Need help wiring Subwoofer with Mid Bass Driver

[Mozencrath]

Hi everyone, this is my first post. I am an electrical engineer, but am not sure how I need to wire my desired setup. I have a Prius with stock 9 speaker JBL system and I want to add an 8" subwoofer and a 6.5" mid-bass driver using one amp. I cannout use my head unit as a signal source. I forget the term for it, but the output from the head unit only stays at one level. Therefore, the only way to tap into the audio source on a Prius is to use the wire going into the rear door speaker from the amp. The signal is not completely flat, but its the only speaker that receives a full range of frequencies from the amp.

My desire is to add one subwoofer and one midbass driver. The highs in my car are already good. My question is what type of amp do I need to do this and will I need any additional crossovers and how do I wire it? I do not want to use two amps, and I also do not want the mid-bass speaker to be receiving the same frequencies as the subwoofer....I would appreciate any responses very much! Also, I am trying to do this as cheaply as possible. I'm hoping that there is a cheap amp out there that will allow me to divvy out the frequencies to each speaker so I dont have to add a crossover. Thanks!

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[All_Logix 10+ year member]

OK bud, as an electrical engineering student I feel I must help you as much as possible haha... I am only slightly familiar with the toyota JBL systems, but JBL is made by harman and they also make infinity which I am very familiar with. I would assume your head unit has some sort of differential balanced output to send information to the factory amp, and the back is the only one getting full range because that is where your low frequencies are headed.... 9 speakers systems slightly allude me because they general attempt to image the system for the driver strait from the factory...ANYWAY, get you a line out converter from your local shop and tie into those lines with full response, RCA to amp...get a nice 2 channel amp with a reasonably high output on each channel, and on with independent xover control for each channel...harder to find. Then 6 1/2 to one channel, sub to the other...keep your gain down on the 6 1/2 as it more than likely will not be as powerful as the sub.... if you cant find an amp with that xover capability, run your xover to in LPF to a frequency that is the max you want the 6 1/2 to run, then run bass blockers in line with the 6 1/2 and lowpass capacitors on the sub line... again your local shop should have these

 

[kramer_212 10+ year member]

yeah what he said

 

[keep_hope_alive Premium Member]

close, but not quite. first, there are no "low pass capacitors". a series capacitor is a 6dB/oct high pass filter and a series inductor is a 6dB/oct low pass filter... but those slopes are pointless for your application. if you don't want overlap you need 24dB/oct. that will need to be active. you can use FMOD filters (available at PE) and double up for a higher slope, but they aren't cheap either.

there is no need for a a separate single midbass and single subwoofer. a subwoofer can play both frequency ranges, and an 8" driver is basically a midbass driver anyway. a separate midbass driver is pointless, unless you wanted to put it up in the dash somewhere. and even then, midbass should be in stereo, not mono. you want your front left and right woofers to play midbass frequenices. if you aren't willing to upgrade your front speakers, then just add a 8" sub. if you have 9 speakers, you have a factory sub - remove it.

you're making this more complicated than it needs to be. you want more low end and more midbass. get a single 8" driver, run it off a single amp (mono or 2 channel doesn't matter - just coordinate impedance). low pass around 160Hz. take note of any phase shift the crossover provides. if that doesn't make you happy, consider upgrading your front woofers.

as far as an amp that gives you that much crossover flexibility while being cheap? no dice. maybe used. flexible crossovers are hard to find in amps, especially bandpass crossovers (which you would need for your separate midbass driver idea). Sundown seems to have some bandpass capability in their amps. but you can get an external active crossover for cheap and have the filtering you need.

i agree you'll need a LOC if the amp you choose doesn't have high level inputs. there are summing LOC's that can get you a full range signal. definately sum the woofer output and factory sub output. Audio Control has some nice OEM integration products. or teh MTX ReQ

lastly, it's possible you have an Active Noise Cancelling (ANC) system. if so, you need to defeat that system to add a sub.

 

[All_Logix 10+ year member]

Whoopse...that makes alot more sense though now that i think about it, i always wondered how limiting voltage drops would filter high frequencies out sense the AC drop would make it more apparent...but opposing current change....good call, had no idea they were 6db/oct either

 

[vaiboy 10+ year member]

as far as an amp that gives you that much crossover flexibility while being cheap? no dice. maybe used. flexible crossovers are hard to find in amps, especially bandpass crossovers (which you would need for your separate midbass driver idea). Sundown seems to have some bandpass capability in their amps. but you can get an external active crossover for cheap and have the filtering you need.

The MB Quart Q series amps have bandpass crossovers and are inexpensive, the Q4.80 is $139 and the Q4.150 is $199. They are four channel amps but they can be bridged to two channels to run a pair of midbass drivers.

 

[keep_hope_alive Premium Member]

The MB Quart Q series amps have bandpass crossovers and are inexpensive, the Q4.80 is $139 and the Q4.150 is $199. They are four channel amps but they can be bridged to two channels to run a pair of midbass drivers.

thanks for the info!!!

 

[keep_hope_alive Premium Member]

Whoopse...that makes alot more sense though now that i think about it, i always wondered how limiting voltage drops would filter high frequencies out sense the AC drop would make it more apparent...but opposing current change....good call, had no idea they were 6db/oct either

caps in series don't behave the same as caps in parallel. just keep in mind what the impedance curve of a cap and inductor look like, and it makes sense.

 

[Mozencrath]

Thanks for all the info guys. I think what I'm going to do based on your advice is replace my two front door woofers with good components that will act as my midbass drivers and run my single 8 or 10 inch sub. I'll run both off of a 2 channel amp. I suppose I wouldnt have any problems with the factory amp by removing the two door speakers from it?

 

[keep_hope_alive Premium Member]

a single 2 channel amp would need to be run in tri-mode with passive crossovers. you need your fronts to be in stereo, so that's two channels. the sub is an additional amp channel.

a single 4 channel amp will be able to run your front speakers and your rear sub.

you will want to use the front speaker outputs as inputs to your amp's high level inputs for the front channels. this will retain the use of your fader. of course, you'll need to verify the frequency response of those outputs. the front door woofers should be a full range signal, but it is possible they have a low-pass filter on them.

note that buying a component set will push you into replacing the factory tweeters as well, or you could just use the woofers. in lieu of a component set, you could buy raw drivers and save money. you'll need to verify opening diameter and available depth. this is best accomplished by actually removing the factory speakers to see what you have to deal with for both top and bottom depth.