Quick back story; last Friday night / Saturday morning I yanked the trusty CV B52 / Infinity Kappa audio gear and replaced them with a Diamond Audio Micro4v2 and Hertz MPX 165.3 coax speakers. I know these "new to me" components are faux pas in today's audio sled world, but I found a good buy on the MIcro4v2 from another forum member here, and scored a decent price on the Hertz speakers back during the Christmas Holiday. Now onto this latest installation.

In past installs I've always relied on the BT355 LOC presets to get me close enough to fine tune the BT355 gain and HPF settings. Using the Cerwin Vega B2, B52 and B54 I always set the AMP to Full Pass instead of High Pass. I've tried HP on the CV AMPs before, but when used in conjunction with the filtering on the BT355 the sound was just too bright, especially at highway speed volume. I worked around this by using Full Pass on the AMP and then tuning the HPF on the BT355s to "open" up the frequency range just a little bit.

On this latest install I went against my previous procedures, set the AMP to HP and then turned the BT355 HP filter down to it's minimum setting (completely counter-clockwise). Then used the HP filter on the AMP to tone down the low frequencies that can cause distortion at the volume I need on the highway. My initial tuning was all by ear, but afterwards disconnected the speakers and put my TPI 440 o-scope to work. Using a 1kHz 0dB test tone I measured 240W coming out of the AMP (the Micro4v2 is rated at 300W bridged 4 Ohms). I may have to be careful with the volume control on the radio Voltage check - higher than expected but I'll take it. Sine wave - clean no clipping.

Maximum un-distorted volume was achieved (6.5GT at 13 out of 17 clicks on the volume) and the Micro4v2 HP dial set almost exactly at the 12 o'clock position. The Micro4v2 installation sheet said to start the HP frequency setting at the 8-9 position and go from there. So I thought I must have really killed the 100Hz frequency by setting the HP control to the 12 o'clock position (even though that setting sounded the cleanest at maximum volume). I put a 100Hz test tone on my thumb drive and checked. To my surprise 100Hz was still clearly audible and it was just a little lower in volume than the 1kHz test tone. The main drawback with this approach is that the bass control on the radio doesn't really add or subtract a lot to the bass frequencies.

Now to be completely forthcoming, this installation approach wasn't exclusively my own idea. While I was down at the local Indy last week (he does a lot of audio installs but deals exclusively DD and RF) I was asking him about radio flashes since my local HD dealership won't flash the radio unless the Boom! Audio gear is already installed (another story for another day). Russ told me that he has the capability to flash various configurations but didn't think it was really worth it since I was only running fairing speakers with no plans to add, and since I was already using the BT355. Although he told me that we could flash away and we could try as many different configurations as I wanted for a whopping $20

At any rate, that got us talking about the BT355, tuning and his installation procedures. Russ told me that on their installs (fairing only, BT355, AMP with active filtering - no DSP) that they turn the gains on the BT355 to provide maximum input voltage to the AMP, and then turn the HPF to it's lowest setting. Afterwards they use the HP filter on the AMP to tune the frequency. I listened to a recent install he had in the shop and it did sound really good. Good enough that I kind of regretted not just dropping the coin and going with his DD "package" installed.

However, my new system sounds good with the bike running and standing still in the garage. I finished most of the work Friday night, but at around midnight the Mrs. started complaining about the noise. I hit it again Saturday morning and by the time I had everything buttoned back up the rain set it. I may have to fine tune a bit more after a few road tests, but my gut feel is that I'm close.

This system is loud. Really loud. Hope the volume and SQ pan out at road speeds.

 

How many watts r u feeding those speakers?

T

 

From what I gathered it's enough to let out the Magic Smoke.

 

I have messed with the bt355 a lot and can tell you that if you max out the gains (on the end), it will over power the amp especially on low frequencies and eventually cause harm to the amp.The boom eq curse enhances the low frequencies to accommodate the lack of lows from the stock speakers. Keep in mind that signal is feeding your amp and your hp filters on the amp are then feeding the speakers. The whole reason for the bt355 is to flatten out that drastic signal feeding the amp. You are better off adjusting the bt355 to the amp and running the amp in full pass so not to hurt the amp in the first place.

 

I wouldn’t mess with the LL at all unless your amp doesn’t have any settings. Plug the LL in leave the settings alone and
use your xover and Hp and Lp settings on the amp. The LL is not a DSP as some are using it for that purpose and there’s no way to tell what your setting it to like you are wit a DSP. And when you do have all the settings messed up on the LL and want to get them back to default it’s a process and you prob won’t get them back to default perfectly anyway.

 

Depends on what the head unit volume is set at Seriously though, after setting the gain by ear, head unit volume 13 clicks, base and treble centered, adjusting HP on AMP and using "turn down for what" as my test song. I checked voltage and sine with my TPI 440 and I'm sitting at 30.98v or 240W give or take. My biggest challenge is volume range. Most of my music sources are my USB drives that contain songs that were converted to MP3 format 20 years ago up to MP3's files that I purchased last Saturday. All of the old stuff is 128 to 192kbps at 85-88dB. Whereas much of the newer stuff is 256kbps or 320kbps at 92-95dB. Hence my reference to watching my head unit volume. I'm not trying to melt stuff and only turn the volume up loud enough so that I can hear the music depending on the riding conditions.

 

Hey Gypse, I went back and re-read my OP and can see where the words I chose could lead someone to believe that Russ "cranks" the gains. He does not crank the gains all the way up. He just turns them up so that he is feeding 2.0 - 3.0v input to the AMP (depending on the rated low level input spec of the particular AMP he is installing). In my case he pointed out that the DA Micro4v2 has a rated low level input voltage of .10v to 5.0v

That reminded me of some BT355 experiments we were doing back in 2015, it was me and one or two other people that used to visit the audio forum at roadglide.org, but seemed to have gravitated here for the most part. The BT355 as delivered with the preset gain settings only output somewhere between 1.13 to 1.19v at 3/4 head unit volume. Ultimately I think we ended up targeting 2.0 - 2.5v low level input voltage to the AMP.

With that said, your observation about allowing the BT355 to trim the frequencies is valid. However, as long as the low level input voltage remains within specification there shouldn't be any risk to the AMP regardless of the frequency. I'd venture to say that 99% of OEM integration these days has to deal with custom EQ curves programmed into factory radios, and then there are plenty of aftermarket installations where the user will crank various EQ frequencies to their liking (i.e. not running a flat EQ).


If burning out the low level input side of the AMP due to frequencies was a thing, I'd think there would be a lot more chatter about it. Until someone can provide me with some empirical evidence that input frequency is more important that input voltage, I'll stick with the input voltage being the more important of the two.

I guess the only other consideration is whether or not the BT355 has better filters that are more pinpointed to the "harley bass boost" when compared to the HP filter on a decent , good or great AMP. I could see that as being a valid argument. But then I'd have to step back and say that the BT355 was originally designed to compliment the Biketronic AMPs that didn't have adjustable frequency settings. Then I'd have to ask what makes the default settings intended for the non-adjustable BT AMPs, the correct settings for every other aftermarket AMP / speaker combination.

Then they went and added the additional harnesses and speaker plugs, that makes the BT355 a no-brainer regardless of any other questions. There's a lot to be said about not having to hack up any of your OEM harnesses for sure.

 

Right on brother. Just curious what ur watts plan was and it sounds like u have a plan.
I have seen some local guys puff the magic smoke out of those speakers in the 200w range but I didn't inquire too deep into their setup & tuning process so no telling how much dirt they were throwing at them.

T

 

Maybe, we'll see. If I burn it up it will give me another excuse to continue chasing the unicorn The MPX 165.3 are rated at 100w RMS / 200w Peak Power Handling so I am overshooting a bit (but refer back to my music collection).

I fed 225W to my Kappas for 3 years and never smoked anything. Again, I don't go crazy with the volume, just loud enough to hear.

 

I did misread the OP post and was thinking he cranked the gains up. You are right about the BT LL being designed for the BT amps and with that those LL are set VERY conservatively. Leaving them at default will leave a lot on the table when trying to tune a system. I have tweaked ever LL that I have installed only to get a ton more out of the setup. It is a fine balance on tuning either the LL, amp and the gains to make it sound right.