TMM thoughts

[tvor-ceasar]

Looking at some readily available speakers and some have been fairly received. Looking at the offerings from Dayton, the T652s ($157-$170) and the MK442T ($268), I was already thinking of what was available to work for a TMM design.

I was thinking of a slim style tower design, so whatever driver was chosen would mean the tower would be at least 1″ (2.54 cm) on either side, so driver + 2″ (5.08 cm). I had already looked at those 6-1/2″ drivers, but the box needed would be too big. Most 4″ drivers didn’t go low enough or have enough SPL in the useful range. Then I split the difference and started with 5″ drivers. 

Came up with the Visaton W130S-4 and W130S-8 5″ drivers. The -4 WAS on sale for $19, but is no longer available. The -8 goes for $30.59 and is in stock. Ran rough #’s in my Qbasic and I get about a 1.5 CuFt box for the drivers in a compound configuration with FB of 43Hz and F3 of 39 Hz. Not a bad size for a tower with decent bottom and SPL.

Threw them both in WinISD and worked a 1.75 CuFt box with a 1.1″ x 7″ port tuned to 39 Hz and an F3 of 35 Hz for both the -4 and -8.

Thing is, the 5″ will start beaming at about 2700 Hz, and most tweeters have a hard time hitting that for a crossover point. Enter the Peerless by Tymphany XT25TG30-04 1″ Dual Ring Radiator Tweeter going for $28.47. FS is 436 Hz, so a crossover at 900-1000 Hz is quite comfortable for both.

I would have liked the -4’s since putting them in Series would have pumped the SPL up to about the level of the tweeter, ~ 89 dB, whereas the -8’s in parallel will drop down to ~ 84 dB. Hmm, wonder if I go through the #’s and put the drivers in as 1 total at 16 ohm, what that’d do… HexiBase’s video helps explain all that.

Anyway, keeping my mind active. Have lots of other things going still. What do you all think?

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Charlie https://www.youtube.com/TheTrueVoiceOfReason

[123toid]

I love the idea.  I personally think that Peerless tweeter is one of the best values out there. I especially like the bigger brother to it, and have used it a few times. They are almost identical, but for two dollars more you get higher sensitivity, lower distortion and a double magnet. So I might consider that as well. Although, it might be overkill in something like this. 

That visaton woofer looks nice.  I would try to cross it over closer to 2Khz or below if I could.  That should help reduce that cone breakup.  It does appear you might struggle with bass, since you are very xmax limited. I didn’t run the simulations, but this should be good for a normal room listening to music. 

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https://www.youtube.com/123toid

[tvor-ceasar]

Yeah, that 2.25 mm Xmax is a bummer, but it does have a +-8 mm Xmech. Holding it to the 2.25 limits things to around 10 – 20 watts max. I can keep Xmech under 8  with up to 60 watts. Of course, I’m not entirely sure how WinISD calculates that because it doesn’t exactly tell you how they assume the 2 drivers are hooked/wired together.

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Charlie https://www.youtube.com/TheTrueVoiceOfReason

[mistersota]

Posted by: @tvor-ceasar

Thing is, the 5″ will start beaming at about 2700 Hz, and most tweeters have a hard time hitting that for a crossover point. Enter the Peerless by Tymphany XT25TG30-04 1″ Dual Ring Radiator Tweeter going for $28.47. FS is 436 Hz, so a crossover at 900-1000 Hz is quite comfortable for both.

 

I have some measurements of that tweeter that might help you decide if it’s right for you.

Here are the on-axis and distortion measurements from the tweeter mounted in a speaker. These were taken at 1m 2.83V within a reasonable margin. (there are some diffraction effects around 1-4khz due to the woofer, ignore them).

You can see that the response goes plenty low, but the 2nd order distortion is rising to concerning levels at around 1.5hz. Now, 3rd and higher don’t start to rise until around 800hz so it’s unlikely that the driver is actually going to be damaged with a steep 1000hz crossover, but even 2nd order distortion at 5-10% distortion is probably going to be audible at those frequencies, and that’s only 2.83V. 

Just take the data into account.

To add to the woofer discussion, if you are putting 5-inch drivers in a 1.75 cubic foot box, you are seriously going to lose power handling. Many drivers with low motor strength shouldn’t use quasi-butterworth designs, they should be put in a small box with a lowish port tuning. JBL actually does it a lot. Here is an example of the JBL HLS 810. The driver is high Qts, low BL, which means it looks like it would play low, but JBL knows better.

 The quasi design is able to handle 10 watts before bottoming out and their design is able to handle 25 watts, which translates to safer operation at the loss of low end response. Just something to keep in mind if you want high spl. 

 

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