I am mounting a 12 inch woofer behind 1.2 inches of plywood baffle and running the woofer up to 300 Hz... no roundover on the front facing edge of the baffle cut out, just a very small 1/4 inch chamfer. I assumed that this short pipe would help boost bass and dynamic punch but not introduce any resonance or diffraction problems if just running 20-300 Hz.
Is this an OK idea, or am I going to have some regrets???
My design is here:
http://www.diyaudio.com/forums/multi-way/261785-javelin-4-way-digital-active-project.html
Is this an OK idea, or am I going to have some regrets???
My design is here:
http://www.diyaudio.com/forums/multi-way/261785-javelin-4-way-digital-active-project.html
It will not have any effect in the frequency range you are using. There will not be any horn loading either I'd assume by doing the formulas roughly in my head but you can calculate the horn loading effect of a 1.2 inch length horn (baffle thickness + distance from gasket to cone) with a 11" diameter throat (cut-out diameter) and a 11½" inch diameter mouth (baffle exit diameter) and the standing wave resonance of the same yourself if you want to double check it.
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I am fairly certain there will be no cavity resonance based on what I have read about H and W frame dipole subs, but not 100 percent. I am not expecting any horn loading as I know that horn dimensions need to be substantial at those frequencies, but perhaps some slot loading effect though there doesn't seem to be much agreement as to wether this is real or not.
In my design it is really done more for aesthetic reasons, so more so than hoping for any particular benefit, I am just hoping there is no downside to worry about.
In my design it is really done more for aesthetic reasons, so more so than hoping for any particular benefit, I am just hoping there is no downside to worry about.
If there is any downsides it would not be on the woofers. The baffle cut-out (or the suspension on a flush mounted modern speaker) however creates a baffle boundary seen from the tweeter and mid-range drivers you are using, so the shape and level of round over/chamfer could affect the diffraction effects of those drivers. Particularly the effect on the mid-mids in your design as that seem to be placed directly centered between the woofers and on the same vertical line on the baffle itself. That could create problems that I would certainly investigate before settling on the design as is. I'd consider not using the mid-mids at all if I were you.
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Thanks for the feedback... all good points for me to investigate once I get things ready for measurements.
Pipe resonances for a baffle thickness of 12-18 mm. The 1/4, 3/4, 5/4 pipe resonances would occur in the range of 5k-7k upwards. If there is an effect at lower frequencies I cannot see how they are pipe resonances.
A couple of questions for Saturnus: you talk of the pipe created by front mounting, which is largely eliminated with rear mounting and rounding over the cut out. Firstly I cannot see how rear or front mounting the speaker alters the pipe. One has the pipe in front of the cone and one has it behind. Is it that the proximity of the frame to the cut out with front mounting creates what you refer to as a pipe?
Secondly, would rounding over the cut out when the driver is front mounted, eliminate a lot of the problems?
Third. A lot of the examples of rear mounting you give are professional monitors, and the measurements you refer to are at sound levels that most people in their homes would not listen at. At domestic listening levels are the problems less pronounced?
I would be very greatful to hear your answers.
Secondly, would rounding over the cut out when the driver is front mounted, eliminate a lot of the problems?
Third. A lot of the examples of rear mounting you give are professional monitors, and the measurements you refer to are at sound levels that most people in their homes would not listen at. At domestic listening levels are the problems less pronounced?
I would be very greatful to hear your answers.
1) Forgive my lousy paint skills as I've tried to illustrate it. Also note that I have just placed the driver on top of (or beneath) the baffle. In both front and back mounting it is naturally better to flush mount it.
2) Yes, it would but not as much as just eliminating it.
3) The original question herein was for midwoofers. As they need to produce low frequencies the cone needs to physically move quite significantly which changes the physical characteristics. Measuring at 20V test signal equal 50W into 8 ohm. I don't think that is excessive peaks even for a home system (it corresponds to about 4W RMS with music signals). I'd figure it to be quite normal in fact. If a speaker designer only designs a speaker on how it measures with small signal values then how can he have any idea how it performs at reasonably expectable use conditions?
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A few comments.
The cavity or pipe resonances may occur on the front side if the driver is rear mounted or on the rear side if front mounted. Rear mounting is, of course, the worse case as the cone can not act as a barrier to the effect. Cones are a fairly effective barrior, especially if cone mass is high.
Roundovers or flairs will help smooth response compared to front mounting, but even a wide flair, if deep, will impact response as directivity is increased for some band of frequencies. This is the primary reason why Genelec and others mount units in a large flair. They are trying to give narrower CD response to the woofer to widen a range of higher directivity.
This is a good approach if done well with a long and well designed flair. Just rear mounting a unit behind a baffle thickness is not the same, though!
50 Watts peak for 4 Watts average is a pretty generous peak to average based on todays loudness wars.
You are still conflating small signal effects and large signal effects. You have not sufficiently explained how the response problems of rear mounting magically correct some large signal surround problem (rear smoke vortexes!)
David
The cavity or pipe resonances may occur on the front side if the driver is rear mounted or on the rear side if front mounted. Rear mounting is, of course, the worse case as the cone can not act as a barrier to the effect. Cones are a fairly effective barrior, especially if cone mass is high.
Roundovers or flairs will help smooth response compared to front mounting, but even a wide flair, if deep, will impact response as directivity is increased for some band of frequencies. This is the primary reason why Genelec and others mount units in a large flair. They are trying to give narrower CD response to the woofer to widen a range of higher directivity.
This is a good approach if done well with a long and well designed flair. Just rear mounting a unit behind a baffle thickness is not the same, though!
50 Watts peak for 4 Watts average is a pretty generous peak to average based on todays loudness wars.
You are still conflating small signal effects and large signal effects. You have not sufficiently explained how the response problems of rear mounting magically correct some large signal surround problem (rear smoke vortexes!)
David
Didn't I specifically write you had to calculate the round over/chamfer or flare if you like? Pretty sure I did.
Is it? It's the de facto standard of RMS being -12dB under peak. If you're listening to music so heavily influenced by the loudness wars that there is a significant difference, you're probably better of listening to a mobile phone instead of high performance monitor. Even reducing the crest factor to -10dB under peak which would be quite heavily compressed 50W peak would still only equal 5W RMS.
I'm not going to take you through fresh man acoustics, Dave. I'm only doing comments related to the original question of why near field monitors (and a growing share of smaller bookshelf speakers) typically use rear mounted midwoofers.
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I never get anywhere near 4 watts average. My present speakers are about 89 dB efficient. Would it be right that 4 watts equates to 93 dB average approx.
Average!?
A couple hours a day of that would contravene my work place regulations.
Average!?
A couple hours a day of that would contravene my work place regulations.
4 Watts is 6 dB over 1 Watt so you probably would get 95. That is one speaker at 1 meter. Subtract level for listening at a greater distance then add something for the second speaker and your room acoustics. The answer then is...I don't know.
Also, as soon as we start talking Watts or SPL and music then we need to discuss what type of metering is used. Are we measuring average fast, average slow, impulse? 4 Watts on a VU meter?
You are correct that OSHA allows 85dB (A) for 8 hours and then cuts time in half for every 3 dB above that. Of course, if we are going to loose our hair cells it might as well be on music we enjoy!
David
Also, as soon as we start talking Watts or SPL and music then we need to discuss what type of metering is used. Are we measuring average fast, average slow, impulse? 4 Watts on a VU meter?
You are correct that OSHA allows 85dB (A) for 8 hours and then cuts time in half for every 3 dB above that. Of course, if we are going to loose our hair cells it might as well be on music we enjoy!
David
@speaker dave
Hypothetically: If one was to buy from Moldova a LS3/5A cabinet to make a "look-a-like" a new fangled version (and grille recessed as per LS3/5A) with modern drivers would you still want to mount the mid-bass at the rear of the baffle or on the front?
This considering reflections from the sides - somewhere I read (and we know how unreliable the internet is) that mounting the B110 at the back helps reducing the side reflections from the grille. I also read a mounting remark by KEF that the B110 may be mounted up to 12mm from the front.
Thanks
(One thing I've never understood is why the screws holding the baffle are placed at the middle of the sides of the B110 - surely having a set of screws at the "top" and the "bottom" of the B110 (where the bolts are) will result in less potential for the B110 chassis to vibrate.)