Dayton RS HiFi 12" Sub using Linkwitz Transform EQ--Design Proposal

[dfdye]

Hi!

I have been searching for some design ideas for the Hi-Fi version of the Dayton RS 12" sub, especially since they are sale this month, but I have yet to find any that have caught my eye. Thus, I figured I would throw something out there for comments before diving into building a new sub. This is my first attempt at designing a speaker, so any comments are more than welcome!

Here are my design goals:
“Moderate” box size
Sealed box
Usable response down to 20 Hz
Cheap!!!

I want to use a sealed box, both for ease of construction and to avoid port issues/noise. Of course, a good starting point would be to model the response of the speaker in the box, so I used WinISD and got the response below in a 1.9 cu. ft. sealed box. Obviously there is a lot missing on the low end. To solve this, I would like to use a Linkwitz transform circuit as an EQ to bring up the low end. Modeling this circuit to try and get f3 of 20 Hz gives, what I believe to be, pretty reasonable values without too drastically having to boost the low end. (If the circuit/component values would be helpful, I’ll post them too!) I know the ~8dB boost at 20Hz is a lot to ask of the amp, but as I said, I am not looking for massive output in that frequency range—just something reasonable.

I figured a Bash 300W plate amp would be a nice fit for this since I am not trying to tear the house down with this sub. Also, I would be worried about too much power for this driver if I went with a 500W amp. If I do need more output, I can add another unit, but I am not really a volume fiend (not that that is bad or any thing!) so I doubt that I will ever push this unit to its max. (Famous last words, right??)

If anyone has comments as to the viability of this design or comments about using Linkwitz transform circuits, I would love to hear them!

Thanks!
David

[mazurek]

I would suggest not to linkwitz transform it down to 20 hz, 30hz is a more reasonable target in my opinion for the sealed subwoofer. I have solely a rumble filter at 16hz, and the cone looks like it is excursing about as far as it should at respectable listening levels, I wouldn't want it to go further.

Also, try playing with the sub and test tones once you build it. I can't hear anything below 30 hz even though I'm sure there is output (spl meter, plus parts of house resonate). I would like to hear other's thoughts on this.

I believe linkwitz discusses somewhere on his site the pros and cons of his transform with respect to excursion limits. Look at his thor subwoofer, it is very similar in my opinion to a sealed dayton rf.

Another issue, factor in the lowpass to the sub into the winisd model. It looks more like an upside down parabola, and the -3db point relative to the peak spl output from the sub will be lower in frequency.

[dfdye]

I have indeed looked at Linkwitz's web page, and his Thor sub based on the Peerless XLS 12" was what gave me the idea for this design. He uses a more complicated crossover topology for the Thor than what I am interested in, but he also takes the boost out well past 20 Hz. That may very well be driver dependent, so I will definitely heed your suggestions about the excursion limits of this driver and play with the LT circuit before making anything permanent.

From your comments it sounds like you have one of these drivers already--is this accurate? I would like some feedback (positive or negative) about this sub since so few opinions exist from people who have actually used this driver.

As for your question regarding hearing below 30 Hz, I think I can hear down to ~20, though below 25 it is primarily feel with a little reinforcement with the ears, if that makes any sense. For me there is definitely a steep roll-off below 25, though I am not confident that I have ever really heard a system capable of producing high SPL low frequencies that would let me claim this 100% yet. Anyway, I would love to have down to 20 Hz just to have all of my bases covered (though I am still a LONG way away from considering one of those fan subs to get down to 1Hz!)

[mazurek]

Yes, I have 2 x sealed subwoofers with 2.2 cubic feet and the dayton hf 12". I definitely don't think they are holding my system back (stereo martin logan mosaics to be replaced with diys). I'd say they are clean, but that will depend on how you design the sub crossover, I think Linkwitz transforms are good for group delay. The way I have them crossed now (just a rumble filter), they make movies fun but don't quite rattle the house.

I can't give any critical audiophile comments as I don't have golden ears, and they are not crossed over correctly into my mains because they will be moved shortly(should be 24db/oct).

If you want, I can post a measurement for 25 hz spl, just tell me, but I got to go to class now.

[dfdye]

I would love to see what they do at 25 Hz if it is not too much trouble. Thanks for offering!

[owdi]

Before you design a sub to be flat down to 20hz consider the impact of room gain. Check the help in WinISD for how to estimate room gain with a Linkwitz Transform.

Dan

[DSP_Geek]

Originally posted by owdi
Before you design a sub to be flat down to 20hz consider the impact of room gain. Check the help in WinISD for how to estimate room gain with a Linkwitz Transform.

True enough, but room gain comes in at +6 dB/octave while sealed boxes roll off at -12 dB/octave, so there's still a case to be made for Linkwitz transforms. The good doctor himself offers crossovers with both a LT and a switchable 50 Hz first-order high pass.


Cheers,
Francois.

[dfdye]

Originally posted by DSP_Geek
True enough, but room gain comes in at +6 dB/octave while sealed boxes roll off at -12 dB/octave, so there's still a case to be made for Linkwitz transforms.

Indeed, but I made the classic mistake of forgetting that I will actually use the speakers in a room and not in the computer! I am trying to rectify that now.

[mazurek]

I was watching the cone, and playing a 25 hz test tone. From watching some white dot on the cone moving back and forth, it looked like about 12 mm peak to peak excursion resulted in 90 dB at 1 meter using an uncalibrated radioshack digital meter (+5db if same calibration as analog). I stopped there because my house was going to explode, and my subwoofer is my baby and I don't want to hurt it.

I think it would get about 6db more at full excursion according to winisd.

[dfdye]

Originally posted by mazurek
I stopped there because my house was going to explode

Nice!! Thanks for the measurement.

As another EQ option I have been looking at the built in bass boost of the Bash amp. Taking room gain into consideration (thanks owdi! though I am not sure I am doing it right yet. . . .), enabling a +5 db boost at 20-24 Hz smooths out the low end fairly nicely. Of course, without room gain, the bass boost doesn't do enough--thus the original proposal for using a LT. There is a little peaking, so I am sure I am going to have to play with the system to get it right once it is in the room, but eliminating the LT would definitely simplify things.