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The ultimate small speaker - final design peer review thread


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#41 lowerFE

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Posted 01 September 2016 - 01:47 AM

I'm not an engineer.  :(  I wish I had CAD skills to draw this up and send it to a 3D printer or something. Certainly would be much easier than working with wood!

 

Just ordered the woofers and tweeters. Will be ordering parts slowly throughout the next week or so to soften the financial sting  :lol:

 

Next up, designing a grill for these speakers to hide the "magic" design. I look forward to seeing some shocked faces when demoing this :D .



#42 SME

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Posted 01 September 2016 - 06:10 AM

Cool.  Good luck with this build.


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#43 lowerFE

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Posted 03 September 2016 - 04:33 AM

Houston, we have a problem. 

 

In fact, this is sort of a big problem. The Tang Band W5-1138SMF cannot be converted into a useful passive radiator. I was under the impression that the amount of mass to tune a PR for a given Sd, frequency and enclosure size is a constant when this isn't the case. The amount of mass needed is dramatically changed by the Fs of the PR. The lower the Fs, the less mass it needs. Therefore, Cms can dramatically affect the mass needed. The TB driver has a very stiff suspension, so the mass requirement for tuning is much much greater, about 4x higher than the original Mms, and there's no way the suspension can handle this much weight. 

 

The backup option is to use the Peerless 5.25'' PR. However, it only has a 6mm Xmax when I need around 11mm. Any ideas? Or am I forced to just set the limiter higher so it doesn't blow up the Peerless PR near/below tuning?



#44 Contrasseur

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Posted 03 September 2016 - 07:23 PM

If weight is evenly distributed, your suspension could probably handle it. If it sags slightly, there's no top plate for the VC to scrape into. If you've already bought the driver, give it a try and see what happens. 



#45 andy497

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Posted 04 September 2016 - 02:55 PM

I use https://shapeways.coma fair bit for prints. The quality is very high, but it's still FDM, so things usually have a slightly rough finish. They do a variety of materials including fiber reinforced (extra cost and requires a human to verify your model) and a bunch of metals (speakers still too inexpensive? Try printing the enclosures out of platinum!)

It gets pricey fast however, and the maximum dimensions are typically small (e. g. < 30cm), but that's easy enough to check. All of their material pricing is on the site as well, without having to upload a model.

All that said, I don't know why you'd want to print over using wood. Maybe to make complex curves/shapes?

#46 lowerFE

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Posted 04 September 2016 - 07:39 PM

So I did some playing around, and I could not find a reasonable cost driver suitable to be converted to a passive radiator. There are ~$100 drivers that could, but they're a bit too expensive to experiment with. 

 

So the option that I'm considering is just to use the Peerless 5.25'' PR for the following reasons:

 

1. The Peerless PR has extremely suitable PR parameters: High Cms, Qms, Mms, low Fs, and decent Vas. The Tang Band has low Cms, low Vas, decent Qms and high-ish Fs. 

 

2. Even though it only has 6mm of Xmax while modeling shows I need up to 11mm of excursion on the PR at the deepest usable frequency, the modeling software does not account for PR losses, which I think is non-trivial. Looking at my previous speakers where I used 2 of the 4'' version of the Peerless PR, the actual PR excursion was only a little more than half of what modelling suggests (partially because I used stuffing).  Note this is non scientific, just comparing with my eye and comparing it with the ruler I had in hand. I saw a video of someone that used a Tang Band 3.5'' RBM woofer (7mm Xmax!) with just one of the 4'' Peerless PR (jump to 11:20). Modelling shows one would need *4* of those PR's to keep the PR excursion below the 5mm Xmax. Yet, in the video he clearly drove the RBM woofer to the max and the lonely 4'' PR did not go flying into the room (although it was doing way more excursion than what I can drive my PR's and looks like it was doing a lot more than 5mm of excursion).

 

3. The 11mm excursion is only achieved with 150 watts of input power. With that much power, I expect at least 3dB of compression, which would further reduce PR excursion. That said, I do still have to watch out for transients. I'm hoping the 6mm rating is actually Xmax, and the Xmech is higher (hopefully a lot higher)

 

Has anyone blown a passive radiator before? I'm thinking of sacrificing 2 PR's by turning it louder and louder until the PR's are physically damaged from over-excursion in order to find the limits so I can dial the compressor properly. Good idea? (Probably not  :lol:). Main concern is hoping the broken parts don't damage anything inside the speaker. 

 

I use https://shapeways.coma fair bit for prints. The quality is very high, but it's still FDM, so things usually have a slightly rough finish. They do a variety of materials including fiber reinforced (extra cost and requires a human to verify your model) and a bunch of metals (speakers still too inexpensive? Try printing the enclosures out of platinum!)

It gets pricey fast however, and the maximum dimensions are typically small (e. g. < 30cm), but that's easy enough to check. All of their material pricing is on the site as well, without having to upload a model.

All that said, I don't know why you'd want to print over using wood. Maybe to make complex curves/shapes?

 

 

The only reason I mentioned printing is because it'll be a lot easier than going to the woodshop. But realistically, I'm going to the woodshop for this. There's no fancy curves on the enclosure. I just want a good looking finish on the wood. 



#47 SME

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Posted 07 September 2016 - 05:57 AM

Passive radiators may be a bit more forgiving than drivers as there are fewer parts to potentially ram each other.  However, the suspension of any driver can still be damaged if it's over-driven repeatedly.  For your application, I think Xmech may be more important.  You have to make many compromises to achieve big sound from a small box, and I think a bit of THD in the bass from high excursion at loud playback levels will probably not be a big deal.



#48 lowerFE

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Posted 09 September 2016 - 11:42 PM

Passive radiators may be a bit more forgiving than drivers as there are fewer parts to potentially ram each other.  However, the suspension of any driver can still be damaged if it's over-driven repeatedly.  For your application, I think Xmech may be more important.  You have to make many compromises to achieve big sound from a small box, and I think a bit of THD in the bass from high excursion at loud playback levels will probably not be a big deal.

 

 

With a better modelling tool, the Peerless is a noticeably more "efficient" passive radiator (1-2dB) than the Tang Band. Looks like I will just use the Peerless PR's. I tried very hard to have as small of compromises as possible with this design, but it looks like this will have to be something I have to compromise in this ultra small speaker. Good thing the limitations won't show until it gets close to the limits of the speaker. 

 

I've ordered the 4 ICEpower amps and the miniDSP's. It's coming along, slowly but surely.



#49 lowerFE

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Posted 08 November 2016 - 08:27 AM

As I am working on tuning this speaker on the DSP and making it linear phase, I was reminded of a problem that I will have horrible group delay in the bass region because of the combination of a vented enclosure and massive shelf boost to flatten the bass response. 

 

I remember for my previous speaker, group delay exceeded 2 cycles below a certain frequency, let's say 60Hz. I don't have anywhere near enough taps to brute force correct the phase shift. But what if, say I separated the <60Hz band, and I delay the >60Hz band by the equivalent delay in ms of 2 cycles at 60Hz, which is 33ms. Would doing this improve sound quality more than it hurt it?



#50 SME

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Posted 10 November 2016 - 07:59 AM

As I am working on tuning this speaker on the DSP and making it linear phase, I was reminded of a problem that I will have horrible group delay in the bass region because of the combination of a vented enclosure and massive shelf boost to flatten the bass response. 

 

I remember for my previous speaker, group delay exceeded 2 cycles below a certain frequency, let's say 60Hz. I don't have anywhere near enough taps to brute force correct the phase shift. But what if, say I separated the <60Hz band, and I delay the >60Hz band by the equivalent delay in ms of 2 cycles at 60Hz, which is 33ms. Would doing this improve sound quality more than it hurt it?

 

Probably not, or at least, not enough to make it worth the effort.  Part of the trouble is that the filters you need to separate the high and low contribute group delay themselves, and the summed response has some non-minimum phase group delay character as well.



#51 lowerFE

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Posted 11 November 2016 - 06:24 AM

Probably not, or at least, not enough to make it worth the effort.  Part of the trouble is that the filters you need to separate the high and low contribute group delay themselves, and the summed response has some non-minimum phase group delay character as well.

 

I spent some time trying, and had all the problems you mentioned. It is extremely sensitive to the amount of delay I apply, and the resulting FR is quite different with different delays in increments of 1ms. I got something reasonable after an hour or so of playing around. The group delay around tuning was significantly reduced, but I wouldn't call it optimal. The FR curves down a bit, probably due to some cancellation from phase differences, and I'm not sure if that reduces maximum clean output. The group delay is measured on my desk, nearfield. Not sure if that's valid for measuring group delay. I also only played with IIR filters and did not attempt to use FIR filters for the crossover or any attempt at correcting phase. A quick A/B revealed no sound quality improvements, but it might be because my new room is quite bad for bass. I haven't figured out whether I have a huge 50-80Hz null or I have 2 huge 45 and 90Hz room modes. 

 

I will investigate this further at a later time as it seems like it could be promising. Right now still focused on building the speaker. The enclosure proved far more difficult and time consuming to build than expected because of accuracy issues when squeezing every bit of space possible. Looking at options to CNC the enclosure now or make it with fibreglass. 



#52 lowerFE

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Posted 11 November 2016 - 07:08 AM

A few pictures of the truncated drivers. This alone took half a day!

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#53 andy497

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Posted 11 November 2016 - 05:46 PM

As I am working on tuning this speaker on the DSP and making it linear phase, I was reminded of a problem that I will have horrible group delay in the bass region because of the combination of a vented enclosure and massive shelf boost to flatten the bass response. 

 

I remember for my previous speaker, group delay exceeded 2 cycles below a certain frequency, let's say 60Hz. I don't have anywhere near enough taps to brute force correct the phase shift. But what if, say I separated the <60Hz band, and I delay the >60Hz band by the equivalent delay in ms of 2 cycles at 60Hz, which is 33ms. Would doing this improve sound quality more than it hurt it?

 

I don't see why you can't correct that with FIR.  Let's say you want to compensate down to 2 cycles at 20hz = 100 ms.  At 44.1 khz sample rate, that's 8,000-ish taps.  How many do you have available?



#54 lowerFE

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Posted 11 November 2016 - 06:26 PM

I don't see why you can't correct that with FIR.  Let's say you want to compensate down to 2 cycles at 20hz = 100 ms.  At 44.1 khz sample rate, that's 8,000-ish taps.  How many do you have available?

 

I only have around 1500 taps available, and I'm running on 96KHz, not because I want to, but because that's the only option on the miniDSP 2x4 HD. 



#55 Ricci

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Posted 21 November 2016 - 03:24 PM

Any further progress?



#56 lowerFE

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Posted 22 November 2016 - 01:46 AM

I have bought every single component needed for this speaker. Unfortunately I learned the hard way that it must be done by a CNC machine. Just working on the CAD drawings for this speaker for CNC. Because now I'm doing this on a CNC machine, it opens up other possibilities of what could be done. Here's a rough drawing to give you an idea of what the speaker looks like and how crazy space limited it is. 

 

I always knew this speaker would be very difficult to build, but I had no idea just how insane it is until actually doing it. In my mind it didn't seem so bad, probably doable in a weekend. But in reality, every little thing is so much more difficult because of how darn space limited I am. Simple things such as just how to rear mount the drivers became another exercise because of the 1/4'' thick wood. It took nearly a full day just to cut the frames off the drivers. The incredibly small midrange and tweeter spacing causes problems in sealing the drivers, not to mention the extreme difficulty of cutting it to shape without a CNC machine. 

 

There are other things that happens when you actually build it out or model it in a 3D software. The depth of the speaker was forcibly increased by 1'' from 6'' to 7'' for several reasons such as the two woofers cannot be mounted magnet to magnet because the magnets repel each other when placed that closely and not having enough space for the larger amp. This increases internal volume, and now 2 PR's might not be enough. Should I add a third PR and lose the inert enclosure, or convert a high excursion Tang Band woofer to be a PR, increasing the baffle size and decreasing PR "efficiency", so I have to put more thought into questions like this. 

 

Originally I aimed to have this speaker completed by about now. Unfortunately I'm looking at around late December to finish the model and have the parts cut, and another month for putting everything together and applying finishing, and another few weeks for outdoor measurements and tuning. So I'm looking at February before it's done. 

 

Believe me I want nothing more than to get this speaker done. The anticipation is killing me. I also don't want to ever setup my current mini speaker again. It is a massive wiring mess where 11 boxes (3 amps, 3 power supplies, 2 miniDSP's, 2 stereo to mono boxes, one optical cable splitter), 26 sets of cables (10 RCA, 6 banana plugs, 5 power cables, 3 optical, 2 USB) and a standalone power bar are needed to power 2 little speakers. I can't wait to cut that to just 2 speakers, 2 miniDSP's, and an optical splitter. Unfortunately I will have to set it up at least 3 more times in the next 2 months...

 

I attended the Burning Amp last week, and I heard the LXmini from Linkwitz Labs. Sounded really spacious and big (a little too big for my taste actually), but nevertheless got me curious about dipoles. The LXmini is omnidirectional to 800Hz. Mine is omnidirectional to 400Hz. Both speakers also follow the 1/4'' wavelength crossover frequency for a lobing error free radiation pattern. I had an idea on having the option to turn the speaker into a dipole by adding another set of tweeter and midrange to the rear baffle of the speaker. The ICEpower amp for the midrange and tweeter have no problem supporting the second driver, in fact it is specifically rated to be able to handle 20W 8 ohm on one channel (2 tweeter) and 82W at 2 ohm on the other channel (2 midrange). If I feel like blowing $5000 and a whole bunch of time I'll attempt this. Only reason I'm not doing this on the current speaker is that I don't have room for the rear tweeter because the woofer amp is mounted on the top baffle. And I thought a small speaker can't get more expensive than this...... (Well, I could have used some $300+ woofers, but they would have performed worse for bass than the $140 woofers I used here) 

 

But before that I want to look at moving away from a miniDSP setup and maybe to a Intel NUC setup for DSP, inspired by BassThatHz's work on a PC based DIY DSP setup. This is why the miniDSP's weren't inside the speaker, even though there is space. One feature I feel that is very important for sound quality is the equal loudness contour to maintain tonal balance at any volume. At low volume I want a more V shaped curve, at high volumes I want the bass and especially the treble to be reduced, otherwise the speaker could sound too bright at higher volumes. I'd also get much more taps for FIR filters, and can actually do more than 2 bands for the compressor without the tedious wiring solutions right now involving combining signals back into mono for the woofers. Not to mention, it would be much cheaper than 2 miniDSP's

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#57 Ricci

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Posted 22 November 2016 - 04:05 PM

$5k! Whew that's an expensive pair of mini speakers.

 

The amount of cables, amps, power supplies, etc...Is exactly the reason I'm leaning toward active with built in amplifiers for my "someday" speaker build. More expensive but only 2 cables needed.

 

That's a cram packed little speaker. Did you think about moving the active 3 way section closer to center and mounting the PR's on the ends with perhaps an end cap on each? Wasn't sure if you thought about that arrangement or if it would even work.



#58 lowerFE

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Posted 23 November 2016 - 01:12 AM

$5k! Whew that's an expensive pair of mini speakers.

 

The amount of cables, amps, power supplies, etc...Is exactly the reason I'm leaning toward active with built in amplifiers for my "someday" speaker build. More expensive but only 2 cables needed.

 

That's a cram packed little speaker. Did you think about moving the active 3 way section closer to center and mounting the PR's on the ends with perhaps an end cap on each? Wasn't sure if you thought about that arrangement or if it would even work.

 

 

Damn it Ricci! Your comment just cost me another $5000 because you just suggested something that opened up a whole bunch of new possibilities for improvement for this speaker! Now I can't call the speaker I'm building as good as it gets for a small speaker!  :angry:

 

In all seriousness, I did consider that, but I originally brushed it off because if the speaker is used as a stereo pair, it would be placed vertically, and the PR's would sag from being mounted vertically, especially with all the added weight. Also, the speaker would need feets on the right side, so when vertically placed, the PR has a slot for the sound to escape. However, the protruding feets would not look nice when placed horizontally. 

 

However, I didn't consider all the benefits that this configuration can bring that I only realized after you mentioned this again. 

 

1. First, the speaker can be made smaller!  :). I really didn't like having to increase the speaker size from the planned 14" x 6" x 6" WHD to 14.5" x 6" x 7". I can probably drop the size to 13" x 6" x 7" with this configuration. The depth increase isn't so bad because it is not very noticeable, but decreasing baffle width from 14.5'' to 13'' is very noticeable. 

 

There is a lot more baffle space for the TMW drivers, which means the driver can be placed in the same plane, like a TMW. There are several benefits

 

2. There is a lot more baffle area around the tweeter. This opens up the possibility to make a waveguide for the tweeter. It would be a very shallow waveguide that only controls directivity above 5000-6000Hz where the tweeter stops radiating 180 degrees and starts narrowing. This would make for a smoother power response above 6000Hz, as well as reducing diffraction effects.

 

3. I can use the Audax HM100Z0 midrange. This is a slightly larger but much more (~5dB higher, 93dB @ 2.83V 8 ohms) sensitive midrange. This would allow the speaker to play even louder and more dynamic than it already is, and likely exceeding most bookshelf/floorstanding speakers, but of course below high efficiency pro speakers. The 2 woofers can do ~110dB to 400Hz, but the original Scanspeak 10F mid can only play to about 102dB in its pass band. This mid can play ~107dB across its pass band. Many have mentioned this as one of the most detailed drivers ever, and some have mentioned this midrange to be even more detailed than the Scanspeak 10F. 

 

4. I can use the Tang Band W5-1138SMF as a PR without increasing the speaker size. On the original, I would need to increase the baffle width by 0.375" if I wanted to use the TB woofer as a PR. When placed on the side, the speaker can still maintain the smaller baffle size! This woofer will provide higher excursion limits than the Peerless PR currently used. 

 

5. There is space for another tweeter and midrange on the rear baffle for dipole configuration. 

 

But what's potentially more interesting is that this configuration would make the speaker a lot more deceiving as it seems like the speaker only has 3 drivers, and only 1 woofer that is pumping out the ridiculous amount of bass rom a mini speaker. 

 

So all of this would go into the V3 of this speaker. There is way too much complexity to be adding this to the V2 speaker I'm building now. I thought the V2 will be as good as it gets, and I won't be able to improve on the physical speaker itself much more. But looks like I can! However, I need a lot more knowledge in dipoles and waveguides before I can tackle this. If you know anyone that can help with waveguides, please let me know. 

 

As to the cost, I probably only need $4000, about $900 more for extra drivers for dipole, and still not as expensive as your nuclear options! But really, even the current speaker I'm building will spank any traditional (non HE) commercial $5000 speaker for sound quality. In fact, if I do this right, it might be quite difficult to find any traditional commercial of any price that'll outperform this speaker for sound quality. It will take a special speaker, like high efficiency, horn, all out DSP speakers like JBL M2, B&O Beolab 90, Kii Audio Three, or others to outperform this. It is using some of the finest drivers available with a proper crossover implementation that takes into directivity, off axis response, power response, lobing error (where it has none), phase (linear phase), time alignment, group delay and of course flat response into proper account with no compromises to dynamics or maximum volume compared to traditional speakers. Most mega bucks high end speakers do poorly for most of those aspects of speaker performance mentioned above, which is kind of sad. 



#59 Ricci

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Posted 23 November 2016 - 04:42 PM

Didn't mean to throw the project off course but if it helped you think of some options you hadn't considered that's good.

 

Waveguides aren't so bad. In this case since everything is so compact that's likely going to be the #1 design criteria. As far as building a custom one this small it might be worth looking into having it rapid prototyped.



#60 3ll3d00d

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Posted 23 November 2016 - 06:58 PM

How would a decent NUC plus audio interface be cheaper than 2 minidsp's?




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