4x12 Guitar cab using guitar and bass speakers help - diyAudio
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Old 10th April 2009, 03:39 AM   #1
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Default 4x12 Guitar cab using guitar and bass speakers help

Ok, so I'm working on a project. I bought two wood only half stacks (slanted, which makes it harder) for cheap. My plan is to put two eminence red coat man o war's in the top two holes and two eminence basslite (the only 12" they make) on bottom.

guitar: http://www.eminence.com/guitar_speak...2&SUB_CAT_ID=4

bass: http://www.eminence.com/guitar_speak...2&SUB_CAT_ID=5

the cab is made of 3/4" plywood and the dimensions are 29.75" x 29.75" x 14" at bottom and 9.5" at top. and the slant starts at 15" from the bottom. I've looked everywhere and can't find a speaker design program that will do more than one speaker type in a box. I want to do a ported box for the lows but since I can't find a program I have to do a sealed (unless you can help me).

All the speakers are at 8ohms using series/parallel. I'm doing this because I want to crossover the speakers at around 330hz. I have the capacitor and inductor I need to do a first order 6db xover. so the lows come out of bass and highs out of the guitar speakers.

I want to keep the opening back plate. But should I put a board in to separate the two? so it would be like two 2x12 cabs inside?

Basically I'm wondering if you can help me with the math, or tips on what to do.
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Old 10th April 2009, 08:27 AM   #2
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Ok - so it's a guitar amp

So why are you putting bass speakers in???

Guitars go to pretty high frequencies, so the bass speakers won't play those aswell, leaving you with lower SPLs at high frequencies.

Go for 4x12" guitar speakers, all the same, and you don't need to cross-over, or use bass-port.

Take a look here for guitar speakers - they're designed for guitar, instead of general PA.


And if you really want to use the drivers you've found, use winISD, put the cab size etc and driver specs in, for both speakers, then take the driver which goes lowest.
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Old 11th April 2009, 07:35 AM   #3
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Hey Andrew,

If you want a two-way guitar cab you should seal off the red coats from the basslites. To calculate the vents for the basslites you can simulate a single driver and then double it to account for the second. Just be sure to recalculate the port dimensions for the increased enclosure size. Using the winisd vent calculator is probably the easiest way to do it. see http://www.linearteam.dk/default.asp...ventcalculator

You might also think about leaving the back open for the red coats, it would eliminate some of the problems associated with box resonances.

Regards, Roger
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Old 11th April 2009, 10:21 PM   #4
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well chris661 I've heard myself and from other that they like adding in a bass cab to get more lows. I also realized that most guitar speakers only go down to 70hz. If you're playing in C open you're c string is at 69.2hz. If you drop any lower that's even more sound lost. so my goal is to get more low end and be able to support drop tuning and also have the clarity of bi-amping.

and roger lew thanks for the site. now im putting the board in to separate the two different speakers. so I found the volume of the bottom bass cab part. do i put in the total volume or half then just multiply everything by two? or would i just double the wattage?
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Old 11th April 2009, 11:17 PM   #5
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Putting your drivers in anything other than a box with an open back is risky in a guitar stack. You just open yourself up to a load of problems.

Biamping or using a crossover similarly just leads to a bunch of different problems for no improvement in the sound. Crossover systems are all about fidelity, which is not the point in a guitar amp. When 2 amplifiers are used for a single guitar this is usually some kind of 'stereo', perhaps with split pickups.

Your appreciation of how the LF cutoff works in a guitar amp is exaggerated. Even practise amps with small speakers and comparatively high cutoffs have appreciable output on the 6th string. This register properly belongs to the bass player anyway, you shouldn't be in his space too much of the time.

4 identical 12" Celestions or Jensens or even 2 + 2 mix'n'match in an open back cab is the traditional way to go for a reason.

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Old 12th April 2009, 03:29 AM   #6
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If your modeling a single basslite you want to enter one half of the volume available in the separated part of the enclosure. Keep in mind the volume for the ports and the volume taken up by the speakers eat into your available volume and should be accounted for as well.

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Old 15th April 2009, 10:09 PM   #7
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ok i've decided just to go with a sealed cab because my box really isnt big enough and will be cheaper. I'm separating the two sets of speakers. Im going to put acoustic foam inside to take care of the 'standing' or back waves.

I have another question that may not have an answer but here it is.
I want to find out how much power is getting to the speakers after the inductor/capacitor. I know about dcr and how it reduces power but is there any way to measure how much is getting to them? The reason why is I'm trying to find the rms of the entire cab. It's 300w on bottom and 240w on top. I know it should be able to handle around 600w. that 600w splits into two 300w (because speakers are in parallel) on top and bottom then goes through the xovers.

I'm guessing that the bass spkrs will have more power reaching them then the guitar spkrs because lows require more power (inductors taking out highs) and the guitar spkrs lows will be taken out resulting in highs which should be less power then the bass spkrs are getting. I know that there is also the variable of turning up the EQ but I don't think that will be a problem cause the bass spkrs are 5dbs lower than the guitar spkrs (resulting in louder highs)

I know that was a lot but any help is great.
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Old 15th April 2009, 10:41 PM   #8
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re:'acoustic foam inside to take care of the 'standing' or back waves.' - this is an important part of guitar/bass sound - this isn't a hifi cab, try it without

Re power handling - this is determined by the speaker with the lowest power rating - so it's 480w for the cab, although you're right, bass freqs move the cone more & will be the practical limiting factor
Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 15th April 2009, 11:39 PM   #9
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i have read reviews that said that foam helps guitar cabs too. the one cab i bought that has the woofers in it needs it. you can hear the resonation and it's really bad. they say it cleans up the sound and will, logically also, help the speakers preform better because the backwave wont be messing with the speaker
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Old 15th April 2009, 11:42 PM   #10
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Well, the damper is only good down to a certain frequency. If the cabinet is resonating, it won't help. It's best suited to frequencies 100 Hz znd up. If there is resonation, consider some light bracing. The side with the high pass, you might want to leave open backed.
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