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Discussion Starter · #1 ·
Hi guys, first post here, so a bit about me first!

I built a HTPC a couple of years ago and have been hooked on DIY AV stuff ever since, since its been a massive success with the WAF sky high. :clap:Documented my journey from AV noob to someone who knows a bit more than average on a blog buildingahtpc.blogspot.com.

Massively increased my commitment to DIY AV by taking on a Tony Gee LBS floorstander design over 6 months back and finally completed them (well almost) in partnership with a HifimeDIY TK2050 amp. Turned out to take longer and cost a lot more than expected, but the result is amazing. WAF is not so high though... as she doesnt like loud "noise".:nono:

Since I've now thoughly hooked myself on the hobby of DIY Hifi, I wonder whether anyone can help me... I've posted over at DIYAudio, but my thread hasnt got any traction for some reason.

I'm planning out a subwoofer build to match with the pair of Tony Gee LBS floorstanders – since I bought all the tools and stuff to build the floorstanders, adding new speakers will be relatively cheap (thats what I say now... ask me when its finished) – and first cab off the rank is a subwoofer! :) I expect that the WAF will be rock bottom.:devil:

I would have liked to build the Passive Radiator sub using the now discontinued Peerless XLS PR, but since I can't reliably find them anywhere, I've been experimenting in WinISD Pro with a Scanspeak 26W/4558T00 driver and the matching passive radiator 26W/0-00-00 – apparently 'newly released' and sold by WES in Sydney.


www.scan-speak.dk/datasheet/pdf/26w-4558t00.pdf
www.scan-speak.dk/datasheet/pdf/26w-0-00-00.pdf

Has anyone built a Passive Radiator design with these Scanspeaks? I heard that the max excursion is not great in the Scanspeak, and I understand that Xmax measurement can be a little inconsistent between manufacturers – but the Scanspeak value seems to be the same as the Peerless design (12.5mm)

I plugged the stats into WinISD and chose a box size of 30L and added 600g to the PR (as per the similar Peerless design) – the graphs come out like below for the Scanspeaks:

As I'm not yet adept at knowing what I should be looking for in these charts – I wonder whether someone whose done it before would be kind enough to comment on whether this design would be a goer, or whether I've overlooked something catastrophic in the graphs or in entering the parameters. It looks good to me, but only because it seems similar to the Peerless results and doesn't seem to blow up in excursion.


Scanspeak 26W driver in WinISD:


System Transfer function:



Passive radiator transfer function:



Driver cone excursion @ 120W:



Passive radiator cone excersion @ 120W:



Any comments appreciated! :bigsmile:

thxs, b
 

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Discussion Starter · #3 ·
Hi Mike,

It would be mainly for music, but having said that, I'd like to have a decent output at the low 20's, just for the challenge.
 

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30 liters with 600 grams of mass is a 14 hz tune, way to low for what you want. 40 liters with no mass added is a 20 hz tune, more in line for what you stated.
The driver will handle 200 watts with a hi-pass filter at 20 hz. Cone excursion is in check as well as PR excursion, which would be around 20 mm, as far as I'd go with this specific PR. Here a project file, save it to the "Projects " folder in WinISD.

View attachment The billyo Project.wpr


scanspeak.JPG
 

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Discussion Starter · #5 ·
Thanks Mike!

I really appreciate you taking the time to do that simulation. After comparing it to the original simulation and playing with the box volume and weights - resonant frequency of the box seems fairly sensitive to the PR weight and not very sensitive at all to the box volume. Is that correct?

Complete noob questions coming up.

1. As I understand it, this driver has a resonant frequency of 20.94 Hz, and the PR has a resonant frequency of 11 Hz (when unweighted?)... leaving the box volumes and PR weights as the only other thing that is adjusted to change the resonant frequency of the box.

As I understand it, the optimum box size is such that it starts resonating when the driver and PR roll off their resonant frequencies - either on the upper or lower sides.

So given that the driver has a resonant frequency of 20.94Hz and the PR is at 11 Hz, should I be aiming for a different box resonant frequency? Probably a higher box frequency?

I guess the ultimate question is... what criteria determines the best box frequency? I've searched the web but can't find a good explanation anywhere.. (or at least one that I can understand!)

2. Also, I was thinking of powering this with a Bash 300 plate amp - do you think that would a good match?
 

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seems fairly sensitive to the PR weight and not very sensitive at all to the box volume. Is that correct?
The resonant frequency of the box is sensitive to both the box volume and PR weight. Change just the PR weight and the tuning changes, change just the box volume and the tuning changes.
and the PR has a resonant frequency of 11 Hz (when unweighted?).
The PR has resonant frequency of 11 hz in open air, when placed in a 40 liter cabinet (unweighted) it now has a resonant frequency of 20 hz.

what criteria determines the best box frequency
The best box (tuning) frequency depends on the parameters of the driver, PR, cabinet volume, and what your goals are. In this specific case since you want 20 hz output, the above model is the best this combination of driver, PR, and cabinet size can do. Personally I would see if there are other drivers out there that would model with more low end extention.

If the Scan Speak driver is your choice, the Bash amp will work well with it.




 

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Discussion Starter · #7 ·
Personally I would see if there are other drivers out there that would model with more low end extention.
Unfortunately, there seem to be relatively few passive radiator manufacturers in the world, and even less in Australia.

Someone else has said that the design could sound "muddy" for music, would I be better off tuning to 25Hz or so in order to get a better balance for music and the occassional movie... or are the Scanspeak drivers and PR just fundamentally flawed and I won't ever be able to get a great sub out of them?

thanks once again for your assistance!
 

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I don't see this design as being muddy since the response is already down 5.5 d at 30 hz. It would be 8 db down at 30 hz with a 25 hz tuning. Where the design will be shy in output is in the 20 - 30 hz range for movies.
How big is your room this sub will be going in and do you have a cabinet size limit that would be acceptable? I ask because Creative Sound Solutions have an Australian dealer, the SDX10 driver with a pair of CSS PR's in 70 liters with the Bash 300 would really outperform the Scan Speak in the 20 - 30 hz range.
 

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Discussion Starter · #9 ·
Ummm.... I was hoping to get away with a cube less than 40 cm on each side, preferably more down to 30 cm. I didnt realise that Creative Sound Solutions had an Australian distributer - their site is down at the moment but I'll call them tomorrow if I get time. Maybe if I glued a pot plant on the top of it, the wife wouldnt mind.:foottap:

So are you saying that the Scanspeak design that you helped me with would be great for music but struggle with movies that were heavy on the 20-30 Hz range?

The room is quite large, I'd estimate 8m x 5m - which I understand runs the risk of setting up some interesting standing waves.
 

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Discussion Starter · #11 ·
Yup - I think I'm on a loser with a PR system, with the size, driver availability and budget all against me.

Will investigate a sealed system.
 

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Discussion Starter · #13 ·
I reckon that a cube roughly 30-35 cm is about the max. Say a 10" sub.

Can you recommend any nice 10" drivers? I was toying with WinISD and noted that with a peaking filter (+6db @20Hz) there is a nice boost to low end extension.
 

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Discussion Starter · #15 · (Edited)
Were you modeling the Scan Speak driver?
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Yep, but only because there are a thousand or so drivers in there, and I've got little idea as to which one is suitable or available here!:scratch:

I'm gonna spend a little while looking at the projects database and see if I can find one that's possible.
 
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