IB makeover.......... - Page 16 - Home Theater Forum and Systems - HomeTheaterShack.com

Old 04-15-07, 07:53 AM
Elite Shackster
brucek

Join Date: Apr 2006
Posts: 7,514
Re: IB makeover..........

Yeah, I do mean (and changed) that the impedance will be riding up and down as shown in the first diagram. Its lowest point is around 12Hz, so the current will be the greatest and so the applied power. The phase curve shows where the load becomes near purely resistive when it reaches 0 degrees. I think the power used will be close to the inverse of the impedance curve, will it not.

Quote:
Looking at your estimate of velocity vs frequency, I would say we're probably only going to get a result for 10hz.
The velocity sure spikes at that frequency. Do the flares allow a speed over the 5% to not create the chuffing noise?

brucek
brucek is offline

Old 04-15-07, 05:24 PM
Senior Shackster

Collo

Join Date: Dec 2006
Location: Newcastle, Australia
Posts: 284
Re: IB makeover..........

The science of inductive loads is a bit beyond me, so I defer to the experts on this one.

I do know that when a load contains a resistive and an inductive component, the voltage and current aren't exactly in phase.

If the power delivered to the driver followed the impedence graph, you would expect the SPL graph to do the same, yet this is not the case.

Since I'm using WinISD to do the analysis, and the voltage measurement method was given the OK by one of the WinISD authors, I'll use it.

----

Adding flares definitely allows you to use a higher velocity before chuffing occurs.

This is not as simple as saying a flare of x mm allows a velocity of 20 m/sec

You need to take into account port diameter, flare radius and frquency.

You can also allow a small amount of chuffing which is not heard due to the distance to the seating position and masking by content.

If you follow the link in my earlier posting, you'll see how this was discovered.
collo is offline
Old 04-15-07, 08:20 PM
Elite Shackster
brucek

Join Date: Apr 2006
Posts: 7,514
Re: IB makeover..........

Quote:
Since I'm using WinISD to do the analysis, and the voltage measurement method was given the OK by one of the WinISD authors, I'll use it.

Quote:
If the power delivered to the driver followed the impedance graph, you would expect the SPL graph to do the same, yet this is not the case.
Well, I think the fact that the SPL units being logarithmic (dB) have a lot to do with that. Doubling the applied power only nets a +3dB increase in SPL. Kinda smooths the SPL graph out in relation to large swings in power. You could increase the power from 500 watts to 1000 watts and the SPL graph would only show an increase (for example) from +113dB to +116dB.
But certainly the reactive components will store and release energy that can be reflected back to the load and result in heat being dissipated by the output stage of the amplifier itself. The power graph that WINISD provides is apparent power ( expressed in volt amps). This would be a combination of the RMS or real power dissipated in the resistive load (Re) plus the reactive power as a result of the inductance and capacitance of the driver. It would simply be the product of the current squared times the impedance over the frequency range.

brucek
brucek is offline
Old 04-16-07, 10:54 AM
Senior Shackster

Mark Seaton

Join Date: Jun 2006
Location: Chicago, IL
Posts: 107
Re: IB makeover..........

Quote:
brucek wrote: View Post
Yeah, I do mean (and changed) that the impedance will be riding up and down as shown in the first diagram. Its lowest point is around 12Hz, so the current will be the greatest and so the applied power. The phase curve shows where the load becomes near purely resistive when it reaches 0 degrees. I think the power used will be close to the inverse of the impedance curve, will it not.

brucek
Hi Bruce,

I wanted to jump in as this matter is one often confused. Despite common terminology and specifications, we drive speakers with Voltage, not power. Power ratings on amplifiers are defined by driving specific, resistive loads (nothing earth shattering here). Real electromechanical devices have impedances that vary with frequency. Nominal impedances are about as precise as a "2x4" is 2" x 4" .

You are correct that actual power dissipated in the voice coil is inversely proportional to the impedance curve for a constant Voltage input. The feedback from the creaters of WinISD might have been from confusion of terms. "Power" input could be, and by their description might be, defined by Voltage into the Re or Dcr of the driver. Different programs handle input signal a little differently in how you specify it, but the results should be the same when using the same modeled Voltage.

In short, if you want to correlate the driving signal to a theoretical vent velocity, you want to measure RMS Voltage. Many meters are not True RMS meters, and you will have less confusion in calibrating the Voltage at 60Hz with the meter and then using the frequency response measurements of the electrical signal to extrapolate from there. In taking such measurements, do be sure to include some casual observation to correlate what you are modeling and observing. For example, from the above model you would expect to see ~1/2 the excursion at the tuning frequency as at ~20Hz.

Mark Seaton
"Make no little plans; they have no magic to stir men's blood..." - Daniel H. Burnham
Mark Seaton is offline
Old 04-16-07, 07:51 PM Thread Starter
Senior Shackster
Platinum Supporter

Rodny

Join Date: Apr 2006
Location: Millbrook AL
Posts: 826
Re: IB makeover..........

.....................
Rodny Alvarez is offline
Old 04-17-07, 06:20 AM
Elite Shackster
brucek

Join Date: Apr 2006
Posts: 7,514
Re: IB makeover..........

Sorry Rodny. I didn't mean to hijack your thread with my babbling....
brucek is offline
Old 04-17-07, 08:06 PM Thread Starter
Senior Shackster
Platinum Supporter

Rodny

Join Date: Apr 2006
Location: Millbrook AL
Posts: 826
Re: IB makeover..........

Quote:
brucek wrote: View Post
Sorry Rodny. I didn't mean to hijack your thread with my babbling....
Its all good!!! As long as somebody will benefit from it!
Rodny Alvarez is offline
Old 04-24-07, 07:54 AM Thread Starter
Senior Shackster
Platinum Supporter

Rodny

Join Date: Apr 2006
Location: Millbrook AL
Posts: 826
Re: IB makeover..........

Collo and I conducted some testing via PM's to save cluttering up this thread. It was concluded that the airspeed was too low to account for the noises heard at 10hz. The most likely culprit was driver noise.

Rodny Alvarez is offline
Old 04-24-07, 04:44 PM
Elite Shackster
Chrisbee

Join Date: Apr 2006
Posts: 1,018
Re: IB makeover..........

Quote:
Rodny Alvarez wrote: View Post
Collo and I conducted some testing via PM's to save cluttering up this thread. It was concluded that the airspeed was too low to account for the noises heard at 10hz. The most likely culprit was driver noise.
Hi Rodny

What sort of levels dB(C) were you running at to hear noise at 10hz?

Was this on sinewaves? I'm wondering if the signal you were feeding it had heavy distortion which produced an audible harmonic.

I ran my IB array at 10Hz up to nearly 100dB(C) (uncorrected RS meter) using REW in the "Frequency follows cursor" mode.

The IB was completely silent though the room was shaking violently. I stopped at about 1/4" cone movement because I feared the windows would break if I pushed it any harder.

Are you sure your box or something else isn't vibrating in sympathy somewhere?
Chrisbee is offline
Old 04-24-07, 07:23 PM Thread Starter
Senior Shackster
Platinum Supporter

Rodny

Join Date: Apr 2006
Location: Millbrook AL
Posts: 826
Re: IB makeover..........

Quote:
Chrisbee wrote: View Post
Hi Rodny

What sort of levels dB(C) were you running at to hear noise at 10hz?

Was this on sinewaves? I'm wondering if the signal you were feeding it had heavy distortion which produced an audible harmonic.

I ran my IB array at 10Hz up to nearly 100dB(C) (uncorrected RS meter) using REW in the "Frequency follows cursor" mode.

The IB was completely silent though the room was shaking violently. I stopped at about 1/4" cone movement because I feared the windows would break if I pushed it any harder.

Are you sure your box or something else isn't vibrating in sympathy somewhere?
It was about 90dbs with only one side, the signal was from the REW sine waves, I was using the RS meter, and yes the house made some real loud noises:holycow:

I went back and listen to the subs at 10Hz and one of the subs its making a noise, its like the aluminum cone rubbing on something, if I have time this weekend I will check all the subs, it could be a speaker wire behind the sub.
Rodny Alvarez is offline

 Bookmarks

 Tags ib , makeover

Message:
Options

## Register Now

Random Question
Random Question #2

User Name:
 PLEASE READ BELOW PRIOR TO ENTERING AN EMAIL ADDRESS! ATTENTION! YOU MUST ACTIVATE YOUR ACCOUNT!Activation requires you reply to an email we will send you after you register... if you do not reply to this email, you will not be able to view certain areas of the forum or certain images... nor will you be able download software. AN INVALID EMAIL ADDRESS WILL CAUSE YOUR ACCOUNT TO BE DELETED! See our banned email list here: Banned Email List We DO NOT respond to spamcop, boxtrapper and spamblocker emails... please add @hometheatershack DOT com to your whitelist prior to registering or you will get nowhere on your registration. Email Address:
OR

## Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.