IB makeover.......... - Page 15 - Home Theater Forum and Systems - HomeTheaterShack.com

Old 04-14-07, 05:03 PM
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Collo

Join Date: Dec 2006
Location: Newcastle, Australia
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Re: IB makeover..........

Hi again Rodny,

I just had another look at your photos and see that the inside end of the ports is unflared. This would invalidate any test results because any chuffing you hear is probably coming from inside the port.

Thanks anyway
Collo
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Old 04-14-07, 05:32 PM Thread Starter
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Rodny

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Location: Millbrook AL
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Re: IB makeover..........

Quote:
collo wrote: View Post
Hi again Rodny,

I just had another look at your photos and see that the inside end of the ports is unflared. This would invalidate any test results because any chuffing you hear is probably coming from inside the port.

Thanks anyway
Collo
I did build the flare on the inside, so inside and out use a 1" 1/4 flare!!
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Old 04-14-07, 06:38 PM
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brucek

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Re: IB makeover..........

Quote:
I did build the flare on the inside, so inside and out use a 1" 1/4 flare!!
Aren't you adding length to the port with those flares and so lowering your tune?

Or did you calculate that into the original design.......

brucek
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Old 04-14-07, 07:08 PM
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Collo

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Re: IB makeover..........

Quote:
Rodny Alvarez wrote: View Post
I did build the flare on the inside, so inside and out use a 1" 1/4 flare!!
OK, that's great.

The voltage measurement is AC RMS, which is what you get with a multimeter on the AC volts setting.

It's OK to measure this at the amp.

When calculating the power, use the DC resistance seen by the amp. If the drivers are in series, this would be Re * 2, if they're in parallel it would be Re /2, (where Re is the value for one driver)

You would need to feed the sub a sine wave and slowly increase power until port noise is first detected, sitting close to the port.

I used the signal generator built into WinISD. You just have make sure you're getting a clean sine wave out of your PC

The frequencies I used in my testing were 20, 25, and 30 hz.
Since you mentioned that you heard some noise at 10hz, I would start there.

If you get a result, then move up in frequency by 5hz steps - ie 15, 20, 25, 30hz

Because of your low tune, as you move up in frequency, the port velocity will fall away. More power will be needed to get the velocity back up.

Also, port performance increases with frequency, requiring higher velocities for "chuffing", needing even more power.

Because of these two factors, you'll quickly get to the point where you can't add any more power. If you make 30hz, that would be fantastic, but I suspect that 20hz is about as far as you'll get!

regards
Collo
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Old 04-14-07, 07:23 PM
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Steve

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Re: IB makeover..........

I suspect his house will start complaining quite vocally before he can collect much useful data - it will be interesting to see how this turns out, good stuff
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Old 04-14-07, 07:26 PM Thread Starter
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Rodny

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Re: IB makeover..........

Quote:
collo wrote: View Post
When calculating the power, use the DC resistance seen by the amp. If the drivers are in series, this would be Re * 2, if they're in parallel it would be Re /2, (where Re is the value for one driver)
The subs are dual 4 ohm running in series to 8 ohms and then parallel to 4 ohm load.

Quote:
I used the signal generator built into WinISD. You just have make sure you're
getting a clean sine wave out of your PC
Can I use the REW or I need WinSD??
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Old 04-14-07, 07:32 PM Thread Starter
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Rodny

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Re: IB makeover..........

Quote:
brucek wrote: View Post
Aren't you adding length to the port with those flares and so lowering your tune?

Or did you calculate that into the original design.......

brucek
I cut the port to 33", the original design was 35", I measure the port after installing the flares and they are 34.5", its pretty close, I dont think 1/2" will make a difference!
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Old 04-14-07, 07:58 PM
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Collo

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Re: IB makeover..........

Quote:
Rodny Alvarez wrote: View Post
The subs are dual 4 ohm running in series to 8 ohms and then parallel to 4 ohm load.
A little detective work.....
This shot from the Sound Splinter page for the RLP-15

For the Dual 4 ohm driver, it shows the Re as 6.1 ohms. This would be the total dc resistance with the voice coils in series. Since you are running a pair of these in parallel, the value we need for our calculations is 6.1 / 2 = 3.05 ohms

Quote:
Can I use the REW or I need WinSD??
You can use the generator in REW
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Old 04-14-07, 11:09 PM
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brucek

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Re: IB makeover..........

Just thinking out loud...

I know for the purpose of INPUT POWER, WINISD is using RMS E^2/Re, where they're assuming that at some point the complex impedance of the drivers will be their DCR, (and that would be the near maximum power, so it's a decent assumption), but I suspect Rodnys impedance will have a wild ride at those various frequencies if you examine the impedance curve of his LLT shown below.

Qty 2 SS D4 drivers
10" ID vent, 35" long, two flares.
38 cu. ft box
11.29Hz tune.....

I added an electronics 1st order rolloff at 10Hz for these - a standard assumption I suppose.

IMPEDANCE CURVE.
Minimum impedance at ~12Hz. That's where the highest AC current will be.

AIR VELOCITY
Shows maximum velocity at ~10.5 Hz. The highest chuffing possibility I suppose.
I used 2500 watts for Input Power for this graph.
I had to go to Input Power of ~630 watts to get the velocity down to 17m/sec (=5% - 340m/sec)

EXCURSION
Again I used 2500 watts input power for this diagram. Somewhat over spec for excursion, but I guess he'd never be applying this much power.

Since the EP2500 is likely in bridge mode, one channel will be inverted across its positive terminal, so you'll be measuring a double rail voltage between the speaker terminals.

I suspect that amplifier would realistically produce ~500 watts per channel into 8 ohms, so it would be using about +100 DC volt rails. RMS of that, less the drop across the output stage of the amp, would yield a maximum of about 64 AC volt RMS capability. So 64^2/8 = 515 watts. Seems about right.

So, you have the theoretical AC voltage of 64 + 64 across the two bridged positive terminals. But since it's in bridge mode they likely have reduced the rails a bit so not to fry the thing, but anyway, be aware and careful when you are measuring not the short anything out.......

I guess you'll only be turning it up to the point where it chuffs........

brucek

edit: changed voltage to impedance..... shouldn't write stuff at night......
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Old 04-15-07, 12:22 AM
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Collo

Join Date: Dec 2006
Location: Newcastle, Australia
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Re: IB makeover..........

Hi Bruce,

I ran the idea of using the voltage measurement to determine input power past the WinISD people when I first started the experiments.

Janne replied... "Power means actually that sinusoidal RMS voltage of U=sqrt(Power*Re) is applied to the driver. This does not change with the impedance"

I seem to remember from my Electrical engineering days, that whilst impedence moves around with frequency, the power used remains resistive.

Looking at your estimate of velocity vs frequency, I would say we're probably only going to get a result for 10hz. I do have a range of figures in mind, but don't want to predudice any results by mentioning it just yet.
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