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Multi-Way Conventional loudspeakers with crossovers

Matching amplifier to loudspeaker question(s)
Matching amplifier to loudspeaker question(s)
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Old 31st December 2017, 07:05 PM   #21
planet10 is offline planet10  Canada
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Matching amplifier to loudspeaker question(s)
An amplifier & speaker are a system, they have to be symbiotic.

Althou not always the case, it is often that a speaker with a crossover will have a roller-coaster impedance response (as seen in Eric's plots). An amplifier with low output impedance (voltage amp) will ignore that, an amplifier with high output impedance (current amp) will vary in output power and have FR variations that mirror the impedance plot.

If you have a speaker with flat impedance response, typical of FR speakers, Joe Rasmussen’s latest multiways, a few others and active speakers as OllBoll describes, the amplifier impedance makes little difference. You can take advantage of amps that tend towards current amp status and these will often sound better (as Oli points out a speaker is a current device and using a current amp avoids using the impefect speaker impedance as an I/V converter).

One other thing to consider is that almost every speaker has an impedance rise at the rersonant frequency of the box/speaker. If the output impedance is too low one can get one can get an overall overdamped response and thin bass. It is also possible to use a highish output impedance amp and the resonance peak to get an extension in the bass response.

So, the amp needs to be matched to the speaker, there is no universal choice. In an ideal world, you will design a speaker with perfectly flat impedance and use a current amp. In the real world something like OliBoli describes is more realistic.

dave
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Old 31st December 2017, 07:43 PM   #22
Lojzek is offline Lojzek  Croatia
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Quote:
Originally Posted by montana1 View Post
Hi Lojzek,
Thanks for your post here!....Happy New Year,
Rich

Thanks, matching amps to loudspeakers is very easy when your amp is not utter rubbish. Those with significant output impedance can benefit from flattening loudspeaker impedance as seen by the amp. These speakers have simple RLC and RC networks in parallel with amp out terminals tailored for exact impedance peaks. You can turn any loudspeaker with such networks into one that can be good partner to any amp, as long as nominal impedance is within acceptable limits that amp is comfortable working with. A dead short of a loudspeaker is obviously not our goal.


Happy New Year and God bless, my friends!
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Old 31st December 2017, 07:54 PM   #23
montana1 is online now montana1  United States
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Dave,
Thanks for your very detailed explanation! Your explanation makes perfect sense and is easily understood (even a novice as myself). I'm going to spend considerable time before making a purchase.

Happy New Year,
Rich
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Old 31st December 2017, 07:59 PM   #24
montana1 is online now montana1  United States
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Lojzek,
When you speak of RLC and RC networks used to tame impedence peaks; are you referring to those implemented in the X over design?

Thanks once again!
Rich
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Old 31st December 2017, 08:08 PM   #25
Lojzek is offline Lojzek  Croatia
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These networks can be physically placed anywhere you prefer, directly on amp OUT, or at speaker terminal IN from the outside of loudspeaker enclosure, or directly on crossover board where the low and high pass filters are, as long as it's electrically as depicted.
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Old 31st December 2017, 08:29 PM   #26
montana1 is online now montana1  United States
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Lojzek,
Thanks for your explanation! Your diagram has made it easy to understand what you had in mind.

Best Regards,
Rich
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Old 2nd January 2018, 01:31 AM   #27
head_unit is offline head_unit  United States
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Originally Posted by montana1 View Post
Lojzek,
When you speak of RLC and RC networks used to tame impedence peaks; are you referring to those implemented in the X over design?
Yes. Once upon a time, KEF implemented complex crossovers with networks like that, to make the impedance peak-free (I don't recall ever seeing measurements of the results). Their advertising quoted Richard Small as saying "We've made your amplifier twice as powerful!" and he got a lot of flak for it. Later on when I talked to him about that he laughed and said that yeah, perhaps that had not been a good phrasing.

What he meant was that many amplifiers have trouble delivering current into impedances with severe phase angles which many speakers have. The amps will exceed the transistors' SOA (Safe Operating Area),* distorting and/or going into protection mode. All kinds of evil things may happen at the outputs which are not good for sound quality or your speakers. The KEF setup would let many amplifiers deliver more actual power to the speakers. This is probably more relevant to receivers than to massive outboard amps. I don't think KEF does this any more, at least they don't market it, probably because the huge capacitors and inductors needed to try and notch out bass impedance peaks get really expensive.


*I don't know what the tube equivalent is. A KEF benefit with tubes would be flatter frequency response due to less impedance interaction.
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Old 2nd January 2018, 01:47 AM   #28
head_unit is offline head_unit  United States
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Quote:
Originally Posted by montana1 View Post
...suggestions as to what amplifier specifications to look for in properly matching loudspeakers...
Tough question. I firmly believe there is still a lot of mystery about what actually makes good sound. I tend to want an amplifier that is an accurate amplifier, i.e. with:
- Low noise,*
- Low output impedance**
- Low distortions (there are many kinds, but we don't really know how relevant each is or what is a meaningful number)
- Rated to deliver significantly more power into 4 ohms compared to 8. This indicates the amplifier hopefully has enough "beefiness" to deliver into the varied impedance of an 8 ohm speaker ha ha
- Crosstalk
but really we have no idea how to measure the "sweetness" or various other aspects of an amp, and many folks don't believe in any such things. Personally, I suspect there are dynamic behaviors that we haven't conceived and thus don't measure, and distortions that don't get measured either. Another aspect that rarely gets measured is HOW the amp clips-gracefully? Huge positive and negative DC spikes? Ultrasonic oscillation? Usually we don't know.

What is definitely true is you can find a lot of amps whose adherents LOVE their sound, but the amps "measure bad"


*but watch out: many amps specify S/N (Signal-to-noise) by comparing their raw noise to maximum power. This is not too relevant-what IS relevant would be the noise level compared to 1 watt, since THAT is what you would hear out of a tweeter.
**Also not measured in standardized ways, especially when called "damping factor" PLUS this varies with frequency...
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Old 2nd January 2018, 01:52 AM   #29
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Matching amplifier to loudspeaker question(s)
head_unit… you ar elimiting yourself to voltage amplifiers which are at a disadvantage because a loudspeaker is a current device and a voltage amp is dependent on the speaker impedance to be the R (ideally fixed) in the I/V conversion.

dave
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Old 2nd January 2018, 02:00 AM   #30
eriksquires is offline eriksquires  United States
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To kind of follow up on Dave's statements, head unit, while you are describing a beefy SS amp, you should keep an open mind. Some of the best amps/music I ever heard were from amps which were noisy and had high output impedance by comparison. Seductive liars if you will.

It is absolutely worth the experience, even if you don't buy them.

Best,

E
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