Any interest in an ASR community speaker project?

[Lbstyling]

Drivers sound better after you let the smoke out - it's part of the break-in process. Really loosens them up.

But, yeah - I don't listen at high volumes for extended periods for the most part. There is definitely a reason there is a segment of the population that gravitates to pro audio setups inspired, though. And, having had the Yorkville U15 Unity horns in a teeny-tiny room for a while, there certainly is something about having effectively unlimited headroom.

Lol. Good choice on the unitys BTW!

 

[Lbstyling]

Final driver ranking of the night. Here are 8 and 4 ohm variants of the most viable 8 inchers. Each was modeled in an 1.2 cubic foot enclosure and tuned for maximum output at 30hz. 1.2 cubic feet is about right for some, a bit small for a bunch, and a bit big for the Tang Band.
View attachment 66863

Note the differences here are much smaller. The SB23 NBAC is really made for deep extension in a biggish box rather than high output in a small one. It doesn't do badly but it's not impressive for the price. The RS224p-4 ohm variant and the sb23 NRXS paper cone have a good combination of output and price. The 225-8 and 225-4 demonstrate why they are used in like 20 DIY designs, lagging only a bit in output at mid-band. The SB23 MFC are 8 inch subwoofers which do pretty well - the 8 ohm variant is probably the best best for SPL, but at 130 you're paying over twice the cost of a Dayton Reference for 5db.

I would say the best value option is the RS225p-4, which I give additional points due to its nice treble extension. If you want to spend the money, the sb23 MFCL is a little beast and justifies its cost better than any other option here. The Tang Band looks seriously impressive, with a magnet the size of a mini cooper, and would be a good direction to go in if cabinet volume is to be minimized.

I also tested, for fun, the Dayton "Epique" ECF220 or whatever it's called. It's a funny driver, giving you huge output in a small box but with very little bass extension. It's an unusual combination of features and would be an interesting driver to use, but the price on sale is $300, which is a lot to pay for that performance.

RS225p-4. Would be my preference from that bunch. A great driver.

 

[Lbstyling]

If that is what is desired, then let's focus on how to make that work. I say this selfishly because I want a sealed speaker -- I certainly defer to the group. But what if the budget adjusts to accommodate drivers that will make it work?

Vented increases output by 3db, reduces distortion and IM. There is no evidence whatsoever that group delay at under 100hz is even the slightest bit audiable. So in the spirit of this sub ...(objective data comes first.....)

 

[617]

RS225p-4. Would be my preference from that bunch. A great driver.

Yeah I think 40hz is a better point of evaluation and comparison. Excursion demands grow so much as you go down in frequency, and with DSP we have the ability to put a steep high pass at 40hz to limit over excursion, while still maintaining great low bass. The RS225p in a sealed enclosure ticks a lot of boxes - great headroom, good bass output, good price, excellent treble extension.

I would like more input on what SPL levels really mean. 'Reference level' normally means 105db peaks at listening position, 115db for subs. I think a stand point speaker which will do 90db in room in the bass, and 108db in the midrange is pretty high output.

If you wanted true 'reference levels' you could keep the same form factor and use PA drivers to get 105db at 80hz, but I think this would limit the appeal of the speaker. Something which is 'plenty loud for nice music' and 'very loud with an high pass and subs' is a great compromise in my mind.

Regarding SPL capabilities of midranges - SB Acoustics has a line of little plastic midwoofers with an Sd of 50 cm or so (4" drivers) and a huge xmax of 1cm. This gives you half space SPL of 90/110/132db at 100/300/1000hz. I'm honestly more concerned about tweeters output at the moment.

It's funny, with previous designs I never obsessed with SPL, but the use of DSP really makes SPL one of the major limiting factors in performance. Most drivers of the same size have the same spatial/acoustic performance, harmonic distortion doesn't impact sound quality that much (according to the consensus here) and linear distortion can be remediated with DSP. I feel like one of those car subwoofer guys. Feels dirty if I'm being honest.

 

[617]

Vented increases output by 3db, reduces distortion and IM. There is no evidence whatsoever that group delay at under 100hz is even the slightest bit audiable. So in the spirit of this sub ...(objective data comes first.....)

It would be relatively easy to select a driver which does well sealed and vented, design one bass filter for the vented design, and then plug the port and design another bass filter for a sealed design. In my opinion the big advantage of a sealed design is portability, not sound quality.

 

[Lbstyling]

IME a vented design can only be perfect with pretty large volumes, much larger than typically seen. With "perfect" I mean really zero port noise even at maximum level sine wave exitation at the Helmholtz resonance. This requires low air-flow velocity --> wide port with perfect roundovers on both ends (and even that is not going to be perfectly symmetric for air intake vs outtake). Wide means short as well and that means a large volume for the given resonance, compared to a longer, narrower port in a smaller cab for the same resonance.

Ported designs also also more prone to nasty "jump resonance" (a semi-chaotic phenomenon), the mentioned asymmetry being one reason and the second one being woofers with too soft suspensions (low restoring force for the tendency of the VC to go dynamically off-center at certain frequencies). For a low resonance freq of the driver a hard suspension requires a large moving mass. That's the design rationale behind all of the better pro-sound woofers, B&C notably. Bottom line: Typical HiFi-woofers don't really work in ported designs if we aim for excellent behavior. PR has no port noise and lower midrange leakage but has its own set of problems (the instability can be worse with them sometimes, as can distortion).

Much as I like them, justifying cost for a PR is difficult. A large slot port would address much of your concern, especially if we line the port with foam. Pointing the port to the rear will also reduce audiable box resonances as higher frequencies are directional, meaning firing them at the front wall should increase the SPL loss of anything that gets through.

Thats for the bass driver, If we leave the mid chamber back face open, this will help there. + Improve off axis measurements, bit at the cost of SPL.

 

[dwkdnvr]

Lol. Good choice on the unitys BTW!

It was an absolutely amazing system. As far as I know I was the first to try them as home speakers. I had them tucked directly into the corners of the room, had absorption on the lateral first reflection points and listened at a fairly nearfield position. Worked really well - the 60x60 horn pattern broadened to 1/4 space in the corner, and I used DRC-FIR to correct, augmenting with an NHT1256 sub. Mind-blowing dynamics, but did all the audiophile stuff too. Had to sell when I lost use of the space for dedicated listening, which is ironic as we moved a few years later into a spot where I could have used them as L/C/R across the front. Oh, well.

 

[Mashcky]

Vented increases output by 3db, reduces distortion and IM. There is no evidence whatsoever that group delay at under 100hz is even the slightest bit audiable. So in the spirit of this sub ...(objective data comes first.....)

I actually had no idea this was the case. I imagine that since a port for our speaker would be tuned well below 100hz, it would be making no audible IM distortion? I shouldn’t be surprised given our insensitivity to distortion that low in the spectrum.

617 beat me to it but I suppose that leaves the port decision up to other design criteria - size, portability, ease of construction. Would allowing for a choice mean two different box volumes?

 

[Biblob]

Clearly there is a difference in the liking between going active or passive.
I would say, why not both? If people already have multichannel DAC's and amps, let them use the active version. So someone makes the filters/parameters that can be loaded up any DSP.
And for the people who don't want to mess with that, they could use a passive crossover design.

It would mean that in the designing phase there would have to be made an compromise, so that a passive design would be possible.

 

[Lbstyling]

For cabinet shape, we have to figure out how to make it as good off axis as possible, while keeping construction easy as possible.

For good off axis, you need to transition from 2pi to 4 pi as gently as you can. This is why speakers have roundovers on the sides. It matters. A lot.

Avalon's measure well off axis due to this cabinet shape that has become fairly popular. The chamfer being at a odd angle helps the response as the wave from the drivers don't hit the edge of the cabinet at the same time on all sides and points smoothing out the dips/peaks.

A cheap alternative is to have flat cabinet sides, but use foam to round the corner over. I have also seen grills used to apply foam to the baffle with the aim of breaking up the wave that travels along the baffle gently.

 

[Lbstyling]

I actually had no idea this was the case. I imagine that since a port for our speaker would be tuned well below 100hz, it would be making no audible IM distortion? I shouldn’t be surprised given our insensitivity to distortion that low in the spectrum.

617 beat me to it but I suppose that leaves the port decision up to other design criteria - size, portability, ease of construction. Would allowing for a choice mean two different box volumes?

The port reduces distortion because it reduces the excursion needed for a given SPL at and near the tuning frequency. When you play your ports tuning freq, the driver doesn't move much at all. Most of a drivers distortion profile is a function of excursion.

 

[617]

Clearly there is a difference in the liking between going active or passive.
I would say, why not both? If people already have multichannel DAC's and amps, let them use the active version. So someone makes the filters/parameters that can be loaded up any DSP.
And for the people who don't want to mess with that, they could use a passive crossover design.

It would mean that in the designing phase there would have to be made an compromise, so that a passive design would be possible.

We're doing a lot of things with the active network which would be really expensive, difficult or impossible with passive. Having said that, if the drivers work well together from an acoustic perspective, a good passive design could probably be developed. A hyprid design could certainly be developed, where the mid/high is a passive network and the woofer is active.

It would be an interesting exercise for sure, to do a full passive design. If we use fairly benign driver such as the reference-paper woofers and a friendly midrange, it's possible the passive design could work pretty well; but if we're using dsp to smooth out little wiggles everywhere - good luck doing that with passive. And of course the bass alignment would have to be totally different.

 

[Lbstyling]

Clearly there is a difference in the liking between going active or passive.
I would say, why not both? If people already have multichannel DAC's and amps, let them use the active version. So someone makes the filters/parameters that can be loaded up any DSP.
And for the people who don't want to mess with that, they could use a passive crossover design.

It would mean that in the designing phase there would have to be made an compromise, so that a passive design would be possible.

I think you just volunteered to do a passive filter version!

 

[617]

I actually had no idea this was the case. I imagine that since a port for our speaker would be tuned well below 100hz, it would be making no audible IM distortion? I shouldn’t be surprised given our insensitivity to distortion that low in the spectrum.

617 beat me to it but I suppose that leaves the port decision up to other design criteria - size, portability, ease of construction. Would allowing for a choice mean two different box volumes?

If you make a ported box, you can convert it into a sealed box by plugging the port. That box will be larger than it needs to be, but the performance will be similar to the smaller sealed box. In other words, if a ported prototype was developed, the designer could plug the port and design a new set of filters for a sealed version. On the other hand, if a sealed box is built, and it is made as small as possible, you won't be able to convert that to a ported design.

 

[HooStat]

Tang Band w8 2096B

I have read other places that Tang Band tends to rate their drivers "optimistically". Not sure if it is true, but we should account for that if so.

 

[dwkdnvr]

TL;DR I ramble a lot. Determining adequate bass capacity is an interesting problem. would be cool if we came up with a way of putting some numbers behind it rather than just playing loud and seeing if it breaks.

Yeah I think 40hz is a better point of evaluation and comparison. Excursion demands grow so much as you go down in frequency, and with DSP we have the ability to put a steep high pass at 40hz to limit over excursion, while still maintaining great low bass. The RS225p in a sealed enclosure ticks a lot of boxes - great headroom, good bass output, good price, excellent treble extension.

I would like more input on what SPL levels really mean. 'Reference level' normally means 105db peaks at listening position, 115db for subs. I think a stand point speaker which will do 90db in room in the bass, and 108db in the midrange is pretty high output.

If you wanted true 'reference levels' you could keep the same form factor and use PA drivers to get 105db at 80hz, but I think this would limit the appeal of the speaker. Something which is 'plenty loud for nice music' and 'very loud with an high pass and subs' is a great compromise in my mind.

This is definitely a tough question, and one I've struggled with in my main project. As I indicated, I found a pair of RSS210HFs to be 'not quite enough' in our large main space. So, the question becomes 'what is enough'? I have no idea. I'm not even sure what there wasn't enough of - not enough headroom at 40Hz? Not enough room re-inforcement of lower bass freqs? Too high an F3? Incorrect overall eq leaving upper/mid bass too lean? Working through these types of questions is probably where deep experience in designing systems comes in. The system I have currently set up ironically has only a pair of ported 6.5" woofers (Scan 8545, so very good woofers) set up in a hybrid 3-way of the type we're discussing using the MiniDSP SHD. Sounds very good - not quite good enough to eliminate the motivation for my big project, but quite satisfying. So, I think it's entirely possible that what I'm missing isn't actually output capability but rather appropriate EQ. (current system set up by ear - actually measuring the in-room response will be interesting) (and yes - I probably should have just run Dirac, but I haven't gotten around to that yet either)

I will refrain from making commitments since I don't know how much time I have available, but I have a variety of setups I can evaluate and I'm hitting the point where I have to start doing some measurements anyway. - RS225-4 sealed, RSS210 sealed, dual RSS210 sealed, RSS265ho-4 sealed, and RSS265HO-4+2xRSS265PR. Now, given that sealed alignments in a DSP world differ primarily in their output/headroom, it is probably not actually necessary to test all of these explicitly. It seems that what is needed is a way to evaluate 'how much is enough' for a particular setup. i.e. analyze the bass content of a set of music, somehow set volume levels to match the capacity of an alignment, and then evaluate whether this is satisfying for playback. Or at least I'd feel better if there was some analysis behind it rather than just "crank it up until it breaks, or your ears cry uncle'. (and of course, what I find 'enough' isn't what someone else will feel is enough, so defining a process to help with self-eval would be pretty helpful)

Regarding SPL capabilities of midranges - SB Acoustics has a line of little plastic midwoofers with an Sd of 50 cm or so (4" drivers) and a huge xmax of 1cm. This gives you half space SPL of 90/110/132db at 100/300/1000hz. I'm honestly more concerned about tweeters output at the moment.

It's funny, with previous designs I never obsessed with SPL, but the use of DSP really makes SPL one of the major limiting factors in performance. Most drivers of the same size have the same spatial/acoustic performance, harmonic distortion doesn't impact sound quality that much (according to the consensus here) and linear distortion can be remediated with DSP. I feel like one of those car subwoofer guys. Feels dirty if I'm being honest.

I think the midrange output follows directly from the above - what we're talking about is basically a process of calibrating our everyday experiences to spl values. This is tougher than it seems since basing things off Peak SPL values requires knowing the typical crest factor you're targeting - classical needs more peak-to-average reserve than folk for example. OTOH highly compressed pop/rock might actually raise thermal power handling questions. I'm sure Audacity can analyze a track and spit out stats that would be helpful in this regard - music systems are tougher than HT where there are at least some standards in place and you can use pink noise to set playback levels. I suspect that for a 300-400Hz LR4 crossover, anything more robust than a Scan 10f will be ok for 'average music listening'. The SB10 mentioned here might actually need some care since it's actually notably smaller than the 10f, but in 3-way designs excursion is usually a problem only if a) you're looking at a dome mid b) you're crossing low to a 'sub' style driver in the 150-200Hz range.

As for tweeters - in a 3 way with a crossover in the 3kHz or above range, I suspect that any decent tweeter won't be a problem (at least for a music system where continuous power levels are low-ish). Tweeters become a problem when you try to cross low as this taxes their excursion.

So, my thinking is something like this:
- use Audacity to analyze a set of 'typical' tracks that you use to evaluate a system
- based on those stats, use pink noise to set your playback volume to XXX dB (needs SPL meter or calibrated mic setup)
- playback music, and record for each track how you adjust volume to reach comfortable playback levels (or probably 'as loud as I'd want to play it after a couple glasses of wine levels')
- somehow use that to determine SPL capacity needed

 

[dwkdnvr]

For cabinet shape, we have to figure out how to make it as good off axis as possible, while keeping construction easy as possible.

For good off axis, you need to transition from 2pi to 4 pi as gently as you can. This is why speakers have roundovers on the sides. It matters. A lot.

Avalon's measure well off axis due to this cabinet shape that has become fairly popular. The chamfer being at a odd angle helps the response as the wave from the drivers don't hit the edge of the cabinet at the same time on all sides and points smoothing out the dips/peaks.

Yeah, the DXT-Mon design that does about as well as any non-coax I've seen uses the Avalon-style cabinet facets. I'd vote in favor of using that design strategy - very effective, and IMHO looks quite good.

 

[Peas]

Just some minor remarks:

At max. SPL at 40 or 30 Hz, drivers in a sealed enclosure may demand more than nominal max. power. This should be checked in WinISD.

On the other hand, in-room response doesn't necessarily differ by 6 dB beyond baffle step. As wavelengths are getting longer at the low end, at least one wall or any other surface is always somehow close in terms of directivity / space. A 40 Hz / -6 dB response on paper might be fine in most rooms as the roomgain does the rest.

Anything below that might be kept for a subwoofer when it comes to high SPL. You have extreme room modes in that range, so separating the bass from the main signal is a good option when one wants reach lower than say 40 Hz approx.

 

[617]

Some simulations. These use a 28mm tweeter, a 125mm mid and an 8" woofer. The mid and tweeter are offset, so there is a little assymetry in the horizontal directivity.

Here we have the response with LR4 crossovers. I equalized each driver so it was flat in both directions then applied textbook crossover slopes. This enabled me to move the crossover frequency around easily to see how the drivers blended.

I think I had a simulation with a better response with fourth order slopes, but I can't find it now. Around 1500k there is a bump in the early reflections and room response which could be equalized - I suspect it would be worth have a slight depression in the direct response to mitigate that a bit. There is also a big discontinuity around 3K, which is where the crossover is between the tweeter and mid.*

*Edit - the more I look at it, something is screwed up here. It's definitely possible to use fourth order slopes and getter a better result than this. I think the crossover between mid and tweeter wants to be really high or something.

What happens when you go to LR2? Evertything gets smoother. In reality I wouldn't use LR2 all the way from 0db to -infinity db, it's generally better to do a hybrid sort of approach where the first octave is gentle, and then it gets steeper and steeper. In this case, I'd pay particular attention to the lower bid bandwidth, which is pretty wide, I'd like to trim that back.

This is a lot better. . I wish I had a graph of the Revel Gem2, which uses the same driver sizes. I may try to overlay the Salon 2 with this speaker just to see how wavy the DI is compared to a very good design.

Now, it remains to be seen how this would work with a waveguide. I can't simulate those as easily as direct radiators, but I may speak with the WG author to see if he knows of any studies with the 4" WG and a 4" mid.

I suspect this is about as good as you can do with direct radiators, which isn't bad. Waveguides aren't going to help woofer/mid integration, so you'll always have a little waviness around 300hz, but you could probably get the DI very flat above that with care.

 

[617]

Spinorama comparison. This is with the Salon 2, which isn't a perfect comparison because it is a 4 way speaker. Couldn't find a DI curve for the Gem2. Anyway, it's not worlds worse, but the issue at the tweeter crossover is not going to work. The lesson here? Even with LR2 crossovers and a big tweeter/small mid, getting a really smooth DI through the crossover region is difficult. I'm pretty certain a 4" waveguide is the way to go here.

I'm going to try to contact augerpro (is he here?) and get some input on these waveguides. The one designed for the sb21 is elliptical, but I can make the outer edge a rectangle for easier flush mounting.