Hi ,
those Jamo woofers IIRC are specified for closed box mounting.
You need to consider the motor and the 'elastic suspension' parts
for the duty you are going to use 'em .
Tradeoffs of OB are longer excursion from the woofers to
overcome the acoustical short circuit 'problem'.
(same thing could be said also for little closed box subs )
For your information , I just did one week ago an OB loudspeaker
by just attaching the drivers to a frame ( no baffle at all )
The next step would be to have them suspended , but the
power here it's limited so no great problems of vibrational interaction
between different drivers on a frame
those Jamo woofers IIRC are specified for closed box mounting.
You need to consider the motor and the 'elastic suspension' parts
for the duty you are going to use 'em .
Tradeoffs of OB are longer excursion from the woofers to
overcome the acoustical short circuit 'problem'.
(same thing could be said also for little closed box subs )
For your information , I just did one week ago an OB loudspeaker
by just attaching the drivers to a frame ( no baffle at all )
The next step would be to have them suspended , but the
power here it's limited so no great problems of vibrational interaction
between different drivers on a frame
Hi picowall,
My first choice was actually the Visaton 25E. But unfortunately I could find anywhere that would be able to ship to me in a decent shipping price. Enquiries to the local agent put the shipping at US$220 for 8pcs... A bit too pricey.
The Jamo hs an xmax of 3mm as opposed the visaton of 6mm. However the price is only about US$18 per pc including shipping. The surface area of 4 Jamo drivers is the same as one eminence beta which has a similar xmax. So hopefully it should be about as loud as one eminence beta which in turn hopefully loud enough for me.
My first choice was actually the Visaton 25E. But unfortunately I could find anywhere that would be able to ship to me in a decent shipping price. Enquiries to the local agent put the shipping at US$220 for 8pcs... A bit too pricey.
The Jamo hs an xmax of 3mm as opposed the visaton of 6mm. However the price is only about US$18 per pc including shipping. The surface area of 4 Jamo drivers is the same as one eminence beta which has a similar xmax. So hopefully it should be about as loud as one eminence beta which in turn hopefully loud enough for me.
Conveniently limiting the mission to SPL only, yes. A more comprehensive solution which includes quality bass, a single monopole is unable to do the same job imo.
There are not enough TSP available for the Jamo woofer to do a realistic simulation with the MJK worksheet. So I can't tell what to expect. What I know: Expectations about "enough" bass power vary widely. I know that what I find "comfortably enough" is "hardly sufficient" to some other people - if doubled! With the Jamo Fs=48 Hz don't try to gain any bass below 50 Hz. You will already need some boost between 50 and 100 Hz. Do you have any ability to measure frequency response or to experiment with coils of 8-12 mH value?
The size of the U frame baffle and wings is ok. You would get some more bass (~3 dB?) if you keep the depth of the U frame all the way up, but then you would probably need to equalize the resonance peak of the U frame.
Altogether I don't really feel comfortable with your 4x8" Jamo idea. I don't even know how far the 3 mm Xmax of the Jamos is from their Xlin - which would be of interest too. Last tapered U frame I had my hands on was the Modipo: 3 x Monacor SPP-250 in a row.
If you feel that your proposal is sufficiently comparable, then give it a go. If not - look for drivers with more surface and/or excursion.
Rudolf
Thanks for all the replies. I don't expect the bass of a subwoofer. Probably just about the same amount of bass as if the speaker is in a sealed cabinet. Which would have been enough for me. So how does this question sound. Will 4 speakers in the open baffle achieve the same loudness as the same speaker (one piece) in a sealed cabinet... ?
Oon
Oon
Hi Rudolf,
Thanks, that is loud enough for me. One 8" speaker is loud enough for my small room. Had a look at the monapol speaker link. Couldn't make out the german, but I think it is pretty close. The monacor is 10 inch with xmax of 3.5 mm... 3pcs, which would probably be about the same as 4pcs of 8 inch of the same xmax. That speaker is pretty close to what I have in mind.... what was your opinion on that speaker? Enough bass?
Many thanks, your advice is most helpful.
Oon
Sent from my Milestone using Tapatalk
Thanks, that is loud enough for me. One 8" speaker is loud enough for my small room. Had a look at the monapol speaker link. Couldn't make out the german, but I think it is pretty close. The monacor is 10 inch with xmax of 3.5 mm... 3pcs, which would probably be about the same as 4pcs of 8 inch of the same xmax. That speaker is pretty close to what I have in mind.... what was your opinion on that speaker? Enough bass?
Many thanks, your advice is most helpful.
Oon
Sent from my Milestone using Tapatalk
The Jamo Fs is 48 Hz, the Monacor SPP-250 is 30 Hz. This means that the Monacor drivers will reach at least a half octave lower than the Jamos. My main concern was/is that you might expect thundering and growling bass from the Jamo dipole - which it won't deliver. But it will be perfectly ok for any bass guitar or "normal" drum set.
The Modipo panel happened to develop a sort of NXT behaviour down to 20 Hz - unintentionally. That made it a real attention getter wherever it was presented. Sheer luck.
Please keep an eye on your fullrange baffle. Don't expect the U frame to hold it sufficiently in place. You will need some sort of spine or extra frame to decouple it from the U frame.
mmmh What Rudolf said !!
Indeed , I see that the Modipo Loudspeaker makes use of two tweeters ,
to make a real dipole ...
I would use the Seas FR in dipole ,but just to facilitate its rolloff on the bass
And leave the bass duty to some PS-BR-TL whatever also dipole
Thanks picowall for all your words. I actually planned to have the SEAS to be in OB. The other 4 pieces of 8" Jamo is to help supplement the SEAS. I probably will roll off the SEAS FR at low frequency. But having said that, the SEAS was designed with a large excursion of +-3mm. So I might not need to.
I plan to use a mark and daniel Air Motion trnasformer (AMT) for the tweeters, which also happens to be dipole...
Oon
Dear Rudolf,
First of all, thank you for all the time you spent replying my post. It was really informative.
As far as I know, the maximum loudness (SPL) is a function of the surface area and excursion (but I could be wrong) so theorectically they should have about the same loudness capability. However with regards to frequency response, I agree with you, it will be start to decline at a higher frequency. I plane to add in a +6dB per octave boost with the +3db point adjustable between 100Hz to 200Hz, to compensate for the baffle rool off. The Jamo will a 12dB low pass roll off at about 200Hz or so that it is just a dedicated bass speaker. If I really feel the need to I might just add an additional 3db or so boost at 30Hz to lower the bass response. At present moment, my expectation of it just to perform like a decent floor stander with one 8" woofer ( bass quantity wise), although I hope the quality is a lot higher.
As for the baffle, I planed to break it into two parts, one about 3 foot high (4X Jamos) and the other about 1 foot high (1 X SEAS), with the 1 foot speaker staked on top of the 3 foot one . The 3foot one will have a small flat plank at the top, probably about 3", thick will mate with the additional 1 foot speaker with the same base. Will probaly attach it to each other by screw and nut and a piece of rubber in between the two planks.
Thnaks again for all your time...
Oon
Hi Picowallspeakers,
I think when they said made for close box, this is opposed to Bass reflex (BR). Almost nobody makes speakers for open Baffle except a few.
The rule can be found in this one.
http://www.diyaudio.com/forums/multi-way/181308-how-does-one-determine-sealed-ported-enclosure.html
Even th one that was recomended to me and is used in the W frame don't mention that exclusively.
I think in general, a total Q, Qts of more than 0.7 is desirable to have a nice frequency response. And a Xmax and surface area as big as possible.
My choice for the jamo is more because of economic reason. Couldn't get the visaton shipped at a reasonable price...
Visaton - Lautsprecher und Zubehör, Loudspeakers and Accessories
Oon
Yes, maximum SPL is solely a function of Sd x Xlin. I prefer Xlin over Xmax, but we don't know Xlin in this case.
That's ok.
Forget about that. The Jamo will roll off with at least 12-15 dB/oct below its Fs.
Two additional things to consider:
The Jamos will develop some forward/backward momentum on the U frame. I highly recommend to fix the U frame to a heavy base plate which extends beyond the front of the frame. No need to be wider than the frame though.
Second issue is possible flexing of the U frame wings. You need to brace the wings to keep them from resonating. Random distances between the braces would be scientifically preferable, but even distances between the drivers should be correct too.
As for the baffle and wing material: 3/4" is sufficient. From the touch of the hand I feel that ply is vibrating a bit less than MDF, but the real difference is made by proper bracing and not by the material!
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