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Old 17th February 2008, 14:05   #1
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Question Coaxial Enclosure. How to design it?

Hi,

In this forum itself many a times I have seen coaxial in IB (fitted on parcel trays ~ infinite baffle) setup as well as coaxial in Enclosure. Till now I was under the impression that a speaker made for IB would have fairly large QTC ( around .7), Gurus please correct me if I am wrong. As far as my knowledge goes..
  • For a sealed enclosure to have flat pass band response, the Qts should be < .7 and as it approaches .7 the enclosure size will increase (my experience tells me this ).
  • I have also seen articles in DIY websites which states that in car box can be tuned to have QTS till 1 without major impact on the SQ.
I would greatly appreciate if anybody can answer my queries:
  • Can a sealed/BR etc box be "designed" for a coaxial speaker? If so what QTS should we choose?
  • Won't the mid/tweeter mounted on the woofer have any effect on the box response?
Thanks in Advance,
Venki.

PS: Moderators please note:- I searched the forum and could not find similar post. Please delete this post if its a duplicate.
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Old 17th February 2008, 20:23   #2
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Most coaxials dont have their T-S parameters published by the manufacturer, so thats the biggest obstacle to all that you are planning.
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Old 17th February 2008, 22:46   #3
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Thanks B&T. If that obstacle is crossed by measuring the T/S manually (now that I have WT3 (woofer tester 3) its lot simpler), can I tune the box to around 1 and still get decent SQ? I have never heard a box tuned to damping of 1 inside a car .
Or the other way to put it is has anybody measured the QTS of the off-the-shelf box we get from the installers? May be that will give us an idea on how to design it.

Venki.
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Old 17th February 2008, 23:40   #4
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Quote:
Originally Posted by venki7744 View Post
Thanks B&T. If that obstacle is crossed by measuring the T/S manually (now that I have WT3 (woofer tester 3) its lot simpler), can I tune the box to around 1 and still get decent SQ? ... has anybody measured the QTS of the off-the-shelf box we get from the installers?
Venki, what is the objective that you have set for yourself for this exercise? DIY efforts with Qts and T-S parameters on the lower mid-bass region of coaxials are governed by the Law of Diminishing Returns. Very few people have dared tread that territory.

Buck up, we will be avidly following your research on micro-management of electrical and mechanical parameters in your quest for SQ. Your fundamental research talent would be invaluable for us on TBHP.
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Old 18th February 2008, 00:22   #5
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I am planning to get a new car most probably next month and my first aim would be to setup a decent ICE for my car. And I would like to do it myself (I love DIY).

This thread was started after see pictures in the "Sound off Show off" section showing ICE setup with coax in a box. I am just curious on how the response of these speakers be? If the box is not "designed" to fit the speakers, the how can one assure a SQ setup. The box could potentially spoil the SQ of the whole system as such. If it is "designed" to fit the speaker, how different is it to design this box compared to single woofers/speakers?

As far as I am aware, in a coaxial system the only component which is "not enclosed" is the woofer (experts please correct me if I am wrong). So I assume designing an enclosure for a coax would be similar to any other woofer. My only concern being the QTC of the speaker as such. Pardon me if I am talking nonsense here .


PS: This is based on my limited knowledge of speaker designing. I have more of a bookish knowledge and less of practical knowledge on speaker box building.
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Old 18th February 2008, 10:19   #6
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Good to see a fellow DIYer with us.

But I don't understand what are you trying to say ? You want to make a coaxial enclosure. What are the driver sizes have you chosen? Where do you tend to install the enclosure in the car ?
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Old 18th February 2008, 10:20   #7
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Venki, the drivers do not necessarily have to be kept in a box.

1. Oval coaxes are unsuitable for placing in rear doors (other than the 5x7 that go into Fusion / Fiesta) hence the quest for an alternate location
2. Circular coaxes are almost always fitted in rear doors. 6x9 Oval coaxes give a better lower mid-bass
3. If the rear doors don't have a provision for mounting speakers (most do), the preferred mounting is on the parcel shelf (original or MDF ersatz), especially in hatches. 6x9 coaxes almost always mounted on parcel shelves. But, some don't prefer a parcel shelf (and for some the installer manages to extract more money by advising them to use boxes)
4. The primary aim of box or any other mounting arrangement is to prevent the rear wave from diminishing the front wave, and it should not affect the sound from the driver ideally. Even with IB installs on parcel tray, the hatch door and the boot form the virtual enclosure for the driver
5. A mounting arrangement is not supposed to color the driver response, but theoretically some methods can. A good box presents a spring+damper system behind the cone that keeps the cone movement under control in the usable region - the Qtc etc is a mathematical articulation of the same
6. The effect of the box reduces proportionate to frequency, and is most felt in the sub 80Hz region, i.e. with sub-woofers. For the mid-bass region, the existing empirical methods suffice
7. The SQ of the system in the car is judged over and above such mathematical expressions of physics. It has more to do with the dynamic abilities over the complete audible spectrum

There are a lot of TBHP members near you with very good SQ systems in their cars. Get together with them and listen to their systems.
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Old 18th February 2008, 10:49   #8
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Quote:
Originally Posted by venki7744 View Post
Till now I was under the impression that a speaker made for IB would have fairly large QTC ( around .7),
  • For a sealed enclosure to have flat pass band response, the Qts should be < .7 and as it approaches .7 the enclosure size will increase (my experience tells me this ).
  • I have also seen articles in DIY websites which states that in car box can be tuned to have QTS till 1 without major impact on the SQ.
I would greatly appreciate if anybody can answer my queries:
  • Can a sealed/BR etc box be "designed" for a coaxial speaker? If so what QTS should we choose?
  • Won't the mid/tweeter mounted on the woofer have any effect on the box response?
Stuffing a coax into a small sealed box (QL < 7) would give you a peak in the midbass. I dont see any advantage in this.

Any object in front of a cone will affect the sound to some degree. One reason why components sound nicer than coax speakers.

If you intend to stuff a cox in a box make the box lossy (read as aperidoc). In many cases I would recommend such a box (like when there is a large sub in the trunk or on the rear deck) to acoustically isolate the rear of the coax's cone.

The reason why one can get away with "higher than 0.7" Qtc for a a car sub is becuase of road noise. Road Noise is predominantly in the upper bass (depending on the car/tyres/etc. somewhere between 50 and 100Hz). The peak provided by the high Qtc sub compensates for this Road Noise. However today the same can be done using EQ.
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Old 18th February 2008, 19:54   #9
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Quote:
Originally Posted by low_bass_makker View Post
But I don't understand what are you trying to say ? You want to make a coaxial enclosure. What are the driver sizes have you chosen? Where do you tend to install the enclosure in the car ?
Thanks LBM. I am just trying to understand whether a box can be designed to fit a coax speaker in general. I don't have any specific drivers in mind. The enclosure I am talking about is the one typically seen in the rear (boot) of hatches/station Wagons etc.

Quote:
Originally Posted by [U
[/u]DerAlte;726257]
But, some don't prefer a parcel shelf (and for some the installer manages to extract more money by advising them to use boxes)
Thanks for the info DerAlte..this is what I wanted to hear. So installers do suggest a box for no reason.

Quote:
Originally Posted by navin View Post
If you intend to stuff a cox in a box make the box lossy (read as aperidoc). In many cases I would recommend such a box (like when there is a large sub in the trunk or on the rear deck) to acoustically isolate the rear of the coax's cone.
Thanks Navin. My intension here is to understand if there is any benefit of stuffing a coax in a box. If so how to design it.

Quote:
Originally Posted by navin View Post
The reason why one can get away with "higher than 0.7" Qtc for a a car sub is because of road noise. Road Noise is predominantly in the upper bass (depending on the car/tyres/etc. somewhere between 50 and 100Hz). The peak provided by the high Qtc sub compensates for this Road Noise. However today the same can be done using EQ.
I never knew this was the reason

To summarize this is what I could gather from the thread so far..
  • Coax box seen in cars may not necessarily be designed to fit the coax.
  • Apparently there is not advantage of stuffing a coax in a box unless there is a mechanism by which we can ensure that the "springiness" is not affected and the rear wave doesn't cancel the front.
  • The above point may be achieved by IB (fitting the speakers in the door pad/parcel tray).
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Old 19th February 2008, 10:57   #10
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Also if the co-ax enclosure is in the boot there will be no imaging or sound stage as it will be behind the listener and Might be lying in the boot also.
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Old 19th February 2008, 11:06   #11
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Quote:
Originally Posted by venki7744 View Post
I never knew this was the reason

To summarize this is what I could gather from the thread so far..
  • Coax box seen in cars may not necessarily be designed to fit the coax.
  • Apparently there is not advantage of stuffing a coax in a box unless there is a mechanism by which we can ensure that the "springiness" is not affected and the rear wave doesn't cancel the front.
  • The above point may be achieved by IB (fitting the speakers in the door pad/parcel tray).
one reason is Road Noise the other is that the transfer function of most cars actually allows for the midbass hump to sound good.

if you stuff a coax in a box the front wave will NOT affect the rear wave on the contrary if there is a sub in the neighbourhood (like in a trunk/on a rear deck) the box will isolate the rear of the coax from the sub's output.

what happens when you stuff a high Qts driver into a box that is stoo small is simply that (a) there is a peak in the freq. response in the upper bass (lower midbass) region and (b) a steep drop off in bass after that peak.
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