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View Full Version : Stereo/ subwoofer question ( not which brand is better question)



macjazzy
04-19-2010, 02:50 PM
I have 2 Sony 10 in. subs in my boat. They are mounted under the double helm seat firing forward. They have been in for 2 seasons. This weekend I was playing the stereo and one of the subs blew. Its making a terrible rattle noise when turned up.

My question is, what should I replace it with? Not brand, type.

I think I want to go with either JL audio or Alpine marine type R those seems to be pretty popular and well liked choices on the subwoofer threads.

What I am not sure about is free air or enclosed sub.

The space they are in is pretty enclosed but not air tight, I am not sure how much work I need to do to make them air tight and I dont have any idea how much volume it would be enclosed anyway.

I am not sure how important a specific air volume is for enclosed subs and I understand ported ones need a specific port size to work. But I am worried that since the area is fairly closed off a free air might not be right either.

The other thing is my amps are mono kenwwod 300watt rms, 1000 watt peak.
The JL Audio subs are rated at 250 watt rms/750 max, those are my preferred choice but I am worried about blowing them with these amps. The Alpines are rated at 300 watts rms/900 wattt max so they match up a little better.

Whe I was looking around I also noticed some subs have dual voice coils but most have single voice coils, I have no idea what this means or if I should even be worried about that.

Any help would be greatly appreciated.

fund razor
04-19-2010, 03:10 PM
Ok, for the question on box... free air.

The power question depends on the ohm load and efficiency of the speaker.

Dual voice coil have two voice coils, meaning that they will accept two speaker level inputs. Some people use these to produce independent low freqs from both left and right channels, because super low freqs are very non-directional and you are able to essentially mono sum a stereo source. I used to use one subwoofer on my boat but ran left and right to each of the dual voice coils. In your installation, with two woofers, you do not need DVC.

fund razor
04-19-2010, 03:14 PM
On the power ratings, it is important to know what the efficiency and load of the speaker is. It is also important to know that power doesn't blow speakers, noise or a square wave does. So, what will keep you from blowing speakers is clean signal and clean power.

I used to run a sound company. When I would send out big concert subwoofers I would use 18 inch McCauley subwoofers rated for maybe 800 watts in tuned boxes and then hit them with about 3000 watts. Never blew one, because I would babysit my line level signal so close. No clipping.

fund razor
04-19-2010, 03:17 PM
Specific air volume is really important in designing a sealed box.

macjazzy
04-19-2010, 03:27 PM
Thanks, Fund Razor. So from your response it seems like a definately want a free air sub and I dont need a dual voice coil. That helps a lot.

Where you lost me was in the power ratings.

fund razor
04-19-2010, 03:30 PM
Ok, the JL audio are infinite baffle, 250w rated and 4 ohm. Sensitivity is 83dB
The Alpine is rated 50-150w and 4 ohm with 300w peak power and has an efficiency of 86.7dB

Note: You must DOUBLE the power in watts to increase the volume of a speaker by 3dB.

This means that the JL audio with 300 watts at 4 ohms at 83 dB will be exactlly as loud as the Alpine with 150 watts at 4 ohms at 86.7dB.

fund razor
04-19-2010, 03:32 PM
The Alpine are twice as efficient, given the same power, but will theoretically handle less. It's woofer takes less power to move enough to create the same wave.

The JLs will be more forgiving of peak power transients, but will require more power to get the same bump.

BDiggity
04-19-2010, 03:40 PM
I have 2 Sony 10 in. subs in my boat. They are mounted under the double helm seat firing forward. They have been in for 2 seasons. This weekend I was playing the stereo and one of the subs blew. Its making a terrible rattle noise when turned up.

My question is, what should I replace it with? Not brand, type.

I think I want to go with either JL audio or Alpine marine type R those seems to be pretty popular and well liked choices on the subwoofer threads.

What I am not sure about is free air or enclosed sub.

An enclosure will give you much better sound than free air. Free air's require a lot of power & do not have the same response as a sealed or ported enclosure. A sealed box is the easiest to build. Whatever sub you buy, it will come w/ a spec sheet. You can then use a tool like from Rockford Fosgate http://www.rockfordfosgate.com/rftech/box_wizard.asp to figure out the dimensions. Based on where you plan on installing it, you can customize the LxWxD that meets the airspace requirements. A ported box is more tricky as now you have to account for the port size & length which impacts the sound quality. Probably better off letting a shop build it.



The space they are in is pretty enclosed but not air tight, I am not sure how much work I need to do to make them air tight and I dont have any idea how much volume it would be enclosed anyway.

See above. The sub spec's will drive your box size.



I am not sure how important a specific air volume is for enclosed subs and I understand ported ones need a specific port size to work. But I am worried that since the area is fairly closed off a free air might not be right either.

The other thing is my amps are mono kenwwod 300watt rms, 1000 watt peak.
The JL Audio subs are rated at 250 watt rms/750 max, those are my preferred choice but I am worried about blowing them with these amps. The Alpines are rated at 300 watts rms/900 wattt max so they match up a little better.

That kenwood probably puts out 300w @ 14.4v. You would only be supplying it 12v normally. Either sub will be fine, dont worry about the max on the sub because when your amp tries to push 1000w, it will be 100% distortion & would blow either sub. High, clean power rarely damages speakers, they normally let go when the amp is supplying is bad signals.



Whe I was looking around I also noticed some subs have dual voice coils but most have single voice coils, I have no idea what this means or if I should even be worried about that.


Any help would be greatly appreciated.

Dual voice coils allow your to wire the sub in different ways to change the ohm load to the amp. For example, if you have two subs, that are 4DVC, you can wire it as a 1ohm load or 4 ohm load. The 1ohm load would send your kenwood in shutdown mode. Easiest thing is to just use the wiring wizard http://www.rockfordfosgate.com/rftech/woofer_wizard.asp Yes you need to be worried about it because as the ohms drop, the amp puts out more power, but then has to work harder. With the kenwood, you need to keep it at 4 or 2 ohms.

fund razor
04-19-2010, 03:43 PM
Disclaimer: they rate speaker sensitivity at 1 watt power, and one meter distance. (full range speakers it's 1 watt at 1 meter at 1k frequency) Subs are a little different. So there will be some variance up near maximum power rating, but it still helps you compare what will happen with a given power amp and given ratings.

fund razor
04-19-2010, 03:45 PM
An enclosure will give you much better sound than free air. Free air's require a lot of power & do not have the same response as a sealed or ported enclosure. A sealed box is the easiest to build. Whatever sub you buy, it will come w/ a spec sheet. You can then use a tool like from Rockford Fosgate http://www.rockfordfosgate.com/rftech/box_wizard.asp to figure out the dimensions. Based on where you plan on installing it, you can customize the LxWxD that meets the airspace requirements. A ported box is more tricky as now you have to account for the port size & length which impacts the sound quality. Probably better off letting a shop build it.



See above. The sub spec's will drive your box size.



That kenwood probably puts out 300w @ 14.4v. You would only be supplying it 12v normally. Either sub will be fine, dont worry about the max on the sub because when your amp tries to push 1000w, it will be 100% distortion & would blow either sub. High, clean power rarely damages speakers, they normally let go when the amp is supplying is bad signals.



Dual voice coils allow your to wire the sub in different ways to change the ohm load to the amp. For example, if you have two subs, that are 4DVC, you can wire it as a 1ohm load or 4 ohm load. The 1ohm load would send your kenwood in shutdown mode. Easiest thing is to just use the wiring wizard http://www.rockfordfosgate.com/rftech/woofer_wizard.asp Yes you need to be worried about it because as the ohms drop, the amp puts out more power, but then has to work harder. With the kenwood, you need to keep it at 4 or 2 ohms.

All good stuff. Great info. But if the question is whether to replace his existing setup with the JLs or the Alpines, building a box may not be desired.

fund razor
04-19-2010, 03:47 PM
Parallel vs series will also allow you to change the load that the amp sees, and therefore the output.

Amps create heat. More heat the lower the load goes. (Also less headroom and more clipping) I would avoid going lower than 4 at all costs in this application.

Good luck!

macjazzy
04-19-2010, 04:02 PM
Thanks BDiggity and Fund, I really want to not have to build a box or try to enclose the area the subs are mounted in. I was happy with the sound the Sony's put out but figured if I was replaceing one I would upgrade the quality of speaker and replace.

If I am reading this right, Fund, you are suggesting, in my case, between these 2 subs, my best choice would be the JL Audio's ? Am I correct there? I really don't want this to turn into another endless thread of what brand is better. Just want to know which of these 2 would best suit my specific need.

thanks

phragle
04-19-2010, 07:57 PM
I know you dont want to build a box, but I do think you will be happier with a sealed enclosure. If your hurting for space depneding on how undersized you are some dacron fluff can make a box think its bigger. The box built reasonably to specs will give much better sound and volume at much lower power levels. This will allow you to decrease the gain on the amp, giving you more headroom before it clips and begins distorting. the amp will run cooler and the speakers will live longer. I don't remember off the top of my head but 10"s shouldn't need more than a cubic foot or so.

fund razor
04-19-2010, 09:56 PM
I know you dont want to build a box, but I do think you will be happier with a sealed enclosure. If your hurting for space depneding on how undersized you are some dacron fluff can make a box think its bigger. The box built reasonably to specs will give much better sound and volume at much lower power levels. This will allow you to decrease the gain on the amp, giving you more headroom before it clips and begins distorting. the amp will run cooler and the speakers will live longer. I don't remember off the top of my head but 10"s shouldn't need more than a cubic foot or so.

No argument. But he may have been satisfied with the overall warmth created by the subs but not used that heavy 60-80 Hz bump dance range. If so... if he is just rounding out the low end... then no need to build a box if he doesn't want.

If this were a dB contest car.... I would be suggesting box building class. :D

fund razor
04-19-2010, 10:00 PM
Thanks BDiggity and Fund, I really want to not have to build a box or try to enclose the area the subs are mounted in. I was happy with the sound the Sony's put out but figured if I was replaceing one I would upgrade the quality of speaker and replace.

If I am reading this right, Fund, you are suggesting, in my case, between these 2 subs, my best choice would be the JL Audio's ? Am I correct there? I really don't want this to turn into another endless thread of what brand is better. Just want to know which of these 2 would best suit my specific need.

thanks

Depends on how you use it. If you are going to hit them really hard, buy the JL. If you are in the position to take advantage of the efficiency of the Alpines, buy those. I noticed that the Alpines are pretty cheap. For 200 bucks you would be back in business. I always want to know why something blew though. Are all your settings ok? Is your sensitivity and your crossover point appropriate?

macjazzy
04-19-2010, 10:11 PM
Someone pointed out to me last year that when my stereo is turned up sometimes the bass clips out. So I installed a 5 farad capacitor. I was testing it out and had it turned up louder than I had in the past to see if it clipped out now. It didnt, but one of the subs started rattling.

The settings is something I have struggled with since i installed the system. Between the settings on the head unit and the amps it is very confusing trying to get it set right.

The sensitivity is set on the lower end of the scale, I know enough to do that to keep the distortion down.

But other than that I am sure it is not set to the best possible settings.

fund razor
04-19-2010, 10:29 PM
Without being in your boat... I would say that the line level of your head unit is overdriving your amp. (based on your description of settings) It would be cleaner (as a rule but not law) if your source was lower and your amp was higher.

Not talking about the difference in level between -10 and +4, I am talking about how hard you are possibly driving the op amps or equivalent in the head unit.

phragle
04-19-2010, 10:39 PM
No argument. But he may have been satisfied with the overall warmth created by the subs but not used that heavy 60-80 Hz bump dance range. If so... if he is just rounding out the low end... then no need to build a box if he doesn't want.

If this were a dB contest car.... I would be suggesting box building class. :D
you gotta keep the double bass tight on the slayer cd's when the volumes up!!!

Griff
04-19-2010, 11:12 PM
The Alpine Marine 10" free air subs are rated at 300rms/900 peak.
http://www.alpine-usa.com/product/view/swr-m100/
I have 2 in my boat and am putting about 250watts rms to each of them. They sound pretty decent, but not as good as sealed box sub. Like you I had space constraints on where I wanted to mount them and couldn't use a box. They are about a 1/2 the price of JL's if you get them off ebay and very comparable.

fund razor
04-20-2010, 07:18 AM
you gotta keep the double bass tight on the slayer cd's when the volumes up!!!

Off topic, the kick drum on a slayer album is primarlily above 1k. In fact, most of the signal occurs above that. Listen to it. It "clicks" more than it booms.

(Disclaimer: I used to mix a lot of metal. I recorded and produced the last "Warning" album, and was the front of house engineer on the "Damien" Descension tour. :o) That's for a different thread.
But I like Jazz. :)

If it were me, knowing how I listen... I would probably try the Alpines.

But I would take a close look at the gain structure of the system. Or have someone else check it out. Gain structure is like a series of valves or faucets, you want an even gain structure, not some wide open and some choked off.

macjazzy
04-20-2010, 07:23 AM
Being as that the space they are in in almost enclosed now. Can I just use some silicone to seal the cracks and small holes etc to attempt to enclose it fully? Does the box have to be exact in size and shape?

My boat often times becomes the sound for dock parties and raft-ups. So I end up playing a variety f different music, although my tastes are not hip hop or rap oriented at all. More classic rock and 80's- 90;s music.

fund razor
04-20-2010, 07:45 AM
A real box is screwed and glued. I don't think the result of trying to seal a space that was not designed to be a woofer box will be that discernable. Plus, you don't know the natural resonant freq of the space. The volume of the space is relevant to the performance of the woofer and the volume that the woofer is designed to resonate the best in. If the natrual resonant freq of the space that you are working with is outside of what you want, you may not be doing yourself any favors.

The car audio guys would say you might as well build a box. I say you might as well slap a couple of woofers in there and go boating. :o

macjazzy
04-20-2010, 12:03 PM
That is the way I am leaning. It sounded very good last year, with subs no one seems to mention as being good ones ( Sony) and they were an odd 6ohms per channel speakers. So I think just an upgrade in quality will result in some upgrade in sound output.

Where they are mounted now would not lend itself to a real sub box and I dont want to do any major surgery do accomodate it or chang the layout of the boat to build in a box. As it is now I lost no storage where they are and were easy to route wires to, are out of the way etc.

So I will just go free air subs. I am still confused about JL or Alpine though. I don't want to replace th amps I have. They are not very old, and still work fine. I am open to having someone do the correct adjustments. But they are class D mono amps so they should work fine, I would think.

fund razor
04-20-2010, 12:29 PM
Just a note: your 6 ohm speakers would pull less power from your amp than a 4 ohm speaker.
Switching to a 4 ohm will increase the potential output from what it was with a 6 ohm. So, going by your descriptions we can predict a theoretical increase in sound pressure, all other things remaining equal.

I'll bet that making sure that your gain structure is good would go longer toward preventing future voice coil failure than choosing a speaker with a higher potential power rating. But that's from having sent goo-gobs of clean non-clipping power into speakers for years. I would have no issues hitting a speaker with twice the rated power if I knew it was a good signal from the head unit.

I think that you will be ok either way, again... based on your own descriptions.

fund razor
04-20-2010, 12:30 PM
I am sorry that I am not closer, I would have been happy to come check out your settings for a beer. :D

macjazzy
04-20-2010, 01:10 PM
Thanks for all your help, and I appreciate the offer to check all the settings for me. I would have no problem paying in beer for that:cheers2: