2x15 cab-- 4ohm vs 8ohm config - vent sizing - ??

frankz · #1 10-31-2011, 12:10 AM

so a new problem im having.. tried to start bridging my amp and getting thermal shutdowns (crown 402) @ 4 ohms.. anyhow been reading that bridging cancels even order harmonics increases noise and a few other undesirables

anyhow i have a few days and access to a wood shop just looking for input..

cab is and Acoustic corp 406 1977ish and i was thinking of trying to figure a way to wire it with mabey 4 1/4" plugs.. the problem ive been having is thermal shutdown when trying to bridge it to the amp its powerband is in a bad spot 280watts per channel 8 ohms not quite enough to just use one side of the amp..

anyhow i would like to somehow keep it set up so i could run the whole cab @ 4ohms.. thru a single channel so i could use other cab also have the option to run each speaker seperate (left/right side of amp).

speakers in cab are eminence 3015 kappalites and im guessing much over the 280 watts per speaker is just gonna be heated coils (side question- does running each speaker thru its own channel allow the amp/speaker "breathe a bit more natural"

also any ideas about changing the size of the vent.. the original speakers were only like 100 watts apeice i guess so im sure the xmax is totally diff.. would the cab benefit from say reducing the vent ports to 1/2 size ..

anyhow just have a few days to tinker and looking for ideas ect.. possibly baffling the bottom speaker and not the top..

any ideas?

peace

by the way music is blues and we probably play too loud but most places we play dont have alot of pa support

FrettiYeti's Channel - YouTube
a vid of a hendrix cover from Rev Horton heat show we opened..... has rig and such on it

bongomania · #2 10-31-2011, 01:14 AM

Bridging should not have the negative effects you mentioned. Sounds to me like the amp was not designed to be bridged, or maybe the wrong bridging cable was used, something like that.

Oobly · #3 10-31-2011, 01:32 AM

Hi,

That amp isn't spec'd for 4 Ohm bridged. And I agree that bridging shouldn't introduce those issues. I have an XLS1500 which I run bridged (into an 8 Ohm cab) and it sounds the same as unbridged, just louder.

If the cab is a 4 Ohm, your only options are:

1. Run it off one side of the amp at 450W.
2. Rewire the cab and run each speaker off a different channel to get 300W per speaker.

Those kappalites can handle a huge amount of power, so 450W should be fine through the cab. You might want to think about increasing the size of the port/s depending on your tonal goals, but I must admit I don't know much about that. I would hope that billfitzmaurice add his 2 cents, since he is a true guru in all things bass cab.

Mr. Foxen · #4 10-31-2011, 04:42 AM

Quote:

Originally Posted by frankz

its powerband is in a bad spot 280watts per channel 8 ohms not quite enough to just use one side of the amp..

This sounds a bit like you feel some need to match the power rating of amp and cab. You don't, so try it with one side only.

bassmeknik · #5 10-31-2011, 05:03 AM

down load WINISD (it is freeware) and learn, learn, learn. Don't change that port until you know which direction to go (smaller or bigger). Guessing won't do, cab design is a science and your results will suffer without doing your homework.

You will need T/S parameters for the drivers (readily available on the web) and plug in the box dimensions (INSIDE MEASUREMENTS or outside minus panel thickness), driver parameters, tuning frequency and the program will give you the recommended port size. Be patient and you will be rewarded with a better sounding cab, just guess and you are shooting blindly in the dark (not likely you will improve the sound without it.) Cabs are designed for drivers not necessarily the other way around but using the program can help a LOT in tuning the cab for your use. Post the info and I will try a simulation with mine and post the results (it may take me a couple of days).

billfitzmaurice · #6 10-31-2011, 07:00 AM

Quote:

Originally Posted by frankz

so a new problem im having.. tried to start bridging my amp and getting thermal shutdowns (crown 402) @ 4 ohms..

I went to the doctor, told him my arm hurts when I do that. He said 'Don't do that!

Bridging isn't about watts, it's about voltage swing. Rule of thumb, if you're not an expert with amps and speakers don't bridge, you only run the risk of blown drivers and/or a blown amp.

Quote:

You might want to think about increasing the size of the port/s depending on your tonal goals, but I must admit I don't know much about that. I would hope that billfitzmaurice add his 2 cents, since he is a true guru in all things bass cab.

You can't toss any driver into any box and expect a good result. It may be possible for the 3015 to work in this cab, but without complete and exact details about the cab no one can say for sure.

Quote:

anyhow just have a few days to tinker and looking for ideas ect.. possibly baffling the bottom speaker and not the top..

Here also the penalty for messing around without knowing exactly what you're doing is blown drivers.

Quote:

anyhow i would like to somehow keep it set up so i could run the whole cab @ 4ohms.. thru a single channel so i could use other cab also have the option to run each speaker seperate (left/right side of amp).

I can't tell exactly what you're trying to say, but in any event use a separate jack for each driver in the cab, run one amp channel per driver.

will33 · #7 10-31-2011, 10:25 AM

Without measuring and modeling, you have no idea what if anything to do with the vent. It's not about "breathing", it's about tuning the box to the driver. If you're experiencing chuffing/whistling noise from the ports, excessively boomy sound or a general lack of expected lowend, you may need to modify the ports but what exactly to do with them, you don't know yet.

bassmeknik · #8 10-31-2011, 04:28 PM

"anyhow i would like to somehow keep it set up so i could run the whole cab @ 4ohms.. thru a single channel so i could use other cab also have the option to run each speaker seperate (left/right side of amp)."

If I understand you correctly you would like to be able to use this cab powering the drivers individually or as a single load. Wire each driver to a separate jack and make a special cable to use single channel. In this mode the special cord would have an end for each driver and one for the amp all wired in a parallel connection so you can still use it as a standard one cable 4 ohm cab. Essentially the existing cab wiring would be outside the cab in the special cord.

This Y cable could be three standard cables and a simple junction box with three jacks all wired in parallel. One goes to the amp, the other two go to the drivers. It doesn't matter which jack is used for amp or driver in this use so any jack can be the "input" from the amp. Get a small project box and three 1/4" jacks and mount them wire all the hots together and all the grounds together. If you can't solder get help this is a 5 minute soldering job.

frankz · #9 11-01-2011, 02:24 AM

going with banana plugs.. they work well with my amp and i can just plug for example the right channel into the right top speaker and then run a banana jumper to the bottom speaker @4ohms for whole cab now out one side and use the other side if needed for 8 10

or what ill do 90% of the time is just run 8 ohms per channel.. (look up voltage sourcing vs current sourcing) spent last night reading and i was a bit off on my thinking of amps

also banana plugs are super cheap and can make new ones in 5 min if needed between a set or something incase i lose one or what ever... really happy so far with how its sounding for the $$s i have invested

T-Bird · #10 11-01-2011, 03:49 AM

Hi.

Quote:

Originally Posted by frankz

going with banana plugs.. they work well with my amp and i can just plug for example the right channel into the right top speaker and then run a banana jumper to the bottom speaker @4ohms for whole cab now out one side and use the other side if needed for 8 10

also banana plugs are super cheap and can make new ones in 5 min if needed between a set or something incase i lose one or what ever... really happy so far with how its sounding for the $$s i have invested

You can also create 180 degrees out of phase situation in multiple ways, create very funny loads and speaker configurations (including dead short), so please, do use either Speakon or at least 1/4" instead of the banana jacks on the cab.

Regards
Sam

bassmeknik · #11 11-01-2011, 05:30 AM

Quote:

Originally Posted by T-Bird

Hi.

You can also create 180 degrees out of phase situation in multiple ways, create very funny loads and speaker configurations (including dead short), so please, do use either Speakon or at least 1/4" instead of the banana jacks on the cab.

Regards
Sam

Indeed, phase orientation is most important with bass frequencies so if you decide to use banana plugs mark them clearly and observe proper polarity. Speakon connectors are the connector of choice but even 1/4" jacks will prevent polarity mismatch, banana plugs are a bit dangerous to your equipment as errors are easy on a dark stage... please consider this carefully the difference in cost to use Speakons or 1/4" verses Banana plugs is pennies and blowing up your amp with faulty speaker connections is much more expensive.