Any interest in an ASR community speaker project?

[HooStat]

I think the only other design constraint that needs to be agreed on is exactly how much bass extension and output we need,

Do we assume that people should use a subwoofer, which would be "best practice"? If so, then it seems to make the design easier.

 

[KSTR]

My advice would be against subwoofers unless the XO is linear phase (needs FIR-based DSP-XO). The "lagging bass" a typical subwoofer XO (50...80Hz, LR4) produces would be a deal breaker for me.... but that' just me...

 

[617]

Here is the data for the 12 drivers which were 'above average' in SPL at 40hz.

I added some other data and created a scoring system to find the drivers which represented the best value and performance. I added one star for each driver which was below a certain price threshold (130 seemed to be a good threshold- drivers get a lot more expensive past that point.) I added a star for drivers which 'wanted' a relatively small box for a flat sealed alignment, although this one is very arbitrary - sealed alignments tend to be fairly flexible, especially with DSP in the mix. I added a star for drivers which were in the top 10 or so in terms of SPL at 40hz and 200hz. I then subtracted a star for any driver which had inappropriately high power handling (indicating that 100W wouldn't be able to get the most out of it) or inappropriately low power handling (indicating that the driver couldn't make use of the amp.) This is also somewhat arbitrary, but the scoring is useful because it allows us to focus on the drivers which seem like great fits, say the 3-4 star ones.

Of these, and I feel really proud of myself for thinking this driver would work well, the Dayton RS270p is probably the best, for $100, and for $130 we have the Ciare driver @hardisj mentioned. The Dayton RS270 has more output than the paper version, but it also wants a bigger box. If a seriously low budget option is desired, the Visaton W250 is under $70 dollars and does a lot of things well.

I would like to bring availability and supplier into the equation as well. I heavily favor getting all the parts from one source to save on shipping, and since the amps being tested are sold at PE, I would favor drivers sourced there as well. However, Madisound and Meniscus in the USA are both good options for drivers. I would certainly like to avoid having to buy parts from three suppliers if possible.

Finally, the big factor these ratings don't consider is linearity. I will probably add another column to the chart showing the highest frequency you can use before breakup becomes obvious. Regarding distortion, I would defer to @hardisj , but I would suspect any of these would be pretty good.

Again, at this point due to the supplier, price, reputation for low distortion, bandwidth, and output, I would favor the RS270P, but I am very interested in what other people have to say.

 

[617]

Do we assume that people should use a subwoofer, which would be "best practice"? If so, then it seems to make the design easier.

For a 2 way design, I would target pretty good bass which really ought to have a subwoofer. For a 3 way design, I'd demand robust SPL down to 40hz and below. This would be improved by a subwoofer(s), offering more extension and smoother room response.

Making a 3 way with a woofer smaller than 8" is not unheard of, but if you have a good amount of power and DSP, you might as well use it.

 

[somebodyelse]

Interesting - nice work. What is the range of box sizes that results? If the Peerless 830668 can make it up to ~300Hz, it might be a great choice - I tend to forget about this driver since the ported box requirement is a bit big, but sealed with an LT might work very well.

Like in the pluto sub - 14l sealed box with LT

 

[HooStat]

I might weight cabinet size, distortion, and build quality in the ranking. Availability in the future, and support by the manufacturer would be important. Kind of subjective, but it seems like you guys know about these and they should be factored in.

 

[617]

I might weight cabinet size, distortion, and build quality in the ranking. Availability in the future, and support by the manufacturer would be important. Kind of subjective, but it seems like you guys know about these and they should be factored in.

I agree. Precisely weighting things is not my expertise, so I am more looking for drivers with no 'red flags' than anything else. Dayton for example has a reputation for producing drivers for a long time, as does SB/Scan Speak. Tang Band availability seems more variable to me, and the Ciare driver is currently not available. Regarding build quality; all of these except the very cheapest have nice cast frames, and in my experience, the build quality from SB/Dayton/Peerless/Scanspeak is pretty damn good - the peerless drivers aren't as polished but they're put together well.

When I've done DIY speakers in the past, I've used Dayton and SB Acoustics most often, with some Bohlender Graebner/Vifa/CSS/Rival/SS drivers in the mix.

 

[briskly]

Part of the appeal of DSP is that you can, to a certain extent, use ornery drivers with good harmonic distortion characteristics, but poor linear distortion - rising responses, low breakup and so on

You can sidestep inappropriate Q or cutoffs provided the driver has the excursion to some extent. Harmonic distortion will still receive a narrowband boost from the resonance associated with minimally damped cones. You can see this with the metal cones from SB, Dayton, and Seas. Surround-edge anomalies usually are accompanied by narrow bumps in HD as well.

On an unrelated note, beryllium has very little intrinsic damping properties. It is higher than most other ultra-high sound velocity materials, but itself has lower losses than magnesium.

 

[617]

You can sidestep inappropriate Q or cutoffs provided the driver has the excursion to some extent. Harmonic distortion will still receive a narrowband boost from the resonance associated with minimally damped cones. You can see this with the metal cones from SB, Dayton, and Seas. Surround-edge anomalies usually are accompanied by narrow bumps in HD as well.

On an unrelated note, beryllium has very little intrinsic damping properties. It is higher than most other ultra-high sound velocity materials, but itself has lower losses than magnesium.

Yes, fortunately in a 3 way design, you don't have to deal with these resonances. Finding a woofer that does 40-2200 is not easy, but finding one which does 40-400 is. Looking at the woofers which are sifting to the top, all of them have ample bandwidth for a 500hz crossover.

The next driver to look at is the mid, and this is in some ways a more difficult task as there are a lot more midranges out there, and a lot of them work well. This website:
http://feleppa.com.au/speakermeasmid.html
Hificompass has some other measurements
Summarizes some good options. I suspect the best way to cull the field of midranges is to look at availability, cost, and SPL as well. Most of them have excellent performance to 4K. Just as an example, here is the FR of a $15 sb acoustics unit I chose at random:

Not a lot to complain about. The advantages of using a small midrange become obvious when you start looking at these charts.

Regarding SPL, the woofers we're looking at can go quite loud, so finding a midrange which can keep up is important. Now, if you're crossing a mid down low, you start to need a lot of displacement to get high levels. However, if you can do 400+hz, the displacement requirements are greatly diminished.

Now, regarding xmax limited SPL at midrange frequencies, I have a formula from dear departed Jeff Bagby (RIP, still can't believe he's gone) which you can use to find max SPL at a given frequency as a function of cone area, xmax. I believe this is for 1M in half space but I will try to find out for sure.

 

[Lbstyling]

However, giving builders the option to build a bigger cabinet, using a port, or a PR (or transmission line) QUOTE]

FYI :
TL would be out as it requires a high FS driver to make the cabinet realistic in size=not compatible with other objectives.

 

[Lbstyling]

If DSP is to be used, a 3way starts to look more promising as you can use dirt cheap drivers that have uneven rising responses with high order filters and shelving. It may end up cheaper than a 2 way if you want the best measurements.

A 3/4 + 3 inch + 6/7 inch would be cheap. Toole puts little importance on distortion profiles of drivers, so this can be sacrificed. + C to C spacing can be kept low and the cabinet can be made aesthetically pleasing.

If you are really going for the best bang for buck, cardioid or psudo-cardioid (like the statements) mid would be advantageous as this improves off axis mid measurements and transition between treble and bass.

 

[HooStat]

if you can do 400+hz

Just wondering with the "right" cross-over should be. Since the male voice can go much lower than 400 hz, is it beneficial to have the midrange cross over a little lower than 400? I realize it depends a bit on the cross-over slope. And it seems that most of these can also be crossed at a lower point without too much trouble. In some ways it seems that this is the most important part to get right.

 

[Lbstyling]

My advice would be against subwoofers unless the XO is linear phase (needs FIR-based DSP-XO). The "lagging bass" a typical subwoofer XO (50...80Hz, LR4) produces would be a deal breaker for me.... but that' just me...

Your ears cannot detect even 10ms delay at 100hz. You cannot hear phase at this freq, not even close. You cannot even distinguish the sub from the room if it was a 15m wide room. You only hear room modes.

Besides, you just delay the signal to return it to time aligned when digital anyway.

 

[briskly]

Not a lot to complain about. The advantages of using a small midrange become obvious when you start looking at these charts.

You seem to be settling onto the 3-way idea, a decently large one at that. The DSP approach makes that easier and is along the lines of what I wanted to assemble for a personal speaker, but I wanted to see if people wanted to go in other ways.

I have a formula from dear departed Jeff Bagby (RIP, still can't believe he's gone) which you can use to find max SPL at a given frequency as a function of cone area, xmax. I believe this is for 1M in half space but I will try to find out for sure.

The standard SPL formula (Rayleigh's integral of a disc on-axis, ignoring the phase terms) is about the piston in half-space. TS analysis and simulation are normally written in that same context, piston behavior in half-space.

P= 2π * f² * Vd * ρ / r
ρ is air density, r is distance from driver. SPL in SI units is then:
94 + 20 log (P)

 

[Lbstyling]

Here is the data for the 12 drivers which were 'above average' in SPL at 40hz.

View attachment 66820



Of these, and I feel really proud of myself for thinking this driver would work well, the Dayton RS270p is probably the best, for $100, and for $130 we have the Ciare driver @hardisj mentioned. The Dayton RS270 has more output than the paper version, but it also wants a bigger box. If a seriously low budget option is desired, the Visaton W250 is under $70 dollars and does a lot of things well.

The Visation looks ok. As long as there are no resonances in the FR in the intended passband. I'm sure we can go cheaper.

 

[dwkdnvr]

here is the FR of a $15 sb acoustics unit I chose at random:

You mean the one that I've mentioned at least twice in this thread?

Now, regarding xmax limited SPL at midrange frequencies, I have a formula from dear departed Jeff Bagby (RIP, still can't believe he's gone) which you can use to find max SPL at a given frequency as a function of cone area, xmax. I believe this is for 1M in half space but I will try to find out for sure.

linkwitz has an spl_max.xls spreadsheet that will plot max spl vs frequency based on a drivers xmax and piston diameter. you can search for the link on this page https://www.linkwitzlab.com/publications.htm

Edit: direct link http://www.linkwitzlab.com/spl_max1.xls

 

[Lbstyling]

Just wondering with the "right" cross-over should be. Since the male voice can go much lower than 400 hz, is it beneficial to have the midrange cross over a little lower than 400? I realize it depends a bit on the cross-over slope. And it seems that most of these can also be crossed at a lower point without too much trouble. In some ways it seems that this is the most important part to get right.

This will depend on the driver used, but I will tell you something for nothing, the energy in strong male voice is alot. The majority of systems that don't produce it well simply don't have the SPL capability needed in the 200hz range to pull it off. Many a time have I been working on something and thought the driver was not very good when playing Johnny Cash. Digital crossovers allow you the luxury of crossing over temporarily to as big bass driver, just to check....its SPL. Its almost always SPL, especially when you use EQ to deal with room modes. You need 10db more output than you think in this region.

 

[Lbstyling]

You mean the one that I've mentioned at least twice in this thread?

linkwitz has an spl_max.xls spreadsheet that will plot max spl vs frequency based on a drivers xmax and piston diameter. you can search for the link on this page https://www.linkwitzlab.com/publications.htm

Keep in mind power compression when dealing with low efficiency drivers. Especially cheap ones with no vent on the pole.

 

[617]

@briskly, thanks for the formula. He wrote it like this:
SPL= 20 * log(10) (1.18 / 0.00002 * Sd * Xmax / SQRT(2) * 2 * PI * F^2)
I can't do math so I'm not sure if these are equivalent, but I believe they assume pistonic motion in half space.

Now, regarding your comment about "decently large" it's not a small speaker, DSP enables us to get a lot of output in a relatively small box - under 1 cubic foot in some cases. I'd call that medium sized.

Here is some information about output capabilities of midranges:

Per the assumptions of the formula, this is 1M in half space. The woofer measurements I believe are free space but I could be wrong about what WinISD calculates. Midranges on a relatively big baffle are going to be radiating into half space for the most part, so maybe the comparison is not totally useless.

The purpose of these calculations is to show the SPL sensitivities as you vary driver displacement across three frequencies - 100hz (below midrange) 300 hz (near likely crossover point) and 1000hz (well into midrange bandwidth.) As you can see, if you want to match the 107db kind of levels that our woofer is pumping out, a little dome is not going to do it, and a 3" sort of driver is going to struggle as well. If you really want something which can go loud, you'll need a 6" midrange, but then you run into problems mating this to a tweeter. Getting smooth off axis with a 3" speaker is very easy, 4" is doable, and 5" becomes a challenge in my experience.

This is where I could use some community input. On the one hand, you want SPL capability in a midrange; you want a good amount of headroom and don't want to waste output capability. At the same time, optimizing a speaker so SPL is maximized is not the same thing as optimizing a speaker so directivity is optimized, which is surely more important. So, we need to decide what is 'enough' output, at say 300hz. I think our initial assumptions about midrange size are probably on the money - a 3-4" driver will give adequate SPL while still mating to a tweeter beautifully, but if anyone sees flaws in my reasoning or has a differing opinion, please let me know.

 

[617]

This will depend on the driver used, but I will tell you something for nothing, the energy in strong male voice is alot. The majority of systems that don't produce it well simply don't have the SPL capability needed in the 200hz range to pull it off. Many a time have I been working on something and thought the driver was not very good when playing Johnny Cash. Digital crossovers allow you the luxury of crossing over temporarily to as big bass driver, just to check....its SPL. Its almost always SPL, especially when you use EQ to deal with room modes. You need 10db more output than you think in this region.

I think you are 100% on the money here. That 200hz region is where the 'beef' of the sound is, and asking a 3-4" driver to do the job is just going to cut it. This leads to one of two approaches. The first is to use a big midrange, which makes directivity matching to a tweeter difficult. The second is to use a woofer to reproduce the midrange up to 500hz or so, and using a small and agile midrange above. Maintaining good headroom in the 100-400hz region is critical to making a dynamic speaker, and the numbers above bear this out.