Impedance Question

There are folks who are hardcore experts on this who can answer this better hence ill only put forward my layman view on this

But this impedance is tricky business. since Impedance is R+L+C and L and C depends on the frequency this keeps varying depeding on the signal.

Also from my understanding a speaker impedance is for the Speaker ie Drivers + corssover + any other electronics in it.. And since the crossover has a lot of say in the overall impedance, unless you are going to design/mod a speaker how it is inside should not really matter

Looking forward for some responses form the tech experts on this !

hi xandy,

well this is not an answer but a further question to add to your question.. what exactly does having two drivers in parallel mean? maybe u can answer it since its mentioned in ur post.

Adding a question further.....would having two drivers in parallel and the same two drivers in series mean difference in sound QUALITY (keeping all other electronics constant).

Also will there be a difference in loudness in both the setups ??

Basically what will happen is that in a parallel connection the resultant impedance will be halved(half of that of single driver).
and usually, the output of the amp will be doubled in a parallel connection.

For instance, consider an amp that outputs 180watts at 8 ohms and 250 watts at 4 ohms.
Now if u have two drivers of 8 ohm nominal impedance, then
in parall config- reusltant will be 4 ohm ..
therefore the speakers will be fed with 125 watts a piece.
the only problem is that the amp needs to be 4 ohm stable and will put strain on the amp when driven hard at low impeadance.

However, if you connect two in series the resusltant will be 16 ohms.
so, the power supplied to each driver will be less than 100 watts..
howevre, the amp will be able to handle the speakers easily but chances of clipping increses and also the head room will be lessened.

If i am wrong in any of this please feel free to correct me.

Suggest you look at whitepapers on multiple drivers(search on the net) and also on Rod Elliot's site(a treasure trove of info) am sure all your doubts will be dispelled.

Thanks for the responses.

I was actually thinking of getting an enclosure made. No, NOT like what BENKS did. I can't design those stuff.
So, i plan to get stuff and assemble because of severe budget constraints. The question came up because i wanted 2 bass drivers.

Do i get to buy good crossovers at S.P.Road? Which is the best brand (if there is one)?

hi X and Y i will provide you the crossover values for ur setup just tell me ur drivers names and model no....

I will send you the diagram also...

Extremely Important factor....

when you are using ur drivers in parallel connection then remember that you need high current amplifiers in order to drive your speakers well enough and for very tight kick drum bass. Remember that if you use 2 drivers in Parallel then the current requirement will be min twice than one woofer...

so for 2 channel you need about an amp whose current ratings must be 4 times the single woofer/ enc... and Larger drivers with big magnets need heavy current requirements...

Example...

If you have a subwoofer with double stacked 155mm magnets with 25mm each then for a 12 inch subwoofer you need atleast of 10 amp of CONTINUOUS current for driving it efficiently.

If you parallel this you need about 20 amps of continuous current for driving this...

If you take the same scenario in stereo application in it need 40 amps of current.

Many power supplies are not efficient by its ratings...

The ratings which are given on the transformer willbe like 20 amps but on full Load it gives about 16amps at max... so you need about not less than 50 amps of current for the application...

for 60volts of voltage supply then it needs about 60 x 50

= 3000va of just power needed but

you may be running this amp in class AB then you need about 6000VA of toroidal transformer

A 625VA of transformer will weigh about 5.5 kg so on a average it will be not less than 50kg of power supply and you can compensate 30% with the reserve capacitors only the amp will weigh not less than about 60kg in total see.. this is called solid amplifiers like the same way topend Amp builders like Krell uses.

So remember one thing this is not all that simple task it needs lots of knowledge to decide...

If you tell me ur requirement i can help you.

Frank suggestion just go for a kit for your speakers

dont just buy the stuff from SP road. All crap drivers are available...but if you like some disco kind of sound then go for the some cheap Bolton drivers like 12 inch driver with 100watts RMS which costs you about 2k. But remeber one thing you need a high current amp to drive this efficiently.

best regards,
Sandeep

I think i misled you by saying "assemble". Sorry, I should've told "getting it assembled". Coz' i can't even solder for heaven's sake.

Thanks Sandeep for the offer though.

Regarding the drivers in parallel, i did NOT get any reply from the forum how drivers are connected in enclosures with twin bass drivers.
Actually, my current setup is BOLTON.
Mine is a Pulz RS250 Power amp and few days back the left channel started distorting heavily. Don't know what happened. Got to get it repaired before everything.

XandY,
let me attempt a reply to ur orig question:

perhaps some back-tracking might be in order: when they talk about speaker impedance what they really are talking about is the impedance change versus frequency of the speaker cross-over network. The change over frequency occurs 'cuz the x-over inductor (L) & the capacitor (C) are reactive elements & their impedance is a function of frequency. The driver units (woofers in ur question) do interact w/ the electrical x-over so (as indicated by another member) the interaction of the electrical xover along w/ the actual driver is a complicated equation. hence if you look @ the impedance & phase plots of measured speakers (say, in Stereophile) it appears that the curves are all over the map.
when there are multiple bass drivers in a speaker, to the best of my knowledge, the manuf uses separate x-overs for each driver such that these bass drivers have a small interlapping region of operation but essentially operate in distinct regions of the bass.
For example, I used to own a B&W DM604S2 floor-stander. It had 2 bass drivers. The bottom-most bass driver was above the front port & it was designed (i.e. to say that x-over was configured) to operate in the low bass region. I cannot specify the exact range 'cuz B&W never revealed it! However, if I had to guess, I'd say that the bottom-most bass driver operated in the 44Hz-160Hz region. 44Hz was the -3dB roll-off point of this speaker, if memory serves me correctly. The 2nd bass driver was designed such that it operated in the mid-bass region 160Hz & above until the mid-range driver came into the action. If I remember correctly, the mid-range was crossed over at 400Hz => the 2nd bass driver operated in the 160Hz-400Hz region.

Right behind the speaker terminals, if you could extend your hand into the speaker cabinet, is/are the PC board(s) containing the x-over components. Here, the designer would have separated the frequencies & fed 4 pairs of wires (for the DM604S2) to each of the drivers.
The power amp would see the electrical x-over network impedance, which would vary vs. freq.
The trick in using multiple drivers (be it bass or mid or tweeters) is to "phase" the drivers in such a way that they are seemlessly activated & de-activated with the music signal. This usually entails designing or procuring drivers that have a flat response in their intended region of operation + designing a x-over that'll allow these drivers to seemlessly integrate. It's a really tough job, which is why (I think) that few speakers on the market w/ multiple drivers of 1 type sound good.

So, it's not taking 2 16 Ohm drivers & paralleling them. If the drivers are well-designed, their mechanical & electrical impedance will remain unchanged in the freq band of intended operation & the dominating factor will be the impedance of the electrical x-over & it's variation w/ freq.
There is a network called the "zobel" network that is often used by speaker designer (mostly across the bass unit) so as to trick the power amp into thinking that the low-freq x-over impedance is essentially constant over freq. This makes life much easier for the power amp & it also makes the owner of such a speaker say "this speaker is easy to drive". If correctly implemented, the zobel network has minimal effect on the sonics.
Hope that this helps.

What u are referring to here is the .5 type systems..
example..wharfedale diamond 8.4 is a 2.5 way
in a way it works like you explained but a lot more complicated to explain.

bombaywalla schrieb:

XandY, let me attempt a reply to ur orig question: perhaps some back-tracking might be in order: when they talk about speaker impedance what they really are talking about is the impedance change versus frequency of the speaker cross-over network. The change over frequency occurs 'cuz the x-over inductor (L) & the capacitor (C) are reactive elements & their impedance is a function of frequency. The driver units (woofers in ur question) do interact w/ the electrical x-over so (as indicated by another member) the interaction of the electrical xover along w/ the actual driver is a complicated equation. hence if you look @ the impedance & phase plots of measured speakers (say, in Stereophile) it appears that the curves are all over the map. when there are multiple bass drivers in a speaker, to the best of my knowledge, the manuf uses separate x-overs for each driver such that these bass drivers have a small interlapping region of operation but essentially operate in distinct regions of the bass. For example, I used to own a B&W DM604S2 floor-stander. It had 2 bass drivers. The bottom-most bass driver was above the front port & it was designed (i.e. to say that x-over was configured) to operate in the low bass region. I cannot specify the exact range 'cuz B&W never revealed it! However, if I had to guess, I'd say that the bottom-most bass driver operated in the 44Hz-160Hz region. 44Hz was the -3dB roll-off point of this speaker, if memory serves me correctly. The 2nd bass driver was designed such that it operated in the mid-bass region 160Hz & above until the mid-range driver came into the action. If I remember correctly, the mid-range was crossed over at 400Hz => the 2nd bass driver operated in the 160Hz-400Hz region. Right behind the speaker terminals, if you could extend your hand into the speaker cabinet, is/are the PC board(s) containing the x-over components. Here, the designer would have separated the frequencies & fed 4 pairs of wires (for the DM604S2) to each of the drivers. The power amp would see the electrical x-over network impedance, which would vary vs. freq. The trick in using multiple drivers (be it bass or mid or tweeters) is to "phase" the drivers in such a way that they are seemlessly activated & de-activated with the music signal. This usually entails designing or procuring drivers that have a flat response in their intended region of operation + designing a x-over that'll allow these drivers to seemlessly integrate. It's a really tough job, which is why (I think) that few speakers on the market w/ multiple drivers of 1 type sound good. So, it's not taking 2 16 Ohm drivers & paralleling them. If the drivers are well-designed, their mechanical & electrical impedance will remain unchanged in the freq band of intended operation & the dominating factor will be the impedance of the electrical x-over & it's variation w/ freq. There is a network called the "zobel" network that is often used by speaker designer (mostly across the bass unit) so as to trick the power amp into thinking that the low-freq x-over impedance is essentially constant over freq. This makes life much easier for the power amp & it also makes the owner of such a speaker say "this speaker is easy to drive". If correctly implemented, the zobel network has minimal effect on the sonics. Hope that this helps.

Dear Bombaywalla
Very well put.It is quite thorough,the way you explained the impednce vs frequency graph.Reactive components can only be tested for their quality via the long process of trail and error.
A recent contract lost by Clarity Cap to a competitor(I suspect B&W Nautilus diamond series was the said contract)has sent them into research with Salford University to better understand the mysteries of reactance with regards to materials.
Please contribute more,it will greatly add to the forum wealth.
Regards Deaf

Dear Bombaywalla,

Thanks for the clarification.....and that brings my hopes of PARALLELING two drivers and calling it a TWIN bass driver crashing down.

So, do i get crossovers meant for such configuration?

Deaf, thanks for your kind comments.

XandY:
no I wouldn't say that your hopes to have twin bass drivers are dashed.
Several manuf (like PSB, Athena, Paradigm & hordes of others) have twin bass drivers. What I do observe there is that the top driver is usually not ported & is a mini sealed box within the larger cabinet. The bottom bass unit is ported. Thus, both bass drivers have totally different loading hence their resp. response will be different. The manuf must be doing something to make these 2 units integrate given their diff effective responses. Maybe a DIY speaker-building website can teach you? Or, maybe some other more knowledgable member on this forum knows?

XandY schrieb:

Hi, A silly qn from one who's learning. If an enclosure has 8 Ohms nominal impedance and if it has twin woofers, does it mean that it has two 16 Ohms drivers in parallel? How do they manage if there are 4 woofers (i read that its not good to connect drivers in series)? Thanks.

Dear XandY
It could mean two 4ohm woofer in series.
Drivers in series in many ways is actaully better if both of them are breathing the same air volume.The circuit operates as one,instead of two indepedant circuits.
4 woofers? you are a bass nut.
Regards Deaf.

I'm not a bass nut since i do NOT like subwoofers.
But i don't like tinny sound. Regarding the woofers in series i read about a BACK EMF problem which can spoil the sound, whereas parallel doesn't have this issue.

XandY,

I'm intrigued by this statement of yours: "Regarding the woofers in series i read about a BACK EMF problem which can spoil the sound, whereas parallel doesn't have this issue."

It does not make sense to me.
From the paper/magazine where you read this can you exactly quote what they wrote? Thanks!

bombaywalla schrieb:

XandY, I'm intrigued by this statement of yours: "Regarding the woofers in series i read about a BACK EMF problem which can spoil the sound, whereas parallel doesn't have this issue." It does not make sense to me. From the paper/magazine where you read this can you exactly quote what they wrote? Thanks!

Dear Bombaywalla
With all due respect I don't think so.Infact quite the reverse, as most isobaric systems are wired in series to make the whole circuit operate as one.
Regards Deaf

I'm not an expert in here.

This is where i got it from
http://www.lalena.com/audio/faq/wiring/

You could get lots by doing a google for "speakers in series back emf"

Doing a search for speakers & back EMF helped me some. I think that I can see why the series woofer connection creates back-EMF based distortion: neither series-connected woofer independently sees the amplifier output impedance (which is usually very low). The series connected woofers as a composite see the amplifier output impedance.
So, because neither series connected woofer independently sees the amp o/p impedance, the back/forth movement of one woofer's cone has an influence on the other's cone. The phasing between 2 series connected woofers will be 180 out of phase i.e. when 1 cone moves outward, the other cone moves inwards. This could be made to work but I'm not a speaker designer so I don't immediatetly see how.

Deaf: are you sure that Isobaric woofers are wired in series? Isobaric systems usually have small woofers (6" or 7") & keeping the phase the same between the 2 woofers would create a feeling of more total bass output. If they were out-of-phase, the bass o/p would be totally cancelled, no? Intuitively I always thought that they would be wired in parallel but I could be wrong.

BTW, every bass driver has back-EMF. It's just that w/ parallel woofers each driver independently sees the low amp o/p impedance (damping factor) & if the amp is well designed, it'll handle the bass correctly. i.e. damp the woofer in time so that there is no/minimal bass overhang. Of course, the speaker must also cooperate. If the speaker is a low-Q design then the cabinet is likely to resonate & the amp will be limited to how well it can damp the woofer.