Box for MMC690

[DJOwens]

Hey guys,

I have a 1999 Eclipse Spyder (convertible) and have recently installed a pair of 690's in the rear. The OEM speakers were smaller in the depth; but still 6 x 9. Installing the 690's required some modifications. After installing them, I noticed the low mids (400 hz to about 900hz) had no real definition but the low end (below 200 seemed to be there, but somewhat "echoie". So, armed with a function generator and SPL meter, I went to plot a graph of the speaker. What I found in the graph is exactly what I was hearing. The response was much like a Blows (Bose) system. The highs and the lows were pretty much to spec, but the mids just weren't there.
Mitsubishi's design of the speaker enclosure is quite pathetic IMHO. The back of the speaker is wide open and just resonates in an empty wall behind it. I'm sure the hollow mids were caused by that. So, I proceeded to make a fibreglass shell to make a psudo "box" inside the wall of the car. The result is an airtight seal around the speaker.
What I notice now is that the low mids are nice and crunchy and the highs are pretty much the same. However, the lows (below 130 hz) are pretty much gone. Of course, I assume it's because the fibreglass box I built the enclosure with is too small and it's not ported.
I am running 2 10" Rockford Fosgate HE2 subs. Each powered with 250W RMS.

Now with all that said, here are my questions:

1) Does anyone know the Q or the minimum box size of this speaker?

2) If I plan to cross these over at 120hz anyway, does the box size really matter? I mean, can the speaker even physically fit in a box small enough to drive the Q point up past 120Hz?

3) Should I install a port in that newly constructed fibreglass box? If so, lets say the box is about .175 cubic feet; if a port is needed to tune to lets say 80hz, what size port would I need.


Thanks,

Danny Owens

[exalted512]

I, for one, have no idea...
might I suggest Polk's customer service line??
-Cody

[DJOwens]

Nevermind, I got my answer.

Imagine that, Polk actually does have an existing helpful tech support line. :-) And, I was on hold for less than a minute.

In case another has the same question:

the recommended box size to make the speaker conform to specs is .15 - .2 cubic feet sealed.

and the crossover points are 3k from woofer to mid, and 10 k from mid to tweet.

[exalted512]

Polk has great customer service
Kim is the shiznit!
-Cody

[Jstas]

Originally posted by DJOwens
Nevermind, I got my answer.

Imagine that, Polk actually does have an existing helpful tech support line. :-) And, I was on hold for less than a minute.

It's really sad that customer service in this world has become such a joke anymore that when people experience customer service the way it is supposed to be done, they are stunned and amazed.

I have yet to send someone to the Polk Audio Customer Service Department and have them tell me they were no help.

Polk Audio's Customer Service Department is Polk Audio's best asset.

[exalted512]

Originally posted by Jstas
It's really sad that customer service in this world has become such a joke anymore that when people experience customer service the way it is supposed to be done, they are stunned and amazed.

Yeah, it really is sad. I called Sprint a few weeks ago b/c I was on the internet on my phone and it wouldnt let me log off. This was around 11 o'clock at night
was on hold around 7 or 8 minutes
they forwarded me to somewhere else
estimated wait time 25 minutes
I hung up...eventually it let me log off
I've never had a problem with Polk, they even forwarded me to talk to Kim one time, and he told me to send my subs back with Attn: Kim Jasper
that right there is a sign of excellent customer service!
polk, you kick as
-Cody

[PoweredByDodge]

... or you coulda just waited for good ol me, the oracle of useless and pointless knowledge, who would have told you that around .2 is good for a 6x9... and god dammit go get a huge amp and pour about 200 per channel on them! :) long story -- and i'm not about to tell it. most everyone's heard it... good luck w/ the boxes dude... 6x9's are nice and "meaty" on the bass end in back, and i'm sure once u get the box right you'll be very happy with them.

[DJOwens]

PBD,
I wanted to chime in and tell you my own "long story" :-)

I have to agree with your power recommendation on the 690's. After modifying the box, I still believed these speakers were capable of producing better sound quality at a higher SPL.

I was using a RF 501X into 4 channels. I have the MMC650's in front and the 690's in back. All powered with 65 wpc. I went and bought another 501X and bridged all four speakers. Now they each have a 250W supply. Although, I have the gain set to deliver only 170 W at 75% volume from my HU. I put an O-scope on the output of the amp and it's not even close to clipping. With my gain settings, using a function generator sweeping from 20 to 20k the output voltage is maxed at 26 V to each speaker. Using 1kHz/4 ohms as the nominal, that calculate's to around 169 wpc @ 75% using measured values (E^2/R @ 1kHz).

DAMN, these speakers came to freaking LIFE after about 80 watts(18V)!! I'm using the Pioneer AVH-P7500DVD as the HU (awesome HU). Once I went through the time alignment and auto-EQ, I was even more impressed. I'm getting 122db SPL without the Sub and THE CONVERTIBLE TOP DOWN!!.

I'm just saying all this because, even though I don't know your "long story"; giving these speakers 170% of rated power does make them sound like a totally different class of speaker. It's completely night and day!!! The guitar CRUNCHES, the snare bites my face off, and the highs are absolutely crystal!!

Thanks,

Danny