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Discussion Starter #1 (Edited)
I built a box for my SA-8. Overall I'm pretty happy with the output. I do have a couple questions that I'm hoping someone can help me with.

I didn't mount the sub in the center of the box airspace. It is a wedge shaped slot port box that fits under the rear seat of my f150. Looks like this.



What effects would offsetting the driver from center like that have?


Two calculators have my tuning at 34-35hz, but the sugar/salt test with a sweep puts me at 27-28.... I have some pretty heavy port noise at that low hz though. Its chuffing, but also making some other noise... unloading maybe? It's like a flapping/chuffing. However, doing some after-math on my box I think I botched my port area. Rule of thumb is 16in²/ft³, so I should have 11.8in².... but I have 8.5in² ... :worried: This is probably why my port noise is worse than I expected, but could it be having other effects on things?

Slot port is angled across the top, cause of the wedge. It's avg like 4.75"x1.79"x25.5".

Also, do I measure this red space in my port length measurement?






Box measures in at 0.94 ft³, minus the port which is 0.123ft³, minus the sub displacement which is .08ft³. For a total of 0.737ft³.

So my main question is did offsetting the driver from center like that lower my tuning? Even though the sugar sweep test looked like it was around 27-28hz... the actual output doesn't agree with that.. It sounds more like the best reponse is around 33-35hz...Or is my small port area messing with that?....

Lots of questions here.. thanks in advance to anyone that can help.
 

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Placement across the front won't effect tuning.
Port does seem small and is likely the cause of your chaffing.
Yes, the tail end of the port (red) counts for length.
Are you using a subsonic filter?
 

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This ^^^^^


Also...

According to: Port Length Calculator your cabinet is at 32 Hz (not including the additional red-area length, which would bring it lower still).

While (or because?) I'm no expert, I've always ended up with a somewhat lower tune than WinISD and calculators would suggest; and I've heard this from others as well. Between this seemingly common discrepancy, and the extra unmeasured red-area length of your port, your real-world tune is what I would expect.

While modeling (with WinISD, for example) would be best, here is a vent area calculator that takes amplifier power into account as well (which should be more accurate than a cabinet volume based rule of thumb): https://docs.google.com/spreadsheets/d/1VREceNxz9YOcFlI8O_TG62-4O-l3Q2IjD5qsEkVVh28/edit#gid=0

According to ^this^ calculator, you've got slightly more than half the minimum area required at 750 watts.

Also, angled/smooth corner transitions and flared vent openings (both inner and outer) help to reduce the audible chuffing effect of high vent velocities.

Also bear in mind that high vent velocities, due to less than optimal vent area, will limit output potential accordingly.
 

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Discussion Starter #4
I'm going to have to rebuild this box.

I'm using the subsonic on my amp, I played a test tone at 25hz and just increased the filter until the chuffing/slapping stopped. This seems to have negatively effected my low end above that hz as well, around 30-32hz, which is to be expected. I tried to offset this with gain but the higher 40-50hz ranges didn't like this and was obviously clipping.

I am using high level inputs from my factory B&O amp in my F150. I've measured a voltage change of 50% (!!!) coming from those wires... can't believe that shit...I'm running an SAE-600D. I can dial the voltage to 30v, and watch it sweep all the way down to 15v on a 50hz 0db test tone. Gross. I'm going to have to chop it all out and run my MS-8 after all.

Before I had a multimeter I ran the gain at 100% because I misunderstood the high level inputs. My dust cap got fairly hot, and I could smell the wood glue coming from the box (It had just cured the day before). In one particular instance where I was trying to find the limits of this lil guy, I smelt something a little nastier, for about 10 seconds. The smell came quick and I backed her off right away, then came to my senses and turned down the gain. Could it have been easier to get some coil smell on break in? First time the glue's been heated? Or do you guys think I did damage? The sub still plays 100% from what I can tell.

The 25.5" measurement of my port length includes the red area.

Sucks to have to rebuild this thing, It was a bitch to shim the sub mounting surface on an angle so that the top would fit on. Had to sand a small recess into the top as well to allow clearance for the magnet. I kinda expected to have to do a revised version of the box, but not for this reason. I wonder what I read that made me botch the port area so bad :( .
 

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Discussion Starter #5
Thanks for that calculator Grinder. Using that, and a 33hz tune, I was able to redesign my port for 18.5in² in a way that will still fit the space I have by extending it as shown in the photo.



33hz should be a good compromise for this little SA-8 if I'd like a little more low end hey? With that big port area I should be safe at that hz?

Any problems with a "slot" port being shaped like this?

 

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AlltheWayne, I do not like slot ports as much anymore ever since I tried my first Precision Port from Parts Express. They’re easy to tune and better for sound quality in my opinion. I changed my SA-12 from a slot port design to a precision flared round port design and also did the same for my Alpine SWS 10 in my van, and like them better. They also seemed to have a slight edge in SPL too.

Just some food for thought as you figure this out. At least your port is straight so I think that helps. I also still have my SD3 10 in a box very similar to yours and like that one so it’s all subjective I guess.
 

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Discussion Starter #7 (Edited)
Nevermind... with that added port area I'd need a 56" port. Back to the drawing board... To keep my net volume I guess I'll have to bend the port after all... although I might just stick it outside the box though, seems like it'll be a lot easier and it's under my seat anyways so...
 

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Discussion Starter #8
AlltheWayne, I do not like slot ports as much anymore ever since I tried my first Precision Port from Parts Express. They’re easy to tune and better for sound quality in my opinion. I changed my SA-12 from a slot port design to a precision flared round port design and also did the same for my Alpine SWS 10 in my van, and like them better. They also seemed to have a slight edge in SPL too.

Just some food for thought as you figure this out. At least your port is straight so I think that helps. I also still have my SD3 10 in a box very similar to yours and like that one so it’s all subjective I guess.
Using a 4" port? So an area of 12.5in² ? Is that going to cut it? If so I might try and retrofit a tube into my current box.. although it will be a bit of a challenge. Any of the good aero ports with their large flares is going to be tough.
 

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Using a 4" port? So an area of 12.5in² ? Is that going to cut it? If so I might try and retrofit a tube into my current box.. although it will be a bit of a challenge. Any of the good aero ports with their large flares is going to be tough.
There would be a VAST reduction in port noise (partly due to the increased area, but mostly due to the inner and outer flares), and a significant improvement in output potential

If you do go this route, you're gonna need at least one extra tube and a couple connecting rings (to extend the port past 17"): https://www.parts-express.com/cat/speaker-port-tubes/320?N=19865+4294967118+4294963591&Ne=10166&Nrs=collection()/record[endeca:matches(.,"P_PortalID","1")+and+endeca:matches(.,"P_Searchable","1")]&PortalID=1

Also, be sure to use this port length calculator (as flared ports need to be a bit longer than non-flared ports, to account for the wider flared area):
Products Menu
 

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Discussion Starter #10
That would be a VAST improvement in terms of port noise - partly due to the increased area, but mostly due to the inner and outer flares.

If you do go this route, you're gonna need at least one extra tube and a couple connecting rings (to extend past 17"): https://www.parts-express.com/cat/speaker-port-tubes/320?N=19865+4294967118+4294963591&Ne=10166&Nrs=collection()/record[endeca:matches(.,"P_PortalID","1")+and+endeca:matches(.,"P_Searchable","1")]&PortalID=1

Also, be sure to use this port length calculator (as flared ports need to be a bit longer than non-flared ports, to account for the wider flared area):
Products Menu
So with that calc I use the gross box volume minus sub displacement, not accounting for what the port will take up, seeing as I don't know the length until I enter the values, or is it net?
 

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Allthewayne, I use a 3” diameter precision port for my 10” subwoofer and a 4” diameter precision port for my SA-12 and have no port noise in either setup. I would think a 3” precision port would be more than enough for that SA-8. The kit comes with instructions on how to calculate the port length and if I can find the time, I may be able to use Bassbox Pro to model it for you.

I would go with the largest port you can fit. Use this calculator to help you figure out the length you need based on the diameter you choose. Products Menu
 

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I went ahead and modeled the SA-8v3 D2 in WinISD, at 0.737 ft.^3, 35 Hz, 600 watts (as per your SAE-600D).

Bearing in mind that this thread is in the SPL Forum, I'm under the impression that this is primarily an SPL application. And based on my admittedly non-expert impression of WinISD response curve results for this driver (along with Sundown's own words), this appears to be an SPL driver.

If maximum SPL is what you're after, you're going need at least 20 in.^2 (for vent velocity of 22 m/s or less). If you're primarily concerned with eliminating chuffing, a 4" Precision Port should do the trick (at just over 34 m/s). However, I do not a recommend 3" vent, which pushes WinISD velocity results up to nearly 62 m/s, which would (reportedly) seriously reduce output potential ...if not produce some level of chuffing as well (I suspect that it would, but really don't know).

FWIW, I've run a WinISD calculated 42 m/s in Precision Ports, with zero noise (though I'm far more concerned with SQ than SPL).


Response/SPL:


Corresponding 4"/12.57 in.^2 vent velocity:
 

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Discussion Starter #16 (Edited)
I went ahead and modeled the SA-8v3 D2 in WinISD, at 0.737 ft.^3, 35 Hz, 600 watts (as per your SAE-600D).

Bearing in mind that this thread is in the SPL Forum, I'm under the impression that this is primarily an SPL application. And based on my admittedly non-expert impression of WinISD response curve results for this driver (along with Sundown's own words), this appears to be an SPL driver.

If maximum SPL is what you're after, you're going need at least 20 in.^2 (for vent velocity of 22 m/s or less). If you're primarily concerned with eliminating chuffing, a 4" Precision Port should do the trick (at just over 34 m/s). However, I do not a recommend 3" vent, which pushes WinISD velocity results up to nearly 62 m/s, which would (reportedly) seriously reduce output potential ...if not produce some level of chuffing as well (I suspect that it would, but really don't know).

FWIW, I've run a WinISD calculated 42 m/s in Precision Ports, with zero noise (though I'm far more concerned with SQ than SPL).


Response/SPL:


Corresponding 4"/12.57 in.^2 vent velocity:
Yes, thanks a bunch for this Grinder, much appreciated. I need to figure out how to use winisd.

Would you mind running that again at .7 ft³ and 33hz? I can stick 21.5" of port inside my box, so that knocks it down to .7ft³ even. However, I will probably just use pipe from the hardware store and flare myself because I can't fit the Precision port flare inside my box anyways. That being said, should I follow the recommendation above to use the calc from the precision port website to calculate port length? Because if that's the case I get a 42.5" port length..

Am I risking some port noise by tuning lower with the 4 inch port?

Sorry for all the questions...
 

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Yes, thanks a bunch for this Grinder, much appreciated. I need to figure out how to use winisd.

Would you mind running that again at .7 ft³ and 33hz? I can stick 21.5" of port inside my box, so that knocks it down to .7ft³ even. However, I will probably just use pipe from the hardware store and flare myself because I can't fit the Precision port flare inside my box anyways. That being said, should I follow the recommendation above to use the calc from the precision port website to calculate port length? Because if that's the case I get a 42.5" port length..

Am I risking some port noise by tuning lower with the 4 inch port?

Sorry for all the questions...
You cannot use the precision port calculator for regular round ports; it wont be the same. Attached is a file from Bassbox Pro showning .7 @ 35 Hz and .737 @ 35 Hz. The program suggests .244 at 40 Hz for High fidelity and same size at 31.52 for higher output down lower.

The red line is the .7 box.
 

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Discussion Starter #18 (Edited)
You cannot use the precision port calculator for regular round ports; it wont be the same. Attached is a file from Bassbox Pro showning .7 @ 35 Hz and .737 @ 35 Hz. The program suggests .244 at 40 Hz for High fidelity and same size at 31.52 for higher output down lower.
Sorry .244, that's Port Volume?

I would put 1" flares on the port.
 

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Sorry .244, that's Port Volume?

I would put 1" flares on the port.
That is the box volume noted as Vb of .244 cu ft. Attached is a 31.5 tune and 40.5 tune. Note: none of these are actually buildable without installing a lot of the vent outside the box because a 4" vent requires a very long port. If you give me all the external sizes of your box than I can model it better and even give you cut sizes to build a new one but its a little bit of work.
 

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Discussion Starter #20
That is the box volume noted as Vb of .244 cu ft. Attached is a 31.5 tune and 40.5 tune. Note: none of these are actually buildable without installing a lot of the vent outside the box because a 4" vent requires a very long port. If you give me all the external sizes of your box than I can model it better and even give you cut sizes to build a new one but its a little bit of work.
Seriously?! .244 ?! That's like a third of my current box and seems very very small. Sundown themselves recommend .5-.75? Why so small?
 
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