What i discovered in my LLT build - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 47 Old 04-23-07, 12:02 AM Thread Starter
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What i discovered in my LLT build

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.
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post #2 of 47 Old 04-23-07, 06:52 AM
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Re: What i discovered in my LLT build

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.

If you don't have a BFD for your sub, get one fast!
If you don't have REW, get it now!
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post #3 of 47 Old 04-23-07, 07:53 AM
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Re: What i discovered in my LLT build

Quote:
ccdoggy wrote: View Post
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....?

Last edited by Blaser; 04-23-07 at 07:59 AM.
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post #4 of 47 Old 04-23-07, 08:57 AM
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Re: What i discovered in my LLT build

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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.

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post #5 of 47 Old 04-23-07, 10:05 AM
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Re: What i discovered in my LLT build

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.
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post #6 of 47 Old 04-23-07, 11:39 AM Thread Starter
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Re: What i discovered in my LLT build

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?

Last edited by ccdoggy; 04-23-07 at 12:12 PM.
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post #7 of 47 Old 04-23-07, 02:24 PM
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Re: What i discovered in my LLT build

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ccdoggy wrote: View Post
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?
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post #8 of 47 Old 04-23-07, 03:29 PM
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Re: What i discovered in my LLT build

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Ilkka wrote: View Post
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

Last edited by WillyD; 04-23-07 at 04:00 PM.
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post #9 of 47 Old 04-23-07, 03:59 PM Thread Starter
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Re: What i discovered in my LLT build

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.
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post #10 of 47 Old 04-23-07, 03:59 PM
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Re: What i discovered in my LLT build

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.

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