Sorry if this is a stupid question (I sort of think it is).
I'm now designing a simple WTW speaker. After your valuable help, I've been able to use nearfield + groundplane measurements to get the exact value for BSC, I've minimised reflections, and I'm feeling very confident in my new design.
That is... until I considered the following.
I'm using a pair of Focal 5N421 mid-woofers and a Neo3 PDR tweeter.
The way I measured the drivers was the following:
1) Mic in front of the tweeter.
2) Connect amp to tweeter; measure freq. response.
3) Without changing volume, measure freq. response of upper woofer.
4) Without changing volume, measure freq. response of lower woofer.
5) Without changing volume, measure freq. response of the whole speaker.
Now, I've properly calibrated the Z distance in LSPCad, and everything matches.
But, my question is:
Since I measured each speaker individually, wouldn't that mean that, when connected in series I shouldn't get any gain whatsoever?
As it is, LSPCad is telling me I'm gaining 6 dB from connecting both speakers in series. I assume that, since I measured individually each driver, there's no way for LSPCad to know about this.
Then again, I have compared my measurement of both upper and lower woofers with the simulation of LSPCad. And they are both the same in magnitude!
Is this OK? Can I expect +6dB when I connect woofers in series? I thought this was the case with parallel drivers.
Here's the LSPCad screen I'm getting... thanks for your help!
I'm now designing a simple WTW speaker. After your valuable help, I've been able to use nearfield + groundplane measurements to get the exact value for BSC, I've minimised reflections, and I'm feeling very confident in my new design.
That is... until I considered the following.
I'm using a pair of Focal 5N421 mid-woofers and a Neo3 PDR tweeter.
The way I measured the drivers was the following:
1) Mic in front of the tweeter.
2) Connect amp to tweeter; measure freq. response.
3) Without changing volume, measure freq. response of upper woofer.
4) Without changing volume, measure freq. response of lower woofer.
5) Without changing volume, measure freq. response of the whole speaker.
Now, I've properly calibrated the Z distance in LSPCad, and everything matches.
But, my question is:
Since I measured each speaker individually, wouldn't that mean that, when connected in series I shouldn't get any gain whatsoever?
As it is, LSPCad is telling me I'm gaining 6 dB from connecting both speakers in series. I assume that, since I measured individually each driver, there's no way for LSPCad to know about this.
Then again, I have compared my measurement of both upper and lower woofers with the simulation of LSPCad. And they are both the same in magnitude!
Is this OK? Can I expect +6dB when I connect woofers in series? I thought this was the case with parallel drivers.
Here's the LSPCad screen I'm getting... thanks for your help!
Attachments
I break the problem into the acoustical (efficiency) gain and the impedance sensitivity difference.
Consider that for two drivers connected in series you have doubled the cone area so the acoustical improvement is +3 dB. But you have doubled the impedance (say 8 ohms to 16 ohms for 8 ohms drivers) so that the sensitivity difference is -3 dB. The net improvement is the summation of the acoustical and sensitivity which is +3 -3 = 0 dB change.
For parallel drivers the acosutical improvement is +3 dB (doubled cone area) while the impedance is halved so that the impedance sensitivity change is +3 dB. The total is +3 +3 = 6 dB.
The usual caveat is that their sound fields must overlap. This usually means that their center to center spacing of the drivers must be less than one wavelength at their highest freqeuncy of operation.
Consider that for two drivers connected in series you have doubled the cone area so the acoustical improvement is +3 dB. But you have doubled the impedance (say 8 ohms to 16 ohms for 8 ohms drivers) so that the sensitivity difference is -3 dB. The net improvement is the summation of the acoustical and sensitivity which is +3 -3 = 0 dB change.
For parallel drivers the acosutical improvement is +3 dB (doubled cone area) while the impedance is halved so that the impedance sensitivity change is +3 dB. The total is +3 +3 = 6 dB.
The usual caveat is that their sound fields must overlap. This usually means that their center to center spacing of the drivers must be less than one wavelength at their highest freqeuncy of operation.
infinia said:
I should have made that clearer - I never moved the mic from its position in front of the tweeter. Neither did I change the distance in JustMLS. All I did was switch cables from every driver.
Jim, I'd assume your post to be correct: +3 dB from double the area, -3 dB from doubling the impedance, 0 dB net gain. But the measurements I took with both woofers in series are the same LSPCad predicted for the circuit.
It makes no sense to me!
Should I scale the driver's SPL data to -3 dB each? or -6 dB? Maybe I could scale both drivers' output to equal one driver output...
nunayafb said:
Oh, that's spanish for "Upper Woofer" and "Lower Woofer". I just labeled them as such.
I've given some thought about this situation, and I remembered I took a measurement with both woofers in series and the tweeter in parallel. I'd assume this is the "real" reference for the SPL levels between tweeter and woofers, so, as long as my simulation reflects these levels, I'll be OK... I mean, the real issue is the relative level between woofer and tweeter... so my "all drivers wired" measurement should be my reference level... right?
fjhuerta said:
As long as you the "designer" feel comfort that your measurements are really reflecting theory. Then all is good. I would try to find the error by repeating tests with some better accuracy. Maybe try near and far microphone tests with out changing the woofer circuit. The difference should be +3dB with calibrating for distance losses. In addition, as Jim pointed out the tweeter referenced at the amplifier terminals will be 0 dB from the two series connected woofers far field. Clear as mud now?
infinia said:
I think it's clear
I tried another new thing. I loaded the parameters for one woofer and saw the frequency response graph. Then I told LSPCad there were two identical woofers in series (in the driver configuration section). I got something like +3dB out of it. I then configured the drivers in parallel. The difference was +6dB this time. It still doesn't make any sense. By using the driver configuration section, LSPCad should know the difference in amplitude should be 0 dB with two woofers in series, but it simulates +3 dB. And, the weirdest thing of all is that this simulation equals my measured response.
I'm so confused, I'll take those measurements again!
infinia said:
I fully agree with you.
I was thinking - there's no way for the software to know I did a measurement at X power rating to a driver, and that such power rating will be halved when two drivers are connected in series. I assume the software will just see two SPL measurements and treat them as if they were independent from one another.
I'll use my reference measurement (all drivers driven in phase) in order to set up manually the woofers' levels.
It's amazing how much you learn with each new project.
Thanks a lot for your help!
Are you sure that there is a 3db increase when you put run two speakers with the same combined power as one??
As far as i see it, Volume(of displaced air) = SA x Excursion
As the excursion is half, the SA is doubled or vica versa. As excursion is proportional to power the SPL would remain the same.
Obviously if wired in parrallel then 2 times the power would go through the system hence the 3db increase.
As far as i see it, Volume(of displaced air) = SA x Excursion
As the excursion is half, the SA is doubled or vica versa. As excursion is proportional to power the SPL would remain the same.
Obviously if wired in parrallel then 2 times the power would go through the system hence the 3db increase.
SO YOU ARE SAYING THAT IF YOU HAD AN INFINTE AMOUNT OF DRIVERS. 1 WATT WOULD GIVE AN INFINTE SPL????????
I some how dont belive that and i think you ought to check your facts. This is an audio myth brought along by people that dont understand that putting two drivers in parrallel causes half the resistance hence twice the power. That explains the 3db but the other 3db is unacounted for as the drivers excursion would be the same as with running one driver. and surface area doubles there is a 3db increase due to power. therefore if excursion remains the same
3db = 10log(2) = 2 times the power
6db = 10log(4) = 4 times the power
As SPL (pressure) is allmost equal to SIL (power per meter).
The theory is impossible!!! Although if you can prove it works you would be a VERY rich person!!!
I some how dont belive that and i think you ought to check your facts. This is an audio myth brought along by people that dont understand that putting two drivers in parrallel causes half the resistance hence twice the power. That explains the 3db but the other 3db is unacounted for as the drivers excursion would be the same as with running one driver. and surface area doubles there is a 3db increase due to power. therefore if excursion remains the same
3db = 10log(2) = 2 times the power
6db = 10log(4) = 4 times the power
As SPL (pressure) is allmost equal to SIL (power per meter).
The theory is impossible!!! Although if you can prove it works you would be a VERY rich person!!!
Hi Bob123,
Read the post#3 in this thread, Jim is correct. You have to think of this in terms a of a system. That is a power amp and driver(s), with the amplifier keeping the voltage at it's output constant.
For every driver you add the radiating surface area increases reducing the excursion proportionally for a given SPL. Now figure the power delivered to each driver whether its in in parallel or series using ohms law with a constant voltage available from the amp. Please do a couple of examples and see if that it makes sense for you.
Read the post#3 in this thread, Jim is correct. You have to think of this in terms a of a system. That is a power amp and driver(s), with the amplifier keeping the voltage at it's output constant.
For every driver you add the radiating surface area increases reducing the excursion proportionally for a given SPL. Now figure the power delivered to each driver whether its in in parallel or series using ohms law with a constant voltage available from the amp. Please do a couple of examples and see if that it makes sense for you.
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