My Ripole Project

[zobsky]

Based on a recent thread of mine ( Dipole Sub question ), I plan to use 4 Pyle Pro PPA15 woofers ( http://www.partsexpress.com/pe/pshow...TOKEN=26346424 )to build a pair of double (W profile) ripoles .


Background Theory on Ripoles:
http://www.lautsprechershop.de/hifi/ripol_en.htm

Driver Blurb:

Pyle PPA15
* Power handling: 250 watts RMS/800 watts max * Voice coil diameter: 2-1/2" * Impedance: 8 ohms * Frequency response: 27-4,000 Hz * Magnet weight: 70 oz. * Fs: 26.7 Hz * SPL: 90.2 dB 1W/1m * Vas: 11.36 cu. ft. * Qms: 2.69 * Qes: .89 * Qts: .67 * Xmax: 6 mm * Dimensions: Overall Diameter: 15.06", Cutout Diameter: 13.86", Mounting Depth: 6.02"

JohnInCR suggested that I extend the rear of the ripole to form a U-baffle extenstion. I plan to do that later via a sliding sleeve.

Excuse me while go puy some plywood

[EC8010]

Dipole?

[zobsky]

No, Ripole , .. apparently similar to a dipole except with more restricted front and rear cavities to load the driver better, decreasing Fs, at the expense of some efficiency.

My criteria for sizing the openings are
1. rear cavity cross sectional area approx = 1/3 x driver Sd
2. front common cavity cross sectional area = 2 x rear cavity cross sectional area.

Here are some of my calculations (rounded off where necessary)

All dimensions in inches

magnet diameter 7
driver cutout diameter 13.86
magnet clearance above frame 1.5
nominal mounting depth 5.5

Sd (estimate) 124
internal width 15 (approx)
rear slot height 2.755555556 , .. approx 3"
front slot height 2 x 3 = 6

[Calvin]

Hi,

If You post the data in MKS-values I could do a precise simulation for You.
Anyway on first glance I´d rather use a smaller front opening and larger back chambers.
The TS-parameters look ok so far, apart from Fs and Qts.
Fs is quite low for such a dipole. Expect the Fb to be ~10Hz lower!
Qts is a bit high for a 15" driver. Experience showed that a Qts above 0.5 is ok with smaller drivers, but with drivers >12" Qts-values around 0.4 and even smaller simply sound more precise, tighter and cleaner.
If the driver is usable will show when it is built in and working, but from the datasheet it is ok so far.

jauu
Calvin

[chops]

Originally posted by Calvin
1) Anyway on first glance I´d rather use a smaller front opening and larger back chambers.

2) The TS-parameters look ok so far, apart from Fs and Qts.

3) Fs is quite low for such a dipole. Expect the Fb to be ~10Hz lower!

4) Qts is a bit high for a 15" driver.

5) Experience showed that a Qts above 0.5 is ok with smaller drivers, but with drivers >12" Qts-values around 0.4 and even smaller simply sound more precise, tighter and cleaner.

6) If the driver is usable will show when it is built in and working, but from the datasheet it is ok so far.

jauu
Calvin

1) The front and rear chambers I believe are supposed to match the surface area of the driver used for proper loading for Ripole use.

2) Actually, the PPA15's T/S parameters are near perfect for dipole/ripole use.

3) You WANT the Fs to be low or you will need loads of EQ and power and Xmax to compensate for the low end.

4) Again, for dipole/ripole use, the PPA15's Qts is just about perfect.

5) For a driver operating in a sealed or ported enclosure, this is true. However, for dipole use, these drivers are the most precise, tightest and cleanest I have ever heard. IOW, the PPA15's motor/suspension system has plenty of control over the cone's movement in OB designs.

6) The PPA15 is VERY usable, no doubt about it. Datasheets are worthless and inaccurate when trying to determind the sound of a loudspeaker or subwoofer.

[zobsky]

Originally posted by Calvin
Hi,

If You post the data in MKS-values I could do a precise simulation for You.
Anyway on first glance I´d rather use a smaller front opening and larger back chambers.
The TS-parameters look ok so far, apart from Fs and Qts.
Fs is quite low for such a dipole. Expect the Fb to be ~10Hz lower!
Qts is a bit high for a 15" driver. Experience showed that a Qts above 0.5 is ok with smaller drivers, but with drivers >12" Qts-values around 0.4 and even smaller simply sound more precise, tighter and cleaner.
If the driver is usable will show when it is built in and working, but from the datasheet it is ok so far.

jauu
Calvin

Whsat data do you want in MKS system, .. the TS parameters or my ripole dimensions, so far? I'm thinking the TS parameters. Here they are:

Pyle PPA15

* Power handling: 250 watts RMS/800 watts max 
* Voice coil diameter: 63.5mm 
* Impedance: 8 ohms 
* Frequency response: 27-4,000 Hz 
* Magnet weight: 70 oz. 
* Fs: 26.7 Hz 
* SPL: 90.2 dB 1W/1m 
* Vas: 0.321679377 cu meters
* Qms: 2.69 
* Qes: .89 
* Qts: .67 
* Xmax: 6 mm 
* Sd (approximate value for a 15" woofer with pleated surround) : 0.0856 m2	
* Dimensions: 
   Overall Diameter: 0.382524 meters
   Cutout Diameter: 0.352044 meters 
   Mounting Depth: 0.152908 meters

I've adjusted my dimensions slightly, since the plywood in the store is 48" wide, . not 49" like I had expected it to be. I'l have be rebate away a little wood to allow the driver to fit

[zobsky]

This is what I'll have to do to make sure the driver frame fits . Ths top part won't be glued in, but will be held in place by threaded rod .

Calvin, I'll wait on your simulations and build the baffles in the mean time. I thought I followed the rule of thumb correctly ie.
1. opening cross sectional area (rear) = 1/3 x Sd
2. double the front cross sectional area to account for the fact that I'm using 2 drivers per ripole (facing each other).

What am I not accounting for?

[zobsky]

Originally posted by chops


5) For a driver operating in a sealed or ported enclosure, this is true. However, for dipole use, these drivers are the most precise, tightest and cleanest I have ever heard. IOW, the PPA15's motor/suspension system has plenty of control over the cone's movement in OB designs.

6) The PPA15 is VERY usable, no doubt about it. Datasheets are worthless and inaccurate when trying to determind the sound of a loudspeaker or subwoofer.

Chops, I think what Calvin means is that the ripole construction loads the driver more than a conventional open baffle design and accordingly, the motor has to be able to cope.

We'll find out soon enough. For starters, I'm not going to glue in any of the "spacers" that determine rear or front chamber height, so if the ripole doesn't work out, I'll just make spacers taller to morph the ripole into a conventional w-profile dipole design.


Calvin, if you need, here are the current dimensions in mm
Here's

[chops]

Originally posted by zobsky



Chops, I think what Calvin means is that the ripole construction loads the driver more than a conventional open baffle design and accordingly, the motor has to be able to cope.

Agreed, but still nowhere near as much as coping with the forces within a traditional sealed or vented enclosure.

I have one of these PPA15 drivers in a sealed 4.2cf enclosure for center channel duties, and it does a pretty decent job, considering...

[zobsky]

Nothing exciting yet, .. merely cut the panels to size and routed out the magnet pass-through holes. If you can keep the dimensions of the panels to just a little under 16", you should be able to build a pair of cabinets out of one 4 x 8 " sheet of plywood.