I'm using Speaker Workshop to determine the enclosure volume of a base reflex system. The volume calculation calls for the series resistance - its help file describes this parameter as follows;
"Include cable and crossover series resistance in this amount. Changing this will also change Box Volume and Port Length".
Is it possible to measure this using a multimeter, if so, how should this be done?
Thanks
"Include cable and crossover series resistance in this amount. Changing this will also change Box Volume and Port Length".
Is it possible to measure this using a multimeter, if so, how should this be done?
Thanks
How or where it comes into the calculation for enclosure volume it changes I dont know, this resistance only effects ported enclosures, not sealed according to the Speaker Workshop program! I have the Loudspeaker Cookbook vol 4 & 5 and dont recall reading about this anywhere!
I have just read the example loudspeaker guide available at Speaker Workshops home page, they say this resistance is seen from the Inductors which are in series with the bass driver(s).
I have just read the example loudspeaker guide available at Speaker Workshops home page, they say this resistance is seen from the Inductors which are in series with the bass driver(s).
Hi Allan,
Keeping in mind that your multimeter is probably not that accurate at low ohms, if you have the crossover built, put a short length of heavy gauge wire across the crosover output for the speaker and hook up your speaker cables then measure the the resistance across the amp end of the speaker cable.
As mentioned by DSP_Geek also check what the meter reads when shorting the probes together and subtract this amount. giving the series resistance of the leads/crossover......
I always find this a little odd, as you really need to check the freqency response of the driver before designing the crossover, and to do that properly it has to be in-box..... somewhat of a chicken and egg problem....
Also you might like to consider using something like winisd or Unibox for doing the box design, and only using speaker workshop for the measuring (and possibly crossover design)... Have you downloaded the speaker workshop manual? I think you will find it much better than the built in help files. http://www.audiodiycentral.com/ntutorials.shtml
Tony.
Keeping in mind that your multimeter is probably not that accurate at low ohms, if you have the crossover built, put a short length of heavy gauge wire across the crosover output for the speaker and hook up your speaker cables then measure the the resistance across the amp end of the speaker cable.
As mentioned by DSP_Geek also check what the meter reads when shorting the probes together and subtract this amount. giving the series resistance of the leads/crossover......
I always find this a little odd, as you really need to check the freqency response of the driver before designing the crossover, and to do that properly it has to be in-box..... somewhat of a chicken and egg problem....
Also you might like to consider using something like winisd or Unibox for doing the box design, and only using speaker workshop for the measuring (and possibly crossover design)... Have you downloaded the speaker workshop manual? I think you will find it much better than the built in help files. http://www.audiodiycentral.com/ntutorials.shtml
Tony.
Bill Fitzpatrick said:
The resistance that matters is the output impedance of the amplifier plus any resistive element that is in series with the woofer. IF you know the "Damping Factor" of your amp (it is usually spec'ed at 8 ohms/50Hz) - say the DF is 100, that means the output impedance is 8/100 or 0.08 ohms - you have two wires in your speaker wire - so a 10 foot run is really 20 feet of wire - you add that amount, then usually you would add the DCR of the crossover inductor. This can add up to an appreciable amount.
Qes is then increased by Qes' = Qes *(1+Rs/Re) where Rs is the series resistance and Re is the speaker DC resistance. The modified Qts = 1/(1/Qes'+1/Qms). Bigger Qts means a bigger box and usually lower tuning to maintain flat response, assuming that was your target to begin with.....
In order to measure low resistance accurately, you need to make a low ohms meter - usually some sort of constant current source and voltmeter combination.
A typical DMM will have a resistance accuracy of +/-2% of full scale + 5 digits, meaning that your voltmeter that reads to 0.1 ohm is only accurate at best to 0.5 ohms - so even when you account for lead resistance it is not accurate enough to determine resistances on the order of which we are speaking.
It sure is a good thing that in most cases it doesn't make much difference either way......put in a factor of 0.2 to 0.3 ohms in your designs using passive crossovers and you will be doing more than most DIYers, who fail to account for even amplifier output impedance.
Tony,
No I didn't know of this manual, the download is now in progress.
Yeah your not wrong re eggs and chicken, a bit like wiping ya bum before the job! You know most programs have the order of construction all *** about then, really the best thing to do I guess is to;
1/ software model the system
2/ design & build the crossover
3/ measure all series resistance
4/ double check the software model (stage 1) & verify box volume
5/ build the box, and proceed on.
A bit like a dog chasing its tail
Thanks everyone.
Allan.
No I didn't know of this manual, the download is now in progress.
Yeah your not wrong re eggs and chicken, a bit like wiping ya bum before the job! You know most programs have the order of construction all *** about then, really the best thing to do I guess is to;
1/ software model the system
2/ design & build the crossover
3/ measure all series resistance
4/ double check the software model (stage 1) & verify box volume
5/ build the box, and proceed on.
A bit like a dog chasing its tail
Thanks everyone.
Allan.
Ron E,
thanks very much for a well written explanation, excellent!
I have modeled the design using various series resistance values and its very surprising just how much the resistance can alter the box's volume, so much so that I'm sure had I omitted the resistance in the design and moved on with the box construction I'd have ended up with something I never would have built in the first place, had I known!
So thanks all or you, heaps.
You know, any speaker cable manufacturer who reads this post must surely be now reaching for his jar of Vaseline!
Allan.
thanks very much for a well written explanation, excellent!
I have modeled the design using various series resistance values and its very surprising just how much the resistance can alter the box's volume, so much so that I'm sure had I omitted the resistance in the design and moved on with the box construction I'd have ended up with something I never would have built in the first place, had I known!
So thanks all or you, heaps.
You know, any speaker cable manufacturer who reads this post must surely be now reaching for his jar of Vaseline!
Allan.
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