Just Finished My First Build - Of Course I Have Few Questions - AVS Forum
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post #1 of 24 Old 01-23-2013, 08:06 PM - Thread Starter
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Let me start by saying thanks to everyone in the forum for all the incredible information. Reading through everyone else's threads has given almost every answer I could've asked for. All the contributors here are incredibly knowledgeable and seem to love sharing their info with any who might ask. That being said, I still managed to come up with a few specific questions. If anyone has read any of my other posts, they'll know I get incredibly wordy, so sorry about that in advance.

For background, I just finished I just finished my first build, a ported build with a 8.15 cu ft gross volume (about 7.8 with driver, bracing and port taken into account). I have a 4" dia, 12" long port which should give me about a 18Hz tune according to WinISD (I know, not enough port area, too much port noise). I'm using the Dayton 15" HF and the Bash 300W plate amp from PE (17.7Hz HPF with 1dB boost from 25-30Hz by default according to PE). I built the box out of 3/4" MDF with PL premium on the joints. I used roughly 2" wide planks of the same MDF for bracing; two front-to-back, two side-to-side and 2 top-to-bottom. I don't believe there are any leaks at any of the joints or around the driver but I'm not sure how to tell definitively. My media room is 15x19x8 in a shape generally lake the state of Utah. It's a 2nd floor room of a new construction house with carpet on the floor and no other treatments.

I will say that first impressions were s**t-eating grin incredible. I popped in "Live Free Or Die Hard" and watched the apartment shootout and the tunnel scenes and was blown away by all the sound I've been missing. So much fun to watch that. Now on to my nit-picking...

1) First, a very specific and unimportant question: During the tunnel scene when the car is tumbling (think barrel roll) through the air and lands on the two cars around the protagonists, there is an amazing LFE slide as it falls. In my system, there seems to be a slight blip where the LFE disappears right before the car makes impact. I was just wondering if anyone has the frequency charts to know if that's just below my sub's capability, or if that is an intended effect.

2) Based on advice from I got from other threads, I used 5 lbs of polyfill to stuff the cabinet (slightly less than the 1lb/1ft^3 often cited). I tried to keep it away from the port entrance but didn't know to leave a clear path from the rear of the driver to the port. Is it possible I really screwed up the tuning of my box, and if so, how would it have changed? I'll think about removing the polyfill when I take off the driver to finish the box

3) I've run some test tones though my system and output seems to disappear when I get sub 25Hz. I realize I won't be able to 'hear' frequencies that low, but I can 'feel' the output at 30 Hz. At 25 and below, this seems to go away (even though various things around the room start to rattle). Did I just do some calculations wrong or is there something wrong with my box? I suppose I really won't know unless I get a measurement mic and work with REW.

4) I tried Audyssey 2EQ (on my Onkyo TX-NR609) and it gave me some unexpected results. It had my fronts and centers crossed over at 50Hz and the subwoofer level set to -13dB (although the fronts and center were around -5dB). Do the levels just indicate my subwoofer is much stronger than my mains (which I expect is the case)? I'm at a loss as to why it set the crossover on the mains so low. Everything I read says to cross over the mains, even if they are towers, pretty high (around 100Hz) and let the sub deal with anything lower since that's what it's there for. Is there any reason why I should xover that low (50Hz)?

5) I feel like there's a little extra 'boominess' to my bass in general. I ignored the myth that ported builds are automatically 'loose' but I'm worried I did something wrong in my design. It seems that I've got a lot of rattling from stuff in my room and this may be the contributing factor to the dirtiness. Short of taking everything off the walls is there anything I can due to reduce these rattles/resonance? I pondered the Subdude/isolation route but if it's simply the acoustic noise exciting the stuff, that may not help. I don't really feel the floor vibrates that much so I'm not sure if isolating will help. Some of the speaker spikes claim to 'clean up' bass but I believe that will couple my cabinet with the floor and transfer more of the energy to the structure/wall hangings and maybe exacerbate the problem. Any easy fixes I might be able to make?

Whew. Again, sorry to the length of this post. I'm sure that will scare away a few answers so shame on me. I may be getting to picky for what I can expect out of a single sub in an untreated room but I'm hoping for some tips or reassurance. Thanks again.

-Adam
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post #2 of 24 Old 01-23-2013, 09:13 PM
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the boominess is more than likely a room resonance.

"tight" bass has more to do with stopping the signal than starting it. even if your subwoofer stops fast, if your room resonates, bass could sound slow/boomy.

you may also have some significant peaks/dips because you only have one sub.

the lack of power below 25hz may be a combination of your room and/or the high pass filter in your plate amp. who knows what your frequency response actually looks like.

also, at tuning, most all of the sound will be coming throuh the port, which in your case, as you note, is a little on the small side...hard for a 4" port to move the same amount of air as a 15" driver in the low frequencies. it is probably doing a little chuffing and compressing.

coupling your sub to the floor will make energy transfer to the room worse. try folding up a blanket or something and putting it under your sub.

Listen. It's All Good.
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post #3 of 24 Old 01-23-2013, 10:02 PM
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Quote:
Originally Posted by fleek1116 View Post

Let me start by saying thanks to everyone in the forum for all the incredible information. Reading through everyone else's threads has given almost every answer I could've asked for. All the contributors here are incredibly knowledgeable and seem to love sharing their info with any who might ask. That being said, I still managed to come up with a few specific questions. If anyone has read any of my other posts, they'll know I get incredibly wordy, so sorry about that in advance.

For background, I just finished I just finished my first build, a ported build with a 8.15 cu ft gross volume (about 7.8 with driver, bracing and port taken into account). I have a 4" dia, 12" long port which should give me about a 18Hz tune according to WinISD (I know, not enough port area, too much port noise). I'm using the Dayton 15" HF and the Bash 300W plate amp from PE (17.7Hz HPF with 1dB boost from 25-30Hz by default according to PE). I built the box out of 3/4" MDF with PL premium on the joints. I used roughly 2" wide planks of the same MDF for bracing; two front-to-back, two side-to-side and 2 top-to-bottom. I don't believe there are any leaks at any of the joints or around the driver but I'm not sure how to tell definitively. My media room is 15x19x8 in a shape generally lake the state of Utah. It's a 2nd floor room of a new construction house with carpet on the floor and no other treatments.

I will say that first impressions were s**t-eating grin incredible. I popped in "Live Free Or Die Hard" and watched the apartment shootout and the tunnel scenes and was blown away by all the sound I've been missing. So much fun to watch that. Now on to my nit-picking...

1) First, a very specific and unimportant question: During the tunnel scene when the car is tumbling (think barrel roll) through the air and lands on the two cars around the protagonists, there is an amazing LFE slide as it falls. In my system, there seems to be a slight blip where the LFE disappears right before the car makes impact. I was just wondering if anyone has the frequency charts to know if that's just below my sub's capability, or if that is an intended effect.

2) Based on advice from I got from other threads, I used 5 lbs of polyfill to stuff the cabinet (slightly less than the 1lb/1ft^3 often cited). I tried to keep it away from the port entrance but didn't know to leave a clear path from the rear of the driver to the port. Is it possible I really screwed up the tuning of my box, and if so, how would it have changed? I'll think about removing the polyfill when I take off the driver to finish the box

3) I've run some test tones though my system and output seems to disappear when I get sub 25Hz. I realize I won't be able to 'hear' frequencies that low, but I can 'feel' the output at 30 Hz. At 25 and below, this seems to go away (even though various things around the room start to rattle). Did I just do some calculations wrong or is there something wrong with my box? I suppose I really won't know unless I get a measurement mic and work with REW.

4) I tried Audyssey 2EQ (on my Onkyo TX-NR609) and it gave me some unexpected results. It had my fronts and centers crossed over at 50Hz and the subwoofer level set to -13dB (although the fronts and center were around -5dB). Do the levels just indicate my subwoofer is much stronger than my mains (which I expect is the case)? I'm at a loss as to why it set the crossover on the mains so low. Everything I read says to cross over the mains, even if they are towers, pretty high (around 100Hz) and let the sub deal with anything lower since that's what it's there for. Is there any reason why I should xover that low (50Hz)?

5) I feel like there's a little extra 'boominess' to my bass in general. I ignored the myth that ported builds are automatically 'loose' but I'm worried I did something wrong in my design. It seems that I've got a lot of rattling from stuff in my room and this may be the contributing factor to the dirtiness. Short of taking everything off the walls is there anything I can due to reduce these rattles/resonance? I pondered the Subdude/isolation route but if it's simply the acoustic noise exciting the stuff, that may not help. I don't really feel the floor vibrates that much so I'm not sure if isolating will help. Some of the speaker spikes claim to 'clean up' bass but I believe that will couple my cabinet with the floor and transfer more of the energy to the structure/wall hangings and maybe exacerbate the problem. Any easy fixes I might be able to make?

Whew. Again, sorry to the length of this post. I'm sure that will scare away a few answers so shame on me. I may be getting to picky for what I can expect out of a single sub in an untreated room but I'm hoping for some tips or reassurance. Thanks again.

-Adam[/quote

]Well, I will say that the scenes you are using to demo are some of my favorites. The tunnel scene when it flips through the air actually feels like it hits you when we view it in my room.You can feel the pressure build against your body and our clothes shudder as it flips and crashes. I have never heard it anywhere else, so that is what I have to compare it with.

http://www.avsforum.com/t/1333462/the-new-master-list-of-bass-in-movies-with-frequency-charts/6000#post_22583196




I might be inclined to say that the sub might be running out of juice at the levels you want to recreate. What kind of SPL are you getting? What SPL levels did WinISD predict?

How much does the woofer move at 25 Hertz? What frequency does the driver stop moving? The tuning was calculated, was it actually measured yet?

If I was you, I would run my mains as large to start. I would set the LFE to 120 and see what happens. From there, I would make adjustments. Try it and see what happens.

Do you have an SPL meter?


LTD02 might be right about the port. It might be on the small side. Most of the 12's I have seen that really do the lows justice use at least 2- 4 inch ports. A 15 might need at least that much. There was a thread about this a while back and this might just be proof of the port area being too small although it models OK in WinISD. Any thoughts?


Keep cranking,

Robert
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post #4 of 24 Old 01-24-2013, 06:49 AM - Thread Starter
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Originally Posted by LTD02 View Post


the lack of power below 25hz may be a combination of your room and/or the high pass filter in your plate amp. who knows what your frequency response actually looks like.

also, at tuning, most all of the sound will be coming throuh the port, which in your case, as you note, is a little on the small side...hard for a 4" port to move the same amount of air as a 15" driver in the low frequencies. it is probably doing a little chuffing and compressing.
.

The HPF in the plate amp is supposed to be at 17.7 Hz and the resistor values are correct according to their table. I was hoping that it the filter wouldn't kick in that high. I was planning to modify to move the HPF down to 13.3Hz and move the boost to 20-24Hz but haven't changed the resistors yet. Maybe that could help my perceived issue.

I hadn't realized what you said about the sound coming through the port at tuning. I thought I was only going to have to live with port noise, not hampered output at those frequencies. The difficulty in finding 6" ports and elbows that could get me to the length of my tuning was what drove me to 4" but maybe the extra effort would be warranted. May need to look into adding a second 4" port or converting to a 6" and adding the extra length required.
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post #5 of 24 Old 01-24-2013, 07:01 AM
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Quote:
Originally Posted by fleek1116 View Post

I have a 4" dia, 12" long port which should give me about a 18Hz tune according to WinISD (I know, not enough port area, too much port noise).
Too much port noise and reduced output.
Quote:
Based on advice from I got from other threads, I used 5 lbs of polyfill to stuff the cabinet (slightly less than the 1lb/1ft^3 often cited). I tried to keep it away from the port entrance but didn't know to leave a clear path from the rear of the driver to the port. Is it possible I really screwed up the tuning of my box
Yes. Ported boxes should be lined with up to 2" of damping, not filled.
Quote:
I've run some test tones though my system and output seems to disappear when I get sub 25Hz. I realize I won't be able to 'hear' frequencies that low, but I can 'feel' the output at 30 Hz. At 25 and below, this seems to go away (even though various things around the room start to rattle.
Look at an equal loudness chart.
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Short of taking everything off the walls is there anything I can due to reduce these rattles/resonance?
No. The walls are vibrating in response to the acoustic output of the sub. Anything on them will also vibrate. The only cure is heavier/thicker walls.

Bill Fitzmaurice Loudspeaker Design

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post #6 of 24 Old 01-24-2013, 07:56 AM - Thread Starter
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Originally Posted by robertcharles View Post


I might be inclined to say that the sub might be running out of juice at the levels you want to recreate. What kind of SPL are you getting? What SPL levels did WinISD predict?

How much does the woofer move at 25 Hertz? What frequency does the driver stop moving? The tuning was calculated, was it actually measured yet?

If I was you, I would run my mains as large to start. I would set the LFE to 120 and see what happens. From there, I would make adjustments. Try it and see what happens.

Do you have an SPL meter?


LTD02 might be right about the port. It might be on the small side. Most of the 12's I have seen that really do the lows justice use at least 2- 4 inch ports. A 15 might need at least that much. There was a thread about this a while back and this might just be proof of the port area being too small although it models OK in WinISD. Any thoughts?


Keep cranking,

Robert

Not sure what SPL I'm getting. Hadn't planned on much in the way of measurement equipment at this point. Maybe I'll pick up a cheap SPL meter and see what I'm getting even if it's not the most accurate. WinISD was predicting up around 113dB SPL at 25Hz if I remember correctly (don't have the plots in front of me). That was at a full 300W and I don't think I was pushing even close to that.

Setting mains to large is equivalent to setting them to Full-Band, correct? I think the Onkyo calls it Full-Band as opposed to the Large/Small that I've seen in the past.

Indeed, the single 4" port modeled ok in WinISD aside from port velocity/noise. That was the major compromise in my design since required one readily available 4" port kit. The alternative was creating 2-4" ports or a 1-6" with bends due to the length of my box. I was having trouble finding compatible elbows/45deg so I settled on the single port and hoped I wouldn't hear the noise. Seems the consensus is that reduced output is another symptom of this; I didn't do enough research before making this poor design decision.

The woofer is moving visibly at 25Hz. Obviously can't give you an actual deflection number but it is moving a fair amount. I never got down to a frequency where the driver stopped moving. What would that tell me if I got there? I haven't measured tuning in any way; I was going by the WinISD models.
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post #7 of 24 Old 01-24-2013, 08:08 AM - Thread Starter
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Originally Posted by Bill Fitzmaurice View Post

Too much port noise and reduced output.
Yes. Ported boxes should be lined with up to 2" of damping, not filled.

Look at an equal loudness chart.
No. The walls are vibrating in response to the acoustic output of the sub. Anything on them will also vibrate. The only cure is heavier/thicker walls.

Thanks for the input, Bill. Seems like removing the polyfill and maybe going another way for damping would be prudent.

I'll also plan on changing my port to a 6". Is there a preferred way to do an elbow? I know it will add turbulence to the air movement. Is it better to have the turn as far from the outside of the port as possible? Or put the bend the halfway down the length of the tube?

So equal loudness charts say at low levels I need an extra 5dB of SPL to perceive the same loudness at 25Hz that I do at 30Hz? Interesting to note. Maybe I don't have as big of an issue as I first thought.
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post #8 of 24 Old 01-24-2013, 08:28 AM
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Quote:
Originally Posted by fleek1116 View Post

The woofer is moving visibly at 25Hz. Obviously can't give you an actual deflection number but it is moving a fair amount. I never got down to a frequency where the driver stopped moving. What would that tell me if I got there? I haven't measured tuning in any way; I was going by the WinISD models.

If you play a tone doesn't really move the driver, that is your tuning frequency. So try doing 20, 19, 18hz until it stops moving. Then anything below your tuning frequency will cause uncontrolled movement. The hpf on the bash is perfect for that build.
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post #9 of 24 Old 01-24-2013, 09:12 AM
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Usually when people are in the position as you are they ditch the round ports in favor for a slot port. You can easily overcome port velocity with slot ports and it's cheaper as you'll usually have scraps of wood leftover that you can use for the slot port. Here's a guy who has the Dayton RS315 HF with a Bash 500 amp and built a slot port.

http://www.avsforum.com/t/1431677/slot-ported-dayton-rss315hf-1st-time-ht-build
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post #10 of 24 Old 01-24-2013, 09:44 AM
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Quote:
Originally Posted by fleek1116 View Post

So equal loudness charts say at low levels I need an extra 5dB of SPL to perceive the same loudness at 25Hz that I do at 30Hz? Interesting to note. Maybe I don't have as big of an issue as I first thought.
What's far more pertinent is that at 25Hz you need at least 10dB extra to be perceived as loud as 80Hz. 10dB represents a lot of power and a lot of excursion.

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post #11 of 24 Old 01-24-2013, 10:30 AM
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It typically takes 100db to 120db in the low 20's (and below) to be able to hear it; and that needs to be a real in-room SPL achieved at the LP.
Ported subs roll off fairly fast below their tune, so don't anticipate hearing much beyond 5hz beneath that point.
There are very few systems that can reproduce anything useful below 15hz, probably only the top 1% of systems.
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Contemplated the slot port and discounted it due to the extra construction complexity. When I came across the 6" port issues, I really should have put it back on the list. That box you linked looks quite nice.

Is it feasible to plug my round port and retrofit my box with a slot port on top (think spoiler on a car hood)? I'm imagining cutting a 2in x ?in rectangle out of the top of the box near the back edge. Then I'd build the other three side of the port toward the front of the box to give the proper volume. A slotted box plan below has small piece coming up from the port into the box. Was this likely added to give the port extra length? Or is it a normal part of the slot port to help the air enter less violently?



The first issue I can think of is not being able to roundover the edges entering the slot from inside the box, but hopefully that is a minor turbulence issue and I'll come out ahead of where I was with the 4" port. Any other glaring issues I'm missing with this approach?
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post #13 of 24 Old 01-24-2013, 11:14 AM
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Just get some 4" pvc and 90 degree elbows. At this point it is easier to double up to 2 4" ports than trying to retrofit a slot port.

You really don't need any polyfil at all in a ported sub and definitely shouldn't be stuffing it w/ 5lbs.

I would leave the HPF where it's at. Lowering it is only going to reduce its ability to protect your sub.
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Yes, that lip is to extend the port length. Here's an idea of what I did for my box. The port opening is 4" high x 10" wide and 48" long. That's just for a 10" sub!



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Just get some 4" pvc and 90 degree elbows. At this point it is easier to double up to 2 4" ports than trying to retrofit a slot port.

You really don't need any polyfil at all in a ported sub and definitely shouldn't be stuffing it w/ 5lbs.

I would leave the HPF where it's at. Lowering it is only going to reduce its ability to protect your sub.

I would have to concur with nograve but do remember that as you add another port you have to double the length of both ports to keep the same tuning.
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I would have to concur with nograve but do remember that as you add another port you have to double the length of both ports to keep the same tuning.

Yes, but re-calculate the whole thing. Box volume will go down as the ports displace more volume.
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post #17 of 24 Old 01-24-2013, 09:48 PM
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Yes, but re-calculate the whole thing. Box volume will go down as the ports displace more volume.

I would put the extra 4 inch port or 2 six inch ports, but let them hang out the box in ordeer to see if they achieve the desired effect. Then, You will have to modify the box by allowing them to stay external or build a larger encloser to account for the added port volume.



http://www.subwoofer-builder.com/vent-options.htm


Check these out!!!


Keep cranking,

Robert
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post #18 of 24 Old 01-24-2013, 09:52 PM
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Quote:
Originally Posted by fleek1116 View Post

Contemplated the slot port and discounted it due to the extra construction complexity. When I came across the 6" port issues, I really should have put it back on the list. That box you linked looks quite nice.

Is it feasible to plug my round port and retrofit my box with a slot port on top (think spoiler on a car hood)? I'm imagining cutting a 2in x ?in rectangle out of the top of the box near the back edge. Then I'd build the other three side of the port toward the front of the box to give the proper volume. A slotted box plan below has small piece coming up from the port into the box. Was this likely added to give the port extra length? Or is it a normal part of the slot port to help the air enter less violently?



The first issue I can think of is not being able to roundover the edges entering the slot from inside the box, but hopefully that is a minor turbulence issue and I'll come out ahead of where I was with the 4" port. Any other glaring issues I'm missing with this approach?

Making all kind of modifications without testing them is not the best idea. I would just use external ports to see how the tuning will effect the design and then modify to taste once the desired output is achieved- Lot less building and that way gives you many options to play with just by adding to the port on the outisde of the box

http://www.subwoofer-builder.com/vent-options.htm

You will like these ported systems.


Keep cranking,

Robert
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post #19 of 24 Old 01-25-2013, 04:45 AM
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Originally Posted by robertcharles View Post

I would put the extra 4 inch port or 2 six inch ports, but let them hang out the box in ordeer to see if they achieve the desired effect. Then, You will have to modify the box by allowing them to stay external or build a larger encloser to account for the added port volume.



http://www.subwoofer-builder.com/vent-options.htm


Check these out!!!


Keep cranking,

Robert

Experimenting with external ports is a good approach, but his 7.8cu ft net box is big enough to allow proper port area inside without starting over from scratch.

Speaking of proper port area, 26.23 sq in is what you should shoot for with the 15 HF. That means a single port 5.78" or larger will do. 2x4" ports have an area of 25.1 sq in so they are still just under the optimal size, but close enough with some flared ends. They will end up being about 26" long.
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post #20 of 24 Old 01-26-2013, 03:28 AM
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Originally Posted by nograveconcern View Post

Experimenting with external ports is a good approach, but his 7.8cu ft net box is big enough to allow proper port area inside without starting over from scratch.

Speaking of proper port area, 26.23 sq in is what you should shoot for with the 15 HF. That means a single port 5.78" or larger will do. 2x4" ports have an area of 25.1 sq in so they are still just under the optimal size, but close enough with some flared ends. They will end up being about 26" long.

Only reason I mentioned the external ports was because the designer really does not know what he is supposed to be "hearing" or feeling, so instead of just putting another port or slot in, he could easily change the tuning and then go with the one he finds most appropriate for his situation. So easy to just add a piece of PVC to the end of the tube and adjust the length externally - no driver removal or port length problems to deal with until final assembly. The slot is the best option and I was going to suggest NEO Dan's easy button design but that would require him to build a new box, so I went with the learning process of external ports to help him be able to visualize the effects of changes in the ports without all the building and tearing apart process.


Keep cranking,

Robert
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post #21 of 24 Old 01-26-2013, 11:58 AM - Thread Starter
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Thanks for all the tips guys. Robert, I like the idea of using the external ports to find my ideal tuning without altering the box much. It could be very interesting to hear the different tunings and compare the sounds. I think it is a certainty that I don't have enough port area for my driver so adding a second 4" port seems like the best plan. I need to remove the driver to finish my box and remove the stuffing anyway so it won't be a big deal.

I do have a couple clarifications about the interior locations of the ports. I've read the rule that the port needs to be at least 1 diameter away from the back wall on the box. My assumption was that this meant that the face of the port needs 4" behind for air to enter (assuming it's pointing straight at the back side). Do the sides of the port entrance also need to be 4" away from the side walls, or is this not as important as the space directly behind it?

Are there any considerations on how to place the entrances of the 2 ports relative to each other?

Would it cause any strange behavior if one port is on the front of the box and one is on a different side?

Thanks again for your help.
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post #22 of 24 Old 01-27-2013, 01:13 PM
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You don't want ports too close to the side of the box either. I wouldn't say you need 4". Maybe go with at least 2. I'm sure there are some maths for this though.

You can put the second one on the back. Or you could plug the one you have and put both on the back.
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post #23 of 24 Old 01-30-2013, 02:15 PM - Thread Starter
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Originally Posted by nograveconcern View Post

You don't want ports too close to the side of the box either. I wouldn't say you need 4". Maybe go with at least 2. I'm sure there are some maths for this though.

You can put the second one on the back. Or you could plug the one you have and put both on the back.

I was thinking of plugging the front port and putting the other 2 on top since the back of the sub sits rather near a wall. Any reason I should avoid ports on top of the box?
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post #24 of 24 Old 01-30-2013, 02:36 PM
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I was thinking of plugging the front port and putting the other 2 on top since the back of the sub sits rather near a wall. Any reason I should avoid ports on top of the box?

Little kids. Other than that, not a problem.
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