Thread: Might as well post a system i built

Building speakers for home and pro sound reinforcement is like comparing a Porsche to a tractor.
One use's fineness to achieve nice sound the other use's brute power to go the distance.
Go along to a concert while setting up and chat with the sound guys and see how things are done in the real world(not the online one), you can use all the physic theory you want soon as a few people walk into the area... the physics change and keep changing and changing.

Yes physic's have a major roll to play but when the properties keep changing there's no controlling them(computer aid goes a long way now tho), thats why home speakers can be set up to sound so sweet using nearfield and diffraction/absorption techniques.

Have you used these speakers for sound reinforcement yet?
If Christiaan Huygens was around today you may well have a wave theory on variable sound fields, his mathematical genius was what 300+yrs ago... there was no speakers his theorems were based on naturally produced sounds. No speaker can produce real true life sounds yet, single driver designs are the closest so far.

Don't be so quick to assume I don't have any live sound experiance. I have been behind the mixing desk for a large theatrical production, and a number of rock concerts. I have been involved in the setup of many more. Just so you know i also have quite a few stereo and multi-track recordings under my belt as well (But i don't see that comming up). I have used my subs (and some better EV tops), in a live sound environment before, the set has recieved a lot of use at parties and the like.

You are correct in that the number of sabins in a room will change when people walk in and move around (i have textbooks with figures for this, but it really depends on what people are wearing). However I am principally disputing soundman's incorrect statement about the directivity of horn subwoofers. Because both front loaded and horn loaded subwoofers will have extremely similar anechoic directivity, the way their responses are effected in a room with all these changing variables would be identical, given identical placement. So whilst it is true room acoustics can get pretty complex pretty quickly, the point is moot as far as the directivity of the speaker is concerned.

Playing with horn loaded sub placement in a large area/room, I've found that sub bass can directional depending on placement... try this in open air, face you bass bins forwards step back at least 20m, play some heavy bass dance music... then face them backward and listen from the same spot, guess what... no bass!
Now do the same set up with a conventional sub (sealed/ported/bandpass), it'll make very little difference as they are more omnidirectional.(no horn to guide the waves, hence soundmans comment)

Originally Posted by Harry72

Playing with horn loaded sub placement in a large area/room, I've found that sub bass can directional depending on placement... try this in open air, face you bass bins forwards step back at least 20m, play some heavy bass dance music... then face them backward and listen from the same spot, guess what... no bass!
Now do the same set up with a conventional sub (sealed/ported/bandpass), it'll make very little difference as they are more omnidirectional.(no horn to guide the waves, hence soundmans comment)

I will one up you on that, do it, measure the things and show you it is the harmonic distortion that is directional, not the fundemental. When i have them out of their hole again (won't be for a few weeks). I will have to find a car park or similar for a groundplane measurement.

Cool, keep us posted on your results!

Checkmate

Had a party sooner than i thought, Here is the polar response measured every 30 degrees, outdoors using a swept sine groundplane measurement. The noise floor was approximately 50db below the the level of the measurement. The repeat count was set to 8 for maximum noise immunity. The center of the subwoofers was kept a constant distance from the microphone. As you can see for your self the subs are only beginning to show signs of directivity around 150hz. With the crossover in place this neglible amount would amount to zero.

Here are the measurements:





And the same thing with traces seperated:

Just some questions on your findings

Distance was the mic set at?
What was surrounding the cabs?
Were there any walls or reflective surfaces?

Seems to be a steep roll off after 40Hz no matter what orientation.
How much equalisation do you use to flatten out the response(normally), between 75~85Hz you have a 4db drop after that it gets somewhat raggedy, the response from 40~75Hz is nice tho!
Do they exhibit these characteristics indoors?

Originally Posted by Harry72

Just some questions on your findings

Distance was the mic set at?

I basically followed Dr Joe D'Appolito's recommendations, The mic was placed around 2m, Further than he recommended, but i wanted to make sure i was in the far field. The mic was about 1cm from the ground. Using the formula in his book, this measurement would be accurate up until around 800Hz, more than enough for our purposes.

Originally Posted by Harry72

What was surrounding the cabs?

Grass, But the nearest thing was a tree at around 10m. Making the total path length difference around 20m, making any reflection from the tree down at least 20dB, when compared to the main wave.I made sure the subwoofer was rotated not the microphone, so the acoustics were not effected.

Originally Posted by Harry72

Were there any walls or reflective surfaces?

Well the ground, but that had no effect on the results, and the tree, which would have had neglible effect.

Originally Posted by Harry72

Seems to be a steep roll off after 40Hz no matter what orientation.

Yep, this does improve a bit with corner placement, (30-35hz is possible). With only one sub the response drops off a bit at 50Hz (like a shelf filter), then rolls off at 40hz, corner placement can fix this. The original design (see the link in the first post), states that its a 40hz horn.

Originally Posted by Harry72

How much equalisation do you use to flatten out the response(normally),

I have a BFD, and use that with my mic to equalise them to within 1-2db of flat. This frequency response measurement will be useful to set some default EQ for parties etc.

Originally Posted by Harry72

between 75~85Hz you have a 4db drop after that it gets somewhat raggedy, the response from 40~75Hz is nice tho!

Yep, it'd be interesting to figure out the cause, raggedy or not its still pretty insigificant when compared to room effects, and the humps aren't too nasty (+/- 3dB)

Originally Posted by Harry72

Do they exhibit these characteristics indoors?

Lower extension is possible, but you are at the mercy of room modes, but for the most part yes. Listening tests indoors of directionality indoors is not a good idea, there are too many reflections (at high frequencies), and standing waves to deal with (low frequencies)