First DIY Sub - Sonosub project - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #11 of 14 Old 01-27-17, 08:35 PM Thread Starter
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Re: First DIY Sub - Sonosub project

Feeling under the weather today so those be a short post.


chrapladm - concrete slab foundation, carpeted floors. A house curve seems to sound better than flat. I posted about my listening area in the last one, I don't mind sharing some pics if that matters to anyone.

Will the ultimax 18 be good for:
music
quieter 60db listening or is it more of a come alive at higher sound levels type of driver?
Big xmax isn't as good for music right?

I like the idea of 2 tube subs with 18's. I'll play around with the modeling programs some more also. Modeling is new to me but I learn fast usually. I'd like to see 20 and 22 vs 24 diameter keeping under 50 inches tall.

I have a Behringer fbd for EQ. It's not fancy but it gets the job done.

Thank you for the responses, it's greatly appreciated

Mike
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post #12 of 14 Old 01-28-17, 12:06 AM
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Re: First DIY Sub - Sonosub project

In terms of a driver's "musicality", Xmax isn't necessarily a good indicator. What's far more important is it's Qts. This is a unit-less measure derived from it's mechanical and electrical "Q" parameters, which are descriptions of how much control the suspension (mechanical Q) and motor assembly (electrical Q) have over the motion of the cone. A low Qts has relatively stronger motor/suspension, and can react strongly to a signal. Higher Qts usually means weaker motors and looser suspension... but unfortunately, it's not that straightforward.

The short version is that in the world of low frequency, a higher Qts driver (neglecting all other parameters) wants a bigger encloser, and a lower Qts driver wants a smaller enclosure. However, one cannot design a box effectively using Qts alone as Vas (the volume of air that, when compressed to 1 m^3, exerts the same force on the cone as the suspension) and Fs (cone resonance in free air) are critical parameters.

A very "musical" sub can be designed with a low Qts driver in a small box, as can a high Qts driver in a bigger box... ports, sealed, IB, LLT, horn-loaded... if the design is good for the driver (and the intent of the system), any of it can work.

As for low-level listening, what's going to be make-or-break here is system sensitivity. Feeding a subwoofer signal levels below "reference" with a low-sensitivity driver will be underwhelming, and if you compensate with more power at lower levels, balance and system integration at higher levels may be off and require adjustment. 88.6dB nominal isn't amazing... but it's perfectly workable. The box will help, and with two separate drivers and boxes, your sensitivity is increased by a significant margin and you're much more likely to overbalance the rest of your system than you are to under-balance it. That's an easier problem to solve in the long run. In any case, you're pretty likely to notice the "come alive at higher volumes" phenomenon. It takes vastly more knowledge and experience than I have time left in my life to learn before I can tell you how to get around that problem... that's why good subs are expensive. When it comes time to drop the hammer and dispense some indiscriminate justice, more is more. The 22mm Xmax from those Daytons will displace more air, which is directly proportional to the happiness of the listener and inversely proportional to the happiness of their neighbors.

EQ - the Behringer FBQ is a much more powerful tool than a lot of people give it credit for. You're in good shape there.
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post #13 of 14 Old 02-01-17, 07:34 PM Thread Starter
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Re: First DIY Sub - Sonosub project

Hey all, moving a little slow, been fighting the flu since friday.

Ive been playing with winisd and want to make sure some of my conclusions are correct.
box volume is directly related to the tuning point, port length lets you tune the response curve,
Is there a good resource you can point me to to read, I prefer to understand at least a small percentage of what im doing before winging the rest.

Ive not been unable to get as flat a graph out of winisd as the previous poster so Im definitely missing something.
{Edit} I figured out the flatter looking graph

Last edited by mikeyd; 02-01-17 at 07:47 PM.
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post #14 of 14 Old 02-03-17, 06:27 PM
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Re: First DIY Sub - Sonosub project

Quote:
mikeyd wrote: View Post
Hey all, moving a little slow, been fighting the flu since friday.

Ive been playing with winisd and want to make sure some of my conclusions are correct.
box volume is directly related to the tuning point, port length lets you tune the response curve,
Is there a good resource you can point me to to read, I prefer to understand at least a small percentage of what im doing before winging the rest.

Ive not been unable to get as flat a graph out of winisd as the previous poster so Im definitely missing something.
{Edit} I figured out the flatter looking graph
Unfortunately, setting a box volume and tuning the response curve with the port length is not quite that simple. Yes, the box volume will affect the the tuning point, and yes the port length affects the point at which the port resonates, and yes adjusting the port length will move the resonance frequency of the port and therefore alter the curve of the box. HOWEVER... the total volume of the port is subtracted from the total volume of the port. So an increase in the length of the port results in an increase in the volume of the port, which is then subtracted from the volume of the box. So by increasing the port length without the corresponding change to box volume, you lower the port resonance, but raise the box resonance. If you compute the box volume based on a desired tuning point for the system as a whole, and that volume takes into account the air displaced by the port, and the port dimensions are optimal for the desired tuning point, you'll get a nice curve. If you shorten the port length, it's resonance goes up, but the box volume increases lowering the tuning point of the box. The inverse is true for an increase in port length... longer port means lower port resonance, but smaller box volume and corresponding higher tuning point. Either way you adjust, you're moving away from an optimized system... at least on paper.

The other thing to keep in mind is that the relative volumes make a difference. If you have a small box and a large port, a change to the port length is going to be a larger change to the box volume relative to the total and have a larger effect on the tuning point. Again, the inverse is true... for a large box with a relatively smaller port, changing the port length will amount to a smaller change in the box volume relative to the total and have a correspondingly smaller affect on the tuning point.

It would be nice if something were just easy for a change. Sorry about that.

I use this handy-dandy calculator from Mobile Information Labs to calculate a port length for a given tuning point.
http://www.mobileinformationlabs.com...0lenth%201.htm

It doesn't make account for any of the effects described above, but for a given box volume and tuning point and port diameter (or area for a square port) it will tell you how long the port needs to be.

Hope that helps more than it hurts. Or Hertz.
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