Ripole Test Sub Build

[BoomieMCT]

I've read a little bit about Ripoles (I think that's short for "restricted dipole") and decided I'd make one to play around with. Does anyone know what T-S parameters will work well for ripoles? Is is the same as a dipole? I have two 12" woofers that worked well in a dipole setup that I plan to run in parallel.

As an aside, their T-S parameters are as such;

Power handling: 150 watts RMS/250 watts max
Le: 2.75 mH
Impedance: 8 ohms
Re: 6.9 ohms
Frequency range: 20-3,000 Hz
Fs: 20 Hz
SPL: 84 dB 1W/1m
Vas: 87.8 L
Qms: 4.42
Qes: .48
Qts: .43
Xmax: 8 mm
SD: 480 cm^2

If I can get an F3 of 35 Hz with these I'll be quite happy.

[Mike P.]

It appears from your specs that the Fs and Xmax are both low for ripole. There's an informative thread on ripoles here. Note post #26.

http://www.diyaudio.com/forums/showt...=&pagenumber=1

[BoomieMCT]

Hmm, I may need to build a plain old boring dipole then. I'll have to do more reading on that link. For some reason when I searched for "ripole" on diyaudio earlier that thread didn't pop up.

[Anthony]

Why don't you try one of the weird dipole arrangements like the Linkwitz | < < | or the M configuration? Similar to ripoles, but without the virtual mass loading on the woofer (so no Fs limitations)

[BoomieMCT]

Anthony wrote:

Why don't you try one of the weird dipole arrangements like the Linkwitz | < < | or the M configuration? Similar to ripoles, but without the virtual mass loading on the woofer (so no Fs limitations)

Dipoles would probably work better with these - but I've already done those! Also I don't think the lowish Fs is a limitation, just not optimal. I'm hoping a ripole would be smaller and give more cone control (as these only have 8mm xmax).

I'll do more thinking about this. The baskets are deep enough I may have to make a plain 'ol dipole anyway.

[BoomieMCT]

So I built my test box and dropped my drivers in. I decided to go with a W frame baffle just to make the drivers easier to mount. The drivers I was using were kind of deep too so I couldn't make these very ripoly. The rear openings ended up being 87% the Sd of the driver cones.

I was getting a big peak at about 200 Hz and an F3 of about 65-70 Hz. Not so good. I moved the sub to a different position and added a +6dB boost @ 35 Hz. Now it is flat down to 24 Hz or so. I'm happy now.

With each driver only having 8mm of excursion I think I'm bumping up on that with some Bjork and Mindless Self Indulgence. It sounds good, I'm just not used to seeing a driver move around quite so much. I used these same drivers as woofers in a U baffle diopole speaker before, but then I had a sub take the really low stuff away from them.

So anyway I'm going to test these for a while. I was going to get rid of the Sony reciever that is driving them. Since I might need the built-in EQ it may have a new lease on life. I need to make a clever way to put binding posts in - originally I was going to have both driver in parallel with one set of posts. If the Sony is long term is can't drive 4 ohm so each driver is being run off a seperate channel.

[Anthony]

Looks good. But plots, we need plots!

[BoomieMCT]

Build finished. That is the last time I try to stain or poly MDF! I just moved this thing all around the room and ended up putting it where my Velodyne CHT-10 used to be, but a little further away from the walls. This is where it seemed happiest. With the EQ on the amp driving it giving a 6dB boost @ 35Hz I'm seeing F3's bumping up on 20 Hz. I could possibly go lower but not without risking the drivers. I went so far as to put a 20Hz highpass FMOD on the input to the amp.

FRs to follow.

[BoomieMCT]

Here is a quick FR I ran - lots of room effects (see between 80Hz and 100Hz). I'm still not sure the best way to mike dipoles. I may do some near field measurements this weekend.

[Anthony]

The only way to get rid of the room effects is gating or outdoors.

For a dipole, though, do not make judgments based on near field -- the wave cancellation is important and you will not measure any of it nearfield.

Unfortunately, gating has a floor of about 500Hz in a small sized room. 100 Hz for larger ones. Basically it is limited by the number of samples you can get before you close the gate. You close the gate after 1st reflection arrives at the microphone, hence, large room = lower response measurements.

You can improve on that with 96kHz sampling, but most soundcards only go up to 48kHz for sampling.

There's a good writeup on all this in the Speaker Workshop manual.

For my dipoles, I measure 2m, gated for everything except bass response.

Hope this helps.

[BoomieMCT]

Anthony wrote:

For a dipole, though, do not make judgments based on near field -- the wave cancellation is important and you will not measure any of it nearfield.

Ding! I trust my ears more then a mike to tell me if something sounds right anyway which is why I'm usually tardy getting FR's posted. I should probably learn to do gating even if I won't use it much. As I don't have a laptop outdoor testing probably won't be done.

Right now my ears are pretty happy with this sub. I'm very amused since I built it from a leftover amp, leftover drivers and leftover MDF. I even wired it with leftover wire. Someday I may replace the Sony reciever/amp that is powering it now with this amp. Not sure if I'd attach it to the back or make a seperate housing for it. Having something with auto-off would be nice as I've already left the amp on twice.