crossover setting for new tmm tower?

[frazzled]

I just finished a pair of towers using the Seas TDFC tweeter and two Dayton RS180s. The box has an internal volume of 50L and tuned to 35hz. I also have a Dayton 15" sealed DIY sub. I was told that I should put a sock in the port and cross it over at 80hz (this would be ideal), or try lowering the crossover with the port open. It confused me because I have these speakers that sound awesome and go lower than my bookshelves they replaced, so why would I stick a sock in it (the port, I know what you're thinking).

[ThomasW]

I'd play with 60Hz and 80Hz settings if you have those options. I'd ignore the sock recommendation.

[opt-e]

Frazzled, those look very nice. What crossover design are you using?

[Amphiprion]

Like Thomas I would ignore the sock idea, all it would do is raise your F3 and you'd then have cascading acoustic and electrical roll-offs interfering. Keep the bandwidth as wide and flat as possible for the full range speaker by keeping it vented, then cross over at say 80Hz to keep midbass distortion down (as good as these speakers are, all 6.5" suck under 100Hz) and let the electrical crossover do it's thing free from interference of the speaker's natural roll-off. That way, the effect of the speaker's natural roll-off will only start affecting the final acoustic slope when its 12-24dB down, depeding on the RS180's bass extension and your crossover setting.

My .02 anyway.

[Dennis H]

let the electrical crossover do it's thing free from interference of the speaker's natural roll-off.

The problem is, thanks to THX, most receivers and prepros these days expect to see the speaker's rolloff. They use an electrical 4th order Linkwitz-Riley on the sub and an electrical 2nd order Butterworth on the main. So, for a "perfect" blend the box should be sealed and tuned to an acoustical 2nd order Butterworth alignment at the crossover frequency. The electrical and acoustical B-2s combine to make an LR-4.

Edit: I did a quick check and your box has a pretty low Q if you plug the port -- Q = 0.53, F = 56 Hz. So, you're not going to get a "perfect" blend with most crossovers. The -3dB point is about 80 Hz so the advice to plug the port and use an 80 Hz crossover looks pretty good. However, you'll just need to experiment and see what sounds best. Try the port both plugged and unplugged and try different frequencies.

[Amphiprion]

True, true. I guess I don't think about HT receiver bass management since I don't have one He might also try a simple 2nd order BW active filter in line with the LFE out to make it a true 4th order L-R acoustic. Texas Instruments sends out free samples (I have $50 of Burr Brown opamps sitting on my desk as I type, delivered free of charge) and the rest of the parts should be findable at Radio Shack, Digikey, Parts Express, etc. Might make a fun little side project and an introduction to electronics if frazzled hasn't done that sort of thing before.

[frazzled]

crossover

Frazzled, those look very nice. What crossover design are you using?

Thanks for the compliment. I pretty much stole the design from B&W/Paradigm/Sonus Faber

I decided to go with Roman's 2.5 crossover design from RJB Audio. Roman helped me out a lot with this. I realize that there are a lot of good designs out there with these drivers, but I wanted to try this crossover with a TMM design. The center channel is on its way!

[frazzled]

crossover

The problem is, thanks to THX, most receivers and prepros these days expect to see the speaker's rolloff. They use an electrical 4th order Linkwitz-Riley on the sub and an electrical 2nd order Butterworth on the main. So, for a "perfect" blend the box should be sealed and tuned to an acoustical 2nd order Butterworth alignment at the crossover frequency. The electrical and acoustical B-2s combine to make an LR-4.

Edit: I did a quick check and your box has a pretty low Q if you plug the port -- Q = 0.53, F = 56 Hz. So, you're not going to get a "perfect" blend with most crossovers. The -3dB point is about 80 Hz so the advice to plug the port and use an 80 Hz crossover looks pretty good. However, you'll just need to experiment and see what sounds best. Try the port both plugged and unplugged and try different frequencies.

I never did quite understand why someone would build a tower that goes lower and then cross it over at 80hz. This helps a lot. Thanks

[rj45]

crossover design?

Hi Frazzled -

Can you post your RJB - modified TMM crossover?
The TDFC looks a lot better than the RS28A design posted on
RJB's site.

THX,
-Don

[frazzled]

crossover

He considered this a starting point to be tweaked, but I think it sounds awesome already.

[rj45]

Roman sent me his output and Speaker Workshop project files for the TMM RS180 / TDFC,
so that's what I'll be building. I'll post here when it's done.

-don

[frazzled]

Roman sent me his output and Speaker Workshop project files for the TMM RS180 / TDFC,
so that's what I'll be building. I'll post here when it's done.

-don

You'll be one proud puppy