I decided to conduct a quick experiment in the shed before making my way into to work this morning. After having spent time doing research on not only this forum but elsewhere on the internet (did you know there is stuff other than **** on the net!) I thought I might attempt an experiment of setting my amplifier gains using five test tones and the hum/buzz method.

I own a 2015 Ultra Limited with Biketronics line leveller BT355 running into a Soundstream PN4.320D amplifier (bridged 160watts at 4Ohms) to Hertz ESK165.5 component speakers (100watts RMS, tweeter set to +2db) in the fairing. In the Tourpak I have another Biketronics line leveller BT355, using the speaker outputs in the pods, feeding a Soundstream PN2.350D amplifier (175watts at 2Ohms) driving Infinity Kappa’s 62.11i’s (75watts RMS) mounted in the pods.

I had set my gains by ear and wasn’t really pleased with what I was getting. At speed I found the tweeter exceptionally focused. I was turning this issue over in my mind, then most probably because I had been reading this forum yet again, I decided to analyse my signal patching to the amplifier and realised after I had drawn a schematic that I was splitting the signal incorrectly when running an amplifier in bridged mode, so there is one for BlackPearl#1’s forum thread from last year, along with accidentally drilling a hole in the crossovers after mounting then in the pods and attempting to vent the pod after the install.

I had purchased some new RCA signal leads and Y-splits so I correctly patched the signal and well here’s a red hot tip make sure your patching is correct during install otherwise part of your signal will disappear as it had with my setup. I was probably introducing phase cancellation into the system that totally stuffed the SQ.

Once re-patched the fairing system came to life. I set about doing some tuning using ‘newer’ released music on the USB flash drive. After watching Tailwind’s video using Lorde’s ‘Royals’ I thought I would use this track to start with as it has crisp vocals and a good bass drop. I also used tracks off London Grammar’s ‘If You Wait’ album. I had to turn all of the gains down on the amp and took some of the gain out of the BT355 in the fairing to help too, to remove clipping. However I could still hear some very small elements of distortion in the low frequencies. I don’t have an oscilloscope at my disposal so I did some more research, on various internet sites, and read about running tones through the system and listening to what it would tell me.

I downloaded five test tones from the internet 100, 250, 440, 1,000 & 10,000Hz to a USB and plugged this into the system. Now is a good time to give a **Warning** about doing this to your system. I read that you should exercise extreme caution about doing this because it is a very effective method to blowing a speaker apparently. I confess on one test I thought I had done just that, it’s a dreadful feeling.

Due to time constraints this morning I didn’t explore this test as thoroughly as I would have liked. First of all I didn’t conduct the test with the bike running, I’ll do this again in the future with everything running producing around the 14 volts the system can supply not the 12.(something) volts in accessories mode.

I started with the lowest tone and worked my way up through the frequencies. With the 100Hz found that about 50% volume on the head unit the hum turned to a buzz indicating a clip by the amplifier. With the 250Hz tone I got to about 70% and it started to clip, the 440Hz tone got to 85%. The 1k Hz tone almost got to maximum volume about one unit shy of the full volume display and it started to buzz and the 10k Hz went the whole way without issue. However when testing the 10k Hz tone it did drop into a low tone buzz at one stage after I perhaps left it up for too long. I think this highlights the care that has to be taken when experimenting in this fashion as it could kill a set of speakers. As expected the 1k Hz and 10k Hz tones, even the 440 Hz, are very irritating at volume for any period of time. I repeated this experiment several times with the same results on all occasions. I’ll also try it with a 40Hz tone I have somewhere to see where it goes into clip I presume even lower that the 100Hz.

In theory in order to produce low frequency successfully without clipping I’ll need to roll even more gain out of the system via the BT355 as the gains on the amplifier is now at minimum point. I will also experiment with running the speakers off the front left and right channels only on the amp which produces 60 watts a channel in four channel mode just to see what will happen with 62.5% less power going to the speaker. I dare say different brands of speakers would also result in the ability to reproduce the lower frequencies either better or worse, subject to what they were. Once I conduct more tests I’ll post more updates. Is that the clip clop of a Unicorn I hear outside?

 

Not sure what you are trying to get here? Did you use a DMM to check your voltage? I think you are overthinking this....(are you playing these tones thru your speakers); a 40hz tone should be used to set subwoofers. Using a 6.5 speakers you should be filtering those low freqs out.

Check out the sticky on the main page and if you're going to use test tones you should be checking voltage. You can't do a test tone by hear as that is static wave, but the music you listen to is dynamic.

 

agree. test tone with speakers disconnected using dmm to test ac voltage at amp output side while adjusting gain. here is a chart babyboy sent me which im sure originated on this forum

 

lots of good info in this thread. Credits to Slyedog who posted that chart that's been very useful.

https://www.hdforums.com/forum/audio...-with-dmm.html

 

Yes it was SLYDOG who first posted the voltage chart and I just shared it to members in need

 

Dude that chart makes life easy big time!!

 

I do agree Haze324 I am over thinking this procedure and I shall look at checking voltage with a multi-meter. Yes, music is very dynamic however it is made up of different frequencies of which these test tones constitute points within the range. It also tells me how the speaker performs on that range. You're right concerning the 40Hz as I've just looked at the spec's for the woofer in the Hertz ESK165.5 and its range is listed as 60Hz to 5,000Hz so 40Hz will be an academic exercise.
Check out Part 2 of the experiment shown on this site http://www.crutchfield.com/S-1BD9UGA...fier-gain.html Part 1 discusses use of an oscilloscope the second part discusses use of tones and the ear in setting gains.

 

This is what I mean from that article: "The 40 Hz tone couldn't really be reproduced by the speakers, so was useless. The 100 Hz tone rattled everything on the desk, so it was a little difficult to pick the buzz-point out of the crowd of reverberations."

The hum turning into a buzz could be the speaker simply can't produce that sound at that volume and not necessarily a distorted signal. In the example above it's 100hz, that when you would EQ down the 100hz freqs but keep the gain where the should accurately be. I'd recommend use the DMM method, see where the max "should" be, play some music you like to listen to and then either lower the gains if you have bad sound, raise your HPF, or EQ down the freqs that are distorting. Don't over think it (although messing around with stuff is fun!)

 

I agree Haze324 having a 31-band graphic equalizer or a Digital Sound Processor would be very helpful in tuning the system, however, as it has been mentioned in these forums before our listening environment is far from perfect. Many of the rooms I design PA's for are hard enough at times but at least they have walls and a ceiling!

I've been thinking about the physics of the enclosure and the speaker itself as playing a part too. I'll also experiment with the multi-meter, tones and music.

I have to say that working with the new Rushmore HU is a new level of complexity over the previous HU systems I've worked with, however I enjoy a challenge. The next hurdle will be speakers in the lower fairings in spite of them being water cooled, but hey that hasn't stopped me before.