Accuphase has in general less channel separation and less controlled bass (by design). So just switching the amps without also readjusting the position of the loudspeakers is a useless test. Almost any amp will sound (subjectively) worse if just placed in place of a voiced amp of a carefully tuned system.
-
WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!
Review and Measurements of Purifi 1ET400A Amplifier
- Thread starter amirm
- Start date
Accuphase has in general less channel separation and less controlled bass (by design). So just switching the amps without also readjusting the position of the loudspeakers is a useless test. Almost any amp will sound (subjectively) worse if just placed in place of a voiced amp of a carefully tuned system.
restorer-john
Grand Contributor
What actual evidence do you have for the channel separation claim?
As for the less controlled bass claim, the very first Accuphase integrated amplifier (1973/4) produced by Kensonic Laboratory Inc had a three position rear-panel mounted speaker damping switch with the default (normal) position offering the lowest output impedance.
Channel separation: From memory I recall that some measurements in that regard were poor. About damping factor, the values quoted in your picture are indeed low, and many accuphase power amps do not have the adjustment, and they are fixed at 5 or 10.
We were talking about imaging, not drive capability. Context matters.
And it takes REALLY bad separation to affect image. For comparison, 30dB is way worse than any commercial power amp I'm aware of, yet is near SOTA for phono cartridges.
A look through a few Stereophile reviews showing impedance plots indicates very few speakers have anything close to flat 8-ohm impedance.
Negative feedback is not something many consider "wrong".
This is how a well engineered speaker should measure.Just about all modern speakers are wrong.
This is the JLTI Elsinore.
With engineered amplification, there is absolutely no advantage to adding in piles of extra crossover components to get a flatter impedance curve- especially when the biggest deviation is left in place. Joe has been challenged again and again for evidence that his hobby horse has any technical merit, and his only answer is to whine about being persecuted.
The impedance is indeed beautiful to watch but I disagree that this is how the load of a loudspeaker should look like in absolute terms. Perhaps if your amp is an OTL tube amp you particularly love, or some other amplifier whose response considerably varies with the load. In other word, a crappy amplifier.
I counter with a different example: The loudspeakers I recently designed. Here's the xover and the simulated response using measurements for the drivers in their enclosures (the actual measurement is very very close).
As you can see, not many components in the crossover circuit itself, the response is within +-2Db from about 150Hz to 20Khz (under that there is an active subwoofer that is mostly cut at 60hz – which is where the woofer starts to drop significantly – but offers a bit of support up to 150Hz to keep the bottom quite flat), and It is a 97Db speaker. The impedance is always close to resistive, its peaks are contained, there are not bad drops, therefore any half-decent amplifier would be able to drive the speakers without any trouble. Because of the sensitivity, a SE triode amp would probably drive them well.
The response (with the above caveats) is more or less as good as that of the JLTI Elsinore (I cannot get rid of the little hole at 3-3.4Khz, it is a feature of the driver itself) and its phase is quite close to linear. This was quite tricky to obtain and the solution was to use a 3rd order low pass on the mid-woofer and a 1rst order high pass on the mid-tweeter (which under 1K drops like a 3rd order itself), so the acoustic slopes are close to 4th order, but the actual electrical xover f3 points are not the same, in order to accomodate some quirks in the response (the baffle width for the Faital is part of the design) and allow the two drivers to be wired in phase (a 3rd order + a 1rst order would otherwise behave like a 2nd order filter, which would requires inversion of one of the drivers, with corresponding flipping of the phase). Impulse, decay, CSD in room are all good and THD is mostly at -50Db at 1W.
By the way, the components are
1) Beyma TPL 150H with rear chamber and felt removed, put into a effective 5L closed box, with its original waveguide but with Luis Garcia's acoustic filter/rephaser (discussion and design at DIYAudio) inserted between front magnet and waveguide - we are well in TAD 2001 / Vitavox S2 territory with these mods, at a fraction of the price. With respect to the already highly respected stock driver, distortion is reduced by 20Db, some resonances are tamed including a nasty peak at 8Khz and a 1.5Khz one that leaves a decay tail - in other words it makes it usable from about 1.2Khz.
2) Faital Pro 12PR300 (which, apart from max power, is even better than the Beyma 12p80nd the TPL 150H is often paired with).
Crossing the TPL and the 12PR300 that low allows for the dispersion lobes to roughly match, at least in the horizontal plane. Hence I can use a 12" woofer instead of something smaller, that would have had problems reaching 60Hz. Also, the ridiculously low moving mass of the 12PR300 still allows it to be very fast at 1-2khz allowing for a good transition between the two drivers (cross them higher and you feel you have two different speakers in the room...).
The two subs (one per channel) use each a pair of Goldwood GW‐215/40/8 sound reinforcement woofers. These drivers stink for most applications, but if used in a Ripole they are more than fine, and they are cheap. They look ugly, but another advantage of the Ripole construction is that they are hidden! My Ripole design has intentionally different front and rear chamber depths, and simulations suggested I would get two relatively mild 6-9Db peaks due to resonances (200 and 320Hz) instead of a monster 15-18Db resonance at 320Hz. Measurements confirmed this. It makes much easier to filter the subwoofer. Also, the shape of the rear lobe make if possible to put the sub also relatively close to a room corner.
Of course I am using my Neurochrome/Purifi build here for the top two ways (and a Hypex Fusion 501 plate amp for for each of the subs). Since this is actually a Purifi thread I must mention this. But also my humble gainclone drives them fine.
Last edited:
"Well-engineered" to me is much more than just the impedance plot. With modern amplifiers offering very low output impedance and copious amounts of power, I put the emphasis on things other than impedance (though consider it if very low across the audio band). I had never heard of these speakers, but if they measure well and sound good, you've got your perfect speaker. They are DIY?
Not exactly a pile of parts. More like nothing much there. The only cross-over component for the "top" mid-bass is one single lonely inductor
http://www.joerasmussen.com/elsinore/elsinore_index.htm
Ten parts could be taken out if you eliminate the evidence-free goal of flattening the impedance (other than, you know, the portion of the biggest deviation from constant Z).Not exactly a pile of parts. More like nothing much there. The only cross-over component for the "top" mid-bass is one single lonely inductor
http://www.joerasmussen.com/elsinore/elsinore_index.htm
View attachment 147873
Just about all crossovers have extra components for all sorts of reasons-resistors because drivers sensitivities are not matched,notch filters,zobel networks etc.And you could argue anything other than a first order crossover has too many components. Or that any crossover is bad.Indeed some speaker builders do.
This crossover has extra parts that bring absolutely nothing to the table other than giving Joe something to talk about. About ten of them.
Joe's understanding of electronics is not particularly deep. And he is VERY resistant to testing his own claims. Gets in the way of huckstering, his specialty.
There would be many that disagree .Including many happy users of his Elsinore speakers.Making speakers with benign load charcteristics is an honourable objective and there are many examples of companies that have pursued this approach and achieved both commercial success and satisfied customers.Tannoy Prestige and Harbeth for example.The ability to use simple purist and humble amplifiers with these sorts of speakers and still achieve great sound is an intelligent and considered approach.Amplifiers like the wonderful sounding but affordable 15 watt Bakoon SCA-7511 for example .
Perhaps personal vitriol is best left out of these sorts of discussions?It is disappointing. to come here and encounter that sort of response.
The target market is not people who know enough to recognize bullshit. That leaves a rich field.
First, my apology to our moderator(s) for polluting this review thread. Promise to be my last post on this "off-topic".
I'm highlighting just this 6 components, which forms 2 legs directly across the amplifier output, as parallel loads to the rest of the speaker.
Here is what they do. The top are their impedance magnitude and phase plots, which is parallel to the (rest of the) speaker. The bottom is your precious amplifier power they turn into waste heat (with an output of 2.83 Vrms, which will give 1 W into a 8 ohm load). For what?
The 4 "mid-bass" drivers have no real cross-over to speak of. Only a single inductor in series with the drivers, and these inductors can only add an impedance linearly proportional to frequency. "Well engineered"?
I'm highlighting just this 6 components, which forms 2 legs directly across the amplifier output, as parallel loads to the rest of the speaker.
Here is what they do. The top are their impedance magnitude and phase plots, which is parallel to the (rest of the) speaker. The bottom is your precious amplifier power they turn into waste heat (with an output of 2.83 Vrms, which will give 1 W into a 8 ohm load). For what?
The 4 "mid-bass" drivers have no real cross-over to speak of. Only a single inductor in series with the drivers, and these inductors can only add an impedance linearly proportional to frequency. "Well engineered"?
Probably not audible but definitely measureable if the modules' performance hasn't been degraded by input buffers or other sundry add-on circuitry.
I guess I'm trying to decide whether the extra 1,000 is worth it. I can swallow that if there's a noticeable audible improvement. It just being better on paper makes it much harder for me to just eat that cost.
Similar threads
- Poll
