Lilmike's Cinema F-20 - Page 46

I have certainly loved my F-20 as is.
With my amp and it being able to do the boosts that I listed above without a very hard cutoff at say 15hz or so is there really any thing I can even try without other equipment?
Such as moving the high pass down without adding boosts.
I guess another problem is my failure to understand how to model this kind of stuff.
Seems I just have more and more reading to do
Any suggestions for what to understand would be great.
Thanks for the response.. If i come up with any specific questions hopefully won't mind me asking, but I understand that currently the things I am asking are just way to

^^^ x10. You can certainly boost and see how you think it sounds, I will just say in my experience with the f-20, I didnt like it, and went right back to running it with a highpass and no boost whatsoever. Keep in mind the horn will amplify any distortion you may be getting into by boosting below the corner, and the worst scenario is you may not be able to hear the driver overexcurting until it is too late.

What driver were you using?
Thanks for the response, appreciate the personal experience.

As for overexcursion is there any other factors at play besides the bass boost giving it more power at the lower frequencies than anywhere else. I guess what I mean is, if voltage was the same at all frequencies wheres the greatest excursion? 19hz?

edit: just realized. Is there any difference if I were to boost the sub level (the equivalent of what the bass boost on the amp would be) on my AVR and measure THD at various sine waves that way? I'll post my results later tonight.
Edited by Shinyav - 9/21/12 at 7:39am

I measured my F-20's in my room and reached 110 dBs at 10hz with 10%THD with 4 of them. They reached 125 dBs at 20hz with the same THD. I have 6 sealed subs now and I reach 124 dBs at 10hz and 125 dBs at 20hz with the same THD just to compare. The 4 F-20's cost $1000 and the 6 sealed cost $3000. If you want flatter and louder in the lower regions you need to spend the money. The F-20's are fantastic for what they are.

MK and I had the f-20's around the same time. He was running them with the MFW's in them and had 4, I was running them with tempest x-2's in them and only had two.

Bottom line, as MK already pointed out, if you want more below 20hz, you'll have to go elsewhere.

I really do fully appreciate that for any real output under 20 someone would need to look elsewhere. Currently I am happy with my sub. Just want to mess around with it. Anyways, I figured id post some THD measurement.

I am a bit confused exactly on how to relate some of these numbers so any help would be appreciated. This is with my AVR calibrated for my sub to be at reference and my volume at 0db. I adjusted the rms in REW to increase volume at certain frequencies. However I don't really know how much harder I can push my f-20. As i said its in a small room, 1350cuft. the gain on my amp is just about 35degrees from minimum and my AVR still sets the sub at -6.5db for reference. I would love to measure the voltage going to the sub, but its side is sealed with the amp.. is there anyway I could run wires out the side and measure without having to take the plate amp on and off a lot? or anyone have suggestions for a one time list of measurements to take so i only have to do it once and can extrapolate from there?
anyways here is some of the graphs.. as I said. I don't really know how hard I am pushing the driver.
These were all taken at the main listening point.

rms -5 13hz


rms -5 15hz


rms -10 13hz


rms -10 15hz


rms -10 18hz


rms -10 20hz


rms -10 30hz


rms -20 13hz


rms -20 15hz


rms -20 18hz


rms -20 20hz


rms -20 30hz


edit: rms -5 with sub +5 hot on AVR 15hz

Edited by Shinyav - 9/23/12 at 9:44am

Good stuff, now here's how I do it:

Use the RTA Function, set Mode to Spectrum, FFT Length to 131072, Averages to 4, Window to Hann.

Use the onboard tone generator in REW, fire up a sinewave. Set the THD calculator on (It'll open up a THD tab). Make sure the record button is on.

Increase the volume until you are around 5%-10% THD. Hear what it sounds like at different distortion levels and for different frequencies, set an audibility threshold for yourself (how much THD can you stand?). Make sure you have a voltmeter across the speaker terminals to monitor power going in, to make sure you don't fry the drivers. The difference between feeding a box 250W and 500W is only 3dB....

I think you are perfectly safe below 20V in an F20. To measure voltage, it will be most accurate with a voltmeter at 60Hz.

JSS

If I attach a wire to leads I can use a voltmeter to measure it when its also powering the driver? since I am using a plate amp I might have to run to extra wires out of the cab to make the measurements when its in use.
Edit: seems this is correct, is very small wires ok for this purpose? I guess I am thinking so its ones that are easy to run out the side and still have the plate amp seal 100%

does the 500watt rms on the reference HF and only using a 300watt amp have any effect on how hard I can push it?

Edit: a little more looking seems the bash 300 can put out more than 20v so I will have to monitor it. does the higher rms on the HF protect from thermal problems?
Edited by Shinyav - 9/21/12 at 9:26pm

well according to this my "reckless" messing around was only about 6volts.

edit: notice an air leak I never noticed before, only at high voltage 15hz, going to reseal everything tomorrow. No results for a bit.

edit: everything is put back together ready to go for some testing tonight. Anyone that has the numbers for horn resp available could you run a couple models at various volts for a reference HF. Or provide me all the numbers needed in hornresp. I have been trying to figure it out.. but it's not going great.
Edited by Shinyav - 9/22/12 at 10:34am

Alright everything is sealed perfect. I think I gained a DB so I might have had a small leak all along.

Pretty late here so gonna work on some quieter projects.

Here is an outline of my testing plans.. with also some questions of course.

• 20hz at 18volts, simply to find what the max spl potentially is.
  
• Then 15hz at the highest THD I find acceptable, maximum of 18volts across the driver.
  
• Then find the amount of boost(using my AVRS sub level setting) needed at all the whole frequencies between 10hz and 19hz that either reach my accepted
  level of THD or reach 18volts going to the driver.
  
• Find a pair of resistors that give my bash 300 an amount of boost roughly around that level erroring on the low side.

Two questions:

#1: Since I will be running a lot of sign waves. How long is safe to run them before thermal problems come into play? Any break in between tests? etc.
The driver is rated at 500watts RMS and I am using a BASH 300.

#2: I will be using Audyssey afterwards. The more I think about/read about this seems like it could be potentially a problem.
The things I think I need to figure out is exactly how much boost Audyssey can/will add if it recognizes my sub as being able to go lower.

Thanks again for all your help. Hopefully I am documenting this somewhat usefully so I am not just spamming this thread

Run Audyssey first, as it will provide a bass boost in and of itself, and measure then at different drive levels. It may be just right, or you may need a highpass, depending on how much distortion you can stand. Only one way to find out....

With less than 20V going into the driver, you can do sinewave testing for a few minutes at a time without fear.

20V into the F20 will be quite loud if you thought 6V was. It is amazing how efficient these boxes are.

JSS

Decided to go with 20volts as a limit.

Alright data time.

Going to just post numbers instead of images, If anyone wants the raw REW files or images of anything of these let me know.

with 20volts at 20hz I hit 118db at my listening point with a THD of 4%
With some testing I was able to at least get an idea of what THD sounded like. I settled on 10% being my threshold for acceptable.
My other limit was 20volts.


My amp is currently setup for a fc of 17.7 with a q of 1. (stock bash 300)
This is with a reference HF.

131072-point spectrum using Hann window and 4 averages
I set rew rms to -3 and adjusted with my AVR sub volume. The AVR has the sub set to reference volume, also measured myself. For the title of each measurement the avr volume is how much boost I needed to give the sub using the AVR to reach the voltage listed. My assumption is reference in a movie would be rms -3 in rew and +3 on my avr.

19hz -3rms +5avr 20v
118db 5%thd

18hz -3rms +6avr 20v
116db 8%thd

17hz -3rms +6.5 20v
112db 8%thd

16hz -3rms +7avr 20v
110db 7%thd

15hz -3rms +8avr 20v
109db 9%thd

14hz -3rms +8avr 17v
105db 9.5%thd

13hz -3rms +8.5 16v
104db 8%thd
any higher at this frequency or the following produced a very weird sound from within the sub, perhaps I was reaching some limit, however as far as I understand excursion should only go down.

12hz -3rms +8.5 14v
103db 7%thd

11hz -3rms +8.5 12v
101db 8%thd

10hz -3rms +8.5 8v
99db 5.5%thd



Using this data it seems like a EQ i would like is something around
19hz +2
18hz +3
17hz +3.5
16hz +4
15hz +5
14hz +5
13hz +5.5
12hz +5.5
11hz +5.5
10hz +5.5

Going to think about this a little more, seems like anything under 15hz maybe even 16 was very hard to notice. as I am still thinking high pass filter, but bumping it down to ~15hz instead of 17.7 and having a slight boost between 19 and 16.

Edit: I think I finally got Hornresp right. this look correct?

this is the specs for reference HF http://www.parts-express.com/pdf/295-468s.pdf



If that is correct, 20volts is dead on as the limit before xmax at 19hz.

however, anything over 23hz I could do 40volts O_O

Is there anyway to figure out thermal limits with hornresp or anything else? Or do I simply rely on the RMS listed for the driver and my amps potential wattage. I tried googling this question in multiple ways but have ended up without much info.
for example if I were to put 40volts into it at 70hz I could get 125db.. but that seems like a lot of power going into it.

Thanks again.
Edited by Shinyav - 9/23/12 at 2:31pm

Nope I still have two unpainted muhaha. I think I may have built mine before yours?

Great job finding out your system's (and your hearing) limits.

I still think you should run audyssey and see what it does to your response curve is with it's boost. It may be just right.

Also, with REW on -3, and your AVR on 0, you are still approx 4dB short of reference for the LFE channel. REW sends a L/R signal. If you use bass management, that's 111dB at 0dB volume (105dB from left, + 105dB from right). LFE channel (if set up correctly) is 115dB at 0dB volume.

I still use the Spectrum function in REW, but use the -0.5dB LFE test tones in the Soho54 Audio test DVD. It is a torture test. The only thing tougher on a sub would be -0.5dB tones in all 6 or 8 channels simultaneously sent to the sub, which would be around or over 120dB in a 7.1 system. That is the absolute worst case scenario, and I am not aware of any film soundtrack that does this (Tron:Legacy comes close, with L+R clipped at -2dBFS with strong LFE as well).

I am very impressed with how low the F20 will play cleanly indoors. the most amazing thing: 20V is only [GASP] 100Watts. Blasphemy, I tell you.

Even better: My THTs never see more than 15V each (and that's because of boost below tuning). That's a whole 56W, but I listen at -10dBRef. I would be running 560W into them at reference, which I cannot do, I'd have to disable the below-tuning boost to get there, and prob feed them 25V max. Horns can be pretty amazing, but have their limitations.

I have an unfinished THT that has been built for over 18 months....

JSS

Great post thank you so much for the help. This one has clarified another set of issues.

Here is Audyssey on and off. It seems to really respect the f3 of the sub for when to stop boosting.


Hmm I had rew at -3 my avr at 0db but then had my subs level between +5 and +8.5. I guess it doesnt really matter if I go as loud as possible as it will be EQed down with Audyssey.

I had guesses on the rolloff/boost i wished to apply but I forgot to factor in what was already being done by the default resistors.

-8.855 10
-7.088 11
-5.512 12
-4.121 13
-2.915 14
-1.893 15
-1.051 16
-0.379 17
0.141 18
0.529 19
0.808 20

That is what they currently provide.

So the end goal of messing around with this second order high pass calc will be something like...

-3.355 10hz
-1.588 11hz
-0.012 12hz
1.379 13hz
2.085 14hz
3.107 15hz
3.621 16hz
3.121 17hz
3.141 18hz
2.529 19hz
0.808 20hz

Any thoughts from anyone on these? I am gonna think about it for a couple days in case anything is glaringly wrong and then will go pick up some resistors.
Edit: won't be able to get anywhere near this precise of a boost with just switching resistors. The problem being the boost leaking over into 20+ hz The boosts on the plate amp are very wide.
16hz is the frequency I am going to focus on, making my goal to have the biggest boost of 16hz compared to 20hz.

Might be a good time to get into a miniDSP now that I don't feel so overwhelmed by it after learning so much. thanks maxmercy.



Hornresp question: When I look at diaphragm displacement it goes down after 19hz. However, if I run maximum spl with 100watts and 14mm max displacement it shows it displacement limited below 21hz at lower spl than the diaphragm displacement was shown at. I am having a hard time understanding this relationship. EDIT: Nevermind I think I was just confused.
Edited by Shinyav - 9/24/12 at 4:35pm

I see you are running a 2012 model receiver. Mine is a 2009 model, and has the infamous Audyssey boost (I use it to my advantage). I contacted Chris Kyriakis at Audyssey about the problem and he said there would eventually be a solution. Looks like they found one, as many ported store-bought subs would cry for mercy with a 9dB boost below tuning.

JSS

Yea found some information about that but all seemed to disappear as the post dates got closer to now.
I am curious what audyssey will do with my sub once it has a bit more dbs down low. Ideally it will recognize the same F3 as it does now. Between 17 and 18 I should still have a 4db drop... I wonder what it looks like at 75db though which is what audyssey will look at.

I am going to use these for my resistors so I should be able to make fc and boost changes pretty easily.

http://www.digikey.com/scripts/DKSearch/dksus.dll?Detail&itemSeq=120045341&uq=634841176000882237
http://www.digikey.com/scripts/DKSearch/dksus.dll?Detail&itemSeq=120045581&uq=634841176000882237
Edited by Shinyav - 9/24/12 at 9:28pm

Its late and the stress of soldering has made me very tired.... lol...
but I got them done..

However, the science is in!




-3rms in rew, as well as +4 hot in avr. 115db pink noise. aud off only used for channel level calibration.

Much more results in the next few days.

Next thing I will be doing is a full run of Audyssey to see what it does with this. My hope is it will EQ down the additional boost that spilled over into the 20+hz.
Edited by Shinyav - 9/28/12 at 7:35am

while i understand wanting to know the science and squeeze every ounce of performance out of the sub, this makes me laugh. I plugged in my sub and ran audyssey and went on to other things. music and movies sound awesome and are far more dynamic than I've ever experienced in past setups. my friends bow down in admiration. why mess with it further?

Well the graph says it all. You are close to -20db's across the 20hz to 10hz range, for a reason. Not much you can do with that. The audible differences you will here will be increases in the harmonics, mainly 2nd and third that will be in the subs passband. Ive said all this before. You are flirting with disaster if you are trying to boost something that rolls off that fast.

Same reason anyone messes around with whatever there hobby is. It was all fun to me and an enjoyable experience.
I do completely agree with your sentiments though.

Please don't get me wrong I really do appreciate/respect all the input and things you have said.
I do have some questions about what your saying though.
I made sure to keep thd below 10% which I found to be a hard to notice amount for myself.
As for the flirting with disaster. If I keep the voltage under 20v according to hornresp I should not reach xmax at any time. So if there is another factor I need to consider I would like to know about it.
I plan on upgrading in the near future and all of this learning is simply to be safe and have an understand with more expensive equipment.

Yes my output at 10hz is unnoticeable but the 16+ stuff has definitely picked up which at least dips my toes in subharmonics.

Build 3 more and cut all the humps over 10Hz. Viola! flat, loud And clean.

Probably wont build anymore f-20s. However, I will keep my one for a long long time.

Here's what Audyssey decided to do with my sub.

Everything is within my specs except for the bump around 20hz, I had some headroom around there also though, so what I am going to do now is use the soho -0.5db lfe signal to the sub at every hertz and check out what voltage I am getting.


LFE -.5db (soho54 test tones simulated in rew with -3dbfs and +3.5db sub gain)


at every frequency during this run voltage is below 20, but just.
Edited by Shinyav - 9/28/12 at 10:14pm

I am kicking around the idea of building an F-20 and using the spare MFW-15 driver that I have, as opposed to buying another amp for my MFW-15. I wonder how these two would compare? I would imagine that the F-20 would have a good bit more output, but I would also imagine that the MFW-15 will go lower, right?

One last question, would it be possible to power the F-20 with a Yung 300 watt plate amp? I will eventually purchase a Behringer iNuke 3000dsp, but since I already have the Yung 300 watt plate amp, I figured that I could get by with it for the time being.


Thanks in advanced for any helpful advice and/or tips!

The 300 watt amp is plenty.
As for the comparison read trough the thread. There are several posts with some comparisons of the MFW in different boxes.
I don't have time to find it now but if you haven't found it later on I will look for it.

That freq response is the envy of many here from 20-60Hz, and you have kept voltage levels down below 20V everywhere. You have done well. I'd call it done, until you build another.

JSS

Horn length determines the low corner, not the driver. The 300W amp is plenty.

I certainly agree. Pretty sure I am done messing around a bit for now. Learned a lot also got a little bit more extension down to the high teens while maintaining reference above 20hz, which at least in my opinion is noticeable in a few demo scenes I have watched at least a dozen times.

Yes I am completely aware of that. I was just wondering how the two (MFW-15 vs F-20) would sound compared to each other. My assumptions are that the MFW-15 would go down quite a bit lower than the F-20, but, the F-20 will have substantially more output. Is my assumption correct? I broke down and ordered a Yung 300 watt plate amp that I plan on building a small enclosure for, then using it to power my amp-less MFW-15. I got a good deal on it and figured that if it doesn't end up sounding so good with my MFW-15 then I can build an F-20 and use this amp to power it.