Cabinet for wide range speaker + Class-D amp

[TinkeringSteve]

E.g. this little fella here:
https://www.visaton.de/en/products/drivers/fullrange-systems/bf-37-4-ohm

They have some pages with DIY basics, mentioning: thou shalt not use too small volume, or jumps in diameters etc., but no details or rules of thumb w.r.t. actual sizes.
Basically: what size do I need, and does only volume count, or are there minimum measures in each dimension?
They also have a free to use simulation program that seems to be geared to typical 2-way speakers, alas.

But I want to build an enclosure with exactly one speaker like that (later perhaps another variant with double size, if this test works well, and more scope of application) and some front panel electronics e.g. 5" touchscreen, MCU, audio amp and battery inside, for a special application of mine, for which that single speaker would be optimal and spare me complications, given 1) its specs are accurate and 2) I do ~ get that frequency response with the cabinet I build
I actually need a flat-ish response from 100 to 12000 Hz, thereafter it may fall off as it may.

Edit: as for size I'm aiming at: I am not looking for super small. E.g. Rigol DS1000 scope would not be a bad format. Can be bigger if need be.
Material: Wood. (front panel perhaps 6mm plywood, with some glued-on reinforcements vs. unwanted vibrations?)

There are floating around a bunch of cheap-ish 10W class-D amps around (less with 8ohm speaker - maybe just the fit here), stating something like < 0.1% THD, e.g. using the PAM8160 - now I'm not experienced at all with that. Is that credible when they don't have any LC filter parts in sight, or is that the fine print part (that's usually implicit with cheap modules from China ) ?
There are also MAX98357 based PCBs with ~3W @ 4Ohm, might be enough, but state a 10% THD. Not nice. I do want this to be in the HIFI realm, except allowing rel. early roll off at 12kHz. Can these be extended with filtering & achieve good results?
The nice thing about the latter is that they have I2S input, and my source signal is digital in nature, so adding noise with an extra DAC/ADC and analog line in between is kind of a bummer.

This is for a proto-type (still all hobby realm, and I am not an EE), so I'm looking for modules based approach, not own design.
But if there are some established open source circuits around which I can just copy & be happy & which are superior to these modules, I might look into it, too.
(btw. I know Visaton have a forum, but it seems to take ages to get access there after signing up...)

[themadhippy]

Basically: what size do I need

Speaker building is a dark art,luckily there plenty of software that make life simpler,my ancient spell churns out    
   box volume   0.379260440443311Liters
   box freq   85.3635447096166   Hz
   F3   61.4300174261142   HZ
        port dia   1 cm
       port length   7.32724983255665 cm
ideal sides   
   4.3cm
   7.2cm
   11.7cm

[Coordonnée_chromatique]

Basically: what size do I need

Speaker building is a dark art

Could you say why please ?

You can also look at this : https://www.visaton.de/en/literature-software/software

[themadhippy]

Could you say why please ?

mainly because what you hear is different to what i hear,even with the speaker specs tested yourself and using the  best software your still not certain the sound is how you like it until youve built the thing

[TinkeringSteve]

Speaker building is a dark art,luckily there plenty of software that make life simpler,my ancient spell churns out    
   box volume   0.379260440443311Liters
   box freq   85.3635447096166   Hz
   F3   61.4300174261142   HZ
        port dia   1 cm
       port length   7.32724983255665 cm
ideal sides   
   4.3cm
   7.2cm
   11.7cm

Thanks. Seems surprisingly tight. So I guess if there is more overall space in the device enclosure, I'll just put in extra walls inside, eh?
Would you put any sort of fluffy material vs. standing waves in there? How much?

[themadhippy]

Would you put any sort of fluffy material vs. standing waves in there? How much?

personally i put a layer on the side walls and back panel,some consider it wrong for a ported box as it will change the box volume.Safest bet  is to make a test box  and experiment

[Benta]

Nothing really magic about it.
The ideal speaker mount would be an infinite wall with the speaker mounted in the middle. This would ensure that the front and rear air movement caused by the diaphragm of the speaker unit could not interact, aka "acoustic short-circuit".

Not really possible in practice.

Second best solution is to acoustically isolate the rear side of the speaker unit with an enclosure. This brings up a problem: the speaker unit now has to compress/expand the air within the enclosure. The deeper the bass (= lower frequency), the more air has to be moved/compressed. The size of the enclosure has significant influence on the bass response.

Now, your speaker is rated for 100 Hz upwards, which as a rule of thumb would demand around 10 liters of volume (there's no empirical formula for this, but take it from an experienced speaker builder). Larger is better, smaller is worse, but WAF plays a big role as well.

Take it from there.

Cheers.

[NiHaoMike]

Nothing really magic about it.
The ideal speaker mount would be an infinite wall with the speaker mounted in the middle. This would ensure that the front and rear air movement caused by the diaphragm of the speaker unit could not interact, aka "acoustic short-circuit".

Not really possible in practice.

In the case of the speaker being permanently installed in a building, it's quite possible. The rear vents to the outside, which can be considered infinite for all intents and purposes. Granted, such an effort only makes sense for subwoofers, as higher frequencies already run into diminishing returns with reasonable sized enclosures.

[TinkeringSteve]

I have now tried their "BoxSim" software to try suggested values by "themadhippy", larger values, closed vs. with bass port. The differences in the frequency response shown are not that large, when I change these things, interesting...
I notice a peak, well it's alredy raising a bit before, and then with the peak, it's 6dB over baseline, of all regions in the spectrum, where I really can't have it... :-D
Now I wonder, I could either fiddle with the sizes forever, or...

would it be viable to expect a few dB less max output of the thing, and do a correction curve (e.g. FIR filter) at the digital end that's producing the signal?
I have a cheap-ish measurement microphone (the maker did offer a download with the measurement for my individual mic, though - it's at leats not _that_ cheap ),
and an installation of the now, alas, discontinued ARTA software for sweeping across the spectrum and showing the response.
Now, I don't have an anechoic chamber availble, but: There is a standard room where I will, from a standard position, use the thing. So actually, it could be good to do the correction curve with the room influence, I guess? (well actually, there are two, very different in size, rooms it may be used in, so I might do 2 curves, if that matters)
I'm not expecting to raise a week low end, but at a few kHz, flatten some hills, as it were.

[themadhippy]

As i mentioned above,make a test box and experiment,if you make the box double the optimum size you can reduce its internal  volume easily,same with the port make it  bigger and use drinking straws to reduce its area,the hardest bit is finding a way to easily adjust the port length. Use the actual sounds you'll be using ,leave the test gear in the cupboard and use the tool that will be using the thing to measure it,your ears.

[CaptDon]

Any raw frame speaker capable of going to a decent bass frequency will sound muddy with a muffled mid-range. A one speaker design is not optimal. You should at least consider one of the passive L/C crossover networks and include a mid-range speaker that would cover 750Hz to around 8 to 10KHz. Many woofers say 45 to 3000Hz but they sound like hammered dog shit above 1KHz. The cone can accurately reproduce a steady sinewave from 1KHz to maybe 3KHz but the vocals and mid-range will sound like mush since they are transient and the cone is 'slow'. The closest anyone really came to a 'one-speaker' solution was the woofers with a whizzer cone and a set of concentric relief rings about midway out from center on the woofer cone. The next step was a 'coaxial speaker' which is really a two speaker solution in one unit. Also be aware that most soft surround woofers (butyl rubber or foam) are very inefficient!!! Something like 82-85dB SPL @ 1W/1M compared to other styles of speakers hitting 92-98dB SPL. Some tweeters hit over 100dB SPL @ 1W/1M.

[TinkeringSteve]

Any raw frame speaker capable of going to a decent bass frequency will sound muddy with a muffled mid-range. A one speaker design is not optimal. You should at least consider one of the passive L/C crossover networks and include a mid-range speaker that would cover 750Hz to around 8 to 10KHz. Many woofers say 45 to 3000Hz but they sound like hammered dog shit above 1KHz. The cone can accurately reproduce a steady sinewave from 1KHz to maybe 3KHz but the vocals and mid-range will sound like mush since they are transient and the cone is 'slow'. The closest anyone really came to a 'one-speaker' solution was the woofers with a whizzer cone and a set of concentric relief rings about midway out from center on the woofer cone. The next step was a 'coaxial speaker' which is really a two speaker solution in one unit. Also be aware that most soft surround woofers (butyl rubber or foam) are very inefficient!!! Something like 82-85dB SPL @ 1W/1M compared to other styles of speakers hitting 92-98dB SPL. Some tweeters hit over 100dB SPL @ 1W/1M.

These aren't "woofers", or are they? The linked to BF37, and the not exactly mentioned, only saying "double size", FR8JS, are (claimed to be) optimized for small TVs and stuff, and mid range, with a bit of lower range extension - but 100 (or 80, for the other) Hz is not what "woofers" typically have? Or are you just talking of "usually" larger ones (w.r.t. 45Hz-6kHz), for larger speakers, but in principle these here being the same w.r.t. this problem, just shifted? They explicitly claim them to be "full range" solutions (for certain scenairios).
Well, the bigger one goes up to 15 kHz or so, the smaller even more.
A recording with ~12kHz bandwidth (20 to 12k) seems to reproduce consonants just fine, so if the speaker can do 15k+, it can't be too slow? Or does that "comm channel" logic not work for speakers?

This is for rather close up listening (one arm's length max), at which using > 1 speakers increase the dependence of position & orientation w.r.t. what I hear. And that, is not only utterly unwelcome, it is the very problem why this project exists in the first place: Otherwise I might as well continue to use my battery-powered commercial boombox with the "no bass exaggeration" mode (that I need to enable every single start, lol - "who'd want that?", right?).
It is bugging me to no end (as are other quirks of these things, in my use case), and hence I'm trying out a DIYed system.

[mag_therm]

You mention plywood, and the speaker needs a 32 mm hole saw.
So it might be best in this job   to just build a prototype with wood glue of your preferred outside dimensions.
Leave the back off for testing, then add the back with wadding ( I used old denim jean material.) as comparison.

On a (larger) Bass guitar speaker I built here out of plywood, the performance is better with the back open.
I also restored a practice guitar amp by keeping the vintage controls, removing the old transistor power amp and adding a 30 Watt Class D board ($15 or so)

Experience with the Class D, it works very well.
Precautions:1) don't connect external speakers using 1/4 jack, because the two speaker terminals are above ground
2) Be careful the DC power supply does not rise to the absolute max for the Class D when audio stops.
 The existing power supply here nominal 24V, rose to 31 V at no load, so I added a 24V series pass bjt that saturates at high music power.

[Coordonnée_chromatique]

Could you say why please ?

mainly because what you hear is different to what i hear,even with the speaker specs tested yourself and using the  best software your still not certain the sound is how you like it until youve built the thing

There is a lack of provided data about the "personal subjective preference" of the listener, BUT this problem is solved since that the builder have choosen a small FR driver unit.
The soundfield is in the far field with a very homogenous radiation pattern and a resticted frequency range, the FR tonal equilibrium is preserved by the natural and progessive decay in the low frequencies.
Why have you choosen a bass reflex enclosure ?

 

[themadhippy]

but 100 (or 80, for the other) Hz is not what "woofers" typically have?

What do you mean by that? 80-100hz is defiantly woofer territory

Why have you choosen a bass reflex enclosure ?

Because the spec sheet says

optimized for small vented enclosures/enclosures with passive radiator.

Also the Fs /electrical q  is over 50,which points more towards a vented box

[TinkeringSteve]

but 100 (or 80, for the other) Hz is not what "woofers" typically have?

What do you mean by that? 80-100hz is defiantly woofer territory

Also the Fs /electrical q  is over 50,which points more towards a vented box

I'm not too familiar with the English terminology of this stuff, and might easily have wrong associations with those words.

As for vented box: A box with an opening at the back is one, too, with a port of length 0 (or wall thickness), so to speak? Can that be viable? Like the one guy mentioned, one sees that often in guitar equipment. Though their purposes are not linear reproduction, but actually sound shaping, so one should be careful there, I guess

[madires]

passive radiater != bass reflex
Please see https://en.wikipedia.org/wiki/Passive_radiator_(speaker)!

[Coordonnée_chromatique]

but 100 (or 80, for the other) Hz is not what "woofers" typically have?

What do you mean by that? 80-100hz is defiantly woofer territory

Why have you choosen a bass reflex enclosure ?

Because the spec sheet says

optimized for small vented enclosures/enclosures with passive radiator.

Also the Fs /electrical q  is over 50,which points more towards a vented box

The free software provided by the manufacturer of the loudspeaker driver unit that i have linked in my first post is giving you the polar response of the loaded transducer.
The calculation gives a 61Hz F3, could you say what happen at 61Hz when your ears are at more than one meter of the source ?

[RJSV]

   Sounds like you've become hung-up on various jargon.   People have stayed here, that it's your ears that tell you the qualities you want, not some jargon number.   I think one respondent was even playing with you, by stating overly accurate numbers; like
    64.79463426 hz
...when other places using 6 db is seemingly sufficient, (no 6.453627 db in other words).

Homemade, I pushed a particle board front into a 'cube' that was about 16 inches per side.   The salvaged 6 1/2 inch speaker worked fine, with great bass, thanks to the large volume, and high audio frequencies also were good thanks to the 'nimble' low mass driver.   My little TV had a 1 inch speaker, that I could include in the sound field, (by mis-plugging the external speaker only part way into the mini jack).

Don't sweat the math, or 'special' items like 'flucfy' stuffing.  Try the two options with your ears.

[themadhippy]

, by stating overly accurate numbers; like

or they didn't bother setting the decimal places on the software that started life on a zx spectrum  nearly  40 year ago

[TinkeringSteve]

The advice to "test with your ears" is not good advice for this use case. It is about ad-hoc analysis (by somewhat trained ears) of sound recordings, not for listening pleasure and a subjectively overall "good sound".

[RJSV]

   Yeah well, left to guess what you want ?
   Sounds like you would avoid even building and testing, if some spec. somewhere says
   "Zero point 04 percent total distortion".
But then you seek some (mythical) 'flat' frequency response, using a 'maybe some kind of filter'.   Acoustical science doesn't work that way, there are lots of subjective arguments, vs. straight math, that, btw, gets applied here in a haphazard subjective way.

   My example, of a cheap two-way layout, has decent sound that could be measured along with just listening.   The modestly sized 6 inch speaker, put into an infinite baffle (box) has both qualities of good bass, and small enough to pass speaking voices with good clarity.
What exactly are you asking, regarding placement in a sound field ?   Do you want a system where the speakers can be placed in different orientations / distances ? (without negatively affecting response).

[RJSV]

   Definitely not HIFI Dept.
...But a nice 2-way mono acoustic set-up.   Little B/W TV had 1" inch speaker and nice thing was; it had an RF input mini-jack to which I connected a decent amplified antenna.   Broadcasts are fairly long RF wavelengths.

[RJSV]

   Also we're the usual, jacks for ext. speaker and for DC power (wall wart).   Main vocal material was crisp, smooth, and centered.   Meanwhile that direct and close sound was supported by diffuse, and deep-sounding background bass.   Bottom end that, without it, cheapens to whole experience (tinny sound only).

   Room acoustics mention putting bass boxes positioned in a corner, partially shown.   That effect likely depends more or less on having wood floors / harder wall surfaces, etc.

The little TV was nearly mounted on a gooseneck with all the misc. cables & provided plenty of audio power, for apartment.

[Coordonnée_chromatique]

The advice to "test with your ears" is not good advice for this use case. It is about ad-hoc analysis (by somewhat trained ears) of sound recordings, not for listening pleasure and a subjectively overall "good sound".

The tonal equilibrium and the dispersion are the key factor if you are looking for a good speech intelligibility at the listening point.