Doubling up on the midbass

[robtr8]

So I installed a set of AudioFrog GS62's in the doors of my TR8.  Boppin' around the hood, this system sounds great, but when I hit hwy A to go to work, I loose all the midbass.  Very similar to the boat situation.  I know with the boats, we just add more drivers.  With the TR, I don't have as much real estate for installing drivers all over the place and I'd like to keep some semblance of a front sound stage.  My question for the resident stereo experts is:  Can I just delete the ashtrays and add a set of GS60's to the doors?  I would only be able to high pass them.  At some point I plan to add a TWK-88 to the system but there are a couple other bits the car needs more worser.

Inspiration:  http://www.jehnert.de/en/shop/doorboards-soundsystems/vw-en/golf-3-models/golf-3-all-models/vw-golf-3-doorboards-with-3-way-soundsystem/

 

[MLA]

My first fear, would be that there is glass/window regulator there when the window is down. How deep is the ashtray. When you say you lose mid-bass, you means its just eaten up by wind and engine when the top is down, right? Not that the amp or speaker is actually no longer producing mid-bass? Maybe consider a pair of 6.5" woofers if you have 2 spare amp chnls. Again, this is dependent upon fitment.   

[robtr8]

The GS62/60's require only a 5 1/8 cutout and a 2 1/8 top mount depth.  The GS62's cleared the glass by 1/2 an inch.  If I placed the GS60's in the ashtray location (I'd scootch them as far forward as possible, covering the existing hole) I'd need to add a very thin baffle to clear the glass hardware.  I'm running the GM-D9605 with the four channels bridged, so plenty of power.  I could unbridge the front and run the two sets, no problem.

I guess I'm wondering if there are any unintended consequences with running double mid bass.  I know I won't be able to time align the drivers or play with cross overs and EQ until I get the TWK-88.  I don't want to make a change that then requires additional hardware to correct the correction, yet.  Maybe next summer.  TR needs paint and power steering.  http://easysteer.co.uk

[David]

One byproduct is that the farther back in the door you place a second pair of coaxials, the more you reduce the front soundstage because you are adding unequal bias to the side closest to each front seat listener.

As for improving the midbass, you may be between a rock and a hard place. Adding a second pair of speakers with double the amplifier power will net you at best +6 dB of output across fullrange. But the impact of motion with masking road & motor noise may create far more than a -6 dB deficit at lower frequencies. You would need a touch of equalization within what is safe for 6.5" speakers. Another challenge is that the door coaxials are not all facing in the same direction at one extreme of the vehicle interior. So a +6 dB boost may not fully translate to acoustic results. The vehicle is fighting you every step of the way. The incremental improvement you might get may not be enough. This is a job for a subwoofer with a bass level control.        

[robtr8]

The GS60's are midbass only but run all the way to 7k so, same difference I suppose.  Especially as I can't bandpass them.

I tried running the subs higher, about 130 hz or so and play with the sub knob.  Mostly it wound up sounding like a mess.  Put them back to 60 hz.  Under the seat, as they are, their kind more felt than heard anyway.

What I'm hearing is, to make the additional midbass work, some processing is going to be required.  And even then may not get er done.

[David]

Just thinking out loud.

Ordinarily a 130 Hz crossover might not be totally awful, but in the context of an automobile cabin, it is stacking the subwoofer on top of the cabin effect response. Just way too boomy. You would have to gain the subwoofer so far down that the 50/60 Hz contribution would be all but gone. 80 to 90 Hz could be a good trade off. At minimum the subwoofer would be far more responsive to a little equalization versus the 6.5" midbass drivers. A little bass knob level increase effectively raises the frequency range at which the subwoofer contributes...acting as equalization in a real sense.    

Equalization. Works ideally and in a 1 to 1 ratio to remove peaks. To elevate levels, and fill nulls, you never seem to get a 1 to 1 ratio in that the inherent problem is usually stronger than the fix. Kind of a black hole that sucks power. So you end up wasting a lot of precious power and compressing the system's dynamic range.

Doubling the excursion of the 6.5" midbass creates tons of distortion. But doubling up on the 6.5" midbass and power keeps excursion limited and distortion low.

There is at least a partial fix here somewhere. Just some trial and error.       

[robtr8]

I nudged the crossover up a bit and played with the bass knob.  I don't hate it.  One thing may be that the subs aren't broken in yet.  The other thing I'm beginning to doubt is the source unit.  I have an MBT-RX in the boat, with a first gen ZLD as a preamp.  Very happy with that setup.  I mistakenly thought the MBT-CRX would be similar.  It ain't. Volume adjustment on the -CRX adjusts the BT volume on the phone.  Seems to distort easily.  The -RX always has the BT at max and doesn't seem to distort.  No doubt the ZLD has a better preamp section than the -CRX.