Xmax, efficiency and enclosure confusion

[Myleso]

Hi everyone

I am super new to DIY audio and just audio/electronics in general so you'll have bare with me. This will be my first speaker build.

I have been looking at the Dayton Audio RSS265HF-4 10" Reference HF Subwoofer to put in a sealed enclosure and simulated a few different box sizes using WINisd. The driver has an RMS of 350W, Xmax of 12.3mm and a recommended sealed enclosure volume of 0.53 ft^3. In a 0.53 ft^3 enclosure the driver doesn't reach Xmax at 350W input however, when the enclosure is 1.5 ft^3, the driver exceeds Xmax at low frequencies even with 150W input. I may be thinking about this all wrong and bare in mind I have no history in physics, electronics or anything audio but does that mean that the driver in the 1.5 ft^3 box would be playing just as loud with 150W supplied as the driver in a 0.5 ft ^3 with 350W supplied? Would I only need an amp rated at 150W? If I am wrong please correct me.

My aim with this sub is to get as lower frequencies as possible in a simple to build, relatively small box that will produce quality sound at a reasonable but not ridiculous volume. It will be accompanying my B&W 686 S2 bookshelf speakers. If you know of a great 10'' sub that suits this application please let me know.

Thanks!

 

[doctormord]

It's a (mechanical) damping problem. The bigger enclosure does "underdamp" the chassis, so cone movement is much higher.

The bigger enclosure gives you deeper bass at the cost of power output (limited by x-max), the smaller enclosure gives you more loudness/output at the cost of lower frequencies.

 

[AndrewT]

the maximum volume at any single low frequency is limited by Xmax.
Your driver's 12.3mm Xmax determines the maximum SPL at any single low frequency.

The box loads the driver.
That load changes the resonant frequency of the speaker and changes the Q (damping) of the resonance.
If you use windisd, you can determine the Butterworth roll off. That volume of box makes the Q= 0.7071 = 1/sqrt(2) and gives a fixed resonant frequency. This is the F-3dB of the loaded driver. The T/S parameters determine what volume of box gives the Butterworth roll-off.

Make the box smaller and the resonant frequency and the Q both go up.
Make the box bigger and the resonant frequency and the Q both go down.
The max SPL at any particular frequency is the same from all those different boxes, because the SPL is determined by the Xmax at low frequencies.

At higher frequencies where Xmax is no longer the limiting condition, the SPL is determined by the power input.

 

[Zero D]

Hi, i don't know you've opened a new thread ?

My Sim with that driver with both a Closed "White" & Reflexed "Yellow" box of 1.5 ft^3 The reflex fb = 25Hz. I used a 24db LR HPF @ 20Hz for both

Reflex box vent Int round size = 102mm x 847mm whose area needs to be added to the Net box size. Doesn't have to round, change the shape in WinISD.

The reflex seems ok to me 🙂

 

[just a guy]

... does that mean that the driver in the 1.5 ft^3 box would be playing just as loud with 150W supplied as the driver in a 0.5 ft ^3 with 350W supplied? Would I only need an amp rated at 150W?

Thanks!

Yes and yes. I think that's the 5th time I've answered that now.

the maximum volume at any single low frequency is limited by Xmax.
Your driver's 12.3mm Xmax determines the maximum SPL at any single low frequency.

The box loads the driver.
That load changes the resonant frequency of the speaker and changes the Q (damping) of the resonance.
If you use windisd, you can determine the Butterworth roll off. That volume of box makes the Q= 0.7071 = 1/sqrt(2) and gives a fixed resonant frequency. This is the F-3dB of the loaded driver. The T/S parameters determine what volume of box gives the Butterworth roll-off.

Make the box smaller and the resonant frequency and the Q both go up.
Make the box bigger and the resonant frequency and the Q both go down.
The max SPL at any particular frequency is the same from all those different boxes, because the SPL is determined by the Xmax at low frequencies.

At higher frequencies where Xmax is no longer the limiting condition, the SPL is determined by the power input.

This is a nice answer and pretty much what I've already told him 5x now. With pictures. It seems the only thing that's going to work in this case is simple yes or no answers as I've provided above. Getting into details isn't helping even though the details are pretty important.

 

[Myleso]

the maximum volume at any single low frequency is limited by Xmax.
Your driver's 12.3mm Xmax determines the maximum SPL at any single low frequency.

The box loads the driver.
That load changes the resonant frequency of the speaker and changes the Q (damping) of the resonance.
If you use windisd, you can determine the Butterworth roll off. That volume of box makes the Q= 0.7071 = 1/sqrt(2) and gives a fixed resonant frequency. This is the F-3dB of the loaded driver. The T/S parameters determine what volume of box gives the Butterworth roll-off.

Make the box smaller and the resonant frequency and the Q both go up.
Make the box bigger and the resonant frequency and the Q both go down.
The max SPL at any particular frequency is the same from all those different boxes, because the SPL is determined by the Xmax at low frequencies.

At higher frequencies where Xmax is no longer the limiting condition, the SPL is determined by the power input.

Thanks you. That provides some crucial concepts I hadn't grasped from other explanations.

This is a nice answer and pretty much what I've already told him 5x now. With pictures. It seems the only thing that's going to work in this case is simple yes or no answers as I've provided above. Getting into details isn't helping even though the details are pretty important.

A yes or no answer accompanying a larger picture explanation is very helpful. As I have said many times, I have almost no experience with physics, electronics or audio engineering. Things that seem simple to you are not for me. Thanks so much for the time and effort you have put into explaining these things though. I have a much better grasp on it all now 🙂

Thanks everyone, I'm just going to put this driver in a 1.3 ft^3 sealed enclosure and be done with it.

Cheers

Myles

 

[AndrewT]

........................I'm just going to put this driver in a 1.3 ft^3 sealed enclosure ...............

Find the sealed box Q and see the shape of the response in that 1.3ft^3 box.

You can adjust the Q to change the shape of the roll off using a Linkwitz Transform.
You can adjust the resonant frequency to change the location of the roll off using a Linkwitz Transform.
You can adjust the Q and the resonant frequency to change the shape and location of the roll off using a Linkwitz Transform.

Go to the Linkwitz site and read about the LT. It's a lot of arithmetic when you come to do the sums and start implementing the LT. But at least read about what it can do AFTER you have fixed your box and driver.

 

[Myleso]

Thanks for the tip. I had a little look at the Linkwitz Transform and it all seems pretty confusing. As I said earlier, I have no experience with this stuff and the the arithmetic involved would likely kill me. Is there a simple way to use one that wont require a great deal of understanding?

Thanks,

Myles

 

[picowallspeaker]

Just work with the active crossover that precedes the amplifier.
Set the crossover point at minimum and play with the volume.
The frequency where the subwoofer and the satellites meet should be at -6 dB for both.

The LT in real world is just a bunch of components around a dual op-amp.
About 1 hour work on a perforated board and the necessary PSU ( + and -
12-15 V )

 

[Zero D]

Linkwitz Transform

WinISD can sim that too 😉

Be aware that boosting the LF with a LT etc will cause Xmax to be reached a Lot sooner, & also power max !

 

[AndrewT]

Find the sealed box Q and see the shape of the response in that 1.3ft^3 box.

You can adjust the Q to change the shape of the roll off using a Linkwitz Transform.
You can adjust the resonant frequency to change the location of the roll off using a Linkwitz Transform.
You can adjust the Q and the resonant frequency to change the shape and location of the roll off using a Linkwitz Transform.

Go to the Linkwitz site and read about the LT. It's a lot of arithmetic when you come to do the sums and start implementing the LT. But at least read about what it can do AFTER you have fixed your box and driver.

WinISD can sim that too 😉

Be aware that boosting the LF with a LT etc will cause Xmax to be reached a Lot sooner, & also power max !

the LT does a lot more than boost the LF.
Note I gave three different adjustment scenarios and none mentioned boosting the bass.

 

[AndrewT]

................Go to the Linkwitz site and read about the LT. It's a lot of arithmetic when you come to do the sums and start implementing the LT. ..................

Thanks for the tip. I had a little look at the Linkwitz Transform and it all seems pretty confusing. ...............

Initially forget about the arithmetic. Just read what the LT can do and keep that in your head for later.

But at least read about what it can do AFTER you have fixed your box and driver

 

[Zero D]

@ AndrewT

If he wants an extended LF in a 1.3cuft box, then boosting the bass by EQ/LT is what's required.

Bass boost LF extension shown quite clearly in here Active Filters & here ESP - The Linkwitz Transform Circuit

 

[AndrewT]

I have read about the LT.
I know that it can do lots to change the way a speaker reproduces.

 

[Zero D]

@ AndrewT

So why did post this ?

Note I gave three different adjustment scenarios and none mentioned boosting the bass.

When boosting the bass to get an extended LF is what he wants !

 

[AndrewT]

@ AndrewT

So why did post this ?



When boosting the bass to get an extended LF is what he wants !

what he asked

Would I only need an amp rated at 150W?

and he went on to make the comment

My aim with this sub is to get as lower frequencies as possible in a simple to build,

which turns out to not include the complexity of using an LT because he is afraid of the number crunching.
In the meantime he has learned and acknowledged that he now knows that the Xmax determines his LF SPL and box size determines the resonant frequency and Q of the LF response.
No where did he ask for an LT to extend his bass response.

 

[Zero D]

@ AndrewT

Originally Posted by Myleso

My aim with this sub is to get as lower frequencies as possible in a simple to build, relatively small box that will produce quality sound at a reasonable but not ridiculous volume.

LT will do that

Originally Posted by AndrewT

No where did he ask for an LT to extend his bass response

You suggested LT

Go to the Linkwitz site and read about the LT.

He wasn't asking for Q etc info, but wanted what he said in his quote above. Going to the Linkwitz www etc, he would discover that a LT would extend his bass response, as he wished. Whether or not he decides to do that, is up to him. But now he knows that's one way it can be done

 

[Myleso]

Haha thanks for all the info guys. All information is helpful to me at the moment. I think ill miss the LT this time, I am happy enough with the frequency response anyway. But now at least I know for future subwoofers 🙂 Just quicky, when an amp says for example '6db boost at 30hz' is this a form of equalising? and surely that +6db isn't just at 30hz but also the surrounding frequencies?

Cheers!

 

[Ron E]

Just quicky, when an amp says for example '6db boost at 30hz' is this a form of equalising? and surely that +6db isn't just at 30hz but also the surrounding frequencies?

Any boost or cut is EQ.

Look at the response of a 2nd order sallen-key highpass with a Q of 2 and you will find your EQ response shape.
(Sample)Sallen-Key Low-pass Filter Design Tool - Result -

 

[homebuilder]

Myleso, try a few things.....

I completely understand your "pain". I've been reading this forum for years, and have many of the same limitations you have. I'm trying to get help with a project myself right now. My observation of this forum is that there are a lot of lurkers on this site, who despite their posts, probably never build a project. Then, there are guys who build stunningly beautiful speakers, to the point where I can only imagine that they are supremely talented, or own professional manufacturing spaces. Or both. And then there is this vast area in between. I suspect that many of the people on this site are of the engineering persuasion. I've read posts where they argue about technical points for 50 pages, but won't answer a question for someone like you, in a simple manner.

Although my moniker is homebuilder, that is not my profession. That is my hobby. I sell high technology, cutting edge equipment, and have personally mastered one of the most difficult languages in the world, but I still cannot grasp the math, and the technical aspects of speaker design. That is why guys like Andrew Jones exist. I also work with engineers all of the time, and they tend to be dismissive of other professions. But, put them in front of 200 people and ask them to give a speech, and they will turn red and start puking their guts out due to being nervous.

I think there is an incredible marketing opportunity here, for one of these really smart guys on this forum to offer paid services to guys like you and I. Design us a crossover. I'm not speaking for you, but I'd gladly pay. I've proposed that in the past, and have been ignored. My thought is that I've built a dozen houses by myself...what is holding everyone else up on this site?? It is DIY....

I have a couple suggestions for you on this site:

1. Look for a kit that you can build, that is well documented. Dayton sells some nice kits. I've looked at their Ultimax 15" and 18" drivers, and kits. They seems like a super bargain. May be bigger than what you need.
2. Look at designs like Pi Speakers, DIYaudio, Linkwitz kits from Madisound, etc.
3. Look at the Cult of the Infinitely Baffled site. Don't know if you can apply that in your case though. I can in mine, and they are super easy to build.
4. Consider whether you would rather just work some extra hours, make a few extra bucks, and order something on line, or from a local stereo shop.

Good luck with your project. And, no offense meant to any member of this forum. Differences are what make this world go around, and account for the fact that somehow Donald Trump got elected to the Presidency.