What i discovered in my LLT build

[ccdoggy]

So i just finished a 12Cuft box, all internally braced by 2x2 with some liquid nails glue on everything. Tuned to ~14hz, using a FI caraudio Q 15" sub, dual 1 ohm. powered by a EP 2500.

Tip 1. limit the system by the amp. my problem is that if i turn it up too loud it gets fed too much power, and during scenes like Master and commander it bottoms out like crazy. Make sure to look at the excursion graphs and stay below it, really. lesson learned.

Tip 2. Truck bed liner makes an awesome final finish. very very durable. Use the roll on stuff with the special roller, then sand down any large chunks or bad spots, roll it all again, sand again if needed, then use a spray can of the stuff to add a nice fine texture to it. and the stuff says not to use below 70*, really dont do it, it just clumps up. Ooo and be careful the stuff is made up of at least 5 things that cause cancer. definelty something to do outside in the wind.

Tip 3. Brushed aluminum looks excellent next to the sub. If you find a place that has it ask if you can get some damaged stuff. it was going to cost me like $60 to get the size i wanted, allot longer then what i needed but thats how the sol dit. I got a damaged pice with the samage in the middle right where the cut out for the sub was for $10.

Tip 4. If you are not so good with wood skills, then use wood filler (sand able) to smooth it all out and make everything flush.

Tip 5. Use T-nuts to hold sub in, easy to use and allot more secure.

Tip 6. Have a strong friend, as my box weighs in at about 135 pounds. allotta glue and allot a wood.



that pic is of it almost finished, it just got another coat of bed liner and a bead of black caulk around the inside rim to clean it up. it looks better in person as the brushed is more see able.

What you think for a first real sub project?

Big thanks goes out to Steve Callas, without his personal help none of this would have happened and i would have gotten stuck with a regular ported box.

[Exocer]

Thanks for the informative post...I have a box from last February that I never got around to finishing... Truck bed liner is now at the top of the finishes list...Oh and how do you like the sound of those NHT Classic Threes? I own 3 pairs of NHT SB-2's from a few years ago and they sound pretty good.

[Blaser]

ccdoggy wrote:

So i just finished a 12Cuft box, all internally braced by 2x2 with some liquid nails glue on everything. Tuned to ~14hz, using a FI caraudio Q 15" sub, dual 1 ohm. powered by a EP 2500.

Tip 1. limit the system by the amp. my problem is that if i turn it up too loud it gets fed too much power, and during scenes like Master and commander it bottoms out like crazy. Make sure to look at the excursion graphs and stay below it, really. lesson learned.

This is typically the problem of tuning relatively too low with too big a volume for a respective driver. From an EP 2500 single chanel it will bottom out certainly (according to WIN ISD simulation), but the question is what to do when designing a box? Should the rated amplifier "RMS power" be taken as a max. for the simulation, or should one assume peak power (how much? double the RMS?) for very short loud passages?
Steve, Brucek....?

[brucek]

but the question is what to do when designing a box? Should the rated amplifier "RMS power" be taken as a max. for the simulation, or should one assume peak power (how much? double the RMS?) for very short loud passages?

The Input Power variable in WinISD is defined as the RMS voltage (at the driver) squared, divided by the DC resistance (or Re) of the coil. This makes sense since the lowest value on the impedance curve will be close to purely resistive and as such will be the point of maximum current to the coil for a given voltage. So it would be considered worst case.

Note that bridging theoretically doubles the voltage across the driver and as such the power would increase by four times since it's the square of the voltage divided by the resistance. In reality the rails are usually limited when bridging an amplifier so as not to fry the output stage.

I have no practical experience in this regard, but so far as WinISD is concerned I would simply use the rated RMS power of the amplifier spec as the absolute worst case over relatively short periods. Others may disagree.

brucek

[WillyD]

Are you sure that you aren't clipping the amp? You say you have the dual 1 ohm version. I assume you are running it off of one channel? There is no way that you'd be getting a clean 1000W from the EP2500 in that configuration, that low anyway.

[ccdoggy]

it was bottoming the sub out before the amp cliped, given this is at a specific freq, which happened to be quite loud on master and commander.

I know it was bottoming out because the clip light was not going on, and the noise was a clink noise, not a flat clipping noise. like metal hitting metal. yes, i could only use one channel as the amp does not support bridging 2 ohm loads.

I LOVE THE THREES. they are way power hungry, but very very impressive for the money. I am powering them with a Arcam Avr-300 reciever. there is no way i would put anything less then 100 real watts to these.

I used the duplicolor truck bed liner.

From my WinISD graph it look like i was bottoming it out at about 22Hz.


SO for a first build how does it look? what should i have done differently?

[Ilkka]

ccdoggy wrote:

it was bottoming the sub out before the amp cliped, given this is at a specific freq, which happened to be quite loud on master and commander.

I know it was bottoming out because the clip light was not going on, and the noise was a clink noise, not a flat clipping noise. like metal hitting metal. yes, i could only use one channel as the amp does not support bridging 2 ohm loads.

I know this can be hard to believe but unless you've actually heard these both noises (clipping and hard bottoming) from your subwoofer, it's VERY EASY to make a wrong conclusion. When most pro amps clip (especially these cheap ones), the resulting noise sounds almost like metal hitting metal type of noise.

Have you watches the cone during this noise? Can you estimate the excursion it makes?

[WillyD]

Ilkka wrote:

I know this can be hard to believe but unless you've actually heard these both noises (clipping and hard bottoming) from your subwoofer, it's VERY EASY to make a wrong conclusion. When most pro amps clip (especially these cheap ones), the resulting noise sounds almost like metal hitting metal type of noise.

Have you watches the cone during this noise? Can you estimate the excursion it makes?

Yes. And another reason I brought it up is I read a first hand account on AVS where a user thought his sub was bottoming out. He upgraded to a much more powerful amp and the "bottoming" ceased.

http://www.avsforum.com/avs-vb/showt...&&#post9598876

[ccdoggy]

really? hmmm, well i have experienced the normal clipping in a klipsch 10" sub, would that be considered soft clipping? The clip limiter was not on the 2500, so was that my main problem i was getting the horrific metal sound? I cannot test the results right now as i just moved the sub into my house (still with parents for the next month) and they are not too keen on loud noises.

It did sound like two pieces of metal hitting each other. not sure if it was on both the in and out motion or just the in.

how much do you think the EP2500 realistically puts out into two ohms?


I cannot estimate the actual excursion during that point as i was directly in front of it and hurriedly dashing to turn it down.

[Blaser]

If you make a simulation you will find the Xmax is exceeded, but if bottoming out is related to Xmech, so not very sure it is bottoming.

Blaser

[WillyD]

blaser wrote:

If you make a simulation you will find the Xmax is exceeded, but if bottoming out is related to Xmech, so not very sure it is bottoming.

Blaser

And even that simulation is assuming the EP2500 is capable of that much power output down load given that load.

how much do you think the EP2500 realistically puts out into two ohms?

Check out this post by Thylantr: http://www.avsforum.com/avs-vb/showt...&#post10333605

You can guess on what 2 ohm/ch or 4 ohm bridge mode power is. Since this is an
amplifier based on a conventional power supply, don't expect power to double
when impedance is cut in half. I would estimate ~1800W RMS bridged
mode @ 4 ohms only if your AC line is a constant 117VAC, but this won't happen in
reality. If you did an RMS test on that amp, expect AC line sag. I'd probably
estimate 1200w - 1400w as the real power offered by EP2500 using 1% THD+N,
20hz sine wave test, less than the advertised 2400w.

[Ilkka]

ccdoggy wrote:

really? hmmm, well i have experienced the normal clipping in a klipsch 10" sub, would that be considered soft clipping?

Most commercial subs (also Klipsch) have very aggressive output limiters which prevents the amp from going into hard clipping. A pro amp will make a whole different kind of noise when it clips.

The clip limiter was not on the 2500, so was that my main problem i was getting the horrific metal sound?

Those little lights are not good indicators. One can have the clipping sound before they lit.

I cannot estimate the actual excursion during that point as i was directly in front of it and hurriedly dashing to turn it down.

When you get a chance, raise the volume slowly (1 dB steps) and play the same scene over and over. Monitor the driver excursion at the same time. I'm not sure but I'm assuming that driver has well over 30 mm of Xmech (+60 mm peak to peak). No way 1000 watts or so is able to use all that excursion unless you are under the tuning frequency (which you are not).

Dual 1 ohm coils are a difficult load for any pro amp. You will definitely need a better amp than EP2500. Before that I'd try running both channels at 1 ohm load.

[ccdoggy]

the amp will not support a 1 ohm load, not that i have tried.

27mm of Xmax, no listing of Xmech.

After reading up it looks like the amp is not putting out enough power to get close to the Xmech what ever it might be. hmmm... going to look into seeing how much it would cost to make the sub into a dual 2, for a 4 ohm load to bridge it.

[Ilkka]

ccdoggy wrote:

the amp will not support a 1 ohm load, not that i have tried.

Yes, I know it doesn't "support" it. I'd would still try it.

27mm of Xmax, no listing of Xmech.

Usually Xmech is quite a bit more than Xmax. I'd guess 35-40mm.

After reading up it looks like the amp is not putting out enough power to get close to the Xmech what ever it might be. hmmm... going to look into seeing how much it would cost to make the sub into a dual 2, for a 4 ohm load to bridge it.

That would certainly make your amp choice easier.

[ccdoggy]

well rewiring for a one ohm load would be tough, could i just bridge it into the 2Ohm load? would that not be doing basically the same thing?

P.S. Thanks allot for you're help!

I am currently playing at moderate levels with it bridged at 2 ohms just to see how it handles it before i put it through its paces later tomorrow or so.

[Ilkka]

ccdoggy wrote:

well rewiring for a one ohm load would be tough, could i just bridge it into the 2Ohm load? would that not be doing basically the same thing?

Yes.

P.S. Thanks allot for you're help!

You are welcome.

[Rodny Alvarez]

Hey ccdoggy!! what size port did you use???

What are the dimensions on the box??

[Exocer]

The Q15 appears to use the 12-spoke Venezuelan basket, good for about 35-36mm of Xmech.

[ccdoggy]

the box is ~27" x 27" x 3 feet. its is a 6" port ~27" long with a flare on both ends to 9", with a right angle in the middle to fit in the box.

I played some rock for about 3 hours straight with allot of bass and the amp dident get warm so tomorrow shall be stress testing and seeing what it can and cant do.

Thanks for the info Exocer!

[ccdoggy]

alright, so I did some master and commander scene tests with the FI Q on a single channel and bridged at 2Ohms.

I do get a little bit more excursion before it has trouble, so it does look like a lack of power issue, although everyone i talk to says thats way more then enough. I guess i am just bass hungry and want to optimize everything.

I have a Eclipse TI from my car (sealed) that i am thinking might work well having it on the other channel as some support and strength.

However i also think one of my main problems is voltage drop as every time it hits the lamp next to me dimms a good amount. I dot have the setup very good at all with my arcam, cd player, and the EP2500 all on the same outlet.

[WillyD]

Well at least you've figured out that it is indeed a power problem. I truly thought it was...

Is that outlet a 15A circuit?

[Exocer]

WillyD wrote:

Well at least you've figured out that it is indeed a power problem. I truly thought it was...

Is that outlet a 15A circuit?

My guess would have to be yes, most standard outlets are.

[Blaser]

What's the listening room dimensions is also an important question...

Blaser

[ccdoggy]

oo the listening area really is not ideal at all. its basically in the middle of a room against a wall facing a set of stairs going upstairs, about 20feet of room on either side of it. This is not where it will be forever but just for the next month or so.

I am sure its a 15A circuit, and by looking at the EP2500 it has a 15A fuse, so that means it will top out RMS wise at 1800Watts idealy.

[Blaser]

So I think it is not that your are bass hungry, but maybe need more woofage. FYI, I am using now a 12" sub in my 1800 cuft room but want more.

I have to go for dual 18"

Blaser