I've just learned that the Fostex FE126En is designed for an amp with high output impedance. Does that mean it is not well-matched for an amp with low output impedance? How does one determine the output impedance of an amp?
What kind of amplifier do you have? Tube or SS? You don´t say.
If SS, in principle they are very low impedance (high damping factor), amp brochure should state that number.
SS amps can be made any output impedance, from Low Damping all the way to ultra high Constant Current, but they must be built as such on purpose.
Tube amps in principle are lower damping, and the extreme being Power Pentodes with no NFB ... but that is currently seen only in some Guitar Amplifiers who use their own flavour of Full Range speakers, no crossovers or tweeters anywhere.
With a regular SS amplifier you will not damage your speaker by any means, they will just sound a little flatter, in the duller, less bright and punchy meaning.
Higher source impedance adds a little extra treble in general and some Bass at resonance, but we are just talking a little "extra Free EQ" here; worst case you can add it with a little adjustment of tone controls.
If SS, in principle they are very low impedance (high damping factor), amp brochure should state that number.
SS amps can be made any output impedance, from Low Damping all the way to ultra high Constant Current, but they must be built as such on purpose.
Tube amps in principle are lower damping, and the extreme being Power Pentodes with no NFB ... but that is currently seen only in some Guitar Amplifiers who use their own flavour of Full Range speakers, no crossovers or tweeters anywhere.
With a regular SS amplifier you will not damage your speaker by any means, they will just sound a little flatter, in the duller, less bright and punchy meaning.
Higher source impedance adds a little extra treble in general and some Bass at resonance, but we are just talking a little "extra Free EQ" here; worst case you can add it with a little adjustment of tone controls.
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Solid state. Damping factor "greater than 30". Please recommend a driver, or what "Q" I should look for. Thanks.
Assuming 8 ohm speakers, 8/>30 = < ~0.267 ohms output impedance or only about half of a typical wire run's 0.5 ohm, so for now a ~0.8 ohm load. Anyway, can't give you an exact Qts, just one based on typical specs since it varies with the driver's Re, Qes, Qms specs.
Also, it depends on what the performance goals are, so short of you being able to get very specific, for now just going to recommend from ~0.3-0.36 Qts, a range many drivers fall in.
GM
Also, it depends on what the performance goals are, so short of you being able to get very specific, for now just going to recommend from ~0.3-0.36 Qts, a range many drivers fall in.
GM
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I really just want to build the FH Mk3's with the FE126En, which has a Qts of 0.3. Don't want it to sound dull. Also would rather not lose sensitivity by adding resistance.
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The FExx6 series,by design, like a higher output impedance amplifier to raise up the effective Q. It will be most noticable as a loss of bass. But the bass of FH3 is dependent on placement and amount of damping below the driver. Typically FE126 uses none already (max bass). You are unlikely to notice loss up top, but the lack of bass could exagerate the sting of the peaky bits (if they even bother you).
An ideal amplifier is say 1.5 to 3Ω output impedance, typically the territory of single ended tube amps (althou it can be done in SS).
In the case, like yours, with a lower output impedance amplifier, you can play with small diameter (solid core) wire. I’d start with 24g pulled from CAT5/6, or even 30g wire wrap wire. If that is not enuff one can go to something like nichrome wire or just add a series R (i prefer to get extra impedance from thin wire).
dave
An ideal amplifier is say 1.5 to 3Ω output impedance, typically the territory of single ended tube amps (althou it can be done in SS).
In the case, like yours, with a lower output impedance amplifier, you can play with small diameter (solid core) wire. I’d start with 24g pulled from CAT5/6, or even 30g wire wrap wire. If that is not enuff one can go to something like nichrome wire or just add a series R (i prefer to get extra impedance from thin wire).
dave
That way you eliminate the skin effect for free. If I recall, gauge 20 or smaller is good
for no skin effect in the audio band.
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Run your amp at a low level with
a 1kHz signal and no load.
Monitor the output level.
Put decreasing resistance across the output.
When the voltage is halved the amp
output impedance equals the resistance.
a 1kHz signal and no load.
Monitor the output level.
Put decreasing resistance across the output.
When the voltage is halved the amp
output impedance equals the resistance.
Based on published specs and assuming it's designed based on a ~0.403 Qt for max flat, then 2 ohms total is needed, but specs are likely higher, so less in reality. Still, better to have too much 'fullness' and bleed it off with either damping or a leaky gasket than be left wanting.
GM
GM
So you apply a FLAWED test procedure and blame an excellent amplifier for your mistake? 😕
FWIW you´ll destroy 99.8% of SS amplifiers that way, unless you trigger short protection first 🙄
No amp likes being loaded with, say, 0.1 ohm or thereabouts. 😀
Or in other words: "you do not test a voltage source´s internal impedance by loading it down to death" ... emphasis on "death"
Probably better engineered than 90% (at least) of the amplifiers around these days anyway... 😉
Be that as it may, as has been noted, the Fostex FExx6E[n] series were specifically expected and designed to be used with higher output impedance amplifiers (confirmed to me in person by one of their designers) so in the absence thereof, some series R is needed to ~mimic the behaviour, either fixed or with some higher resistance wiring. Take your pick. Objectively speaking the latter is preferable if the appropriate amount can be so contrived via length, gauge &c. The 126 doesn't require as much as some of the other units in that series, but about 1ohm - 2ohms is usually 'in the zone'.
Be that as it may, as has been noted, the Fostex FExx6E[n] series were specifically expected and designed to be used with higher output impedance amplifiers (confirmed to me in person by one of their designers) so in the absence thereof, some series R is needed to ~mimic the behaviour, either fixed or with some higher resistance wiring. Take your pick. Objectively speaking the latter is preferable if the appropriate amount can be so contrived via length, gauge &c. The 126 doesn't require as much as some of the other units in that series, but about 1ohm - 2ohms is usually 'in the zone'.
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One of my reasons for wanting to build a horn such as the FH Mk3 was to get high sensitivity, so that the overall sound would be effortless and spacious, rather than strained and dull like it is with my current speakers.
If I add resistance to increase output impedance, won't that reduce sensitivity, putting me right back where I started?
Is there a horn/driver combo well-suited for a modest SS amp?
If I add resistance to increase output impedance, won't that reduce sensitivity, putting me right back where I started?
Is there a horn/driver combo well-suited for a modest SS amp?
I don't know what 'effortless' and 'spacious' mean per se, but FH3 using one of the 4in MA drivers is fine with conventional solid state amplifiers. They are in fact the baseline drivers I used when designing it, with the FE126En as an option for those who wanted it. I can't comment on your current speakers of course, since I don't know what they are.
I was under the impression that I needed a more sensitive (greater than 92 dB) speaker to get the effortless sound I'm looking for from my little amp. Unless i am mistaken, the Markaudio drivers are between 85 and 90 dB. Maybe if I go for the FH XL with the FE168EZ? Or does that driver also require a high output impedance amp?
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The Fostex FF165WK has an SPL of 92 dB/W(1m), a Total Q of 0.34, and works in the FHXL--good horn/driver combo for a modestly-powered SS amp?
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