Hopkins' System

[hopkins]

By placing a large 5cm thick PET felt panel on the front of the Silbatone cabinet (with a cut-out for the speaker, obviously), I was able to smooth out the frequency response:



The increase in the level above 800Hz (approximately) that I had measured previously was the result of the "baffle step", I believe.

The response above 4kHz is dependent on the microphone's angle to the speaker, and here with a slight angle I get less of a "hump" and a more pleasant sound.

Reaching perfection is not the objective here - it is more a question of understanding how the speaker behaves in different cabinets. I will be testing it in a larger cabinet soon (but need to make a circular piece of wood to adapt to the larger size of the cabinet's opening).

 

[hopkins]

I ordered a SoundCore Motion X600 bluetooth speaker, for use around the house. It's a step up from using my phone or tablet to listen to music casually in the kitchen, on my terrace, or late at night in my couch when I don't feel like using my system. For that application, I thought the price was "right" for me, but It is always tempting to spend more.

Online reviews of these products address sound quality in a fairly basic way, with essentially two criteria: bass output, and "clarity". Even on ASR you don't find, as far as I could tell, any measurements of these types of speakers. I guess the premise is that the sound quality is so low that it's not worth spending time on them?

Clarity is always a good thing to have, and it is surprising how so many low budget products, such as powered desktop speakers, or even small bookshelf speakers made for "hi-fi", miss the mark.

Anyway, I'm basically happy listening to music on any device - maybe that's because I know that if I really crave for high-fidelity (relatively speaking, of course), I can always choose to listen to my main system? But let's be clear, I would rather give away my hi-fi "rig" than my music collection!



The woman looks happier than her boyfriend - he looks like he's pretending, trying hard to play the role. Maybe he's actually an "undercover" audiophile

 

[hopkins]

i listened to someone else's video of his Altec 755A speaker and found the sound to be very seductive:

Julie London - It Never Entered My Mind. Recorded in 1955. Vocals and guitar (Barney Kessel) - a simple set up in which her voice shines, not being drowned out by the rest of the cast, who here offers delicate support.

Julie Is Her Name - Wikipedia

en.wikipedia.org

The original liner notes (LP, on the Internet Archive) provides the following information about the (spectra-sonic) sound:



I had never heard of "spectra-sonic" sound, and a Google search did not help me out. At least it tells us that the average customer purchasing a record in 1955 felt sound quality of the recording was important, in spite of the fact that they were not listening to 300.000$ Magico speakers

I then listened to that track on Qobuz, and immediately found the vocals to be distorted in some way. WTF? What a shame! This is something I think you will be able to notice from the first syllables she pronounces. I hope it is not a figment of my imagination!

You can hear this on any YouTube version as well:

As a side note, the digital versions are not "pure mono", there is actually a slight channel imbalance. That does not explain the issue with the sound quality (I checked by listening to a single channel panned equally on both channels to compare). If you are curious to hear the difference between the two channels, here it is, and it is roughly 30db lower than the average volume of the track, but as you can see it is still significant:

https://storage.googleapis.com/cloudplayer/samples/Julie%20London%20-%20It%20Never%20Entered%20My%20Mind%20-%20inverted.wav

Anyway, since I enjoy this album, I ordered a 1956 LP on Discogs, and will be curious to listen to it and see if the analog version really provides "purer" vocals.

This may be a case where the difference between analog and digital is sufficiently high that you can hear it even in a system video. To be confirmed (that there is not something else at play).

When listening to the digital version, you will notice that there is significant level of background "hiss" as well, but that is, at least to me, less of an issue, and unless you have a mint LP version and an awesome turntable, it's also going to be there, to some degree, with analog. It could also be embedded in the master tapes. The high volume level of the background noise probably prevented reducing it with digitally processing.

 

[hopkins]

Concerning ECDesigns' powerDAC-SX, some more "under the hood" explanations from the designer highlight some of the specificities of this very interesting product:

"The PowerDAC-SX is a high power D/A converter that uses exclusively electronic on/off switches and resistors to generate the signal for the speaker.

The idea is to remove the entire analog (always loss/distortion) signal path. This allows you to get the most out of digital audio, where every bit is guaranteed to arrive correctly at the speaker without any distortion or degradation that you would always have with analog circuits. In short, a completely transparent, loss-free signal path.

Furthermore, the PowerDAC-SX offers an enormous bandwidth (not possible with conventional amplifiers) so that phase distortion can no longer occur. All local / global feedback loops are also removed, so the output responds without any delay.

With all amplifiers the bandwidth must be limited to prevent instability (oscillation). As a result, the output always reacts with a delay and phase is distorted. Due to this delay, local / global feedback loops (necessary to keep distortion low) in the amplifier can never respond immediately. During the time that the feedback system is adjusting, distortion always occurs for a short time.

Every amplifier has local feedback (relatively fast, small delay) and often also global feedback from speaker back to the amplifier input (relatively slow, large delay). If the amplifier distorts without global feedback (this is always the case), distortion is guaranteed to occur during tracking of the input signal.

Finally, the linearity of an amplifier depends on the linearity of the input stage that must compare the incoming signal with the speaker signal (difference stage, part of global feedback system). I've never seen a perfectly linear input stage, so this basically makes every amplifier non-linear.

With the PowerDAC-SX, each voltage is recorded using precision resistors and switches, guaranteeing almost perfect linearity. Because there are no more local/global feedback loops, related distortion is completely avoided."

 

[hopkins]

Last night I went to see this young trumpeter, Malo Mazurié, play with his trio (piano/bass/drums). His last album is worth listening to. Anyway, I found this video on YouTube where he is recorded in the streets of Paris. It reminds me of the movie "Begin Again". There are not too many onlookers, but they seem to enjoy it!

 

[morricab]

Last night I went to see this young trumpeter, Malo Mazurié, play with his trio (piano/bass/drums). His last album is worth listening to. Anyway, I found this video on YouTube where he is recorded in the streets of Paris. It reminds me of the movie "Begin Again". There are not too many onlookers, but they seem to enjoy it!

Its very good but, as you can see, it is still a produced product as evidenced by all the microphones.

 

[morricab]

OneMic Series - Ismay - The Lonely Stallion (youtube.com)

Not my favorite music but very interesting recording with a single mic!

 

[hopkins]

Its very good but, as you can see, it is still a produced product as evidenced by all the microphones.

Agreed. I just like the concept of recording in the streets!

 

[morricab]

Paul Gilbert OneMic (test session) 05-08-18 (youtube.com)

 

[morricab]

OneMic Series - The David Grisman Quintet - Del and Dawg (youtube.com)

 

[hopkins]

OneMic Series - Ismay - The Lonely Stallion (youtube.com)

Not my favorite music but very interesting recording with a single mic!

It sounds good on my headphones! That big barn-like structure has good acoustics.

 

[hopkins]

By the way, one microphone is how things were first recorded, and it sounds so good!

Can you believe this was recorded in 1928?

 

[morricab]

By the way, one microphone is how things were first recorded, and it sounds so good!

Can you believe this was recorded in 1928?

In some ways we have regressed as it's not about capturing live sound as much as it is producing a "product".

I am assuming it was not recorded on tape but direct cutting of a lacquer?

 

[hopkins]

In some ways we have regressed as it's not about capturing live sound as much as it is producing a "product".

I am assuming it was not recorded on tape but direct cutting of a lacquer?

I believe recording to tape only started after WW2.

 

[morricab]

Tape recorder - Wikipedia

 

[morricab]

STeve Hoffman
"Pre-tape era stuff 1925-41 was recorded direct to disc on thick wax 78 RPM blanks."

A bit crude but contributes to the directness of the sound. A lacquer with modern cutter is a lot quieter and probably a lot more accurate.

 

[hopkins]

Yes, the instruments are not as full sounding, but the overall balance and dynamics are nice.

 

[hopkins]

A slightly smoother response for my Altec 755A in a larger cabinet (with some tweaking). That's pretty flat (straight lines show +/-3db) from 100 Hz to 8-9000 Hz. The measurement is taken around 1.5m away, and at a slight angle. The drop in high frequencies is progressive as you move the microphone to the left or right of the speaker. I tried adding a tweeter (borrowed from someone) with a single capacitor in series (so no filter on the Atlec) and I preferred listening without. A very good quality tweeter is expensive, it makes it difficult to test different ones. The sound of the Altec alone is nice. I would be more curious to try some kind of bass support (sub) and that is something I may explore, just out of curiosity, but I'm in no rush.

More tweaking to be followed...

As a side note, measurement of reverberation times in my living room in even close proximity to the speaker reveal a marked increase (from around 400ms RT60 to 500ms) above 1kHz. I took out my DIY ceiling panels, but should put them back temporarily to see whether it corrects that and how it changes my perception of the sound. I am still considering permanent panels but have not decided how to make them.

Piling absorption material on the floor directly against the bottom of the speaker cabinet affects the frequency response - to a point where it can be heard distinctly. So here I am thinking there is some comb effect - but I need to explore more. It's hard being an amateur!

 

[audioblazer]

Recently I tried to integrate a pair of JL audio F113 to my Focal Stella . Using REW with JL audio crossover , I was able to tackle the 40 hz roll off from the main speaker . Room treatment to tackle the roll off is tough. I have plenty of room treatments in my dedicated room
Attached raw data of my room response curve

 

[hopkins]

Recently I tried to integrate a pair of JL audio F113 to my Focal Stella . Using REW with JL audio crossover , I was able to tackle the 40 hz roll off from the main speaker . Room treatment to tackle the roll off is tough. I have plenty of room treatments in my dedicated room
Attached raw data of my room response curve

Yes, it's not easy getting good bass - there are many dimensions to it and I just don't have the motivation, at this point in time, to address it properly...