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Discussion Starter #201
Well, guess I screwed my port up then. Mine is 4.5 inches high. I'll have to trim some off from the first box. Second one isn't assembled yet. Thanks for the clarification.


4.5" tall internal? By how wide? Maybe we can work with it.
 

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Port is 4.5" tall x 21 wide and tuned to 20Hz. Should be 37.26 inches long. Re-measuring mine, I'm wayyyyyyy off. :(

Full measurements are in this post.

Looking back, I didn't measure from the center of the port either. Just the top edge. This is my first time making a ported box. I'm just glad I caught it now.
 

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Discussion Starter #203
Port is 4.5" tall x 21 wide and tuned to 20Hz. Should be 37.26 inches long. Re-measuring mine, I'm wayyyyyyy off. :(



Full measurements are in this post.



Looking back, I didn't measure from the center of the port either. Just the top edge. This is my first time making a ported box. I'm just glad I caught it now.


I looked at the post but can't decipher your actual physical port length down the middle. What is that? Is the width subtracting the port rails?

If we can get this data we can predict what tune it will be as is.
 

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Apparently I couldn't figure it out either. I find sketchup extremely frustrating because it never does what I think it should do so this entire design was done on paper/in my head. I was going back and forth between a couple different designs and I think i mixed the two for my final dimensions. My current port length by my measurement is 37.25 plus 4.5inches for the extension past the port giving me a total length of 41.75 inches. I really don't want to go any lower than 20Hz for a tune because I couldn't get the excursion under control putting 2200 watts to it without setting a high pass at 24Hz.

Since I'm having so many problems, I also decided to go back an re-calculate the volume of my box. See if this makes sense.

Going back and actually measuring the port, it is 4.5 high by 20.25 wide. This is subtracting the port bracing. Outer dimensions for the box are 48x30x24. This yields a total volume of 20 cubic feet. Since each box is roughly 2 sheets of MDF (only 8% waste) I can subtract 4 cubic feet for the volume of the wood leaving 16 cubic feet. I subtracted .5cuft for the driver and 1cuft for the bracing which gives me 14.5 cubic feet including port volume.

For a 20Hz tune, and a box volume of 12.6 (my newly calculated number) the port has a cross sectional area of .63 cubic feet. This multiplied by the length of the port at 40.64 =should give me the volume of the port or 2.11 cubic feet.

14.5 - 2.11 = a box size of 12.4 cubic feet. This is close enough for me and is also very close to my current port length so perhaps I got really really lucky although I'm still probably missing something.
 

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Discussion Starter #205
Apparently I couldn't figure it out either. I find sketchup extremely frustrating because it never does what I think it should do so this entire design was done on paper/in my head. I was going back and forth between a couple different designs and I think i mixed the two for my final dimensions. My current port length by my measurement is 37.25 plus 4.5inches for the extension past the port giving me a total length of 41.75 inches. I really don't want to go any lower than 20Hz for a tune because I couldn't get the excursion under control putting 2200 watts to it without setting a high pass at 24Hz.



Since I'm having so many problems, I also decided to go back an re-calculate the volume of my box. See if this makes sense.



Going back and actually measuring the port, it is 4.5 high by 20.25 wide. This is subtracting the port bracing. Outer dimensions for the box are 48x30x24. This yields a total volume of 20 cubic feet. Since each box is roughly 2 sheets of MDF (only 8% waste) I can subtract 4 cubic feet for the volume of the wood leaving 16 cubic feet. I subtracted .5cuft for the driver and 1cuft for the bracing which gives me 14.5 cubic feet including port volume.



For a 20Hz tune, and a box volume of 12.6 (my newly calculated number) the port has a cross sectional area of .63 cubic feet. This multiplied by the length of the port at 40.64 =should give me the volume of the port or 2.11 cubic feet.



14.5 - 2.11 = a box size of 12.4 cubic feet. This is close enough for me and is also very close to my current port length so perhaps I got really really lucky although I'm still probably missing something.


That sounds about right. Mine was about 10.5-11cu and was 48x30x20. I modeled with 1800w. I wouldn't go past 20mm excursion. I'll try to replicate your model to see what's up.
 

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I also used 15mm as my target excursion based on the manufacturer's data. Xmax is listed at 15mm and the mechanical limit is 17m.
 

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The Periscope Subwoofer B&C 21DS115

Apparently I couldn't figure it out either. I find sketchup extremely frustrating because it never does what I think it should do so this entire design was done on paper/in my head. I was going back and forth between a couple different designs and I think i mixed the two for my final dimensions. My current port length by my measurement is 37.25 plus 4.5inches for the extension past the port giving me a total length of 41.75 inches. I really don't want to go any lower than 20Hz for a tune because I couldn't get the excursion under control putting 2200 watts to it without setting a high pass at 24Hz.



Since I'm having so many problems, I also decided to go back an re-calculate the volume of my box. See if this makes sense.



Going back and actually measuring the port, it is 4.5 high by 20.25 wide. This is subtracting the port bracing. Outer dimensions for the box are 48x30x24. This yields a total volume of 20 cubic feet. Since each box is roughly 2 sheets of MDF (only 8% waste) I can subtract 4 cubic feet for the volume of the wood leaving 16 cubic feet. I subtracted .5cuft for the driver and 1cuft for the bracing which gives me 14.5 cubic feet including port volume.



For a 20Hz tune, and a box volume of 12.6 (my newly calculated number) the port has a cross sectional area of .63 cubic feet. This multiplied by the length of the port at 40.64 =should give me the volume of the port or 2.11 cubic feet.



14.5 - 2.11 = a box size of 12.4 cubic feet. This is close enough for me and is also very close to my current port length so perhaps I got really really lucky although I'm still probably missing something.



@Jedi940
Hp set at 20hz and all the info you just posted everything looks good from my end.
Your port height would be 3.75” by 20.25 as you posted for width. Vent length is 33.89” so 34 inches and first port resonance is 199hz.

If you made the port length 40 inches long your tune would be 18.66hz. And the rear port air velocity would be at 20ms
 

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So since I already got ahead of my self and started building the box with my original port height of 4.5 inches, the question is, do I need to slide some MDF in the port to bring it down to only 3.75 inches? Of course, that will change my box volume slightly as well which will change the port length etc. At 4.5 inches tall, I'm looking at a first port resonance of 164Hz. Is that too low? When I thought my box volume was 14 cubic feet, it was 189Hz which is what I wanted.

All these issues will be corrected on the second box. I haven't started assembling the port on that one yet.
 

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Discussion Starter #209
So since I already got ahead of my self and started building the box with my original port height of 4.5 inches, the question is, do I need to slide some MDF in the port to bring it down to only 3.75 inches? Of course, that will change my box volume slightly as well which will change the port length etc. At 4.5 inches tall, I'm looking at a first port resonance of 164Hz. Is that too low? When I thought my box volume was 14 cubic feet, it was 189Hz which is what I wanted.



All these issues will be corrected on the second box. I haven't started assembling the port on that one yet.


I modeled it at 12cuft. You are at about 21hz tune as built. Just need a 20hz Butterworth 12db/octave high pass and you're good. Port velocity at 20m/s. First port resonance is plenty high at 178hz. I'd build them both this way. 1hz isn't anything. You will have zero compression issues in my estimation. If you want to tune lower you can add a board too the port or leave it and plug a port later with foam.
 

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I modeled it at 12cuft. You are at about 21hz tune as built. Just need a 20hz Butterworth 12db/octave high pass and you're good. Port velocity at 20m/s. First port resonance is plenty high at 178hz. I'd build them both this way. 1hz isn't anything. You will have zero compression issues in my estimation. If you want to tune lower you can add a board too the port or leave it and plug a port later with foam.
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Cool, that definitely makes it easier :) Big thanks for all your help and @eng-399. And thanks to @LTD02 for posting that information. Not sure how I didn't know that with all my time on AVS but that is the first time in all the build threads I've read that I've heard it was necessary to keep the physical port shorter than what is modeled in WinISD. It was explained very well.
 

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Discussion Starter #212
Have you got any max spl sweeps for these two? Interested in getting a pair and building some more cabs? Cheers


If you go back a few posts you'll see the compression sweeps. Those were taken from 12' away. I think there was more in the tank. I only have a umm6 mic.

A better way would be to look at the databass test x21 subwoofer. My port is specifically designed for 15hz operation where the x21 had a port blocked to achieve it which increases port velocity which could have induced some spl robbing port compression. I think my subs would outperform the x21 as they are a little bigger and would have much lower port speeds. In the test he uses a bridged inuke 3kdsp. I'm using a inuke 6k dsp which is essentially two 3k that are bridged in the chassis.

Here is the link: https://data-bass.com/data?page=system&id=144
 

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If you go back a few posts you'll see the compression sweeps. Those were taken from 12' away. I think there was more in the tank. I only have a umm6 mic.

A better way would be to look at the databass test x21 subwoofer. My port is specifically designed for 15hz operation where the x21 had a port blocked to achieve it which increases port velocity which could have induced some spl robbing port compression. I think my subs would outperform the x21 as they are a little bigger and would have much lower port speeds. In the test he uses a bridged inuke 3kdsp. I'm using a inuke 6k dsp which is essentially two 3k that are bridged in the chassis.

Here is the link: https://data-bass.com/data?page=system&id=144
Thanks for that, how do you perform compression sweep, just keep increasing volume until the response lines don't match down low?

Enviado desde mi SM-G950F mediante Tapatalk
 

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Discussion Starter #214
Thanks for that, how do you perform compression sweep, just keep increasing volume until the response lines don't match down low?

Enviado desde mi SM-G950F mediante Tapatalk


Happy to help. Yes, I set Rew to output at -20db which is the same level as a movie (pretty sure). I set the avr at -20mv and kept turning the dial up 5 on the avr until I was at +5db. Once you have your 6 measurements or whatever range you choose. You can overlay all your measurements and offset them manually in Rew so they overlap to see how performance changes with higher output. I did this a few posts back too with @mtg90 's help.

If you have the means to buy and build these subs, I can't recommend them enough. They reproduce bass and midbass with surgical precision. I am very happy with them.
 

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Happy to help. Yes, I set Rew to output at -20db which is the same level as a movie (pretty sure). I set the avr at -20mv and kept turning the dial up 5 on the avr until I was at +5db. Once you have your 6 measurements or whatever range you choose. You can overlay all your measurements and offset them manually in Rew so they overlap to see how performance changes with higher output. I did this a few posts back too with @mtg90 's help.

If you have the means to buy and build these subs, I can't recommend them enough. They reproduce bass and midbass with surgical precision. I am very happy with them.
I've currently got a pair of Faital pro 18s in 18hz ported boxes in a 1000cuft room and while the midbass is amazing the low end leaves something to be desired. For an actual HT driver as I'm in the UK would cost around £420 and these can be had in the UK for about £450. They model the same down low as say an Ultimax 18 but offer much more midbass which is what I like about them! Seriously tempted and may be my summer project!

Enviado desde mi SM-G950F mediante Tapatalk
 

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I've currently got a pair of Faital pro 18s in 18hz ported boxes in a 1000cuft room and while the midbass is amazing the low end leaves something to be desired.
What about redesigning the enclosure to maximize low-end performance? And/or getting creative with EQ and lowering the midbass?
 

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I'm mid way through building some VBSS style 18hz tuned boxes for the Faitals to be going on with and either adding more or going bigger in the future, I've not got into any EQ yet but I think that could be the key as I've measure 120db from these in room at 20hz!

Enviado desde mi SM-G950F mediante Tapatalk
 

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Discussion Starter #218 (Edited)
The Periscope Subwoofer B&C 21DS115

Finally had time to watch some Ready Player One in Atmos. Besides being a great movie (and even better book IMO) the bass and Atmos is fantastic. These things are always impressing me!

On another note, with the lower speed fans I have had the inuke pop and reboot itself just sitting idle after a while. This has happened 4 times over a period of weeks as I've been working remotely and using the screen/PJ as my "monitor" with no sound playing. Usually I turn everything on and watch TV or a movie so the fans spool up a bit more. I decided to put the stock fans back in to see if it goes away. It was fine yesterday so we'll see. Fortunately the stock fan noise is pretty well damped because it's behind a panel in my screen wall, so I might just leave it stock. It isn't louder than the PJ fan.

I added a note earlier in this thread to warn readers.
 

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Finally had time to watch some Ready Player One in Atmos. Besides being a great movie (and even better book IMO) the bass and Atmos is fantastic. These things are always impressing me!

On another note, with the lower speed fans I have had the inuke pop and reboot itself just sitting idle after a while. This has happened 4 times over a period of weeks as I've been working remotely and using the screen/PJ as my "monitor" with no sound playing. Usually I turn everything on and watch TV or a movie so the fans spool up a bit more. I decided to put the stock fans back in to see if it goes away. It was fine yesterday so we'll see. Fortunately the stock fan noise is pretty well damped because it's behind a panel in my screen wall, so I might just leave it stock. It isn't louder than the PJ fan.


Thank god the amp is ok after the stock fan put back in place. Glad it worked out
 
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