Driver Placement

[jcd]

Still working out the design details of my potential IB, and have a few more general questions. See below for a "preliminary" sketch of what I'm starting with -- figured I'd post this in the "General" section since the questions are still pretty generic.

The design below was working on the assumption that I'd run two 15" drivers in a mono-configuration -- from what I've gleaned from the faq, the drivers should ideally be located directly behind the l/r speakers. What I couldn't figure out was where they should be mounted vertically. High or low? I have absorbers that I had planned to put behind my speakers (which are ported on the back -- see other picture for reference) so either I'd mount the driver on either side of the treatment or above or below.

Then I was thinking "what about a stereo sub". Looking at the FAQ I saw:

Those wanting stereo IB's should place them immediately adjacent to their respective mains.

Is this saying to mount them to the left or right of the speakers? And again, high/low/middle?

Assuming that I'm initially going to have only 2 drivers, would it matter if the drivers were run as mono or stereo?

Finally, I had a suggestion that I mount the drivers in the lower corners (1 in each lower corner) to improve the output of the drivers. As funds and inclination permit, when I jump to 4, I should mount the other two in the top left and right corners. This would make it appear as one huge waveform (below 65Hz) coming from the front of the room due to mutual coupling. Any downside to this approach?

JCD

i6.photobucket.com/albums/y249/JacenD/GarageDesign.jpg

i6.photobucket.com/albums/y249/JacenD/IMG_0713.jpg
i6.photobucket.com/albums/y249/JacenD/IMG_0714.jpg

[ThomasW]

The ports on the back of your speakers aren't going to be doing anything once the sub is operational.

In a space that narrow you're not going to be able to tell a stereo sub from a mono sub.

Make your life, easy by a $50 solid core door to replace the one that's there now, use it as the baffle. That will give you space for more drivers if you need them.

BTW, I changed your images to links since they're so wide..

[jcd]

admin said:

The ports on the back of your speakers aren't going to be doing anything once the sub is operational.

not sure what you mean...

In a space that narrow you're not going to be able to tell a stereo sub from a mono sub.

ok, no benefit by going to a stereo sub setup.

Make your life, easy by a $50 solid core door to replace the one that's there now, use it as the baffle. That will give you space for more drivers if you need them.

So mounting the speakers in the door is better than mounting them in the corners (lower first, and higher later). Thanks for the suggestion/info!

BTW, I changed your images to links since they're so wide..

Thanks!

BTW, the wall between the center area and the storage area hasn't been built yet -- it's going to be the first step in converting my garage into a listening room.

Thanks for the continuing help.

JCD

[ThomasW]

not sure what you mean...

Unless the ports are tuned to something higher than the crossover point to the sub (80Hz?) there isn't going to be any output from them when the sub is being used.

Putting the sub in the door centers the sub between the mains. That's a very good place for them

[jcd]

Putting the sub in the door centers the sub between the mains. That's a very good place for them

Can do and will do.. but other than ease of installation, is there another reason? One of the issues I thought of after reading your response is that, although not used often, there will be times when we need to open and close the door. Of course, the drivers should be installed pretty securely, but I can totally see a situation where the wiring can get fouled up somehow.

Also, since the amp I was going to get (Nady XA-1100) still seems to be MIA, I've been looking at other amps to buy. Any reason why a DJ amp can't be used? I'm just not sure what makes an amp a "DJ" amp. For example, there are a lot of Crown DJ amps on ebay that seem like they'd have the power to run an IB. Of course there are a few amps that look pretty sketchy too.. (see link at bottom). It'd be nice to be rich and famous and not have to worry about such trivial things as money

Again, thanks Tom for taking the time to answer a bunch of inane q's..

JCD


cgi.ebay.com/New-2000-WATT-PRO-AMPLIFIER-2U-DJ-EQUIPMENT-POWER-AMP_W0QQitemZ7407516343QQcategoryZ64451QQrdZ1QQcmdZViewItem

[titch]

If you look in the amps section of these forums you will see all (or should) amps you can get.

[ThomasW]

Generally speaking DJ amps have overhyped specs and aren't built very well. That's why they aren't on our recommended amps in the steal and deals page.

[jcd]

titch said:

If you look in the amps section of these forums you will see all (or should) amps you can get.

I was hoping that there were others that could be recommended -- three is a pretty small selection.

But, it is what it is I guess.

Thanks.

JCD

[jcd]

admin said:

Generally speaking DJ amps have overhyped specs and aren't built very well. That's why they aren't on our recommended amps in the steal and deals page.

Figured as much.. just trying to be chea.. err, frugal.

JCD

[jcd]

Just for the idea of making myself smarter, are there any other resources out there (net, books, etc) that can explain the theory behind IB's? E.g., how the different placements differ from each other, when a stereo setup might work best, etc

The FAQ is a good start, and gives most of the answers directly.. but I'm also interested in the "why's" behind some of the answers. I could pepper this forum with all my questions, but I'm sure that'd get old for everyone (but me) real quick.

"Curious" JCD

[ThomasW]

If you look at the Adire White paper on the FAQ page it has some info.

There are no IB sub resources, that's why I started one.

Other than to understand that an IB is simply a very big sealed box, I'm not sure what theory you'd need.

The criteria for the placement of an IB is no different than the placement for any other kind of sub

There are no studies or comparisons between manifold and line array IB subs.

You can find info about mono vs stereo subs using google.

There's a link to the Harman multi-sub placement whitepaper on the FAQ page.

As usual, the answer to any question containing the word "why", is the word "because".....

[jcd]

admin said:

If you look at the Adire White paper on the FAQ page it has some info.

Will do.

admin said:

There are no IB sub resources, that's why I started one.

Thanks!

That's a bummer though -- I'm still surprised IB's aren't more popular -- better performance at a lower cost with a high WAF (since they can be hidden). Of course, the whole installation process might dissuade the masses..

In any case, I completely appreciate the time, effort and knowledge you've put into this forum.

admin said:

Other than to understand that an IB is simply a very big sealed box, I'm not sure what theory you'd need.

That part I understand.. but some questions I can think of seem pretty specific to IB's. For example, why mounting the speakers vertically on the door of my "soon to be room" might be better than one in each corner. I know a LITTLE bit about speaker design, so I guess if I knew more, more of the questions would be obvious to me.

admin said:

The criteria for the placement of an IB is no different than the placement for any other kind of sub

I'd agree/understand. But I'd say most stand alone subs only have two dimensions to work with (how far to the right/left and how far in/back) whereas an IB is more 3 dimensional (up and down). Of course, I could just not be looking at this the right way.

admin said:

There are no studies or comparisons between manifold and line array IB subs.

That one surprises me too. I would have thought that someone would have done some tests on this one. I guess, unless you're a raw driver manufacturer, it's against your business interest to do a IB study (pretty hard to sell a box sub if there's no box).

admin said:

You can find info about mono vs stereo subs using google.

Duh.. should have done that one already.

admin said:

There's a link to the Harman multi-sub placement whitepaper on the FAQ page.

I'll look at this one too.

admin said:

As usual, the answer to any question containing the word "why", is the word "because".....

LOL.. yeah, I get that from my wife too..

Thanks for the reply.

JCD

[jcd]

There's a link to the Harman multi-sub placement whitepaper on the FAQ page.

The link in the FAQ didn't work -- the new location is now White Paper

If I notice any other dead links, is this the appropriate place to mention them?

JCD

[jcd]

I have a line on a used Crown XLS 602. It can put out 380w/ch into 8ohm, 600w/ch into 4ohm or 1200w into bridged mono/8ohm

I'm currently leaning towards the 4xDayton 15" DVC woofer, although, I still may go to 2 of the DVC's in the short term. This driver is 8ohms per coil. Power handling is 350w RMS/coil, 600w/total.

What I couldn't figure out is:
1) How to wire this. I went to the Rockford Wiring Wizard (RWW) --they didn't have an option for a woofer with 8ohm coils (2 or 4 were the only options).
. If I double up the numbers using the RWW, it looks like I can wire these together
. i) in mono into 4ohms or 16ohms,
. ii) in stereo (with 2 drivers per channel) into 8ohms
2) What is the 'derated' power watt handling of this driver?

I know I'm being retarded, but I wanted to make sure I've got this figured out correctly.

Of course, if I procrastinate long enough, the new drivers ThomasW has been alluding to might materialize and I'll have to go through this process again..

JCD




www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=295-190 Dayton 15" DVC
www.crownaudio.com/amp_htm/xlsspec.htm Crown XLS 602
www.rockfordfosgate.com/rftech/wiringwizard.asp Rockford Wiring Wizard

[ryans]

Since the Dayton DVC's are dual voice coil subs, you also have the option of only driving one coil on each sub. That would allow you to wire them 4 ohms stereo. This would also alow you to play with resistive damping on the other coil.

As a note, the Dayton IB15 really looks to me like a DVC15 with one coil left off. Lets compare for a minute what the DVC15 parameters are like with only one coil driven and the other left open:

Param IB15 DVC15(1 coil open)
Fs 20.8 20.48
Qms 12.08 12.28
Qes 0.69 0.78
Vas 11.11 9.92
Cms 0.33 0.307
Mms 176.8 197
Xmax 14.3 15.1
Re 5.21 5.2
Power 350 350

They're so close that you could mix IB15's and DVC15's in the same application without any ill effects. The main advantage of the DVC15 is the additional wiring options and the ability to play with RDO.

This being said, note that PE already recommends a maximum of 140 watts for the IB15 in an IB install. Since this is based on mechanical limits, which are virtually the same as the DVC, I think 140 watts is a good max for the DVC15 as well.

[ayreonaut]

admin said:

...There's a link to the Harman multi-sub placement whitepaper on the FAQ page.

There's an interview about this paper here - www.onhometheater.com/features/20040801.htm

Todd Welti: ...four subwoofers seems to do the trick -- and we came up with three configurations out of about 100 that we looked at that are the cream of the crop. Actually, there’s a fourth solution -- one that Floyd came up with -- that worked even better than the others, but it involves bringing the subwoofers out from the walls, which I generally didn’t consider.
Floyd Toole: It’s not very practical, unless you could put them in the ceiling. It uses four subwoofers located at the 25% points from all four walls.
Todd Welti: In other words, you shrink the whole room by 25% and put the subwoofers at the corners of that virtual room. You get incredible performance, but that’s just not practical in most rooms...

Instead of co-locating all of the drivers in one enclosure, could you mount one in each of the ceiling quarter points as described? It seems from the Harmon paper that it would provide an excellent frequency response, but would the ouput from the four drivers still combine to yeild acceptable levels? (For woofers I'd probably use the SoundSplinter RL-p 15s.)

[ThomasW]

The Harman paper primarily deals with evening out the performance in a rather large room, something most of us don't have.

Now there's certainly no reason one can't use multiple IB's. My suggestion when this was brought up on the old forum (sorry archives were lost) was for the person to start with a 2 driver IB (expandable to 4 driver) centrally located. Then see if one actually needs more locations vs simply adding more drivers.

With multiple locations one does lose the advantage of mutual (acoustic) coupling since the drivers aren't co-located.

[ayreonaut]

That sounds like a good idea.

My system faces a corner of the room. I can start with a manifold in the quarter point nearest that corner. The I'll measure and find out whether there are big changes in the FR from seat to seat. If there is a problem I would try adding subs at the other quarter points.

Or I could just take one for the team and try it both ways and compare. If one manifold turns out to be better, I'll have three big holes to repair!

[jcd]

admin said:

With multiple locations one does lose the advantage of mutual (acoustic) coupling since the drivers aren't co-located.

I've tried to figure out how close the drivers would have to be to get that coupling effect.. or is more an issue of having the sond wave hit you at the same time? i.e., if the drivers are equidistant to the listening position.

JCD

[ayreonaut]

At the Genelec site I found the following

"When two or more subwoofers...are positioned close to one another mutual coupling is the fortunate by-product. This is due to the long wavelengths, associated with low frequencies, causing constructive superimposition. For mutual coupling, the subwoofers must be placed within ½ a wavelength of one another (85Hz upper crossover frequency ½ wavelength is approximately 2m). For example, two subwoofers give a 6dB increase in acoustical output at the listening position..."

Is it as simple as they make it out to be? Can you really get the same results with feet of distance between the drivers?