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Vented box for bass guitar design - HELP!
Vented box for bass guitar design - HELP!
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Old 23rd October 2017, 09:25 AM   #11
chris661 is offline chris661  United Kingdom
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Fair point, but they do seem to act that way.
Would it be better to say the output impedance effectively raises Qes?

Chris
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Old 23rd October 2017, 11:23 AM   #12
ChurritoTierno is offline ChurritoTierno  Paraguay
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Quote:
Originally Posted by David McBean View Post
Just to clarify - Qes and Qts are Thiele-Small driver parameters, they are independent of the source.

Qes is the driver resonant electrical Q at the driver resonance frequency, due solely to inherent electromagnetic damping.

Qts is the driver total Q.

Changing the value of the amplifier output resistance has no effect on Qes or Qts. This can be readily confirmed using Hornresp by entering a large value for amplifier output resistance Rg and checking the driver Thiele-Small parameter values by double-clicking on the Sd input box. Qes and Qts will remain unchanged.
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Originally Posted by chris661 View Post
Fair point, but they do seem to act that way.
Would it be better to say the output impedance effectively raises Qes?

Chris
I read in a book, actually was an example of enclosure calcutation where the author "modifieded" the Qes of the driver to take in account the output impedance of the amplifier... Qes (new) = Qes*(1+Ramp/Re)
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Old 23rd October 2017, 12:36 PM   #13
xrk971 is online now xrk971  United States
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Vented box for bass guitar design - HELP!
In Akabak, I can add a resistor, cap, inductor or any standard electrical component in the path. A complete crossover even.

So it looks like you are aiming for lower tuning and bigger box?
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Old 23rd October 2017, 04:19 PM   #14
freddi is offline freddi  United States
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Vented box for bass guitar design - HELP!
stacked

http://home.planet.nl/~ulfman/images/soundl12.jpg

Stanley's rig with helper tweeter

https://community.klipsch.com/upload...1928099972.jpg
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Old 24th October 2017, 02:42 AM   #15
ChurritoTierno is offline ChurritoTierno  Paraguay
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Originally Posted by freddi View Post
if just one 10 in a cabinet - then I'd suggest a Karlson enclosure. xrk971's "XKi" tread has dealt with dual stacked drivers with smallish front cavity and K-aperture. Rear chamber volume and system tuning would be set for "punch" - probably no more than 35L per driver. ChurritoTierno might ask xrk971 to run an XKi alignment for that (Eminence?) 10. I have a 0.62 scale "K15" - cutoff with even Beta10cx is quite high - Vb rear ~25 liter). A change in port area will change "voicing" but nothing much on a graph (why ?) The little K has 3-5dB more output in the 100-200Hz octave than Beta10cx in a 5 cubic foot Karlsonator tuned to 37Hz. Under sine conditions, when I played with obstructing part of the inner port with a narrow slot in a board, a lot of harmonics were introduced (modulated noise?)...
incredible job Freddi.
In reallity, i'm not very handy and don't really think that I could do that kind of wood working, even in 10 years..
Doing a simple vented box is really a challenge to me.

Quote:
Originally Posted by Gnobuddy View Post
Hello, and welcome!

The other question you asked - "Could I take some intermediate value for the box volume?" is an interesting one. Firstly, published Thiele-Small parameters for drivers are never exact, and there are also manufacturing tolerances to deal with between one driver (speaker) and another. Then there are correction factors like the volume of the loudspeaker itself (volume of magnet, plus conical volume of speaker cone) which subtract from the volume inside the box.

So there is really no way to get exactly the right volume the first time - usually, if you want it exact, you have to build, measure, modify, measure, and so on, until the speaker behaves the way you want. This is the normal way prototype speakers are developed in a factory, before the design is finally frozen and ready for production.

But how exact does it have to be? If the box volume isn't exact, the low-frequency alignment won't be exactly what you want. This means the frequency response won't be exactly the same shape you intended. But if the difference is slight, you probably won't be able to hear it; particularly because simply moving a perfectly designed bass cabinet into a different room will usually completely mess up the frequency response due to room interactions!

So if you already have a box that is nearly the right size, or perhaps you wind up using one less sheet of plywood by slightly changing the volume of the box, I would go ahead and just do it. It will probably make too little difference to matter.

This is bass guitar we're talking about, not precision audio monitor speakers, where you really want everything flat to less than +/- 1 dB if you can manage it.

And I agree about the bottom octave not being important: I usually use a 60 Hz high-pass filter with my 5-string bass, which has a low B tuned to 30 Hz. It sounds wrong if you come from the Hi-Fi world, but cutting off the bottom octave of the bass actually makes the bass sound better, less boomy, and it sits better in the mix with the drums.

-Gnobuddy
So, is there the posibility of blown the drivers beacouse I do not "hit the volume targed for a specific alignement"??
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Old 24th October 2017, 03:07 AM   #16
Ron E is offline Ron E  United States
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First you should attach some pictures of this driver so people know what they are dealing with. It may not be a suitable candidate.

Assuming it is suitable, I would probably do a 60-90 liter box and tune it to ~60 Hz or so. As another said, if it complains at low frequencies, add a 2nd order subsonic filter at ~60-80 Hz. You won't blow a driver by "not hitting volume target", you blow drivers by applying too much power or driving them with tones below their tuning frequency.

Skip the "Kult of Karlson" with the silly reflector business...
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Old 24th October 2017, 11:02 AM   #17
ChurritoTierno is offline ChurritoTierno  Paraguay
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Originally Posted by Ron E View Post
First you should attach some pictures of this driver so people know what they are dealing with. It may not be a suitable candidate.
Hi Ron.

This is the driver:

4 pack 10" 8 Ohm Eminence SWR Goliath Woofer Midbass Bass Guitar Speaker USA | eBay

I wrote to the seller asking the T/S parameters. He sent me this:

Re 10.87 Ohms
fs 55.9 Hz
Le 1.46 mH
Mms 30.4 grams
QM 8.23
Mmd 26.7 grams
QE 0.48
Cms 0.267 mm/N
QT 0.45
Rms 1.297 N*sec/m
Xmax 3.01 mm
Vas 46.5 liters
Pmax 150 Watts
SD 350.1 cm^2
Bl 15.53 Tm
VD 105.4 cm^3
Coil Diameter 2.00 Inches
EBP 116.1
Gap Height 0.313 Inches
Magnet Weight 38 ounces
Efficiency 1.63 %
Winding Width 0.550 inches
SPL 94.1 dB 1W-1m

By the way, is strange the value of Re = 10,87 Ohms for a 8 Ohm rated driver, don't you think?

I don't compared yet to the eminence CA10 specs,.. but the seller said me that both are very similar.. by the pictures It is obvious that the frame is identical...

I could copy a SWR cabinet but I don't know wich version of the Goliath used this speaker...

My first idea was to build two 2x10 for transportability rather than a 4x10.

Thanks to all for your answer!!!

P.D.: Sorry for my english.. For sure is really bad.
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Old 24th October 2017, 11:20 PM   #18
Ron E is offline Ron E  United States
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so it looks like the drivers are usually in a ~100-120L enclosure for 4 of them. Probably fairly simple to get an upper and lower bound on the tuning frequency. I'd guess the port at the bottom is perhaps 23" x 1.5" or so - 50-51cm x 4 cm Length could be perhaps 8-10" or 20-25cm . Assuming 100-120L is correct, it sims better wit ha ~65-70Hz tuning, IMO

Your english is fine, no need to be self conscious.
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Last edited by Ron E; 24th October 2017 at 11:47 PM.
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Old 24th October 2017, 11:48 PM   #19
PB2 is offline PB2  United States
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Quote:
Originally Posted by chris661 View Post
Fair point, but they do seem to act that way.
Would it be better to say the output impedance effectively raises Qes?

Chris
Yes, you are correct.
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Old 25th October 2017, 10:04 PM   #20
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by chris661 View Post
Valve (tube) amps add a couple of ohms output impedance. This raises Qes (and thus Qts), but not to infinity (which would leave Qms as the only damping).

Chris
We may not be thinking about the same kind of valve amp, but, FWIW, the question of valve amp output impedance came up on a guitar-amp thread on another forum. Valve guitar amps invariably have pentode outputs, and only a few dB of global negative feedback.

Even with 10 dB of global negative feedback (about the maximum you might find in a valve guitar amp), I estimated Zout - for a typical guitar amp with 6V6 outputs - was in the ballpark of one hundred ohms, a lot higher than the DC resistance of a typical loudspeaker.

If that estimate is even close to correct, the loudspeaker is, to all intents and purposes, being driven from a current source, because the amplifier Zout is more than an order of magnitude larger than the voice coil resistance. There would be essentially no damping due to back-EMF driven current flow in the coil, and driver mechanical Q would rise to virtually Qms in free air (and even higher if you then mount it in a sealed enclosure).

Here's the reasoning behind the back-of-the envelope amp Zout estimate I made: a 6V6 datasheet lists anode resistance of 77k at 315V on the anodes. A push-pull pair is typically used with an 8k anode-to-anode output transformer feeding an 8 ohm speaker; each half of the primary is therefore 2k.

Due to the output transformer, the impedance ratio from anode to speaker is therefore (2000 ohms/8 ohms), or 250:1.

Therefore a 77k anode resistance will appear, at the speaker, to be (77000/250), or 308 ohms.

Negative feedback reduces output impedance in proportion to the loop gain. If we have 10 dB global negative feedback, the loop gain is reduced by a factor of 3.16 times. The output resistance of the amp should be reduced by the same factor, to (308 ohms / 3.16), or 97.5 ohms.

It should be noted that there are plenty of valve guitar amps that use no negative feedback whatsoever around the output stage, so for those, the estimated output impedance is in the ballpark of 300 ohms.

Every factor in these calculations is approximate, so I just quoted the ballpark figure, i.e. 100 ohms output resistance.

I've never sat down and measured this, so if I somehow made a huge error in my estimate, please feel free to correct, and educate, me!

-Gnobuddy
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