MM 6501 trouble

adurm

So I installed a set of MM6501 in the front of my car and MM651 (coax) in the rear. The coax sound great. The comps are giving me a hard time. At lower frequencies, not sure the exact numbers, less than 150 Hz I hear this vibration or rubbing from the woofers. I pulled the door panels off to make sure they weren't hitting the door. In fact I pulled the speaker from the door, held it in my hand with no mounting hardware on it and it still made that noise. It sounds like it is from between the cone and spider. I carried the speaker to the amp, ran a fresh short wire from the amp to the speaker and the same noise happened. I tried with each channel and it happened.
I am pushing them with a 5 channel Boston Acoustics amp at 2ohm, upwards of 100w per channel. I ran all new wires to the speakers. I am running speaker level inputs to the amp, well was. Now I have a line out converter that didnt help much. The amp gain is turned up 1/3, and the high-pass crossover on the amp is around 65Hz.

Suggestions? O this is the second set that has done this to me, so it is likely something on my end.
Adam

pentoncm

adurm wrote: »

So I installed a set of MM6501 in the front of my car and MM651 (coax) in the rear. The coax sound great. The comps are giving me a hard time. At lower frequencies, not sure the exact numbers, less than 150 Hz I hear this vibration or rubbing from the woofers. I pulled the door panels off to make sure they weren't hitting the door. In fact I pulled the speaker from the door, held it in my hand with no mounting hardware on it and it still made that noise. It sounds like it is from between the cone and spider. I carried the speaker to the amp, ran a fresh short wire from the amp to the speaker and the same noise happened. I tried with each channel and it happened.
I am pushing them with a 5 channel Boston Acoustics amp at 2ohm, upwards of 100w per channel. I ran all new wires to the speakers. I am running speaker level inputs to the amp, well was. Now I have a line out converter that didnt help much. The amp gain is turned up 1/3, and the high-pass crossover on the amp is around 65Hz.

Suggestions? O this is the second set that has done this to me, so it is likely something on my end.
Adam

It might still be a defective woofer. I had to send back one of my 6501 woofers because of a buzzing sound it was making. Here is the test - hook another woofer to that same amp and speaker wire. If the weird sound goes away - you have a bad 6501.

Vital

Either what is said above or:
1. Too much amp gain
2. Too low of a frequency cut off. If any. Are you using any filters?

adurm

Originally I think I had the gain too high as I was hearing a hiss from the speakers when the music was muted. So I backed off until that went away. I assumed that the supplied crossover from polk would filter too low frequency from hitting the woofers, but I think now that it just filters the tweeter. With that said, I did have the amp in high pass at 40Hz to start. Eventually I had to put it around 80-100Hz to stop the terribleness. The speaker specs said like 35-20kHz, so I figured it could handle a low x-over point with high power. My amp is supposedly 125w x 4 at 2ohm, plus the sub channel. I dont know how to get close to that 125 watts without turning up the gain.
I think I need to bring it to someone with some tuning skills with scopes and stuff. I have to have done something wrong. The coax get loud and have decent bass response cleanly, but the components are killing me. The tweets are crisp. I am expecting much more from the woofers (especially for the price).
I am in the process of adding a line converter (cache COE6) which should increased the voltage to the amp. Hopefully that can help me not have the amp turned up so much and I still get the volume I desire. (not going for SPL, but is should be loud and clear). Its taking a while to dial that in too. FML. Also adding a 2nd MM840 sub.
I will work on tuning the LOC with the amp turned all the way down and work channel by channel until I get what I want.
I appreciate the advice and will keep you posted.

pentoncm

You really don't need to protect the MM6501's from low frequencies, they do fine. I currently have mine HPF'd at 60Hz 24db/octave but that is for SQ purposes. I have tried turning the HPF all the way down to 20Hz and the MM's handle it like a champ - they sounded like little subs in my doors. A HPF of 80Hz on a good 6.5 inch mid is too high and unnecessary.

Vital

While it sure sounds like it in reality gain is not "volume" or "wattage" knob. It is used to match voltage output of your headunit (hence marking on gain knob - 5V-0.2V or whatever you got on your amp) The louder you turn the volume on your headunit the more voltage it'll put out so voltage is not constant either.

Another important thing here seeing how bringing cut off filter to 80-100Hz helped - Do you have any equalizer? Be in on your headunit or amp or anywhere in between? If you boosted lower frequencies it'll have the same effect as having too much gain.
Turn ALL of your eq setting to flat. Do not boost ANYTHING, see if that helps.

Vital

Double post

pentoncm

Agreed

No Bass Boost
No Loudness
No Sound retriever or anything like that for mp3s

adurm

Thanks for the advice guys. I do not have an EQ or sound processor. The levels are flat on the head unit. Im using the stock headunit so there are no RCAs. My loc gives me RCA outs. I still need to pull the door panels off and swap left and right speakers to see what happens. I will try the bad one on all channels of tbe amp to rule out a bad channel. I have the power wire running along the floorboard and the bad speaker output wire runs close to it. Maybe that is a problem. I might need some techflex to block EMIs. I will post again with the results.
Maybe the stock system didnt sound so bad afterall...
Thanks again

adurm

Okay. So i hear more of the awful vibration from the passenger side woofer. I pulled that hog from the door and walked it to the amp in the trunk. Ran a wire to the woofer one channel at a time. The noise was present always. Tried the drivers side woofer and got the same result, well not quite as noticeable. Im not sure what to blame right now. The coax speakers work fine so im leaning towards a 2nd bad set of 6501. Sigh.

pentoncm

I agree. I was frustrated enough with my one bad woofer, it sucks to have them be bad twice. At least they get you the new speaker relatively quick after they receive it.

adurm

I got this set from a very reputable dealer in my opinion (dont know if I can say their name but it starts with a C and ends with field). The first set came from some dealer off amazon. Bad idea. Still havent received my refund from them. The C..field guys are willing to exchange the speakers for another set, same ones or different. I would like to try one more time with the MMs as I have the matching coax in the back. But Cfield is suggesting a different brand that has different resistance. I am not sure how my amp will take having 2.7ism ohm to the rear channel and 4 ohm to the front.
I am not a fan of JL mids and highs. The ones that cost the same as the polks seem cheaply made. My options would be infinity/jbl, alpine, or focal. The infinity/jbl run 2ohm and they may be the only option if the amp wont like a front 4 ohm/ rear 2ohm setup. Still waiting on boston acoustics to get back to me about the amp stability.

I appreciate all of yours and Vital's help.
ps, might have a set of MM 651 coax for sale

Vital

Most (if not all amps) don't care if ohm is different on front and rear channels channels.
IMO Polk is always a better choice in whatever price range be it db or mm. If you don't mind paying more off course theres a lot of options out there.

Try this - hook up your coax's to front channels of the amp. Long shot but i'd def try it just to make sure it is not an amp that is causing these issues.

adurm

Ya the coax dont do it on any channel. Crutchfield is being boss and sending me a 3rd set that they will test before it leaves their place.
Something I overlooked before...I think that noise was mostly happening when I was streaming mp3s from my phone. It dawned on me today that there might be some kind of effect or sound processing to make it sound better. Found that the "3d sound" was on from my phone. Unfortunately, I have to wait another day or 2 until the replacements arrive to test this. Fingers and toes crossed til then.
Thanks again for your help!
Adam

adurm

Welp, the 3rd set from Crutchfield got here yesterday. I had the phone's 3d sound off and tested the woofer. Again the vibration is there...Something must be wrong with my wiring or gains or something. I refuse to cross them above 100 Hz.
I have a hard time believing that crutchfield tested them before shipping as they said they would. None of the packaging was opened. No marks on the speaker terminals. Shoot, they could just be rotating the ones I sent back and sending them back to me for all I know. I doubt it though.
Nevertheless, I am bringing it to a pro installer tomorrow. 2 months of working on it almost every day is becoming a terrible obsession. Hopefully Polk will be vindicated if we find I did something wrong. Otherwise I am going to try infinity Kappas.
Eternally frustrated,
Adam

adurm

So i decided to bail on the polks. Now i have a set of mm651 coax for sale if anyone is interested. I dont have enough posts to list in the classified. So first $100 gets em shipped anywhere in continental us.

Vital

What was the outcome of pro-installer job?
What are you getting instead of Polks?

adurm

The pro install is coming up saturday afternoon. They are just building a box for 2 mm840 subs. Im in a genesis coupe so trunk space is at a premium. Im going to have them facing forward and it should be flush with the back seat opening. I had one sub to start and i put it the stock decklid hole. Much to my dismay there were lots of rattles from the deck and rear window. So i opted to change to 2 forward facing subs. O i did dynomat the top and bottom of the deck and it still rattled. Maybe some greatstuff foam sprayed into some strategically placed holes woulda helped.
As for the mids, im going for infinity kappas all around. They might provide better mid bass response. Maybe not.
I have to find a way to get rid of the hiss from the amp. Im sure its due to over gain. But if i dont turn it up, it dont get loud enough. Im using the stock head unit running the amp off speaker level inputs at the moment. My volt meter is getting 4.2 volts through the input so that should be sufficient. I was testing my amps outputs and got strange results. My left rear was reading negative amps and the right was positive. I think that was the setting. The number was like .37 for the rear but only .14 for the front. Coulda been resistance setting. I did onlt have one front speaker hooked up and it was only a woofer, not the xover and tweet with it.
Wow...where did all that crap come from.
So saturday for the install and infinity kappas to replace polks.