[spanish68]

I'm currently using a TC 3K 15" sub in a 4cf sealed enclousure in my 6,000cf room, it sounds good below 60hz, but I need more mid-bass and low bass in my big room. I ordered one AV15X sub that will go in a 7cf box with two PR18-2100 to replace the TC sub. The AV15X sub in that PR box design will give me the low/mid bass for that size room. The power will be provided by a ED LT1300 (older version) plate amp and ED EQ2 for the equalizer/subsonic filter. This set-up will give me a tune of around 16hz which I think is very good for that size box. Due to size restriction in my room and waf, the box cannot go beyond 7cf (internal), that's why I choose the passive radiator design.

My questions are the following; The box size will be 20"W x 23"D x 39"L. The PR will go on opposite sides on the bottom of the encloure, the plate amp on the back and the sub driver in the front (top of the box). Will this rectangular set-up work similar to a more square set-up? Also, I will be putting some 5-lbs of polyfill which may give me maybe 1-2db's more bass below 20hz or so, will it also lower the tune of the sub from the current 16hz to maybe 15hz or so? Also, should I set the subsonic filter around the tuning point (15hz-16hz) or go maybe at 14hz-15hz? Will I need to run individual tones in the 12hz-17hz or so area to find the exact tuning point of the sub? Thanks.

 

[Mike P.]

I wondering how you got 7 cu.ft. internal from 20"W x 23"D x 39"L. My calculations show an internal volume of 8.6 cu.ft. According to John at A.E. the PR's displace next to nothing, allowing 1.6 cu.ft. for the sub and bracing seems a bit much.

 

[spanish68]

The outside dimensions some out to 10.40cf. Both the sub driver and PR will be flush mounted, meaning double walls for the front and sides of the box, that comes out to around 7.75cf internal, right? The big plate amp takes .35cf, the AV15X driver and PR's take about .15-.20cf and the bracing about .25cf, which gives me around 200L or 7cf, no? Please let me know if (where) I made a mistake, thanks.

 

[Mike P.]

It's right, the double walls made the difference. Just curious why you choose 18 inch PR's with a 15 inch sub. Wouldn't 15 inch PR's be cheaper?

 

[sub_junkie]

Is it ok to use a 18" passive with a 15" driver or 12? I had thought that it was beter to use the same size passive with the driver..

 

[Mike P.]

Is it ok to use a 18" passive with a 15" driver or 12?

Sure, they'll work fine, it's just overkill in most cases.

 

[spanish68]

The reason I'm using PR18 instead of PR15 is because they offer more performance (move more air) and also I'll be able to tune the sub lower 15hz-16hz like I want with the extra mass of the PR18. Also, the price difference between the PR18 and PR15 is small, at least at AE where I'm getting them. One quick question, is leaving 6" of clearance space in each side of the sub enclousure enough for the PR18 to move air? Thanks.

 

[Mike P.]

Yes, that won't be a problem.

 

[spanish68]

Mike, thanks for your response. If you get a chance to answer the questions (or anyone else) on the first post here, I'll appreciate that.

 

[Mike P.]

Will this rectangular set-up work similar to a more square set-up?

Yes.

I will be putting some 5-lbs of polyfill which may give me maybe 1-2db's more bass below 20hz or so, will it also lower the tune of the sub from the current 16hz to maybe 15hz or so?

Yes, poly fill will lower the tuning a bit.

Also, should I set the subsonic filter around the tuning point (15hz-16hz) or go maybe at 14hz-15hz?

15 hz for the subsonic filter will keep the sub at Xmax.

Will I need to run individual tones in the 12hz-17hz or so area to find the exact tuning point of the sub?

Adding ploy fill will affect the tuning, you can get fairly close to finding the exact tuning frequency by using test tones. 5 pounds of poly fill will give the box an effective volume of 7.5 cu.ft. Modeling shows a tuning of 15.6 hz.

With a tuning that low the output from the sub starts dropping around 40 hz, you will be losing mid bass output to gain the low end extension. If you were to use the CSS 15 inch PR's, you can adjust the tuning from the front of the PR by unscrewing a cap and adding or subtracting washers. I modeled the AV15X with the CSS PR's with 3 different weights to give you an idea on how easy it would be to adjust the out put from the sub. The PR18-2100's model identical to the orange line.

 

[spanish68]

Mike, thanks for your detailed response. Your sub models with CCS PR is an interesting idea in the sence that you can control the tuning, I'll look into that. Were the weights used in your model the PR 2100, 1850 and 1600? What power did you use? 1,000 watts? Also, won't room gain compensate somewhat for the dip in the response for the 16hz tune, specially under 25-30hz? I realize I have a big room, about 6,000cf when all the openings are included so room gain might be minimal but it will be corner loaded so hopefully that will help somewhat, maybe 4-6db in gain?

 

[Mike P.]

I only modeled the 2100, the graph was identical to the orange CSS model above. It was 1000 watts input, a HPF at 15 hz and the tuning was 15.6 hz.
Every room is different when it comes to room gain but 6 db is common.