Possible IB with two RL-p 15"s

[JorgenMan]

Well, now that I have my precious SoundSplinter drivers (or will, as soon as I decide which ones I want), I'm having visions of an attic IB. I've done a decent amount of research on IBs, but I thought I'd run my ideas by you all and see what you think. I'll mirror this post on the IB cult forum, too.

Below is a picture of the layout of the room. The light green and light blue boxes are where our speakers and couch are now, and the dark green and dark blue are where I plan to eventually move them, probably when we get a projector. These are all rough locations, of course, so don't try to make any deductions based on how many pixels apart the colored squares are. The red wall is about waist-high, overlooking the stairs. Ceilings are nine feet high.

So, here are some questions I've had:

Output: This isn't going to be too much for a two-RL-p 15" IB to handle, is it? I don't need to listen at insane levels (although I would like to show off if necessary). I can make my manifold for four drivers, to accommodate expansion in the future, but I won't be able to afford two more anytime soon.

Drivers/Amp: What voice coil configuration/amplifier combination would you suggest? My current thought is that with two D2s, I could run the coils in series, with each driver on a channel of an EP1500. That would give 450 W per driver, and if I put in two more, I could do two on each channel, 350 W per driver. I realize that the EP2500 doesn't cost too much more, but do I really need it?

Location: I plan on putting it somewhere in the northwest corner (top left in the picture), so it would be towards the front, no matter which direction things were oriented (I'll stick one driver in a sealed box first, so I can move around the room a bit and find an optimal location). I may cross the IB fairly high, though (~100 Hz), since my mains are a little weak. Will there be any problem with having the sub off-center if it's crossed this high?

Equalization: I doubt I'll be able to afford a BFD right away, maybe not even an SPL meter for a while after I get everything put together. This isn't optimal, I know, but it's not a deal-breaker, right?

Thanks in advance for your comments, and thanks again to Mike at SoundSplinter and Josuah for the drivers. They will be greatly appreciated.

[Sonnie]

I think your image needs an extension so it will show.

Being that the EP2500 doesn't cost all that much more and if you believe you will eventually go with 4 drivers, I'd go ahead and get it. I believe Mike says those drivers will do a tad better with more power anyway, so you'll have it early on and when you get ready for the other two, you're still set.

[Rodny Alvarez]

[Ayreonaut]

I like the quarter point location. 3'-8" off the side wall and 4'-8" off the end wall. An IB has so little distortion that it sounds much less directional than a box sub. Mine's crossed at 80 Hz, but even staring right at it, its hard to belive that the bass is coming from up there. LFE seems to rise from the floor like an earthquake.

[JorgenMan]

I've got an RS SPL meter on the way; it will hopefully be here by the end of the week. This will let me check out the response of my mains, to see how low I can cross the IB. I also plan to test the response at some possible IB locations for nulls, etc.

When we get holiday expenses paid off (next month), I'll most likely get a Buttkicker amp and have Mike send me a pair of D4s, unless I can find a great deal on an EP2500.

More to come...

[SteveCallas]

An IB has so little distortion that it sounds much less directional than a box sub

Unless you mean because most use multiple drivers with an IB, I don't follow. BL nonlinearities present in a driver don't disappear when used in an IB, as the same amount of excursion is required for the same driver in any sealed configuration. All that changes is sensitivity to certain frequency ranges - an IB will require less power to reach full excursion down low. This means that an IB will have a less dramatic rise in distortion as frequency decreases than a small EQ'd sealed...but without the use of limiters or a highpass, you won't be able to extract as much output per driver than you would from a small sealed. Ported will have even less distortion down low, and per a given output level with a given driver, should never have more distortion than a sealed counterpart.

I guess if the box sub in question was poorly constructed then you could have a point as well.

[Chrisbee]

Can Vas be tied directly to subwoofer distortion levels?

Most IB builders go for a minimum number of large drivers (to avoid over excursion at low frequencies).

Ported boxes could be just as easily hidden behind a stud wall, in the ceiling or under the floor.

One could use exactly the same 4 x 15" drivers and have just the drivers and ports exposed to the listening room (or HT).

Box size(s) can now be optimised with no real regard to domestic acceptability.

The shape could even be optimised to reduce internal resonances if thought worthwhile.

A small gain from baffle effects should be possible if the ports and drivers were flush with a room boundary.

How does the performance (output, distortion, excursion & LF extension) of our ported box(es) now compare with an IB?

Four 15" drivers are quite capable of providing more than enough output for most tastes.

So distortion and LF extension become the most interesting areas for comparison with an IB.

Our same 4 x 15" drivers could also be used in a hidden bandpass box of course.

[SteveCallas]

Can Vas be tied directly to subwoofer distortion levels?

I don't see how it could.

Ported boxes could be just as easily hidden behind a stud wall, in the ceiling or under the floor.
One could use exactly the same 4 x 15" drivers and have just the drivers and ports exposed to the listening room (or HT).

Agreed, and you wouldn't even have to build a box, just use the volume of the cavity. The main issue is ensuring this cavity is air tight. Unless one is flat to 3hz with adequate output for their listening habbits, they can always benefit from a well excuted port.

So distortion and LF extension become the most interesting areas for comparison with an IB

Just think of porting the IB where excursion limits are closest to being reached - you'll extend solid output and gain sensitivity in the surrounding region.

Chrisbee, roughly how much volume does your IB use and about what frequency can you extend to while staying relatively flat (let's say -6db point)? I'll see if I can't design a 4 x RLp15 ported sub that would use some portion of that space, stay solid to at least that same -6db frequency, and have more headroom down low. Shouldn't be a problem.

It would work out better with a driver with more Vas than the RLp15 (to allow for a larger port), but I'll make due

[JorgenMan]

It's starting to feel like Toonces is at the wheel of this thread:



Sounds like an interesting discussion, guys, but maybe a new thread is in order.

[SteveCallas]

Ermmm, sorry

[Chrisbee]

Apologies JorgenMan.

I thought I was responding to your thread.

[JorgenMan]

Hope I didn't come off the wrong way. I was really just referring to the discussion of ported subs (and ported vs. IB) that seemed to be materializing. I've actually thought about the ported-IB idea myself, and it looked like that's where this discussion was going.
I do sincerely appreciate your input, I'm just trying to keep this thread focused. No harm intended.

[Chrisbee]

No problem.

Steve and I were off on a bit of tangent there discussing distortion of the IB v his pet ported sports hall.

[JorgenMan]

I did some quick-and-dirty testing of our current "subwoofer" a couple nights ago, to see where I'm coming from. Note that the crossover is disabled in this plot. It looks like I'll be getting a serious upgrade (-40 dB at 35 Hz - that's pretty good, right?).



I hope to have time to measure the bass response of my mains this weekend.

[Sonnie]

That image link isn't working for me Aaron. You might find it easier to use our Home Theater Photos area to host your images... it's free of course.

[JorgenMan]

Short update (and don't worry, I won't try to post an image in this one):

I've now got a BKA1000-4A on the way (thank you, Shacksters, for the deal from Ultimate Home Entertainment) to drive two RL-p D4s, but there have been some Chinese New Year-related delays on the drivers. I've also decided to leave the furniture arranged the way it is now (light green in the floor plan), since the usable portion of the room is almost exactly square, and the current arrangement works better for traffic/aesthetics/etc.

That's all for now. The waaaaay-tin' is the hardest part...

[SoundSplinter]

...Every day you see one more card!

[JorgenMan]

Forgive me if this is a stupid question. Am I going to need an electrical permit to run speaker wire from the wall up to the attic?

[FlashJim]

JorgenMan wrote:

Forgive me if this is a stupid question. Am I going to need an electrical permit to run speaker wire from the wall up to the attic?

I don't think you have to have a permit for any low voltage wiring.

[JorgenMan]

Argh, I just called the Building & Safety Division, and they said I do need a permit for low-voltage wiring. Ridiculous.

[Sonnie]

I've never heard of that before... I even run my own high voltage wiring around here as long as it's my own home and not commercial property.

[JorgenMan]

The RL-p's are on finally on their way! I'll be stopping at HD on my way home from work today to pick up the following:

• a sheet of 3/4" MDF
• a sheet of 3/4" OSB
• some in-wall 12gauge wire - HD has in-wall 12ga speaker wire, but is there a cheaper alternative that doesn't require me to buy 100 feet?
• something to make a sawboard with (any suggestions?)
• 1/4"-20 2-inch socket head machine screws and t-nuts
• wood for blocks to place between the ceiling joists - I forgot to check if my joists are 2x4, 2x6, etc. Is this a standard thing (it's a new house), or should I wait and check?
• tie plates

I'm planning on using these for a wall plate:
http://www.partsexpress.com/pe/showd...umber=091-1206
http://www.partsexpress.com/pe/showd...number=261-402
http://www.partsexpress.com/pe/showd...number=261-110
I'd rather not pay shipping for just the wall plate, but it's still cheaper than anything else I've found.

I think that's it. I've already got conduit clamps, Titebond, Liquid Nails for sealing, and drywall screws. I plan on making a small sealed box to do some placement testing with (and hone my box-making skills) before I do the real thing.

[Darren]

If you call any agency they'll tell you you need a permit to use your bathroom. If you don't call you don't need it

[JorgenMan]

I was planning to install a new power outlet, so I had considered lumping it all into one permit. That project's been canceled, though, so I'm not going to bother. Not worth getting a permit for 10 feet of speaker wire.

The drivers arrived yesterday, and I have tomorrow off of work, so I'll be building a test box to experiment with placement options. I crawled up into the attic on Tuesday night, and it looks like I've only got two places I can put it: over either of the main channels. Hopefully one of them works well.

[Otto]

My local HD has CL2 speaker wire by the foot from big spools. It's something like $1.50 a foot. I've run standard speaker wire in my walls and crawl space without problems.

As far as permits go, I've pulled a couple for projects that some people wouldn't. The only reason I do is that in the event that something goes wrong (i.e., the house burns down), the insurance agency won't screw with me. There is potential for other lawsuits as well (again, when something goes wrong...). I would still do a good job, and to code, for whatever work I'm doing, but I just want that extra layer of security. It's sad that in our litigious, contract-based society, that you can't do much of anything on your own. But that's the way it is.

Sounds like you're not going to get a permit anyway, so no problem, and I'm not trying to convince anyone to get a permit that doesn't want one...