PE 299-145 buyout 5.25 PPcone

[MarkMcK]

Okay, I gave into temptation and bought several of this buyout 5.25 inch polypropylene cone woofer.

Although it doesn't start out all that well, it is going to be great.

Here is the stock performance:



This is just the beginning (the drivers arrived just today), but high fidelity quality is a definite possibility. While this modification will most likely end up using a plug instead of a dustcap, a simple cap/plug substitution doesn't help all that much.



The real problem is with the cone. This is preliminary, but two glue rings provide substantial improvement:



On the things to do list is a three component prefilter/equalizer, an optimized plug shape, and a more precise cone modification series.

All to follow later.

Until then, good designing and good building,

Mark

[MarkMcK]

Hate to burst any “wish bubbles” out there, but you cannot take many horrible drivers, stack them into a vertical array and get accurate sound reproduction. If, however, you stack many accurate drivers into a vertical array, the sound will not be much worse than a single accurate driver.

For those that crave the “deal” and want to make multiple driver arrays, I give you modification 2 of the PE 299-145 5.25-inch polypropylene cone buyout driver. With modification 2, I achieve high fidelity quality performance.



At $4.94 each, they must be considered a deal. For a couple of dollars more in parts and some simple work, you can have a $4.94 high fidelity quality driver. The more you modify the less the cost per unit. As a bonus, since the Qts is relatively high, you might even get a hint of bass if you use them open baffle.

I do not know how many PE has or how long they will last. If you want to join me in my little project here, buy soon.

Modification two consists of four steps.

Step one is to remove the dust cap. Any sharp pointy thing will do to get under the edge of the dust cap rim and peel it away from the cone. Just pry up with the sharp pointy thing until you have enough of the dust cap rim loose to grab with your fingers or needle nose pliers and peel it off. With only a little care, you can remove the dust cap with no damage to either the dust cap or the cone. It is incredibly easy to get off.

Step two, apply four rings (one non continuous) of Gem Tac glue to the cone and allow to set overnight. The first bead of glue is a one mm diameter glue ring at 5 mm in from the inside edge of the surround. The second bead is two mm in diameter and is located 9 mm in from the inside edge of the surround. The third bead is one mm in diameter and is located 13 mm in from the inside diameter of the surround. The fourth bead is one mm in diameter and is located 19 mm in from the inside diameter of the surround. This fourth bead is not continuous. There are four equally space breaks in the ring; each break is 10 mm in length.

Step three is to insert a three component parallel resonant network in series with the driver. This filter network consists of a .2 mH inductor, a 1.5-microfarad capacitor, and a 24-ohm resistor.

Step four is to install a plug or extension to the pole piece. The plug is a simple cylinder 24 to 25 mm in diameter and 19 mm long. I believe you can buy 7/8-inch diameter dowels at most hardware and hobby stores. Simply cut it to 19 mm in length and using the Gem Tac glue or double-sided tape center and attach it to the pole piece. Most any glue will do, just don’t get the glue into the voice coil gap. You might want to seal the wooden plug with paint or urethane, but it is not necessary.

I plan to continue working with this driver. I envision adding a tweeter and perhaps a simple array of the woofers. All further updates will be posted to my Web site. Give me a couple of days to get the information organized and posted and then look for it either under “driver modifications” or “projects.”

Good designing and building,

Mark

[sqlkev]

I can't wait til you're done with the project. So far, the FR looks great. I want to do this to, but a bit confused with step 2.

Can anybody do a quick illustration to what Mark is talking about? I would really appreciate it.

[bzdang]

Like this I think (it's late here)

[thomas997]

damn bzdang had to go and outdo me while I was drawing it up!

oh well another sketch wont hurt

[mike.e]

Thats great value for money stuff!

How does one know exactly where and what modifications to apply! Bell modes,axial modes wrecking the FR yes?

Cheers!

[Nappylady]

Have you measured the effect (if any) of putting some kind of putty on the stamped frame to kill resonances?

[sqlkev]

Originally posted by bzdang
Like this I think (it's late here)

Originally posted by thomas997
damn bzdang had to go and outdo me while I was drawing it up!

oh well another sketch wont hurt

you guys are awesome



I have a question though, would the glue last for at least awhile?
It seems that the rings of glue are essential in this mod.

[MarkMcK]

I am responding to the posts and questions generated to date.

If you use the specified glue, expect 10 to 20 years. Just do not get it wet or leave the driver out in the sun. If you leave the driver out in the sun, the polypropylene will not even last 10 years.

How do you know where to apply? In other words, I would like to do my own modifications to other drivers. In sum, it is not easy. I have been working with material vibration modes for over 20 years. Indeed, I co-authored an article on the control of material vibration modes in the Strathern Ribbon driver 20 years ago.

Lacking my experience and understanding, the next best way is to gain access to a functional laser interferometer. Unfortunately, these are very expensive (about .5 million) and costly to rent.

I have not looked at the two illustrations provided, but I have posted photos and illustrations in my MarkMck's Tang Band thread on on my own Web site of other modification projects.

I will include one of my illustrations and a photo on my Web site when I get the page/project up and running.

My thanks to the two people who did post illustrations.

Good designing and good building,

Mark

[Chris8sirhC]

Hate to burst any “wish bubbles” out there, but you cannot take many horrible drivers, stack them into a vertical array and get accurate sound reproduction. If, however, you stack many accurate drivers into a vertical array, the sound will not be much worse than a single accurate driver.

I'm not totally sure i agree with that. I'm no expert, but with multiple drivers doplar distortion will be reduced since each speaker is having to move much less to achieve a given output at a frequency. There was a big discussion on doplar distortion on another thread, so i dont want to start that up again here.

Also, this is just an asumption of mine, but does regular distortion increase with the % of maximum power a driver recieves? ie, the distortion levels (%) for a driver @.25watts will be much less than that driver at 25 watts. Have there been any studies about this?
So, if both of those things are true, ignoring comb filtering, a line array will increase performance of a driver. (this is more of a question that a statement of fact)

also, if I dont want to threadjack so if this post needs to be moved, feel free to.