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Adding Tweeters to C4

 
Old 01-08-2019, 12:52 PM
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rblakeney
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Default Adding Tweeters to C4

The car is a 1989 with original Bose system and rebuilt amps from Dr. Don and appears to operate normally. The speakers are original and might be tired, but they look healthy. The system suffers from that typical "fried egg" sound on the highs and grows tiresome after awhile.

I am considering adding good quality stand alone tweeters to the front with built in crossovers. I need advice on what to put inline to filter out the highs on the stock Bose 4 inchers so all they have to produce are mids and whatever lows they can. Can anyone point me to something? Are there passive filters that will do this?

For improved bass, I am adding a powered enclosed sub-woofer in the hatch area.
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Old 01-08-2019, 02:15 PM
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You can design a simple 12db/octave passive filter to low pass the stock speakers and high pass your tweeters. You need to look at the specs for your new tweeters and the bose midranges to decide the right frequency to crossover at. Here's a good starting point, but there are lots of crossover calculators available online. See below:

https://www.google.com/url?sa=t&rct=...5EYEqW_s6qtEGU

http://www.erseaudio.com/Second-Order-2-Way
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Old 01-08-2019, 04:48 PM
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Originally Posted by daverulz View Post
You can design a simple 12db/octave passive filter to low pass the stock speakers and high pass your tweeters. You need to look at the specs for your new tweeters and the bose midranges to decide the right frequency to crossover at. Here's a good starting point, but there are lots of crossover calculators available online. See below:

https://www.google.com/url?sa=t&rct=...5EYEqW_s6qtEGU

http://www.erseaudio.com/Second-Order-2-Way
Thanks! The only reference I have on these Bose 4 inchers is from someone that suggested they could use some boosting around the 4000 mark. I have experimented with Android based equalizers on my phone, but they all seem to be buggy as hell. Hence my idea of just turning them into mids and be done with it. The built-in amps/equalizers just torture them to do things they are not meant to do.

I found some nice Focal 1.5 inch tweeters with flexible mounting that have a frequency response range from 4,000-21,000 Hz. Built in crossovers. I'm going to get someone smarter than me at Parts Express on the phone and see what they say.
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Old 01-09-2019, 07:10 AM
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cool, what Focals are you looking at?
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Old 01-10-2019, 06:38 AM
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Focal TWU 1.5 inch. The specs look good and they have flexible mounts.

Last edited by rblakeney; 01-10-2019 at 06:45 AM. Reason: Fixed model
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Old 01-10-2019, 07:35 AM
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Nice, I'm sure you'll see an improvement. Do those tweets come with a crossover? What are you going to run them off of? the bose amp?
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Old 01-10-2019, 01:02 PM
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Yes, they come with built-in crossovers. They are 4 ohms, however, so I am curious how they will behave wired in parallel with the Bose amp, which is also driving the 1 ohm Bose speakers. I found an online tool that calculates 0.80 total ohms across them both. We shall listen. Parts Express has recommended an appropriate air core inductor to filter 4000hz and above on the originals and turn them into mids. I don't think they produce much bass in the first place. I'll report back when I get them installed.
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Old 01-10-2019, 01:19 PM
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I'll just say this...you're on a slippery slope. Before you know it you're going to be looking to pull the bose stuff and for places to stash amps. Just sayin' - this is how it starts.
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Old 01-10-2019, 01:24 PM
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Ha! You are probably right but if this can just get rid of that fried egg sound, I think I will be happy. I don't play the music much with the top off anyway. The exhaust is enough.
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Old 04-23-2019, 05:44 PM
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So, 3.5 months later and I can now report my results. Other projects got in the way.

My goals were to keep the stock system, improve sound quality, staging, get rid of that Bose "fried egg" sound at the high end, and add some real bass. Hope someone finds this useful/interesting.

Here is the work I have done on my original 89 Delco Bose system:
  • Dr Don's rebuilt original Bose amps at each speaker unit.
  • Two watery thin coats of Elmer's wood glue on each speaker cone to stiffen them up. I find paper cones too warm, you may not.
  • Inline Jantzen Audio 0.025mH 18 AWG Air Core Inductor Crossover Coils at each positive speaker terminal to filter out 4,000Hz and above. This specific unit recommended by Parts Express.
  • JL Audio C1-100ct 1" C1 Series Component Tweeters in the front doors right next to the original mids. None in the rear for now. Tapped right into the speaker leads.
  • Kenwood KSC-SW11 Compact Powered Enclosed Subwoofer in the rear. Tapped into the driver side Bose speaker leads only. Bass response is pretty good.
My observations:
  • I think my attempt at making the units mids-only has worked. Adjusting the treble slider all the way up on the radio does not produce any sort of highs, just adjusts the mid ranges. And the things didn't produce that much bass in the first place.
  • The new tweets are amazing and they have really improved the sound staging in the driver's seat. I have the fade biased a bit to the front. I am now hearing instruments that were not produced before.
  • The subwoofer has really rounded out the system and there is real bass in the thing. Would I get more bass if I tapped into the passenger side leads?
Frequency ranges:

Original Bose 4.5 inchers from the 901 are reported to be used in this DelcoBose application. Their range is reported to be 83 - 15,000Hz using the Bose equalizer.

New ranges:

Kenwood Sub = 35 - 125Hz. I have the crossover set at 125.
Bose Mids = 83 - 4000Hz
JL Tweets = 3.6 - 22,000Hz

I'm calling this a success from my perspective. I'd enjoy hearing any comments/suggestions.

Now, let's see if the system holds up!
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