goode's HT dual Rl-p18

**tgoode** · **10-04-07, 05:42 PM**

OK I need help. Plan is two rl-p18 in a box under screen. Box can be 15'6" wide 28" tall want the box as narrow as possible was hopping only 18" deep. With the box being so shallow will that cause any problems? I came up with a internal volume of 40 to 45 cubic feet. Was thinking I would have the port come out the top and be external so it would not take room from the box. Thinking to tune it to 14 to 16 Hz have been modeling it at 15 Hz with each box 22.5 cubic feet a 8" port 21" long. With the d2 speaker. My amp is EP-2500 is the d2 or d4 better.

Room ready and I am looking forward to the project. Last sub box I built was for a car in high school. Now I have such high expectations after seeing others projects.

Thanks for the inspiration
Todd

**WillyD** · **10-05-07, 02:01 AM**

Quote:

With the box being so shallow will that cause any problems?

Nope.

Quote:

Thinking to tune it to 14 to 16 Hz have been modeling it at 15 Hz with each box 22.5 cubic feet a 8" port 21" long.

You have enough volume so you can tune even lower, and I would. Maybe around 13Hz.

I'd go with the D2s because should you ever want to upgrade your amp setup, you could bridge an amp per driver @ 4ohms. And with the single EP2500, the D2s could be run series-seris for a 8ohm load, bridge the EP2500 and it would give you a solid 1300W RMS at 20Hz, under .02% THD. (well, thats best case scenario).

**brucek** · **10-05-07, 07:29 AM**

Don't understand if there is one or two boxes?

**bob1029** · **10-05-07, 07:45 AM**

Yes, it would be 2 seperate boxes, as a 14 hz tune corresponds with ~700L of displacement with this driver. There is about 1500L of total displacement, which would account for some internal port displacement on each box. The D2 is the driver I purchased as well. I would set up 2 boxes with each driver wired in series, then connected as normal to each individual channel of the amp. The reason for this is that you can better control the level of each sub, especially if they are going to be placed in seperate locations. This will also help to prevent bottoming out in an ebs alignment. Just make sure you switch off the 20/50 hz high pass filter on the ep2500

**brucek** · **10-05-07, 09:12 AM**

Quote:

With the box being so shallow will that cause any problems?

I've always wondered how these wide 'stage' boxes compensate for resonance problems in the subwoofer frequencies of interest.

I calculate the ~90" width of each box has a resonant frequency of ~76Hz. There would also be significant driver to side wall reinforcement at that frequency too.

Is this a problem?

brucek

**Bradley** · **10-05-07, 09:42 AM**

Quote:

bob1029 wrote:

Yes, it would be 2 seperate boxes, as a 14 hz tune corresponds with ~700L of displacement with this driver.

Can you explain or qualify that statement? Certainly you could tune to 14 Hz at a smaller volume with reasonable results if you wanted to. Thanks.

**brucek** · **10-05-07, 10:25 AM**

Quote:

Can you explain or qualify that statement? Certainly you could tune to 14 Hz at a smaller volume with reasonable results if you wanted to

Reasonable yes, but I think that the 700 liter results in about the best shelf. Note it runs out at the -3dB shelf.

It also has an acceptable excursion with an 8" port (when electronic rolloff is considered).

Here's the comparison of various sizes from 900 down to 500.............

box compare.jpg

brucek

**tgoode** · **10-05-07, 10:41 AM**

Wow OK now I will try to get my pee brain around all this.

Yes it will be two box they would be right next to each other but was thinking it would be easer two make them separate. That way I could just cut the mdf long ways with each box being just under 8' long.

Looks like d2 it is.

On my port with the way my screen wall is I was planning thinking I could have it coming out the top. So it would be external say I end up with a 30" port 25" would be outside the box. Hidden behind the screen wall.

If tuning it lower it seems that at 13 Hz it starts to drop off is that a problem? Does someone know how I can input my grafts into the thread. I like the idea of tuning lower.

Brucek asked about resonance problems is this a Major problem. Can it be dealt with any suggestions? With box constitution was thinking 2 layers of mdf of speaker side. Should top, back and bottom be 2 layers also.

Thanks
Todd

**tgoode** · **10-05-07, 10:56 AM**

Quote:

brucek wrote:

Reasonable yes, but I think that the 700 liter results in about the best shelf. Note it runs out at the -3dB shelf.

It also has an acceptable excursion with an 8" port (when electronic rolloff is considered).

Here's the comparison of various sizes from 900 down to 500.............

Attachment 4484

brucek

Thanks Brucek I wright a post and then I see these nice graphs. To me it looks like 700 liters it is.

Todd

**Bradley** · **10-05-07, 12:11 PM**

Quote:

brucek wrote:

Reasonable yes, but I think that the 700 liter results in about the best shelf. Note it runs out at the -3dB shelf.

It also has an acceptable excursion with an 8" port (when electronic rolloff is considered).

Thanks for elaborating. 700 liters (for a @ 14 Hz tune) does seem ideal in terms of flattest response and getting the most out of the driver. If you can only go as large as 500 liters, hopefully room gain would still enable you to have reasonably flat in-room response down low.

**Scott S** · **10-05-07, 01:40 PM**

700 liters tuned to 14hz has too much resurgence in that particular comparison. I wouldnt tune any higher than 13hz, personally in that big of a box. The 600 liter looks the flattest. I wanted to tune super low (11hz) so I went with 725 liters to get the flattest response down to Fb. Landing a particular -3dB isnt always as important as it seems....matching it with your room gain is more critical. With the higher tuning you will just have a gigantic hump at Fb. Where you could effectively extend the low end if you tuned lower and have a flatter bottom end.

**brucek** · **10-05-07, 01:45 PM**

Quote:

If you can only go as large as 500 liters, hopefully room gain would still enable you to have reasonably flat in-room response down low.

Yeah, room gain seems to be the key to the whole EBS/LLT situation. And you could certainly also raise the tune to 15Hz and still be in great shape with 500 litres. That would probably be the recommendation of the experts - (read, not me

)

brucek

**brucek** · **10-05-07, 02:00 PM**

Quote:

700 liters tuned to 14hz has too much resurgence in that particular comparison..........................The 600 liter looks the flattest.

Yeah, but in real world would we not consider the electronics. I did not include electronics in those comparisons since everyones electronics (as well as room gain as you say) are different.

If I add a 10Hz first order HPF (fairly typical), then 700 litre looks perfect?

compare with HPF.jpg

Quote:

Landing a particular -3dB isnt always as important as it seems....matching it with your room gain is more critical.

Really good point. If someone is custom building, they should go all the way and match it to their room.

brucek

**tgoode** · **10-05-07, 02:37 PM**

The largest box I can fit is 722 liters not counting any inside bracing or volume of sub. Smaller box would make life simpler. Was planning on putting in a BFD not sure if that helps or not. Is there a way to figure out room gain. The theater is only in drywall plan was to build sub box then screen wall around box. Room is going to have wall treatments and bass traps for sound if that helps or hurts the box design. Room is 3100 cubic feet in volume.
Todd

**Scott S** · **10-05-07, 04:55 PM**

Quote:

If I add a 10Hz first order HPF (fairly typical), then 700 litre looks perfect?

Ahhh, very good point. Seems that it all depends on the user and what the lower limit specifications are for them.

I specifcally designed mine so I wouldnt have to worry about a high pass filter and just let the BFD/LFE out from receiver do all that. Seems to work for me but then again its tuned to 11hz. Practically impossible to bottom it with ANYTHING above 10hz unless I dump >800w into each woofer. Im somewhat amp limited atm.

**tgoode** · **10-22-07, 05:15 PM**

Trying to finish box design this week so I can start building.

First question in one of the other threads it was said that you should have 8" from port to side wall. Was trying to keep box as narrow as possible. Goal was around 18" which would only give 5" from port to sidewall. If I have to can make box deeper. Would 24" be significantly better or some ware between 18" and 24" work. What do you guys think.

On tune for box I think 14hz looks best but I am getting scared that extension is to much and could damage the driver should I tune lower like 13hz or 12hz. Should I just put a high pass filter in or leave it and not worry. Last question I think this is a dumb one but I have looked all over and can't find out how to make a high pass filter or were to buy one.

Thanks for helping a newbie out.

Todd

**tgoode** · **10-23-07, 05:14 PM**

Just got word from mike that the beasts are on the way.

**Bradley** · **10-23-07, 05:27 PM**

SWEET!

The RL-P18s are beautiful... you'll be impressed when you see them in person.

I totally redid my design to get the port farther away from the rear wall after people warned me of things like "early onset of compression". In your case, I would either make the box deeper or perhaps go with two six inch ports. Just keep the port length under 36" so the first port resonance frequency doesn't get too low (above 200 Hz preferable).

Most of the electronics in the chain, from source to receiver to amp, have rolled off frequency response down low (to block DC), so you have some high pass filtering built in by default. Of course you don't know exactly how much unless you measure. Beyond the "BFD" (Behringer DSP 1124P Feedback Destroyer Pro) is immensely popular because it is cheap ($100) and offers multiple parametic EQs. But I'm not sure if it does high pass filtering. Guess I better found out since I'm planning to get one for myself.

**tgoode** · **10-23-07, 06:10 PM**

Quote:

Bradley wrote:

SWEET!

The RL-P18s are beautiful... you'll be impressed when you see them in person.

I totally redid my design to get the port farther away from the rear wall after people warned me of things like "early onset of compression". In your case, I would either make the box deeper or perhaps go with two six inch ports. Just keep the port length under 36" so the first port resonance frequency doesn't get too low (above 200 Hz preferable).

Most of the electronics in the chain, from source to receiver to amp, have rolled off frequency response down low (to block DC), so you have some high pass filtering built in by default. Of course you don't know exactly how much unless you measure. Beyond the "BFD" (Behringer DSP 1124P Feedback Destroyer Pro) is immensely popular because it is cheap ($100) and offers multiple parametic EQs. But I'm not sure if it does high pass filtering. Guess I better found out since I'm planning to get one for myself.

Think I will just make the box 24" deep that should give me close to 8" from port to front and back walls. From what I have seen I don't think BFD has A high pass filter.

I have been watching our build looking good. Impressive craftsmanship and planning.

Also does anyone think my port will be a problem Plan as talked about before is to have must of it externally from the box. Coming out the top. Thinking 15 to 20" would be unsupported. If I had
Bradley talent then I could drew a nice picture. Just wondering if it could be a problem. If needed I could make a box around the port to support it.

Todd

**tgoode** · **10-23-07, 06:43 PM**

Question about making the box deeper it also can grow in size looking like box could be around 800 liters from my modeling think I could tune lower does anyone have a opinion.

Tomorrow I will try to draw what I am thinking but am wondering if I can recess the area around the speaker 3 to 4'" so that I can make the screen wall flush with the box and speaker would be recessed. Say recessed area is the first 30" of the box it would be 20 " deep. The last 60" would then be 24" deep. Giving me the clearance needed for the port. Does any of this make sense.

Todd

**Bradley** · **10-24-07, 01:22 AM**

I'm just a novice here with the woodworking and subwoofer design. Seriously. I've been making one mistake after the next... and you haven't seen my router work up close!

The good news is that I'm learning a lot as I go, have received a lot of good advice from people here and on AVS, and I'm glad I can help others out in their quest for completely unnecessary and disgusting levels of bass!

If you're going to use sonotube coming out of the top, I'd probably enclose it with MDF or something, just to be on the safe side. Is there any room on the ends for the port to exit on the side? Then you might be able to keep the entire port inside the box.

I don't see a problem with recessing the driver as you describe. You might only need three layers of 3/4" MDF to do it... no more than four for sure to get it completely flush.

How much lower do you want to go with the tune? If you do not feel like you need to go below 13.5 Hz, then I'd suggest a 10" diameter port tube. Port air velocity gets pretty bad (above 30 m/s) with an 8" tube around the tuning frequency with 800-1000 watts input.

**buggers** · **10-24-07, 10:25 AM**

I would go with the 8 inch port for the RLP-18.

**tgoode** · **10-24-07, 12:13 PM**

OK lets see if I can figure this out. What if I lower the tune to 11 or 12 hz that lowers it somewhat still over 30 at high power but not as bad. I don't think a 10" port would work because then my box would need to be deeper for clearance from port to side walls. What about Doing 2 6" ports. Also I was modeling at a box size of 725 liters could make it smaller to help.

If I did have the port on the end it would only have 10" to the corner bass trap. Could have more but box would have to be narrower. If 10" of clearance is good then I think I will put the port in the end.

I am beginning to think sub building is just a balancing act. I am sure with your guys help it will sound amazing.

Todd

**Bradley** · **10-24-07, 12:34 PM**

Sorry, forgot about your cabinet space issue with regards to the port, so the 10" port probably isn't an option. (I still like the idea of dual six in ports, though, which are roughly 10% bigger than a single 8.) Many others here are running an 8 inch port and have no complaints about chuffing, so hopefully it won't be an issue. It's just a little bit disconcerting to me to see port air velocity of 34 m/s in WinISD when everybody says the "ideal" is not to go over 17 m/s. In this case the theoretical and the practical would seem to be two different things. I'm sure flaring the ends helps too.

Ido think you'll be OK with 10" of clearance on the side of box if you want to put the port there. That might simplify things greatly and prevent people from making jokes about your "smokestacks".

**tgoode** · **10-24-07, 01:08 PM**

Finale plan until I change something 725 liters tuned to 12 hz one 8" port mounted on the end of the box. If someone sees a problem please let me know. Forgot I will be out of town on Saturday so will not cut wood till Sunday.

Nice thought on the smoke stacks. I could have put red LEDs on it and a smoke generate inside the box. Man maybe I should go for it.

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