TMM or MTM................

[davideckhoff]

> Yes, it goes as follows:

> 4560/7.5 = Baffle Step Frequency or 608Hz

AWESOME link dave thanks, but did I miss something in the reading........

where do we get the 4560 from????

cheers
-d

[dthomas]

> AWESOME link dave thanks, but did I miss
> something in the reading........

> where do we get the 4560 from????

> cheers
> -d

Constant for the speed of sound.

Dave

[davideckhoff]

> Constant for the speed of sound.

> Dave

ok good...............I think this would be something I want to remember!!!

:-)

Thanks again dave!!

[davideckhoff]

what about the c-to-c spacing thing? Is there such a ting as "the tweeter is too close to the mid"?

[dthomas]

Provided Link: http://realtraps.com/sbirlbir.htm


> what about the c-to-c spacing thing? Is
> there such a ting as "the tweeter is
> too close to the mid"?

In an MMT c-to-c spacing on the midwoofers is of little concern however c-to-c spacing with the tweeter is and it limits your crossover frequency. I think I read in another post that c-to-c in your scenario would be 4.75".

The important issue is to know what 4.75" equates to in a wavelength. It would be 2854Hz, so the highest crossover frequency you want to select is 2900Hz or so. Any higher and you will get nulls created at varying distances in front of the speaker in the primary listening area.

If you like you can email me <A HREF="mailto:dave.thomas2@ge.com">dave.thomas2@ge. com</A> your baffle layouts and I can take a look at them. Also as far as baffle step goes the formula I gave you accounts for only you baffle width and in most cases it will suffice fine. I can however simulate your drivers on the baffle in the exact layout you desire and place them in the optimum location along with designing the optimum Baffle step network.

What is your decided configuration? MMT or MTM? 2 way or 2.5 way? Also go to the page below and download the frequency distance calculator. It will tell correlate freq and distance for you.

Dave

Dave

[curt_c]

> I have pics of the three different baffle
> layouts for my drivers in a TMM 2.5 sys and
> would like for you guys to tell me what you
> think but the pics are not on a web sight to
> link to. I only have pics of my own.
> Hmmmmmmmm..............how do I get around
> this?

You can always email them to me...

> One of the choices of layout is to remove a
> chunk of the tweeter faceplate and snug it
> up to the flat side of the mid(830875)
> faceplate. This would give me a c-to-c of
> about 4.375"
> I have the tools to do this properly and was
> wondering what the effect would be on the
> sound. I know I have seen commercial mfg do
> it in the past?????

Probably a good option, and allows you to cross higher. IMO, up to around 3K.

The ideal is all the drivers are coincident, that is, all on the same vertical and horizontal plane. Stacking them vertically as close toghether as possible is the second best choice.

C

[davideckhoff]

I like the first option I sent you in pic No. 1651 if it wouldn't cause any problems. I think I would be able to do it without any problems mechanically.

: -)

D

[curt_c]

> I like the first option I sent you in pic
> No. 1651 if it wouldn't cause any problems.
> I think I would be able to do it without any
> problems mechanically.

Hi David,
Thanks for sending the pics!

The pic 1651 offers a minimum C-to-C of 4.375"
The pic 1652 offers a minimum C-to-C of 5.375"
The pic 1653 offers a minimum C-to-C of 5.750"

Option 1: Spacing equals one wavelength at 3100 Hz.
Are you going to cut the tweeter flange, or mount the woofer over top of it? (Cutting the flange so they both mount flush with respect to each other and the baffle would likely be preferable) But, (this is a BIG but in both cases the proximity of the tweeter dome to the discontinuity caused by the woofer surround may cause some diffraction discontinuities of unknown magnitude, possibly causing more harm to the ultimate response than we gain with the closer spacing. Also, the tweeter could only be fastened on less than ½ of its circumference. While I’m in favor of mounting the drivers together as closely as possible, I feel this may just be too close.

Option 2 Spacing equals one wavelength at 2500 Hz.
Actually I like this one the best, although it may not look aesthetically the best. The crossover frequency should be high enough especially if the shunt conjugate filter is used on the impedance peak at the tweeter resonant frequency.

Option 3 Spacing equals one wavelength at 2350 Hz.
Perhaps the most aesthetically pleasing. You could ‘cheat’ and still cross at 2500, or at a lower frequency and a higher order transfer function. Another option would be to relieve the woofer flange to allow it to mount flush without altering its flange. –OR, just simply mount the tweeter overlapping the woofer flange. In other words recess the woofer down past ‘flush’ by the thickness of the tweeter flange. The same mounting screw could secure both the tweeter and woofer at that point.

I’m thinking we are dwelling too much on this crossover frequency / spacing issue here, -and that of course is my fault as I’m the one who brought it up in the first place! You see vertical off axis performance is just one compromise made out of many. For instance, the tweeter can be crossed lower, with better vertical off axis response, but may not play quite as loud without excessive distortion, or may simply have excessive distortion at those lower frequencies. Likewise, the tweeter can be crossed higher and the vertical off axis suffers somewhat, but the tweeter distortion may be significantly lower. The non linear distortion plots don’t really look very good for this driver at 2K, but are OK at 3K. We can only assume 2.5K will be somewhere in the middle. See Mark K’s plots here:

<A HREF="http://206.13.113.199/ncdiyaudio/mar.../vifa_xt25.htm">http://206.13.113.199/ncdiyaudio/mar.../vifa_xt25.htm</A>

I fear I may be causing you more consternation without helping you find a solution. IMO, the tweeter distortion would be more irritating than a small issue with off axis response. Consequently, I’m still going to vote for Option 2 crossed at 2500 Hz. I’m also going to suggest that IMO, the tweeter isn’t well suited for first order crossovers.

C