Lack of low end in TubaHT

[OrangeJuices]

Hello

I finished building the TubaHT to a width of 70cm (roughly 27 inches).

I loaded it with the Dayton Audio RSS390HO-4.

I placed the subwoofer in a corner with the mouth of the horn facing into the corner 18 inches from the wall per the plans.

I placed the UMIK 1 calibrated microphone in the mouth of the horn in an attempt to measure the output of the woofer "without" room gain.

Microphone placement in horn

Heres a screenshot from REW, purple line being the measurement with the unit tightly screwed down and the sidepanel attached securely. The blue line shows the subwoofer with all loose screws, a 2mm shim to lift the unit and provide a definite leak, with the side panel off.

Microphone placement in horn

Microphone placement in horn

I'm at a loss, why are the two measurements so close together? Am I measuring wrong? Do I have a leak in the horn path?

[OrangeJuices]

I'm starting to think the measurement is somehow wrong, I have the same exact response albeit at a lower SPL with the unit in free air...

[Bill Fitzmaurice]

The only way to measure without room gain is outdoors. Even so those measurements are way off. Something about your setup isn't right. This is my TableTuba 2x4, and the THT goes lower:

[OrangeJuices]

I rotated the subwoofer 90 degrees facing the horn out into the room along a wall. I moved the microphone to a different position ( to the listening position at the couch) and I tried a different amplifier, to no avail...

I also sealed up the inner chamber as best as I could, I applied tons of extra gasking tape around the driver and at the side panel. Then I added "bluetac" to all the screws on the side panel plus the small gap between the side panel and the subwoofer.

What could explain this lack of response?

Perhaps the driver is out of spec?

I thought I did a great job of sealing up the entire horn with the sides, but even if I did leave a small gap in the folded horn, how does this explain a 50dB loss of spl, matching the relative response curve of the driver in "free air".

[Bill Fitzmaurice]

Test another speaker.

[AudioTK]

What crossover do you have set in your AVR or amp or if you also use a DSP? It almost looks like high pass at some higher frequency like 50 or 80Hz and cutting below that.
But also like Bill suggested, test with another sub, even a different model. No matter where it's placed, you should have lots of ridiculous bass, but corner should help.

I just recently bought a 36x36x24 Tuba Horn with a Dayton DVC-385-88 15". I currently have it placed directly behind my 2nd row (not corner loaded at the moment) and had to DSP to get stuff to play nicely with my front three subs, MaelstromX 18 in 13.5ft³ sealed, Cerwin Vega Stroker 18D4 in a ported tuned to 23hZ, and an Ultimax UM15-22 in a small sealed box. It's got so much output! I am going to try corner placement this weekend. Not sure if I want to face it toward the back wall or toward the side wall.

[AudioTK]

I moved my Tuba Horn to the corner and the frequency response is better than when it was directly behind me. I have a BASH 300s amp on it with the gain just under 1/2 to blend with my other subs. For fun, I turned the gain to about 3/4 and it was so loud and clear. Soon, I plan to try it up front and move my 18" subs to the back, just to compare the overall response.

[Seth]

It's usually a steadfast "rule" not to ever mix subwoofers. The reason behind it is, every different cab/driver combo will have different phase response curves. In a perfect world the cone would always follow and faithfully mimic the input signal. But, for most of the frequency spectrum the cone is either leading the signal due to the suspension (mechanical and acoustic) pulling it back toward it's neutral position before the signal does or the cone can be lagging behind the signal at other frequencies due to the mass of the cone overcoming the suspension and returning late. The problem with using different cabs together is one cab can be early and the other cab can be late. In the best cases, this will just cause the cabs not to fully couple over the entire frequency range and EQ only helps if you have the capability to EQ them separately. In many cases it will cause cancellations, both cabs are getting the same signal but one cone is on the way in and the other is on the way out at certain frequencies. This is the reason it's never recommended and always best practice to avoid it.

That said, my personal fuzzy feelings and ever failing intuition lead me to believe it's possibly not such a bad thing in a small room, compared to a concert venue. A small room seems to be plagued with cancellations, dead spots, and frequency dropouts throughout the space no matter what. So, any ill effects of mixing cabs may be masked by ill effects of the small room. Or, it may just work fine. If it were me, I'd run testing on all locations for each cab separately as well as combined and choose whatever works best. Just be aware of it and if you run into problems with low output at certain frequencies that EQ doesn't seem to fix, try unplugging a cab or two and listen for changes. When you boost a frequency when there's deconstructive coupling, the amplitude increases in each direction causing a moot result.

I'm enjoying the read. Please, keep the updates coming!

[Rich4349]

What Seth said. As soon as I read "...my OTHER subs..." I had the exact same thought. Try it alone and see if the SPL increases, or at least sounds better to your human ear.

[invidiosulus]

Your screenshot of REW shows that you aren't using the calibration file for your UMIK.

[Radian]

I’m with AudioTK on this one…the plot looks like a high pass,when it should be a low pass. Check the filter settings. Running the subwoofer LPF too high (above 150) will also do this, but is easy enough detect with a voltmeter as the AC value will track in lockstep with the plot.

[Bill Fitzmaurice]

The OP hasn't been here since last September.