Question re: Dipole Sub amplification

[Arctophile]

Hi all,

I just took delivery of my sub drivers - Pyle PLG15s (see this thread My first Dipole Subwoofer!!!), and now I'm thinking (belatedly) about the amplification for them.

I am going to be driving the main baffles with a JVC RX-F10s, but this will only use 4 channels.

I'm planning to turn the Pyles into one W-frame dipole woofer.

Now the stupid question - can i use both of the JVC's other channels for the two drivers, or do I need to bridge them somehow and drive them connected in series? I can't connect them in parallel because that would be a 2ohm load on the amp.

Thanks for your forebearance,

//Adam F

[JWFokker]

I'd like some info on this too. I'm gearing up to build a dipole sub, but I don't know what design to build for an amp. I'd rather build it myself than use a plate amp.

[johninCR]

Arctophile,

Dipole woofers don't require much power to reach full excursion at their low end cutoff, so the other 2 channels of your amp may be sufficient. As long as you have an even number of woofers, then 2 separate channels can be used. In the same enclosure you want the same signal applied.

JW,

If you go with a 2 channel amp, it will give you more flexibility later, so you can go with 2 units running in stereo. With dipole bass the more the better.

Both,
Just to be clear on terminology, you both talk about subs, however, even Linkwitz calls his W-Baffle a "Dipole Woofer", not a subwoofer. Be careful you don't set your output expectations too high down in the bottom octave. eg my project over the next 2 months includes a pair of dipole subs that get me down to 28hz or lower. I'll be using between 8 and 12 12" woofers per side. Each unit will have 4 drivers and first I'll see what I can get out of a 4 driver unit before deciding if I need 4 units or 6. Of course, my goal is substantial output down to 28hz.

[Arctophile]

12 12" woofers per side? How high are your ceilings?

Anyhoo thanks for the advice once again, I have a sealed sub I can use for the low low end if necessary.


//Adam F

[AJinFLA]

Hi Adam,

I could not find any info on whether your particular model JVC would be stable into a 4ohm load or not, but from just about all the tests that I have seen on those very light digital amp receivers, most (with some exceptions, like the HK) will have problems with lower impedance loads. Their power output drops off quite a bit - and distortion rises rapidly. You may want to consider series wiring in this scenario. I just can't say for sure with your JVC. John is correct about the power requirements at say 25hz will be relatively low to drive both to xmax, although I doubt your JVC could do that with either 2 chs driving each, or 1 ch driving both. The amp might be close to, or at clipping, so it would be tough to tell by ear. What John didn't mention, is that to drive those Pyles xmax at say 80hz, you would need a couple hundred, if not thousand watts! Power requirements are such that too much is a better than too little. Your JVC will drive them to decent volume (even if series wired), but more power would be better, so that you don't have to worry about your amp clipping before your woofer starts to show sounds of distress. A great way to power dipole (or any) subs, it to use a Pro audio amp. The're usually quite inexpensive - and very powerful. I use a QSC model rated at over 400w rms to power my dipole subs (2x12 Peerless XLS/ch). Picked it up a couple years ago for $300. Can now be found on ebay for less than $200
Now I'm not quite sure what John is talking about when he calls a W a woofer because that's how SL refers to it. Its very much a "subwoofer" like the H-frame he uses on the Orions. Actually its a more compact way to get the same performance as an H of similar depth. The main differnce is that it becomes a more complex acoustic stucture, so it will have a different dipole peak than a similar H. Notching this peak is one of the keys to the whole thing. The W will exhibit the same 6db roll off as the H, so you must eq. I assume that you have eq capability if you are going dipole. Good luck if you don't. Now, I'm also assuming that you realize that with a dipole, you are trading bass quantity for bass quality. The 2 Pyle 15s will give you good output for music, but could easily run into trouble for HT. If HT is your game - and you still want to try OB, you may want to consider a U-frame - maybe something like John Marsh's Arvos. There is much, much more, like no room gain from the H or W, but I'm running out of steam here, so....

Cheers,

AJ

ps, the large arrays of woofer/side on each wall IS the way to do it

[Arctophile]

HMM OK well...

1. From what I've read at www.audiocircle.com, the JVC F10s is stable into 4ohm loads, BUT doesn't provide a lot of current, so this might be a problem (how do I know w/o hooking it up?). A pro audio amp is a good idea, I'll look into it thanks.

2. EQ will be done in a Behringer DCX2496's DSP - I just hope there's enough memory!

3. I only want them for music, so quality is the goal.

Thanks,

//Adam F

[johninCR]

Originally posted by Arctophile
12 12" woofers per side? How high are your ceilings?
Anyhoo thanks for the advice once again, I have a sealed sub I can use for the low low end if necessary.
//Adam F

I'm going to use the small air pathway concept of the Ripoles discussed in a previous thread and a W-Baffle type of layout. I can fit 4 12's in a space 14" high by less than 22" wide. I'm going to add some extra depth, but not to the extend of JohnK's "U-baffle" woofer, because I want to retain as close to dipole radiation as possible but increase output down low. I'm pretty sure 8 per side will be enough and double stacking the 4 driver boxes will make a nice firm vibration-free base for my dipole mains.

For HT I'm going to have 2 subs operating below 28hz. They'll operate quazi dipole. I have to test it first, but the plan is a pair of Tempests in a vibration-free coffee table at the seating position and a pair of similarly tuned Shivas at the projection screen. I'll wire the shiva box out of phase, so the sum of the in room response will be near zero. My front to back room mode is at 28hz, the reason for choosing that XO point. The beautiful thing is that my almost 4 meter separation of the out of phase wave fronts will cause the shiva box to actually reinforce my seating area output down to about 16hz.

I love to watch late night movies and with my current setup I'm too self conscious about the neighbors to have my sub at the appropriate level late at night, so my goal is extreme output in the seating area but for most of it to stay in room and keep the neighbors happy. I'm pretty sure my concept will work. I just have to prove it first. Walking through the room to sit down with a low frequency tone generator running should be a very interesting effect to say the least with almost silence when you are halfway between the subs, to extreme output a few steps toward the DIY HT couch.

[Arctophile]

Wow, I'd like to have the space and funds to do half of that!

Re: the neighbours - have you thought of keeping your current subs and soundproofing the room?




//Adam F

[johninCR]

Originally posted by Arctophile
Wow, I'd like to have the space and funds to do half of that!

Re: the neighbours - have you thought of keeping your current subs and soundproofing the room?

//Adam F

I'm going to be sound proofing, but only thick concrete or underground is going to keep 20hz waves contained. My area doesn't even have an attic to help out. Cancellation with sound proofing for the higher frequency stuff is my best bet and I think it will work to a large extent and I may need some bass traps at the ends of the room. The only space I'm really taking up is under the screen which is dead space anyway. Even though the coffee table will be a little larger than usual, it's not wasted space. The drivers are left over from some projects I did for bars, so my only real cost is the wood and other room treatments. The area is my combo office, HT and listening room, so it's my 240sqft to do anything I want and where I spend over 12hrs a day. I want to do it right, since I have the stuff to do it.