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To EQ or not EQ, or simply the vehicle (AKA, the two week saga.)

 

Silver Member
Username: Bobimpact

Danbury, CT US

Post Number: 150
Registered: May-06
This is gonna be long...

So here's the story, about three weeks ago a customer came into my shop with an '05 Scion xA. He's a former sound engineer so is particular about the sound of his stereo. Our budget of 1,000 dollars quickly blew up into $2,500 and we decided on the following setup.

Alpine CDA9856 HU
Looks, tactile feel, budget and IPod Control made this a must. (I know, compression, that's not my problem. I know, 2V outs, but that's not it either, although it may be deck related, stay with me.)

Boston Acoustic Z6 front speakers Coax mounted with the tweeter cup facing towards the bottom-front side of the door.
This choice was made after roughly 6 hours of listening (again, very particular ear.) Position was determined by inability to cut the door and stage quality.

1 JL Audio 10W3V3 Subwoofer.

Alpine PDX 4.150 Amp (fronts running Z6s, Rear bridged to run sub, deck running factory rears, or rears switched off, we've tried both ways.)

The car images brilliantly, stages high and rainbows perfectly. I honestly could not ask for better imaging given the parameters we needed to work it. In every frequency range except sub 30Hz and in my problem area it sounds great.

The problem is that my customer (and myself) hears a hole around 7-12K. He hears this same hole (so do I) in my car (05 Scion tC running IVAW200/PXA-H701 to JL ZRs bi-amped on JL300/4s all around Tweeters mounted off axis in factory locations). I'm thinking that an EQ may patch the problem as I can fill the hole much better in my car, but i've been wondering if this may be no more than a band-aid however. I still have some research to do, but I figured I would throw this out for some of the more experienced board members. Here's what I'm thinking:

1) It could be the deck.
There may be something about Alpine decks that causes this, perhaps in the DACs (although I would doubt that my DVD player and his CD player would share the same DAC)

2) It could be the car.
Both cars have very similar cloth seats, although my tweeters are way up (which I HATE and am changing tomorrow) and his are down, this could be a simple matter of "soak." With the environmental differences I doubt this as well.

3) It could be the recording.
This similarly doubtful as the customer engineered many of the tracks he is listening to and KNOWS that the hole is not there in the original.

4) We're being WAY too picky.
This is the most probable cause, but my shops reputation was built on "It can never be too good."

Any other ideas, and failing that, any recommendations for a good (considering the fact that we're WAY over budget) EQ?
 

Silver Member
Username: Bobimpact

Danbury, CT US

Post Number: 157
Registered: May-06
We've ruled out the deck and recording, songs all sound great on my demo boards.

Anyone?
 

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11641
Registered: Dec-03
reverse the phase on your midranges. mids only.
see what happens ^^
trust me
 

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11643
Registered: Dec-03
reverse the phase on your midranges. mids only.
see what happens ^^
trust me
 

Silver Member
Username: Bobimpact

Danbury, CT US

Post Number: 163
Registered: May-06
Ah, the JL Audio Answer (I had an arguement at a training with my JL Audio Tech Guy about this), we thought of this but haven't got a chance to try this one yet.

We'll give it a shot, the only concern I have is that it images so well I don't think it's coupling in the center of the vehicle, which is what mechanical phase flips intend to combat.
 

Silver Member
Username: Bobimpact

Danbury, CT US

Post Number: 164
Registered: May-06
And by instends to combat I mean to say (for those wondering why glass would recommend that) that because phase is not a simple on/off but a continuum from 0 to 360 degrees. Occasionally if you flip 180 degrees of phase on a midrange it can cause the sound to deaden if the coupling location is "correct" to cause trouble. It can also help increase high end response if the signal paths work out. Esentially to explain it best I would say it's "black magic" in that theres a great deal of calculation involved thats nearly impossible for a single person to do.

In this case I'm not sure if I can "get over the hump" with the customer as I've mentioned this to him and he balked at the idea (as most purists will do.)
 

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11646
Registered: Dec-03
it's a quick and simple dirty little trick worth a shot is all.
my other suggestion will cost him more, which is to throw the car on an RTA and see exactly what is missing, and see if EQing it makes any difference to that hole. Figuring out what's actually causing the problem is ideal but not always easy to do, or correctable the way we'd like.. so sometimes you have to cheat a little
the problem is EQing will hose his imaging most likely, unless you go all digital parametcit of 1/3 octave, to avoid further phase shifts
 

Silver Member
Username: Bobimpact

Danbury, CT US

Post Number: 165
Registered: May-06
Exactly my concern. With this thing imaging as well as it is, throwing a 3dB per octave EQ at him and saying "Go Nuts" may just dump one problem for another. Certainly he understands EQing very well, but my concern is that he is not familiar enough with automotive acousitcs to make it work perfectly. The RTA will be on it's way soon, I can just feel it. :-)
 

Gold Member
Username: Basshead86

Google is your Friend, FL

Post Number: 6097
Registered: Aug-05
whoa, it's like reading arabic in here.......lol
 

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11658
Registered: Dec-03
well, a DSP will avoid the phase shift since all EQing will be in the digital realm, and with good line voltages, you shouldn't have much noise floor from the addition of the EQ.
The RTA will allow you to tweak the 1/3 octave EQ to a C weighted curve and leave it at that like a set-and-forget unit.. not an in-dash play with the sliders EQ.
This way once it's set nd the hole is fixed, he doesn't touch the EQ. Audiocontrol even makes plates to cover their models like the EQT so people don't mess with the settings once a curve is recorded on an RTA.
 

Silver Member
Username: Bobimpact

Danbury, CT US

Post Number: 167
Registered: May-06
Heard from the customer today, when someone is in the passenger seat he "loses" the tweeter and wants to move it off axis to the factory location. This changes EVERYTHING. Time to start all over. Although I was right, the RTA is getting broken out next week.
 

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11661
Registered: Dec-03
solution:
put passengers in back seat or trunk.
thank you for shopping Impact Audio, please come again!
 

Gold Member
Username: Mixneffect

Orangevale, Ca. USA

Post Number: 1088
Registered: Apr-05
Reversing polarity to the mids only;

is a trick used to help the crossover knee. It does not do a thing for the tweeter, especially at 7-12 KHz.

When you have a high efficiency mid and a high Fs on the tweeter, you end up crossing the mid too high to allow the tweeter not to bottom out (blow). This will usually yeald about 3 dB peak starting about 1 octave before and after the knee.

So, by reversing the mid polarity you end up with a sharp 20 dB dip at the knee. This dip is about 1/8 of an octave wide.

I have found that a notch filter usually works better than reversing the polarity.

just my .02:-)
 

Silver Member
Username: Bobimpact

Danbury, CT US

Post Number: 168
Registered: May-06
Interesting ideas both, I'll try 'em both after I relocate the tweeters and ruin the perfect imaging the car has and let you know Tuesday night.
 

Silver Member
Username: Bobimpact

Danbury, CT US

Post Number: 170
Registered: May-06
I just re-read this thread a week later, and you guys rule. Still waiting on the customer coming back, so no news, but in all fairness I should mention that by applying the ideas that mix threw in I was able to solve some problems in my own car. Thinking back to it, I think you may have left one thing out however mix, in that while mechanical flips will not directly impact the tweeter's output, the resulting shift in the phase alignment (as relative to the car) will affect the percieved spl level of the tweeter. Small fields are a hellbeast.
 

Gold Member
Username: Basshead86

Try Google

Post Number: 6697
Registered: Aug-05
one day....one day i will be able to throw around the technical terms you all talk about while describing the difficulties of front staging....

 

Silver Member
Username: Bobimpact

Danbury, CT US

Post Number: 199
Registered: May-06
The customer came in today.

We moved the tweeters off-axis and knocked them down 4dB.

I give.
 

Gold Member
Username: Basshead86

Try Google

Post Number: 7249
Registered: Aug-05
just rip them out and put in 6x9's in custom ported boxes mounted on the b-pillar...he will LOVE it...:-)
 

Silver Member
Username: Johammbass

Cork, Co.Cork Ireland

Post Number: 344
Registered: May-06
Yeah, RTA would make my life so much easier:-(
How much do they run?
 

Silver Member
Username: Bobimpact

Danbury, CT US

Post Number: 221
Registered: May-06
http://www.trueaudio.com/rta_abt1.htm

You can thank JL Audio for that one :-), one of their guys turned me on to that software at a tech meeting, perfect for a DIYer or shop that doesn't use one very often.
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