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Old 19th July 2012, 01:02 AM   #21
tb46 is offline tb46  United States
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Hi FroggySeven,

You could probably reduce the size of the box by giving up a little bit of low frequency extension (still goes well below your initially stated goal of 30Hz); but you'll be picking up a bit more excursion capability at the low end. I'll attach a Hornresp example. The slight peak below 30Hz will disappear after the box is properly stuffed. Also, take a look at permo's thread:

Tang Band Tang Band W8Q-1071F 8 X 12 box reccomendation

From that you should be able to figure out a layout, and once you have determined your final external dimension bjorno can help you with determining the details.

Regards,
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File Type: jpg Monacor_smaller_Input.jpg (38.5 KB, 100 views)
File Type: jpg Monacor_smaller_SPL.jpg (40.4 KB, 96 views)
File Type: jpg Monacor_smaller_Displacement.jpg (34.8 KB, 94 views)
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Old 19th July 2012, 06:08 AM   #22
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Since you are limited on power, I would get the biggest ported sub I could fit.

The dayton TIT400 will extend low and play loud with your amp. The dayton 15 in a 150L box would be awesome.

Last edited by SpinMonster; 19th July 2012 at 06:11 AM.
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Old 19th July 2012, 10:30 AM   #23
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spinMonster : probably a good idea, thanks. But I have already bought the Monacors...

tb46 : I like those "only 130L" a lot, 'cause the upper crossover frequency rises too.
But for the peak at 30Hz : how stuff material coud be efficient at a such frequency !!???
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Old 19th July 2012, 11:53 AM   #24
jwmbro is offline jwmbro  United States
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Quote:
Originally Posted by FroggySeven View Post
[ this first message have been edited twice :
1/ Considering the following answers (thanks a lot for your help !!! )
2/ when I've made my decision]

[....]

Less than 300€ for one speaker, and down to 30Hz would be nice.
As I will use an equalizer, "down to 30 Hz" doesn't mean -3db but just the max SPL between 30 & 40Hz with 250W@4ohms !
If you're after max SPL between 30 and 40Hz, consider a (BIG) horn. Here's one for the Monacor SPH-390TC:

Click the image to open in full size.

118dB from a single sub, with -3dB point at 30Hz.

Xmax limited at 125W@4Ohm input, which is nice because I think having some headroom in your amplifier is a good idea. (typically about 30-100% power headroom).

Beware this is a big box, aimed to maximize SPL to 30Hz. (about 100cm x 60cm x 50cm is how I would fold it). Plywood would cost you about 80€ here (nor sure how french prices are), so still within your 300€ budget

And, typically for tapped horns, you will have to delay your main speakers by a few ms for everything to play in sync.

Just an alternative consideration I'm throwing out there.
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Old 19th July 2012, 01:42 PM   #25
tb46 is offline tb46  United States
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Hi FroggySeven,

Post #23: "...for the peak at 30Hz : how stuff material coud be efficient at a such frequency..."

Reading through the thread linked in Post #21 will give you an idea as to the type, density and application of the stuffing. This is based on the work and spreadsheet by Martin J. King - http://www.quarter-wave.com/ - I think this is the program bjorno is using to evaluate the effectiveness of the stuffing. Bjorno noted before, that peaks up to ~3dB can be handled with this method, so this one should not be a problem. But I hope bjorno will chime in on this.

Regards,
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Last edited by tb46; 19th July 2012 at 01:46 PM.
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Old 20th July 2012, 04:57 AM   #26
Djim is offline Djim  Netherlands
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Hi Oliver,

Just a notification about the inductance value for two voice coils in parallel. If you look on the Monacor website you can find the correct values in relation to the setting of the Voice Coils.

The most practical method for inductance in parallel:
(Le1 + Le2) : 2

The most practical method for inductance in series:
(Le1 + Le2) x 2

I used the word 'practical' because the correct formulas are:

Theta = Impedance Phase Angle
Lvc = VC Inductance

X = Z x sin(Theta)

Cmes = Mms / BL^2

Xl = X + [1 / (2 x Pi x f x Cmes)]

Lvc = Xl / (2 x Pi x f)

Note: these formulas only work for drivers in free air where the air-mass is static (constant).

--------------------------------------------------------

Most modelling software use a static value for Le while Le is also a dynamic value down low in an acoustic load. Especially dynamic for horn-type subwoofers where the 'extra' acoustic air-mass (to have a lower Fb in relation to Fs), is added to the Mms of the driver. The inductance of the Voice Coil can increase up to four times the original value.

Maybe this puts a light on things ;-)

Last edited by Djim; 20th July 2012 at 05:02 AM.
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Old 20th July 2012, 07:18 PM   #27
tb46 is offline tb46  United States
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Hi Djim,

I just worked with bjorno's numbers. As to your formulas, the first two are definitely wrong, something must be lost in the translations; anyway I'm once again on the run.....

Series and parallel inductors : INDUCTORS

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Old 20th July 2012, 08:55 PM   #28
Djim is offline Djim  Netherlands
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Hi Oliver,

Your linked examples have three major differences. The first one is that they are all about air-inductors. The second difference is that they are all based on circuits of two independent inductors. The third difference is that the value of all examples is only the product of an electrical circuit.

In dual Voice Coil drivers the coils have a core so they are not functioning as air-coils. They are not two independent coils, but are functioning as one (since they are electrically too close to be independent). The inductance of a Voice Coil is the product of an inductance in an electrical circuit (L1) and an inductance from an acoustic circuit (L2).

Click the image to open in full size.

I know how things can get lost when you are in a hurry;

Last edited by Djim; 20th July 2012 at 08:59 PM.
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Old 21st July 2012, 01:07 AM   #29
tb46 is offline tb46  United States
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Hi Djim,

Here is a link to a paper I found helpful, "An Improved Electrical Equivalent Circuit Model for Dynamic Moving Coil Transducers":

http://www.tymphany.com/files/resour...-Impedance.pdf

I would expect the term Le, as used in e.g.: Hornresp, to be a measured blocked inductance.

I looked at the T/S parameters again (e.g.: Post #21), and the Re should have been 3 Ohms. Changing the Le from 0.65mH to 1.3mH makes little difference. The model seems to be sensitive to added resistance in Rg.

Anyway, thanks as always,

Regards,
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Old 21st July 2012, 04:26 AM   #30
Djim is offline Djim  Netherlands
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Hi Oliver,

David said that HornResp uses a static value for inductance independent of frequency. The reactance in HornResp is calculated by [2 x Pi x f x Le].

The BL is 16.72 Tm for the SPH-390TC

(you might find this model interesting since it includes the acoustic issues; It's from R. Römer and G. Schwamkrug)

Click the image to open in full size.

Last edited by Djim; 21st July 2012 at 04:39 AM.
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