Crossover between subwoofer and midrange

[Roosteraudio]

Hello, I am building a sound system for my car and I will have both midrange speakers and a subwoofer in the trunk. The midrange speakers will be positioned at the same height as the headrest and the subwoofer will be on the trunk floor. The Subwoofer is an Alpine SWT 12S4 with a Frequency Response 28-200Hz and the four midrange speakers is SPL Revel 6,5” with a Frequency Response 100 - 10kHz.
In the manual for the the midrange speakers it is recommended to use a Crossover of 110Hz/12db or higher. No such information is found from the manual for the subwoofer
Where should the crossover be between the midrange and the subwoofer?

I heard that if you play 80-100 Hz on the subwoofer, then the sound will become directional and you can hear that the low frequency is coming from the trunk. Is it true and would that be a problem even if both midrange speakers and subwoofer is in the trunk?

 

[Chrispy]

The crossover is that point where the slopes crossover between the low pass filter set for the sub vs high pass filters for the speakers. Does your gear even allow for different slopes between the two? Subs in home sized rooms can become localizeable, and can be combatted with multiple subs. Personally haven't the size/space found in a car to be a problem with a single sub myself.

 

[Keith_W]

Welcome to ASR. We are mostly home audio people here, not car audio. You may get more helpful responses if you were to ask in a car audio forum.

1. Nobody can tell you what the crossover point should be without a data sheet or actual measurements of the driver. You did not supply enough information. I tried to Google "SPL Revel 6.5" to find the data sheet for your midrange driver, but I came up empty. Could you please post the data sheet with the Thiele-Small parameters for both the midrange driver and the subwoofer? In particular, we are interested in the resonant frequency Fs.

In general, the more you suppress Fs, the greater your power handling. Suppose the Fs was 100Hz. If you chose a 1st order Linkwitz-Riley at 100Hz, it would be -3dB at 100Hz. 2nd order would be -6dB. Or if you chose a 1st order LR an octave above (200Hz), it would be -6dB at 100Hz. 2nd order at 200Hz would be -12dB ... and so on. The more you can push it down, the more power your speakers can handle without running into driver resonance problems. Unfortunately you run into other limitations - you reduce the usable bandwidth of your driver, the crossover becomes more complex, and certain orders don't sum properly ... etc. And then there are alignment issues. It's quite a complicated subject, and not something that can be easily answered in a forum post. If you were to rely on forum advice alone, you won't get a good result. You need to understand the principles behind crossover design, so I suggest you read a book like Vance Dickason's Loudspeaker Design Cookbook.

2. I seem to recall from my car audio days that it is a very bad idea to have directional sound coming from behind you. So no, I would not put my midrange driver in the trunk with the tweeter in front. And I would not cross my sub over so high that its direction is discernible.

 

[kemmler3D]

Welcome to ASR! Sound can be directional even at very low frequency (60hz even), but because of the small enclosed space of a car I think it behaves differently. If you think about it, a sub in the trunk is still pretty close placement compared to what you will find in many listening rooms where the sub is crossed at 80. So as far as I know that's not a huge issue. I do think it's important to minimize distortion from your mids, so I would cross at 100hz or close to it, but you will need to verify the slope of the LP on the sub to be sure it's right.