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Low THD Tang Band RBM drivers?
Low THD Tang Band RBM drivers?
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Old 13th April 2018, 02:29 PM   #111
TheWaveCarver is offline TheWaveCarver
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Join Date: Apr 2016
I currently have three Peerless Tymphany 3.5inch passive radiators operating in a 2.2L enclosure with the W4-2089 (Same as W5-2053). After doing some last minute research I'm having second thoughts....

I'm worried that 3x 3.5inch Passive Radiators will not do the job based on what others are saying online. In my simulations it appears that 25 grams added to each Peerless 3.5in Passive Radiator will do the trick (They already have 38 grams attached). Yet some people online are suggesting that the W4-2089 would be better suited with 3x or 4x 5.25inch Tymphany Peerless passive radiators.

So I'm considering adding 3x 2inch Dayton Audio passive radiators in addition to the 3 I already have. So 6 passive radiators total... 3x 3.5inch and 3x 2inch. Thoughts? I don't want to starve the W4-2089

Last edited by TheWaveCarver; 13th April 2018 at 02:31 PM.
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Old 15th April 2018, 08:15 AM   #112
Nanoloop is offline Nanoloop  Hong Kong
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Have you measured the actual surface areas? How about the x max of the passives? If they add up to/equal at least the same as the main driver in their ability to shift a volume or air, then it should be okay, even when the driver is at x max. However, up to 50% more for the passives is the usual advice because you don't want them introducing non linear issues near x max, esp given this driver is designed to be low distortion at such limits.
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Old 15th April 2018, 10:23 PM   #113
TheWaveCarver is offline TheWaveCarver
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So here are my calculations. Statistics first...

Passive Radiator (3x of These):
Surface Area: 50.2cm^2
Max Excursion: 6mm

W4-2089 (1x of These):
Surface Area: 75cm^2
Max Excursion: 8mm

Calculations:
Total surface area of the 3x passive radiators is 150.6cm^2 which is double the W4-2089 which is 75cm^2... so that's pretty much perfect since I've read your passive radiators' combined surface area should be anywhere from equal to or double the woofer's surface area. Regarding volume, the passive radiators can displace 90.36cm^3 of air. The woofer displaces 60cm^3... so that should also be good.

Going to add around 25grams to each passive radiator (Not including the 38grams that are already installed). This is a simulation estimate... to tune the passive radiators, I will basically just add weight until at 40Hz the driver isn't moving but the passive radiators are. I believe this is how you tune passive radiators.
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Old 16th April 2018, 03:50 AM   #114
Nanoloop is offline Nanoloop  Hong Kong
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Volume and size look fine. in my experience, the more weight I add, the more the output from the PR reduces with increasing frequency, leading to a PR that only adds the lowest notes. It's probably affecting the transient response which might muddy the bass, which is why I prefer a larger cone and less added weight. So I start with too little weight and do frequency sweeps to see what's happening with the output as weight is added. I've also tried tuning it by measuring impedance before and I recommend this as the best way. I don't think your proposed way will produce very accurate results but no harm in trying and it may work just fine in the end. If it sounds right.... Anyway, here's an easy way to test impedance: Loudspeaker impedance measurement using a multimeter and 2 resistors

Last edited by Nanoloop; 16th April 2018 at 03:56 AM.
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Old 16th April 2018, 04:19 AM   #115
TheWaveCarver is offline TheWaveCarver
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When tuning the passive radiator, how does the impedance plot factor into the tuning? So I have the impedance plot from the manufacturer... or should I re-measure once it's installed with the passive radiators?


The article was useful for showing me how to measure impedance, Just trying to understand how to then use that plot to tune the PR's. Thanks!
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Old 16th April 2018, 12:23 PM   #116
Nanoloop is offline Nanoloop  Hong Kong
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the TB plot shows one impedance peak at 40hz iirc because it's in free air - when you have the driver reflex loaded "correctly", the single peak will split into two equal and smaller peaks. The valley between them is the new resonant frequency, and shows the driver is being damped at its resonant frequency for the enclosure, so the driver excursion is reduced and power handling increased for that enclosure. So yes, measuring impedance when the driver is in the enclosure is usually necessary because it will be different from the TB plot.

In generalised terms, if you put the driver in an undersized enclosure, the resonant frequency will be higher and the mid bass output will be stronger. In an oversized enclosure, the mid bass will roll off gently instead of rising and the resonant frequency will be lower, allowing more deep bass but at reduced output (an extended bass shelf design). With an ideally sized enclosure, the driver will be correctly damped and produce a theoretically flat response in the mid bass until it gets near the resonant frequency roll off. The enclosure size + driver sets this up and it can be tweaked by adjusting the reflex loading, but is largely determined by the driver + enclosure. This is why I got so lucky with my 3" woofer. I guessed around 1.2 litres but it seems to be around 1L is ideal so I got an extended bass shelf, and then the PR is tuned "too low" producing a tail end boost around 65Hz, giving the impression of a deepish bass capability, albeit very uneven and a tendency towards having one deep bass note.

Last edited by Nanoloop; 16th April 2018 at 12:51 PM.
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Old 3rd June 2018, 12:51 PM   #117
TheWaveCarver is offline TheWaveCarver
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It's been awhile since my last post. Still working on this project. Things have been a bit finicky with the 3D printing so I haven't posted much. Producing the cabinet is proving to be the hardest part. I did put together a prototype with 3D pieces I decided I didn't want to use for the final build. The Full Range crossover sounded pretty fantastic. I might do some frequency response testing with the prototype. Biggest concern is the baffle for each driver will be much shorter given that there is only half a cabinet.

Last edited by TheWaveCarver; 3rd June 2018 at 12:53 PM.
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