Being an audiophile I've never been very happy with the Bose (14 speaker) system in either my Stingray or ERAY. Way too bass heavy and it sounded very bright. Last fall I began the process to understand the system and determine if I could make improvements without wholesale replacement. First step was to measure the in-car response. With the EQ set to mid-point, its VERY bad (see below). Next step was to measure each driver individually to determine if it was the drivers or the EQ from the DSP. I pulled one each dash corner, dash center, and door and measured both the electrical and acoustic properties. OMG the dash speakers are so bad (see below). All drivers are 4 ohm. Next step was to source better behaved drivers and install, measure and adjust. This happened last weekend. SO much better. The stock system is full of resonances that just destroys any sense of air or smoothness.

In summary by replacing the front speaker array, three drivers L/R/C, and a little bit of tuning to match levels its, IMHO, much improved. For the corners I used AudioFrog GS-25's and in the center I used a Faital Neo 4" full range. Total cost about $300.00. The dash center is a bit of pain to swap just because it very tight to work in that space. Also I had to modify the Faital a bit to fit by cutting off two ears and then enlarging the dash opening slightly.



Stock system at driver position

Modified system at driver position

 

This is very interesting to me having been involved in car and home audio in varying degrees over the years.

What made you choose those drivers and what are their specs?

Thanks!

 

Interesting, the curve certainly looks a lot better after. For the most part I find the C8 14-speaker "good enough". Especially in my current HTC Z06, which I usually drive around with the exhaust in Sport and in Manual with the top or rear window down. Even top up and all windows up, there's enough extra tire & exhaust noise in the Z06 (vs previous SR/ER I've had), that it's still noisy. With the SR/ER I was a little more dissapointed in the system, but through EQ tweaking (and turning off all the Bose Audiopilot/Centerpoint crap) I could at least get it acceptable. For $300 though, it might be worth looking at, although I really don't feel like screwing with the center speaker if it's a pain. Do you think just doing the GS-25s would be worth it? Otherwise, I might let a shop deal with the install if I decide to try upgrading the speakers.

 

This is excellent because it uses actual measurements to identify a short fall, and then show that it was improved with different speakers. I'm curious though. You mentioned that you measured the "response" using both the electrical signal and the acoustic "signal" which I thought was a really good idea. I assume you measured the electrical response by connecting something directly to the speaker wires. And the acoustic response with a microphone listening to the speaker. I assume this was to determine how much of the problem is with the electrical signal and vs the speaker response to that signal. Which results are you showing in your plots? I realize you made an improvement by replacing the speaker(s), but how much of it was caused by the electrical signal response?

 

Evan - the center is not fun. Its easy enough to expose but getting to the front mounting screw is a PITA. Additionally, the mounting hole needs to be slightly enlarged to fit the 4" Faital since the stock driver is 3.5". Most definitely replacing the front corners is well worth it. Those are very easy to access and replace. The GS-25's drop in. You do need an adapter cable that converts the spade lugs to the GM plug.

 

Andy - I removed the drivers and then used a device called a DAT (digital audio tester) to measure the electrical characteristics such as impedance, inductance and other electrical parameters that allow me to understand what to spec to replace them with. Then I measured the acoustic performance (frequency response, distortion, dispersion) with a calibrated microphone and acoustic software. Having all that I really saw how bad the drivers are and it was very helpful when selecting higher performing alternatives. Hope this helps.
[img alt="DAT measuring dash speaker
"]https://cimg1.ibsrv.net/gimg/www.corvetteforum.com-vbulletin/1080x810/center_top_51819230daccd3e377afe402b8653 020a398113f.jpg[/img]
DAT measuring dash speaker

Measuring acoustic performance in test box

 

Where are you sourcing the speakers from so cheap? The corners themselves are over 300

 

I purchased the AF's from ABT for $225.00 (Im a good customer) and the Faital from Parts Express for $40. With shipping and tax it was ~$300.00

 

I'm curious about how you managed the rear center speaker in the "waterfall". Although I am not at your level I do find it advantageous to avoid higher frequencies from behind especially that close to the ear.
Hope you don't mind me picking your brain!

 

Hi Bob, I don’t use the Bose Centerpoint feature and as a result there is little to no output from it in my use case. It’s the same driver as used in the panels located aft of the doors. It actually measures OK.

 

So it's off if one isn't using "centerpoint". Good to know. Thank you for sharing your info. Very appreciated!

 

So what ohms are the factory 2.5” twiddlers? Any other C8 Bose speaker ohm ratings? I’ve been looking for years!

 

I want to see the rest of your lab.

You can see (most) of mine here.
https://www.qrz.com/db/KJ7E

 

Were those measurements taken with a frequency sweep, or with pink noise? And did you take those with the driver's window open?

I've been meaning to take some measurements myself, just haven't gotten around to it. I was also curious as to what the OEM response curve looked like for the full system.

Did you happen to take a 20Hz - 20kHz frequency sweep measurement, at the driver's location, with the doors and windows closed?

I've been going through and applying sound treatments to the vehicle and wonder how the OEM system response has been impacted from doing so. I imagine once I complete the doors, the lower register should improve.

Something about your measurements though ... the OEM measurement shows a dip around ~38Hz, and another around 110Hz ... Then those areas show significant improvement in the modification measurement ... But you didn't change the drivers in the door, correct? Nothing you did should have really impacted the frequencies below around 1kHz or so. If you didn't do a sweep, and used pink noise instead, did you use any averaging or smoothing on the measurements? Really odd those lower frequencies show such a drastic change.

I'm a fellow audiophile myself, and have built a few systems. I use a modified Harmon curve for my target. The GS-25 is a great little speaker! I used one for the center in my GTO:




And after tuning, here is the result in that car. This is uncorrelated pink noise, with 1/12th smoothing, and 8x averaging:




If I could get the Bose system in the C8 even close to this, I would be happy.

 

All the drivers I measured were 4 ohm. I’d seen some data suggest that they might be 2 ohm. That is not correct for the C8 drivers I tested.

 

The center speaker appears to be crossed at 150, the corners at 200. I used a gated, swept sine wave. I did measurements w/wo the windows open. Not much difference in measured response.

 

I’m a Harmon curve fan. That’s a great looking response. If the head unit had a nice 8-10 band parametric with adjustable center frequency and Q it could be dialed in easily. The factory HK head unit in my X3M has an 8 band that works very well for this purpose. The only redeeming feature of the C8 is it has plenty of output.