How to interpret WinISD (Transfer Function Magnitude)

Vitus

Member
2020-02-13 6:04 am
I just want confirmation that I'm interpreting the Transfer Function Magnitude graph correctly in WinISD.

I'm modeling a 12" passive radiator subwoofer with a 10" Ultimax driver in a 1,25cuft enclosure.

With all 6 discs attached (450g) it yields the following results:


-3dB

20200225112714-46.195.138.78.png



-20dB

20200225112823-46.195.138.78.png



Does this mean that when I have my receiver volume knob turned to -20dB, the subwoofer will be able to generate a 16hz tune?


I understand that F3 is an important value, but is that purely because some people want to listen at reference levels, i.e. F0?

For me personally, having the volume knob at -3dB or 0dB is extremely loud, I much prefer having a lower volume, but a dynamic sound, say -30dB to -20dB range.

Thanks for explaining.
 

4real

Member
2004-05-27 8:51 pm
Steyl
No, the sub will always be able to generate a 16Hz tone (up to a point). The volume knob only tells you how loud it will be. The setting on your amps is totally not related to the graph. The -20 in the graph only tells you that the 16Hz tone will be 20dB less loud then anything on the 0dB line (so roughy 40Hz and up). And note that all of this is excluding any interference with the room, which will usually add a few dB to the low end. But that is a whole other story.. let's first get you to understand this..

So it will play 16hz tones 20 dB less loud than 40Hz tones. Which audibly will amount to about 4x less loud (10dB more is about twice as loud for your ears). Power handling that low down will also be bad. Therefore most amps will have a high-pass, limiting excursion and saving your driver and PR from destruction (you can also model than in WinISD).
 
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Vitus

Member
2020-02-13 6:04 am
No, the sub will always be able to generate a 16Hz tone (up to a point). The volume knob only tells you how loud it will be. The setting on your amps is totally not related to the graph. The -20 in the graph only tells you that the 16Hz tone will be 20dB less loud then anything on the 0dB line (so roughy 40Hz and up). And note that all of this is excluding any interference with the room, which will usually add a few dB to the low end. But that is a whole other story.. let's first get you to understand this..

So it will play 16hz tones 20 dB less loud than 40Hz tones. Which audibly will amount to about 4x less loud (10dB more is about twice as loud for your ears). Power handling that low down will also be bad. Therefore most amps will have a high-pass, limiting excursion and saving your driver and PR from destruction (you can also model than in WinISD).


Right, thanks for an excellent explanation.

Why so much focus on F3 then, shouldn't F0 be what matters most?

F3 is seen as an acceptable -3dB drop as the lowest reference level, so to speak?


Also, do you know how to correctly judge and calculate the loudest possible SPL depending on the amount of available amplifier wattage?

I tried looking at (Maximum SPL) and (Maximum Power) but not really sure what to look for there, and how to interpret the graphs and translate that into amplifier wattage.

Is there a great tutorial somewhere which covers all my concerns and questions?

Thank you an awful lot.
 

wintermute

Administrator
Paid Member
2003-08-03 11:43 am
Sydney
+/- 3db are historically values that manufacturers used to report the frequency response range of their speakers. It's a variation considered to be reasonably flat.

These days when looking at bass extension, figures of -6db or -10 db are more commonly referenced for the lower limit of useful bass output.

Tony.
 

4real

Member
2004-05-27 8:51 pm
Steyl
Right, thanks for an excellent explanation.

Why so much focus on F3 then, shouldn't F0 be what matters most?

F3 is seen as an acceptable -3dB drop as the lowest reference level, so to speak?

Actually F10 is often looked at as more relevant. That is the point where things sound half as loud. Depending on the design you can have a design that has almost equal F3, but vastly differing F10. And since F10 is only half as loud, that is still quite significant.

Also, do you know how to correcttly judge and calculate the loudest possible SPL depending on the amount of available amplifier wattage?

I tried looking at (Maximum SPL) and (Maximum Power) but not really sure what to look for there, and how to interpret the graphs and translate that into amplifier wattage.

Maximum SPL gives you how loud the thing will go, regarding either power or excursion. Max power will just give you how much amp power you can put into it without exceeding physical limits.

if the max power line is always above the amp power you have, you'll he fine. On the low end, you'll probably not be, that where the high-pass will come in to protect sub. If you model that (in the filters section). (Let say 2nd or more order at 20Hz), have a look at the "cone excursion" graph. Just pump up the power (in signal), until you hit the horizontal line. Then you know how much power your sub can handle without damaging it.
 

Vitus

Member
2020-02-13 6:04 am
+/- 3db are historically values that manufacturers used to report the frequency response range of their speakers. It's a variation considered to be reasonably flat.

These days when looking at bass extension, figures of -6db or -10 db are more commonly referenced for the lower limit of useful bass output.

Thanks, -3dB is interesting because it's reasonably flat, got it.

I'll look more closely to -6dB and -10dB in the future.


Actually F10 is often looked at as more relevant. That is the point where things sound half as loud. Depending on the design you can have a design that has almost equal F3, but vastly differing F10. And since F10 is only half as loud, that is still quite significant.

I understand, I've been looking most to F3 because that's what most people rave about, I'll look more into F6 and F10.


Maximum SPL gives you how loud the thing will go, regarding either power or excursion. Max power will just give you how much amp power you can put into it without exceeding physical limits.

if the max power line is always above the amp power you have, you'll he fine. On the low end, you'll probably not be, that where the high-pass will come in to protect sub. If you model that (in the filters section). (Let say 2nd or more order at 20Hz), have a look at the "cone excursion" graph. Just pump up the power (in signal), until you hit the horizontal line. Then you know how much power your sub can handle without damaging it.

Wow, I have never even fiddled around with either (Filter) or (Signal), very powerful tools, I always wondered why my maximum excursion was only like 2mm, I was only feeding it 1W, lol.

Some interesting questions though!

My old subwoofer which is a cheap $300 OEM subwoofer, I find more excursion being directly tied to increased distortion, it's a sealed enclosure, is this a normal phenomenon when increasing the excursion, or is it just a sign of a bad driver?

I don't think that the amplifier is the cause of the distortion, I think it has way more to give than what the driver currently allows for, before distortion, by distortion I mean it's basically breathing/fluttering/shuffing, like it cannot take the amount of excursion and/or power being fed to it.

It's an 180Wrms amplifier, and this phenomenon occurs even before I turn the gain knob to around 40%, very clear distortion at 50%, horrible beyond that, I need to settle on 30% gain for an undistorted sound.

Driver, amplifier?


Less excursion, less distortion, in general?
 
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Vitus

Member
2020-02-13 6:04 am
Have a look at these...

My limitations are mostly enclosure dimensions and box size.

Lastly, I would like to use my existing 180W amplifiers.

Other than that, I'm free to use which elements I like.


The thing I can see with these are, especially the passive radiator model, that a 180W amplifier will not really limit me, as the cone excursion of the main driver is close to it limits due to the small box/enclosure size.

In the sealed enclosure/model I would surely benefit from a more powerful amplifier, but then it wouldn't go just as low as the passive radiator build with the same enclosure size.

Even adding a 4dB boost, fc 22hz, with a Q of 1.0 to the sealed enclosure, given a 500W amplifier is installed, I still wouldn't be able to go as loud as the 180W amplifier and the passive radiator.

Seems like a very weak argument to purchase a $400 amplfier, my 180W amplifier seems to perform better.


Anything I missed?
 

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Vitus

Member
2020-02-13 6:04 am
In general this looks okay. I'm a bit worried about your donor amp however. If it's from an existing sub, chances are great that it already includes a fixed boost somewhere in an area that might not be of advantage, giving you a crappy response.

Yeah, I guess I could throw a question to the manufacturer.

Otherwise, what's your thought on the rather steep roll off the passive radiator build yields?

Advantage/disadvantage?

Sealed builds offer a very smooth roll off, but how is that sort of roll off experienced in the real world, like a gradual decrease of bass?

Otherwise, with a steep roll off, it'd be much like - a lot of bass, then it quickly disappears, like the bass would drop through the floor, sort of?

Vented builds seems to offer a smoother roll off, also a lower and more louder low end, but I'm not sure I'm too much of a fan for the vented builds, as this could introduce port noises etc.

Passive radiator builds seem to offer best of both worlds.
 

Vitus

Member
2020-02-13 6:04 am
Often the specs of the sub will have the information.

As for the rest: do you want low or loud? That is basically the tradeoff..

Type: Subwoofer Cabinet: Sealed
Model: SUB-10 Colur: Oak, Black, White
Power (RMS): 180 W Power (Max): 250 W Frequensy Response: 30-180 Hz Crossover: 40 - 180 Hz Driver: 10 Inches
Dimensions (WxHxD): 325 x 325 x 325 mm Weight: 12,9 kg

Those are the specs, the PR-text is not worth quoting, it's just sales talk.

I'm not really sure what I want to be frank, but I like the idea of a passive radiator, being able to go low without the open design of a vented construction.

I absolutely hate the overly expressive, overly agressive, bloated, muddy bass that a vented design often brings.

Maybe a properly vented design will avoid those issues, but one thing is for certain, I don't want bass all the time when I'm watching my movies, I once visited a store which had Mad Max Fury Road on, there as an assemblance of Klipsch speakers with a 10" vented bass, my god - I told them that bass is way too high up, bloating everything that's Hi-Fi in the mix of the movie.

They checked the back of the subwoofer to see what the amplifier and crossover was turned to (some customers often turn it they way they want they said) but it was tuned just as they wanted it to be.

Maybe I have a bad experience of vented subwoofers, but if you can design something that's lower/deeper than a sealed cabinet, but not bloating the upper end of the mids, I would be very much surprised.

That's why I think a mix of the two is the most optimal, I quite like the sensation of going low I think, it's brings a more dynamic approach to the experience, but I still want a tight, definative, controlled, responsive bass.

I think you know better than me what's best in this case.

Thanks an awful lot, mate!
 
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4real

Member
2004-05-27 8:51 pm
Steyl
With the proper design you can make both sound good. It's mostly about the constraints you set for yourself and what you can get out of it. One is very clear: you can only spend about 35 L or 1.25 cuft.

Looking at how much extra SPL you get with your 10" UM + PR vs 12" UM closed, between 20 and 30 Hz, it's only 3dB (with a decent amplifier) . Is that really worth the effort of a PR? I'd say no.. Better spend the money on a decent amp that can do some DSP'ing, so you can do some room correction. That will probably improve sound more than those 3 extra dB's. Something like a Hypex FA501, Dayton SPA500DSP or even a powerful 1U PA amp with DSP will be lot's of fun.
 

Vitus

Member
2020-02-13 6:04 am
With the proper design you can make both sound good. It's mostly about the constraints you set for yourself and what you can get out of it. One is very clear: you can only spend about 35 L or 1.25 cuft.

Looking at how much extra SPL you get with your 10" UM + PR vs 12" UM closed, between 20 and 30 Hz, it's only 3dB (with a decent amplifier) . Is that really worth the effort of a PR? I'd say no.. Better spend the money on a decent amp that can do some DSP'ing, so you can do some room correction. That will probably improve sound more than those 3 extra dB's. Something like a Hypex FA501, Dayton SPA500DSP or even a powerful 1U PA amp with DSP will be lot's of fun.

Yeah, wisely said.

I'm more an more leaning towards a much simpler design, and as simple of a design as possible.

Adding in the extra cost of an SPA500DSP much quickly increases the final build cost.

All in all, adding all componentes together, I'm starting to doubt this whole DIY-thing.


Currently looking at Rythmik servo subwoofers, wow - they seem bloody amazing, plus they're all sealed, probably a completely different level of performance and a completely different league of bass representation with this servo mechanism, it is more than most likely exactly the kind of bass that I'm looking for.

I can only imagine spending this much money and time, building my own stuff, then realizing or finding out that I'm still not satisfied.

Wow, I need to rethink this, Rythmik look real sweet, I tell you.