MIDTOP 15" + 8" + 1" 3 way |
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FrederikMA
Registered User Joined: 19 July 2017 Location: Copenhagen Status: Offline Points: 76 |
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Leurosound, some of your your facts about the Peter Morris midtop is slightly off.
Crossover is actually around 700Hz. The CD is a very effecient coaxial 1,4 capable of high outputs even at low frequencies, and the parallel walls are intentional and important for pattern control in the crossover region. Throat adaption is actually not critical and the front cavity and the slot shaped throat actually provides a natural sloping above 800Hz while maintaining low frequency output. With that being said I do not consider the Peter Morris midtop to be the speaker to end all speakers. Peter says so himself; it's an optimized speaker on a stick, not the perfect speaker. I'm happy to see someone having a go on their own. Would you care to share some of your thoughts on how you came up with this design? It's a beautiful speaker BTW! Best regards, Fred |
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LeruSound
Registered User Joined: 27 August 2015 Status: Offline Points: 171 |
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As I said, I consider it a very good design, but I just listed what imho are the reasons why I'm not interested to build for me. And to be honest ive just been a little upsetted cuz its not first time ppl is replying to my ideas saying "try this or that design". And more than once it have happened with pete morris design. Ill get another look to that, probabily ill also have to work on it so ill experience in first person.
Btw, I am now crossing my design like this: 135 Hz - 900 Hz 24dB slope. (guess was Butt.) 15" 15NW76 loaded straight horn 56 cm long, 3900 sqcm mouth and 400 sqcm throat, exp. Horn (in reality i'm using T=1,1). 900 Hz - 2,7 kHz (upper is 18 dB/oct , passive cross phase aligned) 8" 8PE21 straight horn around 18 cm long from the comb horn. 2,7 kHz - top end 1" DE400 (no Titanium diaphgram) in the same comb horn. The phase plug goes around 1,5 cm far from the speaker membrane, and fill the horn for the whole lenght, adapting both Vertical and Horizontal cross.s.area to expand as Exp.Hyperbolic law says. The front dimension of the "Phase plug" is 35x35 cm, so the wavefront around 900 Hz is not that easily able to spread as it should, but as i planned, i was supposed to cut it around 400-500, but the really short 8 inches horn didnt allowed the response to be good below 800-900 Hz, i i've been forced to do so.. It performs well, but not completely, as always.. Go hard with advices and critics! Edited by LeruSound - 11 September 2017 at 1:31pm |
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FrederikMA
Registered User Joined: 19 July 2017 Location: Copenhagen Status: Offline Points: 76 |
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I think the 900Hz crossover problem is confined to the very near field and (on-axis) summation should be generally good.
Crossing horns around lower cutoff often means wide or uncontrolled directivity causing audible integration problems off-axis. Your lowmid horn being large, coaxial and expanding in all directions might allow the upper mid to have slightly wider pattern though. I Think playing around with slopes and crossovers with regards to both on - and off axis respons is critical in such a configuration. What's the coverage of the various horns? I'm quit curious about your findings on the upper mid horn. It's quite unusual for a horn to be simply useless until almost an octave above cutoff. As it's mainly a matter of loading at this part of the horns operating range it's very dependent on the driver. Best regards, Fred |
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LeruSound
Registered User Joined: 27 August 2015 Status: Offline Points: 171 |
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I'll post some other misuration of single drivers, and whole box response off axis response asap.
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AndyWave
Registered User Joined: 30 March 2008 Location: Finland Status: Offline Points: 380 |
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Hi Leru
Have you seen this white paper of coaxial horn from JBL pro? There may be some useful information there regarding the crossover frequency and what kind of measuring results to expect. Page 5 onward. https://www.jblpro.com/ProductAttachments/PD_HF_v1no29TechNote.pdf and fine woodwork and execution of the idea by the way best regards, Andy |
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torturing electrons since ......
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LeruSound
Registered User Joined: 27 August 2015 Status: Offline Points: 171 |
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Today i had some time to do some misuration.. Speaker is upon the other one of the pair, so -900cm from ground. This is the graph of the speakerbox (one and the other box, (processed with HS12 to balance the compressuon driver sensitivity, as i decided to not do L-Pad in passive crossover for this desig). Then there's a bit of graphic EQing in the whole band. Both ways are time aligned. This time i used NTM 52 dB/Oct filters, and i tryied to cross below first processing (670 Hz insted of previous 900 Hz). Also i crossed the 15" below, around 570Hz, getting a little flat the first huge peak i had in the 8 inches horn. Bands are time (and phase; as thers around 40 cm between the 2 diaphgrams) aligned. This is just the 8 + 1 response. This is the 15" horn response. Next two are the unfiltered ones, with full band pink noise (still HSF12 instead of L-Pad for filter active) Next are the 45° Horizontal off axix both 15" and 8+1 Horn, without xover filters. (done quickly, have to remeasure, cuz the 800 - 3kHz band looks disappearing while other times it was very very good in full box meas.) and 45° vertical box response floor standing mic. EDIT: Just realized the HORIZONTAL OFF axis measurement are done without HSF for the CD, so nosense, i'll remeasure asap. This is how was the on axis and -6dB @2kHz Horizontal off axis response (guess it was around 45°, but still with the 900 Hz cutoff freq from 15" to 8+1) Edited by LeruSound - 21 September 2017 at 1:49am |
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levyte357-
Old Croc Joined: 27 July 2012 Location: UK, South East Status: Offline Points: 8128 |
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15+8+1, always sound good on paper, then in large venue, under pressure, doesn't really make it.
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Global Depopulation - Alive and Killing.
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fatfreddiescat
Young Croc Joined: 15 October 2010 Location: N.E.Wales Status: Offline Points: 1083 |
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fatfreddiescat
Young Croc Joined: 15 October 2010 Location: N.E.Wales Status: Offline Points: 1083 |
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@ Leru, with a 12dB BuutterworthLP on the 15" overlaying the 15's second order rolloff with a bit of EQ you may be able to achieve an LR24 LP, then use a LR24 HP on the 8" to complement it - may just work, directivity is always going to be a little off and not easy working with limited overlap of bandwidth.
By overlaying the 2nd order Butterworth you will be able to use the full bandwidth of the 15" without resorting to really steep slopes which will accentuate the off axis differences. You may also be able to explore Timo's All Pass filter technique.
Great project BTW. |
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LeruSound
Registered User Joined: 27 August 2015 Status: Offline Points: 171 |
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Thank you all.
Due to the sensitivity issue (I also prefeer use digital eq the less I can) i'll swith to 6ND410 18sound. Will do dispersion misuration on 1 inch and 8 inch separetly and remake passive cross if necessary, then I will achieve more overall efficiency and do a better dispersion design out of it. Ill let you know. |
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LeruSound
Registered User Joined: 27 August 2015 Status: Offline Points: 171 |
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In the end I switched to 6ND410, gaining a lot and getting a better energy balanced system.
Being probabily less finicky, I lowered the cutoff to 650 hz lower order filter without any H axis noticeable dip or problems. H axis stays very balanced, getting well linearly decreasing level by the spectrum in 45° H-offaxis (had 3dB scale in Smaart so guess it was around from 6 to 10dB relative difference from lower band to top-higher, still in good linear slope) Vertical keeps staying with some unavoidable problems off axis, but with the sound 2,7m tall, floor stacked, from 2m to further listenings it's very good for the ears. It sounds very loud and still quite well focused from 2 meter away to further. Stereo image is very good, but still not high pro level (me dumb as I made 1 baffle cutout of 15 larger, and I made passive xovers in different layouts for save time. While space was not too much and I did the best for lower inductor crosstalk, possible they inducts differently as the pattern of components positions is different.) Arrayed them behave really good, and there's almost 0 combing moving left to right. All of the results are good, fi sure more than good for the Soundsystem use I'm involving the boxes in. But the time I started learning ABEC3, discovering some of the leakages of this design, so I stopped trying to improve as them are still very good to the ears. Edited by LeruSound - 01 November 2017 at 10:53pm |
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