4 8's and 1 15" PR ok or not? - diyAudio
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Old 9th October 2004, 11:09 PM   #1
REDSKIN is offline REDSKIN  England
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Default 4 8's and 1 15" PR ok or not?

I am about to build a small ported box for 4 8" speakers but it will require an exessively long port so I thought a passive radiator might be the answer. As this will be my 1st PR design I have a couple of questions....

Will a 15" PR with an xmax of 31mm be ok with 4 8"ers with an xmax of 12mm?

Should I be considering any other parameters when swapping from a port to a PR?

Any help would be greatly appreciated.
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Old 10th October 2004, 05:32 AM   #2
GM is offline GM  United States
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As a rule-of-thumb you want the PR(s) to displace 1.5-2x the driver's Vd. Using ~6" for the effective diameter, four = ~12"*~0.47244" = ~5.6693"^3 Vs the PR's ~12"*~1.22047 = 14.6456"^3, so at a glance it looks good on paper.

My hang up with using a single PR is that it requires the cab to be really massive to keep the sub still/quiet if the PR gets energized to anywhere near its potential, so dual PRs on opposing sides to ~cancel them out is my preference. Now the cab can be made from 19mm BB or Apple ply to get the required rigidity/damping at a ~acceptable weight.

Also, you can heavily stuff a PR design and reduce the cab's Vb ~20% and maintain the alignment.

GM
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Old 10th October 2004, 11:47 PM   #3
owdi is offline owdi  United States
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Is that the Adire Audio PR15? If so, post the t/s parameters for those 8's and I'll model it, and let you know how far the PR will move.

I have a 10", 16mm xmax sub with the Adire PR15 and it doesn't even use half the PRs potential.

Dan
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Old 11th October 2004, 09:37 AM   #4
REDSKIN is offline REDSKIN  England
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Thanks for the replies.

GM- You mention that a cab needs to be "really massive" for a single PR to control the sub. My box will be 3cuft total minus the air space taken by speakers and PR and unfortunately box design and placement restrictions rule out a 2nd PR. Still worth doing?

OWDI- Yes it was the Adire PR I was considering. Thanks for the offer of modelling it. I allready ran this set up through WINSID and as long as I use a subsonic filter I can keep the PR with its xmax at the power I will be using. If you were going to use a different programe for the modelling the TS for the 8" are
fs-23
qts-.34
vas-27.1L
xmax-12
bl-15.4
sd-195cm^2
175w power handling

thanks.
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Old 11th October 2004, 08:53 PM   #5
owdi is offline owdi  United States
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I used Unibox until I found WinISD pro. The two model close enough together that I just use WinISD now.

Looks like the PR15 and your four drivers are a perfect match. They both seem to reach their excursion limits at around the same frequencies, and those frequencies are always below the tuning frequency.

Dan
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Old 11th October 2004, 09:53 PM   #6
GM is offline GM  United States
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Quote:
Originally posted by REDSKIN
Thanks for the replies.

GM- You mention that a cab needs to be "really massive" for a single PR to control the sub. My box will be 3cuft total minus the air space taken by speakers and PR and unfortunately box design and placement restrictions rule out a 2nd PR. Still worth doing?

If you were going to use a different programe for the modelling the TS for the 8" are........
You're welcome!

By 'massive', I mean heavy, such as heavy wall construction and adding a marble or slate and/or heavy potted plant on top (or equivalent) to mass load it to the floor.

If the alignment works for your app, then of course it's still worth doing, it just ideally will take more effort and needs to be heavy enough to require a handtruck to move it around. That, or be able to effectively anchor it to the floor somehow.

Which driver is this?

TIA,

GM
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Old 13th October 2004, 11:57 AM   #7
REDSKIN is offline REDSKIN  England
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Ok this is where I alienate everyone. I will come clean and confess.This proposed set up will not be gracing my delightfull living room nestled between the sofas and soft furnishings amazing everyone with the seemless intergration into the room,no this product of my speaker building knowledge will be proudly sitting in my........CAR! Oh the shame! yes it's true I own a car stereo.

While the idea of pot plants and marble slabs might seem like a good idea and may even sway some away from the neon lights, mirrors and those ever so useful plexi portholes so you can see your speaker moving(oooooooohhh!) I am far more conservative and obviously not the trend setter I thought I was.

As an alternative to the plant/rock idea I will be using the internal bracing/bolt it to the floor idea. Although not as asthetically pleasing I am hoping the end result will be the same.

The speaker to be use is the RE se8, chosen for is physical size and power handling rather anything else. I only have slightly over 5" of mouting depth to play with and need something that can cope with 500w.

May I take this oppertunity to say sorry for my most unaudiophilic goals and the underhand way I tried to get adivce without mentioning that it was for a car. Please forgive me and don't relegate me to the dark places where "how loud is a...." or "why dosen't my xxx wake the neighbours" or the ever popular " everything sucks apart from my xxx" counts as a worthwhile question. Please accept my humble appologies.
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Old 13th October 2004, 01:35 PM   #8
BAM is offline BAM
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Problem: Passive radiators are too heavy to be used in cars. The forces of driving cause the mass to shift around. This can even damage the active driver if the passive radiator is suddenly forced into the box and it has a displacement greater than the active driver(s). Also, when you go over bumps, you'll weaken the foam surround, and its life will be shorter. As you slow down or start up or turn, the passive radiator's mass will try to keep going straight, so it will pull the diaphragm out and push it into the box, so you have much less available excursion. Passive radiators are just plain unsuitable for cars.
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