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Thread: Bass Port size for a DIY JBL 2213h project

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    Bass Port size for a DIY JBL 2213h project

    Hello friends, A while ago I bought an immaculate pair of JBL 2213H for a very fair price. I have always heard that these woofers produce a very clean and deep bass in large enclosures. So I have decided to build a pair of speaker out of them. The only issue is that the woofers still play bass frequencies of 100-50Hz a little too loud for my taste. The test cabinet I have put them in right now were built for a DIY JBL L100T (ten years ago or so). I guess they are like 60L or maybe a little bit larger. I want to make the woofer sound tighter. According to WinISD a volume of about 100L with a tuning of 18Hz should make them sound right. If I use a 4" diameter port, the length is 26.55" and the 1st port resonance is 254.84Hz. If I use a 3" diameter port, the length is 14.38" and the 1st port resonance is 470.35Hz. Which option is acoustically superior?I have decided to use PVC swage pipes and use 90-degree bends to make the port fit. Please see the drawings attached. Do my calculations make sense? Please see the attached pics.Thanks. I could not attach the pics here. To see the pics please click here:https://audiokarma.org/forums/index....#post-16330763

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    Senior Member RMC's Avatar
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    Ramin,

    Driver EBP at 48 suggests a sealed box. But a vented one would still work. The reason the cab would be somewhat large is driver Qts at .49 is pretty high.

    For each halving of frequency, a driver in a sealed cab would see driver excursion quadrupule, which means more LF distortion. Plus you lose some efficiency in sealed which also means more distortion since in well designed systems these two are inversely related.

    In a vented box the port helps the driver with less cone excursion, consequently less LF distortion. Moreover with its higher efficiency the vented cab = less distortion.

    I don't know if you adjusted the QL number in ISD, the standard in the industry is QL 7, but ISD uses QL 10 has default, which is too high to start with, and that number influences proper box size.

    Your 18 hz tuning is pretty low for that 12" 2213H, about 25 hz would be more reasonable. What you see has an exagerated bass output (50-100 hz) is actualy about a 1.5 db bump ( i modeled it in Winspeakerz using 5 cu ft because 3-5 cu ft was mentioned on AK. Your 100 L is 3.5 cu ft). This bump can be easily mitigated by putting the boxes on stand or base and LF diffraction loss will take care of it. Speaker softwares assume a 2 PI box placement meaning directly on the floor for example, giving it some LF reinforcement. You need to experiment stand/base height to please your ear. One may also correct too much bass with LF EQ.

    The minimum recommended port by Winspeakerz is 12.2 sq in, and a 4" tube has an area of 12.56 sq in, pretty close. JBL also used a rule where port diameter should be at least 1/3 of cone diameter, so again a 4" tube for a 12".

    I'll show tomorrow night the pics of the modelings i did, since i gotta go now. Regards,

    Richard
    Last edited by RMC; 04-08-2023 at 12:22 PM. Reason: improper excursion wording used
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    Thank you Richard for the reply.

    So you recommend a 100L volume tuned to 25Hz and 4" diameter port, which makes the port 12.6" long.
    If you have better recommendations please let me know.

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    Senior Member RMC's Avatar
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    No, i used 5 cu ft which is 142 liters, not 100 liters

    25 hz and 4" tube are ok

    i haven't modeled tube length yet

    See you later
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    Quote Originally Posted by RMC View Post
    No, i used 5 cu ft which is 142 liters, not 100 liters

    25 hz and 4" tube are ok

    i haven't measured tube length yet

    See you later
    The largest I can do is 3.5 cubic ft (100L). Can you give me your best suggestion for this?

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    Senior Member RMC's Avatar
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    Ramin,

    My best suggestion was 5 cu ft box.

    A second best suggestion based on a 3.5 cu ft (100 liter) cabinet would be as shown in this 3rd modeling. I had saved the two 5 cu ft modelings (sealed and vented) just in case.

    First pic shows 2213H in 3.5 cu ft box tuned to 25 hz, even though near top left in one place it shows 5 CF in pale color since i imported data from a previous 5 CF modeling and changed things to Vb 3.5/Fb 25 hz.

    Graph shows a 2.5 db bass bump but in reality its 2 db since the driver level (sensitivity) is almost 90.5 db on the right side of graph. As mentioned earlier getting rid of the 2 db bump isn't difficult, in case its a problem.

    As for port size you get two suggestions. First one is 2 X 3" tubes, these are longer. Second one is a single 4" tube having 12.63" long, pretty much the same as you had calculated. Since the 2213H isn't a high power driver with a Pe at 75 W you might not require the larger area and longer 2X3" version? You decide based on cab space available.

    Richard
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    Thank you Richard. Very helpful replies. I have finished cutting the walls of the cabs... once I do the holes, I will post some pics.

    I think I am going for the 4" port...

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    Going for the internal 4" of the port is ok, it exceeds a little the minimum recommended port area from Winspeakerz.

    When time comes to test the speakers for bass boominess, there's an easy and low cost way to test the LF diffraction loss reducing the bass bump. Before thinking of any stand or base i mentioned you can get an idea by simply using a few pieces of wood that will lift the cabs off the floor.

    You can start with two pieces of 1" X 2" or 2" X 3" on edge under each cab that will lift the boxes by about 1.5 or 2.5 inches respectively. While listening to various music if your ears tell you its not enough, then go for two pieces of 2"X 4" on edge that will lift the cabs by about 3.5 inches. I'd be surprised if you need to go even higher since its only a 2 db response bump.

    Once you determined which box lifting works best for you then you can think of a more permanent solution, like making speaker stands or bases. At least you should know from this little experiment how high you need to lift them to please your ears.

    Another method sometimes used to make bass sound thinner is to move the bass cabs well into a room, therefore away from most boundaries. However that option may become a pain in the ass if the boxes are then in your way, bumping into them or having to walk around these all the time, specially in a smaller room...

    Richard
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    Actually I did that last night. Just popped into my mind to put some oak wood pieces which I got from Home Depot, beneath the cabs... Long story short, the bass really got tight and less heavy. The woofers punched like a hammer and sounded deep and controlled. They sounded almost perfect even in the current test cabinets. The whole speaker, sounded like a unified thing, as though they are not really there.

    I didn't have much time to listen to them as it was late, though. I will post some pics and measurements once I am back home.

    Thanks again for your posts.

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