Fiberglass Sub Box Help Needed - now solved and digressed

[Mainah]

I have decided to build sealed sub boxes between the inner and outer hull out of fiberglass as I can't find a way to fit a box in there. My access is from the speaker hole. I have closed cell foam stuffed all around to make the crude shape and am going to use spray foam (shaped after curing) to seal it up better prior to fiberglassing as something to press the fiberglass against. I will have to laminate multiple layers of fiberglass to about 1/4 inch thick and it won't be seen so it does not need to be pretty. I will also be mounting MLV on top of the fiberglass inside the box for a richer sound given the fiberglass box.. It just needs to stand up to the stress and air pressure of the sealed subwoofer.

My question comes in on materials. Would chopped strand or woven work better in this application? if chopped strand should I go with the thicker stuff to build up faster or will that be too hard to work with on tight angles/radius in a tight space. What kind/brand of resin will work best?

I have only done a couple of projects with carbon fiber or fiberglass but this presents its own challenges and I don't have enough experience to know what is best in this application.

-Edit My plan is to prepreg each sheet in a baking pan with a rubber roller so medium to long cure time will be best unless that plan has a hole I don't see.

 

[Adrian @ JB Solutions]

I am curious what the baking pan is for? I have always used chopped strand and then poured resin in small containers, and then poured hardener into each one as I went to use it.

 

[Mainah]

Given the tight spot I will be working in I figure pre impregnating the chop mat will make things easier. So pour some mixed resin and hardener in the pan, lay the chop mat in it, and roll with a rubber roller until fully saturated. This will break down the chop binder and make the chop mat easier to press/roll into the tight area. This is a common method for carbon fiber when when vacuum bagging is not an option. I am not an expert but figure thick chop mat with this method will make my job easier and less likely for air bubbles in the tight area. That said I have never seen this method used for fiberglass but don't see why it will not work.

 

[Adrian @ JB Solutions]

Never heard of it either - have you checked out the fiberglass forums? I haven't been on in years, but I learned a ton over there.

 

[Mainah]

Guess I should have done more searching first. Prepreg fiberglass is used in aerospace applications and certain structural points of boats because the cloth gets fully saturated but there is one key difference from carbon fiber. The you must use a foil backer so the fiberglass cloth does not tear apart. That will make my job harder. Guess I will go with the common hand layup using chopped strand. Three layers of thick chopped strand mat should work for what I am doing.

Anyone have preferences on resin?

 

[swatski]

Anyone have preferences on resin?

Epoxy is considered more versatile, stronger, fewer fumes, shrinks less etc..
And - I hate it.
Me - I would go poly (ester) - for this application for sure.
But that's just me. Make sure what you get if reasonably fresh, especially for poly.

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[jcyamaharider]

I have always wanted to try this but have never the patience to do so. Good luck and I will be keeping close tabs on this!

 

[Mainah]

Epoxy is considered more versatile, stronger, fewer fumes, shrinks less etc..
And - I hate it.
Me - I would go poly (ester) - for this application for sure.
But that's just me. Make sure what you get if reasonably fresh, especially for poly.

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The way you typed (ester) triggered something for me. I can't use that because it will eat the foam. Guess at least a gallon of epoxy and hardener are in order. Not looking forward to doing the project and hopefully the results are worth the effort. Wish I had taken test tone mic feedback sweep readings in the low frequency range before tearing the speakers out for a scientific comparison. There is no doubt that volume matched sealed boxes will sound better for the subs I have but the question is how much better.

When I put it all back together I will tune everything with an oscilloscope. I am going to test the head unit RCA and speaker levels with usb, aux, and bluetooth to find the best source and volume level for both the input device and the head unit across multiple frequencies. After I get that straight I will move on to the amps. I only did this with my amps before but having some hard data behind the head unit will help me decide if I need a WS mixer or even a different head unit not to mention definitive readings on how much source impacts the performance.

 

[jcyamaharider]

The way you typed (ester) triggered something for me. I can't use that because it will eat the foam. Guess at least a gallon of epoxy and hardener are in order. Not looking forward to doing the project and hopefully the results are worth the effort. Wish I had taken test tone mic feedback sweep readings in the low frequency range before tearing the speakers out for a scientific comparison. There is no doubt that volume matched sealed boxes will sound better for the subs I have but the question is how much better.

When I put it all back together I will tune everything with an oscilloscope. I am going to test the head unit RCA and speaker levels with usb, aux, and bluetooth to find the best source and volume level for both the input device and the head unit across multiple frequencies. After I get that straight I will move on to the amps. I only did this with my amps before but having some hard data behind the head unit will help me decide if I need a WS mixer or even a different head unit not to mention definitive readings on how much source impacts the performance.

What I suspect you will find, mainly because I have already tested it, this head units are actually good. They do not clip until about 95%

 

[Mainah]

What I suspect you will find, mainly because I have already tested it, this head units are actually good. They do not clip until about 95%

What is the voltage and any visible noise with 95% gain at 40 hz, 160 hz, 630 hz, 1khz, 2.5 khz, and 10khz. Also what source and source db level? Ideally I want to see 3.7 volts output (best for JL M series) with a 1khz tone input at -12 db from source with a perfect sine wave on narrowband oscope scale and no visual artifacts on wideband oscope scale. I know striving for perfection but it matters once amplified. I am on the fence for purchasing a WS420 now that I know it has internal POTS to adjust input sensitivity.

 

[jcyamaharider]

What is the voltage and any visible noise with 95% gain at 40 hz, 160 hz, 630 hz, 1khz, 2.5 khz, and 10khz. Also what source and source db level? Ideally I want to see 3.7 volts output (best for JL M series) with a 1khz tone input at -12 db from source with a perfect sine wave on narrowband oscope scale and no visual artifacts on wideband oscope scale. I know stiving for perfection but it matters once amplified. I am on the fence for purchasing a WS420 now that I know it has internal POTS to adjust input sensitivity.

You are defiantly taking it farther then I did @Mainah , of course I wouldn't expect anything less from you. Lol

I interested them at 1k is and 40 Hz using my SMD DD-1.

 

[Adrian @ JB Solutions]

So what does 95% equal as far as volume level

 

[jcyamaharider]

95% equals you need ear plugs on the boat. To me the radio volume is irrelevant as long as you tune the rest of the system at that point and do not go above that point.

 

[Mainah]

I know this theead has deviated from the original topoc but for those who wonder what plant I am from I will attempt to explian.

First off I understand electronics a lot better than I understand music so I approach things from the electronics end which makes up for my shortcomings in music end. Testing for clipping is a good thing because it will prevent damage to the amp and speaker from a deformed audio signal. The amplified signal is only as good as its source. If the source is only a value of 1 and you multiply it by a fixed value of 10 based on the max amp gain setting you get 10. But when you increase that source to 4 your net result is 4x louder. The source needs to be clean or you amplify noise at the same time. All of that is in just one bandwidth or chord and each will behave differently. A smd tuner is a good tool for most folks. For those who wish to take it to the next level an oscilloscope is needed and the user needs to understand how to fully use it or it is no better than an smd tuner. There are plenty of videos of folks using an oscilloscope on youtube to tune a system and most fall short of using it to its potential.

I will take screen shots from the oscope when I do my testing and add some visuals to help illustrate where I end up. For now lets call my request for help solved and hope my execution and results are good.

 

[Adrian @ JB Solutions]

95% equals you need ear plugs on the boat. To me the radio volume is irrelevant as long as you tune the rest of the system at that point and do not go above that point.

I agree, but if 95% is a clear signal, then I would like to set my gains to that volume level. It sounds like you tested everything so this would save me a step in testing. I control my volume through my watch so 95% can be almost quiet too.

 

[Mainah]

I agree, but if 95% is a clear signal, then I would like to set my gains to that volume level. It sounds like you tested everything so this would save me a step in testing. I control my volume through my watch so 95% can be almost quiet too.

You seem very knowledgeable in this area so I assume you understand that attenuating the singnal from the root source will likley not equal the best performance. That said it is very practical from a human interface standpoint. There I go sounding like an ass from another planet again. Another planet where one drinks too much wine on a weeknight

 

[tdonoughue]

So, if we ever drift back to the original topic and if @Glassman stops by, this would be the perfect topic for him...

But I am enjoying the electronics talk (being more music than electronics, but passable at both). So, carry on.

 

[swatski]

What I suspect you will find, mainly because I have already tested it, this head units are actually good. They do not clip until about 95%

Funny you mentioned that. I was "tuning" my system over the weekend and noticed exactly that - the HU can be cranked up very high without audible distortion. That surprised me, actually.

You seem very knowledgeable in this area so I assume you understand that attenuating the singnal from the root source will likley not equal the best performance. That said it is very practical from a human interface standpoint. There I go sounding like an ass from another planet again. Another planet where one drinks too much wine on a weeknight

Well, if I understand correctly, than I would think this is where the WS420 comes in handy - I use it as a master volume control. Don't need to go through Connext screens or phone, and just use the main volume knob on WS, which is also perfect for adjusting the balance between tower and cabin speakers.

--

 

[Adrian @ JB Solutions]

You seem very knowledgeable in this area so I assume you understand that attenuating the singnal from the root source will likley not equal the best performance. That said it is very practical from a human interface standpoint. There I go sounding like an ass from another planet again. Another planet where one drinks too much wine on a weeknight

While I am not that versed in the extreme technicalities... if I set my gain to volume X from radio (not clipping) with signal coming from my phone and watch set to volume Y (not clipping), then I should be at the maximum performance for my source (which is my only source I use). However, if there was a performance loss, I do not think it would be audible, and the convenience factor gained far outweighs that.

 

[Mainah]

Funny you mentioned that. I was "tuning" my system over the weekend and noticed exactly that - the HU can be cranked up very high without audible distortion. That surprised me, actually.


Well, if I understand correctly, than I would think this is where the WS420 comes in handy - I use it as a master volume control. Don't need to go through Connext screens or phone, and just use the main volume knob on WS, which is also perfect for adjusting the balance between tower and cabin speakers.

--

Likely better but should also be tuned to find the best volume setting at the two up stream devices that equals the highest volume without clipping, distortion, or bandwith compression prior to the ws420. Then the ws420 should be tuned to output no more than 4 volts rms to most class d amps.