Getting your sound, science or art?

[Phil Starr]

5 hours ago, agedhorse said:

Yes, you want  to be VERY careful with bridged amps, and most class D amps are internally bridged. Most are not protected from a short between 1/2 of the output bridge and ground, this is not the normal way a fault occurs on a speaker out, the protection typically looks at either 1/2 of the bridge or (indirectly) the difference in current between the two halves of the bridge. Also, the level is (or can be) higher than many scopes can handle.

 

This is a common way folks who are new to testing, or are new to electronics, or do electronics as a hobby destroy their laptops or interface (depending on where the interface is located). The fault is large enough that it typically lets the magic smoke out pretty instantaneously and catastrophically.

 

I've been testing class D amps professionally for over 20 years, there are a lot of necessary tricks to get good results and data, especially power and THD data (depending on the modulation scheme and output reconstruction filter type). It's harder than it looks, especially if the numbers need to be accurate.

Thanks this is really helpful. Obviously we were aware of this which is why I mentioned it. We used an isolating transformer to separate the amps from our measuring equipment and spent most of our time checking that this was not affecting the results. Hence our failure to take more measurements. I probably should have warned people not to rush out and home test their class D amps until we have a safe method. Thinking about it there’s no place for probably. 
 

We aren’t proposing to encourage people to make measurements at high power. The kit for that is not something that most people can cobble together and some of the currents and voltages can be dangerous. The aim is to develop a simple method for people to make repeatable measurements of the small signal frequency responses of amplifiers only. It’s good to have you on board and any practical experience you can offer will be really valuable.

 

 

 

[Chienmortbb]

@Phil Starris right, the greatest  care was taken to ensure the integrity of the Amps under test. It has to be remembered that some high powered amps, especially those not using bridging techniques, are capable of over 250v peak-to-peak between the speaker terminals.

 

It is also worth asking the question as to whether you need to use the power amp output to measure the frequency response of an instrument amp. 
 

The figures I got at the preamp output was so close to the response at the speaker terminals that it makes no sense checking the sharp end. 
 

It seems that, excepting @agedhorse’s patent, most designers content themselves with the preamp section and that sets the sound of the integrated amplifier. 

 
Incideny I would love to try one of @agedhorsedesigns and might just start saving up for one. 
 

 

[Kiwi]

On 14/10/2022 at 05:34, Phil Starr said:

So is it better to know all this stuff, seek the 'truth' and hunt the perfect rig or to live in blissful ignorance and just max out the tone controls until it's time to trade your gear for new in the eternal quest for sound nirvana. What do you think?

 

You're describing what nearly 20 years of playing experience has led me to discover for myself.  I'm also a great believe in matching basses to amps (and speakers) for this reason.  Ultimately all three components (bass, amp and speakers) are part of the recipe and we choose flavours that compliment and enhance.  You described the amps in your OP in exactly the terms I expected after playing through them which was affirming.

[Downunderwonder]

6 hours ago, Kiwi said:

matching basses to amps

Got some examples?

 

In my experience I never thought about "what bass with amp X" or "what amp for bass X".  I chose both for their own qualities never once considering how the amp might react differently to another amp with the same bass or vice versa.

 

All my amps have had sufficient input impedance to accept piezos and I don't run stereo.

[agedhorse]

13 hours ago, Phil Starr said:

We were measuring the output of the amplifiers only. No speakers were involved so none of these concerns would be applicable. I wonder if you are confusing these measurements with the speaker shootout I carried out at the same meet-up.

Yes, in part because speakers were being discussed within this thread as well and the combined measurements of speakers and amps tend to go hand in hand with these discussions.

[agedhorse]

Duplicate post

Edited October 22, 2022 by agedhorse

[agedhorse]

11 hours ago, Chienmortbb said:

@Phil Starris right, the greatest  care was taken to ensure the integrity of the Amps under test. It has to be remembered that some high powered amps, especially those not using bridging techniques, are capable of over 250v peak-to-peak between the speaker terminals.

 

It is also worth asking the question as to whether you need to use the power amp output to measure the frequency response of an instrument amp. 
 

The figures I got at the preamp output was so close to the response at the speaker terminals that it makes no sense checking the sharp end. 
 

It seems that, excepting @agedhorse’s patent, most designers content themselves with the preamp section and that sets the sound of the integrated amplifier. 

 
Incideny I would love to try one of @agedhorsedesigns and might just start saving up for one. 
 

 

I would suggest that in general, testing at the preamp out is much safer, and likely to get results that are plenty close enough.

[tauzero]

On 19/10/2022 at 08:39, Phil Starr said:

So turning up the volume of anything amplified makes it sound like you've boosted the bass and treble and here's the punchline: boosting the bass and treble at any frequency makes an amp sound like a bigger more impressive amp. I wonder why anyone would want to do that in a showroom situation

 

There used to be a loudness button on many a hi-fi amp (may still be, I don't seem to have any on mine). What that did was raise the bass and treble levels to make the perceived frequency response flat. There's a good summary of it here: https://www.extron.com/article/loudnesscontrol_ts. That would be just the thing for a home practice button.

[Kiwi]

On 23/10/2022 at 02:26, Downunderwonder said:

Got some examples?

MM Stingray : Mesa Boogie Bass 400+/Warwick Pro Tube with EBS Neo212 (even though the Warwick amps are coloured for Warwick basses,  they suit stingrays too) 

 

Fender Jazz: SWR400 and SWR Goliath 4x10 (slappy stuff)/Mark Bass Little Mark + MB 104HF(fingerstyle) 

 

Fender Precision: Ampeg SVT Classic +8x10 (sounds horrible with any other bass apart from a jazz with flats) 

 

Status Empathy or Modulus Quantum or Zon Legacy :SWR400 and SWR Goliath 4x10/Hughes & Kettner Bassbase 600 + EBS Neo212 (these amps do a great job of making graphite necked basses sound thicker and fuller) 

 

Jaydee Supernatural / Status Series 2000: Trace Elliot MkIV or V + 1048 cab (probably needs no explanation but...that eighties burp). 

 Warwick Thumb or any kind or Warwick Bass really) : Warwick ProFet plus 2x12 or 4x10.  

[nekomatic]

On 16/10/2022 at 12:01, Phil Starr said:

I'm looking at using REW which is free and pretty powerful.

‘Tchuh’ I thought, ‘I bet it’s Windows-only though.’

 

It is not Windows-only!

 

Thanks for the tip and I’ll be happy to contribute measurements of a Laney RB-500H and a Marshall MB15…

[Phil Starr]

OK back on track having got rehearsals and gigs out of the way. So having established that amps aren't neutral 'wires' that just increase the volume and that humans like a smiley faced eq because of the way our hearing works it's time to address Trace Elliott watts in the shape of the ELF that "never ceases to amaze"; magic or clever use of science? Oh, look it's a smiley face with 5db of bass boost at 100Hz and 7db @ 4kHz with the bass rolling off nicely below 80hz. The loudness control is set to always on so an instant hit in the showroom and in home practice and that big peak at 3-5kHz is just where our ears are most sensitive so it is going to sound loud. Interestingly the mid dip and the mid control centre frequency are at 400Hz just like the Warwick and the TC BAM as is the quoted power output.

 

No criticism of any of these amps, a lot of people are going to love the baked in sound of the ELF, I mean really love it and it is boosting those upper mids so it is going to sound loud! Filtering the bass a little just makes sense with a little amp likely to be used with little speakers and with limited ability to dissipate heat, and frankly most of us won't miss it. It's a very different approach to Ashdown with their flat response across the range of a bass.

 

 

 

 

 

 

[Phil Starr]

Now this is where it gets interesting, to me at least. Let's have a look at one of the classic bass speakers used in a lot of mid-priced cabs, the Eminence 12A-2 and beside it what happens to the bass response when you put it in a 50litre box. You can see the speaker has a natural peak of about 4db in the 1-4kHz region and almost 3db of bass boost just above 100hz when you put it in a portable sized cab. Once again you have a smiley faced loudness contour, the auditory version of a high salt, high sugar snack. It's almost the same response as the ELF just slightly less exaggerated. Obviously if you mix these two they are going to add their irregularities to make a super sweet, super salty mix. Only palatable to a few maybe. Can you tame it with the tone controls? Well that depends, you have that 400Hz mid control but it of course is only centred there. Turn it up and it will boost the 120hz as well as at 1kHz where the eminence is starting to peak. Turn down the treble? Well the Eminence is starting to fall off the side of a cliff at this point so cutting a few db at 2kHz is going to cut the highest frequencies right out of your sound. If your sound is Jamerson of course that won't. worry you. (Brilliantly Jamerson is in the spell check)

 

So now we are back to art. No-one is going to sit down with all these graphs and use them to set their tone controls. By the time you've factored in the bass, pups, strings, fx and room acoustics it is just too complex but it is easy to see why some marriages just break down. Marrying the slightly bright old school sound of the ELF with the slightly bright old school sound of one of the bass world's best loved speakers isn't going to let you maneuver very much and you might miss those mids when you are playing with your over loud band. 

 

[3below]

24 minutes ago, Phil Starr said:

....So now we are back to art. No-one is going to sit down with all these graphs and use them to set their tone controls....

 

It certainly gives a starting point for further experimentation, armed with the right kit

[mario_buoninfante]

Really interesting post.

I do believe that as a musician the most important of the 2 is art.

There are so many things that human beings do well in life without knowing anything about the "science" behind it.

That said, knowledge is a good thing though and so, I think it's important to have a basic understanding of the tools used to make art. Just the way painters used to (maybe still do) make their own colours and brushes.

In terms of "flat/perfect" frequency responses, I doubt anything with it would sound great. Humans are imperfect and attracted by imperfections, also our hearing (as pointed out already) is anything but perfect.

 

Few days ago I was looking at these headphones measurements. In a similar way, even some really expensive and "good sounding" HPs have "terrible" graphs

 

https://www.stereophile.com/content/innerfidelity-headphone-measurements

[agedhorse]

3 hours ago, Phil Starr said:

Now this is where it gets interesting, to me at least. Let's have a look at one of the classic bass speakers used in a lot of mid-priced cabs, the Eminence 12A-2 and beside it what happens to the bass response when you put it in a 50litre box. You can see the speaker has a natural peak of about 4db in the 1-4kHz region and almost 3db of bass boost just above 100hz when you put it in a portable sized cab. Once again you have a smiley faced loudness contour, the auditory version of a high salt, high sugar snack. It's almost the same response as the ELF just slightly less exaggerated. Obviously if you mix these two they are going to add their irregularities to make a super sweet, super salty mix. Only palatable to a few maybe. Can you tame it with the tone controls? Well that depends, you have that 400Hz mid control but it of course is only centred there. Turn it up and it will boost the 120hz as well as at 1kHz where the eminence is starting to peak. Turn down the treble? Well the Eminence is starting to fall off the side of a cliff at this point so cutting a few db at 2kHz is going to cut the highest frequencies right out of your sound. If your sound is Jamerson of course that won't. worry you. (Brilliantly Jamerson is in the spell check)

 

So now we are back to art. No-one is going to sit down with all these graphs and use them to set their tone controls. By the time you've factored in the bass, pups, strings, fx and room acoustics it is just too complex but it is easy to see why some marriages just break down. Marrying the slightly bright old school sound of the ELF with the slightly bright old school sound of one of the bass world's best loved speakers isn't going to let you maneuver very much and you might miss those mids when you are playing with your over loud band. 

 

Designers certainly sit down with these graphs when developing amps and speakers. They really aren’t intended for end users, especially because of the misunderstanding of the correlation between the graphs and how this translates to end results.

[Phil Starr]

6 hours ago, agedhorse said:

Designers certainly sit down with these graphs when developing amps and speakers. They really aren’t intended for end users, especially because of the misunderstanding of the correlation between the graphs and how this translates to end results.

I wondered what you'd offer here. I can't imagine you would design anything but systems. You aren't working at the bottom end of the market and there is some quality engineering going on. I guess each new range starts with a design spec and a blank sheet of paper. Everything in a new range of products is going to work well together but do you retrospectively check a new amp will work well with all the old speakers and vice-versa? That would work for a manufacturer with a 'house sound' but limit some innovations.

 

It would be interesting to expand upon this. If all manufacturers are conscientious and competent then buying a whole rig from one range would make a lot of sense. If they are consistent in their house sound then buying an amp from one range and mixing it with a speaker from an older range would still cut down the variables they would have to deal with. There would be advantages to both customer and producer in brand loyalty.

 

People will still mix and match, I guess it's the difference between cooking from a recipe where someone professional has blended the ingredients to produce a consistent and reliable result and trying different ingredients each time in search of the unobtainable best with the risk of something awful.

 

Your detailed thoughts would be really interesting.

[Stub Mandrel]

I'm convinced we can over-exaggerate the significance of some of these curves. 3dB of extra or less bass or treble will be very subtle, 6dB isn't huge.

 

Whrn my live sound isn't right I seem to make adjustments in the "two hours per tweak" sort of range, and that seems to work. My frustration is usually that the pa has too much bottom end, or rather they cut my middle and top too much (then say my amp is booming 🙄 ).

 

I do find myself dialing in a smile for home practice - and why not!

 

Live or rehearsal with the Orange Terror everything starts near 12 o'clock andvgets tweaked. Bass and treble often get a slight boost,  mid can go either way. Sometimes treble needs a big boost to balance the pa...

 

I'd be interested to know the actual response of the Terror, as the rumoured profile would be almost unusable!

 

My venerable 80s Trace with GP11, I have the graphic set to lift the mid and treble about 3dB. Whether it sounnds better with pre-shape in or out seems to depend on:

 

The song

The bass I'm using

Which way the wind is blowing  and the ohase of the moon.

[agedhorse]

On 01/11/2022 at 00:42, Phil Starr said:

I wondered what you'd offer here. I can't imagine you would design anything but systems. You aren't working at the bottom end of the market and there is some quality engineering going on. I guess each new range starts with a design spec and a blank sheet of paper. Everything in a new range of products is going to work well together but do you retrospectively check a new amp will work well with all the old speakers and vice-versa? That would work for a manufacturer with a 'house sound' but limit some innovations.

 

It would be interesting to expand upon this. If all manufacturers are conscientious and competent then buying a whole rig from one range would make a lot of sense. If they are consistent in their house sound then buying an amp from one range and mixing it with a speaker from an older range would still cut down the variables they would have to deal with. There would be advantages to both customer and producer in brand loyalty.

 

People will still mix and match, I guess it's the difference between cooking from a recipe where someone professional has blended the ingredients to produce a consistent and reliable result and trying different ingredients each time in search of the unobtainable best with the risk of something awful.

 

Your detailed thoughts would be really interesting.

I have designed all kinds of products over my career, mostly pro audio and bass products, but some acoustic and electric guitar products too. This includes both high end touring electronics/speakers as well as lower end electronics/speakers (including for some popular brands/models).

 

I first look at the requirements, both performance and cost, and then look to see what components are already on the market that I might be able to use or easily adapt into the enclosure that the product will need. I will also look at my historical designs to see if I have already designed a driver that might be suitable. I really don't like reinventing the wheel, especially at the higher end where the transducer engineers have spent a fair amount of time and money on. That said, I probably put more energy into the lesser models because I NEED to squeeze out the most performance possible for the least cost. This is true in all product lines actually.

 

I find it more challenging to get the maximum performance out of the minimum cost, that's what separates the experienced engineers from the onanists. In the middle, giving up a dB or two of performance may not matter as much but at the low end every dB counts, and may be the difference in a viable product and one that's not. At the very high end, there's a LOT more effort placed on pattern control, the evenness of the response at the edge of the pattern, distortion, power compression (thermal and electromagnetic), and also structural since the cabinets may end up over your heads.