Lilmike's Cinema F-20 - Page 16 - AVS Forum
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post #451 of 1732 Old 05-30-2011, 02:02 PM
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Finally got the two F-20s all installed... and left the rca to xlr adapters 90 miles away. Off to the guitar shop to get two replacements. Thanks for the info beast. This morning I had to wrestle those massive f-20s off the truck by myself. Made a makeshift ramp. My neighbor took pity on me and helped me get them inside thankfully. Running them unfinished for now and will eventually veneer them I think.
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post #452 of 1732 Old 05-30-2011, 02:54 PM
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that is a neat little program. it doesn't sound like it tries every combination, but works down from large panels to the small panels. that's probably just fine for something like this.

btw, for printing to pdf (once installed, it literally just shows as another printer, but kicks out a pdf file), i have had very good results with primopdf

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post #453 of 1732 Old 05-30-2011, 03:23 PM
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well finally got to test stuff... Now to move around the amp as I'm getting ground loop hum in the subs. Subs sound good though
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post #454 of 1732 Old 05-30-2011, 04:58 PM
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what is everyone crossing over their F-20 on their AVR at? 80, 100 or 120hz? Oh and got rid of the ground loop hum
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post #455 of 1732 Old 05-30-2011, 05:35 PM
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Quote:
Originally Posted by blackoper View Post
what is everyone crossing over their F-20 on their AVR at? 80, 100 or 120hz? Oh and got rid of the ground loop hum
Depends on the rest of your speaker system. Does your AVR have an auto setup?
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post #456 of 1732 Old 05-30-2011, 05:42 PM
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Quote:
Originally Posted by blackoper View Post
what is everyone crossing over their F-20 on their AVR at? 80, 100 or 120hz? Oh and got rid of the ground loop hum
You really don't want to cross this much above 95hz, due to the spike at 100.
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post #457 of 1732 Old 05-30-2011, 05:57 PM
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no my avr is old so I've got no auto setup of anything heh. That's the next thing to upgrade after building new LCR set of ewaves. Ok well I have it crossed over at 80 right now. The scene in ironman 2 where he jumps out of the plane with fireworks going was impressive! When he ignited his boots the whole house shook.

I need to get an spl meter and finish building a test microphone for REW so I can get these dialed in
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post #458 of 1732 Old 05-30-2011, 07:53 PM
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Originally Posted by stgdz View Post

You really don't want to cross this much above 95hz, due to the spike at 100.

Good call, that would be quite overwhelming.
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post #459 of 1732 Old 05-30-2011, 09:14 PM
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Pics of the installed f-20s. I will start moving them around to find optimal positions when I get a chance. Also will probably end up veneering them.



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post #460 of 1732 Old 05-31-2011, 06:29 AM
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well finally got to test stuff... Now to move around the amp as I'm getting ground loop hum in the subs. Subs sound good though

how does moving the amp around solve this?

(European models do not accept banana plugs.)

 

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post #461 of 1732 Old 05-31-2011, 06:35 AM
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how does moving the amp around solve this?

Ground loop hum is caused by components going to different grounds and causing a difference in base ground level power and a slight current feeds back into the grounds. Can also be caused by a delay between the grounds of the components involved (ground takes a different/longer path). I moved the computer, the receiver, the minidsp and the amp onto the same outlet and the hum disappeared. When I first hooked things up I was using a completely different circuit for the amp/minidsp. It looks like the one circuit should work fine as nothing has tripped yet
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post #462 of 1732 Old 05-31-2011, 06:54 AM
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oh yea, got that, thought you meant the physical location (not plug) was causing you issues. I was going to say, man, wish my hum was that easy to solve have pretty much gotten mine to dissappear, I have to shove my head into the mouth to hear it, but im still working on it

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post #463 of 1732 Old 05-31-2011, 07:15 AM
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Quote:
Originally Posted by stgdz View Post

You really don't want to cross this much above 95hz, due to the spike at 100.

Realize this is only the crossover from the mains not the LFE channel content which runs up to 120hz. The spike at 100hz may need some EQ.
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post #464 of 1732 Old 05-31-2011, 04:15 PM
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that is one of the funniest pics posted on avs in a while.

can you tell a difference with the f-20's added to the mains?


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post #465 of 1732 Old 05-31-2011, 05:42 PM
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Quote:
Originally Posted by blackoper View Post

what is everyone crossing over their F-20 on their AVR at? 80, 100 or 120hz? Oh and got rid of the ground loop hum

Bass horns are pretty much perfection for two octaves so 80Hz or lower.

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post #466 of 1732 Old 05-31-2011, 05:44 PM
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I believe Im about to order 4 MFW-15s and build 4 F-20s in the fall

I have some Velodyne SC-1250 amps unused that would make for a perfect F-20 amp. I have needed 20-80Hz subs anyways. My < 20Hz performance will be a DIY thigpen rotrary sub at some point but until then Its LMS5400s (2 right now, getting 2 more later).

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post #467 of 1732 Old 05-31-2011, 05:49 PM
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I guess I should ask what is the max SPL, max Watts for one F-20 at 30Hz?

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The more I look at this thread, the more I see the genius of this build. I should totally have built this in the first place.
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post #469 of 1732 Old 05-31-2011, 05:52 PM
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Quote:
Originally Posted by penngray View Post

I guess I should ask what is the max SPL, max Watts for one F-20 at 30Hz?

That top sweep was done at max power (~250 to 300watts?), lilmike says he's not sure if the compression is from the speaker's thermal limit or the amp.

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post #470 of 1732 Old 05-31-2011, 05:59 PM - Thread Starter
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Originally Posted by stgdz View Post

You really don't want to cross this much above 95hz, due to the spike at 100.

I'd really suggest that you measure the response in your room before worrying about crossover points or EQ.

See what your room gives you, and more importantly - see what it takes away. For instance, while it is about the best I can do (within the limits of the architectural review committee) my current room/placement is not so good. I am ruler-flat from 15 to 50, but I have a huge null between 50 and 80 Hz. Yeah, there is a bit of content there, and I do miss it.

If I only had some more capable mains......they're on the list....just a few items down from the top....

Experience says that I can also help the response considerably with a second sub, but I've not had the chance to get that design finalized either.
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post #471 of 1732 Old 05-31-2011, 06:13 PM - Thread Starter
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I guess I should ask what is the max SPL, max Watts for one F-20 at 30Hz?

You're thermally limited. The coil will probably fry before excursion becomes an issue.

Max watts for music, movies, or for sine waves so you can post plots on the interwebz? Long term thermal limit is 225 watts, and I am sure that this is conservative. I just don't know how conservative.

Top sweep was +25 dB from 2.00 volts (1 watt into 4 ohms), so I ran out of amp at 75 watts over the "rated" thermal limit of the driver. There was no complaining, even with a 10 Hz sine wave. The model suggests that there might be a driver complaint at around 19 Hz, but we did not hear anything. The compression in the plot could have been due to a lot of things, I did not let the driver rest between sweeps other than to reset the level and go. There was probably less than a minute between sweeps, so I am sure the coil was warming up. I know I was out of amp, 25 dB of gain is ~316 watts by my math. I'm sure the amp was near its limits if not entirely past them at this point, it is only a 300 watt amp. Also - BL drops precipitously once the coil leaves the gap, so SPL drops too. I'm sure that this was part of what we saw.

I've heard that people have used 500 watt amps with these drivers, but I have not tried that. I have no doubt I'd fry the coil running sine wave tests at high levels though, cause I have in the past. Double the thermal limit is simply that, and if all that power is applied at an excursion minima, the coil gets hot plenty quickly and can't cool itself off.

Music is one thing. Movies are more extreme, but sine wave testing is simply brutal.
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post #472 of 1732 Old 05-31-2011, 06:52 PM
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technical question: why model with a "par" (parabolic) horn shape when you have a "con" (conical) horn shape here?

penn, as you know the power is an inverse function of the impedance, so if you hit the driver with a big sine wave at resonance (an impedance peak) it will consume, and be required to dissipate, very little power. if you hit it at an impedance minimum, then it will consume much more power and have to dissipate it. this is why having a low impendance dip can cause a problem...it sucks too much power out of the amp and/or cooks the driver.

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post #473 of 1732 Old 05-31-2011, 06:58 PM
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"what is the max SPL, max Watts for one F-20 at 30Hz?"

that is tough to answer directly.

my very rough guesstimate is something like this:



red is excursion limited, black is power limited.

at 30hz, between this and properly powered lms 18, i think it would be a wash. this is bigger and less expensive. the lms 18 give you smaller and more depth. all other things equal, most folks report that the bigger drivers and/or horns deliver something that doesn't show up in traditional distortion plots as a more lifelike/effortless reproduction. i've been digging around in order to try to find out what is going on, but at last, i haven't found it (yet).
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post #474 of 1732 Old 05-31-2011, 07:05 PM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

technical question: why model with a "par" (parabolic) horn shape when you have a "con" (conical) horn shape here?

Two parallel sides is not a conical flare.

Conical flares expand in both the X and y planes - there are no parallel sides. This is harder to build and fold than a parabolic flare, which only expands in one plane, and is constant in the other - like an angled board in a box with parallel sides, which is what I usually build.

Admittedly, the differences are small, especially with the slow flare rates used in bass tapped horns. There is a difference though, and in some cases it matters.
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post #475 of 1732 Old 05-31-2011, 07:20 PM
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maybe it is late and maybe my recall of geometry is a little off, but a horn with a constant expansion rate is a conical horn. a horn with an increasing expansion rate is in the family of exponential flare.

the simple test for a cone is if doubling the distance along the path results in four times the cross sectional areas, you have a cone. if it is greater than that you have an exponential, if it is less than that you have something else.

because the waveforms are 'large' relative to the cross sectional area in bass horns, the only consideration for determining the horn type is the rate of cross sectional expansion.

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post #476 of 1732 Old 05-31-2011, 08:12 PM - Thread Starter
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maybe it is late and maybe my recall of geometry is a little off, but a horn with a constant expansion rate is a conical horn. a horn with an increasing expansion rate is in the family of exponential flare.

the simple test for a cone is if doubling the distance along the path results in four times the cross sectional areas, you have a cone. if it is greater than that you have an exponential, if it is less than that you have something else.

because the waveforms are 'large' relative to the cross sectional area in bass horns, the only consideration for determining the horn type is the rate of cross sectional expansion.

Here is one answer.

Here is another discussion.
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post #477 of 1732 Old 05-31-2011, 08:52 PM
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that is one of the funniest pics posted on avs in a while.

can you tell a difference with the f-20's added to the mains?

i'll be upgrading the mains here shortly The whole theater area is temporary while I build out the room it's all going to go in.
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post #478 of 1732 Old 05-31-2011, 09:02 PM
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lilmike, mcbean says that for horns with slow flare rates, it doesn't matter which model one chooses as they are essentially the same in the are of the expanding flare, so we are aguing over nothing...my bad.

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post #479 of 1732 Old 05-31-2011, 09:10 PM
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"i'll be upgrading the mains here shortly"

;-) you are definitely making some big upgrades.

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post #480 of 1732 Old 05-31-2011, 09:30 PM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

lilmike, mcbean says that for horns with slow flare rates, it doesn't matter which model one chooses as they are essentially the same in the are of the expanding flare, so we are aguing over nothing...my bad.

Who was arguing?

No worries.

I choose to model as accurately as I can, and the PAR flare is a better fit to what I build. I have done the math to verify this, I use the PAR flare as implemented in Hornresp as a result.
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