Overloaded with info.. sub/s to suit 250Watt plate amp help

[STRDB2000]

Hi there,

I recently found this forum and have been inspired to try and DIY my first sub, however after reading
dozens of posts and a lot searching online I'm completely lost!

I currently have a 250Watt M&K plate amp (6db boost at 30Hz apparently if thats important?) and wanted to build on a budget a sub that would be used for 70% music 30% HT, I don't really wan't alot of 'boom' but would prefer a tight sound that goes low if possible?

My problem is due to my tight budget and lack of reasonably priced drivers (shipping from overseas is to pricey) I don't have a lot of choice Box size is not too much of a concern (so long as I can fit them in the back of a small station wagon!) and I can do all the constuction myself so I have no extra cost there.

I have the chance to pick up two new cheap car woofers Infinity 1050W's http://manuals.harman.com/INF/CAR/Boxes%20and%20Parameters/1050W.pdf these are 4 Ohm each.

Would the knowledgeable minds here know if these would in any way be suitable drivers to use, or would I be better saving up and getting one decent quality 12" (two of the 1050W's are less than half the price here of a half decent 12" driver)

I planned to house the plate amp in its own enclosure separate from the subs, and had the idea of building a separate enclosure for each sub placing them in different areas in the room- they would then show an 8 Ohm load to he amp and so receive 180Watts each.

If they don't suit what TS spec's should I roughly be looking for in a good driver to suit the amp, I've read so much about spec's now that I don't know what I should look for?

Thanks

[Mike P.]

If you're lost then we'll draw you a map.

Is there a model number or a link to the M&K plate amp? With 2 4 ohm subs they would have to be wired for a 8 ohm load. 4 cu.ft tuned to 20 hz would be the best these subs would do with the amp that has 6 db of boost at 30 hz. I'm assuming the amp has a rumble filter at around 18 hz.

[ridecolby]

I may be mistaken as I am kind of new to this but if you are giving the amp a 8ohm load to get 180 watts rms do you not divide that by 2 to give 90 watts to each of the 12"s or do they actually both see 180 watts?

[Mike P.]

The amp is 250 watts into a 4 ohm load so both subs wired for 8 ohms will see 125 watts.

[ridecolby]

Not to dipute your reply Mike P. but that doesn't sound right to me. If you hook up 1 8ohm sub to that amp it sees an 8 ohm load and will put out 180w rms. so if you give it 2 4ohm subs in parrallel it sees 8 ohms and should still put out 180w correct? So if that is the case then don't the subs each get 90w?

[Mike P.]

Let me clarify, the amp is 250 watts into a 4 ohm load so both subs wired for 8 ohms will see 125 watts, 62.5 watts each.

[ridecolby]

That is more along the lines of what I thought. That makes more sense. Is that enough power to really drive these speakers? Or would he be better off driving 1 at 250w instead of feeding 2 of them such a small amount of power?

[Mike P.]

In the model above the input power the subs see along with the 6 db of boost put the subs at Xmax so this is the best he can do with this setup. Whether that's enough low end output will depend on what he wants.

[dyohn]

ridecolby wrote:

Not to dipute your reply Mike P. but that doesn't sound right to me. If you hook up 1 8ohm sub to that amp it sees an 8 ohm load and will put out 180w rms. so if you give it 2 4ohm subs in parrallel it sees 8 ohms and should still put out 180w correct? So if that is the case then don't the subs each get 90w?

Two 4-ohm speakers in parallel will result in a 2-ohm load on the amp. Two 8-ohm speakers in parallel will result in a 4-ohm load on the amp. Any two speakers of the same impedance connected in parallel will split the available output power equally.

[Mike P.]

He obviously meant series wiring.