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Old 23rd October 2006, 05:55 PM   #1
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Default Sub technical spec.

Hi guys

I’m planning to build my first subwoofer. The problem is that I don’t know anything technical. Of course I can just choose anything on the internet but I like to know what I’m doing.
So here’s my question.
There are a lot of technical specs. I don’t know how to read this. Where do I start learning this?

Here’s a list chosen from the Madison site. MA26WR09-04 10” Black Aluminum cone woofer
.

Vifa 10” Black Aluminum cone woofer
Rubber surround
Magnesium cast frame
Double magnet
F3 of 33Hz in 1.5 cubic foot sealed box!
Flange 271mm
Cut-out 231.2mm
Depth 124mm
Excellent for home or autosound
Very tight bass

Znom 4 ohm
Re 3.44 ohm
Le@1kHz 1.2 mH
fs 21 Hz
Qms 3.53
Qes 0.52
Qts 0.46
Mms 149.3 g
Cms 384.8 mm/N
Sd 333.0 cm2
BL 11.3 Tm
Vas 60.6 ltrs
Xmax 11.6 mm peak
VC Ø 50 mm
Sensitivity
2.83V / 1m 83.3 dB
Nom. Power DIN 300 W
Magnet weight 2.1 kg
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Old 23rd October 2006, 06:49 PM   #2
AndrewT is offline AndrewT  Scotland
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Default Re: Sub technical spec.

Hi,
picking out a few lines from the spec will help you read the information.

F3 of 33Hz in 1.5 cubic foot sealed box!
tells you what to expect for bass extension (this will suit music but less good with film sound effects)

Znom 4 ohm
needs an amplifier that is capable of driving a reactive 4ohm load

fs 21 Hz
allows you to design a cabinet.

Qts 0.46
tells you not to use a vented cabinet.

BL 11.3 Tm
tells you it has a medium strength motor.

Vas 60.6 ltrs
allows you to design a cabinet.

Xmax 11.6 mm peak
combined with the Sd, can be used to estimate the lowest frequency and SPL the driver can achieve (particularly important if you decide to equalise for deeper bass).

2.83V / 1m 83.3 dB
tells you it is atrocious.
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Old 27th October 2006, 09:58 AM   #3
sreten is offline sreten  United Kingdom
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Default Re: Re: Sub technical spec.

Quote:
Originally posted by AndrewT
Hi,
picking out a few lines from the spec will help you read the information.

2.83V / 1m 83.3 dB
tells you it is atrocious.

Hi,

Hardly the case. It tells you you need plenty of power to reach Xmax
and that you have chosen a driver that gives very good bass in a
small enclosure at the cost of sensitivity.

A driver with the same performance but say 86dB would need
a amplifier with half the power but need a box twice as big.

Horses for courses ........

/sreten.
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Old 27th October 2006, 10:13 AM   #4
AndrewT is offline AndrewT  Scotland
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Hi Sreten,
Quote:
need a box twice as big
does that follow when considering the DRIVER specification?

I know there is a loose/strong connection between power, extension and size of the complete speaker box & driver. I have quoted it a few times (pick any two from three).
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Old 27th October 2006, 11:43 AM   #5
bjorno is offline bjorno  Sweden
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Andrew T

I agree with sreten because: As sensitivity in dB is =112 + log No and the efficiency-bandwidth-volume equation is No = kn Vb f3^3.

This equation tells you that for a given efficiency, the efficiency constant No only depends on system order and (if) alignment and for a given driver, you can only trade volume requirement against f3.

But if No is held constant and one chose to alter the efficiency you are then free change both volume and f3.

It follows as sreten wrote: 'Horses for courses'; double No, 10 log No = + 3 dB implies 2xNo=kn (2 x Vb) f3^3 and as a consequence: is also valid for the driver in focus with 83 dB SPL/1m + 3 dB.

B
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Old 27th October 2006, 12:32 PM   #6
AndrewT is offline AndrewT  Scotland
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Hi,
I can see the relationship in a complete speaker assembly. No disagreement. I had not realised there was a formula tying that lot together.

My question related to the basic driver parameters.

If sensitivity is increased and the parameters that follow that increase are altered, will the new sensitivity also DEMAND that the box volume increase pro rata.
I don't know and I cannot recall seeing a similar correlation
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Old 27th October 2006, 12:50 PM   #7
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I'm siding with Andrew. All other things being equal, if the motor was made more powerful for a given electrical input (use of novel materials etc), sensitivity would rise with no effect on box size.

The reference efficiency n0 is almost an arbitrary figure.
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Old 27th October 2006, 02:43 PM   #8
bjorno is offline bjorno  Sweden
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Hi Andrew,

I focused on ‘small enclosure at the cost of sensitivity’ thus system No.

The speaker specification mentioned a 1.5 cubic foot sealed box at an f3 of 33 Hz and I took that for an input parameter too.

For this case it narrows everything down for the specific driver in an enclosure and ‘No = kn Vb f3^3’ is the only equation one needs to tamper with.

The No in’ sensitivity in dB is =112 + log No’ is not same as No in ‘No = kn Vb f3^3’.

The first is driver No and the latter is system No.

But once within a driver specification and when not in prior deciding for system requirements like f3, Vb and so on, then there is a lot of parameters that can affect driver No: No = k x fs^3 x Vas/Qes.

You can double Vas or increase fs by about 26 % or lower Qes 50% or in any combination of fs/Vas/Qes to meet a decision of doubling the No(driver).

Now it looks like I agree with all of you including richieOOboy.

B
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Old 27th October 2006, 03:48 PM   #9
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Thanks for all your answers.
The problem is I can not decipher easily what you all are saying. So if anyone have any link or literature about subwoofer for us newbie’s I’d be more than thankfull.
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Old 27th October 2006, 06:08 PM   #10
sreten is offline sreten  United Kingdom
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Hi,

Semantics scmantics.

None of you are now making sense. Its a good driver for purpose.

All the parameters are interelated and magically doubling efficiency
is hardly an arguement, your talking about doubling the magnet size.

For a given magnet and excursion capability you increase efficiency by
reducing cone mass, for the same Fs you increase Vas = a bigger box.

Generally : spend more and you get a better driver.

GW : driver selection depends on a number of constraints - mainly
budget and what is deemed an acceptable box size, noting that
smallish subs and expensive drivers need expensive amplifiers.

Related to the above is acceptable SPL depending on application.

parts express sub drivers have near ideal parameters for cost.

But if you want something small or very large then ...........

/sreten.
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