I'm exploring the merits of internal vs external locations of the crossover for the Purifi SPK5 Demo Speaker design. For convenience I would prefer an internal crossover but, given the compact cabinet dimensions, I'm concerned about the close proximity of the inductors and drivers.
I would appreciate advice on whether it would it be reasonable to mount the crossover on the back of the internal brace (marked in red in the attached image)? Thanks!
I would appreciate advice on whether it would it be reasonable to mount the crossover on the back of the internal brace (marked in red in the attached image)? Thanks!
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Thanks. That's my main concern. Perhaps a better option may be to split the LF and HF sections of the crossover and mount them on the rear panel, one on each side of the port.
That would be much better.
If this is a scale drawing, the position of the inner opening of the tube is also problematic. It's too close to the wall or the tweeter.
This drawing has been prepared by Purifi and is as shown in the SPK5 PDF. I agree, it does look rather close.
I reviewed the Purifi SPK4 Fantastic! The external passive crossover is pretty big. Not sure what XO components are intended to be used for SPK5, but there is no way this crossover can fit into the SPK4 cab. The passive XO's sit behind the speakers...
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Thanks. I don't yet have the drivers but have built the cabinets and ports and as far as I can tell, there will be sufficient room to fit the crossovers on the side panels if the HF and LF sections are split. The cabinet will need to be increased slightly in volume to allow for the additional real estate occupied occupied by the crossover components. Having said this, it does seem, in looking at your images that the crossovers are quite substantial and may be best located outside the cabinets.
I would make a seperate section below the speaker cabinet to put that big crossover. It makes them a bit taller, but it's easier than with the crossover outside i think. I also have the crossover outside my cabinets (so i could change them fast before they were finished) now with my diy setup, but i'm going to build some boxes to put them in, it's not handy open in the rack...
Good suggestion. I could increase the height of the cabinet by about 80mm to accomodate the crossover within a seperate section. It would be a tight space with little to no ventilation. Not sure of this will be an issue.
you can "port" it, leave a small horizontal slot open on the backside of that space for airflow. It won't affect the sound, and if it's 1cm high and 5cm wide it will be more than enough to dispensate the heath that the crossover generate... To avoid curious child-fingers and dust entering, you could add a kind of grill to it.
IMHO, this is another evidence that manufacturers, no matter how good are the drivers they produce, are better at not publishing designs (examples abound). The SPK5 is flawed in at least 2 points: there isn't sufficient space for the reflex tube to perform correctly, and the choice of the tweeter, and consequently the crossover point, isn't suited for a 6.5" driver. This mid-bass, as almost every same sized driver, should be crossed over at around 2KHz, as can be clearly seen also in the HIFI Compass measurement. The SPK5 FR is remarkably flat on-axis, but I bet that off-axis isn't that great.
I'm sure that the Purifi driver can be used successfully, its parameters are great, but with a different tweeter.
Ralf
PS: never route holes without driver in hands
I'm sure that the Purifi driver can be used successfully, its parameters are great, but with a different tweeter.
Ralf
PS: never route holes without driver in hands
I'm simply saying that this design is sub-optimal, and gave the reasons. The Purifi driver deserves something better. I've seen other sub-optimal designs posted on other manufacturer's sites, if you search on this forum you'll find mentions.
Ralf
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Ralf
PS: this is an extract from the forum rules:
The following are not hard rules, but guidelines to make the forum a better place.
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Don't quote the entire post just above yours.
Do turn off your Tapatalk signature line (it's in the Settings).
I appreciate you providing reasons to substantiate your opinion but this does not constitute evidence.
The evidence from those that have actually heard the finished product suggests otherwise. As an example, the Purifi designed bookshelf was tested/reviewed by Mitchco on Audiphilestyle (Mitchba on this forum) and was shown to perform exceptionally well for a bookshelf speaker.
Purifi PTT6.5 Woofer and 1ET400A Amplifier Technology Review - Reviews - Audiophile Style
@ giralfino, I'd like to play devils advocate on your first point, the port.
I can see that a constricted port looks sub-optimal, especially where this has been done without thought. If it is indeed constricted, but where this has been carefully accounted for then it may not necessarily be a problem. I'm not suggesting it still isn't sub-optimal.
Secondly, I'm reminded of the valves in a four-stroke engine. Travel is restricted due to the need to reduce motional energy. This leads to the circumference being a main determinant as to the area, and hence flow rate (rather than the area of the port itself), and more than a certain amount of movement of the valve from the closed position doesn't help.
I can see that a constricted port looks sub-optimal, especially where this has been done without thought. If it is indeed constricted, but where this has been carefully accounted for then it may not necessarily be a problem. I'm not suggesting it still isn't sub-optimal.
Secondly, I'm reminded of the valves in a four-stroke engine. Travel is restricted due to the need to reduce motional energy. This leads to the circumference being a main determinant as to the area, and hence flow rate (rather than the area of the port itself), and more than a certain amount of movement of the valve from the closed position doesn't help.
Allen, you can be totally right about it, but it strikes that a design for a driver which one of the main strengths is the low distortion also at high volume has a constricted port. I've never worked with a passive radiator, but probably this is a case for which a PR can be useful.
But this is secondary to my main concern of this design about a too high crossover point, dictated from the choice of the tweeter. As with other 6.5" drivers, the Purifi one start struggling with dispersion at 1.5KHz, and should be crossed to a tweeter at 2KHz or even lower. At the chosen crossover point, 3.2KHz, the tweeter is omni-directional while the mid not, and this will be clearly audible. It is without surprise that there is only an on-axis FR published for the design, off-axis the FR would be not that good.
There are great tweeters that can sustain a low crossover point, and I think that a different tweeter should have produced a better result. We are speaking about a mid-woofer that cost something less than 400 Euro, and has great characteristics, and thus deserves a better design, not one that is maybe marketing driven (the AMT looks cool).
wobba, it seems that you can't differentiate between facts and opinions. A review is a subjective opinion, and moreover no one has heard the new SPK5 design as the review was for the SPK4. If you still think that this speaker is great, then OK, but for the price involved it can be far better.
Ralf
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