Playing in xsim yesterday on my 2 way XO. I am down to nearer to 3 ohms than I'd like to be at about 100hz.
More by luck than judgement I tried a resistor between the driver (SB17NBAC35-4) negative terminal and ground and it seemed to lift the impedance nicely. Phase didn't seem to suffer.
I don't recall having seen this done so I thought it must be 'unconventional' or plain wrong? Any advice please.? Thanks
More by luck than judgement I tried a resistor between the driver (SB17NBAC35-4) negative terminal and ground and it seemed to lift the impedance nicely. Phase didn't seem to suffer.
I don't recall having seen this done so I thought it must be 'unconventional' or plain wrong? Any advice please.? Thanks
All you are doing is increasing the DC resistance and reducing the current flow to the speaker as the resistor dissipates some of it depending, on value.
Loss of power is what you will acheive.
There are no phasing issues as the impedance of the speaker is the same.
Loss of power is what you will acheive.
There are no phasing issues as the impedance of the speaker is the same.
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The SB17NBAC35-4 has a specified Re of 3.1Ω, so it would be surprising if you didn't see the system Z drop to near 3Ω once you've added in crossover elements.
It's perfectly valid, if wasteful. You'll also find that the Thiele-Small parameters will shift with series resistance added (Qes effectively rises, and Qts follows), so a new box alignment will be required.
It's worth noting that pretty much any 4ohm driver will drop to below ~3.5ohm in places, and most 4ohm-capable amplifiers will drive that load just fine.
Is there a particular reason why the impedance absolutely cannot drop below 4ohm?
Chris
It's worth noting that pretty much any 4ohm driver will drop to below ~3.5ohm in places, and most 4ohm-capable amplifiers will drive that load just fine.
Is there a particular reason why the impedance absolutely cannot drop below 4ohm?
Chris
Also, why not do it in series with the speaker hot line instead of the ground lead? No reason to mess with the grounding system, since it is all in series it doesn't matter where in the loop it is inserted.
Jan
Jan
Why did you choose a 4 ohm driver to begin with? Is it a car speaker you are building? 4 ohm in domestic is usually used in cases where you want to serial connect two identical drivers through a common crossover ie in a 3-way tower design with double bass or a twin sub. For a single bass system use 8 ohm driver. Most amps will do fine with 4 ohm but the response may not end up as simulated. Some amps have twice the power in 4 ohm compared to 8 ohm while others does not have that. So the sound will very much depend on the amp, more than with a 8 ohm speaker.
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That's plain wrong. The choice of a driver (and that includes also the choice between 4 and 8 Ohm impedance) depends on the application. For domestic use with a "normal" solid state amp, a 4 Ohm bass driver is perfectly acceptable, with the added bonus of higher SPL at given voltage level. My Rotel amp is perfectly happy with a 3-4 Ohm load.
That said, if the OP is worried about low impedance on a bass driver, then frankly the only option is to switch to a higher impedance driver to begin with, AFAIK the SBA BAC is offered also in the 8 Ohm version.
As noted before, a resistor in series with a bass driver (before or after doesn't matter), will lower the SPL, will change the Qts of the driver, and has to be done really carefully because all the power will go though the resistor. All in all I'd say it is a no-no situation.
Ralf
Hi guys. Thanks for the replies. This was all just theoretical on a wet Saturday playing on xsim.The speakers are built and preform well. Indeed Chris661 above helped with measurements and XO design....thanks again Chris. I do like them. I've realised I do prefer the dispersion of a tweeter. My other build uses 8" and 3" FR.
The reason I 'chose' these 4 ohm.....inexperience and a good price on ebay....itchy bidding finger and probably some alcohol involved too!
I have class d and have recently built a TDA7293 and neither are worried by the 3ohms. It was just my enquiring mind that prompted the question.
Even wetter Sunday so maybe more Xsim messing!
Cheers
The reason I 'chose' these 4 ohm.....inexperience and a good price on ebay....itchy bidding finger and probably some alcohol involved too!
I have class d and have recently built a TDA7293 and neither are worried by the 3ohms. It was just my enquiring mind that prompted the question.
Even wetter Sunday so maybe more Xsim messing!
Cheers
I get what you're saying but with today's class D amps it seems you will not get much more higher SPL/power on 4 ohm and you may end up with a bright sounding speaker instead much like a car speaker would sound at home (again depending on the amp). A much safer design is 8 ohm IMHO.
The 7293 about 80w clean before the thd rises fast.
29v rail for 4 ohm and 40v rails for 8ohm load. Both similar power to thd graphs
29v rail for 4 ohm and 40v rails for 8ohm load. Both similar power to thd graphs
With a lower impedance you’ll get more SPL at given voltage, not necessarily this gives you more maximum SPL. But your assumption that a 4 Ohm (bass) driver can lead to a bright sounding speaker is not based on facts.
Since the bass driver is usually the bottleneck SPL wise of a speaker, in order not to attenuate too much mid and tweeter sometimes it is best to use a 4 Ohm bass driver. Remember that most dual bass speakers are 4 Ohm (two 8 Ohm drivers in parallel), you won’t argue that those designs aren’t safe.
Ralf