if your space for enclosure is very limited, then I would go with fiberglass as the material of choice since you will be able to use that avaliable space more efficiently.
One 8" driver in sealed enclosure will have quite low output, Ill rather decide to go ported in your case..... or ported downfiring since you have soft top.....

 

Short answer, for sealed enclosures - strange shape is better then no shape, makes little difference. Just so long as its not like two chambers connected by a small passage.

Being a little smaller then recommended, again better then nothing and doesn't make it unuseable, can compensate a little with stuffing.

As for clearence behind the sub, depends on the sub. Some will need clearence for the pole vent, other subs dont have a pole vent.

More importantly what car? What/where is the factory sub, is getting one of those an option and then upgrading the driver?

 

Without Cabin Gain you need to maximize cone area and box gain - this ends up being ported or bandpass in 99.9965% of the drivers you can find.

The 6 and 3/4" driver you are considering does not meet any of that and unless you run it ported won't even be audible at anything other than idling. Maximum output at xmax in 5 Liters 105dB at 100Hz and -12dB/Octave below that... you can extend that to about 45Hz by running at 20 Liters Ported at 45Hz but all of this is rudimentary to trying to have something be audible in a soft top while in motion.

Maximum output at xmax for:
Red = 20L Ported at 45Hz @ 100 Watts
Yellow = 5L Sealed @ 125 Watts
Green = 20L Sealed @ 75 Watts

 

There are a lot of beefy 6.5's out there that would perform better.

This sub in the classifieds is a steal and models very well. Buy it before I do because I'm trying not to have gear laying around. 🙃

https://www.diymobileaudio.com/threads/db-euphoria-ewx6-neo-sub.466048/

 

Thanks - I am interested in that EWX6NEO but first I would like to model it in WinISD. Looking at the Euphoria website and the user manual it doesn't seem to have a full set of parameters, for example no xmax? Any ideas where I could find those?

Thanks, Andy

 

Wow - thanks for all of the detailed information! Much appreciated!

When driving at 50MPH the noise level is 65dB.

I'm struggling to find a 5L space so 20L is definitely out.

Sorry if this is a stupid question, but at 5L sealed, 125W, the entire range 45Hz to 200Hz is above 90dB. That wouldn't work very well with an ambient noise of 65dB?

Thanks, Andy

 

"Threshold of Audibility at Frequency"

When you measure noise level in motion the area where the human ear is the most sensitive overwhelms the ability of the human anatomy to transmit bass frequencies so you are looking at using a driver that has descending output that is inversely proportional to our sensitivity...

Introducing the Fletcher Munson Curves:

So at 45Hz, the threshold of audibility is around 50dB but if you run sealed your output at MAXIMUM is 92dB which means that your follow the curve above that matches 45Hz at 92dB and you get 70dB at 1500Hz which is only +5dB over your ambient noise level at MAXIMUM output. So you would be able to hear it but only just...

What vehicle are you working with?

FWIW - Miata, S2000 and other roadsters generally benefit the most from Tactile Transducers mounted to the seat pan and seat back to give you the feeling of bass without having a Subwoofer.

 

Thanks! I think what you have shown with WinISD and the chart is enough for me to fiddle around with it and understand better what will work for my situation. Much appreciated. Andy

 

I've been working on this, playing around with WinISD. I wondered - why did you choose a tuning frequency of 45Hz? The Fs of the speaker is 64.5Hz so I thought it would be tuned for 65Hz, but clearly I am wrong on that, not sure why.

Thanks!

Andy

 

Subwoofers are the only driver we commonly use below Fs and we tune the enclosure to try and work out the maximum transfer function with a flat or a flat as possible output. Tuning ported to Fs simply maximizes power handling by reducing excursion the most where the driver reaches xmax the easiest. This flattens the impedance curve the most and makes the driver the easiest to power but does not necessarily give you the flattest output due to other variables like Vas and Cms.

 

Another question - probably a stupid one. If rock music typically goes down to 60Hz, isn't the important volume level going to be 60Hz and up? For example in your WinISD screenshot at 60Hz the yellow line is 98dB. If I look up 60Hz/98dB on the Fletcher-Munson chart it shows 80dB at 1.5kHz. That would be 10dB above my ambient noise level at 50MPH, right?

Thanks, Andy

 

Not sure where you got 60Hz from...

Low E on a standard electric guitar is 83Hz and on a 4 String Bass is 41.5Hz (5 string Low B is 28-30Hz) and Kick standards for rock are generally Low D (36.7Hz) but each artist has their own preference. Then with this information we look at subharmonics which generally start at ½ the fundamental and it's not uncommon for that information to be in the 20s...

Dedicated subwoofers, for the most part, concentrate on 80Hz down because most automotive environments have no problem reaching 80Hz with 6½" door speakers. BMW is a common problem child for bass due to their insipid use of 4" drivers and one of the few candidates where 6½" subs make sense. Is there a reason you're unwilling to divulge the make and model you are working on?

 

Attached are the plots from LSA, the Sundown plays lower. I'd imagine it would get louder as well, but LSA doesn't provide that info or a way to compare 2 designs.

sundown in .3 cu.ft. ported (recommended .25 - .35) F3 24.2

sundown in .25 (plays flatter) to F3 of 31.6

euphoria in .42 ported, F3 25.9

 

Thanks!

 

Thanks for the responses - I appreciate that!

I am hesitant to give the make/model because I have tried that on a vehicle-specific forum and it derailed the discussion into "why don't you put this off-the-shelf unit X in location Y?" and so on, but I have reasons for not wanting to use each location that people suggest and I don't really want to rehash that again. Another issue is that I say a space is occupied with something else and people just ignore that and suggest it anyway. Or they suggest something 2" too large in one dimension that would never work, etc. I'm not saying you @daloudin would do any of that - I'm sure you wouldn't - but someone might. Instead after a lot of consideration I have found an awkward space where I do want to put it, so I am custom designing a box to fit that space. Maybe it will work out, maybe it won't but I am going to give it a try and see.

I hope that helps explain.

Andy

 

That is perfectly fine. The only caveat to that is there are a number of experienced builders here that may have a suggestion you have not heard yet but if you are determined to build a specific enclosure to fit a specific space then that's perfectly fine.

My only suggestion is to go ahead and build the enclosure with a much space as possible and make the mounting baffle as wide as possible and then come back here with the gross volume for the airspace, the baffle width and mounting depth. We may be able to find a driver that works better than the one you are considering.

 

Add the B2 Audio to your comparison:

HN series, the multiple master for the elite & world champions

HN series, the master of all. Pro audio, SQ & SPL equals 100% B2Loud. The choice of the world champions, but with the availability to all.

www.b2audio.com

 

From what I can see, for the same vented box size, same port size, same signal power, same everything as the Sundown U-65SW, the B2 gives 3dB more performance with the same cone excursion and same port air velocity.

Andy

 

It seems my two best options are the B2 and MISCO. Here are some screenshots. I am going to use an external vent so I don't have to try and fold it into my limited volume. However here is where there is a big difference between these two drivers.

B2 = 93.61cm vent
MISCO = 27.31cm vent

Obviously the MISCO is going to be significantly easier for me to implement and I have the option of increasing the diameter to reduce air velocity further. The B2 is going to be a pain. This is for a flared port keeping the peak air velocity below 36m/s.

The tradeoff is that the MISCO has a much faster drop off below 90Hz and I am unsure if that is worth the tradeoff with the vent length. Any thoughts are welcome!

I had thought about a passive resonator but I am not sure I can squeeze one in because the box will be stuffed into a corner. It would have to be very small and at right-angles to the driver.

Thanks, Andy

 

Yeah the B2 looks much better. Misco needs more airspace and you made sure to allow for the 8 ohm voice coil in your wattage input?

If you went with the B2 do you have any options to increase wattage? Push them both to xmax in the excursion tab and see what the SPL difference is...

 

either the parameters are completely different, or the alignment is completely different., hence two very different response curves. Even then, working with 1 to 3ft long ports seems futile in this case. just go sealed. 5L is just too small anyways. Unless you do passive radiators. Then you don't need to worry about port length, and can really kick up the power near tuning to have the PRs give a lot of output assuming the driver has a beefy voice coil to handle it (the reduced driver cone movement will have a low impedance thus lots of power will be going through). I don't think I saw it, but what are the absolute maximum dimensions you would be able to use?

 

working with 1 to 3ft long ports seems futile in this case. just go sealed. 5L is just too small anyways.

Thanks for your reply. Sorry, I am a bit confused. Does that mean WinISD is not giving me valid results that I can rely on? Andy

 

B2 vented 45Hz (red), sealed (green) and PR (blue) for 300W, same box size. Seems like even with a 55.41cm vent that it still the best option?

However if I add 20g of mass to the PR I can improve it's performance down to 40Hz at the expense of a small amount of performance in the 50Hz to 80Hz range.

Andy

 

Red is the classic SQ ported curve and what I would aim for since you don't have any cabin gain.

 

Subs are usually crossed over anywhere from 60-100Hz, so don't worry too much about 90Hz, and you will get some cabin gain for the lower frequencies.

You can apply filters in REW to get get rid of the high frequencies, simulate cabin gain, and a subsonic to control your xmax at lower frequencies. It will give you an idea on how the sub will perform in your car. I've seen the cabin gain filter done different ways, so I'm not sure which is the most accurate, but you could copy my settings for something close enough.

The green is my subs, red is with filters:

 

No cabin gain - "soft top"

 

These are getting into the micro subs that I've built for desktop 2.1 systems with wideband satellites:

Epique 5.5" Subwoofer

PE has a minimum order quantity of 50 for these but if you can find a single somewhere...
Tang Band W6

They still carry the Tang Band W5 in Singles though...

Low Profile:
Dayton LW150-4

Then you get into 6.5" Subs made for Harley Baggers:
Euphoria 6.5 Neo Subwoofer

Or PA Hot Spot Woofers that have low Fs:
Galaxy Audio NeoLite SW6.5

 

Ok so we're talking about different things. What you mention I would call impedance-transformation. Port compression I mention are specifically A) dB losses and B) shifts in tuning frequency (due to non-ideal non-laminar flow conditions). By that virtue I consider them 'never a good thing'.

 

Not sure where you get that but I think we can agree that if the port causes output losses or shifts in tuning frequency that would be a bad thing but laminar flow has nothing to do with port resistance and the amount that port resistance does affect the output is extremely small in comparison with the problems associated with audible artifacts like chuffing or turbulence at the port exit.

Check out the bottom of page 183 in the Thiele excerpt for the calculations pertaining to port resistance and then page 96 from Dickason about Transmission Line theory and folding or bending the path of an acoustic labyrinth design.

 

Here is where I am at. I have made a box that will fit into the intended space, unfortunately it ended up at 2.4L, smaller than I hoped for.

Here are some charts (no filtering) for the MISCO BWX-6501. I am now at the point where I have to decide if this is going to be worth spending money on as so far my investment in this experiment is $0.

Pink = 85W RMS
Green = 170W max

At 60Hz it is 97dB (170W) and 94dB (85W).

As I mentioned before, I am not looking for high-end amazing sound, just "some" improvement in the bass to make the music a bit more enjoyable. I know there are limitations with a soft top.

Any thoughts on if this is worthwhile for my application?

Thanks!

 

So the prediction by WinISD for SPL can only be trusted if you have previously verified the same driver in a previous modeling situation.

Most of the time it's pretty close but you are right in the middle of where the way our ears and brain work you start to really notice changes in bass volume. How much this will contribute and how accurate this prediction is all depends on the ambient noise level and what volume you listen at on average. You are likely to get some additional gain from boundary loading in the corner but the only way to find out is to proceed.

Whether you proceed or not and the financial outlay required is something that only you can decide.

Sorry, that's probably not much help but maybe it helps clear up any questions you have about the accuracy of the model.