Tweeter Flap???

Ricardo

Both the 3.1 TL's and the RTA 15 TL's have this. What's it for? Why only on the top and not in the bottom of the tweeter? What can I expect if I remove it?

Joe08867

I believe it helps dispersion of the tweeter, by blocking the sound waves coming off the Driver from distorting the sound of the tweeter and not allowing these two sound waves to cross paths before they get to your ears.

Ricardo

Joe08867 wrote: »

I believe it helps dispersion of the tweeter, by blocking the sound waves coming off the Driver from distorting the sound of the tweeter and not allowing these two sound waves to cross paths before they get to your ears.

Yes, but then why didn't they put one in the bottom also? Same distance to the driver, and both top & bottom drivers play the same frequencies.

heiney9

I remember reading somewhere on here why they did that. The RTA 8 and RTA 11 are true D'Appolito array's so I'm not sure why it's needed. IIRC, it had something to do with a tighter dispersion pattern.

D'Appolito
A loudspeaker configuration developed by and named for Joe D'Appolito, in which a high frequency driver, or tweeter, is positioned between two midrange or low frequency drivers that each cover the same frequency range. Depending on the exact implementation the speakers can be positioned with a vertical and/or horizontal orientation. In either case the two midrange drivers serve a couple of purposes: they combine to create a larger effective woofer or midrange driver size, and they also serve to control the dispersion of the tweeter. The tweeter's output is somewhat corralled or contained by the sound coming from the midrange drivers in a similar way to how two parallel surfaces control dispersion. There are some variations on the design where two same sized woofer/midrange drivers may cover slightly different frequency ranges, however those aren't considered true D'Appolito designs. The D'Appolito design specifies a third order crossover network. �The tweeter is coordinated with the woofer so that at the selected crossover frequency, the drivers all have similar horizontal dispersion. �(This is not easily accomplished because many drivers behave badly at the extremes of their range.) The advantage of doing it all correctly is one of the most seamless blending of drivers possible. �The result is an absence of any sudden change in directivity with frequency. �This may not mean much for monitors where there is a limited listening area, but in a typical room where a large percentage of the sound is reflected by the room, the effect is dramatic.

Joe08867

That is a good question.

My guess, looking at most speakers built at the time and today the tweeter is above the driver and it was considered the normal placement, but when they placed the driver above the tweeter it narrowed the sweet spot and dispersion of the tweeter.

Placing a deflector above it opened it back up, but maybe using one above and below messed with the mid-range adding to much top end to the sound and limiting the mid-range dispersion and subsequently the soundstage.

I would like to hear what others think on this.

heiney9

Joe08867 wrote: »

That is a good question.

My guess, looking at most speakers built at the time and today the tweeter is above the driver and it was considered the normal placement, but when they placed the driver above the tweeter it narrowed the sweet spot and dispersion of the tweeter.

Sort of, the D'Appolito array actually narrows (corrals) dispersion pattern or atleast focuses it better to actually widen the sweet spot or atleast improve off axis response. It also helps greatly with time alignment and eliminates or drastically reduces lobing.

H9

heiney9

A D'Appolito array straddles the tweeter with two midrange drivers. This creates a virtual phase reference point in between the two midrange speakers, and eliminates lobing between the midrange and tweeter. However it creates new lobing between the two midrange speakers. These drivers are twice as far apart as the midrange and tweeter. However, with the same crossover the variation is less than with a single midrange, as shown in the right-hand Figure. For the D'Appolito Figure the vertical offset is relative to the tweeter. Since the phase shift introduced by the crossover is an important part of this behavior, these curves apply only to 1st order crossovers. I have not made any calculations for other orders.

Lobing is a fairly complicated phenomenon, and the calculations do not include the drop-off in driver response as the angle off axis increases. I measured the response of my system (46 kb) and the null for a vertical offset of 19 inches was there just as predicted (ain't engineering wonderful). The red curve is measured at the sweet spot, and the yellow curve at the elevated position.

The vertical size of the "sweet spot" is increased by decreasing the vertical spacing between the tweeter and midrange, so I put them as close as I could without creating a diffraction problem. For my purposes the "sweet spot" is large enough that lobing is not a problem. But I must say, after starting out very skeptical about the D'Appolito configuration, I have been converted into a believer. For an application where the "sweet spot" needs to be large vertically, it is clearly a superior arrangement with a 1st order crossover.

Joe08867

After reading your original post I can see how that would work. I have seen the same principles applied by Canton for many years.

I have also noticed that not all 15tl's have the flap. So maybe it was something the customers said bothered them about the 15tl's sound that created or eliminated the flap. I would be curios to know when it was used, early on or in later versions.

I would predict that back when these particular 15tl's were built the sound of the time deemed it necessary to brighten up the sound of these speakers. And negate the D'Appolito array type sound.

Ricardo

Thanks guys. I guess this is one more for the projects list; remove the flaps and see if I can hear a difference.

heiney9

Joe08867 wrote: »

After reading your original post I can see how that would work. I have seen the same principles applied by Canton for many years.

I have also noticed that not all 15tl's have the flap. So maybe it was something the customers said bothered them about the 15tl's sound that created or eliminated the flap. I would be curios to know when it was used, early on or in later versions.

I would predict that back when these particular 15tl's were built the sound of the time deemed it necessary to brighten up the sound of these speakers. And negate the D'Appolito array type sound.

Since the RTA15 was always a "TL" and used the sl2500/sl3000 tweeter, the flap should have always been present. The 15TL wasn't in production very long, perhaps 2 or 3 years. My guess is customers removed them or damaged them, but that's just a guess. The flap was used on the 8 and 11 TL's also. Perhaps a property of that tweeter used in that way prompted the flap. Maybe Ken will chime in.

H9

heiney9

Ricardo, I'm not sure the RD0's need the flap.

H9

HB27

Cool question I pondered a month or so ago on my M12Bs. I changed the SL-1000s out to Peerless. With the top hats off and deflector removed the tweeter sounded different. I played with it and found out "at least to me" that the deflector "raised" the tweeter output higher in the sound field to where it came closer to my ear level. It was an obvious difference on the M12b with the deflector on and off. It may have been just me but it was almost like putting them on stands. Directional deflector.

Joe08867

heiney9 wrote: »

Since the RTA15 was always a "TL" and used the sl2500/sl3000 tweeter, the flap should have always been present. The 15TL wasn't in production very long, perhaps 2 or 3 years. My guess is customers removed them or damaged them, but that's just a guess. The flap was used on the 8 and 11 TL's also. Perhaps a property of that tweeter used in that way prompted the flap. Maybe Ken will chime in.

H9

Actually I have seen pictures of the brochures that showed them with and without at different times. So I am just as confused by it.

HB27 wrote: It was an obvious difference on the M12b with the deflector on and off. It may have been just me but it was almost like putting them on stands. Directional deflector.

That is what I was thinking in my first post.

Ricardo

HB27 wrote: »

Directional deflector.

This sounds logic. The tweeters in these speakers are placed very low.

TrashyTrucker

Ricardo,
This may help read page 4 section 3, it tells what that is for. I left the flap on mine.
Thanks for all your help. My 3.1's sound fantastic now.
BTW my HD crashed and I lost all the schematics and such that DarqueKnight posted on the 3.1TL's and I am unable to find them in search mode now. If you have anything I could use it again?


SRS3.1TLBrochure.pdf

regards,
Matt

Ricardo

Matt,

Thanks for the read.

Do you mean these schematics?

http://www.polkaudio.com/forums/showthread.php?t=55888

TrashyTrucker

Ricardo,
Thank you for the schematics.


Matt