Newbie Amp & Enclosure Advice Needed

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,
 
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!
 
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....
 
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.
 
plug

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.
 
peter, i suspect the answer is a bit more complicated than that.

the -3db points according to the white paper are around 30 anechoic and in the mid twenties with room gain according to the white paper for low q alignments.

anyway, on a related note, we shall see what the nearfield f3 is for a sealed tempest is in a couple of weeks when i test mine with a clio setup (i should have it in 2-3 weeks). i'll post the results and compare them with the tempest white paper results.
 
Dave Bullet said:
38Hz anechoic is the theoretical (WinISD and diysubwoofers.org spreadsheet) calculated F3 for *any* sealed box for the published (not necessarily DUMAX) T/S Shiva params.

I'd like to know how Adire get between 29 adn 30 Hz for a sealed box.... also - why do they publish Fb for their sealed box designs (does Fb for sealed boxes make sense?)

Thanks,
Dave.

indeed, 38 is the theoretical f3. suprisingly, i've never actually seem one of them there theoretical drivers in reality, but i'd like to get my hands on one. probably never will though.

No, seriously, there are a couple reasons why the published f3 is lower than what you get plugging the numbers into the ts equations. the first, as my feeble attempt at humor shows, is that the response of a driver rarely parallels it's theoretical response curve exactly. however, i don't think this explains the difference.

Mainly, i think the difference is explained by this quote in the white paper--


Note that the frequencies are referenced to the peak output of the system, not the nominal output. Thus,
increasing any peak in the output frequency response, e.g. increasing the Q of a sealed box, can result in a
higher actual F3, not a lower F3. We choose to use this reference (peak versus nominal) because for higher
Q systems, the nominal output is not achieved until several hundred Hertz (>200 Hz). We believe this is
not applicable to subwoofers. As such, the F3 should be referenced to the highest value below 100 Hz.


is this fair? for a sub, i think so. if you were building a 3-way system and crossing over the shiva above 100 hz then their published f3 doesn't apply.
 
F3..??

Mainly, i think the difference is explained by this quote in the white paper--


Note that the frequencies are referenced to the peak output of the system, not the nominal output. Thus,
increasing any peak in the output frequency response, e.g. increasing the Q of a sealed box, can result in a
higher actual F3, not a lower F3. We choose to use this reference (peak versus nominal) because for higher
Q systems, the nominal output is not achieved until several hundred Hertz (>200 Hz). We believe this is
not applicable to subwoofers. As such, the F3 should be referenced to the highest value below 100 Hz.


is this fair? for a sub, i think so. if you were building a 3-way system and crossing over the shiva above 100 hz then their published f3 doesn't apply.

----------------------------------------------------------------------------------

*****The above was a quote from UCLA88*******.

I screwed something up in trying to reference the above.

In referring to the Adire Sealed Application PDF they reference something as using a Dumax T/S parameter of a sealed box Q of 0.5 as having an in room F3 of 24.4 Hz. Would I be able to actually hear this?

They also site an in room F8 of 15.0 Hz...... ????

Trying my best to decifer some of this but it is one big fog right now.

Regards,
 
for a bit on dumax testing, look here .

people like to talk about in room f3's being 5-12 hz lower.

while this is true, and in some sense more accurate, you have to understand the ground rules. first, room gain varies, depending on the room. unless you've tested your room, you don't really know how much gain you'll get.

also, at any given frequency, all drivers will get the same room gain. Look, the f3 of an NHT 1259 driver in a sealed box is about 25 or so, if my memory serves me. with room gain, maybe you get extension into the high teens. so, a sealed 1259 goes lower than a sealed shiva. NHT could claim an in room f3 of 17hz (i'm guessing here).

however, most people would pick the shiva as the sub with "more bass."


The problem with many LF drivers on the market is not their ability to go low, but the spl generated. If you look here , you'll see that the spl that the shiva can generate at 20 hz beats the other drivers listed. Yes, you need to go low, but you also need decent spls-that's part of the reason these long throw drivers have become so popular.

you definitely will be able to hear and feel the mid twenties bass-more so because the spl produced will be in excess of 100 db.
 
The problm with stating an "in room" F3 is that you will not get a consistent results between different rooms and it seems to me like the marketing department has more to do with this than anything else (F3 of low 20s sounds so much better than 38 Hz but in most music you'll find very little below 40 Hz, except when listening to organ music where you can even find significant output below 16 Hz (64 ft pipe, though rare gives you 8 Hz) and telarcs recording of the 1812 overture has significant energy at 5 Hz). Film effects rarely venture below 30 Hz, but it does happen. BTW F3 referenced to 100 Hz isn't fair either, because you'll want to reference the F3 of the system to its rated efficiency.

Someone mentioned that speakers do not follow T/S response predictions exactly. Due to the approximate piston like behaviour at low frequencies the T/S model gives a very accurate estimation of the response (usually well within 1 dB if one uses accurate T/S measurements) but at higher frequencies the assumption of a piston no longer holds true.

On a different note, do any of you have experience with the Blueprint drivers because I am looking at getting one (the 1201) for myself though the 1503 with a Linkwitz transform sounds positively yummy ;-)