Sub design

[Andrew Pratt]

What I meant is that even if it fires forward wouldn't the location of the floor/sidewalls have an imact as well?

[TEK]

About direction. I have always assumed that downfireing is not the best direction, however, for my usage (view start of thread) I'm afraid down is the only way to go.

About EQ. As the ADA amp only supports 2 EQ bands, it clearly does not cut the cake as the sole EQ solution for my need. :cry:

What do you folks use and what do you reccomend to use to equalize the sub?
According to Andrews input, I guess it should support approx 10 bands.

Spearmint:
The HS is quite expensive from the Norwegian dealer. Approx 1000 USD for the HS500.
The EQ issue was one of the ADA amps advandages, but now that seems to have been lost. Still, the 1200 ADA is way cheaper than even a HS500. So then the question is; Who is the best amp for the task!

Regarding the distance, I assume that the figures you are talking about is related to the distance from the plate the amp is mounted on to the floor.
I would like the sub to be quite close to the floor, preferrable 2". I think I will run into some estetical issues if I lift it more than 3" (and I will start loosing volume).
Does anyone know if issues related to this is of a kind that is possible/easy to handle with a equalizer, or would it be "incorrectable" issues?
Could anyone tell me if the problem is related to the total air-flow below the sub or the fact that the sound waves is reflected when hitting the floor. In my case, the amount of air allowed to flow under the sub will be quite large, as the sub area is mutch larger than the element dimension.

Thanks again for all the inputs.
Best regards, TEK

[ThomasW]

People, people, people, gees.... :roll:

The radius height is the theoritical height for no resistive loading. Below this height there is loading, and how audible it is depends on the room gain.

Designers like Tom Vodhanel go for everything they can get. It makes the sub 'spec' better for measurement/marketing purposes.

Depending on the frequency the resistive loading boost can easily be masked by the effects of room gain.

TEK

2" is too low for a Tumult. Take a look at the Xmax and subract that from your 2". Not much clearance there. This is the first info posted that you were planning on a down firing design. 4" is probably as low as one should go with a Tumult.

[Bent]

I'm guessing that this would be much like (ok, similar loading effect) to a single port band-pass box?

[Spearmint]

Spearmint:
The HS is quite expensive from the Norwegian dealer. Approx 1000 USD for the HS500.
The EQ issue was one of the ADA amps advandages, but now that seems to have been lost. Still, the 1200 ADA is way cheaper than even a HS500. So then the question is; Who is the best amp for the task!

Wow that is expensive...

Stick with the ADA1200 amp, or otherwise buy a pro amp to power the sub. Even the Behringer power amps work well according to users.

Check out Tom's Review

[Andrew Pratt]

For EQ the one most of us use is the Behringer FeedBack Destroyer.

[TEK]

2" is too low for a Tumult. Take a look at the Xmax and subract that from your 2". Not much clearance there. This is the first info posted that you were planning on a down firing design. 4" is probably as low as one should go with a Tumult.

You do of course have a very valid point regarding the xmax vs the height. I'll do some calculation. This will problably cause my total volume to be bit smaller than inititally tought, problably no problem tough.

From the first post:
"I think the control panels for the sub will be on top of the sub box, but under the top covers. The element(s) will have to be pointed downwards."
I'm sorry I did not make it more clear, the statment is kinof hidden within the rest of the text, so it's very understandable that you did not notice it.

[TEK]

For EQ the one most of us use is the Behringer FeedBack Destroyer.

Ahh, the famus BFD.
Guess I will have to get me one of those then :T

[Andrew Pratt]

Guess I will have to get me one of those then

They're mandatory around these parts

[TEK]

I have a little follow up question regarding element vs. volume.

As I have understood, the Tumult driver is at it's best with a volume around 80-100 liters.
How will considerable more volume than this affect the sound result. I know it will give me a lower q, but what will be the sound differences?

In my cabinet I might actually have room for two 15" tumult with 80 liter volume each. How would that affect the total sound quality? (I do not think this is really is an option, but I'm curious about how this stuff works)

A different solution, given the volume, would be to go for a Avalanche 18" with a q around 7.5 or so, or -if the rumors are correct- await for the new Adire Tumult 18"...
What would be gained/lost on going for an even larger element. 18" :E We're talking BIG here 8)

A clue issue here might be:
What differences does actually a how vs low Q give.

Please execues these silly questions, just trying to get a better understanding of the basic "stuff" in work... ops:

[JonMarsh]

Hello Eric,

I usually stay off the sub threads, but maybe I can help with a few points.

First, regarding the change of Q - there are three main effects- but they interact for any given driver.

1) The ouput pressure level at the nomal corner frequency is a function of the Q. A Q of 0.707 (Butterworth alignment, maximally flat) means the pressure (voltage in electrical terms) is 0.707 times the nominal passband input (-3 dB). At a Q of 0.5, the output is 0.5 at the corner frequency (-6 dB). For lower Q's, the output at the corner frequency continues to drop.

2) For a given driver and T/S parameters, dropping the Q means a large box and lower tuning, so though the nominal level is lower at the Fb, the Fb is also lower, as well as the rate of roll off. That is, for a 0.7 alignment, the roll off is at 12 dB per octave even just below the corner frequency. For lower Q alignments, the initial roll off will be at a shallower slope, in the range of 6-9 dB/octave, depending on the Q. This affects the extension in room with room gain. A low Q design will be perceived to go deeper, with a less abrupt drop off.

3) The Q affects the natural transient response. A Q of 0.5 is crtically damped. A Q of 0.7 has some overshoot and a longer settling time.


ALL of these parameters and performance issues can be traded off using a Linkwitz Transform equalizer- up to a point, allowing use of a smaller box. The point being that you need extra power, and the smaller you make your box, the more extra power. The lower the frequency extension, the more extra power. Eventually, your amp runs out of extra power, or your voice coil doesn't have enough thermal power handling.

One way you could get a lot better feel for how these parameters work and interact is to try out your potential designs in Unibox on Excel. You can play with the volume, look at the response traceoffs, power to get a given output, etc. That's free... With a real desgn program like LspCAD standard, you could model the complete setup including EQ, but that's probably not really necessary- may as well save the money for your drivers and amp.

Just remember, what you'll save in box volume, you'll spend in amplifier power and increased thermal stress- but that may be the best trade-off for you and your wife.

Regards,

Jon

[TEK]

Thanks a lot for the input Jon.

I have downloaded the Unibox, and have testet a bit.

I have been testing the spreadsheet with the Tumult 15 and the Avalanche 18.

I believe I got the "correct" answer (shown below).
I'm targeting 140 liter Physical VB as that is approx the size I believe my box will be after bracing and driver

I'm getting the graphs included.

It shows that they will have approx the same SPL at 10hz, given the same amp.
However, if I understand this correct, the Adire will only be able to handle 480W, while the Avalanche will handle 770W, before reaching Xmax .
Using these values as the nominal power result in a graph where the Avalanche has a level of 98db or so at 10Hz. The Tumult 94db at 10Hz. :T

If this is correct, that should indicate that it, theoretical, should be possible to get a even respons down to 10Hz at 94DB using the Tumult and a 500W amp. This can't be correct :E ???

The Avalanche 18 will have to be tuned to a Q of 7,4 for the given volume, while the tumult will be tuned to a Q of 0,46.
So the resulting Q for the same volume is hugely different for the two drivers (as expected).

I notice that, as you said, the roll off for the adire (with the low Q) is less than for the Avalanche 18. However, the Avalanche 18 seems to have a more linear roll off.

If I understood you correctly, a low Q would result in better transistent response, something that is of importency for a "musical" sub. This should indicate that the Tumult would be a better choice for the given volume, or?

For a good music reproduction sub where SPL is not at the highest importancy, which of these curves indicates the best solution?
What other factors should be considered here expect from the curve?

Last: Am I close to some correct conclusions here, or I'm I way off?

[ThomasW]

TEK

10Hz isn't a frequency that anyone should be concerned with (unless it's being aimed at you from a weapon). Human hearing craps out below 20Hz unless the SPL is extremely high, then one can 'hear' down to about 18hz. Below that it's all tactile, and your bones really don't discriminate lower frequencies, it's all just 'shake'.

If you want to drop from 20Hz to 10Hz at the same SPL, doing so requires doubling the swept volume. So use 20Hz as the frequency to compare output levels...

Also comparing the Tumult and the Ave 18" isn't an apples vs apples situation. This is like comparing a V-6 vs a V-8.

Deciding which driver to use should be based on your needs. Most people would be extremely happy with a Tumult. If the room is very large or if very high SPLs are needed then a higher excursion (more swept volume) is needed.

[TEK]

Thanks for the input Thomas.

The most important point with this was to see if I was able to use/read/understand the parameters/values correct. (was I?)

Regarding hearing range:
I'm aware that the human ear is limited down to 20Hz. However, what you actually hear is one thing. What you brain and body register is a different story. When your floor starts to shake, you will feel it and it will influence your impression of what you hear.
A different issue is that it will problably make you sick ;-)

Apart from that I agree that in this discussion 10Hz is not important. I used that value as it was the lowest value indicated by the unibox.

Just curious, will not a overdimensioned solution be working on less strain during normal usage and therefore be likely to give a better end result?
Is the issue here that you might be in danger of overloading the room and be unable to "tame" it down to the correct values for integration?

If I could choose between a V6 and a V8, I for sure know what I would have choosen. Especially if the V8 was 100$ off the price tag...
Given that the V8 was of the same or better quality/peformer as the V6...

I'm very happy about the input, and I'm absolutly planning on following the advices, but I also want to understand what's the idea behind the suggestions...

Best regards, TEK

[ThomasW]

Hi

Jon will run the numbers tomorrow his fingers are numb from typing....

Just curious, will your wife let you keep a V-8 in the living room? :wink:

My head was 'weird' for 24hrs after playing 5Hz test tones when I first built my big IB ....... xx)

[TEK]

Just curious, will your wife let you keep a V-8 in the living room?

The box in the center here is the ekornes "double pallet":



My sub will be a duplicate of this with lether of the exact same type as our other ekornes furniture:



The outer measurement of the ekornes "double pallet" is 60cm x 120cm x 48cm, giving me a outer box size of 345 liters to play with :T

So, yes, I'm allowed to have the V8 :lol:

[Masterp2]

You never want to say

"I could have had a V8! :M "

[TEK]

You never want to say

"I could have had a V8! :M "

I'm not quite sure that I actually can have the V8 ops:
I have done some more detailed calculation of my actual avilable box volume, and come up with the following:

My box seems to be given by the following parameters (all values in cm/liter):
Outer length 120
Outer height 35 (48 - 8cm clearance to the floor - 5cm stuffing on top)
Outer depth 60

Sidewalls 4
Top 4
Bottoms 6

Bracing thickness 2
Number of braces 4

Volume needed by driver 4,04
Volume needed by amp 3
Volume needed by equalizer 6 (I want the qualizer built in, no extra boxes)

Outer volume 252
Inner volume, no bracing 145,6
Inner length 112
Inner height 25
Inner dept 52
Bracing volume 10,4
Available inner volume 122,16

That leavels a bit less than what I was counting on intitially.

Another issue is that a 18 would problably be more likely to break up in the upper bass region, and that is not something I want.

It also does seems like the tumult might have some weeknesses in the area above 50Hz, and that put me a bit on hold regarding it.
If the Avalanche 15 was shipped internaltional, that might be a better choize given my priorities. But nothing is setteled!

Even if the sub of course mainly will be working in frequences below this, it will affect the sound a good way up.

The fun part is that I'm learning stuff all the time here :T