driver impedence doubt

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soundnovice

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hi all,
i have a doubt regarding driver impedence. will there be matching between 8 ohm woofer and 4 ohm or 5 ohm or 6 ohm tweeter? or is it must to have both woofer and tweeter of same impedence?
need input from audio experts.

Thanks in advance.

regards,
pranam
 
IMO the impedance rating alone cannot specify whether the woofer and tweeter can be matched. We must consider the sensitivity of drivers too. Usually tweeters are more sensitive and are rated as 6 ohms to match with the sensitivity of woofers/midbasses. Incase the tweeter is found to be more sensitive then the drive to it is usually lowered by an Lpad. However if the woofer/midbass is more sensitive then lowering the drive to it may cause adverse issues. It is for this reason that one must choose the drivers with matched sensitivities rather than impedance alone.

Sonicbliss
 
thanks sonicbliss and antony.
should the sensitivity values of woofer and tweeter be exactly same? or upto +-2db difference is ok?
 
I think the cross over point will change with change in impedance as xo is built for particular impedance. Same coils and resistors will work differently for different impedance. Experts,more inputs please.

About sensitivity matching issue i think it depends on what kind of music one likes(bass heavy or bright.)If one likes bass heavy, then having higher sensitivity tweet wont work and vice versa.

If you are planning to build a speaker with flat response over full range, i think you need speakers with matching sensitivity.
 
Using an L-pad or having a series resistor affects the way crossover see the tweeter and these will influence the crossover slope and phase. It's always advisable to use matching impedance and sensitivity to keep the crossover design simple.

There is another trick that's easier to implement without modifying the xover characteristics. Use a series resistor before the high pass circuit. This will attenuate the tweeter level without adverse influence on the xover. I had used this method successfully with supertweeters.
 
If one plan to buy new set of drivers, will it not be right to match the impedance between drivers. Or it is immaterial?
 
As the discussion mentions, sensitivity is very important. If you choose woofer and tweet of same impedance but if woofer sens is 88 vs tweet sensitivity 96, the music will be bright.
Even though impedance of each driver is same,once the cross over comes in,the behaviour changes.
The woofer impedance increases if it is fed with frequency above cross over point. Similarly the tweeter impedance increases if it is fed with sound of frequency below crossover point.

E.g. An 8 ohm Tweeter may have impedance of more than 1000ohm at 1khz if it has a high pass filter at say 8 to 10khz. But the same tweeter will have impedance of 8ohm as rated when it is playing frequencies above 10khz.
So ultimately how the woofer -tweet combo behaves depends not only on impedance of drivers but also on crossovers and what frequency is being played.
 
Does it mean we need to match the sensitivity while choosing the drivers?

Another doubt is, if each driver has different impedance, what could the nominal impedance of the speaker as a whole?
 
ukjeyaraj said:
Does it mean we need to match the sensitivity while choosing the drivers?

Another doubt is, if each driver has different impedance, what could the nominal impedance of the speaker as a whole?
Click to expand...

The sensitivity should be matched. If thats not possible, a tweeter with sensitivity higher than woofer with LPAD Attenuator should be used to match the sens. It is not advisable to use attenuator with woofer.

The second question is tricky. If the impedance is not matching, the resultant final impedance will depend upon the cross over point. It is difficult to calculate. Needs to be measured but i dont know how. However with simple logic I can say that if impedance is not matching, the crossover point should chosen such that the driver with lower impedance covers narrower band of frequency than the other one so that the final impedance remains on as higher side as possible.

If you choose 8 ohm and 4 ohm speakers and wire in parallel without xo, the resultant imped will be around 2.5. If you use crossover, it will be definitely higher than 2.5 but how high will depend upon the crossover point.

If woofer is 8 and tweet is 4, keep xo as high as possible(depends upon how high up the woofer can play) so that final impedance is as high as possible.
If woofer is 4 ohm and tweeter is 8 ohm,keep xo as low as possible (depends on how low the tweet can come) so as to keep resultant impedance as high as possible.

If your amp is robustly built, you dont have to bother much about impedance.

I had connected 8 ohm tweeter with 8khz high pass filter, 8 ohm fulls ranger without cross over, 8 ohm woofer with 250hz low pass filters in parallel to my marantz pm6002 and the amp had no issues at all. Did not even become warm,at least for the volume level that I use. So i dont know what was the final impedance but marantz could take it easily.

I hope this helps to some extent without causing much confusion.
 
If woofer is 8 and tweet is 4, keep xo as high as possible(depends upon how high up the woofer can play) so that final impedance is as high as possible.
If woofer is 4 ohm and tweeter is 8 ohm,keep xo as low as possible (depends on how low the tweet can come) so as to keep resultant impedance as high as possible.
Click to expand...

In my opinion,the xover point need not be tinkered with...it should be selected on the basis of the usual design parameters like driver Fs,radiating area,filter slope etc.
The difference in levels between the woofer and the tweeter can then be matched with the help of attenuating circuits on the tweeter like Antony suggested(amp side series resistor) or Lpads....provided the tweeter is at a higher level.

In their pass bands the two drivers would be more or less in parallel, neglecting the effects of coil DCRs and capacitor ESRs
 
Now, I will go bit out of topic.

What about watts?

Should the watts of Tweeter,Mid-range,woofer need to be same or different or any magic proportion?

What will the final watts of speaker as a whole?
 
sashijoseph said:
In my opinion,the xover point need not be tinkered with...it should be selected on the basis of the usual design parameters like driver Fs,radiating area,filter slope etc.
The difference in levels between the woofer and the tweeter can then be matched with the help of attenuating circuits on the tweeter like Antony suggested(amp side series resistor) or Lpads....provided the tweeter is at a higher level.

In their pass bands the two drivers would be more or less in parallel, neglecting the effects of coil DCRs and capacitor ESRs
Click to expand...

What you say is correct. The crossover point must depend upon the driver characteristics other than impedance. Otherwise,just for impedance purpose,
someone would choose crossover point at a frequency which is not covered by either one of the driver causing a big dip in the final frequency resp curve.

I was just trying to explain how the crossover point may affect final impedance of the combo when the driver impedance is not matching.
 
ukjeyaraj said:
Now, I will go bit out of topic.

What about watts?

Should the watts of Tweeter,Mid-range,woofer need to be same or different or any magic proportion?

What will the final watts of speaker as a whole?
Click to expand...

The wattage of woofer and tweeter need not match. One needs to take care that the wattage is sufficiently high so that the driver is not damaged when the amplifier is set at the needed volume.

I dont know how to calculate wattage of final speaker. I dont think it will be simple summation of watts of 2 drivers. However sensitivity sets in again.

Higher wattage does not
necessarily mean louder volume. SPL(Sound pressure level,same as loudness) depends on the watts fed into the speaker AND Sensitivity. A speaker with higher wattage but with lower sensitivity may be less loud than speaker with lower wattage but appropriately high sensitivity.

Experts ,
please chip in with exact maths. I think a 200w rms speaker with 89db sensitivity will give same max loudness as compared to 100w rms speaker with 92db(or is it 95db?) sensitivity.
 
jaudere said:
The wattage of woofer and tweeter need not match. One needs to take care that the wattage is sufficiently high so that the driver is not damaged when the amplifier is set at the needed volume.
Click to expand...

How do we decide what is sufficiently high? Assuming the amp is rated for 100watts @ 8ohms What could be the watts for drivers?

jaudere said:
A speaker with higher wattage but with lower sensitivity may be less loud than speaker with lower wattage but appropriately high sensitivity.

Experts ,
please chip in with exact maths. I think a 200w rms speaker with 89db sensitivity will give same max loudness as compared to 100w rms speaker with 92db(or is it 95db?) sensitivity.
Click to expand...

More inputs on this from others will be really interesting.
 
How do we decide what is sufficiently high? Assuming the amp is rated for 100watts @ 8ohms What could be the watts for drivers?
Click to expand...
Estimating the exact 'watts for drivers' in a multiway speaker would require an analysis of the power distribution vs xover frequency chart,which would still be inaccurate as it involves some difficult to predict variables,like the program material,individual driver sensitivities etc.

look here for a better understanding...BiAmp (Bi-Amplification - Not Quite Magic, But Close) - Part 1

So,like Jaudere has stated,simply get drivers with a power rating greater than or equal to the amp you intend to use.
 
Last edited:
ukjeyaraj said:
How do we decide what is sufficiently high? Assuming the amp is rated for 100watts @ 8ohms What could be the watts for drivers?
Click to expand...
More than rated wattage of the amp,one needs to consider how many watts one actually uses.
E.g. I have used 15 watt rms speaker with 20w amp as well as 250w amp because I was sure that i am not going to use more than 10w from either of the amp in any case. No problems. But suppose by chance my son had cranked up the volume on both amps to full, 20w amp would not have done any damage to speaker while the bigger amp could have easily smoked the speaker.

But even the 20w amp would have definitely damaged my ears if not speakers. Even 10w could have damaged ears. If you calculate, 93 db/w sensitivity speaker fed with 10w will definitely go above 100db at 2 metres (my listening distance) which is not good for ears.

So i feel that for home use in rooms less than 16X12 feet size, one rarely needs more than 10watts. That is why people are happy with Topping amp. It will give adequate loudness with good sensitivity(more than 90) speakers. Even on Topping, people have said that they dont go above 12 oclock position which means they dont use those full 9 watts. It is the same reason why 2 watt tube amps are adequate for similar room when high sensitivity speakers are used.
 
If one has an amp of 100watts@8ohms, should, he go for each driver higher than 100watts or total of all drivers higher than 100 watts
(assumption is all have same impedance and sensitivity say 8ohms and 89db)
 
Not 100% sure but to be absolutely safe, each driver should be above rated wattage of amp.
But remember that the rated wattage is at particuls THD. So an amp may push 100w at 0.1%THD While same amp will push say 130w at 10%THD. The manual may tell wattage at less than 0.1% THD Only. So what should one choose? A difficult question.
E.g. If you use Norge 1000, its 125 watts. It will be difficult to find drivers with higher wattage but small enough in size.
 
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