T Line box idea Thoughts?

[Splatmaster527]

Ok guys Ive been looking around this site on and off for a while now and finally posting.

So I recently moved back into college and I am working on designing a new bass setup. Last year I had a huge Bill Fitzmaurice THT Folded Horn in my room running off a DJ amp from my Surround sound receivers subwoofer output. This year we dont have quite as much space and the Folded Horn isnt really the best for smaller rooms like this.
Anyway I was thinking this year I could do 2 Transmission Line Boxes one with a 15in Dayton RSS390HF Subwoofer tuned down low around 30-35hz for the major room shaking bass and then do another T line box with 4 MCM 8in woofers tuned more up toward 60-70 hz for the hard kicking beats.

I was planning on using an active DJ Crossover to split the two at around 50hz and Bi-amp the system
How does this plan sound? Am I over thinking the setup or do you think I am on the right track??

 

[bjorno]

..How does this plan sound? Am I over thinking the setup or do you think I am on the right track??..

Hi, Looks quite feasible IMO: Quick suggestions to tweak a bit more if necessary:

b

 

[Splatmaster527]

Man thats a lot of data!! Makes me feel like a novice all over again...
I appreciate the effort you put in and I want to get the most out of it, so would you mind explaining to me what some of it is? I can see you plugged in the info for each driver and stuff but what do the graphs down the sides mean? If I understand correctly the single line graph in the middle with a green line is the final frequency response with both subs??

Thanks!!

 

[bjorno]

If I understand correctly the single line graph in the middle with a green line is the final frequency response with both subs??

Thanks!!

Hi,

Quite right. The Dayton driver is first HP and LP filtered at 16 Hz-Bw4 and at 50 Hz-LR4, then summed with the unfiltered MCM Top-box showed in green color.
Note: The in reality FR above ~100 Hz would be as flat as the eventual manufacturers graph, if advertised.

In HR Le can be set to 0.01 mH in order to circumvent the influence of the driver 2.4 mH inductance and as both boxes should be at least partly lined (or stuffed with damping materials):

The expected FR:s would then be summed more flatter from ~20 Hz to above 200Hz than seen in the plot.

IMO,Another good idea (not shown in the submitted simulations) is to XO the TL at ~60 Hz(LR4 LP) to the 4 MCM's(1Hz-safe) in a ~0.9 cu.ft closed box(Qtc=~0.5_f-6dB=~59 Hz).

Time to look at useful design tools of this DIY trade?
Both HR Hornresponse and HOLMimpulse are very good free down-loadable programs, read the Help files,look for tutorials on the Net.

Hornresponse can be used in TL simulations of OD(Offset Driver) configurations where it's important no notice that the effects of eventual inserted damping materials are not shown in the plots.

Rec. Read MJK:s quarter-wave pages of the consequence's when stuffing quarter-wave designs.

Hornresp

Quarter Wavelength Loudspeaker Design

HOLM Acoustics


b

 

[Splatmaster527]

Ok thanks for the explanation... Ive downloaded the programs and I am kind of searching around to become more acquainted with them.

To kind of summarize what you are saying and what I am gathering from you is that you think I should have the Dayton 15in in a T-Line box like I described but what frequency should I have it tuned to? And you think I should skip the T-Line on the MCMs and just go with a small sealed box tuned ~60hz? How much will I lose in a sealed box vs a T-line?

The problem with trying to XO at 60hz is my Active XO crosses at either 50hz or 90hz and does it at -12dB/octave so without making up a custom set of 3rd order low pass and high pass filters I'm kind of stuck around 50hz

I am really only going to be using the MCMs up to about 200hz so the frequency inconsistencies after that dont really matter if thats why you were recommending a sealed box.

Again sorry to ask so many questions and I appreciate your help!!

 

[bjorno]

Hi,

FYI: A much smaller TL:

b

PS: I'll be back later (my tomorrow) to the questions in your post#5.

 

[Splatmaster527]

WOW that is an amazingly helpful sheet
Cant wait to hear what else you have to add

 

[bjorno]

..To kind of summarize what you are saying and what I am gathering from you is that you think I should have the Dayton 15in in a T-Line box like I described but what frequency should I have it tuned to?..

Hi,

IMO:Your options are to design TL:s using enclosure volumes between 157L(~5.54cu.ft_Qt=~0.71) and 237L(8.4 cu.ft_Qt=~0.62).

The tuning would be below fs for the larger box but above fs for the smaller and below fc(=f-3dB) for an optimal closed box where diminishing returns would soon be reached and if surpassed would not contribute to either the FR smoothness or SQ.

I don't see any drawbacks for the larger TL besides a somewhat lower SPL, but the smaller, opposed to the larger, must be properly (evenly) stuffed with the advised Weight/~Density of stuffing material if to work as intended.

The smaller TL is also more sensitive to distance misalignments, in particular to the suggested Driver offset than the larger one is,but for the latter:
If deviating less than a couple of inches off correct offset:
The occurring effects like (FR peaking) can easily be counteracted by partly tweak(increase-decrease) the damping material density at certain locations (Note: Maintain the weight of Stuffing).

This method doesn't solve the situation for the smaller TL that can only successfully be tamed to FR flatness by inserting additional damping material, best if placed near the Terminus.
The Drawback is that the entire in-band FR would be attenuated too.

..And you think I should skip the T-Line on the MCMs and just go with a small sealed box tuned ~60hz? How much will I lose in a sealed box vs a T-line?..

The simulations for the MCM:s suggests a slot-ported BR that would work well using a ~50Hz XO as previously shown but can be substituted with a closed design that only integrates best at ~60 Hz.

One of the reasons why is to preserve perpendicular dispersion from both the TL-sub and the MCM baffles, thus allowing no tilt of the projected sound.

..The problem with trying to XO at 60hz is my Active XO crosses at either 50hz or 90hz and does it at -12dB/octave so without making up a custom set of 3rd order low pass and high pass filters I'm kind of stuck around 50hz..

If you choose the smaller TL-sub I suggest you should choose the 12 dB/octave 90 Hz XO in LP mode and just use the MCM:s in flat FR overlapping mode up to ~200Hz using the ~0.9 cu.ft closed box for the 4 drivers. 60 Hz is ~6dB and at ~80Hz -3dB down.

Adding a simple sketch showing one possibility for a small TL enclosure:

b

 

[Splatmaster527]

Again thank you for all the help you have presented here

That T-Line for the Dayton looks great and that is probably the design I will go with. Ill have to look up a bit more about stuffing because besides lining the inside of a few vented boxes with fiberglass I an pretty new to the idea. Any suggested readings or advice?

As for the MCMs I will take your recommendation as to what you think I should do... When I plugged them into WinISD for a 4th Order Bandpass and a Vented Box I got the results in the attached photo. Not sure if these look similar to what you are getting?

As for the XO I just ordered a fully adjustable XO with a 24dB/Octave cutoff which i can overlap and such. I got a Behringer CX2310 so I hope thats a better option.

I have the XO and MCM drivers in the mail so besides wood I will have everything I need to build this weekend

 

[bjorno]

..As for the XO I just ordered a fully adjustable XO with a 24dB/Octave cutoff which i can overlap and such. I got a Behringer CX2310 so I hope thats a better option.

No doubt,You will IMO end up with a very good system.

Submitting a picture that can be studied in detail considering TL foldings and impact of different placements of stuffing:

b