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-   -   car or PA or home theatre drivers (http://www.diyaudio.com/forums/multi-way/3288-car-pa-home-theatre-drivers.html)

Kilowatt 25th April 2002 08:07 PM

car or PA or home theatre drivers
 
Maybe I should know this by now, but most of my knowledge and experience is in the amp department, so I don't. What's the real difference between car speakers and other speakers. Is there a problem with using car subs for home theatre or sound reinforcement? I have 4 Sony Xpods in my room now, they seem ok, but I don't have a real experienced ear. The xover freq. is 120Hz.

I would like to use Audiobahn ALUM12X subs for my big sound system project, putting 7200W into 8, or maybe later on, 32 of these spectacular subs. They are dual 6 ohm, ideal for my amp, rated 1000W RMS (so they say), 96.4dB@1W@1m, 31mm Xmax, and are only $189 US. I have heard others say that they sound good. These are clearly far and away the most ideal sub for me looking at the specs, but they're car subs, and this system will be for outdoor use. Does it really matter?

bostarob 28th April 2002 06:12 AM

does it really matter?
 
Almost all of my speaker building experience is in PA applications with a little bit in car audio and a little in home. Car speakers can work in home-fi, but I would never use a typical car speaker in an outdoor application. After examining the Alum12x's, I discovered the 96.4dB efficiency rating is a bit of an exaggeration. Maybe 90dB give or take a few. To get 96dB at 1 watt, it would need a Vas of maybe 20 cubic feet. Car subs are inefficient, made for smaller boxes and high excursion (the further the cone is excurting, the further it has to travel back. The higher the excursion the higher the distortion level). Distortion matters less in a car with road noise. In your ampitheater, (I don't know what else to call your awesome and very well funded project) I assume distortion will matter. I also assume you want to move large amounts of air. Your going to need to get bigger cones. Eminence makes 3 18 inch woofers that I have often dreamed about. Eminence has excellent performance at a good price. If you have the money look at celestion, JBL, PAS, Beyma, Volt etc., look around. But stay away from car speakers, you'll end up spending more and getting less.
please, give more details about your ampitheater, I'd love to know
-andy

mgoedeke 28th April 2002 11:32 PM

Bostarob, you are quite right. The is simply no way around Steele’s iron law ;-) BTW, those woofers will probably not handle 1000W as quoted. The figure is probably meant for SPL where they will get burped with that amount. BTW, look at the blueprint 1503 or 1803 for some serious displacement/$, but again not for PA, except if you have a LOT more power to burn.

There was a thread on a very high output system a while ago, where I mentioned the LAB horn ( http://subs.live-audio.com ). This project is starting to materialize and by the looks of it will blow away just about any direct radiating system one could think of. These babies will give you 110 dB @ 2.83V @ 1m (that’s about 50%) in groups of 4 or ideally 6 from below 30 Hz out to about 200 Hz. The designer is Tom Danley, the guy responsible for the Servodrive BT-7. The LAB horn design seems surprisingly similar to it and for a taste, go and have a look at the Servodrive site (the comparison with the double 18s is rather conservative BTW). They have just about finished the cutting plans and the drivers should hopefully follow suit soon. 7kW with that efficiency (and yes, they’ll take about 1200W RMS AES per box) will give you a serious system suitable for concert use and then some. 150 dB peaks @ 1m are not totally out of the question (cleanly, BTW), if you should go for a stack of 6 per side.

Just out of interest, what are you considering for the rest of the system and what do you intend to do with it?

Have fun

Martin Goedeke

Kilowatt 29th April 2002 05:32 AM

First of all, here's what I have in mind for the rest of the beast. For 250-3000Hz, I plan to build 2 more of those 900W channels like the ones 8 of which will make up the 7200W amp, but designed to drive lower impedance, and each powering 3 Electro-Voice EVM 10M midwoofers wired in parallel. These are rated 99dB@1W@1m and 300W RMS. Then for 3kHz and up, I will use 8 100W 8ohm horns and 4 200W into 4 ohm amps (Leach amps). There was a discussion about it here: http://www.diyaudio.com/forums/showt...?threadid=1971 .

I have already drooled over the Eminence Kilomax Pro speakers, but mucho expensive compared to car subs. Another problem is that I must have about 12 ohms for each of the 8 900W channels. The Audiobahns just happen to be dual 6 ohm! I suspected (actually, someone said it in another thread) that they probably can't really handle 1kW RMS, at least taking into account Xmax limitations.

Your right that I need to move a lot of air, and I want low distortion. Maybe I won't be so picky though because it's for the low frequencies. If I have a larger cone with smaller Xmax, then that will have bad distortion characteristics too, won't it?

What I'm actually trying do here is build a tri-amped system, to get as much SPL (bass) as I can from a (water-cooled) 7200W amp for a reasonable price (but also high fidelity) and then go from there with mid and trebble. My original plan would cost about $5000 US, which be all but impossible for me to obtain at once, but I plan to build it by starting with one 900W channel and adding on more and more stuff until it's done.

What will I do with it you ask? I don't know how I got myself in to this project, but there's no turning back now! It will be like a huge hifi system for outdoor use to impress my friends, shake the earth, and play music at concert levels from 100 yards away. Maybe I will think of something really useful to do with it - you never know. I'll probably usually just use it as a regular stereo, operating at only a tiny fraction of a fraction of it's rated power.
I had a thread about this thing a while back in the solid state forum that turned into utter chaos as people learned of my plan to use direct line rectification for this thing and as I (politely) turned down many suggestions to do things that would be impractical or impossible for me with this system.

Perhaps some sort of horn would be the way to go. I'd love to have more info. I'd really like to keep the cost of speakers to under, say, $4000US if that's at all possible. Maybe I could just use lots of lesser subs. What would happen if I built big horns and put the subs mentioned above in them?

Are you sure the Audiobahns are not rated 96.4dB sensitivity? Are they lying? I know I would consider that lying to say that their drivers are more than twice as sensitive as they really are. That rating doesn't vary as far as I know. Also, I have heard somewhere that those sound good. Has anyone heard them? I'd like to know for sure if those would be acceptable for my system. From what you say, however, perhaps I should get Eminence drivers. They also have a sensitivity that is just what I need. However, their Xmax is only 7.9mm. Will this be enough for really low notes?

AudioFreak 29th April 2002 08:48 AM

Just a couple of quick notes,

1. alot of car subs have very little low end in them because they rely on cabin boost.

2. alot of car subs have the efficiency rated @ somewhere between 200 and 500Hz and so when operated outside of the car environment will be far below that which is stated

3. if you plan on "impressing the friends and playing concert levels @ 100 yards, you'll have to get permission from the local authorities and likely have to get a licence and you'd only be able to do it in an area that is rated for this kind of sound levels ... do it in ur back yard and you could be looking @ a multi thousand dollar fine and permanent confiscation of the equipment .... if the authorities got their hands on your system, you'd also get another host of multi thousand dollar fines because of the direct rectification that would not meet safety specs and all this would probably land you in court also.... I'm not joking about any of that btw.

I'm not saying dont do it .... i'm just saying that your playing with fire and if your not careful, someone is gonna get burned.

Kilowatt 29th April 2002 08:33 PM

Yeah, I know it, it's been said too many times to count. I live in a small town in the middle of nowhere, and so I have the option of going way out far from civilization to run my system. I have friends that live miles out of town, and so I won't be violating any noise laws.

Another thing: Isn't it so that because of my using direct line rectification, I would not be able to commercially market or rent out the amplifier, because it would not meet safety codes, however, It would be my own business if I use it for myself. After all, many people, including me, play with very high voltage, high current, transformers, doing things like drawing out big arcs and building Jacob's Ladders and the like. The risk of fire and electrocution accompanied by severe burning is very real in this practice, but it's a common hobby. This is not illegal to my knowledge, and many people do it. I don't know how it is in Australia, but here it is not illegal to play with electricity, but there are of course elecrical codes for wiring in homes, but that's different. Whatever the case may be, perhaps any questions can be eliminated if everything is covered, ie. the speakers would hook up with some sort of plugs, and so no line-level terminals would be exposed. It would be like plugging in an appliance, and I don't think that's illegal.

Anyway, I'll be careful and use common sense, and try not to do anything stupid or to get me in trouble.

I think it's fairly well decided that I won't use Audiobahn subs for this little project, and Eminence's Kilomax Pro speakers are a little pricy, and they're 8 ohm. What I'm thinking I'll do, is put 3 4ohm subs, rated at least 300 watts each, in series for each channel. I have yet to decide just what these drivers will be though. Any ideas?

AudioFreak 30th April 2002 03:16 AM

Jacob's ladders and tesla coils are in many parts across the world highly illegal cause they disrupt TV and Radio broadcasts ....

The other risks of fines etc are real but in your area are probably a miniscule risk. If the risk to yourself or another is deemed large enough, you can still attract legal problems ....

bostarob 30th April 2002 03:42 AM

First, to address your quesitons:
-does distortion of a Larger cone with smaller Xmax = distorion of small cone with larger xmax?
Answer: No, the distortion coming out of the larger speaker would be far, far less. Probably an order of magnitude. Excursion increases exponentially with power increase, and the higher the excursion, the higher the distortion as earlier stated.

-Is audiobahn lying about efficiency?
Answer: Yes. There are no standards for measuring efficiency, and most companies tend to exaggerate. Audax is the only company I can think of that doesn't, correct me if I'm wrong.
-Will 7mm be enough
-plenty. You don't see PA drivers, the biggest baddest drivers in the world, with much more than that.

Right now, Parts Express has on a factory clearance special. Included in that is an 18" Eminence driver with a cast frame, 3" diam. vc, 200 watts RMS (please do not get hung up on power ratings, all it is is a thermal rating, at 200 watts the adhesives will give. Also at 200 watts, with any efficient speaker, the vc will be bottoming out against the back plate so hard that that is all you will be able to hear). Plenty of power, 7mm Xmax, 4 ohm impedance, all for $75. 3 of these for each channel, and you have a system that could kill livestock. Part # is 299-716, tell me what you think.
-andy

Kilowatt 30th April 2002 07:43 AM

Andy, I like it, and that may very well be what I will do. Just think what a sight that would be to behold! 24 18" drivers, stacked 3 high and 4 wide on each side, maybe spread out horizontally quite a bit to get better dispersion. That setup alone would stand almost as tall as I do. Then on top of those, maybe 12 or 18 EV 10" midwoofers, and to top it all off, 16 15"x7" horns. :D

Nice as that all sounds, I really can't afford all those drivers and to build all those amps right now, and I haven't even finished designing the 900W amp channels I will be using so many of in this system. It may be years and years before this system is how I want it to be. Wouldn't it be nice if one day I found about $20,000US in my mail box!:D

Maybe I should start a new thread for this, but I wonder where I can get information about legal stuff that may pertain to the system.

Kilowatt 30th April 2002 09:11 PM

Question about excursion: Car subs move huge distances when say 100W is applied. JL 13" W7 subs, for example, have an Xmax of 1.25". These are rated 1kW. My 12" subs in my room each have about 20W going to each of them, and they can move about 8mm from peak to peak easily at low Hz. These are car subs and are not very efficient comapred to say, an Eminence sub. If I put 300W of deep bass into an 18" Eminence sub, then won't it's comparitively tiny 7mm Xmax run out very quickly? Even though higher excursion gives more distortion, these subs will have to move quite a way anyway with that kind of power level, right? I must find a compromise between excursion and cone area, right? What do I do here?

It appears I have some learning to do about drivers before I select something.

P.S. I'd have to use at least 300W subs, not 200W, Andy.


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