[mnapuran]

Yea... you know, the OB-5's except with a sub in them, like the OB-7's? 

Trying to figure a clean enclosure design... something a little different then the OB-7's.  Although that design works well and is probably the easiest way to build in the sub.

What about making the OB-5's quite a bit taller, to provide the sub the needed air space, and keep the sides even all the way up the cabinet?

[Danny Richie]

Yea... you know, the OB-5's except with a sub in them, like the OB-7's? 

Easy stuff man. Just build the OB-7 cabinet minus the whole upper section. Then use the OB-5 kit.

Although that design works well and is probably the easiest way to build in the sub. What about making the OB-5's quite a bit taller, to provide the sub the needed air space, and keep the sides even all the way up the cabinet?

The tweeter level is already at 40 inches tall. I wouldn't want to see it any taller than that. The flared sides add in the needed stability and thickens up the enclosure to keep that 12" woofer from being so hard on it. It works well as is and changing it would compromise that.

[mnapuran]

Yea.. I figured that as well.

Here's another issue... If we build the OB-5S as you suggest, and it sits on a 6" riser (stage), do you see the height being an issue?

[Danny Richie]

I'd make the whole thing 6" to 8" shorter and move all the drivers down. In other words chop off the area in the lower section. Keep the lower woofers in a sealed box but allow them to have all the air space all the way down to the bottom of the box. Then mount the subs externally.

[mnapuran]

Hrmm... not sure I quite understand what you mean there.  Perhaps it would just be best to do stand alone sub 

[Daygloworange]

Much less drama that way. 

Cheers

[Danny Richie]

I mean build the OB-5 kit, but put the lower woofers in a sealed box instead of the vented box (especially a good idea if there was a wall right behind them). Shorten the cabinet accordingly to get the tweeter height at ear level. By taking 6" to 8" of height out of the air space for the lower woofers, you'll be right at optimal box volume for a sealed box.

[mnapuran]

Hrmm... okay, so if we did that, then add a sub enclosure below it as in the OB-7?  What is the rolloff on the OB5 in that configuration?

[Danny Richie]

Without the sub, -3db low 80's. With the sub, -3db low 20's.

[mnapuran]

Sounds good.... I assume front firing the sealed sub would probably be a little better then side firing as well, or is there a specific reason you side fired them in the OB-7 beyond cabinet design?

[Danny Richie]

That low bass is omni directional. It won't make any difference which way you fire it. I side fired it to keep the front of the cabinet clean and so you wouldn't have to see it.

[mnapuran]

Seems as though you are giving the 12" sub ~1.5 cuft of air space in the OB-7.

I can drop the height of the sub enclosure part of the box about 2" by widening the sub area by 2", and using ~1.58 cuft.   Would it even been worth making this changes to only drop the mids/tweets 2" in this case (putting speakers on a 6" stage).

If the point is to get the tweeter at about ear level (while seated), I'd need to drop it ~6", which would definitely be harder to do if keeping the sub in the overall cabinet.

[Danny Richie]

In a sealed box the sub only needs 1 cubic foot of air space.

You could mount the subs externally in there own boxes near the speaker.

Next, build the OB-5 box, but shorten the cabinet 6" by cutting that much out of the lower end to make the cabinet 6" shorter.

Then instead of the brace, being a brace, that is just below the bottom woofer, make that a solid piece of MDF.

This will put the two lower woofers in near optimal sealed air space.

In the now dead air space lower cavity you can block off about 3" of space at the bottom to fill it with sand and give the speaker stability.

Then in the air space right above that and just below the sealed air space for the woofers, you can mount the crossover.

Then just install the OB-5 kit.  It will work great.

[mnapuran]

As for as the sub box design... do you have various designs (or sizes) with the noted rolloff's and response curves?  I know I could calculate a few using the TS params, but I figured you might have some good real world examples in your notes using this sub (and maybe even the PR?).   Small size is important, but so is SQ and performance

[Danny Richie]

Optimal sealed is 1 cubic foot with a -3db down of 38Hz.

Optimal box size with the PR is here: http://www.gr-research.com/pdf/sub.pdf

It is 2.4 cubic feet and has a -3db down of 20Hz.

[mnapuran]

Hrmmm -3db at 38hz is a bit higher then I'd like to see for a sealed enclosure.    And yes, I'm quite aware of the performance with the PR in a 2.4cuft enclosure, but space is a bit of an issue in this particular case.     As usual, always a compromise. 

Was just curious if a slightly larger sealed enclosure would give a lower -3db down point, or perhaps a smaller PR enclosure might work without any large peaks, etc.

[Danny Richie]

-3db of 38Hz in a sealed box is pretty low.

Consider this: If you set the crossover on a sub amp to 40Hz you are really knocking output out of it in the 35Hz and up range. In a sense you are lowering the output in the upper range. Now it is not really -3db down at 38Hz any more. Now the new -3db is where it was -6db down or so and that will be in the mid 20's. What you lost in reality is output capability. It is 3db or more less than the output of the version with the PR.

You can always use an amp with a slight boost circuit to get a little of it back to flat as well.

[mnapuran]

True... good points