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Old 30th March 2011, 03:57 PM   #21
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Join Date: Jan 2008
Quote:
Originally Posted by chris661 View Post
Ah, I thought you meant actually ripping up the cone - like I said, I've only heard of that in horn enclosures.
And like I wrote, "over the course of years, had many speakers in monitor cabinets torn or kinked from being driven below Fb".

That is torn, ripped, shredded, kinked, in bass reflex and sealed cabinets.
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Old 30th March 2011, 04:33 PM   #22
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Quote:
Originally Posted by BuildByHands View Post
All,
Thank you for all your advice.

I have searched for 300 watt 8 ohm head but could not see one. I have read some blogs and I understand that:

1) I can use amp head with 300 watt 4 ohm. But I will get only around 175 watt

2) I can use an amp head with 500 watt 4 ohm or 300 watt 8 ohm

I want to confirm if my understanding is correct. Therefore, after finish this cabinet (300 watt 8 ohm)

Can I use MarkBass III 500W? Or will it blow the speaker?

The specification is as below.
[*]Output Power: 300W RMS @ 8 ohm, 500W RMS @ 4 ohm[/LIST]
Your Legend CB15 in a 2 cubic foot box will reach Xmax (4.8 mm) at 200 watts.
With 200 watts (maximum power for linear travel)it will only put out about 103 dB at 31 Hz (low B on a 5 string bass) or 108 dB at 40 Hz (low E on a four string bass). Hard to keep up with drums with just a single speaker like that, unless playing dinner music.

Most amps can put out peaks of double the RMS power, so if you like to slap and pop your strings, the speaker could see 600 watts with a 300 watt RMS amp.

This would probably push it to Xlim (9.5mm), which may damage the speaker.

If you put a white dot on the cone, it is easy to see how far it travels.
If it exceeds 3/8" (9.6mm) peak to peak, it will distort if you push it much further.
If it reaches over 3/4" (19mm)peak to peak, it may be damaged.

Damage may not happen in a one time "mistake", but over time if the cone is pushed close to Xlim it will fatigue, and the paper or spider will give out. Before the paper tears, it usually starts to get mushy, which also makes for a mushy sound, which makes you turn up the amp to compensate, hastening the destruction.

Ampeg uses 8 speakers with the 300 watt SVT so the speakers are safe no matter what the player does.

If you have concern over "blowing up" your speaker, get more of them, or build a bigger, louder box.

The same speaker in this box:
Vb = 5.347 cu.ft
V(total) = 5.588 cu.ft
Fb = 47 Hz

is almost twice as loud down low as the 2 cubic foot sealed box with the same power.

Art
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Old 17th April 2011, 02:47 PM   #23
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Join Date: Jan 2011
Thanks Art,

As I said that I have no clue before building this box. Now I have some clue and feel to work with tools by asking poeple like you in here.

Let say I have two cabs. One is 300w 8 ohms and another is 200w 8 ohms. Can I connect them (paralel) to a head which is 300w 8 ohms or 500w 4 ohms? I read some artical that the head will push out 500w. Will the speakers be blown since they are only 300w and 2002?
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Old 17th April 2011, 02:55 PM   #24
tinitus is offline tinitus  Europe
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I doubt you will ever draw that much power
but what do I know

like weltersys/Art say, driver Xmax may indicate your limits, more than power ratings
thus it will help with a low cut filter

one reason why you rarely see the hifiish low Fs in pro systems
might kill them at loud SPL

if amp is rated to be reliable into 4ohm, then it should be ok to paralel two 8ohm speakers
whether amp really is reliable into low impedance, or whether it will sound good is another matter
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Old 17th April 2011, 08:04 PM   #25
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Join Date: Jan 2008
Quote:
Originally Posted by BuildByHands View Post
Thanks Art,

As I said that I have no clue before building this box. Now I have some clue and feel to work with tools by asking poeple like you in here.

Let say I have two cabs. One is 300w 8 ohms and another is 200w 8 ohms. Can I connect them (paralel) to a head which is 300w 8 ohms or 500w 4 ohms? I read some artical that the head will push out 500w. Will the speakers be blown since they are only 300w and 2002?
In parallel, the speakers each get half the power, 500/2 =250 watts.
If the two speakers are tuned the same, or both are sealed, the pair will be about 3 dB more efficient than one speaker, so you only need half the power to be as loud as one speaker.
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Old 26th April 2011, 01:58 PM   #26
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Join Date: Apr 2011
Quote:
Originally Posted by Thawach View Post
hi
select the Dimensions on box wizard that u want. and adjust until Internal Vb is 2 cuf

Rockford Fosgate® - Woofer BoxWizard

the details of bass guitar,u can read from this link.

Speaker cabinets

regard/
As a noob myself this is a good start. Thanks.
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