I am using HT reciever ( 6-8 Ohm ) for my (PC based) digital active crossover, speakers will be 3 way and i use tri-amping, so each driver connected separately to amp. Question is : Is it possible to use 8Ohm woofer + 4Ohm tweeter in this setup?
Ok, so one problem solved. What about impedence matching? is it safe to connect 4Ohm tweeter to 6-8Ohm amp?
no, you need a 4ohms capable amplifier.
That 4ohms capable amplifier will be able to drive a 2r0 dummy load. If it can't do this then it's not 4ohms capable.
It may even be able to drive a 1r0 dummy load.
That 4ohms capable amplifier will be able to drive a 2r0 dummy load. If it can't do this then it's not 4ohms capable.
It may even be able to drive a 1r0 dummy load.
If you use active you can pretty much use any driver with any other driver. Sensitivity, impedance or any such thing doesn't matter as long as you have the source and amps to push it to the SPL you want.
To say 'no' it isn't capable is really a very large blanket statement and generally speaking most amplifiers that say 6-8 ohms are perfectly capable of driving 4 ohms providing you don't turn it up too loud.
Most amplifiers should contain decent protection circuitry that will stop the output devices from being destroyed should they exceed their voltage/current capabilities.
Where the problem comes in is with the heat generated. Driving a 4 ohm load generates considerably more heat than an 8 ohm load and unless the amplifier has excellent thermal protection then it is likely to overheat when driving a 4 ohm load loudly. Especially as the capabilities of the output transistors degrade significantly as temperature increases.
Another factor to consider is what kind of 6-8 ohm load is the amplifier expected to drive? AndrewTs basic - no - comment and saying that a 4 ohm capable amplifier needs to be able to drive a resistive 2 ohm load is based on the 4 ohm load having some difficult phase angles to drive.
Now a raw driver, especially a tweeter with very low inductance, connected directly to an amplifier, is about as close to a pure resistive load as you're going to get over its useful range. The amplifier does not need to be capable of driving a difficult 4 ohm load, just a very very easy one. Then there's the fact that a tweeter only tends to receive a tiny amount of average power with music and this means the amplifier will tend not to heat up at all when driving a tweeter even at high SPLs.
What HT receiver is it?
Have a look inside the manual. Some HT receivers say 6-8 ohms with all loudspeakers connected, or 4 ohms if you're only driving the front pair. This means the amplifiers inside are capable of driving 4 ohm loads, but the heat sinks are not big enough to allow the amplifier to do this when driving all the loudspeakers.
Most amplifiers should contain decent protection circuitry that will stop the output devices from being destroyed should they exceed their voltage/current capabilities.
Where the problem comes in is with the heat generated. Driving a 4 ohm load generates considerably more heat than an 8 ohm load and unless the amplifier has excellent thermal protection then it is likely to overheat when driving a 4 ohm load loudly. Especially as the capabilities of the output transistors degrade significantly as temperature increases.
Another factor to consider is what kind of 6-8 ohm load is the amplifier expected to drive? AndrewTs basic - no - comment and saying that a 4 ohm capable amplifier needs to be able to drive a resistive 2 ohm load is based on the 4 ohm load having some difficult phase angles to drive.
Now a raw driver, especially a tweeter with very low inductance, connected directly to an amplifier, is about as close to a pure resistive load as you're going to get over its useful range. The amplifier does not need to be capable of driving a difficult 4 ohm load, just a very very easy one. Then there's the fact that a tweeter only tends to receive a tiny amount of average power with music and this means the amplifier will tend not to heat up at all when driving a tweeter even at high SPLs.
What HT receiver is it?
Have a look inside the manual. Some HT receivers say 6-8 ohms with all loudspeakers connected, or 4 ohms if you're only driving the front pair. This means the amplifiers inside are capable of driving 4 ohm loads, but the heat sinks are not big enough to allow the amplifier to do this when driving all the loudspeakers.
That would be a great news 🙂 I really would prefer to use SB29RDC-C000-4 in my DIY speakers.
Thanks for comprehensive reply 5th element 🙂
LOW -DAYTON AUDIO RS270S-8 10"
MID - DAYTON AUDIO RS52AN-8 2"
HIGH - like i said i would prefer SB29RDC-C000-4, if not possible ill use 6Ohm seas SEAS PRESTIGE 22TAF/G H1283-06
Class D Panasonic SA-XR700, so there shouldnt be much trouble with heat, also meantime i found that people were running 4ohm speakers on his older brother - SA-XR55 (both HT are very similar).
In Manual its always 6-8Ohm (no matter how many speakers connected), in both XR55 and XR700 (maybe because of dual amping, or filters designed for that impedence?).
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Class D amplifiers are more efficient than the more standard offerings, but this doesn't mean that they don't put out heat. They still need heat sinks and a quick google turned up this.
For what the insides look like.
Now I can't see any heat sink at all! Go class D.
The point is, even if the heat sinking requirements are low, one can still use a smaller heat sink to increase profit margins, or to decrease component cost.
I did a bit of searching and found the MOSFET controller that the amplifier uses, its a TI product and it does include over current and over temperature protection features. This will make sure that the amplifier doesn't explode if short circuited etc so it should be protected against being over driven.
Over current protection is the most important aspect though as with a three way active system you're unlikely to get things too hot.
The woofers will make the amplifiers work hard, but the RS52 will only work from about 600Hz and up and the tweeter most likely from about 3khz and up in that configuration. Neither amplifier will work fantastically hard driving those individual drive units so heat isn't likely to be a concern.
As you rightly point out though, the class D amplifiers output filters are designed around a fixed impedance and attaching a 4 ohm tweeter to one will cause the high frequencies to roll off sooner than expected, but this isn't hard to over come with an active xover, you can just put in a bit of boost if necessary.
For what the insides look like.
Now I can't see any heat sink at all! Go class D.
The point is, even if the heat sinking requirements are low, one can still use a smaller heat sink to increase profit margins, or to decrease component cost.
I did a bit of searching and found the MOSFET controller that the amplifier uses, its a TI product and it does include over current and over temperature protection features. This will make sure that the amplifier doesn't explode if short circuited etc so it should be protected against being over driven.
Over current protection is the most important aspect though as with a three way active system you're unlikely to get things too hot.
The woofers will make the amplifiers work hard, but the RS52 will only work from about 600Hz and up and the tweeter most likely from about 3khz and up in that configuration. Neither amplifier will work fantastically hard driving those individual drive units so heat isn't likely to be a concern.
As you rightly point out though, the class D amplifiers output filters are designed around a fixed impedance and attaching a 4 ohm tweeter to one will cause the high frequencies to roll off sooner than expected, but this isn't hard to over come with an active xover, you can just put in a bit of boost if necessary.
So, this means green light to SB29RDC? 🙂
Will the fillters still do their job at 4Ohm? And how the filtration will change?
I want the SB drivers cause of low distortion, if i get extra distortion from 'leaking' filters, there will be no big advantages of using SB drivers. Guess thats my last concerns 🙂
What about high frequency distortion from fast switching mosfets?
Will the fillters still do their job at 4Ohm? And how the filtration will change?
I want the SB drivers cause of low distortion, if i get extra distortion from 'leaking' filters, there will be no big advantages of using SB drivers. Guess thats my last concerns 🙂
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Leaking filters lol.
You get more attenuation from the switching nasties into the 4 ohm unit vs the 8 ohm.
The output filters are mainly there to satisfy EMI regulations, not for the performance of the class D amplifier.
All that will happen with the 4 ohm unit is that the high frequencies might be rolled off a little, like a dB at 20kHz or so depending on the filter used in the amp.
You get more attenuation from the switching nasties into the 4 ohm unit vs the 8 ohm.
The output filters are mainly there to satisfy EMI regulations, not for the performance of the class D amplifier.
All that will happen with the 4 ohm unit is that the high frequencies might be rolled off a little, like a dB at 20kHz or so depending on the filter used in the amp.
Understand now.
Thanks for explaining 5th element, its really helpfull. Gonna order my SB tweeters now 😀
Thanks for explaining 5th element, its really helpfull. Gonna order my SB tweeters now 😀
The only thing that matters is that your amp is okay with 4 ohm ( Most are, but with possibly lower max output power ). This is a tweeter we are talking about though and not a subwoofer so I'd be really suprised if it became an issue as you will not push many watts into it.
The only difference you will notice is that the SPL might differ from 8 to 4 ohm, if they have the same SPL / Watt. But as you have digital you don't care about this since you can just fix the response into what you want. In short you can ignore all electrical properties like box size, impedance and just focus on output capability ( excursion * surface area, capped by max watts into driver ) and then optimize for the dispersion you want. Mixing 8 with 4 ohm can be a problem if you want passive crossover where the sensitivity of the drivers might not match, but as you go active you don't care.
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