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Old 19th August 2002, 07:36 AM   #1
Raka is offline Raka  Europe
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Default Minimum volume matters

Hi all, I need your opinions:

I'm planning a modest project, and with WINISD and the driver selected I get an enclosure smaller than 3 l, is that a problem?, I mean, is not such a small size going to be problems unknown to me? the specs claim for a 10 to 20 l, but if so, the response is not flat but with a 3db peak. is that audible? Would be this a boominess?

Thank you,
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Old 19th August 2002, 09:44 PM   #2
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Ported speakers frequently can be 3 or 4 times the size of a sealed speaker. The ported speaker will naturally go much lower.

Please give the specific make and model of speaker we are dealing with here. Also, do you want to make it a ported or a sealed enclosure?
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Old 20th August 2002, 02:23 AM   #3
Ron E is offline Ron E  United States
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One thing that matters, when you make a vented box bigger than that calculated by a standard formula, you often need to lower tuning to avoid a peak in response. There is nothing wrong with lowering tuning by trial and error with a program until you reach a response that is suitable. Many drivers with lowish Q's ~.2ish need this treatment.

One caveat, if you do this to extremes, (especially with relatively high Q drivers) you will get a driver that will respond very low, but will handle very little power and perform poorly. It is nice to have a program that calculates excursion to help you know when the limits are being approached.
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Old 20th August 2002, 06:27 AM   #4
Raka is offline Raka  Europe
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Default Minimum volume

Thanks for your replies,

What I mean is if a very small volume, given with the WINISD, would give a problem. I haven't decided yet if closed or ported, but both give an optimum response for 2 or 3 l, and the manufacturer suggest 10 to 12, is that a problem? does this means that the driver can performance a flat curve?
I know how to use the software to avoid a peak with a big volume, and the excursion vs power point, but it looks like 2 liters for a 5,5 driver... maybe is a driver for a line array configuration...
I'm sorry I forgot, the driver is the beyma 5MP60/N, fs=60Hz Qts=0.28 and vas=9,8l.
your help is greatly appreciated, guys
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Old 21st August 2002, 12:04 AM   #5
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Are you using these as standalone speakers, or as satellites to be crossed over to a subwoofer?

I can give you a configuration that will give you actually decent bass. It is ported. If you are going to cross over below 140 Hz to a subwoofer then I would recommend a sealed.

This ported configuration has a group delay of 14 ms, which is a little high. Still, for a 5 inch in such a pint sized box, it will give surprising punch under higher power levels than you'd think you could drive a 5 inch.

One thing. I do not know if this has a symmetrical magnetic field in the magnet structure. Sometimes the voice coil of ported speakers, near the resonance frequency, will travel all the way back to the end of their excursion limits and just move forward from there.

Assuming it does not do this, though, the Beyma can, in a ported box, put out 106 dB at 60 Hz, with 65 watts input. For a 5 inch in a 1/3 cu ft box, that is kicking.

The volume of the box is 10 liters, and the tuning is 60 Hz. It is not a classic response where the level is flat until the end, where it dives down. This gradually moves down 3 dB, then dives at the end. Not a bad response, though.
It should be noted that most PA cabinets that DJ's use-the ones that are about 3 cu ft, (80 liters)-have a 60 dB cutoff. They play much louder, of course, but it is an illustration of how deep 60 Hz is if professional DJ equipment has the same bass cutoff.

Again, if you are going to use these as satellites, I would suggest a much smaller sealed enclosure.
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Old 21st August 2002, 06:36 AM   #6
Raka is offline Raka  Europe
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Default Ported vs sealed vs group delay

Thanks a lot for your reply and your nice volume study!!

They are going to be not satellites but a simple speaker system for "kitchen" and non critic people stereo purposes, but as it is my first design (don't tell anybody...) I want to include all I've learn in the net.

With the same kind of response you gave me, I was thinking of a 7,7 lit, and F3 is 71 Hz, that I think is good enough for the time being. I didn't consider the group delay effect because I don't have the point cleared: Does this mean that (due to the port mainly) some frecuencies are delayed i.e. not time aligned and the bass might not sound "clear"? I imagine that because of that, if the system is crossed to a sub it "needs" to be sealed, am I right?
About the power managed, you stated 65w, I think this has to do something only with the excursion, right?
And what if I want a plain flat response until the cutoff? my winisd tells me that 3 l are to be needed, is there any minimum volume to respect? Does this make appear any problem due to the high pressure inside?
Thanks a veeeery lot,
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Old 21st August 2002, 08:22 PM   #7
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Default Re: Ported vs sealed vs group delay

Quote:
Originally posted by Raka
I didn't consider the group delay effect because I don't have the point cleared: Does this mean that (due to the port mainly) some frecuencies are delayed i.e. not time aligned and the bass might not sound "clear"? I imagine that because of that, if the system is crossed to a sub it "needs" to be sealed, am I right?
I'm not all that sure about what group delay is exactly either. However, I have read that it is a good indicator of transient response, which is the ability to follow a signal exactly. "Overhang" is the opposite of transient response-the speaker is overshooting the point where the audio signal tells it to stop.

All speakers have some of it at the bass frequencies, but some have it much more than others. Too much of it gives a "tubby" bass. I will admit that I lean toward the thinking that unless the bass is just terrible sounding, I would prefer to have it played. In a sense, an inability to play the bass notes on a recording could be considered a form of distortion too!

When it comes to bass notes, I tend to go along with what Woody Allen said about things in general: "Eighty percent of anything is just showing up".


Quote:
About the power managed, you stated 65w, I think this has to do something only with the excursion, right?
Right. I was dealing with excursion only with that figure. Isn't the maximum electrical power listed as 50 watts? Close enough.

Quote:
And what if I want a plain flat response until the cutoff?
If you don't mind the higher cutoff-well over 100 Hz sealed, about 100 hz ported-then you can get a flat response.

Quote:
my winisd tells me that 3 l are to be needed, is there any minimum volume to respect?
There are all many, many varieties of commercial loudspeakers that have a 5" in a small, 2 or 3 liter subenclosure installed into a larger enclosure with a 10" woofer. The 5" bass/mids-that is what you have-cross over to a 1" tweeter between 2,000 Hz and 5,000 Hz. This is a very popular design.

I am somewhat surprised that Beyma listed the volume range as 10 or 20 liters because it looks like the speaker is made to go into one of those subenclosures with with a low cutoff of between 200 or 400 Hz, depending on the size of the subenclosure and whether the designer wants to use the natural rolloff of the 5" speaker in his crossover plans. Some designers like to have a speaker entirely flat to an octave underneath it's cutoff, and then use electrical cutoffs exclusively.

It just so happens that this speaker works reasonably well in a ported cabinet up to 10 liters.

Quote:
Does this make appear any problem due to the high pressure inside?
Not generally. I saw an Infinity system once with an array of 8" cones in a pipelike structure. The volume was so small that the speakers could only use 1/3 of their excursion.

However, I think you are okay with this. The smaller the encloure, the higher the cutoff, which means the less the speaker has to move. At 200 Hz, your speaker would only have to move about one tenth of an inch to produce a whopping SPL of 112 dB. You would have to feed it over 100 watts to do this. To produce 106 dB, the speaker would have to move only .025 inch and would require about 45 watts.
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Old 21st August 2002, 11:28 PM   #8
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Quote:
I'm not all that sure about what group delay is exactly either.
As far as I am aware, (dons fireproof suit ),group delay is the effect of the air loading of the enclosure on the response to the signal, ie in general terms, a speaker which has typically high group delay is one such as a bandpass box, that has lots of different cavities and ports that need to respond to the driver impulse before any sound is transmitted to the outside world.
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Old 22nd August 2002, 06:16 AM   #9
Raka is offline Raka  Europe
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Default Port volume

Thank you all,

I now understand a little bit more, your replies are greatly appreciated.
Now that the volume is selected (7,7l) and the tunning too (77Hz), I only have to design the enclosure: Does the port inside volume have to be considered as volume seen by the driver?
I'm not going to fill all the enclosure, only a felt lining maybe, should be convenient to add some wool? Does this have impact on the volume?
I've seen kind of the design I'm working on many times, and I think the crossover will be put in the 3 or 3,5Khz, will be this a good starting point? the tweeter (TO2010) has a Fs=1050Hz, so should I cross higher and then use 1st order? The mid driver will be overloaded a little bit in the mid-high, but the dispersion will be damaged too?
BTW, I have another question: I listen to classical music with golden ears (I play violin so I suffer with the pitch every time I listen to the radio, how can they always out of tune!!!), and I don't care to have only a perfect point to listen, I'm not going to sit down nothing but in the perfect place, so... can I forget about the dispersion?

Thanks,
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Old 23rd August 2002, 05:27 PM   #10
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Raka:

The volume is the actual free air in the encloure. The space the speaker takes up and the volume of the port are to be subracted from it. Theoretically.

In practice, unless these things take up 10% or more of the interior space of the speaker, they can be ignored. Run your program for a volume 10% less than what you are planning, and you will see how very little difference there is in the curve.

The normal stuffing for a bass reflex enclosure is an inch of stuffing materials around the walls. The material is up to you. Keep it away from the opening of the port-the port needs free breathing to work properly. Only sealed boxes fill with stuffing.

Dispersion matters even if you are going to stand in just one place. It has been shown that even for the best spot in the room, the sound is harsh if there is no dispersion. With a 5 inch woofer and any normal crossover range, it won't be an issue anyway-your woofer has good dispersion high up the scale.

Cross over at least at 1500 or 2000 Hz.-you don't want the resonance of the tweeter in the audible band. I wouldn't use a 6 dB/octave network unless you are crossing over at 3500 or 4000 Hz. You want to keep the real low notes away from the tweeter.
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