Advice for Building Modula MTs

[gee_boi]

Well, after a lot of reading and looking at well-known projects, I think I am going to attempt the Modula MTs with the Seas 27TDFC/H1189 tweeter (seen here, http://htguide.com/forum/showthread....4&page=1&pp=35).

I am building these with the intention of putting them in a small living room in a condo (which I don't own yet) so I'm sure they will have more than enough output. I will be using them for music (various types from jazz to R&B/Hip-Hop to instrumental), and the occasional movie.

What I wanted to know is has anybody made these floor-standing? I really prefer the look of narrow floor-standing speakers and would like to attempt to build these that way. I know that changing baffle width can effect the way speakers sound, but I haven't been able to find anything about baffle height.

I also wanted to know if there will be any effect if I port them through the front as apposed to the rear. I figure this way I would be able to have them close to the wall (which might be desired in a small room).

Also, will changing the enclosure depth be an issue? I was hoping I could use the extra hight to allow for some changes in dimension, while keeping the volume the same.

Thanks!

[sreten]

http://www.geocities.com/woove99/Spk...RS180_2way.htm

Hi,

The above has a simpler crossover. You can check the effect of a long
baffle in the baffle simulator - compare it to one sized as above.

Depth you can change around and note you can angle them to reduce height, e.g. :



Around 20L internal volume, tuned to around 35Hz I'd say.

Near rear wall use is a no-no, so go with rear porting.

/sreten.

[peter_m]

sreten, how does the simplified version you mention compare to the Modula MT? Any audible differences?

Peter

[Jay_WJ]

As you may have noticed in the comparison in my design page, their difference should be minimal (this FR comparison should be very accurate regardless of their actual measured responses). Some people may believe that the breakups of the RS180 need to be suppressed more. But honestly, I don't hear any bad highs. They're clean sounding speakers and very enjoyable.

For a floorstander, I suggested a baffle width and a cabinet volume in my page. The baffle width can be as narrow as 8", which I used for my sealed design. Then choose a good height for you and calculate a depth that gives the desired volume. An option to consider is to make some closed room at the cabinet's bottom for sand filling.

There will be some baffle gain due to the extended baffle, but I didn't put much BSC in the design. So, the current XO should work fine.

As sreten said, speaker placement too close to walls is not recommended. If you have no other option but to place them very close to walls, consider the reduced BSC option suggested in my page. In this case, front porting can also be useful. Front porting will have some effect on the midrange, but if you cover the cabinet's inside walls well with damping materials and the port has some distance from the woofer, the effect will be minimal and won't be audible.

These speakers will have enough output when used in a small room for music only listening, unless you listen to full orchestral music at a concert level.

If you want better dynamics, Natalie P can be another choice. You can make it a floorstander, too. If you want better, cleaner sounding speakers in a narrow floorstander, consider my Usher 8945P 2-way. It can also be in a tall, 8" wide cabinet because I don't use full BSC in my design.

[sreten]

Originally posted by peter_m
sreten, how does the simplified version you mention compare to the Modula MT? Any audible differences?

Peter

Hi,

Simple answer is not much, and I prefer the Jay_WJ (originally Zaph)
( http://www.zaphaudio.com/audio-speaker17.html )
filter approach as it it easier to tune than a series filter. Very high
suppression of the top-end bass-mid unit response does not change
the effect of that areas response on distortion and basically its the
actual (low) c/o point that is the most important factor to distortion.

/sreten.

[peter_m]

Sreten,

sorry to repeat my self, but I should have been clearer in my original question. DId you hear both systems, the original Modula MT and Jay's simplified crossover? Also Is there a major difference between the TDFC and the TBFCG tweeters?

Peter

[sreten]

Hi,

No i have not heard them, just commenting on the c/o design.

The tweeters ? one is metal the other fabric ......
price versus performance both very good ......

from Zaph

Seas 27TBFCG ($30) - Very smooth response, down a few dB at 20kHz. Very low distortion of all types, particularly the near non-existant high order harmonics. No notable energy storage problems. Ultrasonic breakup node at 26.5Khz. The hexagrid cover is ugly.

Seas 27TDFC ($29) - Exactly the same as the TBFCG, but with a fabric dome. Slightly rising top end response but overall very smooth. No ugly hexagrid. Similar to the old 27TFFC, but with a polymer surround and slightly cleaner performance.

http://www.zaphaudio.com/tweetermishmash/compare.html

/sreten.

[Jay_WJ]

For the comparison of the Modula MT and my RS180 design, you don't actually need any measurements. They are basically LR4 design, and frequency responses are very close to each other as shown in the above graph. Note that this comparison uses identical individual driver frequency responses for both designs. So the comparison can be meaninfully interpreted no matter what kind of driver FRs are used (as long as they are identical across both designs).

Thus I don't see any reason for them sounding very different.

As for the TDFC vs TBFC, the TBFC has a bit lower distortion numbers (Also see Mark K's measurements). Otherwise, they are both excellent tweeters.

[gee_boi]

As sreten said, speaker placement too close to walls is not recommended. If you have no other option but to place them very close to walls, consider the reduced BSC option suggested in my page. In this case, front porting can also be useful. Front porting will have some effect on the midrange, but if you cover the cabinet's inside walls well with damping materials and the port has some distance from the woofer, the effect will be minimal and won't be audible.

I might try the reduced BSC option, since ideally I will be placing the speakers flush with the TV, which should be no more than about 2' from the back wall (so the rear of the speakers will be ~ 1' from back wall).

If porting from the front, how far from the midrange would you place the port? Is there a certain distance the port needs to be from the bottom of the enclosure (and the floor) as well? I've seen some floor standing speakers with the port way down near the floor...

As this is my first project I don't want to introduce too many complications, but I still like to customize things a bit to suit my taste and needs. Plus I find you always learn more when you tinker around with things as opposed to following instructions word-for-word...

Hope I'm being realistic with these ideas and not setting myself up for failure

Thanks again for your help guys.

[gee_boi]

Not trying to be difficult but...



With this setup, using Modula MTs (rear ported also), the speakers appear to be pretty close to the back wall, and there's the TV stand between them along with that glass cabinet.

My question is, would this be an example where reduced Baffle Step Compensation should be used?

If the builder of these is on here (Dan, I think...), you did a great job. I think they look awesome.

An option to consider is to make some closed room at the cabinet's bottom for sand filling.

This sounds like a really good idea, I think I'll try to incorporate this somehow. It should really help deaden these things (and keep them from accidentally tipping over). I was thinking I may have to create an empty "chamber" at the bottom to get the correct volume anyways.