Minimum volume matters

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
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,
 
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.
 
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
 
diyAudio Moderator Emeritus
Joined 2001
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.
 

Attachments

  • beyma 5 inch.gif
    beyma 5 inch.gif
    3 KB · Views: 804
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,
 
diyAudio Moderator Emeritus
Joined 2001
Re: Ported vs sealed vs group delay

Raka said:
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".


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.

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.

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.

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.
 
Ex-Moderator
Joined 2002
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.
 
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,
 
diyAudio Moderator Emeritus
Joined 2001
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.
 
Crossover point

Thank you very much,

I was thinking of cross about 3250Hz, and 1st order since this is IMO far above the Fs of the tweeter and the midwoofer plays well until 5Khz. About the tweeter I'd like to put a Beyma because it's available in a shop near, but I'm not sure if it's state of the art stuff. 1st order should be enough to save the tweet from long excursion? To improve better dispersion, and because I plan to cross high,or even higher, should I look for a 3/4' drive?
Besides the port is going to be forward radiating, and square type, for easy building and to help with some kind of bracing.

Thanks for your reply,
 
diyAudio Moderator Emeritus
Joined 2001
Is 3250 high enough of a crossover to go 6 dB slope? I think so. I would be tempted to put a parallel inductor to shunt frequencies below 700 Hz so that the filter is 6 dB from 3250 to 700, and 12 dB from 700 on down. This would give you the advantages of a 6 dB crossover in the crossover region, and the extra protection farther down. But you probably do not need it.

Before just about every tweeter had ferrofluid, a lot of tweeters were rated as 50 watts, crossing over @ 2000 Hz. with a 12 dB crossover or @ 4000 Hz with a 6 dB crossover. The higher the crossover, the less the strain, mechanical and electrical, on the tweeter. Now that you have an additional safety factor with ferrofluid, I think you'll be okay. I like that extra inductor, but it probably is not necessary.

If you want to see the difference between a 3/4" and 1" tweeter, go to the following thread-two charts are there. The ProAc tweeter is the 3/4". The Event tweeter is the 1". Both tweeters are made by Scanspeak, and are expensive. The 3/4" goes for $56. Each. The 1" for $76 each, at Madisound in Amerca. But they will give you an idea of the difference betwen the two. The 3/4" has much better 60 degree off axis response.

This would most likely apply to any 3/4" tweeter at any price.

Of course, a 3/4" tweeter does not have as large a voice coil as a 1", so power handling should be less. But I don't think the difference is major.
http://www.diyaudio.com/forums/showthread.php?threadid=5477
 
Design progressing

Hi,
Thank you for your suggestion with the extra inductor, is something that doesn't appear often in the web papers in the net, but as the good ideas, it's simple and looks good.

I'd prefer to fit a 3/4', but beyma only has 1', and that is a problem for my budget since I can get a nice discount in my electronic shop over the beyma stuff and the tweet is only 19 EURO!! any scanspeak for this price?!?!?! I hoped so...:( I think I will look for in vifa's. Any suggestion? The spanish retailers are more expensive, the 2010 is 59EURO + 16%VAT=68.44EURO.
The beyma t2010 doesn't look bad in the dispersion polar diagram, so if I can't find any better replacement, I will keep this poor beyma. They have an alumminium one, but I was adviced that It's a little metallic sound, I don't know how much harsh it would be...

The midbass shows a narrow 5dB peak centered in the 5KHz, so this would be treated in the crossover, I'm thinking to cross at different points, but I haven't calculated nothing yet. This doesn't worry me, because I don't think this will be audible.

I'm working with CAD to design the box: I'm going to make a "subenclosure" for the tweeter (just a piece of MDF with a hole routed to cover it, nothing else, the tweeter doesn't need minimum volume, does it?), and a rectangular port forward firing.
The left and right corners are to be routed with a 10mm bit, I suppose this won't help very much since this matches a wavelength of very high frequency, but won't hurt. I offset the highs laterally with the golden ratio to avoid standing waves (I'm taking with me everything I read, so don't laugh at me for doing this way with a 19 euro driver (the midbas is more expensive, ha);)

I'm fitting the mid as close as posible to the tweet. This distance, being so small, won't be considered in the Xo, am I right?

Thanks a lot for hearing my tears, you are nice people
Bye
 
diyAudio Moderator Emeritus
Joined 2001
As far as figuring cost goes, the Euro and the American dollar are now virtually equivalent.

$19 is normal for a good quality tweeter in America, I don't know about Europe. Scanspeaks are considerably more.

I don't have much experience with Beyma drivers. There is a member here who sold them, and said that there are good models and bad models, like most lines.

A DJ friend in Ireland says that Beyma PA equipment is considered good quality by the DJ's over there. Though pro equipment is not the same as hifi, if you make a respected product in one field, it makes it likely your offerings in the other field are good.

So, even though I haven't used them, I would feel good about using Beyma tweeters.

Most European speakers seem to be available cheaper in America than in Europe, I don't know why. However, English members have pointed out that Audax is cheaper over there, (England) than in America.

Audax makes good quality tweeters, in fact Audax tweeters are one of the most popular brands that speaker manufacturers use in their own products. And they offer 3/4" models. You might want to check the prices for Audax units in Spain-they might be a bargain.

If you are crossing over at 3250, your wavelength is only 4 inches. Your center-to-center distance is going to be greater than one wavelength. So placement on the front will be a factor.

More on this later. Gotta run. One question-do you have a computer microphone and a voltmeter, (even an extremely cheap one will do)?
 
diyAudio Moderator Emeritus
Joined 2001
Oops, forgot we were talking about a 5 inch woofer, not an 8 inch. Since most tweeters faceplates are 4 inches across, (unless you get the neodynium types that have no faceplate), if the tweeter is mounted directly above the woofer with virtually no space between the edges, the centers will be about one wavelength apart at the crossover frequency, (3250 Hz). The wavelength of 3250 Hz is 4.15".

Many speaker manufacturers do it that way. It might require a slight adjustment in your crossover, though.
 
Measurement and tweets

Hi,

The midbass is a 5' unit, and is fitted very close to the tweet, so the final distance is respected by the crossover I think. Anyway, I'm thinking to lower a little bit the Xo maybe 3K. If I'm right the distance between centers should be smaller than the wavelenght of the xo frequency to avoid lobing effect there, right?

My measurement equipment is the speakerworkshop, my poor laptop and an external mic (this is not a cheap one). I have a cheap and yellow multimeter, and maybe a scope is going to be available.
I've just get the software, the target was to measure caps and chokes, but the measurements are rather chaotic... I suspect that the PC card is crazy, but I can use another soundcard from another PC to measure the coils. If so, I will made my own inductors with copper wire (I work for a motors company, so it's available at a good price).
So I think only need a mic preamp, I will make an ESP design, because it's simple and looks good enough.
I intend to measure the actual parameters of the drivers, as you can see I'm following all the steps to reach the heaven of the cheap speakers...

I will look for an audax tweeter, I've found some cheap vifa but the Fs is not low. At last, the beyma T2010 doesn't look bad at all. I've found that I was wrong, the beyma is not a 1' unit, is a 1,25 one !!! Poor dispersion...

I have another question: The tweet is going to be in it's own enclosure, but if it wasn't, should I cover any space to avoid the pressure get the inside of the driver? Will this eat the space needed for the performance?

Thanks
 
Ex-Moderator
Joined 2002
Hi Raka

Just about all tweeters are designed as sealed enclosures, so manufacturers can mount them straight into a box with other drivers for budgetary reasons.

But you can improve on this by mounting tweeters on a soft neoprene ring to isolate them from box vibrations, in wich case you need a sub enclosure to prevent back pressure from other drivers pushing the whole unit in and out in response to back pressure.
 
diyAudio Moderator Emeritus
Joined 2001
pinkmouse said:
But you can improve on this by mounting tweeters on a soft neoprene ring to isolate them from box vibrations, in wich case you need a sub enclosure to prevent back pressure from other drivers pushing the whole unit in and out in response to back pressure.

I never thought of that. What an excellent idea.

The sub-enclosure only has to clear the back of the tweeter by the narrowest of gaps. So the sub-enclosure should take up only a tiny amount of space.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.