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3 4" Aeroports with only one causing strong resonance at certain frequencies when played very loud


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So the thing to understand about ports is they are either big enough to do the job, or they aren't.  If a port is big enough, going to an even bigger port doesn't really change anything, it just takes up more box volume, but its not going to sound any different.  How an enclosure sounds has a LOT more to do with the net volume and tuning frequency than the port size, as long as the port is big enough (this means having enough port area to avoid port noise and compression).  

Think about it this way, the port on an enclosure is like the intake manifold on an engine.  If the manifold isn't capable of sufficient airflow, it's going to rob you of horse power at full throttle, but at lower throttle it probably won't matter.  If you put a higher flow manifold on so you get max power at full throttle, now everything is great.  If you go to an even higher flow manifold, you don't gain anything since its no longer the intake thats limiting your power, and your previous one was already big enough, but that even bigger intake doesn't hurt anything either, you just have more capacity than you can use.  

 

Having a port that is too big is actually pretty hard to do, I'm not saying it can't happen, but it has to be really REALLY oversized before it will cause performance problems.  Having a port bigger than you need does take up more space though, and space is usually at a premium in car audio we want to size our ports appropriately for what the situation requires.  

In your case two 6" aero ports will work well for the power you are running.  Alternatively, a 65 sq in slot port would work well too.  

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"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

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Ok cool, sounds good. I get what you mean. Im definitely going to build the same box with 2 x 6" Aeroports at least for the type r's and I get what your saying about the net volume and tuning, so that will all remain the same so the way the bass sounds and feels will also remain the same only with ALOT less resonance and annoying sounds. Thanks heaps for your help!

Just curious what is the perfect size and amount of Aeroports to have in the same size/shape box for 2 x Alpine Type X 12's running off 2 x Alpine MRD-M1005 Amps? Im guessing that it would be 2 x 6" but just need to clarify. Or would my current box be more suited for them?

The gains will be set high, one or two notches back from clipping and Alpine's "Subwoofer System 2" will be set to "On", always. And a medium amount of Bass Boost will be used just to a safe level without distortion or clipping. Not sure if you need to know that bit but basically I will be attempting to power the subs as hard as I possibly can without distortion or clipping with those two amps and I will never change those gains, ever. It will always be set that way from the day I put them in.

Cheers mate!

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Ive heard that you can only just get the Type X subs as loud as the Type R subs, even though they have twice the amount of power going to them I guess that is because they are SQ subs and are more quiet than you would think but still will get very loud. Im still going to make the 2 x 6" Aero box for my type r's just curious if the type x subs move a similar amount of air as the type r subs and would work best with 2 x 6" Aeros. Ahh I get it now, just then while I was typing lol, so 2 x 6" isnt going to be like WAY too much for the type x's because they are so similar in air movement, as in there would be no point restricting the subs to 3 x 4" aeros cos 2 x 6" will be fine for them even its a tad over and then my new box is more versatile with letting me put other subs in it if i ever decided i actually wanted to do that. Its just the point isnt it, why go back to the 3 x 4" like ever if it wouldnt ever need to use it again.

So its a new box with 2 x 6" Aeroports for both types of Alpine subs!

So it turns out my box is actually 4.5 cu ft now since I put the shorter Aeroports in (35.6Hz), originally was 31.6Hz, so at my current tuning and box size Im really happy with the sound and decided to make the new box the same size and tuning because of this, but just reading up now on forums on box size for type x subs people are saying 2-2.2 cu ft per sub max and not too go any bigger or it will sound sloppy, they say 2-2.2 but aim for 2 cu ft. Whats your thoughts on this? Is my box a little bit too large at 4.5 cubes for the type x or would my higher tuning make that not an issue at all, which is what im kinda thinking, those guys were all talking about 28-30hz tuning. Because my reason for tuning higher is also so i still get the more normally heard bass freqs not cut out like at 32Hz, I cant stand them being cut out. But anything to still give me those deep lows at a higher tuning is very good. Because if I have to make a separate box at 4.3 cu ft for the type x's i will but would prefer to use my design for 4.5 cu ft.

 

Btw, I use the12volt.com for box volume calculator, PSP calculator for multiple port lengths, this JL website for round port displacement: https://jlaudio.zendesk.com/hc/en-us/articles/224938887-Calculating-Enclosure-Volume-. I know from the manual that sub displacement is 0.071 for the type r swr 1242D and i just say 0.061 cos of my 18mm and 16mm baffles, im not sure how to work that one out so i just guess. I dont think the err amount would affect much. Original box size: 34.05"(w)x18.66"(h)x17.04"(d) (4.54414 cu. ft. after all disp. - 3 x 13.04" Aeroports (minus flare length), new box size: 34.4"x18.64"x18.04" (4.56957 cu. ft. after all disp. 2 x 18.42" Aeroports (minus flare length)). I would use WINisd but i can never work out how to enter the parameters properly, i think there are files i can just import or something that fills that area in so then i can do box design properly and know velocities and stuff, but because i couldnt get past that bit i had to just give up, i kinda knew what sort of box size i needed and stuff so i just did it like that. Can you help me in that area please? How do I use WINisd, properly? Dont worry if its too hard to explain.

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Oh, the only thing I cant work out for winISD is the first bit when it asks for driver info, I cant seem to enter in the parameters manually correctly, it always comes up wrong, is there a good video to explain or where do I get the files for common subs like Alpine SWR-1242D for winISD? Mainly just want to know what you reckon about my new box for the type x's? A bit too big? or nah should be fine with that tuning?

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Ok so I thought I had better update this news, there is no more resonance from any of the ports, at any volumes. Im a little embarrassed to inform that I accidently had the remote wire connected to the PWR ANTENNA Blue wire at the back of the Head Unit for one of the Mono Amps, I normally would never do anything like this because Im so careful with wiring and I always thought that there was only one blue wire behind the Head Unit that was the remote wire, as I had a Blue extension wire coming from the short Blue and Yellow Remote wire which I had one amp attached to and then another amp tapped to that blue wire further along, so I thought I was just splicing onto that first amp but instead the second Mono amp was only coming on when Radio was selected, of course I was always tested loud play with USB mode selected, which is when resonance occurred.

I was troubleshooting a screen problem on the amp at the time I was talking on here as I thought it was just the screen and the amp was still running as there was ALOT of excursion coming from the non-powered sub, but yeah a fair bit less than the powered sub, I kinda thought this was just because of the massive ports behind only that sub. Another reason as when selecting different LPF and subsonic toggles I was POSITIVE I heard a change from the affected sub, so I assumed it was just the screen going out occasionally and kept going with it. It actually sounded not too bad, more muddy but very similar to the working twin subs. Very Deep and Low.

So yeah, I eventually worked it out and the amp is going all the now and wow tidied up the sound really nicely, not quite as Low (well the lows are better and probably as deep but just sounds different, hard to explain) at tuning but better sound, and best yet no resonance at all out of any of the ports. Very happy with it, I hear a very small amount of port noise but yeah not chuffing or really can pick up on anything sound wise. Like you said should be nothing drastic, just a little bit, just like you said. Thank you heaps for all of your help mate. Im not needing to build the 2 x 6" port box now so I wont bother as Im quite happy with the sound Im getting out of my current box and would guess basically no change to performance or sound by rebuilding.

Im thinking of dropping tuning a bit to say 34-34.5hz but I get the feeling Ive got it about as low as Im going to get it with tuning to my liking, maybe not much frequencies will drop off at 34.5-35Hz but lows will obviously improve. I will try 32Hz and go up from there, but I doubt that I will like 32??

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I'm glad to hear you found the problem.  

As far as WinISD goes, its very particular about how you enter in the speaker parameters, here is the "right" way to do it.  

 
1. Enter Mms and Cms
 
This gives fs. If either is not available, then enter fs and other parameter.
 
2. Enter Sd, Bl and Re
 
Now, you should get all but Qms (and Qts), Vas. Please note that Vas may not match exactly what is specified by manufacturer, because exact value of Vas depends on environmental parameters. See FAQ.
 
3. Enter Rms or Qms.
 
Either one will do, although I tend to prefer Qms over Rms, because it can usually be measured in driver measurement procedures.
 
4. Enter Hc, Hg and Pe.
 
If Hc or Hg or either is available, then enter Xmax and optionally either Hc or Hg if available.
 
5. Enter number of voicecoils.
 
This procedure is most accurate. Also note that it also calculates true SPL (1W/1m) value. So it might not match the marketing SPL value, which is generally somewhat vague. Not in all cases, though.
 
6. Correct Znom, if necessary.
 
If there are several voicecoils, then you must be careful when entering parameters in that case, because many manufacturers give Bl in voice coils in series, because it yields double value for Bl against parallel connection. If driver manufacturer gives Qes, Bl and Cms or Mms, then you can check how Bl is specified. For that, you can enter following parameters to calculate Re: Qes, Fs, Mms or Cms and Bl. Connection mode can be changed by changing the combobox selection. The driver editor then converts Bl and Re values accordingly.
 
Equivalently, you can check for Bl by entering:
 
Qes, Fs, Mms or Cms and Re (for desired connection mode).
 
If you enter resistance for parallel connection and get about half of advertised Bl, then you know, that Bl was specified that way.
 
Like in Driver-tab in project window, you'll probably noticed the driver icon in bottom of the driver editor window. you can drag the driver object into some project by just dragging the icon.

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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OMG thank you so much for that Triticum, wow now I can finally use winISD. Gonna be able to build some nice boxes now. Thanks again.

 

 

 

@ 1point21 yeah Big Ass Ports have some nice gear, unfortunately no international shipping. The only Aeroports you can get over here in Australia is ones you make yourself from PVC pipes. I reckon Im gonna build that box with 2 x 6" Aeroports, stuff it, just to make it correct, but it will cost me over $220 to build so Im kinda putting it off for a while. Need cash at the moment.

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  • 2 weeks later...
Posted (edited)

ok so just to clarify, the port length I was thinking was about 35.6hz was actually 33.8hz cos i didnt minus the sub disp. for some unknown reason (musta been really late) when i did that calculation. So i reckon I will prefer 33hz if too many freqs dont drop off to my liking. Im gonna try for 30hz and just keep fine tuning upwards from there. Hopefully 30hz is to my liking, definitely need to get it a bit lower if i can. 33.8 sounds pretty damn nice though, just needs to be a bit lower.

Edited by DAN831111
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  • 4 months later...

Ok so I have got the 2 x Type X 12's in that same box now, running off 2 single Alpine MRD-M1005 amps, got a question, box is about 5 cubes after displacements and I find the sound on the type x seems a tad off to me, not too bad however. Its tuned to 33hz currently and that is perfect tuning for me but curious is 2.5 cubes per type x 12 a little bit too big, like do i need to make another box at about 4.4 cubes or something for better sq?

The just sound a tad muddy, like much better sq than the type r's but a little bit more muddy. weird?

Both type x subs are brand new btw, they are the older type, they had just been sitting in somebody's garage. I did break them in for quite a few hours over a couple of days before putting much volume to them, just to soften them up after sitting for so many years. Do they just need to break in a bit more for better sound?

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