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Old 16th September 2012, 01:27 AM   #31
bjorno is offline bjorno  Sweden
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Hi All,Late

Post#1:
Quote:
...my room being 3.2m wide, 2.4m high and 10m long. The lowest modes should be (according to Room Mode / Standing Wave Calculator) 17.2, 34.4, and 51.6 and so on down the length, and then multiples of 54 across and 72 vertically...
I plugged in your room into this program and found You need more than one sub to get even FR in the room modal region: See the picture:...and...:

Room Response Calculator - Reflective Accumulation Simulation Software

Quote:
...The Tangband WQ-1858 appears to have a very flat response down into the low end in the recommended cabinet size, which might be a useful thing as I don't know where the crossover will be until I've built it. The measured response at Europe Audio WQ-1858.pdf also looks quite flat in this region from 20 to 100 Hz...
Post#9

Quote:
...To get the maximum from the T-Rex footfalls scene is exactly what I want from this in terms of extension and volume. If I can get that without sacrificing timing, then I'll be very happy...
The Tangband WQ-1858 is IMO a very good driver and suitable for a main sub that can be integrated with the Mains without the need of EQ's or signal delay units:See the picture

Post#21:

Quote:
..It might be a bit above the price range but this Vifa NE315W-08 12" Subwoofer Speaker 264-1142 models very nicely in an 85L vented enclosure. edit: the slight wiggle in the step response is from the port resonance, but if you cross it over at say 80Hz it should have a minimal effect I would think...
IMO: The Vifa NE315-08 needs to be reworked:See the picture:


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Old 16th September 2012, 03:04 PM   #32
DrNick is offline DrNick  United Kingdom
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Quote:
Originally Posted by bjorno View Post
Hi All,Late

Post#1:


I plugged in your room into this program and found You need more than one sub to get even FR in the room modal region: See the picture:...and...:

Room Response Calculator - Reflective Accumulation Simulation Software
Thanks for looking at this. I am going to have to work out where to put it with some care, I can see.

As for having two, there's the laws of physics which I try to obey, and then there's She Who Must Be Obeyed. She wins, so I'm going to have one sub, and just try to find the best place place for it!

Quote:
Originally Posted by bjorno View Post

The Tangband WQ-1858 is IMO a very good driver and suitable for a main sub that can be integrated with the Mains without the need of EQ's or signal delay units:See the picture
It does look good. I've been following up on the suggestion from Arty that I should look at a sealed cabinet but use a Linkwitz transform to flatten the bass response down to the required level, and have modelled this driver below using this sort of EQ. It looks very promising.

So, to recap, I looked first at simple sealed designs, not relying on equalisation, but there is no way I could build one big enough to deliver the required low end extension, which I'm still hoping to get to 20 Hz flat, and then if there was anything detectable below that would be nice. I then looked at vented designs, but the length of vents needed would be over 2 m, so again this would not work for me.

Having eliminated these options I have looked at going back to a sealed box, but using equalisation to get the required response. One of the reasons I was resistant to this at first, was that I have not had a sub before and have little idea of how it would fit into my room, and what sort of equalisation might be needed to stop it booming at some frequencies. Anyway, after looking at the possibilities for amplification, I've been drawn to the idea of using a miniDSP to implement a Linkwitz transform. This seems to be common practise, so I'm hopeful it will be what I need.

The drivers I'm considering are:
Dayton RSS390HF-4, 15", £203 (I'm in the UK, please don't tell me how much more I'm going to pay than elsewhere).
Tangband WQ-1858 12", £167.
Peerless 835017 XXLS 12", £195

I was also looking at the Eminence Lab 15 driver, availble for £185 but it does not appear any better than the 12" drivers, and less flat in a small box.

Looking at the models, I've used a 2nd order high pass filter set at 5 Hz to limit the cone extension to xmax, then set the box size to 80 litres, and added the Linkwitz trasform to make fp 20 Hz and Qp 0.707. I then set the signal level to get the cone excursion to equal xmax. I've included the Tangband with and without the Linkwitz transform.

Click the image to open in full size.


Click the image to open in full size.

Click the image to open in full size.

It is clear that with the equalisation, the maximum power that can be used is limited by the cone excursion at the lower frequencies, so from the model it seems that you could only use quite low power levels with equalised speakers like this. Is this correct, or is this an artefact of how the WinISD program works? Looking at the amplifier load the power levels seem higher.

Click the image to open in full size.

I need to sort this out to know what amp power I'll need. I'm hoping 200 W should be fine for the 12" drivers, which is where I'm leaning at present, as I don't think I want so much volume, as long as it will go low.

Just for a laugh I've also looked at how the Peavy Low Rider 18" came up (same as the Dayton 15" if you want to transform it to f0 = 20 Hz) and the Aura NS18-992-4A (18" £600 and will give 103 db at 20 Hz) the B&C 18SW115 which costs and performs the same, and the B&C 21SW150, which is capable of 106 db at 20 Hz, and costs £770. Oh well, if I win the lottery.
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Old 16th September 2012, 08:26 PM   #33
DrNick is offline DrNick  United Kingdom
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I've ordered a Dayton RSS390HF-4, so the plan is

Dayton RSS390HF-4
MiniDSP (with analogue volume pot to go on the back)
BKElectrics Mosfet Module (still working out what power)

I've been working on the basis of an 80 litre box, and modelling this that gives Qtc of 0.875, so not out of the park to correct by equalisation. The box dimensions could be 40 x 55 x 40 cm internal with 8 litres over for the driver and amp volume, and I'm planning to make it from 25 mm plywood, with some braces. Next thing to figure out is how to mount the amp and how get a good smooth paint finish on the casing.

Just wondering what the best way to power the MiniDSP will be, can I run some lines from an appropriate point on the BK amp?
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Old 16th September 2012, 10:51 PM   #34
DrNick is offline DrNick  United Kingdom
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Right, I used the spreadsheet kindly made avaible by Trueaudio, which I found here, to calculate the boost that the Linkwitz transform I was using was applying. Thanks to the guys who wrote this page, for the guidance. It turns out to be 11.67db, so this multiplies the input power by 2^(11.67/3) = 14.8, so the 30 W signal I was modelling is actually effectively 447 W. The model shows a peak of just over 320 VA for apparent amplifier load, so is the difference due to the phase behavious of the system? Anyway, if I need 450 W to drive this to hit the limits, I'm quite happy to drive it with a less powerful amp and not go overboard. The BK amp I was thinking of gives 215 W into 4 Ohms, or to model it, 14.5 W if you divide by the boost factor. This gives 86 db at 10 Hz and 95.5 db at 20 Hz from the WinISD model including the Linkwitz transform. From my very inexact calculations, I needed 78 db to match my regular listening, and up to 82 db for what I'd regard as loud, so this should do okay.

So, that will be the amp, I have ordered the driver, and now I have to get the other bits (mains plug, on off switch), and build the box.
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Old 17th September 2012, 02:27 AM   #35
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Originally Posted by wintermute View Post
As for the question how loud will 20Hz be at 86db I can't really answer except to say, you won't be able to hear 20Hz, you can feel it (if it has enough power) but not hear it.
Tony.
I disagree on not hearing it but due to the hearing sensitivity at the extremes it will have to be pretty loud. As 'proof' I submit that pipe organ builders sometimes use 32 ft stops that go down to 16/17 Hz. If it couldn't be heard (merely felt) would it need to be tuned? You can definitely tell if the wrong note is played. BTW it's a wonderful sound way down at the bottom.

Human Hearing: Amplitude Sensitivity Part 1 — Reviews and News from Audioholics

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Old 17th September 2012, 09:14 AM   #36
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I did a bit of a google search, right here in my own city is a pipe organ that goes down to 8.18 Hz!! Frequencies I will have to keep an eye out for a recital!!

Tony.
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Old 17th September 2012, 09:18 AM   #37
DrNick is offline DrNick  United Kingdom
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Originally Posted by wintermute View Post
I did a bit of a google search, right here in my own city is a pipe organ that goes down to 8.18 Hz!! Frequencies I will have to keep an eye out for a recital!!

Tony.
You won't even have to buy a ticket, just arrange to be within a block or two...
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Old 17th September 2012, 11:14 AM   #38
jwmbro is offline jwmbro  United States
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Originally Posted by DrNick View Post
Right, I used the spreadsheet kindly made avaible by Trueaudio, which I found here, to calculate the boost that the Linkwitz transform I was using was applying. Thanks to the guys who wrote this page, for the guidance. It turns out to be 11.67db, so this multiplies the input power by 2^(11.67/3) = 14.8, so the 30 W signal I was modelling is actually effectively 447 W. The model shows a peak of just over 320 VA for apparent amplifier load, so is the difference due to the phase behavious of the system? Anyway, if I need 450 W to drive this to hit the limits, I'm quite happy to drive it with a less powerful amp and not go overboard. The BK amp I was thinking of gives 215 W into 4 Ohms, or to model it, 14.5 W if you divide by the boost factor. This gives 86 db at 10 Hz and 95.5 db at 20 Hz from the WinISD model including the Linkwitz transform. From my very inexact calculations, I needed 78 db to match my regular listening, and up to 82 db for what I'd regard as loud, so this should do okay.

So, that will be the amp, I have ordered the driver, and now I have to get the other bits (mains plug, on off switch), and build the box.
Hi. You don't mention what frequency you are trying to equalize this box to? The lower you want it to go flat, the more gain you're going to need to have, obviously perhaps. I ran some simulations in HornResp, with the Dayton in an 80l closed box, and it shows that the driver takes 35Volts (around 300W into 8Ohm) to reach Xmax at 30Hz and below. This gives an SPL of 109dB at 30Hz (at 1 meter distance).

It would seem reasonable to me to equalize this box flat to only 30Hz, and let the natural rolloff below 30Hz remain. So try to use 30Hz as the new -3dB point, and this will leave you with a respectable 102dB at the -10dB point of 20Hz. In my opinion if you try to equalize flat to 20Hz, you're using up the xmax so soon that you don't get enough level throughout the rest of the band.

Additionally, due to the very long wavelengths at these low frequencies (5.7m half-wave at 30Hz), you're very likely to get room gain below your chosen cutoff, counteracting the falling response somewhat. Also, for 30Hz, you won't need insane amounts of gain, once you're getting into double digit decibles (10dB = x10 power), you risk amplifying noise as well.

Many people recommend using half again the amp capacity of the maximum power you want to use, so for a box that hits xmax at 300watt/4Ω, you'll ned an amp capable of 450W/4Ω. As for your Minidsp, any 12V source of power will do, in my subwoofer amp, I have my Minidsp connected to the outputs of the amp's power supply (which is a 35V DC supply) using a 7812 linear voltage regulator with some smoothing caps, works just fine.
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Old 17th September 2012, 12:45 PM   #39
DrNick is offline DrNick  United Kingdom
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Originally Posted by jwmbro View Post
Hi. You don't mention what frequency you are trying to equalize this box to? The lower you want it to go flat, the more gain you're going to need to have, obviously perhaps. I ran some simulations in HornResp, with the Dayton in an 80l closed box, and it shows that the driver takes 35Volts (around 300W into 8Ohm) to reach Xmax at 30Hz and below. This gives an SPL of 109dB at 30Hz (at 1 meter distance).
I was going for 20 Hz as the -3 db point. My reasoning was that at lower volume levels, I'll perceive the lower frequencies as less loud relative to the midband, so if they are boosted more, then that would suit my somewhat quieter listing habits.

Quote:
Originally Posted by jwmbro View Post
It would seem reasonable to me to equalize this box flat to only 30Hz, and let the natural rolloff below 30Hz remain. So try to use 30Hz as the new -3dB point, and this will leave you with a respectable 102dB at the -10dB point of 20Hz. In my opinion if you try to equalize flat to 20Hz, you're using up the xmax so soon that you don't get enough level throughout the rest of the band.

Additionally, due to the very long wavelengths at these low frequencies (5.7m half-wave at 30Hz), you're very likely to get room gain below your chosen cutoff, counteracting the falling response somewhat. Also, for 30Hz, you won't need insane amounts of gain, once you're getting into double digit decibles (10dB = x10 power), you risk amplifying noise as well.
Thanks, I do take your point about too much gain amplifying noise up. I might start with no equalisation and then try just flattening out the curve, then setting different f3 values going down and just play about. This is one of the things that attracted me to the idea of using the miniDSP.

Quote:
Originally Posted by jwmbro View Post
Many people recommend using half again the amp capacity of the maximum power you want to use, so for a box that hits xmax at 300watt/4Ω, you'll ned an amp capable of 450W/4Ω. As for your Minidsp, any 12V source of power will do, in my subwoofer amp, I have my Minidsp connected to the outputs of the amp's power supply (which is a 35V DC supply) using a 7812 linear voltage regulator with some smoothing caps, works just fine.
Thanks, I might have to go for the MF450 then! I was wondering if speccing it too small would have a negative impact on transients or on the overall quality of the sound. Thanks for the note on the regulator, I was hoping it would be that simple.
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Old 17th September 2012, 02:37 PM   #40
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Originally Posted by DrNick View Post
I've been working on the basis of an 80 litre box, and modelling this that gives Qtc of 0.875, so not out of the park to correct by equalisation.
I am not so sure this is a good idea. I have read that the HF subs are prone to "oil-can", or pinging when used in a smaller box:

Dayton Titanic vs. Reference HF vs. HO Subs

Low end EQ in a sealed box puts lots of stress on the driver, you may have a problem here. I would suggest either:

-increasing box size, use plenty of fiberglass internally, then EQ.
-increasing box size and porting
-use a HO series woofer instaid, with the thicker cone.

......or you might be just fine.
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