Newbie Amp & Enclosure Advice Needed

[Ron]

Hello,

This is my first post here. I'am a complete novice when it comes to what I'am learning is the 'science' of audio reproduction.

Has any one had any experience with a subwoofer plate amp from KLH Audio, model #119117? This amp comes with the KLH 10 inch ASW 10-120 subwoofer. It has 120 watt output, manufactured by Dong Guan Wei Phon Electronic Co. in China. I can find no specs on the web regarding this amp.

I have just acquired a Shiva Mk III from Adire Audio. I want to build a down firing Sealed box for this driver. As it has dual voice coils, I would like to wire it in parallel as such, and drive it at a nominal 4 ohms. I don't know if this amp can handle that type of load.

Is there a way of testing the amp with meters or anything that would tell me? If I try it wired in parallel, and the amp can't handle it, do I lose the amp only, or worse, both the amp and the driver?

I'am leaning towards a sealed box low Q alignment of .5 as I appreciate musical fidelity, a little more than DVD effects such as the depth charge scene in U 571. Although I may be looking too low here. Any thoughts or cautions would be greatly appreciated.

This is my first attempt at building a box, or any of this, and definately could use all the advice I can get. Should I care about golden ratio aspects in a subwoofer enclosure or not?

I'am using a Denon AVR 2700, with Polk RTi 35 mains, Polk center, with Polk R10 surrounds.

It will be a bit before I can afford to upgrade the plate amp, and was hoping to hear the box and driver first.

Thanks in advance for any advice or experiences you can share.

Regards,

[R. McAnally]

There's really no way to tell if an amp is 4-ohm stable by measuring it with a multimeter. Any decent amplifier can safely handle 4-ohm loads, so just go with it and use the warranty if you need to (which you shouldn't =). Check and make sure it doesn't get too hot (i.e. you can't hold your hand on the heatsink).

If the amp fails, it could blow a fuse (hopefully), sound really bad, or possibly take out the speaker if there is no protection relay built into it and the fuses don't blow (which is usually the case).

I recently noticed a funny smell in my living room, and followed it to one of my Polk RT25i 's. The woofer was completely toast, because of my lack of any protection relays on my amp! =( Since the fault was caused by a cold solder, it somehow fixed itself and it took me weeks to find the problem. I doubt most cheaper subwoofer amps have relays due to the added cost of manufacturing, and the fact that it is not "their" speakers that will be toasted!

[AudioFreak]

most decent subwoofer plate amps can handle a 4ohm load... just go slow and use it @ a very low volume initially... after a while if it doesnt get unpleasently hot you should be able to safely turn up the volume a little... if @ any stage it gets very hot then turn it down and dont exceed that point or you'll probably be risking killing the amp and maybe the driver as well....

[AudioFreak]

I just checked the specs for the shiva ... given the power of the amp, you can use just a single voice coil from the shiva and leave the other one disconnected ... the amp will then get an 8ohm load... problem solved.

[Dave Bullet]

Regarding the enclosure.....

I'm going to build a Shiva sub like you - but make it a "dual vented / sealed' design.

Basically - with a Qtc of about 0.5 - which equates to approx. 130 litres with a shiva - you can run the box in both vented or sealed modes

Basically build the box - tuning the desired Fb - as a vented box with a port. When you want to play movies and want low frequency response - use it as a vented. When you want to play music and want th best transient response - plug the port (the hard part).

I thought about having a threaded port - which sticks out of the box by about 1" - allowing a rubber sealed cap to be screwed on when wanting to run it in sealed mode (I think any other sorts of plugs could get blown out at higher SPL).

If you just build a sealed box - I don't think you'll get an F3 below about 38 Hz. Not that this is high - it just might not be low enough- not knowing what music you play (ie. pipe organ lowest note is 16Hz, bass guitar or double bass is in the low 40s (or possibly high 30s???)). As far as electronic anything goes....

Dave.

[Keld]

Should I care about golden ratio aspects in a subwoofer enclosure or not?

No ! you can even build a cube-shaped enclosure, but I would brace it asymetricly to keep sides from flexing in the same frequens.

Keld

[subwo1]

Yes, I agree, the stiffer and more solid, the better. A cube may actually be better, as it causes more even forces on the woofer cone.

[mikeatfhc]

To Dave Bullet:

Just an idea for plugging your port....

If you don't want to have the port tube sticking out of your sub, and you are concerned about the plug "popping-out" during high spl moments... say "Dark Side of the Moon"...

Go to Home Depot, Lowes. etc. And look in the plumbing dept for a "pipe plug" or a "test cap". They are usually an ugly yellow plastic (safety yellow). But they have a wing-nut in the center that will expand the plug to fit the pipe and hold it there temporarily (usually used for temp blocking pipes or for pressure testing purposes.) They are temporary and assuming you are using PVC for the port tube they would work great.

Hey... maybe you'll find a black one.

[Dave Bullet]

Thanks mikeatfhc. I'll keep my eye out for one (just make sure I choose a PVC diameter with a pipe plug that fits).

Pity I wasn't using Focal drivers - the nice yellow cones might look good with a yellow pipe plug - especially when playing yello.

[Super]

You may be correct, but 38hz as the f3 for a sealed Shiva seems too high. If I recall correctly, you should be able to go down to the mid 20's or so. Somebody please correct me if I'm wrong.