need to consider for an aperiodic design for a nearfield speaker?
Thanks for all the help so far.
The 10F has been tested in an aperiodoc TL and has the right parameters for an extremely compact unit. You could make it like I did out of a tall 3 sided pyramid or Dagger that's 13 in long with 6in wide base (3 pieces) to give a 1.1 liter volume. It can be run sealed or vented at the vertex. Stuffed with increasing density towards the tail with either fiberglass or polyfill works very well. Impedance peak is flattened and there is absolutely no coloration. Sounds open and natural like an open baffle.
Having heard them, they were far better as the bottom halves of 2-ways and could suit as midranges. Above 5-6kHz they had some energy storage, leading to unpleasantness, IMHO.
Thanks sharing research.
Because aperiodic need some time/care/work suggest you also could stay simple sealed and correct impedance peak (resonance compensator) with a LCR network. If you have measurement gear its possible to measure impedance when driver sits in final box build and use free XSim program (http://www.diyaudio.com/forums/multi-way/259865-xsim-free-crossover-designer.html) to develop a in situation flat impedance precise LCR network, also a RC network (inductance compensator) could be added if you like to correct for that.
The four sealed examples from post 55 have BW2 acoustic roll off, if cascaded with a BW2 electric filter with same frq tuning fall off as acoustic box you get a LR4 acoustic slope that normal sum flat excluding XO point is in area with room modes/diffraction/bsc.
For inspiration member gmad had excellent nearfield listning data from a pair alu cone RS100-4 without using a sub (http://www.diyaudio.com/forums/full-range/265053-hypercube-loudspeakers-44.html) see post 432 couch and near field speakers, but okay he also seems a master combine IRR and FIR domain filters and get better than average acoustic performance.
Based 5th element shared info how SB65WBAC25-4 perform real world and relative low cost it seems not bad give it a try. Will ensure your concern having good dispersion at HF and around 4 liter sealed including stuffing will have f3 120Hz, then some 2.order electric and EQ could bring a 150Hz acoustic XO point to sub.
My approach to aperiodic in this situation where you are trying to get some bass extension with good transient response -- as opposed to minimizing issues with a high Q driver -- would be to design a box with my high aspect ratio vents (which already push the box towards aperiodic and are noted for their elegant bas response) and then stuff the vents with foam as needed to push the box more aperiodic if needed.
dave
This is an idea that we have pushed in our miniOnken designs … most of them are in modestly priced plansets.
It started out as a design for the at the time not yet released CSS FR125. Something that had been gestating in my brain for sometime. It didn't really work for the FR125 as they have an abrupt end of capability, somthing like a fart. We ended up pushing foam into the vents topush them fully aperiodic which worked. Chris asked if we could do similar with the FE127e. Turns out only a change in venting was needed. They performed very well, and got better as we learned how to modify the driver. The same design techniques have yielded a large number of enclosures for many drivers. Key are the high aspect ratio vents, which add resistance to the vent. The boxes only go as low as they go, but the resulting bass is very fine, very articulate.
When ustilized with helper woofers the vents can be loaded up with open cel foam to push them as aperiodic as one would like. More damping, less extension. We usually do not find a need to do that.
FF85wKeN in the 2.5 litre µFonkenSET:
An externally hosted image should be here but it was not working when we last tested it.
Here another build with dedicated woofTs:
An externally hosted image should be here but it was not working when we last tested it.
A comment on these: http://www.diyaudio.com/forums/full-range/280225-fast-fr-sealed-all-way.html#post4462849
Nomenclature (a bit out of date, but illustrates how Chris' coining of the name Fonken spread)
http://www.diyaudio.com/forums/plan...-style-box-nomenclature-what-those-names.html
Pictures of some builds
http://www.diyaudio.com/forums/planet-10-hifi/214897-minionken-fonken-gallery-pictures-only.html
dave
Okay but previous talk about multible power amp and HP filter for full ranger wasn't pointing that way.
Had a look my HDD for aperiodic and attached below, seems you get a 3.order roll off.
Regarding planet10 tech a guess what he call high aspect ratio is Fb set very low in a small ported box, need long pipe and other consequences.
If you feed full ranger direct audio stream without electric high pass filter consider if at same any ported behavour is present that below port loading cone abrupt loose control.
Attachments
Ha what a bad guess, makes sense for "somthing like a fart" for FR125 could then be overshoot caused by quite high tuning and then later flattened again pushing foam into the vents.
I just stumbled on this thread, so please excuse the resurrection, but I am puzzled by this. The peak, which looks to me to be at 5k, not 4, would look to be 64dB down with a second order crossover and 33dB down with a first order crossover, given that we would be 3dB down already at 150Hz, by definition of crossover frequency. Am I wrong?
So... 5k is about 5 octaves above 150Hz, no?
By my reckoning, with a 2nd order we are 15dB down at 300, 27dB down at 600, 39dB down at 1200, 51dB at 2400 and 64dB down at 4800Hz.
With 6dB per octave we are down -3, -9, -15, -21, -27, and -33dB at 150, 300, 600, 1200, 2400, and 4800Hz—aren't we?
What an I missing? (apart from my frontal lobe)
OK, I see I misunderstood your wording—you were referring to the level of the peak after attenuation, not the drive signal level.
I cannot imagine using this driver with anything short of a 2nd order low pass, though.
I'm back on this project now, as my JXR6HD drivers after 10 years of use have started to get a rasp (voicecoil rubbing) likely due to lack of rear suspension.
I've been pleased with these drivers but now want to try a more modern driver, although would like a replacement driver with a similar sound signature. As EJJordan did not update the JXR6HD I'm thinking either the new EAD E60 MkII (should be out very soon with some improvements over the MkI) or a Mark Audio driver. As I understand it both the EAD and Mark Audio drivers have similar design philosophies to the Jordans (EAD E60 being a derivation of the JXR6 and Mark from Mark Audio originally working for Ted Jordan).
I know Colin has mentioned above that Ted didn't like the design direction of the E60 however this driver has had positive reviews and has the benefit of many more years of development (the MkII has a number of improvements and the MkI was supposedly an improvement over the JXR6) as the JXR6 is pretty long in the tooth now...
Any other ideas or suggestions for alternative drivers? The Elkona is a bit too big for desktop monitors and I prefer the dynamics of a smaller mass cone for the higher frequencies (sounds like electrostatics). I will be using them with a subwoofer with a cutover of 150Hz.
I've been pleased with these drivers but now want to try a more modern driver, although would like a replacement driver with a similar sound signature. As EJJordan did not update the JXR6HD I'm thinking either the new EAD E60 MkII (should be out very soon with some improvements over the MkI) or a Mark Audio driver. As I understand it both the EAD and Mark Audio drivers have similar design philosophies to the Jordans (EAD E60 being a derivation of the JXR6 and Mark from Mark Audio originally working for Ted Jordan).
I know Colin has mentioned above that Ted didn't like the design direction of the E60 however this driver has had positive reviews and has the benefit of many more years of development (the MkII has a number of improvements and the MkI was supposedly an improvement over the JXR6) as the JXR6 is pretty long in the tooth now...
Any other ideas or suggestions for alternative drivers? The Elkona is a bit too big for desktop monitors and I prefer the dynamics of a smaller mass cone for the higher frequencies (sounds like electrostatics). I will be using them with a subwoofer with a cutover of 150Hz.
Have you checked out EAD in Sweden? They appear to be continuation/evolution of Jordan designs. The EAD60 Mk2 might do the trick once it goes into production. They ship worldwide, too. I've been considering a pair of their updated JX92s to replace mine, which have lovely dents the shape of an 8 year old's fingers.
http://www.eadsweden.com/
http://www.eadsweden.com/
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