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Old 22nd November 2010, 01:46 PM   #101
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The new thread about trying to simulate a bass-reflex boss using LTspiceIV is here :
Marshall Leach vented-box loudspeaker Spice model (AES 1991)
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Old 29th November 2010, 03:58 AM   #102
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I've been amusing myself with manual calculations to try to find a suitable bass driver for a bass reflex system, with a f-3 of 30 Hz. I've found a few that gives satisfying Vb and vent tuning values, but when I come to calculations of the vent diameter and length, my luck is out. I've been trying with dual 10" and 12" drivers.

I get results in the 5-6" for the diameter, and at least around 30" for length. Can it be due to that I use double the Vd value, as I do for Vas when calculating Vb value for the box?

I've used the following formulas, given in Basta! + Dickason's formulas for a SBB4 in LDC. (For vents, I've tried those in LDC and some others, result the same):


1. Öhman
Vb = Vas/1.1 x (Qts/0,40)^3/1+0,4xViso
fp = fs x (0,42/Qts)

2. Keele
Vb = Vas x 15 x Qts^2,87 / 1 + 0,4 x Viso
fp = fs x 0,42 x Qts^-0.9

3. Margolis/Small
Vb = Vas x 20 x Qts^3,3 / 1 + 0,4 x Viso
fp = fs x 0,42 x Qts^-0,96

I've used a Viso value of 20% (Viso = amount of lining material in comparison with total volume)

Suggestions for f-3 calculations for the formulas above?

Suggestions for vent calculations?

Suggestions for two 10" or 12" that might give a f-3 around 30 Hz in a box with a Vb of at the most around 100 liter?
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Old 29th November 2010, 09:13 AM   #103
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Best choice would be Monacor SPH-200KE, two drivers inside a 85 litre box.
Second choice would be Monacor SP-212, one driver inside a 85 litre box.
Big cone doesn't mean deep bass.
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Old 29th November 2010, 10:02 AM   #104
navin is offline navin  India
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Quote:
Originally Posted by buggsson View Post
I've been amusing myself with manual calculations to try to find a suitable bass driver for a bass reflex system, with a f-3 of 30 Hz. I've found a few that gives satisfying Vb and vent tuning values, but when I come to calculations of the vent diameter and length, my luck is out. I've been trying with dual 10" and 12" drivers.

Suggestions for two 10" or 12" that might give a f-3 around 30 Hz in a box with a Vb of at the most around 100 liter?
Why only bass reflex? Sealed boxes roll of much slower and hence with a F3 or say 45Hz might offer lower in room (with room gain).

Suggestions would the SEAS L22RNX/P (bass reflex), W26FX01 (sealed), or Peerless XXLS subwoofers (sealed) see links below.

THE ART OF SOUND PERFECTION BY SEAS - H1252-08 L22RNX/P

THE ART OF SOUND PERFECTION BY SEAS - E0026-08S W26FX001
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Old 29th November 2010, 07:51 PM   #105
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Comparing some bass-reflex arrangements.

Monacor SPH-210 is ruled out because of 50 Hz -3dB point.
Monacor SPH-225C is ruled out because of 51 Hz -3dB point.
Seas W26FX001 E0026 is ruled out because of Box volume 60.7 litre.

Monacor SPH-200KE gives a 29 Hz -3dB point in a 25.8 litre box.
Amazing for such a small box.
Problem may be the port lenght, 182mm long with 50mm diameter.

Seas L22RNX-P H1252 gives a 31 Hz -3dB in a 36.5 litre box.
Port is compact : 119mm long with 50mm diameter.

Monacor SPH-212 gives a 28 Hz -3dB in a 48.6 litre box.
Port is very compact : 98mm long with 50mm diameter.
Attached Files
File Type: pdf 0 - Comparison.pdf (4.1 KB, 15 views)
File Type: zip Marshall Leach vented-box loudspeaker Spice model (AES 1991).zip (333.4 KB, 5 views)

Last edited by steph_tsf; 29th November 2010 at 08:14 PM.
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Old 29th November 2010, 08:32 PM   #106
sreten is offline sreten  United Kingdom
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Hi,

Thought I'd do a quick check of one of the above, the SPH-200KE.
I don't get the same numbers. 26L sealed is around Qbox = 0.67,
I get around 40Hz for -3dB, 30Hz needs a bigger box.

Qts = 0.38, Fs = 28Hz, Vas = 54L, not checked the driver parameters.

rgds, sreten.
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Old 29th November 2010, 11:28 PM   #107
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Ooops ! I agree there is a problem in my post #103 & #105. I'll redo the calculations checking with WinISD beta. In the meantime please ignore post #103 & #105. Please apology.
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Old 30th November 2010, 05:14 AM   #108
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Quote:
Originally Posted by steph_tsf View Post
Ooops ! I agree there is a problem in my post #103 & #105. I'll redo the calculations checking with WinISD beta. In the meantime please ignore post #103 & #105. Please apology.
Also remember that a sealed box with an F3 of say 45Hz might have as much in room response as a bass reflex box with an F3 of 30Hz. The SEAS W26FX001 suggested would give you a F3 of about 45-50Hz in a 35-37 liter SEALED box. The SEAS L26RFX/P also offers similar sealed box perfomance and is half the cost of the W26.

You should maybe look at F3 and F10 numbers to determine which woofer system works best in your room.

We get some Wavecor woofers in India. I dont know if you get them where you are but they perform well in small boxes with passive radators. Yo can check out their 10" and 12" woofers here.
http://www.wavecor.com/
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Last edited by navin; 30th November 2010 at 05:27 AM.
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Old 30th November 2010, 04:56 PM   #109
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Quote:
Originally Posted by steph_tsf View Post
Big cone doesn't mean deep bass.
No, not necessarily, but it does help moving air when going deeper.

Quote:
Originally Posted by navin View Post
Why only bass reflex? Sealed boxes roll of much slower and hence with a F3 or say 45Hz might offer lower in room (with room gain).
I would prefer a sealed solution, but I have not been able to find one as yet that I thought would be usable. But if f-3 dB at 40 Hz is what makes it, I know a few, plus the ones suggested already in this thread. I've heard of room gain, but I was not aware that a sealed box with a higher f-3 dB than a vented box with a lower f-3 dB would equal, or better the vented box.

Quote:
Originally Posted by navin View Post
You should maybe look at F3 and F10 numbers to determine which woofer system works best in your room.

We get some Wavecor woofers in India. I dont know if you get them where you are but they perform well in small boxes with passive radators. Yo can check out their 10" and 12" woofers here.
Wavecor speaker innovations
Now that you mention it, I've seen it a few times before, but not that often, that checking the F10 numbers as well is a very good suggestion, due to the fact that F3 do not tell you that much, was the explanation, if I recall correctly.

We do have Wavecor in my area, and I've checked them up earlier, but I will do it again, and I'm not used to radiator solutions at all, never looked at that solution at all. If someone could just outline the major difference between reflex and radiator, I would be much obliged.

Small box is not that important, if by small you mean something less than around 100 liter in total for the woofer section. Smaller would be nice (WAF), but I think I can handle up to 100 lit.
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Old 1st December 2010, 04:00 AM   #110
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Quote:
Originally Posted by buggsson View Post
I would prefer a sealed solution, but I have not been able to find one as yet that I thought would be usable. But if f-3 dB at 40 Hz is what makes it, I know a few, plus the ones suggested already in this thread. I've heard of room gain, but I was not aware that a sealed box with a higher f-3 dB than a vented box with a lower f-3 dB would equal, or better the vented box.

We do have Wavecor in my area..If someone could just outline the major difference between reflex and radiator, I would be much obliged.
It usually depends on the room and the location of the speakers within that room. In many rooms the speakers get pushed against the rear wall. In such cases if the speaker does go very deep there will be a lot of nodes excited and also a lot of room gain (much of it uneven) and this can lead to lumpy bass which in my opinion is worse than too little bass.

There is no "RIGHT" solution. The room-speaker interaction is what determines the response of a loudpspeaker. Becuase bass has longer wavelenghts it's interaction with the room is more prominent. Dont aim for flat response (+/-3 db as advertised by many manufactuers in their catalogs). The room can add +/- 10db with ease so all those flat response curves are really not worth the paper they are written on. Which is why I discussed F10 numbers earlier.

I have lived on 3 continents (4 countries) and a variety of dwellings from a studio apartment in NYC (with flimsy sheet rock walls) to a large (wooden) house in the boonies with vaulted ceilings to a brick and concrete apartment and once even had a square room (exactly 16ft square). Each dwelling offered it's own challenges. As DIYers I believe it is our abilities to adjust for these "challenges" (as well as adjusting the sound to our ears) that makes DIY such a pleasurable and fulfilling pastime/hobby.

Passive radiators have their uses. If port lengths are too long a PR is often a viable option. Another option is that one can avail of Milo Nestorovic's concept of using cones of 2 different sizes (say a 10" woofer mated to a 12" PR). Adjusting the mass of the PR is also easier than adjusting a port length so in that way a PR is easier to tune to a room that a bass reflex speaker. However a PR has a fixed (static mass) while th mass of air inside a bass reflex port is not nesscarily so and this can pose it's own problems (transient response is not as good as a (SBB4 or even QB3) ported box). Wavecor's website has sample boxes and their transient response curves for your reference. see link below for more.

Audio Innovation - by Dan Marx www.danmarx.org

Before starting out I would advise you to try out a few of your friends' speaker systems in your room and at least determine which systems sound best. From the late 70s to today I must have "gone through" over a dozen speaker systems (from Philips, KEF, Volt/Rogers, JBL, JBL/UREI, Gold Sound, Vifa, Focal, Dynaudio, Morel/Focal, Peerless/Dynaudio, Focal/Morel/JBL, ScanSpeak, Audio Concepts, etc...) and each worked within it's own limiations and enviroment. I have also lived with friends' speakers from Klipsch, Polk, Fried, Vanderstee, Theil, Snell, AR, Infinity, etc.. and each time realised that DIY is a much better option even if you dont save any money by going DIY.

Good photographers have a clear idea of the picture they are going to take before even raising the camera to their eye. Similarly you need to determine what you want your system to sound like before shortlisting the drivers.

Hope this helps.
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Last edited by navin; 1st December 2010 at 04:13 AM.
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