Ok, so I picked up a Soundstream RA-100 MKII at work (there's a MKIII on ebay, I can't post the link yet). They were using them in a distributed audio system and had them laying around. I'd like to build a sub, this thing was $5, I figued why not. I can't find any info on this thing though. I've read that it's a 75W/4Ohm or 50W/8Ohm amp. First, I'm guessing the switch on it that says mono/stereo is for bridging? Also, how do you know if it wants 4ohms or 8? Does it not care? Can I bridge this thing and build a cheap sub? And by cheap, I mean like $30-$40 for a driver cheap. I'm just looking to get my hands dirty in speaker building. When I get more money, I'll go for something better, right now I'd like something to add to my surround system for movies that'll have more bottom end. Would a 10" be better with this amp than a 12"? Can I build it so that I can add a 12" sub to the system later and not make it sound bad? Will the Jets ever win another superbowl?
Another noob sub builder
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You have multiple interdependent questions.
1. No one knows what your old amp will do or how its configured unless they have one, but for 5 bucks, does it matter? If its bridging, then you probably have 150 watts into 4 ohms. Finding a manual will be difficult, and if you do, might cost more to buy than the amp did.
2. Deciding on the sub is more dependent on the T/S parameters and the enclosure size since you already know how much power you have. Download WINISD and start plugging in T/S numbers for woofers that you can afford, looking to get those that have the highest sensitivity(which means look for woofers with better than 90 db sensitivity if you can find them) since you won't have a lot of power to plug into it. Size of the woofer may not be as important as you think. Madisound sells a 10 inch woofer with an FS of 23 for only $55. Try to get as low an FR as you can when you design using WINIsd, but remember that the room will start reinforcing the sub below about 45hz, to as much as 12 db boost by the time you get down to 20hz(unless your room is huge)
Ask other questions as you proceed.
Hope this helps you get started in doing this for yourself. Good luck!
Marlboro
1. No one knows what your old amp will do or how its configured unless they have one, but for 5 bucks, does it matter? If its bridging, then you probably have 150 watts into 4 ohms. Finding a manual will be difficult, and if you do, might cost more to buy than the amp did.
2. Deciding on the sub is more dependent on the T/S parameters and the enclosure size since you already know how much power you have. Download WINISD and start plugging in T/S numbers for woofers that you can afford, looking to get those that have the highest sensitivity(which means look for woofers with better than 90 db sensitivity if you can find them) since you won't have a lot of power to plug into it. Size of the woofer may not be as important as you think. Madisound sells a 10 inch woofer with an FS of 23 for only $55. Try to get as low an FR as you can when you design using WINIsd, but remember that the room will start reinforcing the sub below about 45hz, to as much as 12 db boost by the time you get down to 20hz(unless your room is huge)
Ask other questions as you proceed.
Hope this helps you get started in doing this for yourself. Good luck!
Marlboro
sweet, thanks.
Is there any way to test the amp to see how many ohms it wants, or how many watts it can put out, or if it's bridged? I don't get the mono/stereo switch. Is that for bridging?
Also, are all the parameters required for WinISD?
Is there any way to test the amp to see how many ohms it wants, or how many watts it can put out, or if it's bridged? I don't get the mono/stereo switch. Is that for bridging?
Also, are all the parameters required for WinISD?
The hard way - take it apart and look at the circuits. If you have an electrical engineering degree, you should be able to determine it. Easy way - read the manual.
Either read the manual or you can use a dummy load and a DMM to determine output. I read the description of the MKIII on ebay. I don't think it can be bridged.
No. These are designed for commecial installations. Some music recorded in stereo will have vocals in one channel and instruments in other channels (or different combinations). If you are sending a stereo signal out in a restaurant, one section may not hear the vocals while the other may not hear the lead guitar. Switching to mono combines both channels to be sent to all speakers.
No. Read the Help portion of the application. It tells you the minimum required parameters as well as what gets calculated.
-Robert
The hard way - take it apart and look at the circuits. If you have an electrical engineering degree, you should be able to determine it. Easy way - read the manual.
Either read the manual or you can use a dummy load and a DMM to determine output. I read the description of the MKIII on ebay. I don't think it can be bridged.
No. These are designed for commecial installations. Some music recorded in stereo will have vocals in one channel and instruments in other channels (or different combinations). If you are sending a stereo signal out in a restaurant, one section may not hear the vocals while the other may not hear the lead guitar. Switching to mono combines both channels to be sent to all speakers.
No. Read the Help portion of the application. It tells you the minimum required parameters as well as what gets calculated.
-Robert
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4,421 Posts
Haha, one of my buddies is an EE and he admittedly knows nothing about audio, he thought that a 4ohm speaker should have 4ohms of resistance in the speaker cables. Then when I told him my amp wasn't stable with a 1ohm load, he looked at me like I was from another planet, insisting that 1ohm was easier for an amp to drive than 2, 4 or 8.
Haha, one of my buddies is an EE and he admittedly knows nothing about audio, he thought that a 4ohm speaker should have 4ohms of resistance in the speaker cables. Then when I told him my amp wasn't stable with a 1ohm load, he looked at me like I was from another planet, insisting that 1ohm was easier for an amp to drive than 2, 4 or 8.
Ok, I'm not going to use this amp for my sub. I hooked it up to a small bookshelf and it sounds pretty good. I'll hang on to it for another application.
I'm not finding too many plate amps to choose from though. I've tried parts express, madisound and ebay. What am I missing? Maybe someone could sticky a list of places to get parts from? I saw a list in a thread once, but can't find it.
I'm not finding too many plate amps to choose from though. I've tried parts express, madisound and ebay. What am I missing? Maybe someone could sticky a list of places to get parts from? I saw a list in a thread once, but can't find it.
Update:
Got my driver on friday. I used the plans on partsexpress' page for a vented box. I'm using only one channel off the soundstream amp and if it's putting out 50w, it's pretty good for 50w. Watched Pirates of the Carribean today with it. It makes a very noticeable difference. Thanks for all your input. I'll be back when I'm ready to tackle a 500w 15"
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Got my driver on friday. I used the plans on partsexpress' page for a vented box. I'm using only one channel off the soundstream amp and if it's putting out 50w, it's pretty good for 50w. Watched Pirates of the Carribean today with it. It makes a very noticeable difference. Thanks for all your input. I'll be back when I'm ready to tackle a 500w 15"
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