Apogee Duetta Signature Rebuild

User211 said:

The Parasound A21 was the best SS option tried I think. But after 6 months I found myself hardly ever using it. So it got sold. For short term demo purposes it really impressed.

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As I don't live with you, Justin, (sighs of relief from both of us ) I only heard it short-term - but for me that Parasound A21 was easily the best sound I have heard from your old Apogees - supremely in control, awesome bass power, but with a touch of a warm inviting glow to the mids. Nice. It did have a bit of a sting at the top end, though - a bit baffling that, as a long term A21 user I didn't hear that in my system with MBL 116F speakers, if anything the top end was just a bit too smooth and rounded off.
Speaker/amp interactions can be strange!

Thanks Justin, good to hear the project was a huge success. It makes me want to start mine even more. But alas my project list is not going down as fast as I had hoped. Bernard was right my list keeps growing from the top and speakers aren't gaining on being at the top.
Oh well all in good time.
Still hoping to get to the southeast coast of Florida to hear Brian's Divas. Was going to go this summer but it came and went without me getting there.

I started to dislike the A21s bass after a while Jerry. It had a rather dry grip that annoyed me. But my word when I first heard it hell did it impress, as you know. Beating Rowland 301s for that money is an achievement. Well discovered!

Brad - these took 2 years and 400-500 e-mails. Plus long phone convos. No rush!

OK I had to measurbate these at some stage.

The difference in low end response between these and the old pair is interesting. They are plus 6DB up at 20Hz on the old pair. Also the notorious Duetta 30Hz bass bump has largely vanished.

As can be seen there is quite clearly more bass extension. Both the old and new plots were taken at very high levels - 90DB odd (I had to use hearing protection i.e. fingers). No messing or cheating here.

So the Interstella is within +/- 5DB in-room from 20 to 10KHz. 20Hz looks to be +/- 0DB. An excellent result. Beyond 12KHz I intervened with x-over roll off. Trust me it sounds right. I've been adding it back on with JRiver to see if I have made a mistake and no, I don't think I have. Three people (myself included, LOL) whose opinions I trust agree that flat is subjectively too bright at the volumes I listen at.

I know the roll off looks severe but ears say otherwise. Plot to follow...

User211 said:

OK I had to measurbate these at some stage.

The difference in low end response between these and the old pair is interesting. They are plus 6DB up at 20Hz on the old pair. Also the notorious Duetta 30Hz bass bump has largely vanished.

As can be seen there is quite clearly more bass extension. Both the old and new plots were taken at very high levels - 90DB odd (I had to use hearing protection i.e. fingers). No messing or cheating here.

So the Interstella is within +/- 5DB in-room from 20 to 10KHz. 20Hz looks to be +/- 0DB. An excellent result. Beyond 12KHz I intervened with x-over roll off. Trust me it sounds right. I've been adding it back on with JRiver to see if I have made a mistake and no, I don't think I have. Three people (myself included, LOL) whose opinions I trust agree that flat is subjectively too bright at the volumes I listen at.

I know the roll off looks severe but ears say otherwise. Plot to follow...

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Flat anechoic measurements are the technical ideal, but....plenty of studies - Toole & Olive, Bruel and Kjaer, etc. - have shown that flat at the listening position is generally perceived as too bright. Folks tend to prefer a smooth rolloff from low to high frequencies, which is why RC target curves follow that paradigm.

When you measure LF, Justin, say 20-250Hz, be sure to do it at ~85dB to minimize noise floor contribution, and smoothing should be no higher than 1/12 octave in order to adequately see typical FR peaks/dips.

I actually am not sure of the level I took the readings at Ken. What I did was made sure the volume was in the same ball park as the old Duettas so obvious correlation can be seen. It was loud enough to need fingers but I estimate 85-90DB. I could do another but my SPL meter has a flat battery,

1/3 octave smoothing.

Interstella is red, Signature is green.

Yup the DIRAC s/w I had a while back indeed had the kind of slope you are talking about. For the sake of looks, I'd rather see a slightly less extreme HF roll off but this does sound very good indeed. We can change an inductor value easily in the x-over (it is in a tube so not locked in by potting compound). I feel no compulsion to do so as it matches the old Duettas and I was happy with that for years.

I can only really attribute the bass response of the old Duettas to less than rigid construction. It was still a great sounding speaker despite its bad boy LF behaviour.

BTW mic is where the ears usually are, resting on top of the listening seat. I figure that is where it matters. Bass response can be altered by front wall distance but that is at 40 inches (2 inch tow in) which seems to work very well.

Measurement mic is a UMIK with maker's calibration table downloaded and applied i.e. it is pretty damned accurate.

Bear in mind that this reading is taken with a system that has 30 valves in it all rolled by ear. I know rolling can make up to 3DB difference on system FR for a single tube in parts of the frequency range. I have confirmed this by measurement. I would expect better results with all solid state gear,

Justin, can you do one more 20-250Hz @ 1/12 octave smoothing? 1/3 octave tells us little about what's going on. A chart of bass decay would provide some very useful info, as well.

Nobody ever posts at 1/12 Ken. You can see too much of what is going on!:ROFL:

Nobody ever posts at 1/12 Ken. You can see too much of what is going on!:ROFL:

Oh OK here it is. Only 5DB better at 20 Hz by this plot.

User211 said:

Nobody ever posts at 1/12 Ken. You can see too much of what is going on!:ROFL:

Oh OK here it is. Only 5DB better at 20 Hz by this plot.

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Okay, so here's what I see.... You're 20dB up at those peaks around 30Hz vs. 10kHz. While no one can know what you personally prefer, that's pretty hot vs. general preferences. May be great for movies, but big bass peaks, which usually have long decays, tend to blur LF detail and will also mask midrange content. Same same for the 10dB peak ~62Hz.

The 10dB difference between L and R 25-40Hz probably isn't audible. The 5dB difference between 120-160Hz might be, but you're +- 2.5dB, which ain't bad.

Overall, I suspect that if you could drop those peaks a bit and make your 20-250Hz FR a bit more linear (fewer, smaller peaks and dips), you would easily hear and almost certainly prefer the result.

Here's a suggestion: Instead of the Crown XLS amp I suggested in the other thread, spend a bit more to get one of their DSP-enabled amps, like the CDi 1000. Yeah, it's more money, but what you can do to improve bass response with the built-in PEQ filters may just blow your mind. While I use a different tool for the job, you could easily do something like this:



Yes, that's 1/12 octave.

Hi Ken,

I tried DIRAC a while back on the older frequency response/speakers. I didn't like it ultimately. No offense but I really didn't - it just sounded odd to me. Very much like all you could hear were two speakers and not the 'band in the room". Correcting for the room/speakers is an unnatural affair that never happens with real instruments so why should it with your hi-fi? Others do like it though.

For an uncorrected large dipole in a relatively small room I think that is a very good result. Additionally, the fact we've managed lower than Neolith performance from it is an achievement (though you van do that a lot cheaper LOL), together with the huge drop in 30ish Hz bass emphasis. It is obviously better than the original

I will use a bit of selective PEQ for interest at 60Hz and look into a bass decay chart. Will post the results.

As I said when using DIRAC, I find PEQ correction alone provides much more satsfactory results to my ear than DIRAC, which does rather more.

RUR said:

The 10dB difference between L and R 25-40Hz probably isn't audible. The 5dB difference between 120-160Hz might be, but you're +- 2.5dB, which ain't bad.

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Ooh crikey Ken you haven't read my previous text. That isn't left and right on the plot, that is old versus new Duetta. I'd be flipping worried if I saw that in my rectangular room! You should look at the RED LINE ONLY for Interstella. Things are no where near as bad as you have asserted!

In other words, please re-assess!!

In my room with left and right Duetta independent channel FR measurement is so identical as to be irrelevant.

The Duetta was judged technically excellent when it came out, apart from the bass hump, which could be eradicated with a piece of card, placed behind the panel. See the Martin Colloms review from 1988. Speaker design hasn't changed much for the better since then, though the marketing men would have you believe otherwise!

I am massively proud my judgement and Jon's excellent work have managed to substantially better the one significant "flaw", though excess bass from a planar magnetic panel can be enormous sonic fun with the right material. In fact that response was really enjoyable with most. Really (hard to believe I know).

Justin,

Now I have not read every post on this thread... But the jist of it is this - you are a fanatic and I applaud your hard work.

Bravo sir.

User211 said:

Ooh crikey Ken you haven't read my previous text. That isn't left and right on the plot, that is old versus new Duetta. I'd be flipping worried if I saw that in my rectangular room! You should look at the RED LINE ONLY for Interstella. Things are no where near as bad as you have asserted!

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You are so very right and mea culpa, Justin! The red line (Interstella) is consistent within +- 3dB, which is very good performance, indeed. If you have one handy, I would PEQ the peak @ ~60Hz, but that's about it!

User211 said:

Correcting for the room/speakers is an unnatural affair that never happens with real instruments so why should it with your hi-fi?

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Ever heard a real live band in your room?

The simple answer is that our rooms are EQ-ing the output of our speakers, whether we like it or not. Modal behavior, in particular, becomes increasingly problematic in small rooms and longer frequencies are very difficult to deal with without multiple subs and/or EQ in some form.

In re: your Dirac experience, Justin, I don't comment on others' experiences with these complex RC products unless I've actually heard them in the room under discussion. Way too many variables in play.

No Ken but I know what bands in small venues sound like.

I regularly play bass and electric or acoustic guitar in my listening room, though. Using a high quality digital recorder the electric records terribly. It is full of room interactions that sound awful when played back. By itself, it sounds fine - excellent, as you'd expect. That is with the natural room acoustic.

Studios know this and go to great lengths to prevent the environment from wrecking the recording. Given that, when I play it back in a natural room acoustic without DIRAC it sounds fine. Apply DIRAC and IMHO it does sound unnatural. Not necessarily bad, just unnatural. You need those room interactions to make it sound natural.

Say for instance a chap buys a grand piano and shoves it in a room. He then shoves it in another and his wife say "the piano sounds much better in this room". Real instruments always react with rooms in a similar way a hi-fi system does (well, more or less), Sure, treat the room a bit or use PEQ to equalise any FR anomalies, but completely correcting for the room digitally in a DIRAC type manner does something a real instrument never in practise does.

That pretty much sums up what I think and have experienced.

Anything goes, Ken. This is audio I have nothing against anyone who passionately believes in digital room correction.

User211 said:

Anything goes, Ken. This is audio I have nothing against anyone who passionately believes in digital room correction.

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Fair enough, Justin, but I would suggest that your "sound(s) unnatural" experience may not be representative of what's possible with well-designed, well-implemented SoTA RC.

Have you got bass decay plots for your room/system Ken? Care to post? Not sure it'll say much about the speaker TBH but hey. There is some definite room post-ring here when playing loud and stopping suddenly.

Despite what I have said it doesn't mean I am not curious enough to try and investigate these things of course

If so, best posted on a separate thread?

User211 said:

Have you got bass decay plots for your room/system Ken? Care to post? Not sure it'll say much about the speaker TBH but hey. There is some definite room post-ring here when playing loud and stopping suddenly.

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I only take bass decay measurements when I'm installing or moving speakers/subs, Justin, and I don't keep them. Last set I took was middle of last year when I sold the SubMersive and moved the JL next to my listening chair. Because the sub was now nearfield (and EQ'd), the decay figures were understandably very good and well within general guidelines.

When I finish and install the OB subs I'm building I'll undoubtedly take many decay measurements over a period of days as I sort out where best to place the subs. I'd be happy to share the results then, if you like.