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-   -   Why is floor bounce considered only a bass issue? (https://www.diyaudio.com/forums/multi-way/341043-floor-bounce-considered-bass-issue.html)

system7 7th August 2019 08:35 AM

As I mentioned, floor bounce, which is better described as the "Allison Effect", is a very interesting suckout in a loudspeakers performance which leads you on to considering the whole loudspeaker/room interaction.

If you do your homework, which is not what the Lazy Student does, you reach this impressive understanding of the effect of the floor on the bass performance from Roy Allison:

Quote:

Originally Posted by Roy Allison
Lander: You hold a patent relating to this boundary-effects phenomenon. What does it cover?

Allison: The design of cabinets that get the woofer very close to one or more adjacent room surfaces. That changes the frequency range of the dip, because the closer the woofer is to a surface or to the point where surfaces intersect, the higher in frequency the dip occurs. In the case of a three-way system, it's possible to position the woofer so the dip is above its operating range, and to place the midrange driver far enough away from an intersection for the dip to occur below its range. In effect, that eliminates the problem.

A Glorious Time: AR's Edgar Villchur and Roy Allison Allison Part 2 | Stereophile.com

All this THEORETICAL STUFF is all well and good, but "WHAT DOES IT MEAN IN PRACTICE?" :o

Stuff like this, which is the wall mounted Acoustic Research MST:

https://www.diyaudio.com/forums/atta...rch-ar-mst-png

Aspects of the design I like there... especially those cone tweeters. :o

Or a much more expensive design we just saw:

https://www.diyaudio.com/forums/atta...20-speaker-jpg

One of my heroes in this forum, Joachim Gerhard, also got interested in floor bounce, He got to this:

https://www.diyaudio.com/forums/atta...n-48-dutch-jpg

The Quintessentially German Loudspeaker of the 70th. Modern Interpretation.

TBH, I don't want to get into MTM or MTTM lobing and combing. You either get it about dispersion or you don't. The inverse square law of power at heart. Where we get to, IMO, is the room greatly influences the loudspeaker's sound. For sure, a bit of damping like carpet and rockwool on the walls clears up the midrange clutter. The bass is more difficult. For that you need to know about wall-mounting and floor bounce.

Bill poster 7th August 2019 09:10 AM

Was reading up on this not long ago- floor bounce, floor gain etc
Not sure if it was Jeff Bagby, but one well known designer suggested not putting a bass driver too far down- ie bottom of baffle. Cant remember the reason.
Magico need floor gain to boost the system sensitivity of their sealed drivers, sometimes these are relatively small in diameter. Because of the gap to the mid, Magico usually have a mid only.slightly smaller, I guess for good reproduction of male vocals.

phivates 7th August 2019 05:38 PM

Hey Steve thanks for the reminder about Roy Allison. Of course that was back before science was incorporated into speaker design...
I might have enough AR 4 tweeters to do that MST. No, not CTS phenolic ring jobs, AR. Gosh!

norman bates 7th August 2019 07:16 PM

I've been tempted to add another 12" to my 12" 2-way (28" tall) that sits on the floor now.

I like what I have, just trying to get closer to the midbass that my double 15's had, even at low volumes.

Usually when I lift speakers off the floor, i lose bass, so adding another woofer under it (like a midbass module), may not help me get more bass than what I have.
I like a deep impact-full 2 way with 1 crossover up at 1,200hz.
I got sensitive to crossover in bass region I guess from years of double 15 crossed at 750hz........


Any thoughts / opinions ?

Defo 8th August 2019 11:25 AM

How does speaker/baffle tilting affect floor bounce frequency?

I wonder if tilting the midrange upwards would allow it to be placed closer to the woofer while still keeping the floor bounce frequency the same.

AllenB 8th August 2019 01:29 PM

If it's in the same location the frequency will be the same. The angle may affect the level of the reflection.

Dave Bullet 8th August 2019 08:59 PM

1 Attachment(s)
If you can measure - try the woofer at various heights. If your already have close floor placement, then use bricks / blocks. If too high - put the enclosure on its side and do the same. My placement was largely due to aesthetics and to keep the woofer above "foot kicking" distance - since there are no grilles, such that a clumsy walker doesn't boot it in!

Defo 11th August 2019 12:07 AM

Doing simulations, I still can't get how Gradient can get away with a downfiring woofer...

With normal listening distances between 2,5 and 3,5 meters the floor bounce ends up being around ~300 Hz. Which means the woofer needs to be crossed at about 500 Hz to cover the dip somewhat properly. But they cross at 250 Hz :confused:

GM 11th August 2019 06:45 AM

Quote:

Originally Posted by norman bates (https://www.diyaudio.com/forums/multi-way/341043-floor-bounce-considered-bass-issue-post5876173.html#post5876173)
I've been tempted to add another 12" to my 12" 2-way (28" tall) that sits on the floor now.

I like what I have, just trying to get closer to the midbass that my double 15's had, even at low volumes.

Usually when I lift speakers off the floor, i lose bass, so adding another woofer under it (like a midbass module), may not help me get more bass than what I have.
I like a deep impact-full 2 way with 1 crossover up at 1,200hz.
I got sensitive to crossover in bass region I guess from years of double 15 crossed at 750hz........


Any thoughts / opinions ?

Since you have 12", two = a 'fat' 15", so [4] 'on the floor' to match/best the dual 15" 'on the floor', though of course means a new, wider cab.

Right, you lose the floor's mirror image and even if on the floor it's much reduced at > 3x driver radius, so the closer to the floor the better the mirror image and of course it must be perpendicular and setting on a massive, etc., no carpet, etc., floor for max efficiency, though even my carpeted 'floating' floor does fine, though they calculate in the 300+ lb/ea., so maybe just having really heavy speakers is sufficient.

If near a wall or corner all these 2pi guidelines can get really blurry, so strictly a worst case scenario so may can get by with dual 12", optimized room placement.

GM

iamjackalope 11th August 2019 10:37 AM

Can't this be fixed with an EQ or DSP?


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